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Califo 
legional 
'acility 


THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 

LOS  ANGELES 


GIFT  OF 

John  S.Prell 


WORKS  OF  J.   K.  FREITAG 

PUBLISHED  BY 

JOHN  WILEY  &  SONS. 


The  Fire-proofing  of  Steel  Buildings. 

8vo,  v>  +  319  pages,  137  figures.    Cloth,  $2.50. 

Architectural  Engineering. 

With  Especial  Reference  to  High  Building  Construe* 
tion,  including  Many  Examples  of  Prominent  Office 
Buildings.  Second  edition,  rewritten.  8vo,  xiv-f>4°7 
pages,  196  figures,  including  half-tones.  Cloth,  83.50, 


2  £ 

I  > 


View  of  Post-Office  Square,  New  York. 

The  Park  Row  Building,  in  the  Centre  of  this   Illustration,  is  the  highest 
Office  Building  in  the  World. 

Frontispiece. 


ARCHITECTURAL   ENGINEERING. 


WITH    ESPECIAL    REFERENCE   TO 


HIGH    BUILDING   CONSTRUCTION, 


INCLUDING    MANY    EXAMPLES    OF 


PROMINENT   OFFICE    BUILDINGS. 


JOSEPH    KENDALL    FREITAG,    B.S.,    C.E., 

Associate  Member  American  Society  of  CM  Engineers; 
Author  of  "  The  Fireproof  ing  of  Steel  Buildings." 

JOHfl  S.  PR  ELL 

Civil  &  Mechanical  Engineer. 

SAN  FRANCISCO,  CAL, 

SECOND   EDITION,    REWRITTEN* 
SECOND   THOUSAND. 


NEW   YORK: 

JOHN   WILEY   &   SONS. 

LONDON  :    CHAPMAN  &  HALL,  LIMITED. 

1906 


Copyright,  1895,  1901, 

BY 
JOSEPH  K.   FREITAG. 


ROBERT  DRUMMOND,    PRINTER,  NEW  YORK. 


Eigiaeerug 
Library 

TH 


PREFACE  TO  REVISED  EDITION. 


THE  author  has  endeavored,  in  the  following  pages,  to 
define  and  illustrate,  in  a  manner  as  practicable  as  possible, 
such  of  the  fundamental  principles  in  the  constructive  design 
of  modern  high  buildings  as  may  prove  useful  to  architects, 
engineers,  and  students. 

While  the  technical  press  of  the  country  and' the  transac- 
tions of  various  architectural  and  engineering  societies  have 
contained  a  great  number  of  admirable  papers  and  addresses 
on  many  of  the  individual  subjects  here  considered,  yet  the 
realization  of  the  want  of  some  practical  and  comprehensive 
collective  data  on  the  subject  of  steel  building  construction  has 
induced  the  writer  to  rewrite  and  extend  this  volume. 

Before  the  present  revision  was  undertaken,  the  author's 
descriptions  and  examples  were  mainly  limited  to  Chicago 
practice,  as  previous  to  the  year  1894  Chicago  stood  promi- 
nently first  in  the  construction  of  high  buildings.  Since  then, 
however,  New  York  and  other  Eastern  cities  have  begun  to 
rival  and  even  outstrip  Chicago  in  this  form  of  building,  while 
the  same  interval  has  witnessed  great  changes  and  improve- 
ments in  many  details  of  construction,  especially  in  terra-cotta 
and  concrete  floors,  and  indeed  in  all  methods  of  fireproofing. 
Many  notable  tests  of  fireproofing  methods  have  also  occurred 
since  the  publication  of  the  first  edition  of  this  work,  such  as 
the  tests  of  various  floor  constructions  by  the  New  York  Build- 
ing Department,  the  test  of  methods  afforded  by  the  burning 

iii 

733404 


IV  PREFACE   TO  REVISED  EDITION. 

of  the  Pittsburg  buildings,   and  the  still  more  recent  partial 
destruction  of  the  Home  Life  Building  in  New  York. 

Fireproofing  is  so  intimately  related  to  steel  building  con- 
struction that  the  author  has  been  tempted  to  include  in  this 
revision  considerable  matter  given  in  more  logical  sequence 
and  in  more  detail  in  his  volume  on  ' '  The  Fireproofing  of 
Steel  Buildings,"  published  by  John  Wiley  &  Sons,  New 
York,  1899;  but  in  order  to  avoid  repetition,  and  to  keep 
somewhat  within  former  limits,  the  subject  of  fireproofing  has 
been  introduced  only  as  it  is  necessary  to  a  proper  understand- 
ing of  the  design  and  calculation  of  the  framework. 

The  largely  local  character  of  previous  illustrations  has  been 
supplemented  by  notable  examples  in  different  localities  so  as  to 
make  the  scope  more  general  than  formerly.  Where  previous 
examples  have  been  found  still  to  remain  illustrative  of  the  best 
practice,  they  have  been  retained  as  representing  principles 
rather  than  the  very  latest  examples.  An  effort  has  also  been 
made  to  exclude  such  data  as  are  given  so  admirably  by  the 
handbooks  of  the  various  steel  companies,  but  the  student  or 
architect  is  earnestly  advised  to  supplement  such  points  as  may 
be  found  of  interest  in  this  volume  by  the  more  detailed  tables 
and  illustrations  in  the  many  valuable  handbooks  now  issued. 

The  following  chapters  are  arranged  in  the  order  in  which 
the  calculations  for  such  structural  work  must  proceed,  starting 
with  the  load-bearing  floor  system,  thence  through  the  succes- 
sive stages  to  the  foundations.  The  latter  would  seem  to 
require  the  first  attention ;  but  as  they  are  the  last  to  be  cal- 
culated, being  dependent  on  all  other  considerations,  they 
have  here  been  placed  last.  The  illustrations  and  examples 
given  have  been  largely  obtained  through  the  courtesy  of  the 
architects  of  the  respective  buildings.  An  endeavor  has  been 
made  to  present  only  the  most  practical  methods. 

J.  K.  F. 

BOSTON,  October,  1901. 


CONTENTS. 


CHAPTER   I. 

PACK 

"SKELETON"  OR  "CAGE"  CONSTRUCTION i 

Necessity  for  Skeleton  Construction — Early  Forms  of  Iron  Con- 
struction— Introduction  of  Present  Forms  and  Methods — Origin  of 
Steel  Footings — Origin  01  Skeleton  Methods — Development  of 
Skeleton  Methods — Skeleton  Construction  denned — Cage  Con- 
struction. 

CHAPTER    II. 

FIRE  PROTECTION * ...     12 

Fire  Losses — Fireproof  Construction — Chicago  Athletic  Club  Build- 
ing Fire— Pittsburg  Fire— Home  Insurance  Building  Fire— Intro- 
duction of  Terra-cotta — Fire-resisting  Materials — Slow-burning 
Construction — Mill  Construction — Fire-resisting  Design — Lessons 
from  Past  Fires — Fireproof  Partitions — Fireproof  Doors  and  Win- 
dows—Installation of  Piping,  etc. 


CHAPTER    III. 

TYPICAL  BUILDINGS,  ERECTION,  PERMANENCY,  ETC 31 

Typical  Office  Buildings,  Descriptions  and  Illustrations — Erection 
of  Steelwork — Erection  of  Skeleton  Construction  Buildings — Per- 
manency of  Skeleton  Construction — Painting  of  Steelwork. 


CHAPTER    IV. 

FLOORS  AND  FLOOR  FRAMING 89 

Brick  and  Corrugated-iron  Arches — Introduction  of  Terra-cotta 
Arches — Early  Forms  of  Terra-cotta  Arches — Denver  Tests — Man- 
ufacture of  Terra-cotta  Arch-blocks — Construction  of  Flat  Terra- 
cotta Arches  —  Side  -  construction  Arches  —  End  -construction 
Arches — Combination  Arches  — Segmental  Terra-cotta  Arches — 
Raised  Skew-backs— Choice  of  Terra-cotta  Arch— Concrete  and 

v 


vi  CONTENTS. 

MOT 

Composition  Floors — Roebling  Floors — Columbian  Floor — Ex- 
panded Metal  Co.'s  Floors — Metropolitan  Floor — Selection  of  Floor 
Type — Building  Laws  -  Floor  Loads  -Live  Loads — Dead  Loads — 
Floor-framing — Floor-beam.,  Metliod  of  Calculating,  etc. — Tie- 
rods — Girders — Connections — Detailing. 

CHAPTER   V. 

EXTERIOR  WALLS.— PIERS 144 

Methods  of  Building— Load-supporting  Walls — Self-supporting 
Walls  —  Veneer  Construction  Walls  —  Materials — Fire-resisting 
Qualities — Stone  Masonry— Brick  and  Terra-cotta — Method  of 
Setting — Hooks,  Ties,  etc. — Wall-columns — Free-standing  Wall- 
columns —  Protection  of  Exterior  Metal-work — Protection  of  Col- 
umn Interiors— Anchorage — Party  Walls — Thickness  of  Walls — 
Allowable  Unit  Stresses. 

CHAPTER   VI. 

SPANDRELS  AND  SPANDREL  SECTIONS. — BAY  WINDOWS. 167 

Spandrels  defined  and  illustrated — Anchors,  Ties,  etc. — Typical 
Spandrel  Sections — Court  Walls — Bay  Windows — Calculation  of 
Spandrel  Members — Lintels — Tables  used  in  Calculation  of  Span- 
drel Loads. 

CHAPTER   VII. 

COLUMNS 191 

Cast-iron  Columns — Steel  Columns — Channel  Columns — Plate 
and  Angle  Columns — Z-bar  Columns — Special  Columns — Theo- 
retical Requirements  in  Design — Ordinary  Formulae — Practical 
Requirements  in  Design — Cost,  Availability — Shopwork  and  Work- 
manship —  Eccentric  Loading  —  Method  of  Treating  Eccentric 
Loads — Girder  Connections,  Central  Loading — Convenient  Con- 
nections, Splices — Vertical  Column  Splices — Relation  of  Size  to 
Small  Sections — Fireproofing  Capabilities — Summary — Column 
Bases— Steel  Column  Shoes — Cast  Stands — Column  Loads — Col- 
umn Sheets — Proportioning  Column  Sizes — Details  and  Splices — 
Fireproofing  of  Columns. 

CHAPTER   VIII. 

WIND-BRACING 249 

Diversity  of  Practice — Intensity  of  Wind  Pressure — Methods  of 
Wind-bracing — Analysis  of  Sway  Bracing — Examples — Analysis 
of  Portal  Bracing— Examples — Analysis  of  Knee-braces— Exam- 
ples— Analysis  of  Lattice-girder  Bracing — Examples — Deflection 
or  Vibration  under  Wind  Pressure — Building  Laws. 


CONTENTS.  vii 


CHAPTER   IX. 

PACK 

FOUNDATIONS 284 

Importance  of — Bearing  Power  of  Foundation  Materials — Bearing 
Pressures,  Building  Laws — Examples  of  Foundation  Pressures — 
Test-loads — Test-borings — Adjoining  or  Party  Walls — Shoring — 
Underpinning — Settlement — Concrete — Foundation  Loads — Pres- 
ent Types  of  Foundations — Proportioning  Grillage  Areas — Timber 
Grillage — Masonry  in  Foundations — Comparison  of  Masonry  Foot- 
ings and  Steel  Grillage — Rail  Footings — Beam  and  Rail  Footings 
— Beam  Footings — Combined  Footings — Two  Equally  Loaded 
Columns,  Area  Rectangular — Two  Unequally  Loaded  Columns, 
Area  Rectangular — Two  Unequally  Loaded  Columns,  Trapezoidal 
Area — Three  Unequally  Loaded  Columns,  Area  Rectangular — 
Continuous  Grillage  —  Fibre  Stresses  for  Foundation  Beams  — 
Painting  of  Steel  Foundations — Pile  Foundations — Test-loads  on 
Piling — Formulae  for — Specifications  for — Water-level — Examples 
of  Pile  Foundations  —  Combined  Grillage  and  Piling — Building 
Laws — Foundations  to  Bed  Rock — Open  Cylinders — Pneumatic 
Caissons,  Use  of  and  Design  of — Examples  of. 


CHAPTER   X. 

SPECIFICATIONS.— INSPECTION 371 

Importance  of  Specifications — Structural  Steel — Quality  of  Mate- 
rial—  Chemical  Constituents  —  Physical  Properties  —  Finish  of 
Material — Shopwork — Detailed  Specifications  for  Structural  Iron 
and  Steel — Inspection — Relative  Value  of  Detailed  Inspection. 


LIST  OF  ILLUSTRATIONS. 


View  of  Lower  New  York  from  Dun  Building Frontispiece 

View  of  Post-office  Square " 

TIG.  PAGE 

1.  Early  Form  of  Wrought-iron  Girders,  used    in  Sedgwick  Hall, 

Lenox,  Mass 3 

2.  Cast-iron    Girders   and    Floor-beams  removed   from  old   Boston 

Public  Library 3 

3.  Spandrel  Section,  Tacoma  Building,  Chicago 8 

4.  Foundation  Detail,  Tacoma  Building,  Chicago 8 

5.  Exterior  View  of  Home  Store  and    Office  Buildings,  Pittsburg, 

after  Fire 19 

6.  Interior  View  of  Home  Store  Building,  Pittsburg,  after  Fire....  ai 

7.  Arrangement  for  Pipe-space  in  Corridors 30 

8.  Chicago  Stock  Exchange  Building,  Perspective 32 

9.  Chicago  Stock  Exchange  Building,  Ground  Floor  Plan 33 

10.  Chicago  Stock  Exchange  Building,  Typical  Office  Floor  Plan....  33 

11.  Marquette  Building,  Chicago,  Photograph 35 

12.  Marquette  Building,  Chicago,  Typical  Office  Floor  Plan 38 

13.  Reliance  Building,  Chicago,  Photograph 39 

14.  Reliance  Building,  Chicago,  Typical  Office  Floor  Plan 41 

15.  The  Masonic  Temple  Chicago,  Photograph 43 

16.  The  Monadnock  Building,  Chicago,  Photograph .  45 

17.  New  York  Life  Insurance  Building,  Chicago,  Perspective 47 

18.  New  York  Life  Insurance  Building,  Chicago,  Plan  of  Banking 

Floor 48 

19.  New  York  Life  Insurance  Building,  Chicago,  Typical  Office  Floor 

Plan 49 

20.  Park  Row  Building,  New  York  City,  Photograph 51 

21.  Broadway  Chambers,  New  York  City,  Photograph 53 

22.  Broadway  Chambers,  New  York  City,  Basement  Floor  Plan 55 

23.  Broadway  Chambers,  New  York  City,  Ground  Floor  Plan 55 

24.  Broadway  Chambers,  New  York  City,  Typical  Floor  Plan 55 

ix 


x  LIST  OF  ILLUSTRATIONS. 

FIG.  PACK 

25.  Jewelers'  Building,  Boston,  Mass.,  Photograph 57 

26.  Fort  Dearborn  Building,  Chicago,  Perspective 59 

27.  Fort  Dearborn  Building,  Chicago,  Typical  Office  Floor  Plan 60 

28.  Gillender  Building ,  New  York  City,  Photograph 61 

29.  Champlain  Building,  Chicago,  Typical  Office  Floor  Plan 63 

30.  Old  Colony  Building,  Chicago,  Perspective 64 

31.  Montgomery,  Ward  &  Co.'s  Building,  Chicago,  Photograph 65 

32.  Entrance  Hall,  New  York  Life  Insurance  Building,  Chicago 67 

33.  Reliance  Building,  during  Construction 69 

34.  Reliance  Building,  during  Construction 71 

35.  Broadway  Chambers,  during  Construction 7j 

36.  Broadway  Chambers,  during  Construction 75 

37.  Brick-arch  Construction 90 

38.  Corrugated  Iron  Arch 90 

39.  Terra-cotta  Arch  used  in  Equitable  Building,  Chicago  (1872) 91 

40.  Terra-cotta  Arch  used  in  Montauk  Building,  Chicago  (1881) 91 

41.  Terra-cotta  Arch  used  in  Home  Insurance  Building,  Chicago  (1884)  91 

42.  The  "  Lee  "  Terra-cotta  Flat  Arch 93 

43.  Side  Construction  Terra-cotta  Arch,  Bevelled  Joints 97 

44.  Side  Construction  Terra-cotta  Arch,  Radial  Joints 9& 

45.  End  Construction  Terra-cotta  Arch 99 

46.  End  Construction  Terra-cotta  Arch  "  Pioneer  "  Type 100 

47.  Johnson  Type  of  Terra-cotta  Arch 100 

48.  Combination  Terra-cotta  Arch 101 

49.  Combination  Terra-cotta  Arch  "  Excelsior  "  Type 101 

50.  Segmental  Terra-cotta  Arch 102 

51.  Segmental  Terra-cotta  Arch 103 

52.  Side  Construction  Terra-cotta  Arch,  Raised  Skewbacks 103 

53.  Roebling  Concrete  Floor  Arch  with  Suspended  Ceiling 104 

54.  Columbian  "  Flat-ceiling"  Floor  Construction 106 

55.  Expanded  Metal  Co.'s  Floor  with  Suspended  Ceiling 108 

56.  Expanded  Metal  Co.'s  Concrete  Arch • 108 

57.  Metropolitan  Floor,  Flat-ceiling  Construction 109 

58.  Typical  Framing  Plan,  Fort  Dearborn  Building 127 

59.  Typical  Framing  Plan,  Reliance  Building 128 

60.  Typical  Framing  Plan,  Gillender  Building 130 

61.  Typical  Framing  Plan,  Am.  Surety  Co.'s  Building,  New  York...  131 

62.  Forms  of  Steel  Girders  used  in  Building  Construction 136 

63.  Isometrical  View  of  Connection  of  Floor-beams  to  Girders 137 

64.  Standard  Beam-connections 139 

65.  Connections  for  Beams  of  Different  Depths 139 

66.  Shop  Detail  of  Framed  Beam 142 

67.  Connections  of   Beams,  Girders,  and    Columns   in  "The  Fair" 

Building,  Chicago , 143 

68.  Detail  showing  Masonry  Walls  carried  at  Second-floor  Level 146 

69.  Detail  of  Terra-cotta  Front.     Reliance  Building 153. 


LIST  OF  ILLUSTRATIONS.  xi 

FIG.  PACK 

70.  Section  through  Wall  at  Main  Entrance  to  Masonic  Temple 154 

71.  Fireproofing  of  Columns  in  Exterior  Walls 156 

72.  Detail  of  Corner  Pier  and  Column.     Reliance  Building 157 

73.  Detail  of  Wall-girders  and  Corner  Column.     Reliance  Building..  157 

74.  Detail  of  Columns  in  Exterior  Walls.     Fisher  Building 157 

75.  Detail  of  "  Free-standing"  Wall-columns.     St.  Paul  Building...  158 

76.  Diagram  of  Wall-thicknesses  for  Mercantile  Buildings 163 

77.  Diagram   of  Wall-thicknesses  for   Hotels    and    Office    Buildings 

other  than  Skeleton  Construction 163 

78.  Spandrel  Section.     Ashland  Block,  Chicago 168 

79.  Spandrel  Section.     Reliance  Building 168 

80.  Connection  of  Cast  Mullions.     Reliance  Building 168 

81.  Spandrel  Section,  eleventh  floor.     Fort  Dearborn  Building 169 

82.  Spandrel  Section,  twelfth  floor.     Fort  Dearborn  Building 170 

83.  Spandrel  Section,  first  floor.     Fort  Dearborn  Building 170 

84.  Spandrel  Section,  Roof  and  Cornice.     Fort  Dearborn  Building.. .  171 

85.  Spandrel  Section.     Marquette  Building,  Chicago 172 

86.  Spandrel  Section.     Marshall  Field  Building 173 

87.  Spandrel  Section.     Marshall  Field  Building 174 

88.  Spandrel  Section,  eighteenth  floor.    American  Surety  Co.'s  Build- 

ing, New  York 174 

89.  Spandrel  Section,  twentieth  floor.     American  Surety  Co.'s  Build- 

ing, New  York 175 

90.  Spandrel  Section,  fourth  floor.     Gillender  Building,  New  York..  176 

91.  Spandrel  Section,  fifteenth  floor.     Spreckels   Building,  San  Fran- 

cisco   176 

92.  Spandrel  Section,   sixteenth   floor.      Broadway   Chambers,    New 

York 177 

93.  Spandrel  Section,  fourth  floor.     Broadway  Chambers,  New  York  177 

94.  Spandrel  Section,  Court  Walls.     Marshall  Field  Building 178 

95.  Spandrel  Section.     Typical  Court  Wall 179 

96.  Lintel  Section,  Court  Windows.     Cable  Building,  Chicago 180 

97.  Lintel  Section,  Court  Opening.     Cable  Building,  Chicago 180 

98.  Lintel  Section,  Alley  Windows.     Cable  Building,  Chicago 180 

99.  Spandrel  Section  through  Bay  Window.  Masonic  Temple,  Chicago  181 

100.  Spandrel  Section  at  Bottom  of  Bay  Window.     Masonic  Temple, 

Chicago 181 

101.  Half  Plan  of  Framing  for  Bay  Window.     Reliance  Building 182 

102.  Half  Plan  through  Bay  Window  Walls.     Reliance  Building 182 

103.  Spandrel  Section  through  Centre  of  Bay  Window.    Reliance  Build- 

ing   183 

104.  Spandrel  Section  at  Side  of  Bay  Window.     Reliance  Building 183 

105.  Floor   and    Ceiling  Supports   in   Bay  Window.     Reliance  Build- 

ing   184 

106.  Section  through  Bay  Windows,  fifth  to  eleventh  floors.    Gillender 

Building 184 


X"  £757  OF  ILLUSTRATIONS. 

ric.  PACE 

107.  Plan  of  Bay  Windows,  fifth  to  eleventh  floors.    Gillender  Building  185 

108.  Plan  of  Bay  Window  Framing.     Gillender  Building 186 

109.  Lintels  in  Masonry  Walls 188 

no.  Details  of  Splices  for  Cast-iron  Columns 192 

in.  Typical  Forms  of  Steel  Channel  Columns 196 

112.  Typical  Forms  of  Plate  and  Angle  Columns 197 

1 13.  Typical  Forms  of  Z-bar  Columns 198 

114.  Special  Forms  of  Steel  Columns 199 

115.  Column  Forms,  showing  required  Punching  Operations 206 

116.  Detail  of  Larimer  Column 207 

117.  Detail  of  Larimer  Column 207 

118.  Detail  of  Gray  Column  and  Connecting  Girders 215 

119.  Detail  of  Phoenix  Column 215 

120.  Detail  of  Phoenix  Column  Splice 218- 

121.  Detail  of  Phoenix  Column  used  in  Old  Colony  Building 218 

122.  Detail  of  Phoenix  Column  Splice  used  in  R.  G.  Dun  Building,  New 

York 219 

123.  Detail  of  Z-bar  Column  Splice.     Monadnock  Building 219 

124.  Detail  of  Box  Column  Splice 220 

125.  Detail  of  Column  Connections  and  Wind-bracing.     Pabst   Build- 

ing, Milwaukee 221 

126.  Detail  of  Column  Splice.     Reliance  Building 222 

127.  Detail  of  Girder  and  Column  Connections.    American  Surety  Co.'s 

Building,  New  York 224 

128.  Column  Section  used  in  Waldorf-Astoria  Hotel,  New  York 226 

129.  Column  Section  used  in  Waldorf-Astoria  Hotel,  New  York 226 

130.  Heavy  Column  Section.     Park  Row  Building,  New  York 226 

131.  Heavy  Column  Section.     Waldorf-Astoria  Hotel 226 

132.  Heavy  Column  Section.     Y.  M.  C.  A.  Building,  Chicago ,227 

133.  Cast-iron  Base-plate 228 

134.  Steel  Column  Shoe 229 

135.  Cast-iron  Column  Stand 231 

136.  Shop  Detail  of  Z-bar  Column 243 

137.  Detail  of  Z-bar  Column  Splice,  for  Same  Size  Columns 244 

138.  Detail  of  Z-bar  Column  Splice,  for  Different  Size  Columns 244 

139.  Method  of  Fireproofing  Phoenix  Columns 247 

140.  Method  of  Fireproofing  Channel  Columns 247 

141.  Method  of  Fireproofing  Z-bar  Columns 247 

142    Method  of  Fireproofing  Columns.     Monadnock  Building 247 

143.  Diagram  of  Wind-bracing.     Sway-rods 258 

144.  Diagram  of  Wind-bracing.     Sway-rods  through  Two  Stories 258 

145.  Diagram  of  Wind-bracing.     Portals , 258 

146.  Diagram  of  Wind-bracing.     Knee-braces 258 

147.  Diagram  of  Wind-bracing.     Lattice-girders 258 

148.  Figure  showing  Analysis  of  Sway-rod  Bracing 261 

149.  Figure  showing   Typical  Sway-rod  Bracing 263. 


LIST  OF  ILLUSTRATIONS.  xiii 

FIG.  PAOB 

150.  Cross-section  of  Masonic  Temple,  Chicago,  showing  Wind-bracing  264 

151.  Floor  Plan  of  Venetian  Building 264 

152.  Wind-bracing  in  Venetian  Building 265 

153.  Detail  of  Channel-struts.     Venetian  Building 266 

154.  Detail  of  Channel-strut  Connections.     Venetian  Building 267 

155.  Partial  Cross-section  of  Venetian  Building 267 

156.  Figure  showing  Analysis  of  Portal  Bracing 268 

157.  Portal-strut  used  in  Monadnock  Building 271 

158.  Cross-section  showing  Portals  in  Old  Colony  Building 271 

159.  Detail  of  Portal  in  Old  Colony  Building 272 

160.  Figure  showing  Analysis  of  Knee-bracing 273 

161.  Detail  of  Knee-bracing.     Isabella  Building 274 

162.  Detail  of  Channel-struts  and  Gussets.     Fort  Dearborn  Building..  275 

163.  Figure  showing  Analysis  of  Lattice-girder  Bracing 276 

164.  Figure  showing  Analysis  of  Lattice-girder  Bracing 277 

165.  Diagram  Elevation  of  Park  Row  Building,  showing  Wind-bracing  279 

166.  Needle-beams  used  in  shoring  at  Standard  Oil  Co.'s  Building. . . .  298 

167.  Underpinning  at  Commercial  Cable  and  Queen  Insurance  Co.'s 

Buildings 300 

168.  Timber-grillage   Foundation,  Fisheries  Building,  World's  Colum- 

bian Exposition 313 

169.  Detail  of  Rail-grillage  Footing 317 

170.  Detail  of  Masonry-pier  Footing 317 

171.  Detail  of  Beam  and  Rail  Footing  in  "The  Fair"  Building 321 

172.  Simple  Beam  Footing.     Marquette  Building 325 

173.  Diagram  of  Calculation  of  Simple  Beam  Footing 326 

174.  Combined  Footing.     Old  Colony  Building 327 

175.  Combined  Footing 329 

176.  Diagram  of   Combined  Footing,  Two  unequally  loaded  Columns, 

Area  Rectangular 330 

177.  Diagram  of  Combined  Footing,  Two  unequally  loaded  Columns, 

Trapezoidal  Area 332 

178.  Diagram  of  Unit  Pressures  for  Footing  as  in  Fig.  177 333 

179.  Line  of  Flexure  for  Continuous  Girder 335 

180.  Diagram  of  Combined  Footing,  Three  unequally  loaded  Columns, 

Area  Rectangular 335 

181.  Diagram  of  Unit  Pressures  for  Footing  as  in  Fig.  180 337 

182.  Continuous  Grillage.    Spreckels  Building,  San  Francisco 340 

183.  Pile  Foundations  in  Chicago  Post-office 352 

184.  Pile  Foundations  in  Park  Row  Building 353 

185.  Pile  Foundation  in  Fisher  Building,  Chicago 354 

186.  Combination  Grillage  and  Piling 355 

187.  Open  Cylinder  Foundation 358 

188.  Section  through  Pneumatic  Caisson 361 

189.  Plan  of  Caissons  in  Manhattan   Life   Insurance  Co.'s   Building, 

New  York fc 364 


xiv  LIST  OF  ILLUSTRATIONS. 

FIG.  PACK 

190.  Cross-section   of   Caissons   in    Manhattan    Life  Insurance    Co.'s 

Building,  New  York 365 

191.  Plan  of  Caisson.     Gillender  Building 366 

192.  Detail  of  Caisson.     Gillender  Building 367 

193.  Detail  of  Caisson  Cutting-edge.      Gillender  Building 368 

194.  Foundation  Piers.     American  Surety  Co.'s  Building,  New  York..  369 


ARCHITECTURAL  ENGINEERING. 


CHAPTER   I. 
"SKELETON"   OR  "CAGE"   CONSTRUCTION. 

SKELETON  construction  is  a  natural  outgrowth  resulting 
from  conditions  imposed  upon  the  owners  of  property  lying 
within  the  business  sections  of  our  large  American  cities. 

The  fact  that  in  large  communities  it  is  found  most  advan- 
tageous as  to  time  and  convenience  for  business  transactions, 
to  have  all  possible  office  buildings  and  commercial  interests 
concentrated  within  limited  areas,  has  caused  the  adoption  of 
buildings  of  such  heights  as  were  not  considered  possible,  and 
still  less  practicable,  before  the  introduction  of  steel-skeleton 
methods. 

Topographical  limitations  have  also  proved  potent  factors 
in  this  tendency  toward  concentration.  In  New  York  City  the 
business  and  financial  centre  has  long  been  established  within 
a  comparatively  limited  area  at  the  extreme  end  of  Manhattan 
Island,  and  extension  in  area  meant  a  growth  in  one  direction 
only,  thus  undesirably  increasing  the  length  of  the  channels 
of  business  intercourse ;  while  in  Chicago,  where  limitations  of 
area  were  first  overcome,  the  commercial  centre  covers  only 
three-fourths  of  a  square  mile  within  topographical  boundaries 
which  make  enlargement  impossible. 


2  ARCHITECTURAL   ENGINEERING. 

The  erection  of  high  buildings  with  greatly  increased  floor 
space  thus  became  a  necessity,  not  only  as  an  accommodation 
for  the  rapid  growth  of  trade  interests,  but  as  a  business 
proposition  in  the  improvement  of  real  estate  so  situated. 
Increased  floor  areas  became  necessary  to  insure  a  realization 
on  the  investment,  and  with  the  enormous  and  seemingly 
ever-increasing  values  of  real  estate  in  the  centres  of  such 
limited  commercial  areas,  the  natural  vertical  extension  of  floor 
upon  floor  has  constantly  increased  in  the  endeavor  to  make 
investment  in  such  buildings  a  safe  and  profitable  business 
venture. 

The  high  building  has  become  a  fixed  and  definite  feature 
in  our  large  American  cities  at  least,  and  its  inception  and 
growth  have  been  made  possible  only  through  the  introduction 
and  rapid  development  of  steel-building  construction  and  fire- 
proofing  methods.  Without  steel  buildings,  the  art  of  fire- 
proofing  would  never  have  been  called  into  existence,  while 
without  the  development  of  fire-proofing  principles,  steel  con- 
struction, as  applied  to  buildings,  must  have  been  discontinued 
long  ago. 

Early  Forms  of  Iron  Construction. — All  forms  of  iron  and 
steel  construction  have  undergone  wonderful  changes  in  com- 
paratively recent  years,  and  there  are  few  fields  where  more 
radical  growth  and  improvement  may  be  noted.  To  appreciate 
this,  it  is  only  necessary  to  remember  that  most  of  our  present 
forms  and  combinations  of  rolled  iron  and  steel  were  unknown 
in  either  bridge  or  building  practice  fifty  years  ago,  and  a 
comparison  of  present  types  with  early  examples  of  cast-  and 
wrought-iron  in  building  work  reveals  many  decidedly  in- 
teresting curiosities.  Take,  for  example,  the  iron  girders 
removed  from  Sedgwick  Hall  at  Lenox,  Mass.,  some  years 
ago.  (See  Fig.  I.)  "These  were  each  made  of  three  plates, 
a  top  and  a  bottom  one,  both  horizontal,  with  a  vertical  corru- 
gated web  plate  between,  the  corrugations  running  up  and 


"SKELETON"   OR  "CAGE"    CONSTRUCTION.  3 

down.  The  three  pieces  were  fastened  together  with  vertical 
bolts  extending  through  the  top  and  bottom  plates,  about  20 
ins.  apart,  and  alternating,  one  on  this  side  and  the  next  on 
the  other  side  of  the  vertical  plate,  the  transmission  of  strains 


j.-1-r-ri  I  i  I  I   IMI  I  II  T-r-H    I 


FIG.  I. — Early  Form  of  Wrought-iron  Girders,  used  in  Sedgwick  Hall, 
Lenox,  Mass. 

from  the  web  to  the  flange  depending  entirely  upon  friction. 
These  beams  were  probably  placed  in  position  about  1 840,  and 
some  of  them  still  remain  in  the  building. ' '  * 

The  strange  forms  employed  in  cast-iron  were  well  illus- 
trated in  some  cast-iron  floor-beams  removed  from  the  old 
Boston  Public  Library  in  1899.  Fig.  2  was  made  from 


FIG.  2. — Cast-iron  Girders  and  Floor-beams  removed  from  Old  Boston 
Public  Library. 

sketches  and  photographs  taken  by  Mr.  C.  H.  Blackall,  the 
architect  of  the  new  Colonial  Building  erected  on  this  site. 
The  cast-iron  girders,  16  ins.  deep,  were  spaced  about  10  ft. 
centres.  The  floor-beams  or  joists,  spaced  about  4  ft.  centres 

*See  "  The  Use  of  Steel  in  Large  Buildings,"  by  C.  T.  Purdy,  Journal 

of  the  Assoc.  of  Eng.  Societies,  vol.  xiv.  No.  3. 


4  ARCHITECTURAL  ENGINEERING. 

and  carrying  segmental  brick  arches,  were  hooked  over  lugs 
cast  on  the  lower  flanges  of  the  girders,  as  shown  in  the  illus- 
tration. 

Introduction  of  Present  Forms  and  Methods.— With  the 
invention  of  the  iron  I-beam  in  France  and  England  in  1853, 
the  manufacture  of  floor-beams  was  at  once  introduced  into  this 
country.  Iron  I-beams  were  first  rolled  in  the  United  States 
at  Trenton,  N.  J.,  in  1854,  while  steel  beams  were  not  rolled 
until  as  late  as  1885,  when  their  manufacture  was  started  by 
the  Carnegie  Steel  Co. 

Iron,  as  a  substitute  for  wood  in  constructive  purposes,  was 
long  thought  to  be  fire-proof,  or  fire-resisting,  because  incom- 
bustible. For  this  reason,  iron  not  only  replaced  wood  in 
many  features  of  building  construction,  but  was  also  used  as  a 
substitute  for  masonry,  as  is  shown  by  the  extended  use  of  cast- 
iron  for  entire  fronts  of  buildings  from  about  1855  to  1870. 
This  practice  was  principally  due  to  the  idea  that  cast-iron, 
because  incombustible,  was  superior  to  marble  or  stone  work, 
which  would  crack  and  flake  when  exposed  to  fire  and  thus  be 
ruined  in  appearance,  even  though  it  did  not  fail  completely. 
A  few  cases  of  total  failure,  however,  in  such  cast-iron  fronts, 
and  the  discovery  that  iron  became  unreliable  under  tempera- 
tures of  1000°  Fahr.,  caused  such  construction  to  be  condemned 
by  fire  departments  and  insurance  interests,  and  after  about 
1870  the  necessity  of  some  adequate  protection  for  constructive 
iron  members  became  generally  recognized.  And  no  sooner 
did  fire  protection  as  a  covering  for  structural  steel  become  an 
established  fact,  than  the  development  of  iron  and  steel  forms 
and  combinations  progressed  hand  in  hand  with  those  improve- 
ments in  fire-proofing  methods  which  furthered  development 
and  encouraged  originality  in  this  field. 

Previous  to  1883,  a  height  of  nine  or  ten  stories  was  very 
nearly  a  practical  limit  in  building  construction.  Beams  and 
columns  usually  formed  an  adjunct  only  to  the  masonry,  as 


"SKELETON"   OR  "CAGE"    CONSTRUCTION,  5 

the  walls  were  made  heavy  enough  to  carry  the  floor-beams 
and  girders,  and  the  resultant  loads.  Circular  cast-iron  or 
Phoenix  columns  of  wrought-iron  were  used  for  interior  sup- 
ports, while  the  floor  arches,  if  intended  to  be  fire-proof,  were 
usually  made  in  segmental  form  of  brick  or  corrugated  iron,  or 
terra-cotta  at  later  dates,  levelled  on  top  with  concrete  to  the 
finished  floor  lines.  On  the  introduction  of  iron  for  construc- 
tive purposes,  in  1854,  the  only  fire-resisting  material  known 
was  ordinary  brick  work,  and  fire  proof  floor  construction  was 
obtained  through  the  use  of  segmental  brick  arches,  sprung 
between  the  beams.  Corrugated  iron  and  concrete  floors  were 
then  introduced,  in  an  effort  to  dispense  with  the  centering 
required  for  brick  arches.  Both  of  these  methods,  however, 
were  heavy,  clumsy,  and  expensive  as  compared  with  present 
types,  but  they  formed  the  only  standards  until  the  introduc- 
tion of  terra-cotta. 

In  buildings  of  this  character,  iron,  where  employed  at  all, 
was  used  with  little  or  no  view  toward  securing  a  closely 
related  or  interdependent  assemblage  of  component  parts. 
Columns  and  beams  were  incorporated  in  the  design  in  a  dis- 
jointed, hap-hazard  fashion,  leaving  the  principal  reliance  for 
stability  or  strength  upon  the  masonry  construction.  This 
naturally  limited  the  possibilities  of  building  design  to  the  safe 
unit  stresses  applicable  to  masonry,  resulting  in  the  large  piers 
made  necessary  for  any  considerable  height,  and  in  bulky 
foundations  of  dimension  stone  which  soon  reached  a  limit  of 
spreading  area,  besides  filling  up  much  valuable  basement 
room. 

Origin  of  Steel  Footings. — The  first  radical  step  toward 
improvement  from  the  older  methods  was  in  the  use  of  iron 
members  to  stiffen  offsets  in  concrete  foundations.  In  the 
Montauk  Block,  ten  stories,  built  in  Chicago  in  1881-2  by 
Burnham  and  Root,  Architects,  the  foundation  piers  were 
made  of  layers  of  concrete  1 8  ins.  thick,  on  top  of  which  were 


6  ARCHITECTURAL  ENGINEERING. 

placed  dimension  stones  forming  pyramids,  thus  nearly  filling 
the  entire  basement.  Under  two  stacks  of  fire-proof  vaults, 
such  foundations  would  have  interfered  with  basement  space 
where  it  was  desired  to  locate  boilers  and  engines,  so  that, 
under  these  conditions,  the  innovation  was  adopted  of  embed- 
ding iron  rails  in  the  concrete  footings  to  increase  the  allowable 
offsets  in  the  concrete  layers.  This  constituted  a  most  im- 
portant precedent,  which  has  gradually  developed  into  present 
grillage  design. 

Origin  of  Skeleton  Methods.— By  far  the  most  important 
step,  however,  in  the  development  of  the  Chicago  construction, 
occurred  in  1883,  when  Mr.  W.  L.  B.  Jenney  prepared  plans 
for  a  ten-story  office  building  for  the  Home  Insurance  Com- 
pany; and  to  this  architect  belongs  the  credit  for  the  concep- 
tion of  skeleton  construction.  His  departure  from  previous 
practice  was  bold  and  progressive,  and  from  the  successful 
carrying  out  of  his  plans  may  be  dated  the  marked  interest 
taken  in  a  construction  which  needed  but  little  stimulus  to 
insure  its  general  adoption. 

In  order  to  obtain  a  maximum  light  for  the  offices  proposed 
in  his  new  design,  Mr.  Jenney  decided  to  reduce  the  width  of 
all  exterior  piers  as  much  as  possible,  and  to  use  cast-iron 
columns  within  the  piers  to  carry  the  floor-loads,  thus  relieving 
the  masonry  piers  of  these  loads,  and  consequently  reducing 
their  areas.  The  question  then  arose  as  to  the  supposed 
expansion  and  contraction  of  continuous  metal  columns  150  ft. 
high,  subjected  to  a  variation  of  some  120°  Fahr.,  and  this 
suggested  carrying  the  walls,  as  well  as  the  floors,  story  by 
story  on  the  columns,  thus  dividing  the  movement.  The 
exterior  piers  were  made  self-supporting,  but  the  spandrel 
portions,  between  the  top  of  one  window  and  the  bottom  of  the 
window  above,  were  carried  on  iron  girders  placed  in  the 
exterior  walls  and  extending  from  column  to  column.  The 
foundation  piers  in  this  building  were  made  of  masonry, 


"SKELETON"   OR  "CAGE"    CONSTRUCTION.  7 

pyramidal  in  form  and  consisting  of  alternate  courses  of  rubble 
and  dimension  stone. 

This  method  of  supporting  the  walls  as  well  as  the  floors 
and  floor-loads  on  beams  and  columns  was  a  most  important 
departure  from  former  methods,  and  attendant  responsibilities 
of  design  were  at  once  encountered.  The  concentration  of 
superstructure  weights  resulting  from  such  design  was  soon 
given  consideration,  and  the  employment  of  iron  rails  in 
foundations,  as  in  the  Montauk  Block,  was  extended  to  more 
important  use  in  the  calculation  of  isolated  footings. 

As  early  as  1872  a  pamphlet  had  been  published  by 
Frederick  Bauman,  entitled  "The  Method  of  Constructing 
Foundations  on  Isolated  Piers, ' '  but,  excepting  the  partial 
adoption  of  these  principles  in  the  Montauk  Block,  it  was  not 
until  the  same  architects  designed  the  Rookery  Building  in 
1885-6,  that  isolated  footings  were  really  employed  with  the 
use  of  steel  members.  In  this  building  the  footings  were  made 
of  two  courses  of  steel  rails  laid  at  right  angles  to  each  other 
and  embedded  in  concrete,  with  I-beams  crossing  the  upper 
courses,  on  which  were  placed  cast  column  bases.  The 
masonry  walls  were  self-supporting. 

Development  of  Skeleton  Methods.— These  improvements 
in  design  were  quickly  appreciated,  and  soon  incorporated  in 
succeeding  buildings,  the  Tacoma  Building,  14  stories  high 
(Chicago,  Holabird  &  Roche,  Architects),  being  probably  the 
first  complete  type  of  skeleton  construction.  A  spandrel 
section  in  this  building  is  illustrated  in  Fig.  3,  while  one  of 
the  column  footings  is  shown  in  Fig.  4.  It  is  interesting  to 
compare  this  spandrel  section  used  for  carrying  a  plain  brick 
wall,  with  the  more  elaborate  spandrel  sections  shown  in 
Chapter  VI,  where  moulded  and  ornamental  terra- cotta  is 
employed. 

From  this  point  on,  buildings  rapidly  improved  on  their 
predecessors  in  matters  of  detail,  and  the  Chicago  or  skeleton 


8 


ARCHITECTURAL  ENGINEERING. 


type  soon  became  well  established.  It  was  found  that  if  the 
concentrated  column  loads  were  properly  distributed  over  the 
available  ground  area,  the  weight  of  the  structures,  and  conse- 


FlG.  3. — Spandrel  Section,  Tacoma  Building,  Chicago. 

quently  the  heights,  could  go  on  increasing  until  the  footings 
covered  the  entire  site,  within  permissible  limits  of  bearing 
capacity  per  square  foot.  Lighter  building  materials  were 
consequently  employed,  and  buildings  were  made  higher,  until, 


FIG.  4. — Foundation  Detail,  Tacoma  Building,  Chicago. 

in  1890,  the  first  twenty-storied  building  (the  Masonic  Temple) 
was  erected  in  Chicago. 

This  revolution  of  old  methods  went  on  simultaneously  in 
both  the  West  and  the  East,  but  building  laws,  industrial 
interests,  and  a  greater  conservatism  in  the  East,  retarded 
there  the  early  development  which  became  particularly  marked 
in  Chicago. 

-    The  Manhattan  Life  Building  in  New  York  was  the  first 
notable  example  in  the  East  of  a  building  erected  after  the 


"SKELETON"   OR  "CAGE"    CONSTRUCTION.  9 

new  methods,  and  this  structure  demonstrated  to  New  York 
the  great  possibilities  afforded  by  skeleton  construction.  The 
number  of  floors  has  gradually  increased  year  by  year,  reaching 
a  height  of  thirty  stories  in  the  Ivins  Syndicate  or  Park  Row 
Building,  while  proposed  structures  of  forty  stories  are  now 
discussed  with  less  astonishment  than  were  twenty  floors  ten 
years  ago.  Nearly  all  of  the  ultra-high  buildings  are  now 
confined  to  New  York  City,  where  the  character  of  the  rock 
foundations,  coupled  with  unrestricted  building  regulations  as 
to  height,  make  such  extreme  examples  possible. 

Skeleton  Construction  Defined. — "Skeleton  construction  " 
very  properly  defines  the  type  of  building  construction  to 
which  it  was  at  first  applied.  This  suggests  a  skeleton  or 
simple  framework  of  beams  and  columns,  dependent  largely 
for  its  efficiency  upon  the  exterior  and  interior  walls  and  parti- 
tions which  serve  to  brace  the  structure,  and  which  render  the 
skeleton  efficient,  much  as  the  muscles  and  covering  of  the 
human  skeleton  (to  borrow  a  comparison  used  by  various 
writers)  make  possible  the  effective  service  of  the  component 
bones.  Skeleton  construction  is  thus  defined  by  the  present 
Chicago  Building  Ordinance: 

' '  The  term  '  Skeleton  Construction  '  shall  apply  to  all 
buildings  wherein  all  external  and  internal  loads  and  strains 
are  transmitted  from  the  top  of  the  building  to  the  foundations 
by  a  skeleton  or  framework  of  metal.  In  such  metal  frame- 
work the  beams  and  girders  shall  be  riveted  to  each  other  at 
their  respective  junction  points.  If  pillars  made  of  rolled  iron 
or  steel  are  used,  their  different  parts  shall  be  riveted  to  each 
other,  and  the  beams  and  girders  resting  upon  them  shall  have 
riveted  or  bolted  connections  to  unite  them  with  the  pillars. 
If  cast-iron  pillars  are  used,  each  successive  pillar  shall  be 
bolted  to  the  one  below  it  by  at  least  four  bolts  not  less  than 
three-fourths  inch  in  diameter,  and  the  beams  and  girders  shall 
be  bolted  to  the  pillars.  At  each  line  of  floor-  or  roof-beams, 


10  .          ARCHITECTURAL  ENGINEERING. 

lateral  connection  between  the  ends  of  the  beams  and  girders 
shall  be  made  by  passing  wrought-iron  or  steel  straps  across 
or  through  the  cast-iron  column,  in  such  manner  as  to  rigidly 
connect  the  beams  and  girders  with  each  other  in  the  direction 
of  their  length.  These  straps  shall  be  made  of  wrought-iron 
or  steel,  and  shall  be  riveted  or  bolted  to  the  flanges  or  to  the 
webs  of  the  beams  and  girders. ' ' 

' '  If  buildings  are  made  fire-proof  entirely,  and  have  skele- 
ton construction  so  designed  that  their  enclosing  walls  do  not 
carry  the  weight  of  floors  or  roof,  then  their  walls  shall  be  not 
less  than  twelve  inches  in  thickness;  and  provided,  also,  that 
such  walls  shall  be  thoroughly  anchored  to  the  iron  skeleton ; 
and  provided,  also,  that  wherever  the  weight  of  such  walls 
rests  upon  beams  or  pillars,  such  beams  or  pillars  must  be 
made  strong  enough  in  each  story  to  carry  the  weight  of  wall 
resting  upon  them  without  reliance  upon  the  walls  below  them. 
All  partitions  must  be  of  incombustible  material." 

"  Cage  "  Construction. — The  more  advanced  and  approved 
practice,  however,  partakes  more  of  the  character  of  a  single 
unit  so  far  as  the  steel  is  concerned,  for  the  framework  is  now 
made  complete  in  itself,  like  a  wire  cage,  and  independent  of 
any  considerations  as  to  aid  or  support  from  any  external 
coverings ;  hence  the  name  ' '  cage  ' '  construction  has  been 
applied  to  this  method  of  high  building.  The  steel  framework, 
originally  introduced  to  carry  vertical  loads  only,  has  been 
gradually  developed  and  systematized  as  increased  attention 
has  been  bestowed  upon  the  questions  of  lateral  strength  and 
stiffness  against  wind  or  other  external  forces.  The  use  of  a 
well-braced  frame  now  permits  the  substitution  of  curtain  or 
veneer  walls  for  the  solid  masonry  construction  formerly 
required,  and  the  reduction  in  thickness  of  such  walls  to  12-in. 
or  i6-in.  protective  veneer  walls  only,  makes  it  possible  to 
obtain  much  larger  window  areas,  besides  giving  large  gains 
in  rentable  floor  areas.  It  is  also  possible  to  omit  heavy 


"SKELETON"   OR  "CAGE1'    CONSTRUCTION.  ix 

interior  walls,  substituting  therefor  light  movable  partitions 
which  may  be  placed  as  desired  by  tenants.  Foundations  are 
now  required  for  large  concentrated  column  loads,  instead  of 
distributed  loads  as  formerly,  and  the  problem  is  more  definite, 
if  not  more  simple,  and  the  design  is  always  considered  with 
reference  to  securing  all  available  basement  or  sub-basement 
areas. 

Cage  construction,  therefore,  as  exemplified  by  the  best 
examples,  consists  of  a  steel  framework  with  well-riveted  beam 
and  girder  connections,  efficiently  spliced  column  joints,  and 
efficient  wind-bracing,  to  secure  its  independent  safety  under 
all  conditions  of  loading  and  exposure. 

Architectural  Engineering. — Architectural  engineering, 
or  the  application  of  engineering  principles  to  architectural 
design  and  construction,  would  properly  constitute  a  treatise 
of  great  range,  including  the  underlying  principles  of  all  build- 
ing construction,  and  the  strengths  of  all  building  materials. 
But,  as  the  modern  office  building  presents  almost,  if  not  quite, 
all  of  the  ordinary  problems  involved  in  architectural  engineer- 
ing, this  type  of  construction  alone  will  be  considered  in  the 
following  pages,  as  being  representative  of  the  ordinary  require- 
ments demanded  of  the  architect  in  constructional  practice. 
Special  forms  of  construction,  such  as  complicated  foundation 
problems,  involving  elaborate  cantilever  design,  or  pneumatic 
caissons,  etc.,  as  well  as  roof  trusses  or  the  special  trussing 
over  large  unobstructed  areas,  must  be  generally  intrusted  to 
the  professional  engineer,  and  more  specific  data  and  theory 
may  be  obtained  from  special  works  on  such  subjects. 

The  following  chapters  are  aimed  to  present,  as  clearly 
and  practicably  as  possible,  such  data  and  practice  as  will  be 
found  of  value  in  considering  such  questions  as  floors  and  floor- 
framing,  columns,  foundations,  and  other  interdependent 
factors  in  constructive  building  design. 


CHAPTER    II. 
FIRE  PROTECTION.* 

BEFORE  considering  the  details  of  skeleton  construction  it 
will  be  well  to  consider  the  general  subject  of  fire-proofing, 
with  its  effectiveness  and  its  limitation. 

The  total  fire  loss  in  the  United  States  during  the  year 
1894  was  about  $128,000,000,  of  which  the  insurance  com- 
panies paid,  as  their  share,  some  $81,000,000.  This  stupen- 
dous drain  on  the  resources  of  the  nation  may  be  better 
appreciated  if  we  consider  that  the  full  value  of  the  pig-iron 
production  for  the  same  year  was  about  $75,000,000. 

When  to  this  fire  loss  we  add  the  estimated  amount  neces- 
sary to  maintain  the  fire  departments,  and  to  sustain  the  fire 
insurance  companies,  the  grand  total  will  exceed  $175,000,000 
annually. 

If,  then,  it  is  true,  as  stated  by  underwriters  that  forty  per 
cent,  of  all  fires  are  attributable  to  causes  easily  prevented,  a 
proper  treatment  of  the  fire  problem  certainly  becomes  a  very 
practical  and  economic  inquiry. 

The  subject  of  proper  fire  protection  is  now  recognized  as 
a  legitimate  and  important  branch  of  engineering.  It  is  no 
longer  confined  exclusively  to  endeavors  to  protect  human  life, 
but  is  greatly  increasing  in  scope,  demanding  very  careful 
thought  from  its  economic  standpoint  as  well.  And  that  this 

*  For  more  detailed  information  pertaining  to  tests  and  methods  of  fire- 
proofing,  see  author's  "  Fire-proofing  of  Steel  Buildings,"  1899.  John 
Wiley  &  Sons,  N.  Y. 

12 


FIRE  PROTECTION.  13 

question  of  fire  waste  is  being  seriously  considered  in  all  its 
aspects  and  by  all  classes  of  society  is  shown  by  the  widening 
facilities  for  the  use  of  fire-proof  construction.  The  realization 
of  low  prices  in  the  building  market  has  served  to  overthrow 
many  of  the  hitherto  unquestioned  prejudices  in  regard  to  fire- 
proof construction,  and  the  economy  of  such  design  as  opposed 
to  the  fire-trap  methods  so  long  in  vogue  is  now  being  daily 
emphasized  by  architects,  engineers,  and  the  technical  press. 
And  what  is  most  gratifying  is  the  fact  that  this  economy  is 
beginning  to  be  appreciated  not  only  by  the  owners  of  large 
office  buildings  and  stores,  but  also  by  the  more  limited  in- 
vestor, as  is  evidenced  by  the  start  already  made  in  fire-proofing 
the  ordinary  city  house,  at  a  figure  but  slightly  exceeding  the 
cost  of  non-fire-proof  methods.  It  was  found,  in  taking 
figures  for  a  building  in  Philadelphia  to  cost  $125,000,  that  a 
thoroughly  fire-proofed  construction  would  cost  only  3.6  per 
cent,  more  than  the  ordinary  method  of  building.  This  in- 
crease would  be  compensated  for  in  a  very  short  time  by  the 
decreased  insurance. 

It  does  not  seem  unreasonable  to  hope  that  fire-proof  build- 
ings may  soon  be  the  rule,  rather  than  the  exception,  and  that 
the  near  future  may  see  all  of  our  mercantile,  manufacturing, 
and  even  dwelling  houses,  except  those  of  the  very  cheapest, 
built  according  to  fire-resisting  principles.  Steel,  the  clay 
products,  and  cement  or  concrete  are  permanent,  fire-resisting, 
of  ready  adaptability,  and  of  remarkably  low  cost.  The  fire- 
trap  timber  construction  with  its  susceptibility  to  dampness, 
drought,  heat,  and  cold,  involving  dry-rot,  as  shown  by  the 
collapse  some  years  ago  of  a  prominent  hotel  in  Washington, 
must  give  way  to  new  conditions  and  further  improvement  in 
a  field  of  such  promise.  The  insurance  burden  will  be  grad- 
ually lightened,  and  human  life  be  better  protected. 

Fire-proof  Construction. — While  buildings  couldbe  erected 
with  absolutely  no  inflammable  material  in  their  construction, 


14  ARCHITECTURAL  ENGINEERING. 

there  would  still  remain  the  contents  or  property  of  the  tenants 
to  feed  possible  fire.  This  element  of  danger  cannot  be 
eliminated ;  and  added  to  this  are  the  dangers  that  come  from 
without  as  well  as  from  within.  For  as  long  as  highly  inflam- 
mable buildings  surround  even  the  most  excellent  of  modern 
fire-proof  structures  the  term  is  misleading.  Fire-proof  struct- 
ures must  stand  in  fire-proof  cities.  Hence  the  word  ' '  fire- 
proof," as  applied  to  a  modern  structure,  does  not  mean 
one  that  claims  immunity  from  all  danger  of  fire,  for  consider- 
able woodwork  must  still  be  used  in  interiors,  and  the  average 
contents  are  dangerous  in  the  extreme;  but  it  does  claim  to 
embody  principles  which  have  reduced  the  fire  hazard,  both 
interior  and  exterior,  to  a  minimum,  according  to  the  best  skill 
and  judgment  of  the  day.  The  term  implies  that  all  structural 
parts  of  the  edifice  must  be  formed  entirely  of  non-combustible 
material,  or  material  which  will  successfully  withstand  the 
injurious  action  of  extreme  heat. 

Following  is  the  definition  given  in  the  new  building 
ordinance  of  Chicago:  "The  term  'fire-proof  construction' 
shall  apply  to  all  buildings  in  which  all  parts  that  carry  weights 
or  resist  strains,  and  also  all  stairs  and  all  elevator  enclosures 
and  their  contents,  are  made  entirely  of  incombustible  material, 
and  in  which  all  metallic  structural  members  are  protected 
against  the  effects  of  fire  by  coverings  of  a  material  which  must 
be  entirely  incombustible  and  a  slow  heat-conductor.  The 
materials  which  shall  be  considered  as  fulfilling  the  conditions 
of  fire-proof  coverings  are :  First,  brick ;  second,  hollow  tiles 
of  burnt  clay  applied  to  the  metal  in  a  bed  of  mortar,  and  con- 
structed in  such  manner  that  there  shall  be  two  air-spaces  of 
at  least  three-fourths  of  an  inch  each  by  the  width  of  the  metal 
surface  to  be  covered,  within  the  said  clay  covering;  third, 
porous  terra-cotta,  which  shall  be  at  least  two  inches  thick, 
and  shall  also  be  applied  direct  to  the  metal  in  a  bed  of 
mortar. " 


FIRE  PROTECTION.  15 

Chicago  Athletic  Club  Building  Fire.— The  success  that 
has  attended  past  efforts  in  fire-proofiing  may  be  judged  by 
such  examples  of  fire  as  have  been  afforded  in  protected  struc- 
tures. One  of  the  earliest  and  most  interesting  tests  of  the 
new  methods  was  the  burning  of  the  Chicago  Athletic  Club 
building  while  under  construction.  Though  not  entirely  satis- 
factory as  a  test  of  present  building  methods,  ' '  this  building 
furnishes  an  assurance  that  was  lacking  before — that  the  metal 
parts  of  a  building  if  thoroughly  protected  by  fire-proofing, 
properly  put  on,  will  safely  withstand  any  ordinary  conflagra- 
tion, if  the  quantity  of  combustible  materials  the  building  con- 
tains is  not  greatly  in  excess  of  that  which  enters  into  the 
construction  of  the  building  itself. ' ' 

This  extract  from  the  report  of  experts  employed  to  inves- 
tigate this  fire  and  its  effects  emphasizes  two  very  important 
facts,  namely,  the  danger  of  the  indiscriminate  use  of  combus- 
ible  material  not  absolutely  necessary  in  the  construction,  and 
second,  the  evident  superiority  of  terra-cotta  as  a  fire-proofing 
substance. 

The  above  fire,  which  occurred  on  November  I,  1892,  was 
the  first  case  on  record  of  a  fire  in  a  building  intended  to  be 
fully  fire-proof  where  the  loss  to  the  insurance  companies  was 
more  than  thirty  per  cent,  of  its  value.  It  is  further  stated  in 
the  report  that  "if  the  building  had  been  completed,  it  would 
never  have  contained  combustible  material  enough  (or  so  dis- 
tributed) to  have  produced  sufficient  heat  to  have  done  any 
considerable  damage  to  the  building  by  burning. ' ' 

The  fire  in  question  was  of  very  intense  heat,  inasmuch  as 
a  vast  quantity  of  scaffolding,  flooring,  trim,  etc.,  was  collected 
in  mass,  preparatory  to  use ;  but,  in  spite  of  this,  there  seemed 
no  reason  for  questioning  the  integrity  and  strength  of  the 
building,  as  a  whole,  after  the  fire,  and  no  doubt  existed  that 
the  fire-proofing  around  the  columns  saved  them  from  utter 
collapse,  because  it  remained  in  place  until  the  fuel  that  had 


1 6  ARCHITECTURAL   ENGINEERING. 

fed  the  flames  was  well-nigh  exhausted.  The  result  to  the 
building  included  the  entire  destruction  of  all  the  interior  finish, 
plastering,  piping,  and  wiring,  as  well  as  parts  of  the  elaborate 
front  of  Bedford  stone  and  pressed  brick.  But  the  steel 
columns  and  beams  were  uninjured,  except  a  few  of  the  latter 
where  unprotected ;  and  the  tile  arches,  built  after  the  end- 
construction  method,  were  almost  uninjured,  in  spite  of  the 
combined  action  of  great  heat  and  frequent  applications  of  cold 
water. 

Pittsburg  Fire. — A  second  notable  fire  of  great  importance 
to  all  those  interested  in  fire-proofing  methods  occurred  in 
Pittsburg  in  May,  1897.  This  fire  resulted  in  the  complete 
destruction  of  a  large  wholesale  grocery  house,  where  the  fire 
originated,  and  in  the  partial  wrecking  of  three  adjoining  build- 
ings, all  of  which  were  presumably  of  modern  fire-resisting 
design.  Of  the  latter  structures,  one  was  known  as  the  Home 
store  building,  one  as  the  Home  office  building,  and  the  third 
as  the  Methodist  building. 

The  Home  store  and  office  buildings,  of  six  and  four  stories 
respectively,  were  separated  from  the  Jenkins  building  by  a 
street  60  ft.  wide,  but  upon  the  falling  of  the  walls  of  the  latter 
structure,  their  unprotected  fronts  were  subjected  to  the  full 
force  of  the  flames,  and  the  almost  complete  destruction  of  the 
buildings  and  their  contents  soon  followed.  The  Methodist 
building,  separated  from  the  Jenkins  building  by  an  alley,  was 
not  threatened  until  the  side  wall  of  the  Jenkins  building  fell, 
as,  previous  to  that  time,  the  iron  shutters  on  the  Jenkins 
building  side  wall  had  stayed  the  flames.  The  Methodist 
building  was,  therefore,  not  subjected  to  such  a  severe  test  as 
the  others,  the  damage  being  confined  to  the  destruction  of  its 
contents  without  serious  injury  to  constructive  features. 

The  Home  store  building,  built  in  1893,  was  a  steel-frame 
structure,  with  front  and  rear  self-supporting  walls.  The  front 
windows  were  of  large  area  and  unprotected,  while  a  light-well 


FIRE  PROTECTION.  17 

extended  from  the  first  story  to  the  roof,  thus  forming  a  most 
convenient  means  of  communication  of  fire  from  floor  to  floor. 
The  floor  construction  consisted  of  p-in.  hard-burned  terra- 
cotta arches,  side-construction,  and  the  columns  were  protected 
by  2-in.  hard-burned  terra-cotta,  %  in.  thick,  with  one  air- 
space. The  roof  framing  consisted  of  lo-in.  beams,  without 
arches,  with  a  suspended  ceiling  beneath,  and  covered  by  light 
tees  at  right  angles  to  the  beams,  to  receive  2-in.  hollow 
book-tile.  A  compression  tank,  about  6  ft.  in  diameter  and 
25  ft.  long,  weighing,  when  filled,  about  52,000  Ibs.,  was  sup- 
ported by  steel  beams  resting  upon  the  roof  girders,  and  as 
this  entire  construction  was  protected  from  the  upward  rush  of 
fire  by  the  suspended  ceiling  alone,  the  inevitable  falling  of  the 
tank  soon  occurred,  with  great  damage  to  the  steelwork  and 
fireproofing.  The  loss  to  the  steel  frame  was  about  twenty 
per  cent,  of  its  original  value,  but  the  appraiser's  report  stated 
that  the  damage  to  the  steelwork  would  not  have  exceeded 
five  per  cent,  of  its  entire  cost,  had  not  so  much  destruction 
been  wrought  by  the  falling  of  the  water  tank. 

The  brick  fronts  were  seriously  injured  by  the  cracking  of 
the  stone,  and  the  fireproofing  throughout  had  to  be  replaced, 
save  a  salvage  of  i6f  per  cent.  The  tops  of  the  hard  tile 
arches  were  generally  found  to  be  in  good  condition,  but  the 
under  surfaces  were  largely  broken  away,  leaving  hollow 
spaces  visible  from  the  rooms  below.  The  skew-backs  and 
girder-casings  were  also  badly  broken. 

The  Home  office  building  was  also  a  steel-frame  building, 
with  self-supporting  walls.  The  floor  construction  was  made 
of  Q-in.  end-construction  porous  terra-cotta  arches,  while  the 
columns  were  protected  by  I  -in.  solid  porous  terra-cotta  cover- 
ing blocks.  The  partitions  were  also  of  porous  tile. 

The  contents  and  wood  trim  were  pretty  thoroughly 
consumed,  but  the  steel  construction  twas  apparently  little 
injured,  so  that  it  was  not  uncovered  for  examination.  The 


1 8  ARCHITECTURAL   ENGINEERING. 

entire  loss  to  the  fireproofing,  excepting  the  partitions,  was 
33^  per  cent,  of  the  entire  cost,  while  the  partitions  suffered  a 
loss  of  some  43  per  cent. ,  this  being  largely  due  to  the  use  of 
wood  nailing-strips  which  burned  out  and  allowed  the  parti- 
tions to  fall.  The  bottoms  of  the  porous  terra-cotta  arches 
were  but  little  broken,  and  the  column  coverings  generally 
remained  intact. 

In  the  Methodist  building,  the  floor  arches  or  slabs,  built 
after  the  Metropolitan  system,  made  a  satisfactory  showing, 
but  the  test  was  -not  severe  enough  to  furnish  any  positive 
deductions. 

The  Pittsburg  fire,  in  brief,  served  to  furnish  additional 
proof  of  a  most  conclusive  character  that  steel  buildings  which 
are  properly  protected  by  porous  terra-cotta,  with  brick  or 
terra-cotta  exterior  walls  and  properly  constructed  interior 
terra-cotta  partitions,  may,  if  reasonable  consideration  is  given 
to  provisions  against  the  internal  spread  of  fire  or  the  external 
communication  of  fire,  be  confidently  relied  upon  to  fulfil  all 
reasonable  requirements. 

Fig.  5  shows  an  exterior  view  of  the  two  Home  buildings, 
after  the  fire,  while  Fig.  6  is  an  interior  view  of  the  Home 
Store  building. 

Home  Insurance  Building  Fire. — The  value  of  fireproof 
construction  was  further  demonstrated  by  an  exposure  fire  of 
considerable  note  which  occurred  in  the  Home  Insurance 
Building  in  New  York  City  on  Feb.  n,  1898.  This  15 -story 
skeleton  structure  was  well  designed  against  internal  hazard, 
but  the  burning  of  a  highly  combustible  adjoining  building 
subjected  it  to  an  exposure  which  it  was  unable  to  withstand, 
and  the  upper  floors  were  considerably  damaged  by  the 
entrance  of  the  up-rushing  flames  into  the  side  and  court 
windows.  The  Home  building  is  of  modern  steel-frame  con- 
struction, with  a  self-supporting  front  wall  of  white  marble. 
The  floor  arches  were  of  hard  tile,  side-construction,  while  the 


FIRE  PROTECTION.  25 

column  casings  and  partitions  were  of  porous  tile.  The 
damage,  except  by  water,  was  confined  to  the  upper  floors, 
consisting  principally  of  the  destruction  of  the  marble  front 
above  the  eighth  floor,  and  the  falling  of  the  terra-cotta  parti- 
tions, due  to  their  being  built  upon  the  wood  flooring  in  many 
cases,  and  with  wood  door-  and  window-frames.  The  floor 
arches  stood  the  test  remarkably  well,  the  action  of  the  column 
covering  was  very  satisfactory,  and  the  structural  steel  was  but 
slightly  damaged. 

It  is  not  to  be  claimed  that  any  of  these  examples  have 
proved  entirely  satisfactory  as  ideals  of  fireproof  construction, 
but  certain  underlying  facts  have  been  clearly  proved  by  these 
tests ;  and  taking  these  essential  points  as  a  basis  for  further 
improvement,  and  using  the  utmost  care  and  judgment  in  the 
matter  of  general  design  and  details,  it  must  be  recognized  that 
the  use  of  terra-cotta,  as  seen  in  the  best  examples  of  recent 
fireproof  buildings,  offers  a  successful  solution  of  one  of  the 
most  important  problems  of  modern  times. 

Introduction  of  Tile  or  Terra-cotta. — Hollow  tile  as  a 
building  material  was  first  introduced  in  the  United  States  in-. 
1871,  shortly  after  the  great  Chicago  fire.  Its  first  use  was  for 
floor  arches,  to  replace  the  old  brick-arch  method.  Terra- 
cotta was  a  direct  outcome  from  conditions  imposed  by  the 
increased  height,  and  hence  weight*  of  a  rapidly  developing; 
architectural  construction,  and  its  necessity  was  doubtless 
made  more  apparent  by  the  great  object-lesson  afforded  by 
Chicago's  disastrous  conflagration.  A  substance  was  necessary 
to  replace  the  heavy  masses  of  masonry  which  constituted  the 
fireproofing  at  that  date,  both  in  the  exterior  walls  and  irt 
floor  arches,  and  the  peculiar  advantages  of  terra-cotta  caused 
it  to  undergo  many  improvements  in  rapid  succession,  affecting 
not  only  its  use  in  floor  construction  and  column  and  beam: 
protection,  but  adapting  it  to  the  needs  of  a  lighter  and  more 
rapid  construction  throughout.  Its  attendant  reduction  in. 


24  ARCHITECTURAL   ENGINEERING. 

weight,  its  great  fire-resisting  qualities,  its  peculiar  adaptability 
to  all  conditions  of  position  and  form,  its  susceptibility  to 
modelling,  and  its  readiness  of  manufacture  in  shapes  conven- 
ient for  transportation  and  erection,  soon  caused  it  to  win  favor 
both  for  its  artistic  possibilities  and  its  enduring  qualities, 
through  which  it  becomes  one  of  our  most  valuable  constructive 
media.  First  used  in  interior  work  only,  it  soon  appeared  in 
belt  courses,  sills,  caps,  ornamental  panels  and  modelled  work 
in  the  hard-finished  terra-cotta,  until  to-day  its  use  is  more 
general  than  stone,  appearing  in  entire  fronts,  as  a  bold-faced 
impersonation  of  solidity  itself. 

Fire-resisting  Materials.  —  From  what  has  been  said 
regarding  the  excellence  of  terra-cotta,  it  must  not  be  under- 
stood that  this  material  constitutes  the  only  satisfactory  fire- 
proofing  medium,  but  it  is  undoubtedly  the  best  (when  of  the 
porous  variety)  if  used  with  discrimination  and  intelligence. 
Terra-cotta  has  long  been  recognized  as  the  standard  to  which 
other  materials  or  systems  have  been  compared,  and  while  its 
satisfactory  qualities  have  never  been  surpassed,  other  materials 
have  been  introduced  from  time  to  time  as  competitors  in  fire- 
resistance,  particularly  on  the  basis  of  price. 

Brick,  which  is  also  a  clay  product,  is  probably  the 
only  material  which  may  be  considered  as  equal  to  the 
best  grades  of  terra-cotta,  and  many  conflagrations  have 
amply  demonstrated  the  fire-resisting  qualities  of  good  brick- 
work. But  of  other  constructive  materials,  concrete  alone  has 
stood  the  test  of  repeated  trials,  regardless  of  the  most  deter- 
mined opposition  from  many  quarters.  Practically  all  kinds 
of  stone  and  stone  masonry  are  wholly  unreliable  under  fire- 
and  water-tests,  but  concrete  is  now  generally  recognized  as 
an  entirely  acceptable  fireproofing  medium. 

But  even  the  most  enduring  materials,  used  with  the 
greatest  discrimination,  are  limited  as  to  their  effectiveness  and 
resistance,  and  the  duration  and  degree  of  exposure  must, 


.    FIRE  PROTECTION.  25 

therefore,  be  kept  within  reasonable  limits.  The  best  that  can 
be  done  is  to  reduce  the  inflammable  elements  to  a  minimum, 
and  endeavor  to  confine  the  fire  by  means  of  fireproof  floors 
and  partitions,  so  that  it  may  do  no  injury  beyond  the  con- 
sumption of  local  woodwork  and  furnishings. 

Fireproofing  Requirements. — With  this  general  review  of 
the  fire  problem,  it  is  evident  that  a  fireproof  structure  must 
possess : 

1 .  General  excellence  of  design. 

2.  All  floors  of  fireproof  construction. 

3.  All  columns  of  masonry  or  steel,  protected  from  fire. 

4.  All  outside  piers  and  walls  of  masonry  or  steel,  protected 
from  fire. 

5.  All  partitions  and  furring  of  fireproof  construction. 
There  are  three  methods  of  general  design  advocated  at 

the  present  time  as  means  of  reducing  the  fire  risk — the 
"slow-burning  construction,"  the  so-called  "mill  construc- 
tion," and  the  still  more  effectual  "  fireproof  construction. " 

Slow-burning  Construction. — The  term  slow-burning  con- 
struction is  applied  to  buildings  in  which  the  structural 
members,  carrying  the  floor-  and  roof-loads,  are  made  of  com- 
bustible material,  but  protected  throughout  from  injury  by  fire, 
by  means  of  coverings  of  incombustible,  non-heat-conducting 
materials.  Thus  the  wooden  floor-joists  are  protected  on  the 
under  side  by  a  single  covering  of  plaster  on  metal  lath,  while 
a  thickness  of  if  ins.  of  mortar  or  incombustible  deadening  is 
required  above  the  joists.  Columns,  if  of  oak,  with  a  sectional 
area  of  100  sq.  ins.  or  over,  need  not  have  special  fireproof 
coverings.  Partitions  and  elevator  enclosures  must  be  wholly 
of  incombustible  material,  and  no  wood  furring  is  allowed. 

Mill  Construction. — Buildings  of  mill  construction  are 
those  in  which  all  floor-  and  roof-joists  and  girders  have  a  sec- 
tional area  of  at  least  72  sq.  ins.,  with  a  solid  timber  flooring 
not  less  than  3!  ins.  in  thickness.  Columns  of  wood  need  not 


26  ARCHITECTURAL  ENGINEERING. 

be  protected,  but  they  should  have  a  sectional  area  of  at  least 
100  sq.  ins.  Partitions  and  elevator  enclosures  are  of  incom- 
bustible material,  and  no  wooden  furring  or  lathing  is  used. 

Fireproof  construction  has  already  been  defined.  The 
two  types  first  mentioned  do  not,  then,  depend  on  the  use  of 
materials  wholly  incombustible,  but  rather  on  the  judicious 
-design  and  careful  use  of  ordinary  building  materials,  the  aim 
being  to  provide  structures  so  open  and  free  from  fire-lurking 
Corners  that  they  may  offer  no  obstacles  to  a  speedy  suppres- 
sion of  the  flames.  These  types  are  peculiarly  adapted  to 
large  mills,  warehouses,  and  the  like. 

Fire-resisting  Design. —The  scientific  fireproofing  of  a 
building  does  not  consist  in  a  proper  selection  of  materials 
alone,  for  a  structure  may  be  reasonably  secure  against  acci- 
dental fire,  or  the  extension  of  fire,  even  when  built  of  com- 
bustible materials;  nor  does  it  lie  merely  in  guarding  against 
the  causes  of  fire.  It  can  be  secured  only  by  a  thorough 
acquaintance  with  all  the  general  features  and  minutest  details 
of  all  kinds  of  structures,  and  by  a  quick  perception  ' '  for  the 
numerous  elements  of  danger  that  are  constantly  creeping  into 
modern  systems  of  buildings. ' '  The  plan  must  be  carefully 
studied  to  secure  means  of  cutting  off  communication  between 
floor  and  floor,  and  between  and  around  dangerous  sources, 
isolating,  if  possible,  all  stairways  and  elevator-shafts  by  means 
of  fire-resisting  walls,  and  confining  all  power  and  mechanical 
plants  in  such  a  way  that  there  can  be  no  possible  means  of 
fire  extension.  It  is  true  that  most  high  office  buildings  do 
not  possess  the  isolated  stair-well  or  elevator-shaft;  but  if  they 
do  not,  great  care  should  be  taken  in  making  the  halls  and 
corridors  of  more  than  ordinary  security.  They  will  still  be 
the  means  for  a  rapid  distribution  of  smoke  from  floor  to  floor, 
and  thus  make  the  danger  from  suffocation  assume  an  impor- 
tance equal  to  that  of  fire. 

No  less  important  is  the  cutting  off  of  all  communication 


FIRE  PROTECTION.  2^ 

between  pipe-  and  air-passages.  Piping  and  passages  of  all 
kinds  should  be  carefully  considered  as  a  part  of  the  fundamen- 
tal design,  for  they  not  only  become  great  eyesores  from  their 
exposed  positions  in  offices,  but  they  also  serve  to  make  many 
of  our  fireproofing  endeavors  quite  useless. 

The  architect  or  engineer  must  finally  be  well  informed  in 
regard  to  the  details  and  varied  uses  of  approved  fireproofing 
materials.  These  must  include  terra-cotta  in  all  the  different 
shapes  made  by  the  terra-cotta  companies,  cement,  concrete, 
fire-brick,  asbestos,  mackolite,  etc.  A  judicious  and  economic 
use  of  all  these  materials  is  necessary,  so  that  the  most  prac- 
ticable form  may  be  chosen  to  secure  the  desired  end. 

Some  of  these  important  minutiae  may  properly  receive 
detailed  attention,  when  we  remember  that  the  strength  of  a 
structure  is  gauged  by  its  weakest  point. 

The  metal  columns,  for  example,  are  properly  figured  for 
their  safe  dimensions,  but  from  this  step  on  they  are  apt  to 
become  a  bugbear  to  both  architect  and  owner,  the  former 
desiring  to  reduce  their  size  to  a  minimum  on  account  of 
appearance,  while  the  latter  considers  that  they  deprive  him  of 
the  revenue  of  just  so  much  floor  space.  Any  measures  are 
therefore  adopted  to  reduce  their  size.  First,  the  various 
waste-,  heat-,  and  supply-pipes  are  run  up  alongside  the 
columns  from  floor  to  floor.  For  the  passage  of  these  pipes 
openings  must  be  made  in  the  tile  floor  arches,  which,  in  the 
rush  of  building  operations,  may  never  be  properly  filled  up 
again.  These  openings  come  inside  the  line  of  the  fireproof 
slabs  of  the  column,  thus  forming  one  long  continuous  flue 
from  basement  to  roof.  The  finished  line  of  the  fireproofed 
and  plastered  column  is  often  not  more  than  2  ins.  from  the 
extreme  points  of  the  metal-work,  and  then,  deducting  \  in. 
or  £•  in.  for  plaster,  little  enough  is  left  for  the  fireproofing 
proper.  The  various  pipes  before  mentioned  will  very  often 
project  even  farther  than  the  column  itself,  thereby  tempting 


2.8  ARCHITECTURAL  ENGINEERING. 

the  fireproofer  to  trim  and  shave  till  the  original  little  has 
become  still  less. 

Lessons  from  Past  Fires — In  the  Athletic  Club  Building 
fire  some  of  these  points  were  illustrated  with  glaring  promi- 
nence. A  steel  framework  and  fireproof  covering  having 
been  used  as  the  main  elements  of  construction,  further  con- 
sideration of  fire  hazards  were  apparently  slighted.  In  no  case 
did  the  fireproofing  extend  more  than  2  ins.  from  the  outer- 
most edge  of  the  ironwork,  while  wooden  nailing-strips  were 
embedded  in  the  tile  at  intervals  of  about  3  ft.  starting  from 
the  floor  (a  4-in.  face  exposed),  making  successively  3  ft.  of 
tile  and  4  ins.  of  wood.  These  nailing-strips  were  employed 
as  grounds  for  the  panelled  oak  wainscoting,  and  a  further 
error  was  made  in  leaving  an  air-space  behind  this  panelling, 
with  no  ' '  back  ' '  plastering.  The  ceiling  also  left  an  air- 
space, due  to  i -in.  raised  nailing-strips. 

As  a  matter  of  course  the  wooden  grounds  around  the 
column  burned  out,  letting  the  fireproofing  fall  in  3-ft.  sec- 
tions. It  so  happened  that  but  two  columns  were  badly  bent 
by  the  intense  heat,  but  who  can  say  what  the  stability  of 
those  re-used  unbent  columns  really  is  ?  Were  they  cooled 
slowly,  or  suddenly  by  the  application  of  streams  of  water,  and 
thus  rendered  brittle,  and  were  they  heated  unevenly,  thus 
causing  great  strain  in  the  material  on  but  one  side  of  the 
column  ?  What  was  the  amount  of  expansion  and  contraction  ? 
No  experiments  could  be  made  with  reasonable  economy  and 
safety  to  satisfy  these  queries,  leaving  the  present  state  of  the 
building  an  uncertain  conjecture. 

Fireproof  Partitions. — Both  the  Pittsburg  fire  and  the 
Home  Insurance  Building  fire  demonstrated  the  necessity  for 
better  partition  construction,  and  the  unreliability  of  plaster 
and  metallic  lath  substitutions  for  terra-cotta  blocks.  In  the 
Home  office  building,  wooden  nailing-strips  used  for  the 
attachment  of  the  base-boards  were  responsible  for  the  resetting 


FIRE  PROTECTION.    -  29 

of  nearly  all  the  partitions.  Aside  from  this  defect  the  parti- 
tions were  nearly  as  good  after  the  fire  as  before.  In  the 
Home  Insurance  fire,  many  of  the  terra-cotta  partitions  were 
weakened  or  wrecked  completely  through  being  built  upon  the 
wood  flooring,  while  the  extended  use  of  wooden  door-  and 
window-frames  in  such  partitions  was  also  responsible  for  a 
great  deal  of  damage. 

Fireproof  Doors  and  Windows. — Again,  these  two  fires 
clearly  showed  the  necessity  for  protecting  exposed  window 
areas  against  possible  external  attack  by  fire,  and  this  danger, 
as  well  as  the  objection  to  wood  doors  and  window-frames,  etc., 
in  fire-resisting  partitions,  may  be  met  through  the  use  of  a 
system  which  is  now  largely  growing  in  favor.  Doors,  door- 
frames, window-frames,  and  sash  are  now  made  with  a  wood 
body  or  core,  covered  with  sheet  steel  or  copper  which  is 
hydraulically  pressed  to  give  the  proper  form  to  the  panels, 
mouldings,  etc.  For  exterior  use,  pure  sheet  copper  is  prefer- 
ably used,  of  bright  or  green  acid  finish,  while  for  interior  use 
in  partitions,  etc.,  plain  sheet  steel  is  employed,  ready  for 
painting  or  graining.  Sheet  bronze,  brass,  or  electro-plated 
metal  may  also  be  obtained.  Fire-tests  have  proved  the  doors 
to  be  of  admirable  fire-resisting  qualities,  while  the  window- 
frames  and  sash,  combined  with  wire  glass,  form  a  most 
admirable  protection  against  external  hazard.  A  building 
built  in  Boston,  1898,  for  the  New  England  Telephone  and 
Telegraph  Co.,  has  every  exterior  window  and  door  of  this 
character,  the  windows  being  glazed  throughout  with  wire 
glass. 

Installation  of  Piping,  etc. — The  proper  installation  and 
distribution  of  the  mechanical  features  in  a  modern  office  build- 
ing have  been  given  considerable  attention  by  John  M.  Carrere 
(see  Engineering  Magazine,  October,  1892),  and  the  system 
proposed  by  him  will  undoubtedly  add  greatly  to  the  efficiency 
of  fireproofing,  and  remedy  many  of  the  weak  details  just  con- 


3° 


ARCHITECTURAL  ENGINEERING. 


sidered.  In  order  to  avoid  chases,  or  continuous  flues,  the 
lowering  of  the  hall  ceilings  is  suggested,  "  thereby  obtaining  a 
horizontal  space  under  the  floors  of  the  halls  at  each  story,  lined 
and  fireproofed,  where  all  the  mechanical  features  except  steam 
heat  can  be  placed  "  (see  Fig.  7).  An  arrangement  of  this 


OFFICE 


OFFICE 


OFFICE 


FIG.  7. — Arrangement  for  Pipe-space  in  Corridors. 

character  would  certainly  possess  many  great  advantages — it 
would  always  be  accessible  for  repairs,  easy  of  connection  with 
all  offices,  and  would  serve  as  a  safe  and  at  the  same  time 
hidden  conduit  for  all  wiring,  piping,  and  ventilating  air-ducts, 
either  exhaust  or  indriven.  The  additional  expense  would  not 
be  great  either,  and  when  its  permanency  is  considered,  never 
being  affected  by  the  moving  of  partitions,  etc.,  as  is  now  the 
case,  it  is  surprising  that  such  a  system  has  not  attained  more 
general  use. 

At  the  ends  of  these  horizontal  ducts  are  vertical  chases  or 
ducts  built  solidly  of  fireproof  blocks  or  brick  from  cellar  to 
roof,  and  connected  at  each  floor  with  the  horizontal  leads, 
but  still  partitioned  off  at  every  story  with  wire  and  plaster 
partitions,  to  prevent  the  spread  of  possible  fire.  All  of  the 
vertical  risers  could  be  placed  in  these  chases,  thus  avoiding 
the  unsightliness  of  pipes  in  the  office  space,  or  the  necessity 
of  placing  such  piping  within  the  column  space. 


CHAPTER   III. 
TYPICAL  BUILDINGS— ERECTION,   PERMANENCY,   ETC. 

MANY  of  the  details  which  will  be  discussed  in  the  follow- 
ing pages  may  be  better  appreciated  in  their  relation  to  the 
whole  subject  if  a  few  typical  skeleton  structures  are  examined. 
The  scope  of  this  outline  will  not  permit  of  a  discussion  of  the 
architectural  problems  involved  in  the  design  of  a  modern 
office  building,  hotel,  or  any  of  the  structures  which  are  now 
built  according  to  skeleton  methods.  The  points  here  con- 
sidered are,  rather,  those  of  construction  pure  and  simple. 
But  the  comprehensive  view  of  the  subject  necessary  to  the 
architect  or  architectural  engineer  may  only  be  obtained 
through  an  accurate  knowledge  of  the  manifold  items  which 
become  parts  of  a  successful  plan.  These  accessories  to  the 
mere  framework  lie  within  the  province  of  the  engineer  as  well 
as  of  the  architect,  and  here,  as  in  the  execution  of  the  external 
expression  of  architectural  engineering,  a  perfect  harmony 
must  exist  between  the  two  branches  in  the  perfection  of  all 
mechanical  details,  if  results  are  to  be  secured  which  may  be 
looked  upon  as  creditable  to  both  professions. 

The  value  of  such  accessories  may  be  more  fully  realized 
when  the  self-sufficiency  of  a  typical  office  building,  containing 
all  modern  improvements,  is  considered.  Electric  light,  the 
telephone,  mail-chutes,  and  well-appointed  toilet-rooms  are 
already  demanded  as  absolute  necessities,  while  many  examples 
provide  telegraph  and  messenger  service,  cigar-  and  news- 

31 


32 


ARCHITECTURAL  ENGINEERING. 


stands  and  barber-shops,  besides  restaurants  and  cafes  in  the 
basements.  It  is  true  that  many  of  these  factors  would  seem 
to  have  little  bearing  on  the  duties  of  the  engineer,  and  yet  it 
was  just  such  conditions,  imposed  on  the  designer  of  the  foun- 
dations of  office  buildings,  that  produced  the  successful 
development  of  the  so-called  raft  or  floating  foundations,  in 
order  that  the  basements  might  be  unencumbered  by  the  large 


H^^~^&- 

Hjlrt^rr^-.--^-^  J£~-  - 


iSsjgpSI 


fn 


FIG.  8. — Chicago  Stock  Exchange  Building.  Adler  &  Sullivan,  Architects, 
pyramidal  masses  of  stone  previously  used  as  footings,  and  the 
basement  space  might  be  added  to  the  available  renting  area, 
or  be  used  for  the  mechanical  plants.  The  rigid  economy  of 
floor  space  which  is  demanded  may  only  be  obtained  by  careful 
attention  to  the  most  advantageous  uses  to  which  the  different 
floors  and  rooms  in  the  structure  may  be  put. 

Typical  Office  Buildings.  —Some  examples  of  typical  office 
buildings  in  various  cities  will  now  be  given,  as  illustrating 
prominent  types  of  veneer  construction. 


TYPICAL   BUILDINGS— ERECTION,  PERMANENCY,  ETC.          33 


FIG.  9.— Chicago  Stock  Exchange  Building.     Ground-floor  Plan. 


FIG.  io.— Typical  Office-floor  Plan,  Stock  Exchange  Building. 


34  ARCHITECTURAL   ENGINEERING. 

The  Chicago  Stock  Exchange  Building  is  illustrated  in 
Fig.  8.  The  entire  fa£ades  are  constructed  of  a  yellow-drab 
terra-cotta,  the  lower  stories  and  the  main  cornice  being  richly 
modelled  in  intricate  ornamentation  peculiar  to  the  work  of 
these  architects.  The  interior  court  is  faced  with  white 
enamelled  brick. 

Fig.  9  is  a  plan  of  the  ground  or  street  floor,  showing  the 
entrance  vestibules,  elevators,  cafe,  and  store  areas. 

Fig.  10  shows  the  arrangement  of  the  offices,  etc.,  on  the 
sixth  floor.  The  toilet-rooms,  barber-shop,  vent  spaces,  and 
the  arrangement  of  the  lighting  courts  are  plainly  shown. 

The  Marquette  Office  Building,  Chicago,  is  shown  in  Fig, 
II.  The  exterior  walls  are  built  mainly  of  dark-red  brick, 
with  terra-cotta  cornice  and  trimmings.  A  spandrel  section 
at  one  of  the  upper  floors  is  given  in  Chapter  VI. 

Fig.  12  illustrates  one  of  the  typical  floor  plans,  with  possi- 
ble sub-divisions  of  large  office  areas.  Many  of  the  floors  in 
the  larger  office  buildings  are  never  sub-divided  until  rented, 
in  order  that  the  arrangement  of  the  partitions  may  be  made 
to  suit  the  tenants. 

Fig.  1 3  is  the  Reliance  Building,  Chicago,  the  typical  floor 
plan  being  as  shown  in  Fig.  14.  This  arrangement  of  offices  is 
intended  for  rooms  to  be  used  in  suites.  The  pipe  space  at  the 
side  of  the  elevators,  and  the  space-for  counterweights  behind 
the  elevators  are  plainly  shown,  as  is  the  circular  smoke-flue. 

The  elevator  accommodations  in  these  various  buildings 
may  be  seen  on  the  plans.  Rapid  passenger  and  freight 
service  must  both  be  provided  for,  and  the  necessary  space 
allowed  for  the  hydraulic  cylinders  in  the  basement,  as. well  as 
for  the  vertical  counterweights.  Beams  must  be  supplied  to 
support  the  elevator  sheaves,  and  water-tanks  located  to  supply 
the  hydraulic  cylinders. 

If  the  basement  lies  below  the  street  or  sewer  level,  and  it 
is  to  be  occupied  by  stores,  cafes,  or  by  the  boiler-  and  engine- 


FIG.  ii. — Marquette  Building,  Chicago. 


Holabird  &  Roche,  Architects. 

35 


TYPICAL  BUILDINGS- ERECTION,  PERMANENCY,  ETC.         37 

rooms,  an  ejector-pit  will  be  necessary  to  raise  the  sewage  to 
the  proper  level.  Pumps  for  water-supply,  dynamos  for  elec- 
tric light,  boilers  and  steam  plant  for  power  and  heating — all 
must  be  definitely  determined  and  carefully  weighed  in  their 
relation  to  the  character  of  the  building,  and  as  affecting  the 
design  of  foundations  and  all  structural  details. 

The  following  data  may  be  of  interest  as  descriptive  of 
some  of  the  mechanical  furnishings  of  one  of  Chicago's  most 
celebrated  office  buildings,  the  Masonic  Temple,  shown  in 
Fig.  15: 

The  entire  drainage  is  carried  through  the  building  by 
means  of  a  system  of  vertical  risers,  about  one-half  of  which 
connect  directly  with  the  street  mains,  through  piping  sus- 
pended from  the  basement  ceiling.  The  remainder  of  the 
risers,  and  all  drainage  from  the  boiler-room  and  basement 
space,  are  connected  by  a  system  of  underground  piping  with 
two  5O-gallon  Shone  ejectors,  placed  in  a  pit  in  the  basement, 
from  which  the  sewage  is  forced  to  the  street  sewer.  This  was 
necessary  in  order  to  keep  the  basement  stores,  cafes,  etc.,  free 
from  exposed  pipes.  All  vertical  pipes  in  the  building,  both 
for  water-supply  and  drainage,  are  carried  in  fireproof  pipe- 
spaces  especially  provided.  The  water-supply  is  pumped  from 
the  city  mains  by  pumps  located  in  the  basement,  to  storage 
tanks  on  the  twentieth  floor,  with  a  combined  capacity  of  7,000 
gallons.  On  the  twentieth  floor  also  are  four  compression 
elevator  tanks  of  18,500  gallons  capacity  total.  For  elevator 
and  water-supply  service  seven  pumps  are  required,  having  a 
total  capacity  of  from  2,000  to  3,800  gallons  per  minute. 

Each  office  and  store  has  a  private  wash-basin,  with  general 
toilet-rooms  and  barber-shop  on  the  nineteenth  floor.  The 
main  toilet-room  contains  64  closets,  besides  additional  rooms 
on  the  third  and  twelfth  floors  and  in  the  basement,  with  from 
8  to  1 8  closets  each. 

Forty  thousand  square  feet  of  radiation  surface  are  required, 


38  ARCHITECTURAL  ENGINEERING. 

all  in  direct  radiation.  The  steam  is  supplied  on  the  "over- 
head "  system  through  i6-in.  mains  running  directly  to  the 
attic,  thence  around  the  exterior  walls  and  down.  Six 
dynamos  supply  7,000  1 6-candle-power  lamps.  For  the  power 
and  steam  plant,  eight  horizontal  tubular  boilers  are  used,  with 
a  total  of  1,000  horse-power. 

There  are  several  features  in  the  Masonic  Temple  design 
worthy   of   especial    note.      Several    of  the   upper    floors    are 


m  (  r  11    (  ( 


FIG.  12.— Marquette  Building,  Chicago.     Typical  Office-floor  Plan. 

devoted  to  Masonic  purposes,  and  the  large  assembly-,  drill-, 
and  banquet-rooms  were  kept  free  from  columns  by  spanning 
the  areas  with  lattice  girders,  on  which  rest  the  arched  ceiling 
and  roof-trusses.  The  interior  court  also  possesses  a  special 
feature,  viz. :  galleries  provided  at  each  story  for  the  lower 
ten  floors.  This  plan  was  intended  to  attract  small  store- 
keepers and  the  like  as  occupants  of  the  adjoining  stores  or 
offices,  thus  concentrating  many  tradesmen  under  one  roof. 
The  scheme  has  not  proved  a  success. 


FIG.  13. — Reliance  Building,  Chicago.      D.  H.  Burnham  &  Co..  Architects. 

3'-) 


TYPICAL  BUILDINGS— ERECTION,  PERMANENCY,  ETC.          41 

The  roof  of  the  Masonic  Temple  is  covered  by  an  enclosure 

of  glass,  serving  as  a  summer- garden  and  place  of  observation. 

A  perspective  of  the  New  York  Life  Insurance  Building, 


FIG.  14.     Reliance  Building,  Chicago.     Typical  Office-floor  Plan. 

(For  framing-plan,  see  Fig.  59.) 

Chicago,  is  illustrated  in  Fig.  17.  The  lower  three  stories  are 
built  of  granite,  with  brick  and  terra-cotta  above.  The  plan 
of  the  first  floor,  devoted  to  banking  purposes,  is  shown  in 


42  ARCHITECTURAL   ENGINEERING. 

Fig.  1 8,  while  the  typical  office-floor  plan  is  given  in  Fig.  19. 

Fig.  20  is  a  photograph  of  the  Park  Row  Building,  New 
York  City  (R.  H.  Robertson,  architect).  A  skeleton  eleva- 
tion of  the  side  wall  shown  in  this  illustration  is  given  in  Fig. 
165. 

The  Park  Row  Building  is  the  highest  office  building  ever 
erected,  and  it  is  very  doubtful  whether  it  will  be  found  either 
desirable  or  profitable  to  erect  other  buildings  as  high  as  this 
one.  This  building  was  built  in  1897-98,  and  a  number  of 
the  constructive  details  are  given  in  other  chapters.  The 
height  includes  26  stories  from  curb  to  main  roof,  or  33  stories 
from  the  foundation  to  the  extreme  portion  of  the  accessible 
interior.  The  height  from  the  street-level  to  the  base  of  flag- 
staff, which  is  the  highest  accessible  portion  of  the  building,  is 
390  ft.  9  ins.,  or  from  head  of  piles  to  base  of  flagstaff  equals 
424  ft.  6  ins.  The  building  is  equipped  with  nine  electric 
passenger  elevators  running  from  the  basement  to  the  twenty- 
sixth  floor,  besides  which  two  other  elevators,  one  in  each 
tower,  run  from  the  twenty-sixth  to  the  twenty-ninth  floor. 

A  photograph  of  the  Broadway  Chambers  (Mr.  Cass 
Gilbert,  architect)  is  given  in  Fig  2 1 .  The  lower  three  stories 
are  built  of  granite,  the  main  shaft  is  of  brick,  while  the  upper 
three  stories  are  constructed  entirely  of  terra-cotta.  The  color- 
effect  in  this  building  is  as  successful  as  it  is  unusual. 

Figs.  35  and  36  show  this  structure  in  process  of  erection. 

Figs.  22,  23,  and  24  show  the  basement,  ground-floor,  and 
typical-floor  plans  respectively. 

The  Jewelers'  Building,  Boston,  Mass.  (Winslow  & 
Wetherell,  architects),  is  shown  in  Fig.  25.  The  lower  two 
stories  are  of  cast-iron,  with  buff-colored  terra-cotta  above. 

Fig.  26  is  of  the  Fort  Dearborn  Building,  Chicago.  A 
typical  office-floor  plan  is  shown  in  Fig.  27,  while  the  typical 
framing  plan  is  given  in  Fig.  58,  Chapter  IV.  A  number 
of  spandrel-sections  for  this  building  are  given  in  Chapter  VI. 


Fi<;.  15. — The  Masonic  Temple,  Chicago. 


Burnham  &  Root,  Ajchitects. 
43 


New  Half, 
Veneer  Construction. 


FIG.  16. — The  Monadnock  Building,  Chicago. 


TYPICAL   BUILDINGS— ERECTION,  PERMANENCY,  ETC.         47 

The  Gillender  Building,  New  York  City  (Berg  &  Clark, 
architects),  is  shown  in  Fig.  28.  This  example  constitutes 
about  the  extreme  of  great  height  compared  to  narrow  width. 


FIG.    17. — New    York    Life  Insurance  Building,  Chicago.     Jenney   & 
Mundie,  Architects. 

A  framing  plan  is  given  in  Fig.  60,  Chapter  IV,  and  spandrel- 
sections  and  bay-window  details  are  illustrated  in  Chapter  VI. 
Fig.  29  shows  a  typical  office-floor  plan  of  the  Champlain 
Building,  Chicago  (Holabird  &  Roche,  architects). 


ARCHITECTURAL   ENGINEERING. 


Fig.  3°  gives  a  perspective  of  the  Old  Colony  Building,  by 
the  same  architects. 

Fig.  3 1  is  a  photograph  of  the  new  building  erected  for 
Montgomery,  Ward  &  Co.,  Chicago  (Richard  E.  Schmidt, 
architect). 


-\ 

=-  'VAULT 

-J     * 

\  GLOSIT 


FIG.  18. — New  York  Life  Insurance  Building,  Chicago.     Plan  of  Banking 
Floor. 

Fig.  32  shows  the  main  entrance  hall  to  the  New  York 
Life  Insurance  Building,  Chicago,  in  which  the  walls,  ceiling, 
and  stairs  are  finished  in  Italian  marble  with  mosaic  floor.  In 
many  buildings  the  richness  of  the  first  story  is  further 
increased  through  the  use  of  solid  bronze  for  the  elevator 


TYPICAL   BUILDINGS-ERECTION,  PERMANENCY,  ETC.         49 


grilles,   stairs,  transom-  or  door-grilles,  directory-frames,  and 
lamps. 

The  foregoing  illustrations  will  serve  to  show  the  architec- 
tural treatment  employed  in    representative    office    buildings, 


"  f,\\"' "  \  i  i  ^"U  J* *"T"%  +^* 

f  j|i  ^^  | 


FIG.   19. — New  York  Life  Insurance  Building,  Chicago.     Typical    Office- 
floor  Plan. 

while  the  floor-plans  indicate  the  general  arrangement  of 
offices,  halls,  and  entrances,  besides  the  minor  details  of  plan, 
thus  making  the  conditions  which  determine  the  general 
features  of  construction  apparent,  in  so  far  as  the  plan  may 
affect  the  conditions  of  design. 


5°  ARCHITECTURAL   ENGINEERING. 

Erection. — In  skeleton  or  cage  construction  building's, 
present  demands  as  to  the  rapidity  of  construction  make  the 
method  and  apparatus  for  hoisting,  handling,  and  assembling 
the  various  members,  of  great  importance.  Sharp  competition, 
close  estimates,  and  the  demands  of  owners  and  architects 
regarding  the  speedy  completion  of  contracts,  serve  to  make 
the  economy  and  rapidity  of  erection  scarcely  less  important 
than  economy  and  excellence  in  design.  Many  different 
systems  of  handling  the  steel  frame  have  been  adopted,  and 
much  special  apparatus  has  been  designed  for  this  purpose,  but 
the  methods  employed  vary  so  much  with  locality  and  con- 
tractor, that  no  very  general  practice  can  be  classed  as 
standard.  Simple  gin-poles,  single  derricks  or  combinations 
of  derricks,  towers,  steam-cranes,  and  elaborate  travellers  have 
been  used  under  their  own  peculiar  conditions ;  but  that  system 
will  generally  be  found  most  advantageous  which  either  facili- 
tates the  moving  of  the  plant  itself,  or  which  renders  much 
moving  unnecessary.  Any  saving  in  shifting,  anchorage,  or 
guying,  tends  to  reduce  the  time  employed,  and  hence  the 
labor  and  expense. 

Old-fashioned  gin-poles  and  single  derricks  are  still  em- 
ployed on  small  work,  but  on  buildings  of  considerable  size, 
some  form  of  tower  or  traveling-derrick  is  generally  used. 
Special  steam-cranes,  built  for  the  purpose,  have  been  used  in 
some  cases,  these  being  operated  on  tracks  which  were  quickly 
laid  over  the  floor  system.  Such  cranes  would  pull  themselves 
up  an  incline,  from  story  to  story,  as  fast  as  erected.  The 
crane-boom  and  engine-platform  revolve  on  a  pivot,  so  that 
the  steel  beams  or  columns  require  very  little  handling. 

When  the  building  floor-plan  is  of  such  dimensions  that  a 
derrick  or  traveler  may  move  from  end  to  end  of  the  building, 
and  at  the  same  time  reach  out  on  either  hand  to  the  side  walls 
(or  even  when  only  a  portion  of  the  width  can  be  handled),  a 
tower-derrick  will  be  found  advantageous,  providing  other 


FIG.  20.— Park  Row  Building,  New  York. 


R.  H.  Robertson,  Architect. 
Si 


FIG.  2i.—"  Broadway  Chambers"  Building,  New  York  City.     Cass  Gilbert, 
Architect. 

53 


TYPICAL  BUILDINGS    ERECTION,  PERMANENCY,  ETC.          55 


CHAMBERS Sf 

FIG.  22. — Broadway  Chambers,  New  York  City.     Basement-floor  Plan. 


FIG.  23.— Broad  way  Chambers,  New  York  City.     Ground-floor  Plan. 


FIG.  24. — Broadway  Chambers,  New  York  City.     Typical-floor  Plan. 


56  ARCHITECTURAL  ENGINEERING. 

conditions  are  suitable  for  the  use  of  a  group  of  central  booms. 

Such  a  traveling-derrick  or  tower-derrick,  which  has  been 
used  with  good  results  on  skeleton  buildings  in  New  York, 
may  be  briefly  described  as  follows:  The  derrick  consists  of  a 
rectangular  tower,  about  24  ft.  long,  24  ft.  high,  and  1 2  ft. 
wide,  made  of  a  horizontal  rectangular  steel  framework  at  the 
bottom,  which  supports  four  wooden  corner-posts.  These 
corner  verticals  are  connected  at  the  top  by  horizontal  timbers, 
running  from  post  to  post,  and  also  by  transverse  struts  placed 
about  half-way  up  the  tower.  Diagonal  rods  with  sleeve-nuts 
and  pin-ends  are.  placed  in  each  of  the  vertical  planes  of  the 
tower,  also  in  the  top  and  bottom  horizontal  frames.  The 
vertical  corner-posts  are  so  arranged  as  to  set  back  somewhat 
from  the  ends  of  the  bottom  iron  frame,  which  projects  at  each 
end  sufficient  to  receive  the  boom-seats,  one  at  each  corner. 
All  joints  are  connected  by  steel  cover-plates  and  bolts,  the 
whole  being  arranged  with  a  view  to  rapidity  in  erection  or 
removal.  The  floor  of  the  tower  is  supported  on  transverse 
I-beams  which  rest  on  the  bottom  frame,  and  on  these  beams 
planking  is  placed  to  receive  the  engine,  besides  the  necessary 
coal-  and  water-supplies.  The  traveler  is  run  on  rails,  spaced 
about  12  ft.  apart,  placed  on  loose  flooring  about  3  ins.  thick, 
laid  from  beam  to  beam.  To  further  facilitate  the  handling  oi 
material  the  moving  derrick  is  often  supplemented  by  a  dis- 
tributing-car which  runs  on  a  narrow-gauge  track  of  light  rails. 
The  traveler,  including  engine  and  all,  is  easily  raised  from 
floor  to  floor  by  hand,  by  means  of  four  breast-derricks. 

This  type  of  traveler  was  employed  on  the  Commercial 
Cable  Building,  New  York,  and  on  the  Siegel-Cooper  Build- 
ing, where  seven  complete  tiers,  aggregating  between  7,000  and 
8,000  tons,  were  erected  in  nine  weeks  actual  working  time. 
In  this  case  two  travelers  were  installed  on  opposite  sides  of 
the  same  floor,  and  a  gang  of  twenty  men  with  each  derrick 


FIG.    25. — Jewelers'    Building,     Boston,    Mass.      Winslow    &    Wetherell, 
Architects. 

57 


TYPICAL  BUILDINGS—ERECTION,  PERMANENCY,  ETC. 


59 


would  erect  about  twenty  bays  of  ironwork  in  a  day,  each  bay 
being  about  24  ft.  square. 

The  rapidity  of  erection  is  not  proportional  to  either  the 


^pg^^gji^trr-     "  ;-^^r^^€^^. -^^? 

FIG.  26. — Fort  Dearborn  Building,  Chicago.    Jenney&  Mundie,  Architects. 

cubical  contents  of  ordinary  buildings  or  to  the  linear  height, 
as  an  average  rate  of  setting  steel  frames  may  be  placed  at 
about  two  tiers  of  beams  per  week  of  six  working-days  of  ten 
hours  each.  This  rate  is  largely  independent  of  the  actual  size 


6o 


ARCHITECTURAL  ENGINEERING. 


of  the  building,  except  in  large  areas  where  the  material  cannot 
be  handled  directly  from  the  street  to  final  position  with  one 
operation  of  the  boom.  In  many  cases  of  quick-time  contracts, 


YiiY  i  _i_ri.i  T  iif 
FIG,  27.  Fort  Dearborn  Building,  Chicago.     Typical  Office-floor  Plan. 

this  rate  is  often  greatly  bettered.  In  the  Unity  Building, 
Chicago,  seventeen  stories,  the  erection  of  the  metal  framework 
from  basement  columns  to  finished  roof  was  accomplished  in 
nine  weeks.  Cast  columns  were  employed  in  this  case.  In 


FIG.  28.— Gillender  Building.  New  York  City.      Berg  &  Clark.  Architects. 
American  Surety  Building  in  Background  to  left. 

61 


TYPICAL  BUILDINGS— ERECTION,  PERMANENCY,  ETC.         63 

the  Fisher  Building,  Chicago,  1895,  the  entire  steel  skeleton 
above  the  first  floor  was  erected  in  twenty-six  days,  without 
overtime  or  night  work.  This  included  nineteen  stories  and 
an  attic. 

Figs.  33  and  34  show  the  progress  made  in  the  erection  of 
the  Reliance  Building,  Chicago,  from  July  16,  1894,  to 
August  i,  1894. 

Figs.  35  and  36  show  the  Broadway  Chambers,  New  York, 
1900,  during  construction.  The  eighteen  stories  of  this  steel 


FIG.  29. — Champlain  Building,  Chicago.     Typical  Office-floor  Plan. 

frame,  aggregating  2,000  tons,  were  erected  complete  between 
the  dates  Oct.  15  and  Dec.  18,  1899. 

For  the  successful  erection  of  the  frame,  much  depends 
upon  an  accurate  alignment  of  the  column  bases.  These 
should  be  carefully  tested  as  to  both  position  and  level.  The 
bases  are  either  grouted  with  cement,  or  bolted  to  the  founda- 
tions, but  where  cast  column  bases  rest  on  masonry  piers  or 


64 


ARCHl  1 ECTURAL  ENGINEERING. 


FIG.  30. — Old  Colony  Building,  Chicago.     Holabird  &  Roche,  Architects. 


FIG.   31.— Montgomery    Ward    &   Co.'s    Building,  Chicago.      Richard    E. 
Schmidt,  Architect. 

65 


TYPICAL  BUILDINGS -ERECTION,  PERMANENCY,  ETC. 


67 


footings,  any  considerable  grouting  is  not  advisable.  The 
only  grouting  that  should  be  permitted  in  tall  buildings  would 
be  in  leveling  up  the  tops  of  the  concrete  footings  to  receive 
the  masonry  courses,  or  in  a  very  thin  layer  between  the 


FIG.  32.— Entrance  Hall,  New  York  Life  Insurance  Building,  Chicago, 
column  pedestal  and  the  masonry  bed.  The  cap-stones  should 
always  be  brought  to  the  most  accurate  bed  possible,  with 
grouting  used  as  a  thin  cement  and  not  as  a  leveler.  Accurate 
re-dressing  of  the  cap-stones  after  setting  is  much  to  be 
preferred. 

All  riveting  and  punching  of  the  steel  members  is  done  at 


68  ARCHITECTURAL  ENGINEERING. 

the  shop,  besides  the  usual  coat  of  oil  or  paint.  This  leaves 
only  the  assembling  and  field  riveting  to  be  done  on  the 
ground,  including  the  adjustment  of  the  laterals  or  wind-brac- 
ing, the  placing  of  separators  and  tie-rods,  and  the  field 
painting. 

The  columns  are  now  generally  made  in  two-story  lengths, 
or  occasionally  in  three-story  lengths,  and  this  practice  aids 
much  in  saving  time  and  expense  in  erection.  The  column 
splices  are  placed  from  12  to  24  ins.  above  the  floor-levels 
(see  "Column  Splices,"  Chapter  VII),  so  that  the  floor- 
beams  or  girders  may  rest  on  brackets  or  shelf-angles  near  the 
tops  of  the  columns,  thus  acting  as  braces  during  erection. 
In  the  splicing  of  columns,  shims  or  wedges  should  never  be 
permitted,  as  such  practice  leads  to  serious  abuse  in  careless 
hands,  and  nails,  pieces  of  slate,  etc.,  are  often  used  by  the 
men  to  secure  proper  adjustment.  The  work  should  be  made 
true  and  perfect  through  the  accurate  planing  or  ' '  facing  ' '  of 
all  contact  bearing-surfaces,  the  facing  of  column  ends  always 
being  done  at  exact  right  angles  to  the  column  axis. 

Beams  and  girders  are  first  bolted  temporarily  in  place, 
about  one-third  of  the  holes  being  filled.  The  riveting  gang 
then  follows  behind  the  erectors,  making  permanent  connec- 
tions with  iron  rivets  heated  in  portable  forges.  Field  riveting 
has  now  entirely  superseded  the  use  of  bolts  in  skeleton  or 
cage  construction,  or  indeed  in  any  character  of  high-class 
building  work.  Bolted  connections  were  tried,  but  were  soon 
discarded  on  account  of  the  cracks  which  developed  in  the 
plastered  ceilings.  These  cracks  were  always  found  to  radiate 
from  the  column  connections  with  the  floor  system,  thus 
demonstrating  the  play  of  the  bolts  in  the  holes.  A  list  of  the 
required  field  rivets  is  made  in  the  shop,  including  an  excess 
of  from  5  to  25  per  cent,  of  the  actual  number  required.  This 
percentage  is  added  for  waste,  loss,  and  the  burning  of  rivets 
in  the  field.  A  greater  percentage  should  be  added  for  short 


FIG.  34. — Reliance  Building,  during  Construction. 
Aug.  i,  1894. 


FIG.  35. — Broadway  Chambers,  during  Construction. 
Nov.  9,  1899. 


73 


FIG.  36. — Broadway  Chambers,  during  Construction. 
Dec.  21,  1899. 


75 


TYPICAL  BUILDINGS-ERECTION,  PERMANENCY,  ETC.          77 

rivets  than  for  long  ones,  as  long  rivets  may  be  cut  down  to 
make  shorter  lengths.  A  riveting  gang  of  five  men  will 
average  about  200  rivets  a  day  of  nine  hours,  under  good  con- 
ditions. This  makes  a  cost  of  about  7  to  8  cents  per  rivet. 

After  erection,  the  steelwork  should  receive  one  or  two 
coats  of  paint.  If  the  cost  need  not  be  too  carefully  consid- 
ered, two  coats  in  the  field  are  to  be  recommended,  in  which 
case  the  first  and  second  coats  should  be  specified  of  different 
colors.  This  enables  one  to  see  at  a  glance  that  the  second 
coat  has  not  been  skimmed  or  slighted,  as  will  often  be  found 
to  be  the  case  unless  given  very  careful  inspection.  For  one 
coat  of  red-lead  paint,  one  gallon  may  be  allowed  to  about 
two  tons  of  average  weight  structural  steelwork. 

Rapidity  of  Erection. — The  skeleton  or  "veneer"  type 
of  construction  possesses  great  advantages  in  economy  of  time 
required  for  erection,  as  work  can  be  pushed  on  the  walls  at 
different  stories  at  one  and  the  same  time.  Thus  on  the  Man- 
hattan Building,  Chicago,  the  main  cornice  of  terra-cotta  was 
completed  before  the  wall  was  built  up  beneath  it.  On  the 
Unity  Building  the  granite  base-wall  was  being  built  at  the 
first  and  second  stories,  the  pressed-brick  face  was  being 
placed  at  the  twelfth-floor  level,  while  the  hollow-tile  arches 
were  being  set  for  the  fifteenth  floor, — all  at  the  same  time. 

The  rapid  progress  made  in  the  erection  of  the  New  York 
Life  Building,  Chicago,  is  shown  by  the  following: 

July  17.      Old  building  torn  down  to  grade. 

July  31.      Laid  out  new  footings. 

August  17.      Started  setting  basement  columns. 

August  31.      Started  laying  granite. 

September  5.      Started  setting  tile  arches. 

September  18.     Started  laying  terra-cotta  facing. 

September  29.      All  steel  set. 

November  9.      Tile  floors  all  set. 

November  1 1 .     Terra-cotta  all  set. 


78  ARCHITECTURAL  ENGINEERING. 

November  12.      Started  plaster. 

December  2.  Steam  plant  completed — turned  steam  on  in 
building. 

Of  the  671  individual  columns  in  this  building,  but  a  single 
one  required  ' '  shimming. ' '  A  thin  steel  wedged  plate  was 
used,  forged  to  fit.  The  columns  were  tested  for  alignment  at 
frequent  intervals.  An  average  of  twenty-five  working  hours 
was  required  to  set  the  steelwork  for  a  complete  story. 

The  following  dates  will  serve  to  show  the  time  required 
in  the  erection  of  one  of  the  latest  New  York  office  buildings, 
viz.,  the  eighteen-story  Atlantic  Building,  corner  of  Wall  and 
William  streets  (Clinton  &  Russell,  architects): 

May  9,  1900.      Tearing  down  started. 

June  15,  1900.      Caisson  foundations  started. 

September  I,  1900.      Steel  frame  started. 

October  8,  1900.      Brickwork  started  on  street  fronts. 

December  10,  1900.      Building  topped  out. 

January  i,  1901.      Steam  turned  on. 

January  22,  1901.      First  hydraulic  elevator  started. 

March  I,  1901.      First  offices  ready  for  tenants. 

Permanency  of  Skeleton  Construction. — Aside  from  the 
question  of  fire  resistance,  much  discussion  has  arisen  from  time 
t!o  time  as  to  the  permanency  of  skeleton  construction.  This 
controversy  between  friends  and  indifferent  observers  of  skele- 
ton methods  was  also  aggravated  by  the  reluctance  of  the 
supervising  architect  of  the  Treasury  seriously  to  consider 
such  construction  as  worthy  the  dignity  and  solidity  of  gov- 
ernment edifices — notably  in  the  new  Post-office  Building  for 
Chicago.  While  the  architectural  pros  and  cons  of  terra-cotta 
and  steel,  or  concrete  and  steel,  versus  solid  masonry  construc- 
tion may  not  here  be  discussed,  the  engineering  side  of  this 
matter  becomes  one  of  great  importance.  Serious  as  it  is,  it 
must  still  be  admitted  that  it  depends  largely  on  personal  views, 
for  the  want  of  reliable  data  under  present  conditions.  Many 


TYPICAL  BUILDINGS-ERECTION,  PERMANENCY,  ETC.         79 

architects  are  not  slow  to  pronounce  judgment  against  such 
practice,  while  others  warmly  champion  the  cause  of  steel  in 
combination  with  tile,  concrete,  or  cement.  This  divergence 
of  opinion  was  well  shown  in  an  interesting  discussion  before 
the  American  Institute  of  Architects  on  this  very  subject, 
where  examples  of  the  deterioration  of  iron  or  steel  under 
peculiar  conditions  were  emphatically  offset  by  instances  of 
remarkable  preservation  under  other  peculiar  conditions.  The 
point  would  then  seem  to  be  to  define  these  conditions. 
Prominent  architects,  engineers,  and  builders  have  said  that 
experience  seems  to  show  that,  if  no  lime  mortar  is  used,  the 
corrosion  of  the  metal  will  not  amount  to  enough  to  be  of  any 
danger;  while  others  point  to  the  well-known  preservative 
qualities  of  lime,  and  urge  its  exclusive  use  in  connection  with 
iron  or  steel.  Our  knowledge  of  wrought-iron  or  steel,  there- 
fore, under  definite  variations  of  heat  and  moisture,  and  in 
association  with  limes,  cements,  and  concrete,  as  found  in 
present  practice,  must  continue  to  be  unsatisfactory  until 
defined  by  more  accurate  data.  American  engineers  and 
builders  show  their  daily  faith  in  such  combinations  of  material, 
and  this  type  of  construction  is  rapidly  becoming  more  and 
more  general  in  the  United  States. 

The  effects  of  lime,  whether  as  one  of  the  ingredients  of 
mortar  or  of  limestone,  as  a  corrosive  factor  in  connection  with 
ironwork,  seem  to  depend  very  largely  upon  the  peculiar  con- 
ditions of  each  particular  case.  Examples  are  recorded  of 
anchorage  cables  in  American  suspension  bridges  which  were 
found,  on  disclosure  after  some  years,  to  be  partly  eaten  away 
where  the  strands  had  come  into  permanent  contact  with  the 
limestone  masonry.  The  presence  of  water  was  possibly 
accountable  for  this  corrosive  action;  but  it  becomes  a  very 
difficult  matter  to  construct  masonry  which  will  allow  of  no 
permeation  of  moisture,  especially  in  walls,  piers,  or  founda- 
tions, as  found  in  building  practice.  Dry  air  and  pure  water 


8o  ARCHITECTURAL  ENGINEERING. 

produce  but  slight  oxidizing  effects  on  iron  or  steel ;  ' '  but 
when  the  former  becomes  moist,  and  the  latter  impure  or 
acidulated,  oxidation  of  the  material  is  speedily  set  up,  and, 
when  once  commenced,  unless  the  process  is  arrested,  its  ulti- 
mate destruction  becomes  a  simple  question  of  time. ' '  The 
use  of  lime  mortar  would,  therefore,  seem  limited  to  localities 
where  no  fear  of  moisture  may  be  anticipated ;  for  any  damp- 
ness in  combination  with  the  lime  must  soon  show  its  effects 
on  the  metal-work. 

Considering  the  parts  of  a  skeleton  structure  which  are 
exposed  to  the  weather,  or  liable  to  the  presence  of  moisture, 
we  have:  all  exterior  walls,  piers,  etc.,  and  the  basement 
members,  including  foundations.  From  the  foregoing  it  would 
seem  that  lime  mortar  should  not  be  used  in  any  of  these  posi- 
tions. The  foundations  and  basement  walls,  columns,  etc., 
are  either  surrounded  by  constant  moisture,  or  by  wet  clay  or 
earth  itself,  while  the  exterior  walls  and  supporting  steelwork 
are -subjected  to  the  climatic  changes,  frost,  rain,  and  penetrat- 
ing dampness,  which  must  sooner  or  later  pierce  the  terra- 
cotta and  brick  envelope,  and  so  reach  the  metal-work.  For 
such  positions  cement  mortar  should  undoubtedly  be  used ;  it 
seems  a  most  perfect  conservator  of  metal-work,  and  instances 
are  recorded  of  iron  found  in  perfect  condition  after  a  4OO-years' 
entombment  in  cement  concrete  below  water.  Links  of 
anchorages  in  American  suspension  bridges  have  been  taken 
up  after  many  years  in  a  perfect  state  of  preservation  where 
embedded  in  cement.  A  further  recommendation  of  the  use 
of  cement  lies  in  the  fact  that  the  thermic  expansion  of  Portland 
cement  is  practically  the  same  as  that  of  iron — a  fact  which 
insures  perfect  cohesion  under  any  changes  of  temperature. 

The  interior  members  of  the  framework  do  not  need  as 
careful  consideration,  being  maintained  at  a  more  uniform  tem- 
perature, and  protected  from  the  exterior  dampness.  Interior 
columns,  the  floor  system,  and  wind-bracing  would,  therefore. 


.  TYPICAL  BUILDINGS -ERECTION,  PERMANENCY,  ETC          Si 

seem  safe  in  connection  with  lime  mortar,  but  it  is  questionable 
whether  the  best  work  should  not  call  for  cement  mortar  and 
even  cement  plaster  throughout.  Cement  has  rapidly  cheap- 
ened of  late  years,  and  cement  plasters  are  largely  being  used 
on  account  of  their  better  fire-resisting  qualities. 

It  has  been  suggested  to  rely  entirely  on  the  preserving; 
qualities  of  cement  rather  than  on  a  proper  painting  of  the 
metal-work.  Prof.  Bauschinger  states  that  his  experiments 
show  a  cohesion  between  iron  and  concrete,  after  hardening,  of 
from  570  to  640  Ibs.  per  square  inch.  This  is  even  more  than 
the  tensile  strength  of  the  best  concrete,  but  in  building  work 
a  perfect  union  between  the  cement  mortar  and  metal-work  can1, 
never  be  attained  at  all  points,  and  a  thorough  coating  of  paint 
must  largely  be  relied  upon. 

In  the  surrounding  of  the  metal  framework  by  masonry  or 
terra-cotta,  it  has  been  found,  after  an  experience  of  fifteen 
years,  that  wherever  masonry  or  terra-cotta  shapes  are  so  em- 
ployed as  entirely  to  cover  the  surfaces  of  the  beams,  girders, 
or  columns  with  the  cement  mortar  in  which  these  coverings- 
are  laid,  practically  no  oxidation  takes  place;  while  beams,, 
girders,  or  columns  which  are  simply  protected,  but  which  do- 
not  have  the  direct  contact  of  the  mortar  with  the  steel,  have 
frequently  been  found  seriously  oxidized. 

In  selecting  materials  for  fireproofing  purposes,  their  influ- 
ence and  action  upon  the  life  of  the  framework  must  not  be 
neglected.  Thus,  while  cinder-concrete  is  most  enduring  from 
a  standpoint  of  fire  resistance,  more  so  than  stone-concrete, 
still  the  employment  of  cinder-concrete  in  direct  contact  with 
steelwork  is  to  be  seriously  questioned,  due  to  the  corrosion 
caused  by  the  alkalies  contained  in  the  cinders. 

Deterioration  due  to  the  leakage  or  radiation  from  supply-, 
waste-,  or  vent-pipes,  must  also  be  considered  and  provided 
against  by  keeping  all  such  piping  in  ducts  or  chases  outside  of 
the  fireproofing  or  protective  coverings  around  the  metal-work. 


82  ARCHITECTURAL  ENGINEERING. 

For  more  extended  data  as  to  permanency  and  corrosion, 
and  the  relative  values  of  ordinary  building  materials  when 
considered  in  relation  to  this  subject,  the  reader  is  referred  to 
the  more  complete  discussion  given  in  the  author's  "Fire- 
proofing  of  Steel  Buildings. ' ' 

Painting. — Excepting,  therefore,  such  steel  members  as 
are  completely  surrounded  by  cement  mortar,  no  more  prac- 
ticable method  of  protection  is  known  than  a  good  paint  well 
applied,  and  the  painting  of  the  metal  framework  must  thus 
constitute"  the  principal  safeguard  against  deterioration  and 
corrosion,  and,  as  the  annual  tonnage  of  steel  shapes  entering 
into  building  construction  is  increasing  so  rapidly,  the  impor- 
tance of  adequate  protection  is  correspondingly  increased. 

The  entire  question  of  painting  (including  the  condition  or 
preparation  of  the  steel  or  iron  before  paint  or  oil  is  applied, 
the  kind  of  paint,  the  quality  to  be  employed,  and  the  best 
methods  of  application) ,  is  one  of  the  utmost  importance,  and 
yet,  in  many  particulars,  of  wide  divergence  in  practice. 
For  a  more  extended  reference  to  this  subject,  several  very 
interesting  and  valuable  books  and  papers  may  be  referred  to,* 
a  study  of  which  will  reveal  great  differences  of  opinion  as 
regards  materials  and  methods,  and  yet  concurrence  as  to  the 
principal  considerations  involved. 

All  agree  that  almost  any  attempt  to  prevent  the  deteriora- 
tion or  corrosion  of  metal-work  by  painting  is  of  some  benefit, 
and  that,  the  more  conscientious  the  effort,  especially  in  the 
method  of  application  rather  than  in  the  material,  the  more 
trustworthy  will  be  the  result. 

To  secure  painting  of  permanent  value,  a  clean  scaleless 
and  rustless  surface  is  first  necessary.  Steel  plates  and  shapes, 

*  See  "  Metallic  Structures:  Corrosion  and  Fouling,  and  their  Preven- 
tion," J.  Newman.  "  Painting  of  Iron  Structures  Exposed  to  Weather," 
and  discussion,  Trans.  Am.  Soc.  C.  E.,  vol.  xxxiii.  No.  6.  M.  P.  Wood  in 
Trans.  Am.  Soc.  M.  E.,  vol.  xv. 


TYPICAL   BUILDINGS— ERECTION,  PERMANENCY,  ETC.         83 

when  delivered  from  the  rolls  which  form  them  to  the  cooling 
beds,  are  largely  covered  with  scales,  which,  adhering  only 
partially  to  the  surface,  offer  the  intervening  cracks  or  joints 
as  vulnerable  points  for  rust.  Almost  at  once  after  being 
rolled,  structural  steel  is  stored  or  handled  out  of  doors  for  a 
varying  period,  both  at  the  mill,  and  then  again  at  the  bridge 
shop  before  the  fabrication  is  started.  This  period  of  open- 
air  exposure  allows  the  process  of  rust  to  start  under  the  scales, 
and,  "if  the  rust  so  covered  up  has  not  begun  to  pit  the  iron, 
the  chances  are  it  will  never  do  any  harm ;  but  if  it  is  already 
well  developed  and  of  some  thickness,  it  will  have  enough 
oxidizing  agents  in  its  pores  to  develop  more  oxide,  swell  up, 
crack  the  paint,  and  the  continuation  is  obvious."  * 

The  first  requirement,  therefore,  for  efficient  painting,  lies 
in  the  careful  removal  of  all  mill-scale,  rust,  grease,  or  foreign 
substance,  before  even  the  priming  coat  is  applied.  And  this 
initial  condition  is  the  most  difficult  to  obtain  of  all  the  require- 
ments for  good  painting,  as,  with  present  mill  and  shop 
methods,  the  cleaning  of  scale  or  rust  is  done  only  very  super- 
ficially, if  at  all,  and  even  if  inspected  the  average  inspector  is 
satisfied  with  the  mere  uniform  coloring  of  the  surface.  All 
authorities  agree  that  the  first  step  in  the  preservation  of  metal- 
work  against  deterioration  or  corrosion,  is  in  obtaining  absolute 
cleanness  of  metal  before  the  application  of  paint  or  oil,  but 
this  result  can  only  be  obtained  at  increased  initial  cost  of  the 
metal,  and  through  more  rigid  and  conscientious  inspection. 
The  result  would  be  well  worth  the  added  cost. 

' '  Better  results  would  be  achieved  in  this  direction  if 
engineers  in  charge  of  important  new  work  were  to  specify  that 
the  material  shall  go  directly  from  the  rolls  to  an  adjoining 
closed  shop  or  cleaning  shed,  where  the  scale  is  to  be  removed 
by  light  portable  power-driven  wire  brushes  or  other  suitable 

*Sec  E.  Gcrber  in  Trans.  Am.  Soc.  C.  E.,  vol.  xxxiii. 


84  ARCHITECTURAL  ENGINEERING. 

means,  and  the  pieces  are  at  once  to  be  immersed  in  a  bath  of 
pure  linseed  oil.  Then  these  are  to  be  sent  to  riveting  or  other 
shops  when  dry  enough  to  handle,  and,  when  the  work  is  com- 
plete, they  are  to  be  sent  to  an  enclosed  paint- shop,  where  a 
good  coat  of  paint  approved  or  specified  by  the  engineer  is  to 
be  given  before  shipment,  ample  time  being  allowed  for  dry- 
ing. "* 

With  present  mill  methods,  the  best  that  can  be  done  is  to 
secure  the  most  careful  cleaning  practicable,  after  which  a  coat 
of  oil  is  generally  preferred,  especially  if  the  work  is  to  receive 
two  coats  of  paint  in  the  field.  Oil  forms  a  transparent  protec- 
tive covering,  thus  leaving  visible  defects  which  might  have 
escaped  detection  at  the  shop;  it  penetrates  joints  and  surface 
cracks  better  than  when  mixed  with  pigment;  it  will  not  rub 
off  as  easily  as  paint,  and  it  forms  a  better  priming  coat  than 
either  the  new  metal  or  dried  paint.  Pure  boiled  linseed  oil  is 
generally  specified,  because  it  dries  more  quickly  than  raw  oil, 
and  the  latter  remains  sticky  for  a  considerable  time,  gathering 
cinders  and  dirt  in  transportation  which  require  cleaning  before 
paint  is  applied.  If  thoroughly  coated  with  pure  linseed  oil, 
steel  members  will  not  suffer  by  waiting  several  weeks  or  even 
months  for  the  final  coats  of  paint  in  the  field. 

The  field  painting  should  be  done  as  soon  as  practicable 
after  erection,  and  this  leads  to  the  question  as  to  what  consti- 
tutes a  good  paint.  Present  practice  is  pretty  well  confined  to 
the  use  of  oil  paints,  such  as  iron,  lead,  or  other  pigments 
ground  and  mixed  with  linseed  oil  or  some  substitute  for  lin- 
seed oil;  coal-tar,  or  asphalt,  or  mixtures  in  which  asphalt  is 
the  principal  ingredient.  Competent  and  disinterested  authori- 
ties differ  widely  in  their  estimates  as  to  the  value  of  these 
coatings.  While  many  engineers,  chemists,  and  men  of  long 
practical  experience  recommend  oxide  of  iron  paint,  others, 

*  See  Geo.  A.  Just  in  Trans.  Am.  Soc.  C.  E.,  vol.  xxxiii. 


TYPICAL   BUILDINGS-ERECTION,  PERMANENCY,  ETC.          85 

•equally  qualified  to  advise,  advocate  the  use  of  red  lead, 
graphite,  and  carbon  paints.  The  rivalry  between  oxide  of 
iron  and  lead  paints  is  of  long  standing,  while  graphite  paints 
are  of  more  recent  introduction,  and  hence  of  more  limited 
use.  Patent  paints,  and  compounds  which  have  had  but  a 
very  limited  use,  should  not  be  seriously  considered  unless 
recommended  by  those  qualified  to  judge  as  to  the  ingre- 
dients employed  and  the  preservative  qualities  which  could  or 
would  be  attained. 

With  a  careful  initial  cleaning,  good  inspection,  and  proper 
application,  it  is  safe  to  assume  that  either  oxide  of  iron,  red 
lead,  asphalt,  or  graphite  paint  will  give  good  results,  provided 
the  materials  are  of  the  best.  In  the  summary  of  the  paper 
previously  referred  to,  Mr.  Gerber  (see  Trans.,  vol.  xxxiii. 
p.  529)  states  as  a  conclusion  based  on  his  very  extended  in- 
vestigation that  "Iron  oxide  is  far  preferable,  as  the  author 
sees  the  matter,  aside  from  the  question  of  cost,  and  in  cost 
the  advantage  is  certainly  with  it. ' '  Also :  ' '  If  metal  has  been 
properly  cleaned  and  paint  properly  applied,  there  need  be  no 
fear  that  any  paint,  composed  of  pure  oil  with  a  good  pigment, 
will  not  protect  the  metal  so  long  as  the  paint  lasts. " 

In  the  discussion  which  follows  the  above-mentioned  paper, 
many  well-known  engineers  and  men  of  large  experience  in 
structural  metal- work  advocate  red  lead,  citing  tests  and 
experiences  to  substantiate  their  opinions.  The  government 
specifications  for  ironwork  in  the  Congressional  Library  at 
Washington  stated  that  ' '  all  work  not  bower-barffed  must  be 
given  one  coat  of  pure  red  lead  paint  before  leaving  the  shop. ' ' 

As  to  asphalt  or  carbon  paints,  the  following  opinions  are 
quoted  from  a  paper  by  Mr.  M.  P.  Wood  entitled,  "Rustless 
Coatings  for  Iron  and  Steel."*  Speaking  of  true  asphalt 
paint,  made  from  natural  or  Trinidad  asphalt — not  the  artificial 

*See  Trans.  Am.  Soc.  M.  E.,  vol.  xv. 


86  ARCHITECTURAL  ENGINEERING. 

product  of  coal-tar  distillation — he  says:  "  Its  toughness,  and 
adhesiveness  to  all  bodies,  wooden,  fibrous,  as  well  as  metallic, 
are  remarkably  persistent  and  durable,  its  covering  quality  is 
also  excellent,  and  for  the  exclusion  of  moisture  and  preven- 
tion of  rust  it  has  no  superior,  if  any  equal."  As  to  lamp- 
black or  carbon  paints,  he  states  that  "Lamp-black  as  a 
carbon  is  practically  unchangeable  and  indestructible  under 
ordinary  atmospheric  conditions,  and  being  itself  of  an  oily 
and  elastic  nature,  its  combination  with  oil  forms  an  elastic, 
close-clinging  coating, — one  of  the  best  preservative  paints 
known  in  the  arts. ' ' 

All  authorities,  however,  insist  on  the  use  of  perfectly  pure 
materials,  and  as  the  oil  is  the  principal  preservative  ingredient 
in  paint,  the  quality  of  the  oil  is  of  the  utmost  importance. 
From  its  many  good  qualities,  linseed  oil  stands  preeminently 
at  the  head  of  the  list,  but  ' '  the  number  of  non-drying  oils  of 
a  vegetable  character  that  are  available  for  the  adulteration  of 
linseed  oil  are  over  thirty ;  the  greater  number  of  which  are 
commercially  cheaper  than  linseed."  To  these  must  also  be 
added  many  other  fish,  animal,  and  mineral  oils.  These  sub- 
stitutes or  adulterations  are  extensively  used,  but  on  drying  or 
being  exposed  to  the  air  they  are  sure  to  crack,  thus  greatly 
lessening  the  durability  and  value  of  the  preservative  coatings. 
Many  methods  are  employed  for  detecting  the  adulteration  of 
oils,  the  most  common  being  by  means  of  bringing  the  oil  into 
contact  with  strong  sulphuric  acid.  See  Ure's  "  Dictionary  of 
Arts,  Manufactures,  and  Mines,"  vol.  ii.  p.  301.  Oil  or  spirits 
of  turpentine,  or  "  turps  ",  and  benzine  dryers  should  never  be 
used. 

Equal  care  is  necessary  to  avoid  oxide  of  iron  paints,  con- 
taining a  large  proportion  of  clay  as  adulteration,  or  red  lead 
paints  with  chalk  and  lime.  Fraud  can  generally  be  avoided 
by  dealing  directly  with  manufacturers  of  good  standing,, 
instead  of  buying  from  low  and  irresponsible  bidders. 


TYPICAL   BUILDINGS-ERECTION,  PERMANENCY,  ETC. 


Finally,  no  painting  should  be  allowed  in  freezing  or  stormy 
weather.  Paint  should  be  applied  when  the  material  to  be 
painted  is  as  free  as  possible  from  dampness,  and  it  must  be 
remembered  that  the  more  area  a  paint  covers,  the  thinner  the 
film  is,  and  hence  the  less  it  is  able  to  protect  the  metal.  A 
good  heavy  coat  is  far  preferable  to  a  thin  one,  and  the  spread- 
ing qualities  claimed  by  paint  manufacturers  for  their  products 
should  be  considerably  discounted.  The  relative  cost  and 
covering  capacity  of  the  paints  in  most  general  use,  may  be 
tabulated  about  as  follows,  the  prices  varying  somewhat 
according  to  market  fluctuations.  The  prices  given  are  for 
absolutely  pure  materials. 


Cost  per 
Gallon. 

Reputed  Cov- 
ering-Capacity 
of  i  Gallon. 
Square  Feet. 

Cost  of  Paint 
per  100  sq.  ft.* 

Red  lead                      .... 

P           g     P 

*  Light   structural   work   will  average  about   250    sq.   ft.,   and    heavy 
structural  work  about  150  sq.  ft.  of  surface  per  net  ton  of  metal. 

Building  Laws. — The  following  are  the  requirements  of 
the  New  York  building  law  in  regard  to  the  protection  of  iron 
or  steelwork  against  corrosion,  etc. : 

"All  structural  metal-work  shall  be  cleaned  of  all  scale, 
dirt,  and  rust,  and  be  thoroughly  coated  with  one  coat  of  paint. 

' '  Cast-iron  columns  shall  not  be  painted  until  after  inspec- 
tion by  the  Department  of  Buildings. 

"Where  surfaces  in  riveted  work  come  in  contact,  they 
shall  be  painted  before  assembling. 

' '  After  erection  all  work  shall  be  painted  at  least  one  addi- 
tional coat. 

' '  All  iron  or  steel  used  under  water  shall  be  enclosed  with 
concrete." 


88  ARCHITECTURAL  ENGINEERING. 

The  Chicago  ordinance  makes  no  mention  of  paint  or  coat- 
ings to  prevent  rust  in  the  metal  framework,  except  as  specified 
for  fireproofing  purposes  as  follows :  ' '  In  all  cases  the  brick 
or  hollow  tile  shall  be  bedded  in  mortar  close  up  to  the  iron 
or  steel  members,  and  all  joints  shall  be  made  full  and  solid." 

The  Boston  law  requires  a  protection  from  heat  only,  by 
means  of  brick,  terra-cotta,  or  by  three-fourths  of  an  inch  of 
plastering. 

The  requirements  for  the  protection  of  metal-work  in  foun- 
dations are  given  in  Chapter  X. 


CHAPTER   IV. 
FLOORS  AND   FLOOR   FRAMING. 

THE  engineering  or  constructive  problems  involved  in  steel 
building  construction  must  naturally  start  with  the  load-bearing 
floor  system,  for  upon  the  floors  and  floor-loads  depend  the  cal- 
culations of  the  columns  and  foundations.  In  skeleton  or  cage 
construction,  the  walls  are  not  relied  upon  for  load-carrying 
capacity,  but  are  themselves  carried  by  those  members  of  the 
floor  system  which  connect  the  exterior  columns, — while  pro- 
visions made  for  wind-bracing  may  most  properly  be  treated 
as  a  portion  of  the  column  design. 

Starting,  then,  with  the  floor  areas,  the  first  requisite  is  the 
choice  of  a  satisfactory  floor  arch  of  terra-cotta,  concrete,  or 
other  material,  or  combinations  of  materials — and  here  a  wide 
choice  is  offered  the  architect  or  engineer.  A  preference  must 
not  be  based  on  form  or  appearance  alone,  as  fulfilling  archi- 
tectural requirements,  nor  upon  strength  only,  as  satisfactory 
to  the  engineer;  but  form  or  appearance,  strength,  and  fire- 
resisting  qualities  must  all  be  given  due  weight  in  an  intelli- 
gent selection. 

Brick  and  Corrugated-iron  Arches. — The  oldest  so-called 
fireproof  arches  consisted  of  I-beams,  placed  about  5  ft. 
centres,  with  4-in.  brick  arches  turned  between,  then  levelled 
up  with  concrete  containing  the  nailing-strips  for  the  wooden 
flooring.  Corrugated-iron,  sprung  from  flange  to  flange,  was 
also  used  in  place  of  the  brickwork,  and  this  latter  type  may 

89 


9°  ARCHITECTURAL  ENGINEERING. 

still  be  seen  in  some  of  the  more  substantial  buildings  of  that 
epoch,  which  have  survived  to  the  present  time.  This  con- 
struction was  decidedly  faulty,  however,  not  alone  in  the 
weakness  of  the  arch  itself  under  the  action  of  fire,  but  in  the 
fact  that  the  lower  flanges  of  the  supporting  I-beams,  and  the 
entire  cast  columns  then  in  use,  were  left  exposed  to  view, 
and,  what  was  much  more  serious,  to  the  possibility  of  contact 
with  fire. 

These  heavy  and  unsatisfactory  types,  shown  in  Figs.  37 


FIG.  37.— Brick  Arch  Construction. 


FIG.  38.— Corrugated-iron  Arch. 

and  38,  usually  approximated  75  Ibs.  per  sq.  ft.  dead  load,  for 
the  arch  and  concrete  filling  alone. 

Introduction  of  Terra-cotta  Arches. — Present  methods  of 
terra-cotta  floor  arches  practically  resulted  from  the  great 
Chicago  fire  in  1871.  While  this  conflagration  exhibited  many 
admirable  examples  of  fire-resisting  brick  and  concrete  arches, 
it  plainly  demonstrated  the  necessity  for  better  methods,  at 
reduced  weight  and  cost.  In  1872,  therefore,  flat  hollow-tile 
arches  were  first  patented  and  introduced  in  Chicago  by 
Mr.  Geo.  H.  Johnson,  and  at  about  the  same  time  a  similar 
but  heavier  construction  was  used  in  New  York  City  in  the 
corridors  of  the  Post-office  Building. 

These  early  examples  were  naturally  very  crude  as  to 
workmanship  and  materials,  but  as  terra-cotta  arches  proved 
to  be  light,  substantial,  and  fire-resisting,  their  use  soon 
became  greatly  extended,  indeed  almost  universal  in  this 
country. 


FLOORS  AND  FLOOR.  FRAMING. 


Early  Forms  of  Tile  or  Terra-cotta  Arches. — The  earlier 
forms  of  tile  arches  were  made  as  in  Fig.  39,  which  shows  the 


FIG.  39. — Terra-cotta  Arch  used  in  Equitable  Building,  Chicago  (1872). 

arch  used  in  the   Equitable   Building  in  Chicago  (1872),  and 
Fig.   40,   which    shows  tile   arch    in   the  Montauk  Building, 


FIG.  40.— Terra-cotta  Arch  used  in  Montauk  Building,  Chicago  (1881). 

Chicago  (1881).  The  latter  may  be  said  to  have  been  the  first 
building  of  modern  design  in  Chicago.  The  arches  were  6  ins. 
deep,  with  a  span  of  3  to  4  ft.  But  as  these  forms  still  left  the 
lower  flanges  of  the  I-beams  unprotected,  they  were  soon 
superseded  by  the  type  shown  in  Fig.  41.  This  arch  was  used 


FIG.  41.— Terra-cotta  Arch  used  in    Home    Insurance    Building,  Chicago 
(1884). 

in  the  Home  Insurance  Building,  Chicago  (1884),  the  tile  being 
9  ins.  deep  and  6  ft.  span.  This  was  the  first  instance  in 
which  the  beam  soffits  were  protected  against  fire  by  anything 
more  than  plaster ;  and  it  is  interesting  to  note  that  the  intro- 
duction of  soffit  pieces,  under  the  beam  flanges,  was  due  to  an 
attempt  to  remedy  the  discoloration  of  the  plastered  ceilings, 


92  ARCHITECTURAL  ENGINEERING. 

rather  than  to  improve  the  fire-resisting  quality.  Previous  arch- 
blocks  had  been  made  to  project  about  one-half  inch  below  the 
bottoms  of  the  beams,  thus  leaving  recessed  spaces  under  the 
beam  flanges.  These  recesses  were  filled  with  mortar  at  the 
time  of  applying  the  first  coat  of  ceiling  plaster,  but  it  was  soon 
found  that  the  cooler  surfaces  under  the  beams  condensed  the 
moisture  in  the  atmosphere  along  these  lines,  and  caused  the 
soot  or  smoke  from  soft-coal  fuel  to  accumulate,  and  to  indi- 
cate the  beams  by  black  lines  on  the  ceilings.  This  trouble 
first  suggested  the  use  of  protection  tiles  for  the  beam  flanges, 
a  detail  which  greatly  increased  the  fire-resisting  qualities  of 
terra-cotta  arches. 

Previous  to  the  year  1883,  the  arch-blocks,  excepting  the 
skew-backs,  had  all  been  made  without  interior  webs,  but 
requirements  as  to  strength  and  the  increase  of  spans  between 
the  supporting  beams  soon  caused  the  introduction  of  heavier 
and  stronger  types.  In  1883,  contracts  for  the  floors  in  the 
Mutual  Life  Insurance  Company's  building,  on  Nassau  Street 
in  New  York  City,  were  awarded  to  a  Chicago  fireproofing 
company,  and  arch-blocks  with  both  vertical  and  horizontal 
interior  webs  were  employed.  The  arches  weighed  33  Ibs.  per 
superficial  foot,  and  were  practically  as  shown  in  Fig.  41, — 
the  arches  used  in  the  Home  Insurance  Building,  Chicago, 
built  at  about  the  same  time. 

In  the  foregoing  examples  of  arches,  known  generally  as 
the  "Pioneer"  arches  (because  made  by  the  Pioneer  Fire- 
proofing  Company  of  Chicago),  the  voids  in  the  tile  blocks  ran 
parallel  to  the  supporting  beams,  and  hence  the  principal  or 
side  webs  of  the  individual  tile  blocks  also  ran  parallel  to  the 
beams,  or  at  right  angles  to  the  line  of  thrust  in  the  arch. 
This  limited  the  effective  arch  area  to  the  top  and  bottom 
flanges,  involving  a  serious  waste  of  material. 

To  remedy  this  defect  a  new  arch  was  patented  in  about 
1890,  known  as  the  "Lee"  arch,  in  which  the  voids  ran 


FLOORS  AND  FLOOR  FRAMING.  93 

parallel  to  the  line  of  thrust,  or  at  right  angles  to  the  support- 
ing beams.  One  of  these  arches  is  shown  in  Fig.  42,  and  it 
will  be  seen  that  the  effective  area  now  comprises  the  vertical 
webs,  as  well  as  the  horizontal  ribs;  in  other  words,  all  of  the 
material  performs  useful  work  as  an  arch.  A  further  improve- 
ment was  attempted  by  the  use  of  a  porous  terra-cotta,  made 
from  a  fire-clay  which,  before  it  is  burned,  is  mixed  with  saw- 


I- - 1 


FIG.  42.— The  "  Lee"  Terra-cotta  Flat  Arch. 

dust  and  finely  cut  straw.  These  ingredients  are  consumed 
during  the  firing,  leaving  the  material  in  a  very  porous  condi- 
tion, and  thus  greatly  reducing  the  dead  weight  of  the  arch 
itself.  A  comparison  of  the  weights  of  the  old  Pioneer  and  the 
newer  Lee  arch  may  be  made  as  follows  (weight  given  is  per 
square  foot) : 

Pioneer.  Lee. 

9"  arch 33  Ibs.  25  Ibs. 

10"     "  ..: 37   "  30  " 

12"     " 40  "  35   " 

IS"     "   40  " 

Another  step  of  progress  lay  in  the  skew-back  or  butment 
pieces,  which  gave  a  better  bearing  against  the  beam  webs  by 
means  of  intermediate  cross-ribs,  as  well  as  by  the  top  and 
bottom  flanges. 

Denver  Tests. — Some  very  interesting  and  valuable  tests 
of  fireproof  floor  arches  built  after  the  Pioneer  and  Lee 
methods  were  published  in  No.  796  of  the  American  Architect 
and  Building  News — undoubtedly  forming  one  of  the  most 
satisfactory  and  extensive  series  of  public  tests  yet  attempted 
on  such  construction.  The  trials  were  made  in  Denver,  Col., 


94  ARCHITECTURAL  ENGINEERING. 

1 890,  for  the  Denver  Equitable  Building  Company,  under  the 
supervision  of  a  board  of  architects.  The  arches  were  sprung 
from  beams  placed  5  ft.  centres,  as  shown  in  Fig.  42,  and  the 
conditions  included  static  loading,  a  drop  test,  a  fire  and  water 
test,  and  a  continuous  fire  test. 

In  the  test  for  static  loads  the  Lee  arch  deflected  gradually 
under  the  increased  weights  to  .065  of  a  foot,  sustaining  a  final 
load  of  1 5, 145  Ibs.  for  two  hours.  The  Pioneer  arch  gave  way 
suddenly  at  the  haunches  under  a  load  of  5,429  Ibs. 

In  the  drop  test  a  piece  of  wood  12"  X  12"  X  4'  was  let 
fall  from  a  height  of  6  ft.  The  Pioneer  arch  was  shattered  at 
the  first  blow,  while  the  Lee  arch,  under  the  same  test,  stood 
up  to  the  eleventh  drop,  the  former  blows  shattering  but  parts 
of  the  arch. 

In  the  fire  and  water  tests,  three  applications  of  water  com- 
bined with  fire  destroyed  the  Pioneer  arch,  while  the  Lee  arch 
received  eleven  applications  of  water,  and  at  the  end  of  twenty- 
three  hours  remained  practically  uninjured,  requiring  eleven 
blows  from  the  ram  to  break  it. 

In  the  continuous  fire  test  the  fire  was  maintained  contin- 
uously beneath  a  Lee  arch  for  twenty-four  hours,  and  the  arch 
then  supported  a  load  of  bricks  of  12,500  Ibs.  on  a  space  3  ft. 
wide  in  the  central  portion  of  the  arch. 

Considering  the  static  loads,  the  results  may  be  better 
judged  as  follows: 


Pioneer. 

Lee. 

Breaking-load  per  square  foot  of  9  sq.  ft.  loaded  area  
Reduced  to  equally  distributed  load,  3'  o"  X  s'  °  '  «  .  •  • 

Ibs. 
603 
360 

Ibs. 
1670 
1008 

Assumed  load  per  square  foot,  as  occurring  in  practice  
Coefficient  of  safetv  

150 
2.4 

150 
6-7 

Manufacture  of  Terra-cotta  Arch-blocks.— Terra-cotta 
floor  arches  now  in  common  use  are  made  of  either  "  porous," 
1 '  semi-porous, "  or  "  hard-burned  ' '  terra-cotta.  These  desig- 


FLOORS  AND  FLOOR  FRAMING.  95 

nations  are  indicative  of  the  methods  employed  in  the  manu- 
facture of  the  clay. 

Porous  terra-cotta,  sometimes  called  cellular  pottery,  soft 
tile,  porous  tile,  or  terra-cotta  lumber,  may  be  briefly  described 
as  consisting  of  pure  clay  mixed  with  sawdust  or  finely  cut 
straw.  This  mixture  is  passed  through  the  "tile-machines," 
where  the  blocks  are  manufactured  to  the  required  form,  after 
which  they  are  placed  in  dry  rooms  for  a  sufficient  time  to 
permit  of  handling,  the  final  burning  or  hardening  being 
accomplished  in  kilns  where  a  temperature  of  from  2,100  to 
2,500  degrees  is  maintained  for  from  three  to  four  days.  The 
sawdust  or  straw  in  the  clay  is  completely  consumed  during 
the  firing,  thus  leaving  the  finished  product  in  a  honey-combed 
or  porous  state,  thereby  reducing  the  weight  of  the  original 
mass. 

Porous  terra-cotta  can  be  readily  cut  with  ordinary  tools, 
and  the  blocks  are  often  soft  enough  to  receive  nails  or  screws 
used  in  applying  the  interior  trim.  Such  nailing  blocks  are 
usually  made  solid. 

Semiporous  terra-cotta  differs  from  that  of  the  porous 
variety  principally  in  the  composition  of  the  mixture.  The 
ingredients  are  usually  fire-clay  containing  about  60  per  cent, 
of  silica,  coarsely  ground  calcined  fire-clay,  and  coarsely  ground 
bituminous  coal.  The  resulting  product  is  slightly  more  porous 
than  the  best  grades  of  fire-brick,  but  not  as  soft  as  porous 
terra-cotta. 

Hard-burned  terra-cotta,  also  termed  hard  tile,  or  dense 
tile,  is  made  of  pure  clays,  without  the  addition  of  any  com- 
bustible materials.  During  its  manufacture,  the  clay  is  sub- 
jected to  a  high  pressure,  thus  giving  the  material  a  dense 
texture,  and  great  strength  under  crushing  loads.  Hard- 
burned  terra-cotta  cannot  be  readily  cut.  but  must  be  broken, 
and  as  the  material  is  brittle,  it  is  unreliable  under  shocks  or 
suddenly  applied  loads. 


96  ARCHITECTURAL  ENGINEERING. 

Construction  of  Flat  Terra-cotta  Arches. — Flat  arches, 
constructed  of  terra-cotta  blocks,  are  composed  of  two  "skew- 
backs,"  "skews,"  or  "  butment  pieces, "  which  bear  against 
the  beam  webs  and  fit  around  the  lower  flanges  of  the  beams  • 
one  centre  block  or  "key,"  and  "fillers,"  "part-fillers,"  or 
"intermediates  ' '  which  fill  the  spaces  between  the  skew-backs 
and  key.  In  end-construction,  a  filler  or  whole  intermediate 
block  is  usually  considered  as  12  ins.  long,  a  part-filler  being 
less  than  this  in  length.  In  side-construction  the  lengths  of 
the  fillers  vary  according  to  the  manufacturers'  practice. 

All  types  of  flat  arches  are  usually  made  with  bevelled 
joints — that  is,  all  of  the  joints  in  each  half  of  the  arch  are 
made  parallel  to  the  side  of  the  key.  Radial  joints,  or  such  as 
would  meet  at  a  common  centre  if  prolonged,  are  occasionally 
employed,  and  these  make  an  arch  better  and  stronger,  and 
more  theoretically  correct,  but  the  increased  number  of  shapes 
required  for  arches  of  varying  span,  makes  the  cost  of  manu- 
facture almost  prohibitory. 

The  protection  of  the  bottom  flanges  of  the  beams  is  usually 
made  by  introducing  separate  strips  of  terra-cotta,  or  "beam- 
facings,"  which  are  held  in  place  under  the  beam  flanges  by 
means  of  bevelled  lips  on  the  skew-backs,  as  shown  in  Fig. 
41.  Some  manufacturers  have  dispensed  with  separate  beam- 
facings,  substituting  therefor  projecting  lips  made  on,  and  as  a 
part  of,  the  skew-backs,  the  lips  from  the  two  skew-backs 
meeting  at  the  centre  line  of  the  beam  as  shown  in  Fig.  49. 
But  in  manufacturing  such  skews,  with  the  beam  protections 
made  as  a  part  of  the  blocks,  these  flanges  were  so  liable  to 
deformation  by  warping  in  the  drying  or  burning  that  the 
skews  could  often  not  be  placed  upon  the  beams  without 
breaking  the  flange  from  the  block.  The  majority  of  manufac- 
turers have  consequently  abandoned  this  method,  and  separate 
"beam-facings  "  are  now  generally  used. 

The  arches  are  set  on  ' « centres  ' '  of  plank  (hung  from  the 


FLOORS  AND  FLOOR  FRAMING. 


97 


beams  by  hook-bolts),  which  should  remain  in  place  at  least 
forty-eight  hours  in  good  dry  weather,  and  considerably  longer 
in  damp  or  wet  weather.  Clear  cement  mortar  should  prefer- 
ably be  used,  many  of  the  blocks  being  "scored  "  or  grooved 
on  the  outer  surfaces  as  shown  in  Fig.  43,  to  provide  a  better 
key  for  the  mortar  in  the  joints,  and  for  the  plastered  ceiling. 

The  depth  of  the  terra-cotta  arch-blocks  depends  upon  the 
span  and  the  load  to  be  carried.  The  maximum  spans  for  the 
varying  depths  of  blocks  under  specified  loads  per  square  foot 
are  usually  furnished  by  the  manufacturer,  and  for  ordinary 
requirements  such  data  will  generally  be  found  reliable  if  fur- 
nished by  responsible  firms.  A  safe  rule  for  ascertaining  the 
allowable  span  for  any  depth  of  arch-block  is  that  the  maxi- 
mum span  in  feet  should  not  exceed  two-thirds  the  depth  in 
inches  of  the  arch-block  employed. 

Present  Types  of  Terra-cotta  Arches Flat  terra-cotta 

arches  now  in  ordinary  use  include  "side-construction" 
arches,  "end-construction"  arches,  and  "combination" 
arches  made  of  part  side  and  part  end  methods. 

Side-construction  Arches  are  made  of  blocks  in  which  the 
voids  run  parallel  to  the  supporting  beams,  as  in  the  early 
forms  of  Pioneer  arches,  before  illustrated.  A  side-construc- 
tion arch  with  bevelled  joints  is  shown  in  Fig.  43.  This 


^maraBHHH  B/BB/BB/BB 


FIG.  43. — Side-construction  Terra-cotta  Arch.     Bevelled  Joints. 

represents  a  deep  arch,  the  blocks  of  which  have  one  vertical 
and    two  horizontal    interior  webs    or    partitions.      Shallower 


9»  ARCHITECTURAL  ENGINEERING. 

arches  have  less  interior  webs,  one  horizontal  web  or  partition 
being  generally  used  for6-in.,  7-in.,  or  8-in.  blocks,  two  webs 
for  9~in.,  io-in.,  and  12-in.  blocks,  and  three  or  four  webs  for 
J5-in.  and  i8-in.  blocks. 

The  average  permissible  spans  and  weights  per  square  foot 
for  arches  of  this  type  are  as  follows : 


Depth  of  Arch. 

6  ins. 

7  ins. 

8  ins. 

9  ins. 
10  ins. 
12  ins. 


Width  of  Span. 

3  ft.  to  4  ft. 

4  ft.  to  4  ft.  6  ins. 

4  ft.  6  ins.  to  5  ft. 

5  ft.  to  6  ft. 

6  ft.  to  6  ft.  6  ins. 
6  ft.  6  ins.  to  7  ft. 


Weights  per  sq.  ft.  in  Ibs. 
Hard-burned.     Porous. 


27 
29 
32 

37 
40 

44 


25 
26 
28 
32 
36 
40 


Side-construction  arches  are  made  of  both  hard-burned  and 
porous  terra  cotta. 

A  side-construction  arch  with  radial  joints  and  segmental 
interior  webs  is  shown  in  Fig.  44.  This  arch  is  made  in  8-, 


FIG.  44. — Side-construction  Terra-cotta  Arch.     Radial  Joints. 

9-,  io-,  and   12-in.  depths,  weighing  respectively  28,  29,  35, 
and  46  Ibs.  per  square  foot. 

End- construction  Arches  are  made  of  blocks  in  which  the 
voids  run  at  right  angles  to  the  beams,  or  from  beam  web  to 
beam' web.  The  skew-back  pieces  are  of  the  same  general 
form  as  the  intermediate  blocks,  but  are  made  to  fit  against 
the  beam  web  and  flange,  without,  however,  any  continuous 
bearing-surface,  as  is  obtained  in  the  side-construction  skew. 
The  vertical  and  horizontal  webs  and  partitions  run  directly  to 
the  beam,  and  as  these  are  the  load-bearing  areas,  a  stronger 


FLOORS  AND  FLOOR  FRAMING. 


99 


and  better  skew  is  obtained.  The  skew-backs  are  made  with 
dovetailed  lips  to  hold  the  beam-facings  in  place.  These 
arches  are  usually  made  of  porous  terra-cotta  and  always  with 
bevelled  joints. 

Fig.  45  shows  an  end-construction  arch  of  porous  material 


FIG.  45. — End-construction  Terra-cotta  Arch. 

in  which  the  blocks  break  joints  with  those  in  adjacent  arches,, 
each  arch  being  continuous  from  beam  to  beam.  This  is  con- 
sidered the  best  practice.  The  depth  of  arch-blocks  varies 
from  6  ins.  to  1 5  ins.  Maximum  spans  and  average  weights 
per  square  foot,  set  in  position,  are  as  follows: 


Depth 

of  Arch. 

Max! 

mum  Span. 

Weight 

per  sq. 

ft. 

6 

ins. 

4 

ft 

.  6 

ins. 

29 

Ibs. 

8 

ins. 

5 

ft 

.  6 

ins. 

31 

Ibs. 

9 

ins. 

6 

ft 

32 

Ibs. 

10 

ins. 

6 

ft 

.  6 

ins. 

33 

Ibs. 

12 

ins. 

7 

ft 

39 

Ibs. 

15 

ins. 

8 

ft 

46 

Ibs. 

An  end-construction  arch  intended  for  extremely  heavy 
service  has  been  introduced  by  the  Pioneer  Fireproof  Con- 
struction Co. ,  of  Chicago,  the  arch-blocks  being  made  of 
I5~in.,  i6-in.,  i8-in.,  and  2O-in.  depths  of  the  form  shown  in 
Fig.  46.  This  type  of  arch  with  recesses  or  voids  between  the 
individual  blocks  affords  a  very  stiff  floor,  due  to  the  increased 


100 


ARCHITECTURAL   ENGINEERING. 


depth,  and  yet  at  no  increase  in  weight,  while  a  further  advan- 
tage is  gained  in  permitting  the  tie-rods  to  span  the  bays  with- 


FIG.  46. — End-construction  Terra-cotta  Arch,  "  Pioneer"  Type. 

out  cutting  into  the  blocks.     The  span  lengths  and  weights  as 
given  by  the  manufacturers  are  as  follows: 


Depth  of  Arch. 

15  ins. 

1 6  ins. 
1 8  ins. 
2O  ins. 


Maximum  Span. 

8  ft.  o  ins. 


12  ft.  o  ins. 


Weight  per  sq.  ft. 
38  Ibs. 
42  Ibs. 
50  Ibs. 
56  Ibs. 


This  arch  is  a  development  of  the  form  shown  in  Fig.  47. 

Combination  End-  and  Side- construction  Arches  are 
formed  of  side-construction  skew-backs,  and  end-construction 
intermediates,  the  combined  use  being  largely  due  to  the 
greater  ease  with  which  side-construction  skew-backs  can  be 
set,  while  the  intermediate  blocks  may  still  be  retained  of  the 
superior  end-construction  type. 


FIG.  47. — Johnson  Type  of  Terra-cotta  Arch. 

One  of  the  first  combination  arches  was  as  shown  in  Fig. 
47.     This  was  known  as  "Johnson's  patent  flat  arch,"  and 


FLOORS  AND  FLOOR  FRAMING. 


101 


this   type   has    been   used  extensively  in    many  of  Chicago's 
largest  buildings. 

Fig.   48   illustrates  a  combination    arch  made  in  8-,    10, 


FIG.  48. — Combination  Terra-cotta  Arch. 

II-,  and  12-in.  depths,  weighing  respectively  27,  34,  36,  and 
41  Ibs.  per  sq.  ft. 

The  ' '  Excelsior ' '  combination  arch  is  shown  in  Fig.  49. 


FIG   49. — Combination  Terra-cotta  Arch,  "  Excelsior"  Type. 
This  also,  like  Figs.  46  and  47,  possesses  the  recessed  sfdes 
or  voids  between  the  arch-blocks,  which,  while  reducing  the 
weight,  permit  a  free  passage  for  the  tie-rods.      The  followingJ 
spans  and  weights  per  square  foot  are  given  by  the  manufac 
turer : 


Depth  of  Arch. 

8  ins. 

9  ins. 
10  ins. 
12  ins. 


Safe  Span. 

5  ft.   to  6  ft. 

6  ft.  to  7  ft. 

7  ft.  to  8  ft. 

8  ft.  to  9  ft. 


Weight  per  sq.  ft. 
27  Ibs. 
29  Ibs. 
33  Ibs. 
38  Ibr 


102  ARCHITECTURAL  ENGINEERING. 

Segmental  Terra-cotta  Arches  are  usually  limited  tc  use 
in  warehouses,  factories,  or  breweries,  where  heavy  floor-loads 
have  to  be  carried  regardless  of  the  ceiling  appearance.  In 
office  or  mercantile  buildings,  a  flat  ceiling  is  desirable  on 
account  of  appearance  and  the  greater  light  reflected  from  an- 
unbroken  plane. 


FIG.  50. — Segmental  Terra-cotta  Arch. 

Segmental  arches    are    usually  made  of   side-construction 
blocks,  4,  5,  6,  or  8  ins.  square,  and  about  12  ins.  long.     Both 
porous  and  hard-burned  materials  are  used.      The  spans  em- 
ployed vary  from   5  ft.  to  20  ft.,  and  the  rise  should  never  be 
less  than  one  inch  per  foot  of  span,  or  preferably  one  and  one- 
half  inches  per  foot.      The  usual  form  is  shown  in  Fig.  50,  for 
which  the  spans  and  weights  per  square  foot,  exclusive  of  con- 
crete filling  and  plastering,  will  average  about  as  follows: 
4-in.  blocks,     8 -ft.  span,  16  Ibs.  per  sq.  ft. 
6-in.  blocks,  i6-ft.  span,  26     "      "      " 
8 -in.  blocks,  2O-ft.  span,  28     "     "     "       . 

tThe  skew-back  blocks  should  be  either  very  heavy  or 
entirely  solid,  and  the  concrete  levelling  should  be  of  good 
quality  and  levelled  up  to  a  point  at  least  one  inch  above  the 
crown.  The  concrete  at  the  haunches  is  sometimes  made 
with  voids,  as  in  Fig.  51. 

Raised  skew-backs  with  flat  arches  are  often  employed,  as 
in  Fig.  52.  These  are  frequently  used  in  roof  construction, 
where  long  and  deep  beams  are  necessary,  but  where  the  arch 
depth  may  be  reduced  on  account  of  lighter  floor-loads  per 
square  foot. 


FLOORS  AND  FLOOR  FRAMING. 


103 


Filler  blocks  of  terra-cotta  are  sometimes  used  instead  of 
the  usual  concrete  rilling  over  the  arches.  These  are  to 
decrease  the  weight.  See  Fig.  49. 

Choice  of  Terra-cotta  Arch.— As  to  a  choice  between  the 
various  forms  and  materials  in  which  terra-cotta  arches  are 
manufactured,  the  reader  is  referred  to  the  author's  "Fire- 
proofing  of  Steel  Buildings,"  in  which  volume  a  complete 


FIG.  51.— Segmental  Terra-cotta  Arch. 


FIG.  52. — Side-construction  Terra-cotta  Arch.     Raised  Skew-backs, 
discussion  will  be  found  relative  to  all  ordinary  forms  of  terra- 
cotta, concrete,  and  composition  floors. 

Briefly,  it  may  be  stated  that  a  porous  terra-cotta  end-con- 
struction arch,  with  thick  webs,  well  rounded  interior  corners, 
level  soffit,  and  of  the  full  depth  of  the  beams,  will  best  answer 
all  requirements  as  to  load-bearing  capacity,  shock,  and  fire- 
and  water-tests. 

Concrete  and  Composition  Floors.* — The  widespread  in- 
terest displayed  in  the  subject  of  fireproof  floors  is  well  indi- 

*  For  complete  descriptions  as  to  the  construction,  setting,  comparative 
advantages  and  disadvantages,  and  fire-resisting  qualities,  etc.,  see  the 
author's  "  Fireproofing  of  Steel  Buildings,"  John  Wiley  &  Sons,  N.  Y. 
1899. 


104  ARCHITECTURAL  ENGINEERING. 

cated  by  the  numerous  types  which  have  entered  the  field  in 
competition  with  the  hollow-tile  flooring.  These  newer  systems 
differ  greatly  in  principle,  and  while  many  of  them  are  founded 
on  sound  constructive  practice,  others  are  open  to  serious  ques- 
tion and  should  be  used  with  much  discrimination.  While  it  is 
no  difficult  matter  to  construct  a  floor  of  concrete  or  various 
compositions  which  will  be  of  sufficient  strength  and  possess 
apparently  satisfactory  fire-resisting  qualities,  it  is  still  not  so 
easy  to  secure  a  minimum  cost,  a  minimum  weight,  and  a 
minimum  of  repair  made  necessary  by  possible  fire  and  water 
exposure. 

Only  the  more  ordinary  and  commendable  forms  of  con- 
crete and  composition  floor  systems  will  here  be  described. 

The  most  widely  known  forms  of  concrete  floors  include 
the  Roebling,  Columbian,  and  Expanded  Metal  Company's 
floors. 

Roebling  Floors. — The  concrete  floors  made  by  the  John 
A.  Roebling 's  Sons  Company  include  three  distinct  forms, 
viz.,  a  concrete  arch  with  exposed  soffit,  a  flat  construction 
somewhat  similar  to  the  Columbian  floor  (made  of  metal  bars 
and  a  concrete  plate,  with  a  suspended  ceiling  beneath),  and 
a  concrete  arch  with  suspended  ceiling.  The  latter  is  the  most 
common  form,  and  is  illustrated  in  Fig.  53. 


FIG.  53.— Roebling  Concrete  Floor  Arch  with  Suspended  Ceiling. 

The  arch  is  formed  on  a  permanent  arched  centering  made 
of  wire  cloth  stiffened  with  f-in.  to  ^-in.  diameter  steel  rods 
woven  into  the  cloth  about  p-ins.  centres.  These  wire  centres 


FLOORS  AND  FLOOR  FRAMING.  105 

are  made  of  the  proper  size  and  form  at  the  factory,  and  in 
erection  the  sheets  are  lapped  at  the  joints,  and  securely  laced. 

A  cinder-concrete  arch  (generally  made  of  I  part  Portland 
cement,  2^  parts  sand,  and  6  parts  clean  anthracite  coal  cin- 
ders) is  then  filled  in  up  to  the  tops  of  the  beams,  giving  a 
thickness  of  not  less  than  3  ins.  at  the  crown  of  the  arch. 

A  suspended  ceiling  is  made  by  attaching  flat  bars,  spaced 
about  i6-in.  centres,  to  the  under  sides  of  the  I-beams  by 
means  of  patent  clamps.  Stiffened  wire  lathing  is  then  laid  at 
right  angles  to,  and  on  the  under  sides  of  these  bars,  the  laps 
being  laced  with  galvanized  wire.  In  spans  over  3  ft.  6  ins., 
the  ceiling  is  further  supported  by  means  of  wire  hangers 
dropped  from  the  crown  of  the  arch  about  3O-in.  centres, 
which  fasten  to  a  T6T-in.  diameter  steel  rod  laid  over  and  laced 
to  the  ceiling  bars. 

Permissible  spans,  with  their  attendant  weights,  will  aver- 
age about  as  follows: 


Depth  of  Beams 
or  Thickness  of 
Concrete  at 
Haunches. 

Maximum  Span. 

Thickness  of 
Crown  at 
Centre  of 
Arch. 

Weight  per  sq.  ft. 
Including  Con- 
crete and  Wire 
Centering. 

8  ins. 

4ft. 

o  ins. 

3  ins. 

33  Ibs. 

9  ins. 

4  ft. 

6  ins. 

3  ins. 

34  Ibs. 

10  ins. 

5ft. 

o  ins. 

3  ins. 

36  Ibs, 

12  ins. 

6  ft. 

o  ins. 

3  ins. 

41  Ibs. 

15  ins. 

/ft. 

6  ins. 

3  ins. 

47  Ibs. 

Many  tests  have  shown  remarkable  strength  qualities  for 
this  arch  form,  and  fire-  and  water-tests  have  demonstrated 
generally  satisfactory  fireproofing  qualities;  but  any  system 
of  fireproofing  which  relies  entirely  upon  a  suspended  ceiling 
for  the  insulation  of  the  beam  flanges  is  not,  in  the  author's 
opinion,  to  be  very  highly  recommended.  Such  ceilings  will 
undoubtedly  protect  the  beams  to  a  large  extent,  but  the  ceil- 
ings will  fail  under  severe  conditions,  and  possibly  too  early  to 


io6  ARCHITECTURAL  ENGINEERING. 

save  the  beams  from  collapse,  while  even  the  reconstruction 
of  the  ceilings  would  form  a  large  item  in  repairs. 

A  still  more  satisfactory  form  of  the  Roebling  floor  is  the 
concrete  arch  with  exposed  soffit,  where  the  form  is  the  same 
as  that  previously  shown  in  Fig.  53,  except  that  the  curved 
soffit  is  left  exposed,  and  the  lower  flanges  of  the  beams  are 
surrounded  by  wire  lathing  and  concrete  of  semicircular  form. 
But  as  level  ceilings  are  considered  a  requisite  in  office  or 
dwelling  buildings,' this  type  has  generally  been  limited  to  fac- 
tories, warehouses,  breweries,  etc. 

Columbian  Floor.  — The  concrete  floor  manufactured  by 
the  Columbian  Fireproofing  Company  is  of  the  flat  or  plate 
construction,  consisting  of  a  combination  of  rolled-steel  bars 
and  concrete.  See  Fig.  54.  The  bars  are  suspended  from 


FIG.  54. — Columbian  "  Flat-ceiling  "  Floor  Construction. 

the  upper  flanges  of  the  floor-beams  by  means  of  steel  stirrups, 
which  are  perforated  to  the  shape  of  the  bars  employed.  A 
concrete  plate  is  then  filled  over  a  temporary  centering,  the 
top  of  the  concrete  coming  flush  with  the  upper  flanges  of  the 
beams.  The  mixture  usually  employed  for  all  but  the  very 
heaviest  construction  is  composed  of  i  part  Portland  cement, 
2|  parts  sand,  and  5  parts  broken  stone.  Bars- 2  ins.  deep  are 
generally  used  for  hotels  or  office  buildings,  U-in.  bars  for 
residences  and  apartment  houses,  and  2^-in.  sections  for  ware- 


FLOORS  AND  FLOOR.  FRAMING. 


107 


houses,  storage,  and  mercantile  buildings.  The  bars  are 
spaced  from  20-  to  24-ins.  centres. 

The  ceiling  slab  is  made  of  i-in.  bars  of  the  same  form, 
which  rest  on  the  lower  flanges  of  the  beams.  These  support 
a  cinder-concrete  ceiling  slab,  made  of  I  part  Portland  cement, 
5  parts  cinders,  and  2^  parts  sand. 

The  beam-webs  are  either  left  exposed,  or  are  encased  in 
concrete.  The  flat-ceiling  construction  is  not  usually  employed 
for  spans  exceeding  7  ft.,  while  in  the  case  of  less  span,  and 
light  loads,  the  bars  are  sometimes  made  to  pass  directly  over 
the  floor-beams,  resting  on  them,  thus  dispensing  with  the 
stirrups. 

A  panelled  construction  is  also  made  by  the  same  company, 
this  being  like  the  former  type  as  far  as  the  floor-plate  is  con- 
cerned, but  without  the  ceiling-plate.  In  this  type,  the  beams 
are  encased  in  concrete,  thus  showing  a  panelled  construction 
from  below.  This  is  more  applicable  to  warehouse  or  mercan- 
tile building  construction. 


Size  of  Bars. 
Inches. 

Thickness 
of  Floor. 
Inches. 

Panelled  Construction. 
Solid  Casing 

Flat  Ceiling  Construction. 

Stone-Con- 

Cinder-Con- 

Stone-Con- 

Cinder-Con- 

crete.  Pounds. 

crete.  Pounds. 

crete.  Pounds 

crete.   Pounds. 

I 

•i 

42 

261 

48i 

37 

I* 

2} 

42 

26^ 

48J 

37 

2 

3f 

46 

29 

^ 

3! 

54 

35i 

59* 

43i 

The  Columbian  floors  are  very  satisfactory  as  to  strength, 
and  acceptable  as  to  fire-resisting  qualities,  although  the  stone- 
concrete  employed  is  inferior  to  cinder-concrete  under  fire-tests. 
As  regards  corrosive  influences,  however,  stone-concrete  is  to 
be  preferred  to  cinder  mixtures. 

Expanded  Metal  Co.'s  Floors. — Several  types  of  concrete 
floors  are  manufactured  by  the  various  companies  acting  as 
licensees  from  the  Expanded  Metal  Company. 


io8 


ARCHITECTURAL  ENGINEERING. 


The  floor  shown  in  Fig.  5  5  is  employed  for  spans  under 
8  feet,  either  with  or  without  a  suspended  ceiling.  A  wooden 
centering  is  employed,  suspended  from  the  beams  at  a  proper 
level  to  receive  the  concrete  plate.  Expanded  metal  is  then 
stretched  lengthwise  across  the  beams  in  sheets,  and  concrete 
is  spread  to  form  a  slab  about  3  ins.  thick  for  ordinary  floors, 
this  being  tamped  so  that  the  expanded  metal  becomes  em- 
bedded in  the  lower  inch  of  the  floor  plate.  The  concrete  is 
usually  made  of  I  part  cement,  2  parts  sand,  and  6  parts  fur- 
nace-cinders, weighing  about  84  Ibs.  per  cu.  ft. .  Cinder  filling 


FIG.  55. — Expanded  Metal  Co.'s  Floor  with  Suspended  Ceiling. 

is  placed  between  the  floor  screeds,  weighing  about  60  Ibs.  per 
cu.  ft.  .  If  a  suspended  ceiling  is  desired,  small  channels  or 
angles  spaced  12-  to  i6-ins.  centres  are  attached  to  the  bottoms 
of  the  beams  by  means  of  malleable-iron  clips.  Expanded 
metal  is  then  fastened  to  these,  ready  for  the  plastering. 

A  still  different  form,  which  corresponds  very  closely  to 
the  Roebling  floor,  is  shown  in  Fig.  56.  In  this  case  sheets 
of  expanded  metal  are  sprung  between  the  beam  flanges  as  a 


FlG.  56. — Expanded  Metal  Co.'s  Concrete  Arch. 

permanent  centering  to  receive  the  concrete  arch.  This  type 
is  adapted  to  heavier  loads  than  the  floor  shown  in  Fig.  55, 
but  it  should  only  be  employed  when  the  span  is  narrow 
enough  to  permit  of  a  central  height  of  ^  to  £  of  the  span. 


FLOORS  AND  FLOOR  FRAMING. 


109 


Fireproof  floors  employing  expanded  metal  have  been  very 
extensively  used,  and  have  generally  met  with  much  favor. 
They  are  easily  adapted  to  all  conditions  of  framing,  and  are 
comparatively  light  and  reasonable  in  cost;  but,  except  in  the 
arched  form  shown  in  Fig.  56,  the  reliance  for  tensile  strength, 
in  employing  concrete  as  a  beam,  is  placed  upon  the  thin 
sheets  of  expanded  metal,  the  ultimate  life  of  which,  sur- 
rounded by  cinder-concrete  with  corrosive  tendencies,  is  open 
to  serious  question.  If  the  expanded  metal  were  always 
thoroughly  encased  in  cement  mortar  at  the  bottom  of  the  con- 
crete plate,  these  forms  would  be  far  more  commendable. 

Metropolitan  Floor. — The  Metropolitan  system  of  fire- 
proof floors  is  illustrated  in  Fig.  57.  Wire  suspension-cables 


...    -- 


FIG.  57.  — Metropolitan  Floor.     Flat  Ceiling  Construction. 

are  used  for  the  supporting  members,  each  consisting  of  two  No. 
12  galvanized  wires,  twisted  together  and  laid  across  the  tops 
of  the  beams  with  hooks  or  anchors  where  they  terminate  at  the 
end  beams  or  walls.  These  cables  are  spaced  from  $-in.  to 
i^-in.  centres,  according  to  spans  and  loads.  They  are  laid 
parallel,  and  are  then  depressed  slightly  in  the  centre  of  each 
bay  by  means  of  |-in.  round  iron  rods  which  are  laid  length- 
wise on  the  cables  so  as  to  cause  a  uniform  sag  of  about  2  ins. 
below  the  tops  of  the  I-beams.  Wooden  centres  are  placed 
between  the  beams  and  about  I  in.  below  the  iron  rods,  and  a 
composition  formed  of  I  part  plaster  of  Paris  to  2  parts  of 
shavings,  with  sufficient  water  to  form  a  plastic  mass,  is  then 
poured  in  place  and  tamped  to  a  level  of  about  £  in.  above  the 


HO  ARCHITECTURAL   ENGINEERING. 

tops  of  the  beams.  The  floor-plate  is  thus  about  4^  ins.  thick, 
not  including  the  screeds  or  finished  flooring. 

The  suspended  ceiling  is  made  by  clipping  f-in.  by  £-in. 
flat  bars  to  the  lower  flanges  of  the  I-beams,  ready  to  receive 
wire  lathing.  The  beam  webs  and  flanges  are  also  protected 
by  the  same  mixture,  as  shown  in  the  illustration. 

This  system  has  also  been  extensively  used  in  fireproof 
structures,  and  its  decided  lightness  forms  a  great  advantage 
in  certain  instances.  The  load -carrying  qualities  are  also 
excellent,  but  disadvantages  occur  from  discoloration  due  to 
the  sap  in  the  shavings  employed,  and  from  the  sometimes 
uneven  drying  of  the  mass.  The  fireproof  qualities  are  fairly 
acceptable.  The  suspended  ceilings  when  exposed  to  fire  and 
water  are  apt  to  be  thoroughly  destroyed,  and  the  floor-plate 
will  be  partly  washed  away  or  rendered  soft  at  the  surface,  but 
reconstruction  is  comparatively  simple  after  such  possible 
injury. 

Selection  of  Floor  Type.  —The  above-mentioned  concrete 
and  composition  floors  may  not  include  all  of  the  commendable 
types  now  on  the  market,  but  as  before  stated,  those  described 
constitute  the  better-known  examples  of  trustworthy  character. 
Several  other  so-called  fireproof  floors  have  been  used  to  a 
considerable  extent,  many  of  them  in  very  important  struc- 
tures, but  their  ultimate  value  will  not  always  bear  close  inves- 
tigation. It  will  be  noticed  that  little  has  been  said  as  regards 
the  comparative  cost  of  the  types  of  terra-cotta  a*id  concrete 
floors  here  mentioned.  This  question  will  undoubtedly  serve 
as  a  prime  factor  in  making  a  choice  between  the  various 
methods,  but  the  question  of  first  cost  can  in  nowise  be  taken 
as  a  guarantee  of  ultimate  wisdom.  The  true  value  of  a  con- 
struction can  only  be  determined  by  the  tests  of  time  and 
destructive  elements,  such  as  corrosive  action,  and  fire-  and 
water-tests.  These  considerations,  with  practical  questions  as 
to  weight,  depth,  form,  and  a  minimum  of  repair  required  by 


FLOORS  AND  FLOOR  FRAMING.  Hi 

possible  damage  under  fire  and  water,  should  govern  a  selec- 
tion, regardless,  in  so  far  as  may  be  judicious,  of  the  first  cost. 
Almost  all  of  the  better-known  floor-systems,  whether  terra- 
cotta, concrete,  or  composition,  will,  under  all  ordinary  condi- 
tions, show  a  reasonable  factor  of  safety  under  usual  loads.  As 
to  choice  of  concrete  vs.  terra-cotta  floors,  the  best  constructors 
agree  that  either  type  may  be  made  perfectly  satisfactory  if  well 
designed  and  executed,  while  both  are  equally  bad  where 
defective  design,  materials,  or  workmanship  are  employed. 

Building  Laws — Floor  Arches. — The  following  require- 
ments are  specified  in  the  Chicago  building  ordinance,  Section 
1 08:  "  The  filling  between  the  individual  iron  or  steel  beams 
supporting  the  floors  of  fireproof  buildings  shall  be  made  of 
brick  arches,  or  concrete  arches,  or  hollow-tile  arches.  Brick 
arches  shall  not  be  less  than  4  ins.  thick,  and  shall  have  a  rise 
of  at  least  f  in.  to  each  foot  of  span  between  the  beams.  If 
the  span  of  such  arches  is  more  than  6  feet,  the  thickness  of 
the  same  shall  not  be  less  than  8  ins.  If  hollow-tile  arches 
having  a  straight  soffit  are  used,  the  thickness  of  such  arches 
shall  not  be  less  than  at  the  rate  of  2  ins.  per  each  foot  of 
span.  If  concrete  arches  are  used,  the  concrete  in  the  same 
shall  not  be  strained  more  than  100  Ibs.  per  sq.  in.,  if  the  con- 
crete is  made  of  crushed  stone,  nor  more  than  50  Ibs.  per  sq. 
in.,  if  the  concrete  is  made  of  cinders.  In  all  cases,  no  matter 
what  the  material  or  form  of  the  arches  used,  the  protection  of 
the  bottom  flanges  of  the  beams  and  so  much  of  the  web  of  the 
same  as  is  not  covered  by  the  arches  shall  be  made  as  before 
specified  for  the  covering  of  beams  and  girders." 

Also,  Section  90:  "Hollow  tile  and  porous  terra-cotta 
may  be  used  in  the  form  of  flat  arches  for  the  support  of  floors 
and  roofs ;  such  floor  arches  having  a  height  of  at  least  2  ins. 
for  each  foot  of  span.  The  arches  must  be  so  constructed  that 
the  joints  of  the  same  point  to  a  common  centre ;  the  butts  of 
the  arches  shall  be  carefully  fitted  to  the  beams  supporting 


H2  ARCHITECTURAL  ENGINEERING. 

them;  and  there  shall  be  a  cross-rib  for  every  6  ins.  or  frac- 
tional part  thereof  in  height;  and  in  addition  to  these  there 
shall  also  be  diagonal  ribs  in  the  butts.  Floor  arches  made 
in  the  form  of  a  segment  of  a  circle  or  ellipse  must  be  con- 
structed upon  the  same  principle.  Such  arches,  whether  flat 
of  curved,  shall  have  their  beds  well  filled  with  mortar,  and 
the  centres  shall  not  be  struck  until  the  mortar  has  been  set. ' ' 
The  Building  Code  of  Greater  New  York  specifies  that  fire- 
proof floors  shall  consist  of:  segmental  brick  arches,  flat 
terra-cotta  arches  (of  a  depth  not  less  than  if  ins.  per  foot  of 
span,  not  including  any  projection  of  the  arch  below  the  under 
side  of  beams) ;  segmental  terra-cotta  arches  (with  the  depth 
of  arch-blocks  not  less  than  6  ins.,  and  with  a  rise  of  not  less 
than  ij  ins.  per  foot  of  span);  segmental  Portland  cement 
concrete  arches  (the  thickness  at  crown  of  arch  to  be  not  less 
than  6  ins.,  the  rise  to  be  not  less  than  ij  ins.  per  foot  of  span, 
with  the  soffit  reinforced  with  some  form  of  metal  weighing 
not  less  than  one  pound  per  square  foot,  and  with  no  openings 
larger  than  3  ins.  square);  or  "various  fillings"  subject  to 
fire-  and  water-tests  as  per  the  following  requirements : 

' '  Or  between  the  said  beams  may  be  placed  solid  or  hollow 
burnt  clay,  stone,  brick,  or  concrete  slabs  in  flat  or  curved 
shapes,  concrete  or  other  fireproof  composition,  and  any  of 
said  materials  may  be  used  in  combination  with  wire  cloth, 
expanded  metal,  wire  strands,  or  wrought-iron  or  steel  bars; 
but  in  any  such  construction  and  as  a  precedent  condition  to 
the  same  being  used,  tests  shall  be  made  as  herein  provided 
by  the  manufacturer  thereof  under  the  direction  and  to  the 
satisfaction  of  the  Board  of  Buildings,  and  evidence  of  the  same 
shall  be  kept  on  file  in  the  Department  of  Buildings,  showing 
the  nature  of  the  test  and  the  result  of  the  test.  Such  tests 
shall  be  made  by  constructing  within  inclosure  walls  a  platform 
consisting  of  four  rolled-steel  beams,  10  ins.  deep,  weighing 
each  25  Ibs.  per  lineal  foot,  and  placed  4  ft.  between  the 


FLOORS  AND  FLOOR  FRAMING.  113 

centres,  and  connected  by  transverse  tie-rods,  and  with  a  clear 
span  of  14  ft.  for  the  two  interior  beams  and  with  the  two  outer 
beams  supported  on  the  side  walls  throughout  their  length, 
and  with  both  a  filling  between  the  said  beams  and  a  fire- 
proof protection  of  the  exposed  parts  of  the  beams  of  the 
system  to  be  tested,  constructed  as  in  actual  practice,  with  the 
quality  of  material  ordinarily  used  in  that  system,  and  the  ceil- 
ing plastered  below  as  in  a  finished  job;  such  filling  between 
the  two  interior  beams  being  loaded  with  a  distributed  load  of 
150  Ibs.  per  sq.  ft.  of  its  area  and  all  carried  by  such  filling; 
and  subjecting  the  platform  so  constructed  to  the  continuous 
heat  of  a  wood  fire  below,  averaging  not  less  than  1,700 
degrees  Fahrenheit  for  not  less  than  four  hours,  during  which 
time  the  platform  shall  have  remained  in  such  condition  that 
no  flame  will  have  passed  through  the  platform  or  any  part  of 
the  same,  and  that  no  part  of  the  load  shall  have  fallerp. 
through,  and  that  the  beams  shall  have  been  protected  from 
the  heat  to  the  extent  that  after  applying  to  the  under  side  of 
the  platform  at  the  end  of  the  heat-test  a  stream  of  water 
directed  against  the  bottom  of  the  platform  and  discharged 
through  a  i^-in.  nozzle  under  60  Ibs.  pressure  for  five  minutes, 
and  after  flooding  the  top  of  the  platform  with  water  under  low 
pressure,  and  then  again  applying  the  stream  of  water  through 
the  nozzle  under  the  6o-lbs.  pressure  to  the  bottom  of  the 
platform  for  five  minutes,  and  after  a  total  load  of  600  Ibs.  per 
sq.  ft.  uniformly  distributed  over  the  middle  bay  shall  have 
been  applied  and  removed,  after  the  platform  shall  have  cooled, 
the  maximum  deflection  of  the  interior  beams  shall  not  exceed 
2^  ins.  The.  Board  of  Buildings  may  from  time  to  time  pre- 
scribe additional  or  different  tests  than  the  foregoing  for  systems 
of  filling  between  iron  or  steel  floor-beams,  and  the  protection 
of  the  exposed  parts  of  the  beams.  Any  system  failing  to 
meet  the  requirements  of  the  test  of  heat,  water,  and  weight,  as 
herein  prescribed  shall  be  prohibited  from  use  in  any  building" 


H4  ARCHITECTURAL  ENGINEERING. 

hereafter  erected.  Duly  authenticated  records  of  the  tests 
heretofore  made  of  any  system  of  fireproof  floor  filling  and 
protection  of  the  exposed  parts  of  the  beams  may  be  presented 
to  the  Board  of  Buildings,  and  if  the  same  be  satisfactory  to 
said  Board,  it  shall  be  accepted  as  conclusive." 

The  above  section  of  the  New  York  Building  Code  gives 
substantially  the  test  conditions  required  in  the  fire-  and  water- 
tests  on  various  fireproof  floors,  made  by  the  New  York 
Building  Department  in  1896.  A  detailed  description  of  the 
test-kilns,  method  of  testing,  and  results  as  to  the  Rapp, 
Roebling,  Thompson,  -M'Cabe,  Columbian,  Bailey,  Clinton, 
Wire-cloth,  Manhattan,  Expanded  Metal  Company's,  Metro- 
politan, Fawcett,  Guastavino,  and  Terra-cotta  floors,  is  given 
in  the  author's  "  Fireproofing  of  Steel  Buildings." 

Floor  Loads. — Before  considering  the  details  of  floor-beams 
and  girders,  the  question  of  loads,  which  will  largely  govern 
the  design  of  the  floor-system,  must  be  examined. 

Loads  occurring  in  building  construction  may  be  classified 
as  live,  dead,  wind,  and  eccentric  loads.  These  will  all  be 
considered  in  their  proper  places.  The  principal  loads  affect- 
ing the  floor-system  are : 

Live  Loads,  comprising  the  people  in  the  building,  office 
furniture,  movable  stocks  of  goods,  small  safes,  elevator  and 
tank  loads,  or  varying  loads  of  any  character.  Large  safes 
require  especial  provision  for  support. 

Dead  Loads,  comprising  all  of  the  static  loads  due  to  the 
constructive  parts  of  the  building  (such  as  floors,  roofs,  walls, 
columns,  etc.),  stationary  machinery,  and  any  other  permanent 
loads. 

Live  Loads. — The  live  loads  to  be  provided  for  in  the 
design  of  the  floor-system  are  usually  specified  in  the  local 
building  ordinances,  according  to  the  purposes  for  which  the 
building  is  intended.  The  designer  is  therefore  limited  by  the 
requirements  under  which  he  is  obliged  to  work. 


FLOORS  AND  FLOOR  FRAMING.  115 

For  office  buildings,  both  the  Chicago  and  Boston  laws 
require  a  unit  of  100  Ibs.  per  sq.  ft.,  while  the  New  York  law 
specifies  live  loads  of  75  'Ibs.  per  sq.  ft.  for  the  upper  floors, 
and  i  50  Ibs.  for  the  first  floor.  In  the  author's  opinion,  all  of 
these  requirements  are  excessive,  providing  proper  restrictions 
are  enforced  as  to  wind-strains,  heavy  safes,  and  vibratory  in- 
fluences due  to  printing  or  manufacturing. 

Without  reference  to  building  laws,  the  following  live  loads 
have  always  been  considered  standard  practice: 

For  floors  of  dwellings 40  Ibs.  per  sq.  ft. 

For  dense  crowd  of  people 80    "      "       " 

For  theatres,  churches,  etc 80    "      "       " 

For  ball-rooms  or  drill-halls 90    "      "       " 

For  warehouses,  etc from  250  Ibs.  up. 

For  factories 200  to  450  Ibs. 

While  80  Ibs.  is  the  maximum  possible  live  load  per  square 
foot  from  a  crowd  of  people  (unless  dancing  be  considered), 
still  we  can  hardly  expect  to  realize  any  such  load  under  the 
conditions  governing  an  office  building.  Large  crowds  very 
seldom  collect  in  offices,  except,  perhaps,  on  the  two  or  three 
lower  floors  devoted  to  stores  or  banking  purposes,  and  greater 
allowances  are  generally  made  for  such  places.  The  ordinary 
office  furniture  will  certainly  not  exceed,  and  seldom  equal, 
the  weight  allowed  for  persons,  and  hence  additional  security 
is  introduced. 

A  very  valuable  and  interesting  article  in  the  American 
Architect,  August  26,  1893,  gives  the  results  of  some  experi- 
ments made  by  Messrs.  Blackall  &  Everett,  Boston  architects, 
on  the  actual  weights  of  all  moving  loads  in  some  of  the  larger 
Boston  office  buildings.  The  loads  considered  were  those  due 
to  people  and  all  possible  movable  articles,  including  all  office 
fittings  except  such  as  were  a  part  of  the  floors  or  partitions, 
radiators  excepted.  The  results  were  as  follows:  In  210 


Ii6  ARCHITECTURAL  ENGINEERING. 

offices  in  the  Rogers,  Ames,  and  Adams  buildings,  an  average 
of  16.3  Ibs.  per  sq.  ft.  was  found  for  the  Rogers  Building,  17 
Ibs.  for  the  Ames,  and  16.2  Ibs.  for  the  Adams  Building. 
The  greatest  moving  load  in  any  one  office  in  the  three  build- 
ings was  40.2  Ibs.  per  sq.  ft.,  while  the  average  for  the 
heaviest  ten  offices  in  each  of  these  buildings  was  33.3  Ibs.  per 
:sq.  ft.  Mr.  Blackall  concludes:  "If  these  figures  are  to  be 
trusted  to  any  extent  whatever,  then  even  under  the  most 
extreme  circumstances,  taking  the  pick  of  the  heaviest  offices 
in  the  city  and  combining  them  into  one  tier  of  ten  stories,  the 
average  load  per  square  foot  would  be  only  a  trifle  over  33  Ibs., 
while  for  all  purposes  for  strength  an  assumption  of  20  Ibs. 
would  be  amply  sufficient  in  determining  the  loads  on  the 
foundations,  as  well  as  on  the  columns  of  the  lower  stories." 

These  experiments  plainly  indicate  that  a  live  load  of  40 
Ibs.  per  sq.  ft.  is  amply  sufficient  for  office  areas,  and,  where 
not  restricted  by  building  laws,  35  and  40  Ibs.  per  sq.  ft.  have 
been  used  as  the  assumed  live  loads  in  many  important  and 
very  satisfactory  modern  office  buildings. 

In  the  Mills  Building,  erected  in  San  Francisco  in  1891, 
the  live  loads  were  as  follows : 

Beams.  Girders.  Columns.      Footings. 

First  floor 60  50  40 

Second  floor  to  attic  ...   40  30  20 

Roof 20  15  10 

Rotunda 60  50  40 

In  the  Venetian  Building  in  Chicago  the  beams  were  cal- 
culated for  the  following  live  loads: 

Upper  floors 35  Ibs. 

Second,  third,  and  fourth  floors 60   " 

First  floor. ....   80  « ' 

Girders  carry  80  per  cent.,  columns  50  per  cent. 


FLOORS  AND  FLOOR.  FRAMING.  n? 

Mr.  E.  C.  Shankland,  who  has  designed  and  superintended 
the  construction  of  a  large  number  of  the  most  prominent  high 
buildings  in  Chicago  and  elsewhere,  states  that  "  the  live  load, 
consisting  of  the  weight  of  the  tenants,  the  furniture,  and  the 
partitions,  which  are  frequently  changed,  is  taken  between  60 
Ibs.  and  75  Ibs.  per  sq.  ft.  for  the  upper  floors  of  an  office 
building,  and  between  75  Ibs.  and  100  Ibs.  per  sq.  ft.  for  the 
first  and  second  floors,  which  are  generally  used  for  shops  and 
banks.  The  weight  of  the  tenants  and  furniture  of  a  typical 
office  have  been  found  by  experiment  to  be  only  6  Ibs.  or 
7  Ibs.  per  sq.  ft.;  it  certainly  does  not  exceed  12  Ibs.  The 
average  weight  of  the  partitions  is  25  Ibs.  per  sq.  ft.  of  floor. ' '  * 

Deducting,  then,  the  partition  load  of  25  Ibs.  per  sq.  ft. 
from  the  live  loads  recommended  by  Mr.  Shankland,  the  live 
loads  as  given  above  become  35  Ibs.  to  50  Ibs.  per  sq.  ft. 

The  small  live  loads  found,  by  actual  experiment,  to  exist 
in  office  areas,  such  as  12  Ibs.  per  sq.  ft.  according  to  the  last 
data  quoted,  and  16  or  17  Ibs.  per  sq.  ft.  according  to 
Mr.  Blackall's  article,  have  tempted  the  use  of  unit  loads  as 
low  as  20  Ibs.  per  sq.  ft. ;  but  such  recommendations  are  to  be 
seriously  questioned,  and  even  heartily  condemned  in  conserva- 
tive practice. 

While  20  Ibs.  per  sq.  ft.  may  be  amply  sufficient  for 
average  loads  at  present,  we  must  remember  that  the  use  of 
an  average  is  always  dangerous,  while  provision  should  be 
made,  but  not  recklessly,  for  all  possibilities  of  extremes, 
either  present  or  future.  For  it  must  be  remembered  that  the 
character  of  a  building's  contents  is  very  liable  to  extreme 
change.  The  entire  building,  or  possibly  only  portions 
thereof,  may  be  devoted  to  very  different  uses  from  those 
primarily  assumed,  so  that  it  becomes  a  very  nice  problem  to 


*  See  Minutes  of  Proceedings  of  The   Institution   of  Civil  Engineers, 
vol.  cxxviii. 


118  ARCHITECTURAL  ENGINEERING. 

balance  present  economy  with  maximum  present  requirements 
or  future  possibilities.  The  present  live  load  per  square  foot 
may  not  always  be  taken  as  the  maximum  occurring  during  the 
life  of  the  building.  Most  building  ordinances  provide  against 
radical  change  in  the  character  or  degree  of  the  floor-loads, 
and  against  the  -introduction  of  vibratory  or  manufacturing  ele- 
ments not  provided  for  in  the  original  design.  But  the  line  is 
sometimes  difficult  to  draw,  and,  as  in  the  strength  of 
materials,  a  sufficient  factor  of  safety  should  always  be  em- 
ployed. 

If  the  building  is  to  be  used  for  the  purposes  of  printing  or 
manufacturing,  the  assumed  live  loads  must  be  substantially 
increased  to  care  for  the  vibration  always  induced  by  the  pul- 
sations of  machinery,  the  pull  on  belts,  and  especially  the 
shocks  due  to  the  starting  and  stopping  of  all  dynamic  forces. 

For  purely  office  purposes,  however,  it  would  seem  that 
the  present  requirements  of  the  Chicago  and  Boston  building 
laws,  and  even  of  the  New  York  law,  are  too  high.  Live 
loads  of  80  Ibs.  per  sq.  ft.-  for  the  lower  or  busier  floors,  and 
40  Ibs.  per  sq.  ft.  for  the  upper  or  office  floors,  are  certainly 
safe  and  ample,  and  good  averages,  considered  in  all  lights. 
But  while  the  live  loads  per  square  foot  might  be  reduced 
to  these  figures  over  large  areas  in  proportioning  the  metal- 
work,  the  maximum  possible  live  load  should  still  be  used 
when  any  single  floor  arch  is  considered  by  itself,  or  subjected 
to  tests  to  determine  its  strength.  For  the  working  factor  of 
safety  required  of  terra  cotta  or  concrete-floor  constructions, 
(which  may  be  considered  as  forming  the  poorest  class  of 
masonry  construction),  should  be  considerably  greater  than  the 
factor  of  safety  required  in  as  reliable  a  material  as  steel. 
Rankine  advises  the  use  of  -^  to  -J  the  ultimate  strength  in 
metals,  -|  to  T17  in  wood,  and  ^  to  ^  in  masonry. 

The  live  loads  recommended,  viz.,  40  and  80  Ibs.  per  sq. 
ft.,  are  independent  of  the  partition  loads.  Partitions  are 


FLOORS  AND  FLOOR  FRAMING.  119 

sometimes  classed  as  live  loads,  because  liable  to  change  in 
location,  as  is  made  possible  by  present  constructions,  while 
in  other  cases  they  are  assumed  as  a  portion  of  the  dead  load. 
The  present  New  York  and  Chicago  laws  both  require  parti- 
tions to  be  considered  as  a  part  of  the  dead  load. 

Prior  to  the  enactment  of  the  last  Building  Ordinance  of  the 
City  of  Chicago,  March,  1898,  practice  was  well  defined  in  the 
matter  of  decrease  of  live  loads  per  square  foot,  as  they  are 
transferred  from  beams  to  girders,  from  girders  to  columns, 
and  thence  down  the  columns  to  the  footings.  This  practice 
was  founded  on  the  supposition  that  it  is  quite  possible  that  the 
beams  may  some  time  have  to  carry  their  full  capacity  in  live 
loads,  while  the  chances  are  increasingly  less  that  the  girders 
or  columns  will  ever  be  required  to  carry  anywhere  near  their 
full  capacity,  if  a  full  load  had  been  assumed.  The  fully 
loaded  area  would  probably  never  be  large,  and  a  girder  or 
column  would  rarely,  if  ever,  lie  in  the  centre  of  such  an  area. 
The  effect  of  a  live  or  moving  load,  causing  vibration  in  the 
parts  of  the  structure,  is  also  gradually  lessened  as  the  vibra- 
tion is  taken  up  in  the  transfer  of  the  load  from  member  to 
member,  so  that  by  the  time  it  reaches  the  footings  or  founda- 
tions the  live  load  is  ignored  entirely.  In  fact,  we  can  hardly 
imagine  the  perceptible  effect  on  the  foundations  of  the  people 
in  an  office  building,  as  compared  with  the  infinitely  greater 
dead  load,  due  to  the  structure  itself. 

The  former  Chicago  law  required  the  floor-beams  to  be 
calculated  for  the  entire  assumed  live  load,  while  the  girders 
could  be  taken  as  sustaining  eight-tenths  of  the  assumed  live 
load  plus  the  dead  load,  and  the  columns  six-tenths  of  the  live 
load  plus  dead  load.  This  practice  seems  rational,  and  it  was 
employed  in  much  the  greater  proportion  of  Chicago's  high 
buildings,  but  the  revised  or  present  ordinance  prohibits  such 
practice  by  requiring  "the  floors  to  be  designed  and  con- 
structed in  such  manner  as  to  be  capable  of  bearing  in  all  their 


120  ARCHITECTURAL  ENGINEERING. 

parts,  in  addition  to  the -weights  of  partitions  and  permanent 
fixtures  and  mechanisms  that  may  be  set  upon  the  same,  a  live 
load  of  100  Ibs.  per  sq.  ft." 

A  possible  reduction  in  or  omission  of  the  live  load  on 
foundations  is  permitted,  as  follows :  "In  determining  the 
areas  of  foundations  for  many-storied  buildings,  allowances  are 
to  be  made  for  the  fact  that  the  before-mentioned  live  load  is 
but  an  occasional  load,  which  rarely  occurs  simultaneously  upon 
corresponding  parts  of  many  floors,  and  if  so,  for  a  very  brief 
period  only. ' ' 

In  New  York  City,  the  previous  building  law  required 
girders  and  columns  to  be  calculated  for  the  total  live  and  dead 
loads,  and  also  this  total  load  to  be  assumed  to  rest  upon  the 
foundations.  The  present  Building  Code,  adopted  December, 
1899,  still  requires  the  full  floor-loads  on  girders,  but  provides 
for  a  reduction  in  the  live  loads  on  columns  as  follows: 

' '  For  the  purpose  of  determining  the  carrying  capacity  of 
columns  in  dwellings,  office  buildings,  stores,  stables,  and 
public  buildings  when  over  five  stories  in  height,  a  reduction 
of  the  live  loads  shall  be  permissible  as  follows : 

"  For  the  roof  and  top  floor  the  full  live  loads  shall  be  used. 

"For  each  succeeding  lower  floor  it  shall  be  permissible 
to  reduce  the  live  load  by  five  per  cent,  until  fifty  per  cent,  of 
the  live  loads  fixed  by  this  section  is  reached,  when  such 
reduced  loads  shall  be  used  for  all  remaining  floors." 

Building  Laws :  Live  Loads  on  Floors. — For  the  purpose 
of  comparison,  the  requirements  of  the  Building  Laws  of  New 
York,  Chicago,  Boston,  and  Philadelphia,  for  live  loads  per 
square  foot  of  floor  area,  over  and  above  the  dead  weight  of 
the  floor  itself,  may  be  classified  as  as  on  page  123. 

Nearly  all  of  these  municipal  requirements  seem  high  when 
used  by  intelligent  designers,  except  those  for  warehouses  and 
manufacturing  buildings.  For  dwellings,  Kidder  shows  that 
actual  loads  in  parlors  (including  piano),  dining-rooms,  etc., 


FLOORS  AND  FLOOR  FRAMING. 


average  only  14  to  23  Ibs.  per  sq.  ft.  of  the  whole  area.  Data 
regarding  experiments  on  the  live  loads  in  office  buildings  has 
already  been  given  and  with  careful  design  and  attention  to 
detail,  the  writer  believes  that  the  requirements  of  most  build- 
ing laws  are  still  too  high.  Loads  for  warehouses  or  manufac- 
turing buildings  are  more  difficult  to  calculate,  and  more 
difficult  to  enforce,  for  which  reasons  higher  load  units  are  to 
be  expected  and  even  desired  than  under  more  definite  condi- 
tions. 


New  York. 

Chicago. 

Boston. 

Philadelphia. 

60  (a) 

4O  (e) 

2.   Office  Buildings  j 

Upper  floors  75 
ist  floor  150 

IOO 

IOO 

3.   Public  Buildings  

90 

IOO 

150  (g) 

ISO 

4.  Stores,     warehouses, 

factories,  etc  

1  20  to  150  (b) 

IOO  (/) 

250  (/) 

200  up  (/) 

5     Roofs                           .    \ 

5^  (^") 

25  (A) 

30  (d) 

6.  Sidewalks..  

300 







(a)  Includes  apartment  houses,  tenements,  and  hotels. 

(t>)  For  ordinary  stores,  and  light  manufacturing  or  storage,  not  less 
than  120  Ibs.  For  stores  of  heavy  contents,  warehouses  and  factories,  not 
less  than  150  Ibs. 

(e)  For  a  pitch  less  than  20  degrees. 

(d)  For  a  pitch  more  than  20  degrees,  measured  on  a  horizontal  plane. 

(e)  Includes  hotels,  boarding-  and  lodging-houses,  and  apartments. 
(f/f)  Require  posted  notices  of  allowable  loads. 

(£•)  Except  schoolhouses,  which,  except  assembly  rooms,  require  80 
Ibs.,  and  assembly  rooms  require  150  Ibs. 

(h)  Additional  allowance  required  for  wind-pressure  at  30  Ibs.  per  sq. 
ft.  No  roofs,  except  dwellings,  to  have  pitch  greater  than  20°. 

The  minimum  load  of  1 20  Ibs.  in  the  New  York  law  is  far 
too  small  in  many  cases,  but  the  loads  for  warehouses,  etc., 
are  hard  to  classify,  and  are  best  left  to  the  care  of  com- 
petent designers  under  the  approval  of  the  building  departments. 
Mr.  W.  L.  B.  Jenney  had  occasion  to  estimate  the  loads  in  the 
wholesale  warehouse  of  Marshall  Field  &  Co.  in  Chicago,  and 


ARCHITECTURAL  ENGINEERING. 


the  surprisingly  low  average  of  50  Ibs.  per  sq.  ft.  was  found 
for  the  total  floor  area,  including  all  passageways.  The  maxi- 
mum load  on  limited  areas  was  found  to  be  57  Ibs. 

Dead  Loads. — The  dead  loads  to  be  considered  in  the  floor- 
system  include  the  arch  itself,  beams,  concrete  filling,  floors 
(wood,  marble,  or  mosaic),  ceilings,  and  partitions. 

The  weights  of  the  iron  or  steel  beams  and  tile  partitions 
are  actually  calculated  for  a  typical  floor  plan,  and  then  rated 
at  so  much  per  square  foot  of  floor  surface.  This  is  absolutely 
necessary  in  regard  to  partitions  in  office  buildings,  as  they  are 
constantly  being  changed  to  suit  the  convenience  of  tenants. 
The  weight  of  the  arch  varies  with  the  depth;  the  depth  is 
dependent  on  the  span.  In  the  annex  of  the  Marshall  Field 
Building,  Chicago,  the  following  weights  were  used : 

Flooring,  f-in.  maple 4  Ibs. 

Deadening 9  " 

1 5 -in.  tile  arch 45    " 

Iron 12   " 

Plaster 5    " 

Partitions,  3-in.  mackolite 20  " 

Total 95  Ibs.  dead  load. 

We  have,  therefore,  for  live  and  dead  loads  as  follows : 


Beams. 

Girders. 

Columns. 

Footings. 

gr 

gc 

Dead  

95 

95 

95 

qc 

Total 

1  80 

160 

Store  floors  :  Live  

95 

75 

55 

Dead  

95 

95 

95 

95 

Total... 

190 

170 

150 

95 

The   dead    loads    assumed  in  the    Old  Colony    Building, 
Chicago  (1893),  comprised: 


FLOORS  AND  FLOOR  FRAMING. 


123 


Flooring , 4  Ibs. 

Deadening 1 8   " 

Tile  arches 35    " 

Iron 10  " 

Plaster 5   " 

Partitions 18   " 

Total 90  Ibs. 

The  dead  and  live  loads  used  in  the  calculations  of  the  floor- 
systems  and  columns  of  this  building  were,  in  pounds  per 
square  foot: 

Beams.        Girders.      Columns.       Footings. 

Live 70  50  40 

Dead 90  90  90  90 


Total.. 


1 60 


140 


130 


90 


The  floors  for  the  Fort  Dearborn  Building  were  calculated 
in  accordance  with  the  following  data: 


Dead  Load. 


Live  Load. 


Girders. 


ist  floor 

2d  to  1 3th  floors 

Roof 

Sidewalk 

Prismatic  lights 

Skylight 

Stairs 


85 
75 
40 
140 
50 


50 


85 
75 
40 
140 
50 

50 


125 

70 

40 

200 

200 

40 

70 


no 
60 
40 
1  80 
1  80 
40 

00 


The  live  load  on  the  beams  from  the  second  to  thirteenth 
floor  inclusive  was  taken  at  70  Ibs.  per  sq.  ft.,  and  an  addi- 
tional load  of  20  Ibs.  per  sq.  ft.  was  added  to  the  dead  load  to 
care  for  all  partitions  which  were  likely  to  be  moved  at  any 
time. 


124 


ARCHITECTURAL  ENGINEERING. 


The  girders  were  figured  for  partition  loads  at  20  Ibs.  per 
sq.  ft.  for  all  movable  partitions,  and  for  the  actual  loads  of  the 
main  partitions. 

The  live  load  on  the  columns  was  taken  at  50  Ibs.  per  sq 
ft.  from  the  second  to  the  twelfth  floor  inclusive,  plus  the 
girder  reactions  for  partitions. 

The  following  table  gives  the  unit  loads  used  in  figuring 
the  columns: 


Live  Load 
on 
Floor. 

Live  Load 
on  Columns 
from  Floors 
above. 

Total  Load 
on 
Columns. 

Roof  

40 

I3th  floor 

50 

40 

40 

1  2th 

45 

85 

nth 

41 

126 

loth 

35 

161 

gth 

3i 

192 

8th 

25 

217 

7th 

21 

238 

6th 

15 

253 

5th 

II 

264 

4th 

5 

269 

3d 

i 

270 

2d 

o 

270 

ISt 

125 

o 

270 

Basement 

50 

320 

The  dead  load  on  the  floor-beams  was  made  up  as  follows, 
a  9-in.  porous  end-construction  arch  having  been  used: 

9-in.  arch 26  Ibs.  per  sq.  ft. 

9-in.  2i-lb.  I-beams 4   "  "         " 

6  to  i  cinder  concrete 30   "  "        " 

Mosaic  and  wood  floors,  average ..    10   "  "        " 

Plaster 6   "  " 

Total 76  Ibs.  per  sq.  ft. 

In  the  Fisher  Building,  Chicago,  1895,  the  distribution  of 
the  loads  for  the  roof,  attic,  and  various  floors  was  as  follows. 


FLOORS  4ND  FLOOR  FRAMING. 


125 


Load. 

Joists. 
Lbs. 

Girders 
Lbs. 

Col- 
umns. 
Lbs. 

Footings 
Lbs. 

Roof                                                          -1 

Live 

20 

15 

15 

Dead 

40 

40 

40 

40 

Total 
Live 

60 
30 

55 
20 

55 
20 

40 

Dead 

75 

75 

75 

75 

Total 
Live 

105 
60 

95 
50 

95 
50 

75 
25 

Dead 

75 

75 

75 

75 

Total 
Live 

135 
60 

125 
50 

125 
45 

IOO 

25 

Dead 

75 

75 

75 

75 

Total 
Live 

135 
60 

125 

50 

1  20 
40 

IOO 

25 

Dead 

75 

75 

75 

75 

Total 
Live 

135 
60 

125 
50 

"5 
35 

IOO 
25 

Dead 

75 

75 

75 

75 

6th  floor  to  3d  floor  \ 

Total 
Live 

135 
60 

125 
50 

no 
30 

IOO 

25 

Dead 

75 

75 

75 

75 

Total 
Live 

135 

75 

125 
60 

105 
40 

IOO 

25 

Dead 

75 

75 

75 

75 

Total 
Live 

150 
90 

135 

75 

"5 

55 

IOO 
25 

Dead 

75 

75 

75 

75 

Total 

165 

150 

130 

IOO 

N.B. — The  weights  of  the  fireproofing  around  the  columns,  and  of  the 
columns  themselves,  are  added  to  the  above  column  loads. 


126  ARCHITECTURAL  ENGINEERING. 

The    dead    loads    in  the  same  building  were  assumed   as 
follows : 

For  floors, 

•|-in.  maple  flooring 4  Ibs. 

Cinder  concrete  deadening  over  floor  arch.  .  15   " 

I5~in.  hollow-tile  floor  arch 41    " 

Floor  beams  and  girders 10   " 

Plaster  on  ceiling 5    " 

Total 75  Ibs 

For  roof, 

3~in.  terra-cotta  book  tile 22  Ibs. 

6-ply  tar  and  gravel  roof 6   " 

T-irons  to  support  terra-cotta  book  tile 4  " 

Steel  roof  framing 8   " 


Total 40  Ibs. 

Floor  Framing. — Methods  of  floor  framing,  that  is,  the 
arrangements  of  columns,  girders,  and  floor  beams  in  skeleton 
structures,  are  illustrated  in  Figs.  58,  59,  60,  and  61. 

The  first  requisite  in  the  design  of  the  floor-system  is  the 
location  of  the  columns.  In  a  great  measure  the  placing  of 
the  columns  is  governed  by  the  arrangement  of  the  exterior 
piers,  the  architectural  effect  striven  for,  or  the  arrangement 
and  proper  planning  of  the  interior  according  to  the  intended 
uses.  The  column  locations  are  thus  usually  the  result  of 
conditions,  rather  than  any  attempts  at  economy,  but,  unless 
complicated  and  expensive  framing  is  to  be  expected,  the  dis- 
tances between  columns  must  always  be  kept  within  the  limits 
of  simple  girder  construction. 


FLOORS  AND  FLOOR  FRAMING. 


127 


It  is  quite  impracticable  to  make  any  comparisons  as  to  the 
relative  economy  of  many  columns  and  short-span  girders,  and 
fewer  columns  with  girders  of  longer  span.  Both  types  are  to 
be  found  in  practice,  even  to  extremes,  but  the  conditions 
governing  the  design  of  any  particular  building  are  usually  so 
~.J*yHj?tMG-L'JXE.. 


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a§H 


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Srty\L/gH7\  OVER 
:£h 

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'S.B   2-/S.T*55t.Bs. 


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ELEV. 


c-w. 


Bs\2-S 


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2-3'* 


BS. 

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9". 

2-9 


7^7. 


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FIG.  58. — Typical  Framing  Plan,  Fort  Dearborn  Building. 


potent   that  a  rule  of  column  spacing  in  one  instance  would 
not  be  applicable  in  the  next  case. 

For  office  buildings,  the  floor  plans  illustrated  in  Chapter 
III  will  indicate  the  arrangement  of  columns  with  reference  to 


128 


ARCHITECTURAL  ENGINEERING. 


office  widths.      The  panels  are  usually  made  of  such  dimen- 
sion as  will  give  one  wide  office,  or   two  suitable   narrower 

I 


FIG.  59. — Typical  Framing  Plan,  Reliance  Building. 

offices,  from  centre  to  centre  of  piers.  Thus  the  practice  of 
Messrs.  Holabird  &  Roche,  is  to  space  both  the  exterior  and 
interior  columns  23  ft.  centres,  where  possible,  thus  making 


FLOORS  AND  FLOOR  FRAMING,  129 

two  offices  of  II  ft.  6  ins.  in  each  bay.  See  floor-plan  of 
Champlain  Building,  Fig.  29. 

The  column  centres  having  been  determined,  girders  must 
next  be  located  connecting  the  columns.  The  girders,  running 
from  column  to  column,  in  one  direction  at  least,  serve  to  sup- 
port the  floor-beams,  transferring  their  loads  directly  to  the 
columns.  The  girders  also  serve  to  brace  the  columns  during 
erection,  and  they  provide  stability  in  the  completed  structure. 
Before  the  girders  can  be  accurately  calculated  as  to  sec- 
tion, however,  the  floor-beams  must  be  located,  as  the  con- 
centrated loads  resulting  from  the  beams  determine  the  girder 
loads. 

Floor-beams. — The  spacing  or  distance  centre  to  centre  of 
the  floor-beams  will  depend  somewhat  upon  the  type  of  fire- 
proof flooring  employed.  The  permissible  spacing  of  beams 
for  some  of  the  more  prominent  fireproof  floors  has  been  given 
earlier  in  this  chapter.  For  terra-cotta  arches,  which  consti- 
tute by  far  the  most  general  construction,  ordinary  practice  in: 
skeleton  buildings  has  made  5  ft.  to  6  ft.  the  most  common 
span  for  panels  of  ordinary  length.  Where  the  columns  are 
spaced  a  considerable  distance  apart,  thereby  causing  long 
beams,  the  floor-beams  are  spaced  nearer  together — or  not 
over  4  ft.  to  4  ft.  6  ins.  Reference  to  Figs.  58  and  59  will 
show  the  practice  in  beam  spacing  in  two  Chicago  examples;, 
while  Figs.  60  and  61  illustrate  framing  plans  for  two  promi- 
nent New  York  buildings. 

The  spacing  of  floor  beams  also  depends  upon  the  amount 
and  character  of  the  floor  load,  upon  the  length  of  span,  and 
sometimes  upon  consideration  as  to  permissible  deflection.  If 
the  loads  to  be  carried  are  largely  static  or  motionless,  as  is 
usually  the  case,  and  if  the  span  is  small  in  comparison  with 
the  depth  of  the  beam,  the  floor  joists  may  be  readily  propor- 
tioned by  means  of  the  tables  for  "safe  distributed  loads  "  as 
given  in  the  hand-books  issued  by  the  more  prominent  steel 


1 3o  ARCHITECTURAL  ENGINEERING. 


ir **; - 

fo . — ._.    _ — 


rto 


— r '•- — ' ' ' " J 

jrftf a&- — -i/sf 

-»••»• i_.^i 


.^r//' 


FLOORS  AND  FLOOR.  FRAMING. 


companies.*  These  tables  give  the  loads,  in  tons  of  2,000  Ibs., 
which  the  various  beams  and  channels  will  safely  carry  (dis- 
tributed uniformly  over  the  length)  for  distances  between  sup- 
ports, as  tabulated. 


FIG.  61.— Typical  Framing  Plan,  Am.  Surety  Co.'s  Building,  New  York. 

Or,  if  a  section  is  to  be  selected  to  carry  a  certain  load  for 

a  length  of  span  already  fixed,  as  is  usually  the  case  in  build- 

*For  much  valuable  information  and  many  useful  tables  concerning 
steel  construction,  the  student  is  referred  to  the  handbooks  issued  by 
The  Carnegie  Steel  Co.,  Pittsburg,  Pa.,  The  Pencoyd  Iron  Works,  Phila- 
delphia, Pa.,  and  others. 


I32  ARCHITECTURAL  ENGINEERING. 

ing  construction,  the  required  beam  or  channel  may  be  found 
by  means  of  the  coefficients  given  in  tabular  form  for  all  rolled 
sections.  For  a  uniformly-distributed  load  these  coefficients 
are  obtained  by  multiplying  the  load,  in  pounds  uniformly  dis- 
tributed, by  the  span  length  in  feet.  If  the  load  is  concen- 
trated at  the  centre  of  the  span,  multiply  the  load  by  2,  and 
then  consider  it  as  uniformly  distributed.  Such  maximum 
coefficients  of  strength  for  I-beams  and  channels  of  different 
depths  and  weights  per  foot  are  given  in  the  hand-books  issued 
by  The  Carnegie  Steel  Company,  L'd,  and  the  Pencoyd  Iron 
Works,  the  values  being  based  on  fibre  strains  of  16,000  Ibs. 
per  sq.  in.  (as  used  for  ordinary  loads),  and  12,500  Ibs.  per 
sq.  in.  for  rapidly  moving  or  vibratory  loads. 

The  Carnegie  and  Pencoyd  hand-books  also  give  tabulated 
values  of  the  "Section  Modulus"  for  all  beams,  channels, 
angles,  Zs,  Ts,  etc.,  and  in  many  respects  the  calculation 
of  floor-joists,  etc.,  by  this  method  is  to  be  preferred  to  the 
calculation  by  means  of  coefficients.  The  Section  Modulus, 
wrongly  called  the  Moment  of  Resistance,  represents  a  con- 
stant property  of  any  shape  which  may  be  considered  as  an 
index  of  the  strength  of  such  shape.  The  Section  Modulus  is 
constant  for  all  spans  and  conditions  of  loading,  as  is  also  the 
weight  per  foot  of  the  section  considered,  so  that  the  former 
may  be  readily  compared  with  the  latter  in  determining  the 
efficiency  or  economy  of  the  section  under  consideration. 

The  Section  Moduli  are  also  very  useful  in  determining  the 
fibre  stress  per  square  inch  for  a  beam  or  other  shape  subjected 
to  bending  or  other  transverse  stresses.  The  Bending  Moment 
in  inch-pounds,  divided  by  the  Section  Modulus,  will  give  the 
extreme  fibre  stress  to  which  the  member  is  subjected. 

Let  5  —  Section  Modulus,  in  inch-units; 
M  —  Bending  Moment,  in  inch-pounds;* 

*  For  Bending  Moments  under  various  conditions  of  loading,  see  hand- 
books issued  by  the  steel  companies. 


FLOORS  AND  FLOOR  FRAMING.  133 

f  =  allowable  stress  per  square  inch  in  extreme  fibres, 

usually  taken  at  16,000  Ibs.  ; 
W  =  total  load  in  pounds,  uniformly  distributed; 
/=  length  of  span,  in  feet; 

d  —  distance  centre  to  centre  of  beams,  in  feet; 
w  =  load  per  square  foot  in  pounds  ; 
Then 

M  =  fS,     or     S  =  j- 

Wl 
But  M  =  -~—  for  a  beam  supported  at  both  ends  and  uniformly 

loaded.      Hence 

12       3  07  . 


Also,  as  W=  dwl, 


-      ......      .       . 

Having  found  5  from  equation  (i),  the  proper  beam,  channel, 
or  other  shape,  may  be  selected  from  the  tabulated  values. 

The  most  economical  arrangement  of  floor-beams  has  had 
little  investigation,  and  there  seems  to  be  no  uniformity  of 
practice.  If  the  framing  plans  could  be  so  arranged  that  the 
floor-beams  and  girders  would  be  strained  to  the  full  allowable 
fibre  strain,  it  would  certainly  be  more  economical  than  where 
the  framing  plans  require  the  use  of  beams  heavier  than  those 
actually  needed.  Take,  for  example,  a  framing  plan  calling 
for  a  bending  moment  in  a  floor-beam  of  65,000  ft.  -Ibs.  This 
would  require  a  Section  Modulus  of  48.75.  The  Section 
Modulus  for  a  12-in.  4O-lb.  beam  is  only  44.8,  while  S  for  a 
i5-in.  42-lb.  beam  is  58.9.  The  latter  would  have  to  be  used, 
with  an  excess  in  strength  of  some  20  per  cent.  ;  and  if  such 
panels  occurred  frequently  in  a  floor  system,  an  excess  of  20 
per  cent,  would  therefore  occur  throughout.  Hence  an 


134  ARCHITECTURAL  ENGINEERING. 

economical  framing  plan  would  be  one  in  which  the  beams  are 
so  arranged  in  span  and  distance  centre  to  centre,  as  to  carry 
a  given  floor-load  with  the  beams  strained  to  the  full  allowable 
fibre  strain.  A  very  small  variation  may  make  this  possible 
or  impossible. 

If  no  beam  can  be  found  whose  Section  Modulus  compares 
closely  with  the  required  value  of  S,  it  may  be  found  practic- 
able so  to  rearrange  the  spacing  of  the  floor-joists  as  to  permit 
of  the  economical  use  of  some  particular  size  of  beam.  In  such 
cases,  equation  (2)  may  be  solved  for  d,  after  substituting  the 
desired  value  of  S,  thus  obtaining  the  maximum  spacing  centre 
to  centre,  of  the  given  I-beams. 

Tables  giving  the  maximum  spacing,  centre  to  centre  of 
beams,  will  be  found  in  both  the  Carnegie  and  Pencoyd  hand- 
books for  loads  of  100,  125,  150,  and  175  Ibs.  per  sq.  ft.,  for 
spans  varying  in  length  from  5  to  30  ft.,  and  as  the  spacing 
of  the  beams  is  inversely  proportional  to  the  loads,  the  required 
spacing  may  be  readily  interpolated  for  loads  other  than  those 
tabulated. 

Also,  in  proportioning  floor-beams,  it  is  well  to  remember 
that  it  is  seldom  economical  to  use  the  heaviest  weight  of  any 
depth  of  beam,  if  a  deeper  beam  can  be  used.  There  is  neces- 
sarily a  great  waste  of  material  toward  the  ends  of  heavy  rolled 
beams,  and  as  the  strength  increases  as  the  square  of  the  depth, 
the  deeper  beam  is  always  the  more  economical.  Thus  the 
Section  Modulus  for  a  12-in.  3i£-lb.  beam  is  36,  while  for  a 
lo-in.  40-lb.  beam  5  =  31.7.  The  former  is  lighter,  and  far 
stronger.  A  2O-in.  65-lb.  beam  is  also  stronger  than  a  I5~in. 
8o-lb.  beam. 

It  will  also  be  noted  that,  for  the  same  depth  of  beam,  the 
Section  Moduli  do  not  vary  in  proportion  to  the  weight.  The 
lightest  weight  of  beam  is  invariably  the  most  economical,  pro- 
viding its  Section  Modulus  is  slightly  in  excess  of  the  value 
required  by  equation  (i).  ' 


FLOORS  AND  FLOOR  FRAMING.  135 

Care  must  be  taken  in  figuring  floor-beams  to  see  that  the 
length  of  clear  span  is  not  too  great,  giving  a  deflection  suffi- 
cient to  crack  the  plaster  ceiling  beneath.  A  deflection  of 
about  3^-0  °f  the  clear  span,  or  ^  of  an  inch  per  foot,  has  been 
found  by  experiment  and  practice  to  be  the  maximum  per- 
missible deflection,  or  d  =  L  x  O-33,  where  tf  =  greatest 
allowable  deflection  in  inches,  at  centre  of  beam,  and  L  = 
length  of  span  in  feet.  This  safe  deflection  limit  is  also  indi- 
cated for  each  size  and  weight  of  beam  given  in  the  tables  for 
uniformly  loaded  I-beams  in  the  mill  handbooks. 

Tie-rods. — With  any  arched  form  of  fireproof  flooring, 
whether  flat  or  segmental,  tie-rods  are  necessary  in  each  bay 
to  take  up  the  arch  thrusts  without  dependence  on  the  adjoin- 
ing arches.  If  all  bays  of  the  floor  system  were  always  loaded 
equally,  tie-rods  would  be  unnecessary,  except  in  the  outside 
panels;  but  with  shifting  live  loads,  tie-rods  are  almost  in- 
variably used,  and  are  sometimes  required  by  law.  They  are 
generally  made  f  in.  in  diameter,  and  spaced  from  5  to  7  ft. 
apart.  Intervals  of  eight  times  the  depth  of  the  floor-joists 
will  about  constitute  average  practice.  Rods  •$-  in.  diameter 
are  sometimes  used  in  heavy  work.  Tie-rods  are  made  with 
thread  and  nut  on  each  end,  to  pass  through  open  holes 
punched  in  the  joists,  usually  at  the  centre  of  the  beams. 
Some  engineers  specify  that  the  holes  shall  be  placed  one-third 
the  depth  of  the  beam  up  from  the  bottom. 

Girders. — The  girders,  running  from  column  to  column, 
support  the  floor-joists,  and  also  the  wall  or  spandrel  loads 
when  located  between  the  exterior  columns.  The  girders  are 
usually  deeper  and  heavier  members  than  the  regular  floor- 
joists,  being  made  of  one  I-beam,  two  I-beams  side  by  side 
and  connected  by  separators  only,  two  I-beams  with  top  and 
bottom  riveted  cover-plates,  or  lattice,  plate,  or  box  girders. 
Deep  single  beams,  or  lattice  or  plate  girders  are  preferable. 
Closed  sections,  such  as  double  I-beams  or  box  girders,  cause 


I36  ARCHITECTURAL  ENGINEERING. 

inaccessible  interior  spaces  which  prevent  future  painting,  and 
also  require  bolted  connections  through  the  webs.  Separators 
should  always  be  used  in  the  case  of  double  beams,  unless 
connected  by  cover-plates,  in  order  to  equalize  the  load  on  the 
two  beams,  and  also  to  act  as  spacers,  keeping  them  a  uniform 
distance  centre  to  centre.  Tables  of  standard  ^size  separators 
are  given  in  the  mill  handbooks. 

Ordinary  forms  of  girders  applicable  to  building  construc- 
tion, other  than  single  beams,  are  shown  in  Fig.  62. 

nmin 

FIG.  62. — Forms  of  Steel  Girders  used  in  Building  Construction. 

Tabulated  coefficients  of  strength  for  these  sections,  for  vary- 
ing spans,  are  given  in  the  handbooks  before  mentioned.  Such 
coefficients  of  strength,  or  safe  loads,  are  based  on  uniformly 
distributed  loads, for  fibre  stresses  of  13,000 to  15,000  Ibs.  per 
sq.  in.,  but  they  may  also  be  used  for  concentrated  loads  by 
following  the  directions  given  for  use  of  tables. 

Girders  supporting  floor-joists  are  usually  calculated  for 
concentrated  loads  instead  of  uniform  loads,  since  the  concen- 
trated loads  of  the  joists  usually  give  smaller  bending  moments 
than  would  result  from  uniform  loads  over  the  tributary  areas. 
Where  a  girder  carries  floor-joists  on  one  side,  and  a  floor  arch 
on  the  other  side,  the  member  should  be  calculated  for  both 
cases  of  loading. 

A  point  to  be  remembered  in  the  design  of  girders  is  that 
a  much  more  economical  girder  can  be  had  when  two  floor- 
beams  are  to  be  supported  than  three;  or  an  even  number 
instead  of  an  odd  number  of  beams.  In  the  latter  instance  a 
load  will  occur  at  or  near  the  centre  of  the  girder,  resulting  in 
a  much  greater  bending  moment.  If  but  two  beams  are  used, 


FLOORS  AND  FLOOR  FRAMING.  137 

the  arm  is  but  one-third  the  span  of  the  girder.  All  of  the 
floor-beams  and  girders  in  the  floor  system  are  usually  so 
arranged  as  to  be  flush  on  the  under  sides,  as  shown  in 
Fig.  63.  This  is  to  provide  for  the 
plastered  ceiling.  The  inequalities 
in  the  arch  depths  are  made  up  in 
the  concrete  filling. 

If  considerably  deeper  beams  or 
lattice  or  plate  girders  are  used  for 
interior  girders,  the  portions  project- 
ing below  the  ceiling  line  may  be 

located  on  partition  liries,  and  thus 

FIG.    63.  —  Isometrical   View 

covered    by    plastered    cornices,    or        of    Connection   of  Floor- 
false  beams  may  be  made  to  show        beams  to  Girders, 
in  the  rooms  below,  by  means  of  fireproofing  or  metal  furring 
and  plaster. 

In  proportioning  the  sizes  of  floor-joists  and  girders,  and 
columns  as  well,  it  is  best  to  specify  as  few  sizes  of  material 
and  as  few  weights  of  beams  and  channels,  or  angles  and  zees, 
as  may  be  practicable.  Thus  in  the  floor  system,  the  calcula- 
tions for  the  various  spans  and  loadings  may  require  a  great 
number  of  beams  and  channels  of  different  depths,  and  of 
different  weights  per  foot  for  the  same  depths ;  but  the  inevit- 
able delay  in  securing  such  a  list  of  sizes  and  weights  from  the 
mills  will  often  more  than  counterbalance  the  extra  cost  made 
necessary  by  using  more  uniform  sizes  and  weights.  Nearly 
all  large  orders  from  the  rolling  mills  are  rolled  to  order,  and 
the  sizes  will  be  furnished  as  the  rolling  programme  of  the  mill 
may  permit.  The  lightest  weights  of  the  various  sizes  of 
beams  and  channels  are  almost  always  rolled  first,  while 
heavier  or  special  weights  may  require  a  long  delay  before  the 
orders  of  the  mill  make  it  desirable  to  roll  such  material. 

Connections. —In  buildings  of  moderate  height,  especially 
if  constructed  with  solid  masonry  walls,  bolted  connections 


I38  ARCHITECTURAL  ENGINEERING. 

may  be  used  lor  almost  all  portions  of  the  frame,  but  in  veneer 
buildings  of  considerable  height,  riveted  connections  should 
invariably  be  specified. 

For  the  connections  of  beams  to  beams,  or  beams  to 
girders,  connection-angles  made  after  the  standards  adopted 
by  the  Carnegie  Steel  Co.  or  the  Pencoyd  Iron  Works  are 
almost  universally  employed  on  good  work.  The  adoption  of 
such  uniform  "  standards  "  is  certainly  a  great  help  to  the  mills 
and  bridge  or  iron  shops,  as  well  as  to  the  designer,  but  in  the 
hands  of  the  careless  or  ignorant  designer  is  apt  to  be  an  ele- 
ment of  weakness.  From  careful  observation  of  building 
methods,  as  practised  in  general,  the  writer  is  convinced  that 
faulty  details  constitute  an  even  greater  part  of  the  defects  in 
the  general  run  of  buildings,  than  arises  from  poor  materials 
employed,  or  imperfect  general  features  of  design.  Any 
"standards"  are  therefore  to  be  used  with  caution,  as  they 
tempt  the  careless  designer  to  use  them  under  all  conditions, 
whether  they  be  adequate  or  not.  They  are  standard,  hence 
they  must  be  all-sufficient. 

Standard  connection-angles  are  designed  on  a  basis  of 
10,000  Ibs.  per  sq.  in.  allowable  shearing  strains,  and  20,000 
Ibs.  per  sq.  in.  allowable  bearing,  and  for  regular  details 
as  found  in  ordinary  practice  these  are  usually  of  sufficient 
strength.  But  in  extreme  instances,  where  beams  of  short 
spans  are  loaded  to  their  full  capacity,  it, is  often  found  neces- 
sary to  provide  additional  strength  in  the  connections.  In 
such  cases  the  limiting  span  lengths,  or  tables  of  minimum 
spans  for  fully  loaded  beams,  must  be  followed.  Typical 
standard  connections  are  illustrated  in  Fig.  64,  while  Fig.  65 
shows  connections  for  beams  of  different  depths  framing  into 
opposite  sides  of  a  girder. 

On  account  of  the  difficulty  of  designing  sufficient  connec- 
tions, no  beam  should  frame  into  another  one  of  less  depth 
than  itself,  even  though  the  calculated  sizes  would  warrant  it. 


FLOORS  AND  FLOOR  FRAMING. 


139 


The  additional  cost  of  special  connections  in  shop  labor  and 
erection  will  generally  more  than  offset  the  additional  weight 
required  in  a  deeper  beam. 

In  cases  where  it  is  impossible  to  make  a  sufficiently  strong 


& 


J" 


J" 


5"  I  and  6"  I. 


18"  I  and  20"  I.  12"  I.  8"  I  and  9"  I. 

FIG.  64. — Standard  Beam  Connections. 


15"  I  and  10"  I.  12"  I  and  9'(  I.  10"  I  and  8"  I. 

9"  I  and  8"  I. 
FIG.  65. — Connections  for  Beams  of  Different  Depths. 

connection  through  the  web  of  a  member  only,  a  seat  or  shelf- 
angle  may  be  riveted  to  the  web  of  the  girder  immediately 
below  the  connecting  member,  to  provide  additional  support, 
and,  if  necessary,  this  seat  may  in  turn  be  reinforced  by  verti- 
cal stiffening  angles. 


140  ARCHITECTURAL   ENGINEERING. 

In  considering  the  connections  of  joists  to  girders,  and 
especially  girders  to  columns  and  columns  to  columns,  in  high 
buildings  subject  to  considerable  wind  strains,  Mr.  Julius  Baier 
lays  especial  emphasis  on  the  following  points,  as  the  result  of 
his  investigations  as  to  the  behavior  of  building  construction  in 
the  St.  Louis  tornado:* 

' '  Well  riveted  joints  in  steelwork  will  stand,  even  under 
jar  and  shock,  an  excessive  amount  of  abuse  and  distortion 
before  actually  separating  into  individual  pieces. 

"That  for  any  twisting,  wrenching,  or  bending  strain,  a 
f-in.  rivet  is  far  superior  to  the  ordinary  |-in.  bolt. 

"That  the  tension  value  of  three  f-in.  steel  rivets  is  suffi- 
cient to  distort  the  web  of  a  I5~in.  42-lb.  I-beam  \  in.  out  of 
line,  without  failure  of  the  rivets,,  and  is  also  far  in  excess  of 
the  bending  resistance  of  the  metal  in  a  TVin.  connection- 
angle. 

' '  That  an  eccentric  tension  strain  will  readily  cause  a  bolt 
to  fail  by  bending  or  breaking  in  the  thread,  while  the  steel 
rivet  will  stand  considerable  distortion  without  failure." 

Detailing. — It  is  comparatively  seldom  that  complete  detail 
plans  for  the  steelwork  of  a  building  are  made  by  the  architect. 
Still  less  frequent  are  the  cases  Where  such  detail  plans  could 
be  used  as  actual  shop  drawings  by  the  contractor,  as  in  nearly 
every  case  the  manufacturer  much  prefers  to  make  his  own 
shop  drawings,  to  conform  to  the  usage  of  his  own  plant.  The 
architect  has  generally  been  content  to  specify  the  sizes  and 
weights  of  the  material  to  be  used,  leaving  the  details  to  be 
worked  out  by  the  contractor  with  the  approval  of  the  architect. 

The  experienced  architect  or  engineer,  however,  is  not 
usually  satisfied  with  such  license  on  the  part  of  the  contractor, 
and  the  best  classes  of  work  are  made  in  accordance  with 

*See  "Wind  Pressure  in  the  St.  Louis  Tornado,  with  Special  Reference 
to  the  Necessity  of  Wind  Bracing  for  High  Buildings,"  by  Julius  Baier, 
Trans.  Am.  Soc.  C.  E.,  vol.  xxxvii. 


FLOORS   AND  i-LCOR  FRAMING.  141 

definite  details  furnished,  after  a  careful  consideration  of  the 
conditions  -to  be  fulfilled.  This  does  not  mean  that  complete 
shop  drawings  are  made,  but  rather  such  connections  and 
special  points  in  the  design  as  need  particular  attention.  The 
balance  of  the  detailing  may  be  made  to  suit  the  contractor 
(with  the  approval  of  the  architect),  in  conformity  with  the 
sizes  of  material  marked  on  the  plan,  and  the  carefully  drawn 
specifications. 

The  idea  of  allowing  the  manufacturer  to  prepare  complete 
details  after  his  ov/n  general  scheme,  and  to  follow  specifica- 
tions only,  is  not  consistent  with  best  results,  in  the  judgment 
of  the  writer,  though  such  an  arrangement  has  often  been 
advocated.  It  is  true  that  it  has  been  a  very  common  practice 
with  bridge  engineers  to  furAish  the  moving-load  diagram,  and 
allow  the  bidders  to  design  the  structure  as  they  saw  fit,  so 
long  as  it  fulfilled  all  requirements  of  the  specifications.  This 
has  probably  been  one  reason  for  the  high  degree  of  excellence 
shown  in  the  work  of  the  better  bridge  companies,  as  each 
bidder  endeavors  to  use  his  material  to  the  best  possible  advan- 
tage. Such  a  practice,  however,  in  building  work  will  require 
a  very  careful  supervision  of  the  work  by  the  architect,  and  as 
the  various  contractors  will  use  those  shapes  most  in  favor,  or 
of  least  cost,  at  their  particular  works,  the  calculations,  con- 
nections, details,  etc.,  must  all  be  gone  over  and  thoroughly 
checked,  that  all  conditions  may  be  satisfactory.  A  careful 
checking  is  necessary  in  any  case,  but  where  such  complete 
freedom  is  accorded  the  bidder,  it  will  rarely  be  that  he  is  able 
to  grasp  the  general  ensemble  in  such  a  manner  as  to  make 
satisfactory  details  in  the  required  time.  Again,  only  the  most 
responsible  and  experienced  firms  could  be  intrusted  with  such 
a  task. 

Carefully  drawn  specifications,  complete  and  accurate  fram- 
ing plans,  sufficient  spandrel  sections  and  any  special  details, 
with  all  sizes  and  dimensions  of  material,  will  insure  rapid  and 


142 


ARCHITECTURAL  ENGINEERING. 


satisfactory  work  on  the  part  of  the  iron  contractor.  The  shop 
drawings  may  then  be  examined,  and  stamped  with  the 
approval  of  the  architect  as  received. 

In  detailing  the  floor  system,  the  joists  should  frame  into 
the  webs  of  the  girders  in  preference  to  resting  on  top  of  the 
girders.  The  latter  method  is  cheaper,  as  the  framing  of  the 
beams  is  avoided,  but  the  former  arrangement  provides  more 
stiffness  and  rigidity,  besides  avoiding  the  increased  depth  in 
the  floors  or  the  projection  of  the  girders  below  the  ceiling  line. 

Where  the  floor-joists  are  of  the  same  depth  as  the  girders, 
or  where  flush  either  top  or  bottom,  ''coping,"  or  a  cutting 
away  of  the  ends  of  the  flanges  is  necessary  in  the  joists,  to 
fit  against  the  flanges  of  the  girders.  About  £  in.  clearance  is 
usually  allowed  at  each  connection  between  floor-beams  and 
girders,  and  $  in.  between  columns  and  girders.  This  is 
sufficient  to  overcome  slight  variations  in  the  evenness  of  the 
material,  and  to  permit  of  easy  erection.  Where  beams  or 
girders  rest  on  column  seats,  the  distances  between  the  con- 
nection holes  must  be  exact,  with  the  allowances  for  clearance 


J3'-2±' 


FIG.  66. — Shop  Detail  of  Framed  Beam. 

made  in  the  extreme  ends  between  the  end  hole  and  the  end 
of  beam.  Fig.  66  illustrates  the  shop  detail  for  a  framed 
beam.  Fig.  67  shows  the  connections  of  beams,  girders,  and 
columns  in  4'The  Fair"  Building,  Chicago. 

Beams  and  girders  are  usually  numbered  on  the  framing 
plans,  to  aid  in  detailing  the  various  pieces,  and  to  identify  the 
parts  for  quick  erection.  The  several  floors  or  tiers  are  often 


FLOORS  AND  FLOOR  FRAMING. 


143 


designated  by  letters,  as  "  A  "  for  first  floor,  "  B  "  for  second 
floor,  etc.  Columns  are  generally  designated  by  one  num- 
ber for  the  entire  height,  while  the  various  stories  are  given 
letters  as  in  the  beams.  Thus,  "  Col.  No.  2,  tier  '  B,'  "  would 
indicate  a  second-story  column  where  the  second  floor  was 
lettered 


FIG.  67 — Connections  of  Beams,  Girders,  and  Columns  in  "The  Fair" 
Building,  Chicago. 

It  is  to  be  remembered  that  the  cost  of  fabricating  the 
material  and  the  cost  of  erection  are  materially  affected  by  the 
detailing  employed.  Strength  and  economy  of  manufacture 
and  erection  all  require  careful  attention  in  detailing,  as  much 
may  be  saved  or  wasted  in  good  or  bad  designing;  and,  as  a 
structure  is  always  gauged  by  its  weakest  point,  so  may  an 
adequate  amount  of  material  be  rendered  insufficient  through 
faulty  minor  details. 


CHAPTER   V. 
EXTERIOR  WALLS— PIERS. 

A  MOST  striking  example  of  the  rapid  and  radical  change 
which  occurred  in  building  practice  as  regards  the  construction 
of  exterior  walls,  is  shown  in  Fig.  16,  Chapter  III,  where  the 
old  and  new  portions  of  the  Monadnock  Building,  Chicago,  are 
illustrated.  The  terms  "old"  and  %<new"  are  simply  rela- 
tive, as  the  newer  addition  was  built  some  three  or  four  years 
only  after  the  original  structure. 

At  the  time  of  designing  the  older  portion  of  this  building, 
the  owners,  in  spite  of  the  protests  of  the  architects,  insisted 
on  having  the  more  conservative,  and  then  eastern  practice, 
of  solid  masonry  piers,  which,  for  the  height  of  sixteen  stories, 
resulted  in  walls  six  feet  thick  at  the  street-level.  A  few  years 
later  an  addition  was  designed  for  the  south  half  of  the  block, 
seventeen  stories  in  height,  and  in  this  instance  the  walls  were 
built  after  the  veneer  method,  which  had  previously  been 
rejected  by  the  owners  in  the  older  portion.  The  difference 
in  window  areas  and  pier  widths,  especially  near  the  sidewalk 
level,  is  apparent,  even  in  the  greatly  fore-shortened  illustra- 
tion. 

The  exterior  masonry  walls  for  steel-frame  buildings  may 
be  either  ' '  load-supporting  ' '  (as  represented  by  the  older 
portion  of  the  Monadnock  Building  just  mentioned),  or 
"veneer-construction,"  i.e.,  entirely  dependent  for  support 
upon  the  steel  frame  (as  in  the  newer  portion  of  the  Monadnock 

144 


EXTERIOR   WALLS-PIERS.  145 

Building),  or  "self-supporting,"  the  latter  being  an  expedient 
between  the  above-mentioned  extreme  cases. 

Load-supporting  Walls. — Load-supporting  walls,  built  of 
solid  masonry,  and  carrying  all  of  the  wall-,  floor-,  and  roof- 
loads  which  come  upon  them  without  the  use  of  steel  or  iron 
members,  constitute  the  ordinary  practice  in  buildings  of 
moderate  height,  whether  of  fireproof  or  non-fireproof  con- 
struction. Eight  or  ten  stories  is  about  a  maximum  height 
for  load-supporting  walls,  so  that  in  higher  structures,  which 
are  here  being  considered  in  particular,  it  is  a  rare  exception 
under  modern  methods  to  rely  entirely  on  masonry  piers. 

The  objections  to  such  piers  of  solid  masonry  are  threefold : 

a.  The  modern  requirements  of  plenty  of  light  and  air  in 
all  offices,  demand  that  the  windows  be  broad  and  numerous 
and  the  piers  narrow.      In  the  highest  buildings  of  the  present 
day  hardly  any  masonry  construction  is  strong  enough  to  carry 
the  necessary  roof-  and  floor-loads  besides  its  own  weight,  for 
so    great   a   height  and   with   so   small  a  cross-section   as   is 
desired.      There  are  prominent  office  buildings  in  almost  all  of 
our  large  cities,  in  which  the  exterior  walls  carry  their  proper 
share  of  all  loads ;  but  a  little  observation  will  show  that  in 
high  buildings  of  this  type  the  comfort  of  the  tenants  has,  in 
a  large  measure,  been  sacrificed  for  architectural  effect. 

b.  Th'e  second  objection  to  such    large  masonry  piers  is 
that  they  take   up  too  much  valuable,  renting-space.      When 
the  rent  of  offices  is  proportioned  at  so  much  per  square  foot, 
this  becomes  a  matter  of  no  inconsiderable  importance  to  the 
owner. 

c.  The  weight  of  these  solid  masonry  piers  would  so  add 
to  the  load  per  square  foot  on  compressible  foundations  that 
many    of  the    most    remarkable    examples    of    architectural 
engineering  would  be  well-nigh  impossible. 

In  commercial  buildings,  of  even  considerable  height, 
masonry  piers  are  often  used  to  carry  all  loads,  but  a  mercan- 


.146 


ARCHITECTURAL   ENGlNEERfNG. 


tile  structure  does  not  present  as  exacting  conditions  as  an 
office  building,  and  the  exterior  piers  may  be  widened  for 
architectural  effect  without  seriously  inconveniencing  the  plan 
of  the  interior. 

A  detail  very  common  to  store  buildings  is  shown  in  Fig. 
68.      In  such  cases  the  first  story  especially  is  desired  to  have 


FIG.  68.— Detail  showing  Masonry  Walls  carried  at  Second  Floor  Level. 

small  piers  and  large  windows  for  show  purposes,  in  which 
case  the  solid  masonry  piers  of  the  upper  stories  are  supported 
at  the  level  of  the  second  or  third  floor  on  girders  which  are 
carried  on  steel  columns  running  through  the  lower  stories. 
In  this  illustration,  the  masonry  walls  are  shown  as  carried  at 


EXTERIOR   WALLS— PIERS.  HT 

the  second-floor  level,  below  which  the  girders  and  steel 
columns  must  be  properly  fireproofed,  and  covered  with. 
ornamental  cast-iron  fascias  and  column  pilasters. 

Self-supporting  Walls. — Self-supporting  masonry  walls  or 
piers  are  sometimes  used,  in  which  case  additional  metal 
columns,  carrying  the  tributary  floor-  and  roof-loads,  are 
placed  inside  the  masonry  piers,  while  the  latter  support  them-- 
selves  and  the  ' '  spandrels  ' '  only.  The  spandrels  constitute 
those  portions  of  the  exterior  walls  lying  between  the  piers  and 
over  and  under  the  window-spaces. 

If  this  method  is  employed,  great  care  must  be  taken  that 
the  masonry  does  not  touch  the  columns,  in  order  that  the 
unequal  settlement  of  the  metal-work  and  the  masonry  may 
not  cause  undesirable  strains.  On  account  of  the  numerous 
mortar-joints,  the  masonry  will  settle  faster  than  will  the 
metal  columns  under  the  gradual  settlement  of  the  whole 
structure.  As  an  example  of  initial  compression  in  freshly 
laid  mortar,  Mr.  Geo.  B.  Post,  architect  of  the  New  York 
Produce  Exchange  Building,  states  that  a  measured  height  of 
9  ft.  6  ins.  at  the  time  of  building,  compressed  about  \  in. 
under  a  maximum  pressure  of  62  Ibs.  per  sq.  in.  of  base; 
induced  by  the  finished  wall.  The  whole  wall  was  built  very 
rapidly. 

If,  then,  the  masonry  bears  on  rivet-heads,  plates,  or  con" 
nections  on  the  columns,  a  heavy  strain  is  produced  which  has 
not  been  provided  for.  Great  care  is  necessary  in  such  com- 
binations of  metal  columns  and  masonry  piers  to  leave  sufficient 
"  open  joints  "  at  points  over  cornices  and  the  like,  where  they 
will  least  be  noticed,  to  allow  for  such  settlement  Also  where 
the  mass  is  not  homogeneous,  as  in  stone  facing  and  brick 
backing,  the  result  is  likely  to  be  that  the  stone,  with  fewer 
mortar-joints,  settles  less  and  receives  more  than  its  share  of 
the  load,  thus  producing  cracks  and  spalling  off  the  angles. 


148  ARCHITECTURAL   ENGINEERING. 

This  was  the  case  in  the  old  portion  of  the  Washington  Monu- 
ment. 

The  objections  of  size  and  weight  will  also  hold  in  the  piers 
of  this  type,  as  in  the  first  method,  if  the  building  be  very 
high.  Thus  in  the  Masonic  Temple  of  twenty-one  stories, 
metal  columns  of  plates  and  angles  were  placed  within  the 
masonry  piers,  but  it  was  found  that  the  maximum  allowable 
pressure  of  12  tons  per  square  foot  on  brickwork,  as  was  used 
in  this  instance,  would  be  .reached  at  the  level  of  the  fifth  floor; 
hence  below  that  level  the  load  exceeded  the  safe  compressive 
resistance  of  the  material ;  and  this  without  any  floor-  or  roof- 
loads,  as  the  latter  were  carried  by  the  metal  columns  within 
the  piers.  The  expedient  was  therefore  adopted  of  carrying 
the  masonry-work  on  brackets  attached  to  the  metal  columns 
.at  the  sixteenth-  and  fifth-story  levels,  thus  making  the  pier 
consist  of  three  separate  columns  of  masonry,  and  the  one 
continuous  metal  column. 

As  has  been  seen  in  Chapter  I,  self-supporting  exterior 
walls  were  employed  in  most  of  the  earlier  examples  of  the 
so-called  skeleton  construction,  the  walls  serving  to  carry  their 
own  weights,  while  all  floor-  and  roof-loads  were  supported  on 
metal  columns  placed  within  the  walls. 

The  "World  "  Building,  New  York  City,  erected  in  1890, 
is  an  extreme  example  of  high  building  construction  with  self- 
sustaining  walls.  The  main  roof  is  191  ft.  above  the  street- 
level,  making  thirteen  main  stories,  above  which  is  a  dome 
.containing  six  stories,— in  all,  a  height  of  275  ft.  above  the 
street.  The  self-sustaining  walls  are  built  of  sandstone,  brick, 
and  terra-cotta,  the  thickness  increasing  from  2  ft.  at  the  top 
to  as  much  as  1 1  ft.  4  ins.  near  the  bottom,  where  the  walls 
.are  offset  to  a  concrete  footing  15  ft.  wide.  The  walls  are 
vertical  on  the  outside  faces,  the  thickness  being  varied  by 
inside  offsets,  so  that  the  columns  are  recessed  into  the  walls 


EXTERIOR.   WALLS— PIERS.  1 49 

at  the  bottom,  but  emerge  and  are  some  distance  clear  of  the 
walls  at  the  top. 

Veneer- construction  Walls. — The  first  example  of  a  purely 
skeleton  construction  in  Chicago  occurred  in  the  rear  wall  of 
the  Phenix  Building,  now  the  Western  Union  Telegraph 
Building,  by  Burnham  &  Root,  architects.  In  the  wall  behind 
the  elevators,  cast  columns  were  used  with  two  sets  of  hori- 
zontal supports  at  each  story.  The  outside  supports  were  made 
of  I-beams  resting  on  brackets  connected  to  the  columns,  these 
I-beams  carrying  a  4|-in.  wall  of  enamelled  brick.  The  inner 
supports  consisted  of  I-beams  placed  between  the  columns, 
supporting  a  4-111.  wall  of  hollow  tile.  Thus  the  wall  was 
formed  of  two  layers  or  ' '  skins  ' '  held  together  by  the  window- 
frames,  etc. 

But  it  was  not  until  the  introduction  of  the  ' '  cage-con- 
struction ' '  steel  frame,  that  veneer-construction  walls  and  piers 
were  fully  developed ;  whereas  now,  with  the  general  use  of 
the  independent  steel  framework,  this  type  constitutes  the  most 
approved  method — the  one  which  has  undoubtedly  opened  up 
the  means  for  building  the  highest  structures.  In  this,  all 
weights  are  thrown  on  the  metal  columns,  which,  in  place  of 
solid  piers,  are  surrounded  with  a  protective  shell  or  covering 
only,  made  of  ornamental  terra-cotta  or  brickwork,  securely 
anchored  to,  and  supported  by  the  columns  at  the  various 
floor-levels. 

This  construction  undoubtedly  gives  the  minimum  weight 
per  foot  of  height,  and  makes  possible  such  small  piers  as  are 
indispensable  for  light  and  desirable  offices.  The  "Chicago 
type  "  is  a  popular  name  for  this  method ;  a  type  which  has 
developed  very  remarkably  during  the  past  few  years  of 
American  architecture,  while  the  height  of  municipal  buildings 
has  been  increasing  steadily  from  ten  to  thirty  stories.  The 
increasing  value  of  ground-space,  the  demands  for  rapid  con- 


150  ARCHITECTURAL  ENGINEERING. 

struction,  and  the  necessity  for  the  lightest  possible  loads  on 
the  subsoil,  have  all  contributed  to  the  success  of  this  detail. 

Veneer  construction  thus  does  away  with  masonry  as  a 
supporting  member,  and  the  load-bearing  brick  wall  or  masonry 
pier  is  replaced  by  an  envelope  of  terra-cotta  or  brickwork, 
enclosing  the  steel  columns  and  filling  the  spandrels  or  spaces 
between  the  windows.  This  envelope  is  not  used  as  a 
strengthener  to  the  supporting  members,  but  as  a  protection 
against  the  elements  and  the  dangers  of  fire.  The  brick  wall, 
once  the  fundamental  factor  in  building  construction,  now  fulfils 
simply  a  decorative  and  protective  function.  The  great  possi- 
bility for  external  effect  through  this  use  of  brick  and  terra- 
cotta in  connection  with  skeleton  construction,  has  opened  up 
a  vast  market  to  the  manufacturers  of  fine  qualities  of  face- 
brick,  moulded  brick,  and  terra-cotta  in  all  its  varieties. 

The  terra-cotta  companies  design  their  pieces  with  especial 
reference  to  tying  them  to,  or  suspending  them  from  such  a 
framework;  so  that,  in  reality,  the  building  becomes  nothing 
more  nor  less  than  a  vital  skeleton  of  steel,  with  an  architec- 
tural and  protective  wrapper  of  terra-cotta,  tile,  or  brickwork, 
inside  and  outside.  The  terra-cotta  arches,  which  to  the 
casual  observer  seem  to  carry  some  heavy  wall  or  pier  above, 
prove  to  be  made  of  hollow  clay  blocks,  held  by  clamps  to  the 
concealed  beams  or  girders  which  really  support  the  loads. 

Materials  used  in  Exterior  Walls. — In  the  construction  of 
exterior  walls,  piers,  and  spandrels  (see  Chapter  VI  for  especial 
reference  to  spandrels),  the  selection  of  methods  and  materials 
must  be  made  with  a  view  to  fulfilling,  as  far  as  may  be  possi- 
ble, the  requirements  as  to  adaptability  of  form  and  facility  of 
handling,  the  protection  of  the  steel  frame  against  corrosion 
and  deteriorating  influences,  and  protection  against  damage  by 
severe  fire  and  water  tests,  either  from  internal  or  external 
sources. 

In  general,  it  may  be  stated  that  brick  and  terra-cotta  are 


EXTERIOR.    WALLS— PIERS.  151 

generally  preferred  to  other  building  materials  for  the  exterior 
walls  of  high  buildings,  on  account  of  the  ease  with  which  they 
may.  be  handled,  the  facility  with  which  they  may  be  built  into 
and  about  the  forms  of  columns  and  beams,  as  well  as  on 
account  of  their  superior  fire-resisting  qualities.  For  more 
detailed  information  as  to  the  materials  of  fireproof  construc- 
tion, the  reader  is  referred  to  Chapter  V,  Materials  used  in 
Fire-resisting  Construction,  in  the  author's  ' '  Fireproofing  of 
Steel  Buildings." 

Fire-resisting  Qualities. — As  regards  protection  against 
internal  or  external  fire  hazard,  the  selection  of  proper  fire- 
and  water-resisting  materials  is  of  the  utmost  importance  in  the 
construction  of  walls  or  piers.  If  the  aim  is  simply  to  secure 
incombustible  materials,  almost  any  form  or  character  of  metal- 
work  or  masonry  may  be  employed — presuming,  of  course,  that 
the  load-carrying  steel  frame  is  properly  protected  against 
possible  injury,  regardless  of  the  character  of  the  decorative 
facings.  But  such  construction  is  very  liable  to  prove  a  poor 
investment,  as  may  be  shown  by  numerous  examples  of  notable 
fires  in  which  large  portions  of  so-called  fireproof  buildings 
have  required  reconstruction  to  such  an  extent  that  the  losses 
occasioned  through  the  use  of  injudicious  materials  have  proved 
quite  the  most  considerable  items  involved.  This  experience 
has  been  particularly  true  of  stone,  where  the  material  is  non- 
combustible,  and  hence  adds  no  fuel  to  the  conflagration,  but 
ivhere  the  inevitable  destruction  under  severe  test  conditions 
often  makes  reconstruction  both  difficult  and  expensive. 

Brick  masonry  and  terra-cotta,  however,  are  unsurpassed 
as  fire-resisting  materials,  as  has  been  amply  proven  by 
innumerable  conflagrations.  These  products  have  stood 
repeated  fire  and  water  tests  of  great  severity  and  consider- 
able duration,  where  all  other  ordinary  building  materials  have 
suffered  complete  destruction  or  at  least  extensive  damage. 
The  endurance  of  brickwork  was  fully  demonstrated  in  both 


I$2  ARCHITECTURAL   ENGINEERING. 

the  Pittsburg  and  Home  Insurance  Building  fires,  where  face- 
brick  suffered  but  little  damage  except  through  discoloration. 
In  the  latter  fire,  the  excellent  qualities  of  architectural  terra- 
cotta were  also  clearly  shown. 

Stone  Masonry. — Marble,  limestone,  or  granite  should 
never  be  relied  upon  as  forming  protection  against  fire,  or  to 
carry  loads  other  than  their  own  weight.  If  used  at  all,  they 
should  be  employed  in  such  manner  that  the  strength  of  the 
structure  is  in  nowise  dependent  upon  their  use;  and  even  then, 
from  the  consideration  of  reconstruction,  the  more  limited  the 
use,  the  better.  Four-inch  or  five-inch  slabs,  such  as  are  fre- 
quently found  in  veneer  construction,  form  very  little  protection 
against  fire,  and  even  where  such  facing  slabs  are  made  of 
greater  thickness,  they  should  be  backed  up  with  sufficient 
brickwork  or  terra-cotta  to  insure  the  full  protection  of  the 
steelwork  in  case  the  stone  veneer  is  destroyed.  Furthermore, 
the  backing  or  true  fireproofing  should  be  independent  of  the 
facing  for  support,  so  that  the  destruction  of  the  latter  would 
not  cause  the  failure  of  the  fireproofing. 

The  financial  loss  due  to  the  use  of  limestone  was  well 
shown  in  the  Chicago  Athletic  Club  Building  fire ;  the  danger 
to  life  from  dropping  stone  during  fire  and  the  practically  com- 
plete destruction  of  marble  was  illustrated  in  the  Home  Life 
Building  fire;  the  large  Boston  fire  on  Bedford  Street  showed 
the  injurious  effects  of  fire  and  water  on  brown  sandstone, 
while  examples  too  numerous  to  mention  might  be  cited  as  to 
the  utter  unreliability  of  granite. 

Stone  has  not  been  extensively  employed  in  skeleton  con- 
struction, except  in  the  lower  stories  only,  as  a  base  for  the 
superimposed  brick  or  terra-cotta  work,  or  in  conspicuous 
exceptions  where  used  throughout.  This  has  been  largely  due 
to  the  difficulty  experienced  in  properly  attaching  the  stone- 
work to  the  metal  framework,  as  well  as  to  considerations  of 
fire  resistance  previously  mentioned.  In  some  instances,  stone 


EXTERIOR    WALLS— PIERS. 


153 


FIG.   69. — Detail  of  Terra-cotta  Front.     Reliance  Building. 


'54 


ARCHITECTURAL   ENGINEERING. 


has  been  used  in  thin  slabs  in  the  lower  stories,  as  in  the  first 
floor  of  the  Reliance  Building,  where  highly  polished  slabs-  of 
granite  were  enclosed  within  ornamental  frames  or  grilles  of 


FIG.  70. — Section  through  WaM  at  Main  Entrance  to  Masonic  Temple. 

cast-iron,  over  the  fireproofing,  as  shown  in  the  lower  part  of 
Fig.  69. 

An  example'  of  the  attachment  of  stone  masonry  to  the 
steel  frame  is  shown  in  Fig.  70,  where  the  box  girder  over  the 
main  entrance  of  the  Chicago  Masonic  Temple  is  illustrated  in 


EXTERIOR    WALLS— PIERS.  155 

connection  with  the  granite  arch  which  extends  up  into  the 
third  story,  as  shown  in  previous  Fig.  15.  The  box  girder 
supports  two  steel  columns  within  the  piers  over  the  entrance, 
the  masonry  'piers  themselves  and  their  share  of  the  spandrel 
loads,  besides  the  fourth-floor  beams  and  the  granite-work 
above  the  arches  shown. 

Brick  and  Terra-cotta. — It  has  already  been  said  that  both 
brick  and  terra-cotta  possess,  in  a  remarkable  degree,  great 
advantages  as  to  erection.  This  is  due  to  the  ease  with  which 
they  may  be  handled,  as  well  as  to  their  ready  adaptation  of 
form.  Terra-cotta  is  easily  moulded  into  almost  any  required 
shape,  thus  providing  for  a  suitable  attachment  to  the  steel 
frame ;  it  is  susceptible  of  elaborate  ornamentation  or  model- 
ling ;  it  may  be  obtained  in  a  wide  range  of  colors  and  finishes ; 
and  it  may  be  used  to  produce  a  great  variety  of  architectural 
effects,  either  separately  or  in  combination  with  brickwork. 
These  considerations,  in  addition  to  most  admirable  fire-resist- 
ing qualities,  all  contribute  to  the  success  which  has  attended 
the  wide  use  of  terra-cotta.  The  rich  decorative  possibilities 
which  brick  and  terra-cotta  possess,  are  well  illustrated  in  the 
new  Broadway  Chambers  Building,  New  York. 

Method  of  Setting.— The  terra-cotta  blocks,  as  used  in 
exterior  wall  construction,  are  usually  built  up  in  advance  of 
the  brick  backing,  one  course  at  a  time.  They  should  always 
be  backed  up  with  brick  masonry,  or  with  structural  terra-cotta 
as  is  sometimes  employed.  The  voids  in  the  rear  of  the  face 
blocks  should  always  be  filled,  where  possible,  with  bricks  or 
parts  of  bricks,  well  filled  in  with  mortar,  to  make  the  con- 
struction as  firm  as  possible.  A  thickness  of  8  ins.  for  external 
terra-cotta  and  backing  should  be  taken  as  a  minimum. 

After  setting,  all  joints  in  terra-cotta  work  should  be  well 
raked  out  to  a  depth  of  f  in.,  and  be  "pointed  "  with  Port- 
land cement  mortar,  colored  to  suit  the  architectural  effect 
required. 


156 


ARCHITECTURAL   ENGINEERING. 


Hooks,  Ties,  etc.— The  individual  terra-cotta  blocks  should 
be  anchored  to  the  backing,  or  directly  to  the  steelwork,  by 
means  of  anchors  or  hooks  made  of  galvanized-iron,  or  iron 
dipped  in  coal-tar  or  graphite  paint.  Methods  of  anchoring 
are  shown  in  more  detail  in  Chapter  VI  in  connection  with 
spandrel  sections. 

The  brick  backing  should  also  be  anchored  to  the  steel- 
frame,  either  by  hooking  anchors  over  members  of  the  frame, 
or  by  passing  them  through  open  holes  provided  in  the  beams, 
columns,  etc.,  for  that  purpose. 

Wall  Columns.— The  earlier  method  of  surrounding  ex- 
terior columns  by  masonry  piers  is  shown  in  Fig.  71.  The 


FIG.  71. — Fireproofing  of  Columns  in  Exterior  Walls. 
cast-iron  or  steel  columns  were  placed  within  the  walls  in  such 
manner  as  to  leave  from  4  ins.  to  12  ins.  of  masonry  between 
the  columns  and  the  exterior  face  of  the  wall,  with  the  balance 
of  the  columns  projecting  into  the  room  areas,  where  terra- 
cotta fireproofing  was  placed  around  the  thus  exposed  portions. 
Not  infrequently,  drainage,  water,  or  even  steam-piping  was 
run  alongside  the  metal  columns,  and  within  the  fireproof 
coverings. 

A  later  and  better  example  is  shown  in  Fig.  72,  which 
illustrates  a  corner  pier  in  the  Reliance  Building,  Chicago, 
1894.  Fig.  73  is  a  plan  of  the  supporting  framework  for  the 
same  corner,  showing  the  shelf-angles  on  the  column  for  the 
support  of  the  pier,  and  the  plate  girder  and  spandrel  angles 
for  carrying  the  spandrel  portions  of  the  walls  between  the 


EXTERIOR    WALLS— PIERS. 


157 


piers.      These  two  figures   also    show  the   cast-iron  uprights 
employed  to  stiffen  and  secure  the  terra-cotta  mullions. 


"T 


FIG.  72. — Detail  of  Corner  Pier  and  Column.     Reliance  Building. 

| 

— 4:o£ 


J.L 
FlG.  73. — Detail  of  Wall  Girders  and  Corner  Column.     Reliance  Building. 


FlG.  74.— Detail  of  Columns  in  Exterior  Walls.     Fisher  Building. 

In  still  later  and  better  examples  of  exterior  piers,  the  fire- 
proofing  is  made  to  surround  the  steel  columns  completely,  so 


158 


ARCHITECTURAL  ENGINEERING. 


that  the  brick  or  ornamental  terra-cotta  front  is  not  relied  upon 
as  the  only  external  protection.  See  Fig.  74.  This  illustra- 
tion also  shows  the  most  approved  method  of  caring  for  all 
piping  within  slots  or  recesses  provided  in  the  fireproofing, 
these  being  separated  from  the  metal  members  by  a  thickness 
'of  terra-cotta,  or  wire  lath  and  plaster  sufficient  to  prevent  cor- 
rosion or  deterioration  from  changes  in  temperature,  moisture, 
or  deleterious  gases,  etc. 

"  Free-standing "  Wall  Columns — A  special  detail  of 
exterior  piers  and  columns  has  been  developed  by  Architect 
Geo.  B.  Post,  and  used  by  him  in 
the  St.  Paul  Building,  New  York 
City.  In  this  building,  all  of  the 
exterior  columns  are  located  en- 
tirely within  the  interior  face  of  the 
brickwork,  thus  standing  free  within 
the  rooms.  This  arrangement  is 
shown  in  Fig.  75.  The  outside 
flanges  of  the  columns  are  placed 
not  less  than  16  ins.  from  the  out- 
side  of  the  masonry.  The  piers  are 
carried  by  horizontal  plates  and 
wall  beams,  which  are  in  turn 
carried  by  cantilevers  formed  by 
projecting  the  members  of  the  floor 
system  out  beyond  the  column. 
For  this  purpose  the  floor  girders 
are  made  double,  so  that  one  mem- 
ber may  pass  the  column  on  either 
side.  Knee-braces,  made  of  gusset- 
plates  and  angles,  are  riveted  to 
FIG.  75. —  Detail  of  "Free-  the  column  above  and  below  the 

standing"      Wall     Columns.    cantilevers,     thus     providing     rigid 
St.  Paul  Building. 

bracing. 


EXTERIOR.   WALLS— PIERS.  159 

Before  the  building  of  the  masonry  walls,  the  columns  were 
encased  with  porous  terra-cotta  4  ins.  thick,  and  between  this 
casing  and  the  masonry  a  further  protection  against  corrosion 
was  introduced  in  the  form  of  asphalted  felt,  laid  to  form  a 
damp-proof  course  on  the  sides  of  the  column  next  to  the  brick- 
work. A  space  left  between  the  asphalt  sheet  and  the  masonry 
was  later  filled  with  a  grouting  of  cement  mortar. 

This  design  was  intended  to  secure,  first,  improved  exclu- 
sion of  moisture  and  prevention  of  corrosion ;  second,  superior 
fireproofing;  third,  accessibility  for  inspection  or  repairs  if 
necessary;  and  fourth,  connections  of  the  floor  system  and  pier 
loads  so  as  to  avoid  the  eccentric  loading  of  the  columns. 

Protection  of  Exterior  Metal-work. — The  protection  of 
the  steel  frame  against  corrosion,  deterioration,  etc.,  was  dis- 
cussed in  Chapter  III,  but  in  considering  exterior  walls  and 
spandrels  the  fact  must  be  borne  in  mind  that,  while  less  is 
now  required  of  the  brick  or  masonry  wall  as  a  supporting 
member  than  formerly,  when  the  walls  fulfilled  the  function  of 
bearing  dead-loads,  much  more  is  now  demanded  of  it  as  to 
quality  and  perfection  of  workmanship,  in  order  that  adequate 
protection  may  be  afforded  the  vital  steel  frame  within. 

In  order  to  render  the  exterior  impervious  to  moisture,  and 
thus  protect  the  metal  framing  against  corrosion,  brick 
masonry,  whether  employed  as  a  backing  for  other  materials 
or  as  finished  brickwork,  should  be  built  of  the  best  possible 
materials.  Only  the  very  hardest  and  most  thoroughly  burned 
brick  should  be  used,  and  cement  mortar  is  generally  specified 
in  the  best  classes  of  work,  with  well-filled  joints  and  careful 
bonding  and  anchoring.  Cement  mortar  is  especially  impor- 
tant where  the  mortar  comes  in  contact  with  the  steelwork. 

A  thickness  of  4  ins.,  or  a  single  brick,  is  often  used  for 
external  protection,  but  a  minimum  of  8  ins.  is  greatly  to  be 
preferred  for  efficient  security  against  fire  and  corrosive  in- 
fluences. 


160  ARCHITECTURAL  ENGINEERING. 

Protection  of  External  Members ;  Building  Laws. — The 

Chicago  Building  Ordinance  requires  the  following  for  the  pro- 
tection of  external  structural  members:  "  All  iron  or  steel  used 
as  a  supporting  member  of  the  external  construction  of  any 
building  exceeding  90  ft.  in  height  shall  be  protected  as  against 
the  effects  of  external  changes  of  temperature  and  of  fire  by  a 
covering  of  brick,  terra-cotta,  or  fire-clay  tile,  completely 
enveloping  said  structural  members  of  iron  and  steel.  If  of 
brick,  it  shall  be  not  less  than  8  ins.  thick.  If  of  hollow  tile, 
it  shall  be  not  less  than  8  ins.  thick,  and  there  shall  be  at  least 
two  sets  of  air-spaces  between  the  iron  and  steel  members  and 
the  outside  of  the  hollow-tile  covering.  In  all  cases  the  brick 
or  hollow  tile  shall  be  bedded  in  mortar  close  up  to  the  iron  or 
steel  members,  and  all  joints  shall  be  made  full  and  solid. 

"Wherever  stone  facing  is  used,  it  shall  be  an  additional 
thickness  to  the  column  covering  above  specified. 

' '  Where  skeleton  construction  is  used  for  the  whole  or  part 
of  a  building,  these  enveloping  materials  shall  be  independently 
supported  on  the  skeleton  frame  for  each  individual  story. 

"  If  terra-cotta  is  used  as  part  of  such  fireproof  enclosure, 
it  shall  be  backed  up  with  brick  or  hollow  tile ;  whichever  is 
used  being,  however,  of  such  dimensions  and  laid  up  in  such 
manner  that  the  backing  will  be  built  into  the  cavities  of  the 
terra-cotta  in  such  manner  as  to  secure  perfect  bond  between 
the  terra-cotta  facing  and  its  backing. ' ' 

The  New  York  law  prescribes  the  following:  "Where 
columns  are  used  to  support  iron  or  steel  girders  carrying  en- 
closure walls,  the  said  columns  shall  be  of  cast-iron,  wrought- 
iron  or  rolled  steel,  and  on  their  exposed  outer  and  inner 
surfaces  be  constructed  to  resist  fire  by  having  a  casing  of 
brickwork  not  less  than  8  ins.  in  thickness  on  the  outer  sur- 
faces, not  less  than  4  ins.  in  thickness  en  the  inner*  surfaces, 
and  all  bonded  into  the  brickwork  of  the  enclosure  walls. 

' '  The  exposed  sides  of  the  iron  or  steel  girders  shall  be 


EXTERIOR    W 'ALLS— PIERS.  161 

similarly  covered  in  with  brickwork  not  less  than  4  ins.  in 
thickness  on  the  outer  surfaces  and  tied  and  bonded,  but  the 
extreme  outer  edge  of  the  flanges  of  beams,  or  plates  or  angles 
connected  to  the  beams,  may  project  to  within  2  ins.  of  the 
outside  surface  of  the  brick  casing. 

' '  The  inside  surfaces  of  girders  may  be  similarly  covered 
with  brickwork,  or  if  projecting  inside  of  the  wall,  they  shall 
be  protected  by  terra-cotta,  concrete,  or  other  fireproof 
material. 

' '  Girders  for  the  support  of  the  enclosure  walls  shall  be 
placed  at  the  floor  line  of  each  story. ' ' 

Protection  of  Column  Interiors. — If  the  steel  columns  em- 
ployed are  of  a  box  section,  or  closed  form,  as  is  often  the  case 
in  such  types  as  Z-bar  columns  with  cover-plates,  or  plates 
and  angles  in  rectangular  form,  a  further  protection  against 
corrosion  may  be  obtained  by  filling  the  column  interiors  with 
rich  Portland  cement  concrete.  Closed  columns  naturally  do- 
not  permit  of  finished  painting  after  the  fabrication  of  the 
members,  nor  of  inspection  nor  renewal  of  painting  at  later 
dates.  Columns  in  exterior  walls  or  other  exposed  locations 
are,  therefore,  sometimes  lined  with  Portland  cement,  or  filled 
with  cement  concrete  as  a  permanent  precaution  against  possi- 
ble deterioration.  All  of  the  exterior  columns  in  the  Ellicott 
Square  Building,  Buffalo,  N.  Y.,  were  thus  filled  with  Portland 
cement  concrete. 

Anchorage. — The  question  of  proper  anchorage  of  the 
brickwork  and  terra-cotta  to  the  steel  frame  has  been  men- 
tioned before,  but  this  point  is  worthy  of  especial  emphasis. 
This  subject  is  often  entirely  overlooked  in  writing  specifica- 
tions, but  in  all  classes  of  work,  of  whatever  character,  adequate 
anchorage  is  very  important.  In  load-supporting  walls, 
efficient  bracing  must  be  obtained  by  means  of  connections  to 
the  interior  frame,  and  proper  anchorage  will  often  prevent  the 
collapse  of  the  walls  from  hot-air  explosions,  etc.  In  veneer 


1 62  ARCHITECTURAL  ENGINEERING. 

construction,  also,  the  comparatively  thin  curtain  walls  must 
largely  rely  for  stability  on  their  anchorage  to  the  steelwork,  as 
well  as  upon  their  inherent  strength.  Speaking  of  experience 
gained  through  the  St.  Louis  tornado,  Mr.  Baier  states  that 
' '  the  great  amount  of  explosive  action  was  largely  due  to  the 
comparative  weakness  of  ordinary  walls  against  pressure  exerted 
from  the  inside  of  buildings.  A  more  efficient  anchorage  of 
the  walls  might  limit  this  explosive  action  to  the  windows.  In 
numerous  instances  the  windows  were  blown  in  on  the  wind- 
ward side,  while  the  entire  walls  were  blown  out  on  the  leeward 
side.  Brick  walls  are  materially  stronger  if  well  bonded  with 
the  vertical  joints  filled  with  mortar,  and  a  wall  laid  in  cement 
will  undoubtedly  withstand  a  greater  lateral  force  than  one  laid 
in  lime  mortar. ' '  * 

Party  Walls. — Columns  or  beams  located  within  party 
walls  should  always  be  efficiently  protected  by  their  own 
masonry,  without  reference  to  the  walls  of  adjoining  buildings. 
In  many  cases  the  steel  columns  and  wall-beams  for  large  and 
important  new  structures  have  been  placed  directly  against  the 
walls  of  neighboring  buildings,  which,  in  case  of  fire,  are  apt 
to  suffer  complete  destruction,  thus  exposing  the  steel  members 
of  the  newer  building. 

Thickness  of  Walls. — As  regards  the  thickness  of  walls 
required,  for  whatever  class  of  building,  this  is  generally  speci- 
fied by  the  local  building  ordinances.  There  is  considerable 
variance,  however,  in  the  requirements  for  veneer  walls  in  cage 
construction. 

A  brick  wall  carried  to  the  height  of  the  Manhattan  Life 
Insurance  Building  in  New  York  City  (241  ft.)  would,  accord- 
ing to  the  building  laws  of  most  cities,  have  to  be  about  6  ft. 
thick.  Through  the  use  of  skeleton  construction  the  enclosing 
walls  in  this  building  were  made  only  12  and  16  ins.  thick. 

*  See  Julius  Baier  in  Transactions  Am.  Soc.  C.  E.,  vol.  xxxvii. 


EXTERIOR   WALLS— PIERS. 


163 


Fig.  76  shows  the  required  thickness  of  walls  under  the 
Chicago  ordinance  for  buildings  devoted  to  the  sale,  storage, 
and  manufacture  of  merchandise.  Fig.  77  is  for  the  walls  of 


i 

*•- 


4-4 


FIG.  76. — Diagram  of  Wall  Thick- 
nesses for  Mercantile  Buildings, 
Chicago  Ordinance. 


FIG.  77.— Diagram  of  Wall  Thick- 
nesses for  Other  than  Skeleton 
Construction. 


hotels,  apartments,  and  office  buildings,  of  construction  other 
than  the  skeleton  type. 

These  thicknesses,  in  Figs.  76  and  77,  are  for  the  maxi- 
mum allowable  height  of  130  ft.  from  the  sidewalk  level  to  the 
highest  point  of  external  walls. 

For  skeleton  construction,  the  Chicago  ordinance  allows 
veneer  walls  of  12  ins.  thickness  for  any  height  within  the 
maximum  limit  of  building  height  above  stated.  The  New 
York  City  building  law  requires  the  use  of  12-in.  curtain  walls 
tor  75  ft.  of  the  uppermost  height  thereof,  and  4  ins.  additional 


1 64  ARCHITECTURAL   ENGINEERING. 

thickness  for  every  lower  6o-ft.  section  down  to  the  sidewalk 
level.  But,  on  account  of  the  severity  of  these  requirements 
as  applied  to  very  high  cage-construction  buildings,  permission 
is  frequently  given  by  the  Board  of  Examiners,  who  are  em- 
powered to  modify  the  building  laws  within  certain  limits,  to 
reduce  the  above-mentioned  thicknesses  to  12  ins.  and  16  ins. 
for  buildings  greatly  exceeding  100  ft.  in  height.  They  have 
never,  however,  permitted  a  uniform  thickness  of  12  ins.  for 
buildings  over  twelve  stories  in  height. 

Allowable  Unit-stresses.  —  The  allowable  pressure  per 
square  foot  on  brick  masonry,  as  used  in  the  highest  masonry 
piers  in  Chicago,  namely,  in  the  Masonic  Temple,  has  been 
mentioned  before  as  12  tons. 

Prof.  I.  O.  Baker,  in  his  "Treatise  on  Masonry  Construc- 
tion," gives  the  following  allowable  strains  on  brickwork  as 
the  practice  of  the  leading  architects : 
IO  tons  per  sq.  ft.  on  best  brickwork  laid  in   I  to  2  Portland 

cement  mortar; 
8  tons  per  sq.  ft.  for  good  brick  laid  in   I  to  2   Rosendale 

cement  mortar; 
5  tons  per  sq.  ft.  for  ordinary  brick,  laid  in  lime  mortar. 

He  shows,  however,  that  these  figures  are  very  conserva- 
tive, as  his  tables  of  the  ultimate  strength  of  best  brickwork 
give  from  I  IO  tons  with  lime  mortar  to  180  tons  with  Portland 
cement  mortar  per  square  foot.  So  while  the  unit  of  12  tons 
in  the  Masonic  Temple  was  even  greater  than  ordinary  Chicago 
practice,  Prof.  Baker  adds  that  "reasonably  good  brick  laid 
in  lime  mortar  should  be  safe  under  a  pressure  of  20  tons  per 
sq.  ft." 

The  safe  loads  given  in  the  Boston  law  are  about  double 
those  recommended  by  Prof.  Baker,  while  the  New  York  re- 
quirements, using  T1¥  of  the  average  ultimate  strengths  given 
by  Prof.  Baker,  allow  1 14  tons  on  granite,  90  tons  on  lime- 
stone, and  72  tons  on  sandstone,  per  square  foot. 


EXTERIOR   IV ALLS— PIERS. 


165 


BRICKWORK  :    ALLOWABLE  PRESSURES  IN  TONS  PER  SQUARE 
FOOT,    SPECIFIED    BY    BUILDING    LAWS. 


New  York. 

Chicago. 

Boston. 

Brickwork 
mortar.. 
Brickwork 
and  lime 
Brickwork 

laid   in   cement 

laid    in   cement 
mortar  
laid     in     lime 

"  1 

Hi   \  («) 

I2j  tons  with  Port- 
land cement. 
9    tons   with    ordi- 
nary cement. 
6ij  tons   with   lime 

15" 

12        (t) 

mortar.  . 

8    J 

mortar. 

8j 

(a)  Isolated  brick  piers  shall  not  exceed  12  times  their  least  dimensions. 

(6)  In  brick  piers  in  which  the  height  is  from  6  to  12  times  the  least 
dimension,  these  pressures  are  reduced  to  13,  10,  and  7  tons  respectively 
for  the  mortars  as  above  given. 

STONE    MASONRY:      ALLOWABLE      PRESSURES    IN     TONS    PER 
SQUARE    FOOT,    SPECIFIED    BY    BUILDING   LAWS. 


New  York. 

Chicago. 

Boston. 

|TV  of  the 

60  )  First  quality, 

Marble  and  limestone. 
Sandstone  

ultimate 
strength. 

Not  specified. 

.-  (  dressed  beds,  laid 
4U  (solid  in  cement 
30  J  mortar. 

The  use  of  ashlar  masonry  in  wall  facings  is  limited  as  fol- 
lows: Boston  law:  "  In  reckoning  the  thickness  of  walls,  ashlar 
shall  not  be  included  unless  it  be  at  least  8  ins.  thick.  In 
walls  required  to  be  16  ins.  thick  or  over,  the  full  thickness  of 
the  ashlar  shall  be  allowed;  in  walls  less  than  16  ins.  thick, 
only  half  the  thickness  of  the  ashlar  shall  be  included.  Ashlar 
shall  be  at  least  4  ins.  thick,  and  properly  held  by  metal 
clamps  to  the  backing,  or  properly  bonded  to  the  same." 

Chicago  law :  ' '  Stone  may  be  used  as  facing  for  brick  walls 
under  the  following  conditions :  If  the  facing  is  ashlar,  without 
bond  courses,  and  the  individual  courses  thereof  measure  in 
height  between  bond-stones  more  than  six  times  the  thickness 
of  the  ashlar,  then  each  piece  of  ashlar  facing  shall  be  united 
to  the  brickwork  with  iron  anchors,  at  least  two  to  each  piece, 


1 66  ARCHITECTURAL  ENGINEERING. 

and  reaching  at  least  8  ins.  over  the  brick  wall,  and  hooked 
into  the  stone  facing  as  well  as  the  brick  backing.  Wherever 
ashlar,  as  before  described,  is  used,  it  shall  not  be  counted  as 
forming  part  of  the  bearing-surface  of  the  wall,  and  the  brick 
backing  shall  be  of  the  thickness  of  wall  herein  specified  for 
the  different  kinds  of  building. 

' '  If  stone  facing  is  used  with  bond  courses  at  a  distance 
apart  of  not  more  than  four  times  the  thickness  of  the  ashlar, 
and  where  the  width  of  bearing  of  the  bond  courses  upon  the 
backing  of  such  ashlar  is  at  least  twice  the  thickness  of  the 
ashlar,  and  in  no  case  less  than  8  ins.,  then  such  ashlar  facing 
shall  be  counted  as  forming  part  of  the  wall,  and  the  total 
thickness  of  wall  and  facing  shall  not  be  required  to  be  more 
than  herein  specified  for  walls  of  the  different  classes  of  build- 
ings. ' ' 

New  York  law :  ' '  All  stone  used  for  the  facing  of  any 
building,  and  known  as  ashlar,  shall  not  be  less  than  4  ins. 
thick.  Stone  ashlar  shall  be  anchored  to  the  backing,  and  the 
backing  shall  be  of  such  thickness  as  to  make  the  walls  (inde- 
pendent of  the  ashlar)  conform,  as  to  the  thickness,  with  the 
requirements  of  this  ordinance. ' ' 


CHAPTER   VI. 
SPANDRELS  AND   SPANDREL  SECTIONS— BAY  WINDOWS. 

THE  spandrels  constitute  those  portions  of  the  exterior 
walls,  either  on  the  street  fronts  or  on  interior  courts,  which 
lie  between  the  piers  and  between  the  window-spaces  of  suc- 
cessive stories.  "Spandrel  sections,"  as  they  are  called, 
must  be  made  for  every  different  type  of  spandrel  support  in 
the  building,  and  they  must  clearly  show  the  supporting  beams 
or  metal-work  required  to  carry  the  veneer  walls  in  the  manner 
desired.  These  sections  vary  greatly,  depending  largely  on 
the  architectural  effect  contemplated  by  the  designer  in  his 
arrangement  of  the  material,  and  general  descriptions  of 
spandrels  can  hardly  be  given  as  applicable  to  general  practice. 
Illustrations  of  numerous  examples  will  better  serve  to  show 
the  methods  employed. 

The  spandrel-beams  are  supported  by  the  masonry  piers 
where  such  load-bearing  piers  are  used,  or,  in  the  veneer  con- 
struction, by  the  metal  columns  in  the  walls.  The  face  of  the 
spandrel-walls  may  be  "  flush  "  with  the  piers,  or  -'in  reveal," 
that  is,  set  back  from  the  face  of  the  piers.  In  the  first  case 
the  wall  presents  a  nearly  unbroken  surface,  except  for  the 
terra-cotta  sills  and  window-caps,  while  the  second  method 
accentuates  the  piers,  and  throws  the  spandrel-walls  in  reveal. 
The  architectural  treatment  will  determine  these  conditions. 
The  former  case  is  generally  of  far  simpler  construction,  as  the 
spandrel-beams  come  at  or  near  the  centres  of  the  columns, 
thus  avoiding  many  embarrassments  in  the  irregular  bracketing 
from  the  columns,  which  becomes  necessary  in  the  support  of 

167 


i68 


ARCHITECTURAL   ENGINEERING. 


the  spandrel-beams  where  the  spandrel-  or  curtain-walls  are 
recessed. 


FIG.  78. — Spandrel  Section. 
Ashland  Block,  Chicago. 


FIG.  79. — Spandrel  Section. 
Reliance  Building. 


Fig.  78  shows  a  very  simple  form  of  spandrel  section  from 
the  Ashland  Block,  Chicago,  where  flush 
walls  were  used.  The  veneer  wall  is  but 
9  ins.  thick. 

The  use  of  plate  girders,  as  the  main 
spandrel  supports,  is  shown  in  Fig.  79, 
which  is  a  section  taken  from  near  the 
corner  of  the  Reliance  Building.  The 
connections  of  these  plate  girders  to  the 
Gray  columns  used  are  shown  in  Fig.  118, 
Chapter  VII.  The  connections  of  the  cast 
uprights  which  support  the  terra-cotta  mul- 
FIG.  8o.-Connection  lions  between  the  windOws  are  shown  in 

of    Cast     Mullions. 

Reliance  Building.     Fig-   8o-      Compare  with  Figs.  72  and  73. 
Figs.  8 1  and  82  are  taken  from  the  eleventh-  and  twelfth- 


M 


SPANDRELS  AND  SPANDREL  SECTIONS-BAY   WINDOWS.     169 

floor  levels  respectively  of  the  Fort  Dearborn  Building.  The 
section  given  in  Fig.  83  is  taken  at  the  first-floor  or  sidewalk 
level,  and  shows  the  prismatic  lights  in  the  sidewalk,  as  well 


$£ 


FIG.  81.— Spandrel  Section,  Eleventh  Floor.     Fort  Dearborn  Building. 

as  the  small  windows  which  help  to  light  the  basement 
restaurant  space.  Fig.  84  is  a  section  taken  at  the  attic  floor, 
showing  the  main  cornice  and  roof  construction. 

The  materials  generally  used  for  veneer  buildings  consist, 
as  before  stated,  of  pressed  brick  and  terra-cotta,  the  latter 
being  used  for  the  window-caps  and  sills,  horizontal  bands, 
ornamental  capitals,  brackets,  etc.,  or  even  in  entire  fa9ades, 
according  to  the  architectural  treatment  desired. 

The  brick  or  tile  work  of  the  piers  is  usually  supported  by 
bracket-angles,  attached  to  the  columns,  as  has  been  described 


170 


ARCHITECTURAL   ENGINEERING. 


,FiG.  82. — Spandrel  Section,  Twelfth  Floor.     Fort  Dearborn  Building. 


FlG.  83. — Spandrel  Section.     First  Floor.     Fort  Dearborn  Building^ 


SPANDRELS  AND  SPANDREL  SECTIONS— BAY   WINDOWS.     171 

in  Chapter  V,  while  the  body  or  backing  of  the  spandrel-walls 
is  supported  directly  by  the  main  spandrel-beams,  as  indicated 
in  the  previous  figures. 


FlG.  84. — Spandrel  Section,  Roof  and  Cornice.     Fort  Dearborn  Building. 

Anchors,  Ties,  etc. — The  ornamental  terra-cotta  work, 
however,  can  seldom  be  supported  directly  by  the  spandrel- 
beams,  and  a  system  of  anchors  must  be  resorted  to,  to 
properly  tie  the  individual  blocks  either  to  the  brick  backing 
or  to  the  metal-work  itself.  These  anchors  are  usually  made 
of  \  in.  square  or  round  iron  rods,  which  are  hooked  into  the 


172 


ARCHITECTURAL   ENGINEERING. 


ribs  provided  in  the  terra-cotta  blocks,  and  then  drawn  tight 
to  the  brickwork  or  metal-work  by  means  of  nuts  and  screw- 
ends.  Such  anchors  are  shown  in  Fig.  86.  Hook-bolts  are 
also  largely  used,  as  in  Fig.  82,  where  the  ends  are  shown 
bent  around  the  spandrel-channels  or  I-beams.  Clamps  are 
frequently  employed  where  the  terra-cotta  block  lies  snugly 
against  a  metal  flange,  as  indicated  in  Fig.  86.  The  many 


FIG.  85. — Spandrel  Section.      Marquette  Building,  Chicago. 

possible  methods  which  may  be  employed  in  securing  proper 
anchorage  cannot  always  be  shown  by  drawings,  and  a  proper 
execution  of  the  work  can  only  be  secured  by  most  careful 
superintendence,  and  study  in  the  field.  The  general  scheme, 
however,  must  always  be  indicated  on  the  spandrel  sections, 
as  the  holes  necessary  in  the  structural  metal-work  to  receive 
the  anchors  should  be  included  in  the  detail  drawings  of  the 
iron-  or  steel-work,  in  order  that  such  punching  may  be  done 
at  the  shop. 


SPANDRELS  AND  SPANDREL  SECTIONS-BAY   WINDOWS.     1 73 

Typical  Spandrel  Sections. — Fig.  85  shows  a  spandrel 
section  from  the  Marquette  Building,  at  the  fifteenth-floor 
level.  Heavy  separators  were  used  between  the  I-beam  girder 
and  the  outside  spandrel  channel. 

A  rather  complicated  spandrel  section  is  that  indicated  in 
Fig.  86,  taken  from  the  Marshall .  Field  retail  store  building. 


FlG.  86.— Spandrel  Section.     Marshall  Field  Building. 

The  spandrel-beams  were  here  carried  by  the  masonry  piers 
used  in  the  exterior  walls.  The  section  shown  is  taken  where 
small  ornamental  balconies  occur  in  the  recessed  wall  between 
the  piers.  The  vertical  mullion-angles  are  plainly  shown. 

Fig.  87  is  from  the  same  building,  taken  at  the  level  where 
the  granite  facing  stops  and  the  brick  and  terra-cotta  work 
begins. 

A  spandrel   section   at  the   eighteenth-floor    level   of  the 


ARCHITECTURAL  ENGINEERING. 


FlG.  87.— Spandrel  Section.     Marshall  Field  Building. 


FIG.  88.— 


Spandrel  Section,  Eighteenth  Floor.     American  Surety  Co.'s 
Building,  New  York. 


SPANDRELS  AND  SPANDREL  SECTIONS— BAY  WINDOWS.     1 75 

American  Surety  Co.  's  Building,  New  York,  is  shown  in  Fig. 
88.  In  this  building,  the  entire  fronts  are  constructed  of 
granite,  and  the  granite  lintel  over  the  window-space  is  shown 
as  supporting  the  courses  above. 

Fig.  89  illustrates  the  construction  of  the  cornice  at  the 
twentieth-floor  level  of  the  same  building. 


FIG.  89. — Spandrel  Section,  Twentieth  Floor.     American  Surety  Co.'s 
Building,  New  York. 

A  section  through  an  end  bay  of  the  Gillender  Building, 
New  York,  at  the  fourth-floor  level,  is  given  in  Fig.  90.  The 
lattice  girder  here  shown  in  section  is  also  shown  in  plan  and 
elevation  in  previous  Fig.  60  (framing  plan). 

Fig.  91  shows  the  overhanging  cornice  at  the  fifteenth- 
floor  level  of  the  Spreckels  Building,  San  Francisco,  Cal. 
The  hook-bolts  and  clamps  used  to  secure  the  marble  cornice- 
stones  are  plainly  indicated. 

A  spandrel  employed  at  the    sixteenth-floor  level  of  the 


ARCHITECTURAL   ENGINEERING. 


FIG.  90. — Spandrel  Section,  Fourth  Floor.     Gillender  Building, 
New  York. 


FlG.  91.— Spandrel  Section,  Fifteenth  Floor.     Spreckels  Building, 
San  Francisco. 


SPANDRELS  AND  SPANDREL  SECTIONS— BAY    WINDOWS.     i?7 


FlG.  92. — Spandrel  Section,  Sixteenth  Floor. 
New  York. 


Broadway  Chambers, 
\ 


FIG.  93.— Spandrel  Section,  Fourth  Floor.     Broadway  Chambers, 
New  York. 


178 


ARCHITECTURAL   ENGINEERING. 


Broadway  Chambers,  New  York,  is  shown  in  Fig.  92,  while 
Fig-  93  is  from  the  same  building  at  the  fourth-floor  level, 
showing  the  termination  of  the  granite  used  in  the  lower  three 
stories. 

Court  Walls. — The  spandrel  sections  of  the  court  walls 
differ  in  no  way,  as  far  as  general  principles  are  concerned, 
from  those  of  the  exterior  walls.  They 
are  generally  simpler,  however,  due  to 
the  plainer  character  of  the  wall,  and  to 
their  usual  decrease  in  thickness  as  com- 
pared to  the  exterior  walls.  A  glazed 
brick  is  commonly  employed  to  reflect 
all  possible  light,  while  the  sill-courses, 
etc.,  are  of  terra-cotta  as  before. 

A  section  of  the  court  wall  in  the 
Marshall  Field  Building  is  given  in  Fig. 

94- 

A  simple  court-wall  spandrel  section 
is  shown  in  Fig.  95. 

Some  extremely  simple  and  well- 
designed  spandrel  sections  for  court 

walls  are  shown  in  Figs.  96,  97,  and  98, 
FIG.  94.— Spandrel  Sec- 
tion, Court  Walls.  Mar-  these  being  taken  from  the  Cable  Build- 
shall  Field  Building.  ing,  Chicago,  1899.*  They  represent 
about  as  simple  wall  construction  as  can  be  devised,  and  in 
court  and  alley  walls  a  single  beam  and  a  Z-bar  or  possibly 
angle-iron,  will  usually  provide  sufficient  support  for  the  plain 
character  of  spandrels  required.  These  sections  illustrate  very 
commendable  methods  of  fireproofing  lintels  or  spandrel- 
beams,  and  if  similar  details  are  employed  for  all  spandrel  sec- 
tions, the  severest  of  test  conditions  by  fire  will  undoubtedly 
be  met  successfully. 


*  See  author's  "  Fireproofing  of  Steel  Buildings." 


SPANDRELS  AND  SPANDREL  SECTIONS-BAY   WINDOWS.     179 


Bay  Windows.  —  With  the  introduction  of  steel  construction 
and  veneer  methods,  came  the  demand  and  possibility  of  con- 


!  "tt 

k--.^— J 
FIG.  95.— Spandrel  Section.     Typical  Court  Wall. 


"p-AS^-f—  /<^H 
k ;?-/tfj- H 


structing  the  bay  window,  a  feature  which  has  become  more  or 
less  prominent  in  modern  office  building  and  hotel  design. 

As  in  the  ordinary  spandrel  section,  the  material  for  each 
story  must  be  carried  in  such  a  manner  as  to  make  it  independ- 


I8o 


ARCHITECTURAL  ENGINEERING. 


ent  of  the  other  stories.  This  is  accomplished  by  means  of 
brackets  at  each  floor-level,  and  in  order  that  the  bracket  loads 
may  not  become  too  heavy  the  bay-window  walls  must  be 


FlG.  96. — Lintel  Section,  Court  Windows.     Cable  Building,  Chicago. 


FlG.  97. — Lintel  Section,  Court  Opening.     Cable  Building. 


FlG.  98.— Lintel  Section    Alley  Windows.     Cable  Building. 

constructed  as  light  as  possible.  No  yielding  or  deflection  is 
permissible  in  these  brackets,  and  if  the  supporting  member  is 
a  floor-beam  or  floor-girder,  as  in  Fig.  99,  taken  through  a 
bay  window  of  the  Masonic  Temple,  the  girder  should  be 
rigidly  connected  to  the  floor  system,  to  prevent  any  twisting 


SPANDRELS   AND  SPANDREL   SECTIONS- BAY   WINDOWS.     l8l 


FIG.  99. — Spandrel  Section  through  Bay  Window      Masonic  Temple, 
Chicago. 


*->      !»'        .i 
gri^Tl 

FIG.  loo.— Spandrel  Section  at  bottom  of  Bay  Window.     Masonic  Temple. 


182 


ARCHITECTURAL  ENGINEERING. 


tendency  due  to  the  weight  of  the  bay.  This  is  accomplished, 
as  in  the  above-mentioned  figure,  by  means  of  the  top  and 
bottom  tie-plates  shown. 

Fig.  100  shows  a  section  at  the  bottom  of  a  bay  window  in 
the  Masonic  Temple. 


FIG.  ioi.— Half  Plan  of   Framing  FIG.     102.  —  Half    Plan     through 

for     Bay     Window.        Reliance  Bay   Window   Walls.     Reliance 

Building.  Building. 

Fig.  ioi  shows  a  half  plan  of  the  metal  framing  for  the 
State  Street  bay  window  in  the  Reliance  Building. 

The  terra-cotta  mullions  of  the  bay  and  the  pier  are  shown 
in  plan  in  Fig.  102. 


SPANDRELS  AND  SPANDREL  SECTIONS— BAY   WMDOWS.     183 


i-jr+tf'l 


FIG.    103. — Spandrel  Section  through  Centre  of   Bay  Window.     Reliance 
Building. 


" I— /^ 


± 


FIG.   104. — Spandrel  Section  at  side  of  Bay  Window.      Reliance  Building. 


I84 


ARCHITECTURAL  ENGINEERING. 


The  column  bracket  in  the  bay  is  given  in  Fig.  103,  while 
Fig.  104  is  a  section  at  the  side  bracket. 


-9\~6'-l 3*8" \ 


FIG.   105. — Floorand  Ceiling  Supports  in  Bay  Window.     Reliance  Building. 


The  method  of  supporting  the  floors  and  ceilings  in  the  bays 
is  shown  in  Fig.  105. 


FIG.  106.— Section  through  Bay  Windows.  Fifth  to  Eleventh  Floors. 
Gillender  Building. 

A  section  through  one  of  the  bay  windows  in  the  Gillender 
Building,  fifth  to  eleventh  floors  inclusive,  is  shown  in  Fig. 


SPANDRELS  AND  SPANDREL  SECTIONS— BAY   WINDOWS.     185 

1 06.      The  plan  is  shown  in  Fig.   107,  while  the  steel  framing 
detail  is  illustrated  in  Fig.  108.     The  latter  should  be  com- 


pared with  the  general  floor-framing  plan  shown  in  previous 
Fig.  60. 


1 86 


ARCHITECTURAL   ENGINEERING. 


Calculation  of  Spandrel  Members. — In  veneer  construc- 
tion the  masonry  or  piers  around  the  columns  is  almost 
always  carried  on  brackets,  shelf-angles,  or  plates  attached  to 
the  steel  columns  at  each  floor-level.  This  leaves  the  spandrel 
members  to  carry  the  curtain  or  spandrel  walls,  which  lie 
between  the  piers  and  extend  from  the  top  or  head  of  one 


FIG.   108.— Plan  of  Bay  window  Framing.     Gillender  Building. 

window  to  the  head  of  the  next  higher  window.  The  spandrel 
framing  members  are,  therefore,  to  be  calculated  for  the  uni- 
formly distributed  wall-  and  window-loads  which  they  carry, 
in  precisely  the  same  manner  as  explained  for  floor-joists.  A 
table  of  weights  of  material,  useful  in  such  calculations,  is 


SPANDRELS  AND  SPANDREL  SECTIONS— BAY   WINDOWS.     187 

given  at  the  end  of  this  chapter.  If  several  spandrel  members 
are  used,  at  somewhat  different  levels,  and  for  distinctly  differ- 
ent conditions  or  magnitude  of  loading,  each  piece  should  be 
calculated  independently,  as,  for  instance,  in  Fig.  84.  Or,  if 
several  like  members  are  to  be  used  side  by  side,  they  may  be 
considered  as  subject  to  one  uniform  loading,  each  piece  to 
carry  its  proportional  share  of  the  total. 

If  the  floor  arch  is  also  to  be  carried  by  the  spandrel  mem- 
ber, in  addition  to  the  spandrel  load,  as  in  Fig.  94,  the  total 
load  must  be  figured — or  a  uniform  load  per  foot  consisting  of 
the  spandrel  weight  plus  the  floor-load  due  to  one-half  the 
floor  arch  adjacent  to  the  wall. 

Spandrel  members  with  brackets,  as  in  Fig.  86,  must  be 
calculated  for  concentrated  loads,  while  bay-window  brackets, 
etc.,  must  be  figured  as  cantilevers,  with  especial  attention 
given  to  the  flange  connections  with  the  supporting  floor-beam 
or  girder. 

If  the  window  areas  are  narrow,  and  the  piers  wide,  with 
the  latter  partially  supported  by  the  spandrel  beams,  such  pier- 
loads  may  be  considered  as  concentrated  at  the  centre  lines  of 
the  portions  resting  on  the  spandrel  members,  and  provided 
for  accordingly  in  addition  to  the  uniform  load  of  the  window 
width. 

Lintels. — For  openings  in  interior  or  exterior  walls  where 
lintel  beams  or  members  are  supported  directly  by  the  walls, 
without  any  connections  to  columns,  the  load  generally 
assumed  to  be  carried,  in  masonry  of  usual  bond,  may  be 
represented  by  a  triangle  whose  base  equals  the  clear  span, 
and  whose  height  equals  one-third  of  the  span,  see  Fig.  109. 
If  openings  occur  in  the  wall,  as  shown  in  the  figure,  the 
load  is  usually  assumed  to  be  the  wall  area  included  within  the 
outside  heavy  dotted  lines  shown. 

Two  or  more  beams  bolted  together  with  cast-iron  separa- 
tors, and  resting  on  cast-iron  or  steel  bearing-plates  at  the 


i88 


ARCHITECTURAL   ENGINEERING. 


ends,  are  usually  employed  to  insure  lateral  rigidity  and  better 
bearing  for  the  wall  to  be  carried.     The  following  table  *  gives 


35 


FIG.   109. — Lintels  in  Masonry  Walls. 

suitable  beams  for  openings  in  properly  bonded  solid  brick 
walls,  with  deflections  less  than  -j^  of  the  span  up  to  10  ft., 
and  -5-^  of  the  span  if  from  15  to  20  ft. : 


Thickness 
of  Wall 
in 
inches. 

Spans  in  Feet. 

8  or  9  ft. 

10  or  ii  ft. 

12  or  13  ft. 

14  or  15  ft. 

16  or  17  ft. 

18  or  20  ft. 

9  

22    

2-4"  7l  'b. 
2"4"  71  IK' 

2"5     9f   K- 
a-5"  9j  lb. 

2-5"  9J  lb 

2-6"  I2j  lb. 

2-7"  15  'b. 
2-7"  15  lb. 

2-7;;  ,s  ib 

2-7"  15  lb. 
2-8"  18  lb. 
2-8"  18  lb. 

2-8"  18  lb. 
2-8"  18  Ib. 
2-9"  21  lb. 
2-9"  21  lb. 

2-9"  21  lb. 
2-9"  21  lb. 
2-10"  25  lb. 
2-10"  25  lb. 

•a-i2"3i»lb 
2-12"  3,  ^lb. 
2-12"  3iJ  Ib. 
3-12"  3ii  lb. 

Cast-iron  lintels  may  be  computed  as  follows :  assume  a  J. 
section,   the  horizontal  member  of  which  is   12  ins.  wide  by 

1  in.  thick,  and  the  vertical  web  of  which  is  7  ins.   high  by 

2  ins.  thick.      The  lintel  is  therefore  1 2  ins.  broad,  and  8  ins. 
high.      Assume  the  clear  span  as  8  ft.  o  ins. 

The  neutral  axis  may  then  be  computed  from  the  base  line 
of  the  lintel;  or 

(2  X  7)4+ (12  X  i)4 


14+   12 


=  2.38  ins. 


*  See  "  Steel  in  Construction,"  issued  by  A.  &  P.  Roberts  Co. 


SPANDRELS  AND  SPANDREL  SECTIONS-BAY   WINDOWS.     189 

The  neutral  axis  is,  therefore,  2.38  ins.  up  from  the  base  line, 
and  5.62  ins.  down  from  top  of  web.      /then  equals 

2  X  5-623  +  12  x  2.383  —  10  x  1.38* 

—  -  =  ,63. 

Wl 

M=  —  j-  for  a  uniformly  distributed  load,  and,  as  /  =  96  ins. , 
o 

M  therefore  equals  1 2  W  inch-pounds. 

But  M '  =  — ,  and  f  for  the  upper  fibres  in  compression  may 

y\ 
90,000 

be  taken  at  — ^ — =  15,000  Ibs.      Hence, 


433.°°o 


W  =  36,000  Ibs. 

For  the  lower  or  tension  fibres,  /=  —  ~  —  =  3,  3  34  Ibs. 
Hence, 

M  =  12W=  3.334  X  .63  =  ^^  ^ 

W=  19,000  Ibs. 

Hence,  the  safe  distributed  load  for  a  factor  of  safety  of  6  in 
tension,  should  not  exceed  19,000  Ibs. 


190  ARCHITECTURAL  ENGINEERING. 

TABLE  OF  WEIGHTS    USED    IN    THE   CALCULATION  OF 
SPANDREL   LOADS,    PIER    LOADS,   ETC. 

Brick  masonry,  common  brick 112  Ibs.  per  cubic  foot. 

pressed  brick 140  "  "  "         " 

hollow  brick 90  "  "  "         " 

Concrete,  cinder 84  " 

"          stone 150  "  "  "         " 

Masonry,  bluestone 160  "  "  "         " 

"          granite 170  "  "  *         " 

"          limestone 160  "  "  "         " 

"          marble 160  "  "  "         " 

"          sandstone 144  "  "  "         " 

"          slate   160  "  "  "         " 

Terra-cotta,  brick  backing 112  "  "  "        * 

Glass,  sash,  etc 5  Ibs.  per  square  foot. 

Plaster,  on  terra-cotta  arches 5  "  "  "         " 

"         on  lath 7  "  "  "         " 

Slate,  on  roofs,  etc.,  laid 6  "  "  "         " 

Snow,  fresh-fallen 7  "  "  "         •' 

"        wet  and  packed 15  to  50  "  "  "         " 

Skylights 50  "  ' 


WEIGHTS    PER    SUPERFICIAL   FOOT    FOR    BRICK  WALLS 
OF   DIFFERENT    THICKNESSES. 

(On  a  basis  of  112  Ibs.  per  cubic  foot.) 

9-inch  wall 84  Ibs.  per  superficial  foot. 

13-inch     "     121     "      "  " 

17-inch     "     168    "      "           "  '* 

21-inch     "     205    "      "           "  " 

25-inch     "     243    "      "           "  " 

29-inch     "     289    "      "           "  " 

33-inch     "     326    "      "           "  " 

38-inch     "     .: 373 

42-inch     "     410    "      "           ••  M 

46-inch     "     448    "      "           "  ** 

50-inch     "     486    "      "           "  4fc 

54-inch     "     532    "      "          "  <•'- 


CHAPTER   VII. 
COLUMNS. 

THE  subject  of  the  interior  columns  forms  one  of  the  most 
important  steps  in  the  modern  problem  of  design,  and  greater 
variations  are  probably  to  be  found  here  than  in  any  other  of 
the  vital  features  .in  iron  or  steel  construction.  The  many 
forms  of  columns  now  in  the  building  market,  each  having  its 
own  good  points,  and  the  many  types  of  connections  between 
the  columns  themselves  and  with  the  floor  system,  permit  of  a 
choice  from  a  dozen  or  more  types,  with  the  details  varying 
widely  in  each  case,  to  suit  the  shape  chosen.  We  shall 
endeavor  to  investigate  the  more  prominent  forms,  and  point 
out  the  advantages  and  disadvantages  of  each  one.  The  most 
satisfactory  for  general  or  specific  cases  may  then  be  selected, 
as  combining  the  features  desired. 

Cast-iron  Columns. — A  discussion  as  to  the  relative  values 
of  cast  versus  steel  columns  should  hardly  seem  necessary  at 
the  present  time,  but  the  repeated  use  of  the  cast-iron  column 
in  ten-  to  sixteen-storied  buildings,  and  even  higher  (as  exem- 
plified by  their  use  in  the  Manhattan  Life  Insurance  Building 
of  seventeen  stories),  shows  that  the  questionable  economy  of 
cast  columns  does  still,  in  the  opinion  of  some  architects, 
compensate  for  the  dangers  incident  to  their  use.  The  best 
practice  has  declared  so  uniformly,  during  the  last  few  years, 
in  favor  of  the  steel  columns  that  the  employment  of  cast  metal 
is  now  pretty  generally  confined  to  buildings  of  very  moderate 
height  or  to  special  cases  where  advantages  are  to  be  gained, 

191 


I92 


ARCHITECTURAL  ENGINEERING. 


as  in  the  use  of  a  number  of  ornamental  cast  columns.  The 
great  uncertainty  as  to  the  uniformity  of  cast  metal  led  to  the 
use  of  a  very  low  unit-stress,  while  in  the  case  of  steel  the  unit- 
stresses  can  be  assumed  on  a  very  definite  reliance  on  the 
trustworthiness  of  the  metal.  Among  more  progressive 
designers  the  use  of  cast-iron  in  large  buildings  has  become  a 
thing  of  the  past,  and  would  no  more  be  seriously  considered 
than  would  the  use  of  cast-iron  compression-members  in 
bridges. 

Considering   the    cast    sections    in    more    general    use    as 
columns,  the  circular,  square,  and  H-shaped,  and  their  indi- 
vidual connections  (see  Fig.  no), 
it  will  be  seen  that  these  splices 
cannot  result  in  as  rigid  a  frame- 
work as  the  riveted  joints  in  steel- 
work.      The     columns     in     the 
modern  design  must  be  capable 
of  affording  stiff  connections  so  as 
to  withstand  both  the  direct  dead- 
and   live-loads    transferred    from 
the  floor  system,  as  well  as  suffi- 
cient connections   for  the  wind- 
FIG.  no.—  Details  of  Splices  for  bracing.      These    cannot  be    se- 
Cast-iron  Columns. 


( 


\-vfAGe0' 


passing  through  the  horizontal  flanges  of  cast  columns,  even  if 
the  workmanship  be  considered  accurate.  The  workmanship, 
however,  can  seldom,  if  ever,  be  relied  upon  as  perfect;  the 
bolts  never  completely  fill  their  holes,  and  "  shims  "  are  con- 
stantly employed  to  plumb  the  columns.  These  constitute 
elements  of  weakness  which  may  easily  allow  considerable  dis- 
tortion. The  girder  connections  to  the  columns,  resting  on 
cast  brackets  and  bolted  through  the  flanges,  are  bad  in  the 
extreme,  especially  for  cases  of  eccentric  loading  and  the 
irregular  placing  of  beams. 


COLUMNS.  195 

To  offset  these  dangers  of  weak  design  it  is  true  that  cast 
columns  are  cheaper  per  pound  and  perhaps  easier  of  erection 
than  the  steel — considerations  that  naturally  have  much  weight 
with  the  owner  of  the  building.  But  considering  the  risks  that 
are  run,  as  in  the  building  at  14  Maiden  Lane,  New  York, 
which  was  blown  eleven  inches  out  of  plumb  through  the 
inability  of  the  cast  columns  to  resist  the  wind  pressure,  it  is 
hard  to  understand  why  architects  will  persist  in  the  use  of 
such  methods,  even  if  requested  by  the  owner.  Cast-iron,  in 
spite  of  its  apparent  stiffness,  has  a  much  lower  coefficient  of 
elasticity  than  steel,  breaking  suddenly  when  it  breaks,  while 
steel  suffers  distortion. 

Steel  is  now  being  rolled  at  such  a  low  price  that,  con- 
sidering the  extra  weight  necessary  in  cast-iron,  on  account  of 
its  unreliability,  the  saving  in  cost  by  the  use  of  the  latter  will 
be  found  to  be  small  indeed,  even  disregarding  the  dangers 
assumed  by  its  use. 

The  formula  ordinarily  used  in  proportioning  cast-iron 
columns,  and  commonly  known  as  Gordon's  or  Tredgold's 
formula,  is 

80,000 

P=l ,  j_/r 

"T  400  d* 

The  only  basis  for  this  formula,  or  for  the  same  form  wftlx 
different  coefficients  as  used  by  various  writers,  consists  of  a 
series  of  tests  made  by  Hodgkinson  in  about  1840  on  nine 
so-called  "long"  pillars,  and  thirteen  "short"  pillars.  The 
long  specimens  were  7  ft.  6  ins.  in  length,  with  external 
diameters  ranging  from  if  to  2\  ins.,  while  the  short  pillars 
were  not  over  2  ft.  6  ins.  long,  with  external  diameters  of  I  to 
i\  ins.,  and  a  thickness  of  metal  in  no  case  exceeding  \  in, 
Considering  the  nature  of  cast-iron,  and  the  methods  of  manu- 
facture employed  in  making  large  cast  columns,  it  is  evident 
that  any  such  experiments  as  the  above  are  in  no  way  suitable 


194  ARCHITECTURAL  ENGINEERING. 

to  form  the  basis  for  any  formulae  to  be  used  in  proportioning 
members  of  such  size  as  ordinarily  enter  into  building  con- 
struction. For  this  reason,  the  use  of  cast-iron  members  in 
bridge  construction  has  not  been  countenanced  by  civil  en- 
gineers for  more  than  twenty  years  past,  yet  Gordon's  formula 
has  continued  in  use  for  building  work,  and,  until  1899,  the 
formula  given  above  has  been  practically  required  by  the  New 
York  Building  Law. 

During  the  past  few  years,  however,  additional  tests  have 
been  made  on  full-sized  sections — including  the  tests  of  Prof. 
Lanza  at  the  Watertown  Arsenal,  and  the  later  and  more  im- 
portant tests  made  at  Phcenixville,  Pa.,  by  the  New  York 
Building  Department  in  1896  and  1897;  and  although  these 
experiments  do  not  cover  any  great  range  of  sectional  forms 
or  of  the  ratio  of  length  to  diameter,  still  the  results  are  suffi- 
cient to  show  the  complete  unreliability  of  the  formulae  com- 
monly employed. 

According  to  the  Phcenixville  tests,  I5~in.  columns  which, 
by  Gordon's  formula,  should  possess  a  breaking  strength  of 
57,143  Ibs.  per  sq.  in.,  failed  under  stresses  varying  from 
24,900  Ibs.  to  about  40,400  Ibs.  per  sq.  in.,  while  6-in.  and 
8-in.  columns,  with  a  calculated  strength  of  40,000  Ibs.  per 
sq.  in.,  showed  a  breaking  strength  of  from  22,000  Ibs.  to 
31,900  Ibs.  per  sq.  in.  only.* 

From  the  foregoing  tests,  Prof.  Wm.  H.  Burr  has  deduced 
the  straight-line  formula 

p  =  30,500  —  160^, 

where  p  equals  the  ultimate  resistance  per  square  inch.  This 
gives  about  a  mean  of  the  tests  as  plotted,  "and  represents  as 
near  as  any  that  can  be  found,  a  reasonable  law  of  variation  of 
ultimate  resistance  with  the  ratio  of  length  over  diameter. ' ' 

*See  Engineering  News,  Jan.  20,  1898. 


COLUMNS.  195 

The  plotted  values  of  the  formula 

/=  52,500-  563^. 

determined  by  actual  tests  made  on  mild  steel  angles  by 
Mr.  James  Christie  of  the  Pencoyd  Iron  Works,  ' '  show  that 
the  ultimate  resistances  per  square  inch  of  mild  steel  columns 
are  from  40  to  50  per  cent,  greater  than  the  corresponding 
quantities  for  cast-iron,  the  same  ratio  of  length  over  diameter 
being  taken  in  each  comparison. ' '  * 

Prof.  Burr  gives  as  his  conclusion: 

' '  When  the  erratic  and  unreliable  character  of  cast-iron  is 
considered,  it  is  no  material  exaggeration  to  state  that  these 
tests  show  that  the  working  resistance  per  square  inch  may 
probably  be  taken  twice  as  great  for  mild  steel  columns  as  for 
cast-iron;  indeed,  this  may  be  put  as  a  reasonably  accurate 
statement. 

' '  The  series  of  tests  of  cast-iron  columns  represented  in  the 
plate  largely  destroys  confidence  in  the  cast-iron  column 
design  of  the  past.  The  results  of  the  tests  constitute  a  revela- 
tion of  a  not  very  assuring  character  in  reference  to  cast-iron 
columns  now  standing,  which  may  be  loaded  approximately 
up  to  specification  amounts.  They  further  show  that,  if  cast- 
iron  columns  are  designed  with  anything  like  a  reasonable  and 
real  margin  of  safety,  the  amount  of  metal  required  dissipates 
any  supposed  economy  over  columns  of  mild  steel.  As  a 
matter  of  fact,  these  results  conclusively  confirm  what  civil 
engineers  have  long  known,  that  the  use  of  cast-iron  columns 
cannot  be  justified  on  any  reasonable  ground  whatever. ' ' 

Steel  Columns.  —  The  more  prominent  forms  of  steel 
columns  as  used  in  American  building  practice  include  channels 
connected  by  plates  or  lattice,  plates  and  angles  in  various 

*See  Prof.   Wm.    H.    Burr   in    School  of  Mines  Quarterly,  April,   1898; 
also  in  Engineering  News,  June  30,  1898. 


i96 


ARCHITECTURAL   ENGINEERING, 


forms,  and  Z-bar  columns.  Besides  these  types,  and  the  con- 
siderable number  of  variations  found  in  each,  special  forms 
such  as  the  Keystone  Octagonal,  Phoenix,  Larimer,  and  Gray 
columns  have  been  used  to  more  or  less  extent,  but  these 
patented  or  restricted  forms  have  not  been  employed  as  exten- 
sively as  those  columns  which  are  made  of  shapes  in  common 
use,  without  any  restrictions  as  to  patent  rights  or  availability 
of  material. 

Channel  Columns. — Ordinary  forms   of  channel    columns 
are    shown   in   Fig.    ill.      For   light   members,    as    in   upper 


(7) 


(i)  (2)  (3)  (4) 

FIG.   in. — Typical  Forms  of  Steel  Channel  Columns. 

stories,  the  channels  are  often  placed  back  to  back  or  flange  to 
flange,  and  connected  by  means  of  tie-plates  and  lattice  bars. 
The  former  method  of  placing  the  channels  back  to  back  is 
somewhat  easier  as  regards  the  riveting.  The  third  form 
shown,  with  cover  plates  either  single  or  double,  is  one  of  the 
most  common  column  sections  employed.  The  fourth  form 
shows  a  combination  of  two  channels  and  an  I-beam.  A 
variation  of  this  section  is  sometimes  made  by  substituting  a 
plate  and  four  angles  in  place  of  the  I-beam,  or  one  or  more 
plates  and  two  angles  for  the  channel  sections.  These  forms 
were  used  in  the  Harrison  Building,  Phila.,  and  are  shown  in 
the  sections  5,  6,  and  7. 


COLUMNS. 


197 


Plate  and  Angle  Columns. — Typical  forms  of  plate  and 
angle  columns  are  shown  in  Fig.  112.     The  simplest  combina- 


(5)  (6)  (7) 

FIG.   112. — Typical  Forms  of  Plate  and  Angle  Columns. 

tion  is  that  made  in  the  form  of  a  beam.  One  or  more  webs 
may  be  used,  or  fillers  between  the  angles  as  shown  by  the 
dotted  lines,  but  any  additional  material  is  placed  to  better 
advantage  if  used  in  the  form  of  cover-plates,  riveted  to  the 
outer  legs  of  the  angles.  The  I  section  of  plates  and  angles 
is  extensively  used  in  cases  where  the  loads  are  sufficiently  light 
to  permit  of  its  use.  This  form  of  column  was  used  in  the 
Manhattan  Life  Building,  New  York  City.  The  box  form  of 
plates  and  angles,  shown  as  the  second  type  in  the  illustration, 
is  one  of  the  most  ordinary  as  well  as  commendable  forms  in 
common  use.  This  section  may  be  readily  strengthened  by 
using  additional  web-plates,  cover-plates,  or  filler-plates,  as 
illustrated  by  the  dotted  lines,  or  by  section  3.  Columns  of 
this  form  have  been  used  in  a  great  many  notable  high  build- 
ings; as,  for  example,  the  St.  Paul,  the  American  Surety,  and 
the  Park  Row  Buildings  in  New  York  City,  and  the  Masonic 


198  ARCHITECTURAL  ENGINEERING. 

Temple  in  Chicago.  Section  4  illustrates  a  particularly  heavy 
section  employed  in  the  Manhattan  Life  Building.  Special 
corner  wall-columns  used  in  the  Dun  Building,  New  York,  and 
in  the  Worthington  Building,  Boston,  are  shown  in  forms  5 
and  6  of  Fig.  112,  while  form  7  shows  a  variation  of  the 
beam  and  channel  column,  as  used  in  the  Harrison  Building, 
Phila. 

Z-bar  Columns. — Z-bar  columns  and  variations  are  shown 
in  Fig.  113.     The  ordinary  section  is  as  in  form  I,  this  being 


d)  (2)  (3)  (4)  (5) 

FIG.  113. — Typical  Forms  of  Z-bar  Columns. 

made  in  the  standard  sizes  of  6-in.,  8-in.,  io-in.,  and  12-in. 
columns,  by  using  3-in.,  4-in.,  5-in.,  and  6-in.  Zees  respectively. 
When  the  load  can  be  safely  carried  without  the  aid  of  cover- 
plates,  and  if  the  size  of  the  column  does  not  become  too  large 
for  its  relative  position  in  the  building,  it  is  more  economical  to 
use  the  simple  section,  but  when  additional  area  is  required, 
one  or  more  cover-plates  may  be  added  as  shown  by  the  dotted 
lines.  Form  2,  known  as  the  "standard  dimension"  Z-bar 
column,  was  designed  to  allow  of  the  outside  dimensions  of 
such  columns  being  kept  standard  for  all  stories,  irrespective 
of  the  size  or  thickness  of  Z's  required,  but  on  account  of  the 
tie-plates  required  in  either  one  or  both  directions  increasing 
the  shop  costs,  and  decreasing  the  efficiency  of  the  column 
under  eccentric  loading,  the  form  has  never  come  into  ex- 
tensive use.  Sections  3  and  4  show  heavy  columns  combining 
Zees  with  plates  and  channels.  These  forms  were  used  in  the 
Manhattan  Life  Building.  Section  5  shows  a  combination  of 


COLUMNS.  199 

two  Z-bars  with  one  I-beam,  as  used  in  the  Dubuque,  Iowa, 
Bank  Building.      The  ordinary  sections  were  made  of  lo-in. 
I-beams  and  5 -in.  Z-bars,   while  in  the  heavier  sections  the 
Zees  were  reinforced  by  angles,  as  shown  in  the  dotted  lines. 
Special    Columns. — Fig.    1 14    illustrates    what    may   be 


(i)  (2)  (3)  (4) 

FIG.  114. — Special  Forms  of  Steel  Columns. 

termed  special  forms  of  steel  columns,  inasmuch  as  these  sec- 
tions are  either  controlled  by  patents,  or  else  their  manufacture 
is  restricted  to  certain  mills  which  roll  the  special  shapes 
required.  Form  I  shows  the  Keystone  Octagonal  column, 
which  is  now  rarely,  if  ever,  seen  in  building  practice.  The 
Phoenix  column,  form  2,  will  be  discussed  in  a  later  portion  of 
this  chapter.  This  form  has  many  commendable  points,  but 
the  special  shapes  of  material  required  restrict  its  manufacture 
to  certain  mills.  The  Larimer  column,  shown  in  form  3,  is 
controlled  by  Jones  &  Laughlins,  L'd.,  while  the  Gray  column, 
form  4.  is  still  controlled  by  patents. 

The  foregoing  examples  will  serve  to  show  the  great 
number  of  forms  offered  the  designer,  from  which  a  selection 
must  be  made.  Nearly  all  of  the  sections  illustrated,  save  the 
Keystone  Octagonal  column,  are  to  be  found  in  prominent 
examples  of  building  construction,  while  various  other  special 
forms  or  combinations  have  been  proposed  or  actually  em- 
ployed. These  latter  may,  however,  be  classed  as  curiosities, 
or  designs  dependent  upon  very  special  conditions. 


200  ARCHITECTURAL  ENGINEERING. 

Theoretical  Requirements  in  Column  Design. — The  rela- 
tive advantages  of  these  standard  sections  are,  obviously,  of 
considerable  importance  in  influencing  a  choice ;  but  that  any 
particular  type  can  be  selected  as  the  best  for  universal  appli- 
cation, is  manifestly  impossible.  In  actual  practice  the  treat- 
ment of  these  different  shapes  will  be  found  to  vary  greatly 
with  the  designer — not  only  in  the  relative  value  of  the  sections, 
but  in  the  treatment  of  any  one  section.  In  the  first  place, 
column  formulae  differ  greatly,  not  in  fundamental  principles 
perhaps,  but  in  the  treatment,  being  often  empirical,  and  con- 
taining factors  deduced  from  some  special  case.  These 
formulae  also  generally  assume  ideal  loading,  which  will  seldom 
occur  in  the  modern  building,  and  practically  no  full-sized  tests 
have  ever  been  made  on  the  effects  of  eccentric  loading.  Full- 
sized  tests,  on  columns  of  concentric  loads  even,  have  been  far 
too  limited  to  show  the  relative  values  of  the  most  ordinary 
column  sections. 

Prof.  Burr,  in  his  "Strength  and  Resistance  of  Materials, " 
states  that  ' '  The  general  principles  which  govern  the  resist- 
ance of  built  columns  may  be  summed  up  as  follows : 

"The  material  should  be  disposed  as  far  as  possible  from 
the  neutral  axis  of  the  cross-section,  thereby  increasing  R ; 

' '  There  should  be  no  initial  internal  stress ; 

"  The  individual  portions  of  the  column  should  be  mutually 
supporting ; 

"The  individual  portions  of  the  column  should  be  so  firmly 
secured  to  each  other  that  no  relative  motion  can  take  place, 
in  order  that  the  column  may  fail  as  a  whole,  thus  maintaining 
the  original  value  of  R.  " 

The  experiments  given  by  Prof.  Burr  would  indicate  that 
a  closed  column  is  stronger  than  an  open  one,  due  to  the  fact 
that  the  edges  of  the  segments  are  mutually  supporting  when 
held  in  contact  by  complete  closure.  From  a  theoretical  stand- 
point, therefore,  the  Phoenix  column  is  undoubtedly  the  most 


COLUMNS.  201 

favorable  form  for  compression,  as  it  forms  a  closed,  and  thus 
mutually  supporting  section;  and  because  the  capacity  of 
columns  of  equal  areas  varies  as  the  metal  is  removed  from  the 
neutral  axis.  It  must  also  be  remembered  that  any  form  of 
column  having  a  maximum  and  minimum  radius  of  gyration 
is  not  economical  for  use  under  a  single  concentric  load,  as  the 
calculations  must  be  based  on  the  minimum  radius  of  gyration. 
The  metal  represented  by  the  excess  of  the  maximum  radius 
of  gyration  is  of  necessity  disregarded,  and  part  of  the  section 
is  thus  lost  or  wasted,  when  we  consider  the  ideal  efficiency  of 
the  column.  But  practice  does  not  always  support  theory, 
and  many  other  questions  besides  mere  form  arise  in  connection 
with  the  judicious  choice  of  a  section.  Indeed,  it  will  be  seen 
that  several  practical  considerations  in  the  use  of  columns  in 
buildings  call  for  a  form  very  different  from  the  ideal  circular 
section ;  such  points  as  the  transfer  of  loads  to  the  centre  of 
the  section,  the  maximum  efficiency  under  eccentric  loading, 
and  the  requirements  for  pipe-space  around  or  included  in  the 
column  form,  all  tend  seriously  to  restrict  the  use  of  closed  or 
circular  sections. 

Ordinary  Column  Formula. — To  determine  the  relative 
importance  of  these  practical  considerations  to  the  theoretical 
requirements  of  column  design,  consider  the  formula 


p  = 


where  /  =  ultimate  strength  in  pounds  per  square  inch; 
/"=  elastic  limit  of  the  material  in  compression; 
a  =  constant,  varying  according  to  end  bearings; 
/  =  length  of  column  in  inches ; 
r  =  radius  of  gyration  of  cross-section  m  inches ; 
x0  =  distance    of  application    of    eccentric    load    from 
centre  of  gravity  of  the  column  section,  in  inches ; 
yv  =  distance  of  extreme  fibres  from  centre  of  gravity 
of  column  section,  in  inches. 


202  ARCHITECTURAL   ENGINEERING. 

This  is  the  form  of  Gordon's  or  Rankine's  formula  for 
columns,  including  the  effect  of  eccentric  loading,  besides  the 
expressions  for  the  strains  in  the  column  due  to  the  uniformly 
distributed  load,  and  those  due  to  the  flexure  of  the  column. 
The  term  for  eccentric  loading  does  not  occur  in  the  ordinary 
form  of  Gordon's  formula,  but  in  building  construction  this 
term  must  not  be  neglected  in  considering  the  relative  impor- 
tance of  the  strains  to  which  the  great  majority  of  building 
columns  are  subjected.  The  girder  loads  are  necessarily 
applied  to  the  sides  of  the  columns,  and  unless  these  loads  are 
equal,  and  on  opposite  sides  of  the  columns,  the  eccentricity 
of  the  resultant  load  tends  to  increase  the  strains  on  the  side 
where  the  greater  load  occurs. 

Considering  now  the  three  terms  in  the  denominator  of  the 

previous  value  for  p,  the  first,  namely  I,  or  — ,  represents  the 

strain  due  to  the  uniformly  distributed  or  concentric  load. 
This,  of  course,  is  the  principal  strain  to  which  the  column  is 
subjected,  and  in  short  columns,  with  perfectly  concentric 
loads,  would  represent  the  only  load  or  condition  to  be  used 
in  proportioning  the  number  against  crushing. 

/2 
The  second  term  in  the  denominator,  a—^,  representing  the 

strain  due  to  the  flexure  or  bending  of  the  column,  is  usually 
so  small  that  it  really  makes  this  term  of  the  least  importance 
in  the  above  equation,  due  to  the  ordinarily  short  lengths  of 
columns  in  buildings,  and  to  the  fact  that  the  bases  or  ends  are 
broad  and  flat  bearing.  Prof.  J.  B.  Johnson  shows*  from 
examples  selected  from  actual  building  practice  in  a  sixteen- 
story  building,  that  the  value  of  this  term  varies  from  0.022  in 
the  basement  columns,  to  0.220  in  the  smallest  columns  of 
reduced  section  at  the  top  of  the  building. 

*  See  "  Modern  Framed  Structures,"  page  451. 


COLUMNS.  203 

The  third  term  of  the  denominator,  namely  -jpi   or  the 

expression  for  the  strains  due  to  eccentric  loading,  is  shown 
by  Prof.  Johnson  to  be  more  important  than  considerations  as 
to  flexure.  He  gives  an  ordinary  value  for  this  term  of  0.07 
or  more  in  basement  columns,  taken  from  the  same  building 
example  previously  quoted,  while  in  the  columns  for  the  upper 
floors  the  value  is  shown  to  be  0.6  or  0.7,  which,  in  these  small- 
section  columns,  "occasionally  doubles  the  section." 

These  figures  ' '  show  that  the  important  effects  of  eccen- 
tricity of  loading  increase  rapidly  as  the  section  of  the  column 
decreases,  and  that  the  importance  of  this  element  in  columns 
thus  eccentrically  loaded  is  three  or  more  times  as  great  as  that 
of  the  element  dependent  upon  the  flexure  of  the  column. 
These  effects  are  entirely  independent  of  the  character  of  the 
column,  varying  of  course  in  values  with  different  kinds  of 
columns,  but  always  true  when  the  loading  is  as  irregular  and 
eccentric  as  the  architecture  of  modern  high  buildings  necessi- 
tates." 

In  columns  of  one-story  lengths,  therefore,  where  the 
length  is  usually  under  90  radii,  considerations  as  to  flexure 
may  generally  be  disregarded,  and  the  differences  in  the  ideal 
strengths  of  the  various  sections  tend  to  disappear.  If  the 
columns  are  well  made,  and  subject  to  concentric  loads  only, 
almost  any  of  the  ordinary  column  sections  will  give  satisfac- 
tory results  if  used  with  ordinary  unit  stresses.  And  by  far  the 
larger  number  of  columns  used  in  modern  building  construction 
is  under  90  radii,  as  they  are  used  in  single-story  lengths  of 
from  10  to  14  ft.  The  determining  factors  in  a  selection  are, 
therefore,  such  practical  considerations  as  effect  columns  of 
these  lengths ;  so  that  the  ideal  disposition  of  the  metal  must 
be  considered  in  connection  with  other  very  important  require- 
ments. 


204  ARCHITECTURAL   ENGINEERING. 

Practical  Requirements  in  Column  Design. — The  follow- 
ing elements  of  design  should  be  carefully  considered : 

1.  Cost,  availability. 

2.  Shopwork,  and  workmanship  of  column. 

3.  Ability  to  transfer  loads  to  centre  of  column — eccentric 
loading. 

4.  Convenient  connections.      Splices. 

5.  Relation  of  size  of  section  to  small  columns. 

6.  Fireproofing  capabilities  of  the  section. 

Points  i  and  2  are  of  the  greatest  importance  to  the  owner 
and  builder,  and  often  govern  the  selection  of  the  column. 
Points  3,  4,  and  5  are  for  the  engineer's  consideration,  while 
point  6  is  of  chief  interest  to  the  architect  and  decorator. 

Cost,  Availability.  —  The  question  of  the  cost  of  the 
material  as  it  comes  from  the  mill  is  a  purely  commercial  one, 
depending  upon  the  market  price  per  pound  of  the  section 
used. 

The  prices  of  plain  beams,  channels,  Zees,  plates,  and 
angles,  vary  from  time  to  time,  as  fixed  by  agreement  among 
the  steel  producers,  and  while  Zees  may  sometimes  be  more 
expensive  than  beams  and  channels,  at  other  periods  it  will  be 
found  that  there  is  no  great  difference,  if  any,  between  the 
more  ordinary  marketable  shapes.  The  cost  of  the  raw 
material,  however,  will  practically  never  determine  the  relative 
costs  between  various  column  forms,  as  the  expense  of  manu- 
facture, the  weight  of  the  columns,  and  the  question  of  simple 
vs.  complex  details  and  the  duplication  of  members,  will  all 
influence  the  ultimate  cost  to  much  greater  extents  than  the 
simple  cost  of  the  plain  material.  All  of  the  special  columns, 
such  as  the  Phoenix,  Keystone  Octagonal,  Larimer,  and  Gray 
forms,  have  the  great  disadvantage  of  being  rolled  or  manu- 
factured by  certain  mills  only,  and  the  quickest  possible 
delivery  of  material  is  a  very  essential  point.  The  demands 
for  structural  steel  at  good  seasons  of  trade  in  this  country  are 


COLUMNS.  205 

so  great  that  it  is  often  next  to  impossible  to  secure  such 
prompt  delivery  of  material  as  is  required  for  the  completion 
of  a  large  building  within  the  contract  time.  The  contracts 
that  have  been  executed  in  American  cities  during  the  last 
three  or  four  years  have  undoubtedly  shown  the  most  wonder- 
ful construction  in  points  of  excellence  and  time  that  the  world 
has  ever  seen ;  and  it  is  said  of  a  large  building  in  New  York 
City  that  the  masonry  for  the  twelfth  story  was  laid  before  the 
mortar  at  the  first-floor  level  was  dry. 

The  steelwork  for  a  building  of  any  considerable  size  is 
almost  invariably  rolled  to  order,  and  the  best  arrangements 
as  to  time  of  deliveries  can  be  made  when  the  plans  call  for 
such  shapes  as  are  manufactured  by  several  competing  mills. 
The  conditions  of  orders  or  contracts  in  hand  may  preclude  the 
possibility  of  quick  deliveries  by  certain  mills  or  shops,  while 
if  the  material  be  of  common  marketable  forms,  the  contract 
may  be  placed  to  advantage  with  other  parties  better  able  to 
name  the  required  time  agreements. 

The  Phcenix  shape,  although  the  patent  has  long  expired, 
is  rolled  by  but  one  mill  in  this  country.  The  Keystone 
column  was  also  controlled  by  one  particular  mill,  but  this 
section  is  now  seldom,  if  ever,  used.  The  Larimer  column  is 
controlled  and  manufactured  by  a  single  mill,  while  the  Gray 
column  is  made  of  angles  and  is  consequently  easy  to  obtain 
as  to  material,  and  the  shop  labor  may  easily  be  executed  by 
any  first-class  plant,  but  the  privilege  of  use  must  be  secured 
at  an  additional  cost. 

Advantages  as  to  availability  are  therefore  possessed  by  the 
columns  which  can  be  most  readily  bought  and  manufactured, 
and  there  is  consequently  little  difference  between  any  of  the 
forms  shown  in  Figs,  in,  112,  and  113,  provided  the  sizes 
and  weights  of  material  are  limited  to  the  more  ordinary 
varieties. 


206 


ARCHITECTURAL  ENGINEERING. 


Shopwork  and  Workmanship. — With  the  present  uniform 
low  price  per  pound  of  most  of  the  steel  sections,  the  items  of 
shopwork  and  workmanship  become  of  far  greater  importance 


Larimer  column,  i  row  of  rivets. 

Plate  and  angles,  2  rows. 

Z-bar  column,  without  covers,  2  rows. 

4-section  Phoenix  column,  4  rows. 

Channel  column,  with  plates  or  lattice,  4  rows. 

Gray  column,  4  rows. 

Z-bar  column,  with  single  covers,  6  rows. 

Channels,  web-plate,  and  angles,  6  rows. 
Box  column  of  plates  and  angles,  8  rows. 
Latticed  angles,  8  rows. 
8-section  Phcenix  column,  8  rows. 
Z-bar  column  with  double  covers,  10  rows. 


FIG.  115.  —  Column 
Forms,  Showing 
Required  Punch- 
ing Operations. 

in  the  cost  of  the  completed  column  than  the  cost  of  the  sec- 
tion at  the  mill — assuming  the  sectional  area,  and  hence  the 
weight  per  foot,  to  be  the  same.  Lattice  bars,  fillers,  gussets, 
etc.,  add  just  so  much  more  weight,  without  increasing  the 


COLUMNS. 


207 


section,  and  must  therefore  be  considered  from  an  economical 
standpoint.  The  methods  of  riveting  the  sections  together  in 
the  various  forms  must  also  be  taken  into  account. 

The  number  of  rows  of  rivets  required,  and  the  consequent 
punching  operations,  are  shown  in  Fig.  115. 

The  Larimer  column,  manufactured  and  controlled  by 
Jones  &  Laughlins,  and  first  used  in  Chicago  in  the  Newberry 
Library  Building,  consists  of  two  I-beam  sections  bent  down 
along  the  middle  of  the  web,  the  two  beams  being  riveted 
together  with  a  small  I-beam  filler  between.  The  rivets  are 
spaced  3-in.  centres  for  about  18  ins.  from  each  end  of  the 
column,  and  then  5-in.  centres. 

Where  necessary  to  strengthen  the  column,  this  filler  is 
made  of  two  channel-sections,  back  to  back,  extending  out  on 
either  side  as  far  as  necessary.  Small  angles  are  riveted  to  the 
faces  of  the  I-beams,  and  a  plate  is  riveted  across  the  top,  on 
which  the  girders  and  column  rest  (Fig.  1 16).  Where  only 
two  girders  occur,  the  remaining  faces  are  used  to  rivet  the 
upper  column  to  the  plate.  Another  method  has  been  used 
instead  of  the  small  angles,  in  the  shape  of  a  square  or  octag- 


FIG.  116.— Detail  of  Larimer 
Column. 


FIG.  117. — Detail  of  Larimer 
Column. 


onal  sheet  which  is  cut  from  the  centre  out,  part  way  to  the 
edge,  and  the  lips  so  formed  are  bent  down  in  a  press,  thus 
making  a  solid  and  continuous  angle.  Still  another  detail  has 
been  made  by  pressing  out  in  a  hydraulic  machine  a  circular 


2o8  ARCHITECTURAL  ENGINEERING. 

sheet  to  conform  in  the  lower  part  to  the  shape  of  the  outside 
of  the  flanges  of  the  column  (Fig.  117).  In  this  way  not  only 
the  upper  flange,  but  the  vertical  flange  also,  is  made  continuous 
around  the  top  of  the  column.  Also  the  thickness  of  the  hori- 
zontal flange  is  retained  uniform,  the  thickness  of  the  vertical 
flange  being  somewhat  tapered. 

This  column  possesses  one  great  disadvantage  in  the 
smaller-sized  columns.  This  lies  in  the  difficulty  of  driving 
the  rivets  that  connect  the  bracket  angles  with  the  I-beam 
flanges.  In  a  6-in.  column,  where  5-in.  I-beams  are  used,  or 
in  smaller  columns,  it  is  often  very  difficult  on  account  of  inter- 
ference to  drive  the  rivets  through  the  holes,  unless  the  rivets 
are  driven  in  a  slanting  direction.  This  often  results  in  weak 
connections. 

The  Larimer  column  is  not  adapted  to  heavy  work,  as  the 
form  of  the  section  does  not  permit  of  easy  reinforcement  under 
large  loads.  The  splicing  facilities  are  also  bad,  as  horizontal 
cap-plates  must  invariably  be  used.  The  difficulty  of  shopwork 
in  the  bending  of  the  I-beams  is  also  very  liable  to  result  in 
poor  workmanship,  unless  the  greatest  care  is  exercised ;  and 
riveting  through  the  beam  flanges  is  apt  to  contribute  to  shop 
difficulties  and  imperfections.  In  general,  it  may  be  said  that 
all  column  sections  composed  of  combinations  of  I-beams  are 
difficult  to  manufacture,  on  account  of  the  trouble  in  riveting 
through  the  bevelled  flanges. 

The  Larimer  column  has  had  no  very  extensive  use  in  high 
building  construction,  and  is  now  seldom  used  in  any  impor- 
tant work. 

The  Phoenix  column  has  been  used  in  several  prominent 
high  buildings,  notably  in  the  "World"  and  Dun  buildings, 
New  York  City,  but  on  account  of  the  difficulty  of  connections, 
which  will  be  discussed  under  a  later  heading,  this  form  has 
gradually  lost  favor.  In  the  matter  of  shopwork,  the  Phoenix 
column  has  disadvantages  as  regards  the  special  devices  neces- 


COLUMNS.  209 

sary  to  secure  adequate  connections,  and  in  the  limitations  as 
to  the  rolling  of  the  special  segmental  forms. 

The  Gray  column  requires,  as  will  be  seen  by  Fig.  115, 
no  less  than  sixteen  punching  operations  for  the  four  rows  of 
rivets  employed,  besides  the  additional  expense  of  the  special 
shaped  tie-plates  which  are  necessary  to  connect  the  four  indi- 
vidual struts,  but  which  do  not  contribute  to  the  effective  area. 
This  column  has  been  used  in  a  number  of  prominent  buildings, 
including  the  Ellicott  Square  and  Guaranty  Buildings,  Buffalo, 
the  Reliance  and  Fisher  Buildings,  Chicago,  and  the  Chamber 
of  Commerce  and  Mabley  Buildings  in  Detroit,  but  by  many 
engineers,  this  form  of  column  is  not  regarded  with  favor,  as 
will  be  pointed  out  under  the  later  consideration  of  eccentric 
loading. 

The  same  objections  as  to  the  superfluous  metal  required 
by  tie-plates  which  cannot  be  counted  on  as  available  sectional 
area,  and  the  weakness  under  eccentric  loading,  are  true  of 
the  standard  dimension  Z-bar  column. 

Columns  made  of  latticed  angles  or  channels  are  usually 
limited  to  very  moderate  loads  in  upper  stories,  or  in  buildings 
of  no  very  considerable  height.  The  lattice  bars  and  tie-plates 
constitute  excess  material,  besides  contrfbuting  largely  to  the 
cost  of  manufacture.  Columns  made  of  channels  and  web- 
plates  are  very  satisfactory  where  the  loads  do  not  become  so 
great  as  to  require  more  than  one  cover-plate.  In  heavier 
sections,  a  box  column  of  plates  and  angles  becomes  more 
desirable. 

For  buildings  of  moderate  height  and  loading,  no  more 
advantageous  section  can  be  employed  than  the  Z-column. 
In  such  cases,  the  advantages  of  simplicity  of  shop  labor, 
requiring  but  two  rows  of  rivets,  the  availability  of  material, 
and  the  facility  for  obtaining  good  girder  connections  and 
column  splices,  outweigh  the  advantages  possessed  by  any 
other  column  form.  For  higher  buildings,  or  heavier  loads, 


210  ARCHITECTURAL  ENGINEERING. 

where  the  required  sectional  area  is  greater  than  can  be 
obtained  by  using  Z-bar  columns  without  cover-plates,  the 
box  column  of  plates  and  angles  will  be  found  most  satisfactory. 
This  column  form  possesses  great  advantages  regarding  con- 
nections, in  that  square  surfaces  are  always  presented.  Box 
columns  were  used  in  the  Masonic  Temple,  the  highest  build- 
ing in  Chicago,  and  in  the  Park  Row  Building,  the  highest 
structure  in  New  York  City.  In  the  Masonic  Temple,  latticing 
was  used  on  two  sides  of  the  columns  in  the  upper  stories. 

The  character  of  workmanship  will  vary  somewhat  with  the 
different  shops,  as  well  as  with  the  different  sections  used. 
The  reputation  of  the  shop,  seconded  by  careful  shop  inspec- 
tion, will  largely  determine  the  excellence  of  the  workman- 
ship. 

Ability  to  Transfer  Loads  to  Centre  of  Column— Eccen- 
tric Loading. — It  will  be  seen  at  a  glance  that  some  of  the 
sections  under  consideration  are  totally  unfitted  for  the  transfer 
of  loads  to  the  centre  of  the  column.  The  conditions  in 
designing  a  framework  are  seldom  so  favorable  as  not  to  require 
many  of  the  columns  to  be  loaded  unsymmetrically,  for  even 
where  equal-size  girders  meet  on  opposite  sides  of  a  column, 
one  of  them  may  carry  a  heavy  live  load  while  the  other  may 
be  required  to  carry  only  the  dead  load  of  the  floor  system, 
though  both  are  figured  for  the  same  proportion  of  total  loads. 
In  more  extreme  cases,  wide  variations  often  exist  in  the  sizes 
of  the  opposite  girders,  as  in  the  loads  which  they  carry ;  and 
in  exterior  columns,  unless  designed  with  particular  regard  to 
concentric  loading,  eccentricity  will  almost  always  occur  to  a 
greater  or  less  degree. 

Views  as  to  the  importance  and  treatment  of  eccentric 
loads  vary  considerably  with  different  designers.  In  many 
large  and  important  buildings,  eccentric  loading  has  had  little, 
if  any  consideration,  and  some  writers  who  might  properly  be 
called  authorities,  hold  that  any  very  careful  calculations  for 


COLUMNS.  211  ' 

eccentricity  are  unnecessary,  inasmuch  as  a  single  eccentric 
load  usually  constitutes  so  small  a  percentage  of  the  total  load 
on  the  column,  and  further  because  the  building  laws  in  most 
large  cities  require  such  large  factors  of  safety,  both  in  the 
assumed  loads  and  in  the  unit-stresses  employed  in  propor- 
tioning the  members. 

Other  authorities  and  designers  lay  particular  emphasis  on 
the  treatment  of  eccentric  loading,  as  the  relatively  short 
lengths  of  building  columns  is  considered  as  being  more  than 
offset,  in  many  if  not  most  cases,  by  the  conditions  of  eccen- 
tricity of  loading.  Calculations  for  eccentric  loads  are  tedious 
and  unsatisfactory  as  far  as  present  formulae  are  concerned, 
notwithstanding  which  they  are  still  required  in  any  work  of 
importance  or  magnitude. 

It  was  shown  earlier  in  the  examples  quoted  from  Prof. 
Johnson's  "Modern  Framed  Structures,"  that  the  term  for 
eccentric  loading  in  Gordon's  or  Rankine's  formula  was  of 
much  more  importance  in  cases  taken  from  actual  practice  than 
the  term  representing  the  flexure  or  bending,  and  dependent 
upon  the  length.  Mr.  Leopold  Eidlitz,  in  a  theoretical 
analysis  of  the  strength  of  pillars,  states  that:  * 

"  Engineering  handbooks  published  by  various  rolling  mills 
and  others  having  the  authority  of  competent  engineers  com- 
pute pillars  planed  top  and  bottom  or  pillars  of  continuous 
length  held  in  position  by  girders  and  beams  abutting  upon 
them,  and  fastened  to  them  with  bolts  or  rivets  at  every  story, 
as  subject  to  compound  flexure  under  a  safe  load. 

"Deflection  of  pillars  usually  employed  in  building  are 
exceedingly  small  under  safe  loads ;  for  instance,  deflections 
of  wrought-iron  pillars  from  12  to  20  diameters  long  (under 
loads  varying  from  11,790  to  10,600  Ibs.)  are  0.003  to  0.022 
diameter. 

*  See   "The   Strength   of    Pillars:    An  Analysis,"  by  Leopold  Eidlitz. 
Transactions  Am.  Soc.  C.  E. ,  vol.  xxxv. 


212  ARCHITECTURAL   ENGINEERING. 

' '  The  movement  of  the  pillar  head  from  a  horizontal  posi- 
tion to  one  sufficiently  inclined  to  correspond  with  the  stated 
deflections  is  so  small  that  the  strains  generated  are  inopera- 
tive, because  the  movement  is  abundantly  practicable  within 
the  limits  of  inaccuracy  of  construction  such  as  exists  in  prac- 
tical building. 

''If  bending  were  continued  to  the  breaking  point,  then, 
no  doubt,  compound  flexure  would  ensue,  but  in  the  absence 
of  loads  greater  than  safe  loads,  pillars  bend  with  single 
flexure." 

Also,  the  same  author  calls  attention  to  the  importance  of 
eccentric  loading  as  follows: 

' '  Breaking  loads  for  cast-iron  pillars  and  for  wrought-iron 
pillars,  also  the  respective  safe  loads,  being  computed  on  the 
assumption  that  the  load  is  applied  in  the  centre  of  gravity  of 
the  pillar,  it  is  essential  that  this  should  be  the  case  accurately, 
inasmuch  as  slight  deviations  cause  material  differences  in  their 
magnitude.  A  cast-iron  pillar  10  ins.  in  diameter  and  1 1.9  ft. 
in  length  (L  equal  14.3)  will  break  under  a  load  of  32,000  Ibs. 
per  inch  metal  area,  when  the  load  is  placed  in  the  centre  of 
gravity  of  the  pillar.  When  placed  i  in.  to  one  side  of  the 
centre  it  will  break  under  21,150  Ibs.,  and  when  placed  0.5  in. 
off  the  centre  of  gravity  of  the  pillar  the  breaking  load  is  26,050 
Ibs.  or  19  per  cent,  less  than  when  exactly  in  the  centre." 

"It  is  also  a  well-known  fact  that  eccentric  loading  is 
under-rated  in  the  absence  of  a  working  formula  which  by  one 
process  gives  eccentric  breaking  loads  as  compared  with  centric 
breaking  weights  and  the  strength  of  material. 

' '  These  considerations  have  resulted  in  the  analysis  of  the 
strength  of  pillars,  and  go  to  show  that  safe  loads  are  governed 
by  maximum  strain,  and  not  by  breaking  weights,  or  else  many 
buildings  constructed  under  the  old  system  would  show  more 
serious  defects  than  have  been  discovered  as  yet,  and  also  that 
with  a  table  of  safe  loads  at  the  command  of  the  engineer  or 


COLUMNS.  213 

architect,  no  eccentric  load,  no  matter  how  small,  should  be 
neglected  on  the  plea  that  the  factor  of  safety  being  applied  to 
weights  instead  of  strains  covers  a  multitude  of  defects  not 
critically  examined." 

Every  care,  therefore,  which  may  be  taken  in  the  treatment 
of  eccentric  loads  will  surely  add  to  the  capacity  of  the  column, 
for  an  eccentric  load  will  necessitate  the  use  of  a  less  mean 
unit-stress  than  where  the  load  is  applied  directly  to  the  centre 
of  gravity  of  the  column  section. 

Method  of  Treatment  for  Eccentric  Loads.  —  As  has  been 
previously  said,  the  calculations  are  extremely  tedious  and 
lengthy,  but  until  some  more  simple  and  rational  formula  is 
devised,  eccentric  loading  should  be  treated  as  follows: 

(a)  Determine  the  section  required  for  the  total  load,  both 
eccentric  and  concentric,  the  whole  considered  as  concentric. 

(7?)  Find  y^  ,  or  half  the  width  of  the  column. 

(c)  Find  the  radius  of  gyration  r  in  the  plane  of  eccentric 
loading. 

(*/)  Find  the  area  of  section  required  to  resist  the  bending 
moment  arising  from  the  eccentric  loading,  using  radius  of 
gyration  and  yl  as  in  the  assumed  section.  The  moment  due 
to  eccentric  loading,  MQ  ,  will  equal  the  eccentric  load  X  its 
distance  of  application  from  the  axis  of  column,  and  as 


we  have      A  = 


(e)  If  this  second  area  can  be  added  to  the  first  assumed 
area  of  section  without  changing  the  radius  of  gyration  and  yl 
materially,  it  may  be  done,  thus  obtaining  the  total  area  of 
section  without  a  new  solution. 

(_/")  If,  however,  the  radius  of  gyration  and  yl  are  changed 
materially,  in  providing  for  the  new  area  required,  then  a  new 
assumed  sectional  area  is  taken,  radius  of  gyration  and^  found 
for  it,  the  solution  proceeding  as  before. 


214  ARCHITECTURAL  ENGINEERING. 

Such  calculations  involve  the  use  of  the  radius  of  gyration, 
and  complete  tables  are  therefore  necessary  giving  the  moments 
of  inertia  and  radii  of  gyration  for  all  ordinary  column  sections 
of  the  type  employed. 

Other  designers  use  Rankine's  formula  for  eccentric  load- 


where f  =  fibre  stress ; 

5  =  section  required ; 

P  =  concentric  load ; 

Pl  =  eccentric  load ; 

X9  =  distance  from  neutral  axis  to  extreme  fibre ; 

Xl  =  distance  from  neutral  axis  to  point  of  application 

of  eccentric  load ; 
/  =  the  moment  of  inertia  of  the  section. 

Girder  Connections  ;  Central  Loading. — However  carefully 
or  slightly  the  calculations  for  eccentric  loading  may  be 
treated,  certain  practical  considerations  at  least  must  be 
regarded  in  an  attempt  to  secure  the  best  possible  transfer  of 
girder  loads,  etc.,  to  the  centre  of  gravity  of  the  column  sec- 
tion. It  is  very  important  that  the  brackets  or  girder  seats 
which  transmit  the  girder  loads  to  the  columns  should  be 
designed  with  reference  to  bringing  such  loads  to  the  centre  of 
the  column  as  soon  as  possible,  and  also  that  the  column 
should  be  capable  of  acting  as  a  unit  under  the  application  of 
such  loads. 

In  Fig.  1 1 8,  showing  the  connections  between  girders  and 
the  Gray  column,  it  will  be  seen  that  the  girder  loads  are  not 
directly  transmitted  to  the  column  centre,  nor  can  they  be  in 
any  proper  manner,  owing  to  the  absence  of  continuous  webs. 

*See  Rankine's  "  Applied  Mechanics,"  p.  305. 


COLUMNS. 


215 


For  short  pillars,  where  flexure  may  be  disregarded,  and  under 
concentric  loads  only,  this  form  of  column  may  be  satisfactory, 
but  under  eccentric  loading,  or  under  any  transverse  stresses, 
such  as  wind  pressures,  this  type  is  decidedly  objectionable. 
The  Gray  column,  as  shown  in  Fig.  118,  is  composed  of  four 


3       ( 

3       C 

> 

•  • 

i  "s.':«i 

•     •  :O  O 

O  O 

i   ""( 

r 

^ 

• 

J  r 

i 

•  ''       ° 

•   • 

I     i'.'.4 

O: 

•JO  0  0  O 

j 

FIG.  118.— Detail  of  Gray  Column 
and  Connecting  Girders. 


FIG.  119.— Detail  of  Phoenix 
Column. 


pairs  of  angles,  connected  by  bent  tie-plates  which  are  usually 
made  8  ins.  or  9  ins  wide,  and  spaced  2  ft.  6  ins.  centres. 
These  tie-plates  cannot  transmit  either  eccentric  or  transverse 
loads  from  the  point  of  application  to  the  several  flanges,  nor 
from  one  flange  to  the  other,  owing  to  the  lack  of  any  form  of 
continuous  web.  The  column  loads,  if  eccentric,  are  borne 


210  ARCHITECTURAL  ENGINEERING. 

mainly  by  the  T-shape  to  which  the  girder  is  connected,  and 
not  by  the  whole  column,  while  transverse  stiffness  must  be 
measured  by  the  dimensions  of -the  component  T-sections,  and 
not  by  the  width  of  the  column  itself. 

The  ' '  standard  dimension  ' '  Z-bar  column  is  open  to  the 
same  criticism,  as  the  tie-plates  which  connect  the  Z-sections 
are  spaced  3  or  4  ft.  centres,  thus  making  the  distribution  of 
eccentric  or  transverse  loads  purely  problematical.  The 
Larimer  column  has  a  continuous  connection  between  the  two 
component  I-beams,  but  the  connection  employed  cannot  fulfil 
the  office  of  a  continuous  web-plate  in  transmitting  the  neces- 
sary shears.  "  In  other  words,  no  pillar  is  properly  designed 
unless  it  has  a  web  which  forms  a  continuous  bracing  like  the 
web  of  a  girder  or  truss." 

The  use  of  Phcenix  columns  with  "pintle"  connections 
would  seem  to  possess  the  greatest  theoretical  advantages 
under  this  consideration  of  central,  loading.  See  Fig.  119. 
This  system  has  been  employed  under  very  heavy  loading, 
with  pintle-plates  over  8  ft.  deep.  Unless  pintle-plates  can  be 
used,  however,  any  form  of  closed  column  is  bad  under,  the 
consideration  of  central  loading,  and  here  the  practical  method 
of  loading  columns  conflicts  seriously  with  the  use  of  an  ideal 
closed  section. 

The  connections  of  girders  to  Z-bar  columns  are  better 
than  in  most  of  the  forms  of  closed  columns,  and  even  when 
cover-plates  are  used  this  is  so  (though  not  in  as  great  a 
degree),  as  the  column  may  almost  always  be  turned  so  that 
the  heavily  loaded  beam  may  be  introduced  between  the 
Z-flanges.  This  advantage  is  especially  great  at  the  tops  of 
buildings  where  small  columns  without  cover-plates  carry 
beams  with  heavy  loads,  for  here  the  column  is  open  on  all 
four  sides,  so  that  all  loads  may  be  taken  to  the  centre  of  the 
column.  The  box  column  of  plates  and  angles,  however, 
possesses  this  same  advantage,  though  not  to  as  great  an 


COLUMNS.  217 

extent  in  the  lighter  sections.  The  possibility  of  changing 
the  section  of  a  column  so  that  the  radius  of  gyration  shall  be 
greater  or  less  in  either  direction  across  the  section  must  not 
be  overlooked,  for  if  all  the  loads  occur  on  one  side  of  a 
column,  it  is  a  great  advantage  to  have  the  radius  of  gyration 
greater  in  the  line  of  the  load. 

Convenient  Connections  —  Splices.  —  These  features  in 
column  construction  are  very  important  ones,  and  as  column 
splices  usually  occur  at  or  near  the  floor-levels,  where  the  con- 
nections between  the  columns  and  the  floor  system  occur,  it  is 
best  to  consider  these  two  details  together. 

Satisfactory  details  can  easily  be  made  for  almost  any  of 
the  various  column  sections,  provided  continuous  column 
splices  are  not  required,  and  provided  the  beams  or  girders  are 
symmetrically  placed  and  loaded,  and  all  occur  at  the  same 
elevation ;  but  where  irregularity  in  the  girders  is  necessitated, 
on  account  of  load,  position  and  elevation,  as  is  almost  always 
the  case,  and  where  continuous  vertical  splices  are  desired,  as 
should  always  be  secured  if  possible,  it  will  be  found  that  the 
various  column  forms  differ  widely  in  their  adaptability  to  these 
conditions. 

It  will  be  seen  at  a  glance  that  several  of  the  column  types 
are  totally  unfitted  for  satisfactory  vertical  splicing,  or  else  for 
irregular  girder  connections,  or  possibly  for  both.  Thus  the 
Larimer  column  oflers  no  practical  method  of  splicing  except 
through  the  use  of  horizontal  cap-plates,  while  very  heavy 'or 
irregular  girder  loads  are  difficult  and  oftentimes  impossible  to 
support,  due  to  the  difficulties  experienced  in  making  proper 
connections  to  the  very  limited  column  surfaces. 

The  use  of  cap-plates  in  Phcenix  columns  is  as  shown  in 
Fig.  1 20,  consisting  of  angles  riveted  to  the  extended  fillers, 
on  which  a  plate  is  placed,  holding  the  girders  and  the  super- 
imposed column.  The  upper  column  is  held  down  by  angles 
riveted  to  the  bed-plate.  Under  eccentric  loading  a  consider- 


218 


ARCHITECTURAL  ENGINEERING. 


able  tilting  movement  occurs  in  this  column,  unless  used  with 
pintle-plates,  as  before  suggested.  Connections  were  made 
with  bent  plates  in  the  Old  Colony  Building,  Chicago,  as 
shown  in  Fig.  121. 

In  the  "World"  Building,  New  York  City,  8-section 
Phoenix  columns  were  employed,  with  horizontal  diaphragms, 
or  bed-plates  for  splices  and  girder  connections,  very  similar  to 


FIG.  120.— Detail  of  Phoenix 
Column  Splice. 


FIG.  121. — Detail  of  Phoenix  Column 
used  in  Old  Colony  Building. 


the  detail  shown  in  Fig.  120.  In  the  R.  G.  Dun  Building,  New 
York  City,  8-section  Phcenix  columns  were  spliced  by  means 
of  vertical  diaphragms  or  pintle-plates,  these  being  in  the  form 
of  an  X,  and  shop  riveted  to  the  lower  column  section.  The 
ends  of  the  columns  were  faced,  and  slots  were  left  between 
the  segments  of  the  upper  section  to  receive  the  pintle-plates 
projecting  above  the  joints,  the  connection  being  field  riveted 
after  bringing  into  proper  position.  See  Fig.  122.  All  of 
these  connections  are  rather  complicated,  and  result  in  a  large 
amount  of  work  in  the  preparation  of  details  and  in  shop  labor. 
Also  the  necessary  changes  in  the  diameters  of  Phcenix 
columns  for  members  of  different  capacities  make  butt-joints 
impossible  except  through  the  use  of  horizontal  bearing  plates. 
Before  the  introduction  of  vertical  splices,  Z-bar  columns 


COLUMNS. 


219 


were  generally  detailed  as  shown  in  Fig.  123,  taken  from  the 
Monadnock  Building,  Chicago.  The  column  shafts  were 
placed  centrally  over  one  another,  with  a  horizontal  cap-plate 
between  (varying  from  •£  in.  to  I  in.  in  thickness),  which  was 
attached  to  the  column  shafts  by  means  of  upper  and  lower 


FIG.  122.— Detail  of  Phoenix  Column 
Splice  used  in  R.  G.  Dun  Build- 
ing, New  York. 


FIG.  123. — Detail  of  Z-bar 
Column  Splice.  Monad- 
nock  Building. 


connection  anfks.  The  girders  rested  on  the  cap-plates 
direct,  and  if  t%e  loads  were  large,  vertical  stiffening  angles 
were  riveted  to  the  column  shaft  beneath,  to  aid  in  supporting 
the  bed-plate  as  shown  in  the  illustration.  The  girders  were 
riveted  or  bolted  through  the  lower  flanges  to  the  bed-plate, 
and  through  the  upper  flanges  to  a  knee  attached  to  the  upper 
column  section.  Small  steel  "gibs"  or  wedges  were  some- 
times dropped  in  between  the  top  ends  of  the  girders  and  the 
column  shaft,  to  take  up  any  possible  transverse  stresses.  If 


ARCHITECTURAL   ENGINEERING. 


the  girders  occurred    at  different    levels,   or  were  of  different 
sizes,  cast-iron  bolsters  were  used,  resting  on  the  cap-plates. 
Single-story  lengths  of  box  columns  of  plates  and  angles 
are  often  detailed   as   shown    in 
Fig.    124.     f-in.    cap-plates  are 
used,  with  angle-knees  connect- 
ing to  the  upper  and  lower  column 
sections. 

These    methods    (Figs.     125 
and  124)  of  connecting  the  tiers 

FIG.  124.— Detail  of  Box-          of  columns  together  by  means  of 
column  Splice.  cap-plates  and  small  connection 

angles,  are  far  from  satisfactory,  and  in  good  classes  of  work 
have  been  entirely  discontinued.  Such  details  may  be  suffi- 
cient to  prevent  lateral  displacement,  but  becaust  of  the  bend- 
ing or  elasticity  of  the  horizontal  bed-plates  and  connection 
angles,  and  the  large  ratio  of  the  height  of  the  column  to  the 
base,  these  horizontal  splices  contribute  very  little  to  the 
rigidity  of  the  structure. 

The  overturning  or  lift  on  the  windward  side  is  almost 
always  less  than  the  resistance  due  to  dead  weight;  but  the 
shear  is  liable  to  be  overlooked,  tending,  as  it  does,  to  topple 
over  all  of  the  columns  of  a  story.  The  column  connection 
described  is  not  stiff  enough  to  prevent  a  slight  movement, 
which  can  be  prevented  by  wind-bracing  only;  and,  even  with 
wind-bracing,  it  introduces  a  weakness  of  the  column  at  the 
floor-level,  which  can  largely  be  obviated  by  means  of  con- 
tinuous columns. 

Vertical  Column  Splices. — In  the  Masonic  Temple,  the 
use  of  two-storied  column  lengths  was  first  tried,  as  an  addi- 
tional factor  of  stiffness  in  so  high  a  building,  with  the  joints 
"  staggered, "  or  each  column  breaking  joints  with  its  neighbor. 
The  next  step  was  to  discard  the  bed-plates  entirely,  using; 


COLUMNS.  221 

vertical  connection-plates  for  all  column  splices.  Fig.  125 
shows  a  column  splice  with  connections  for  the  floor-girders 
and  wind-bracing,  employed  in  the  Pabst  Building,  Milwaukee, 
by  S.  S.  Beman,  architect.  The  floor-girders  are  made  of 
latticed  channels,  and  the  sway-rods  are  connected  to  the 
vertical  splice-plates  of  the  columns,  much  as  the  laterals  in 
bridge-work  are  connected  to  the  chords. 


FlG.  125. — Detail  of  Column  Connections  and  Wind-bracing. 
Pabst  Building,  Milwaukee. 

The  following  clauses  relating  to  the  splicing  of  the  Gray 
columns  used  in  the  Reliance  Building  are  from  the  specifica- 
tions for  the  steelwork:  "The  columns  will  be  made  in  two- 
story  lengths,  alternate  columns  being  jointed  at  each  story. 
The  column  splice  will  come  above  the  floor,  as  shown  in  the 
drawings.  No  cap-plates  will  be  used.  The  ends  of  the 
columns  will  be  faced  at  right  angles  to  the  longitudinal  axis 
of  the  column,  and  the  greatest  care  must  be  used  in  making 
this  work  exact.  The  columns  will  be  connected,  one  to  the 
other,  by  vertical  splice-plates,  sizes  of  which,  with  number  of 
rivets,  are  shown  on  the  drawings.  The  holes  for  these 


222 


ARCHITECTURAL   ENGINEERING. 


splice-plates  in  the  bottom  of  the  column  shall  be  punched 
|  in.  small.  After  the  splice-plates  are  riveted  to  the  top  of 
the  column,  the  top  column  shall  be  put  in  place  and  the  holes 

reamed,  using  the  splice-plates 
as  templates.  The  connections 
of  joists  or  girders  to  columns 
will  be  standard  wherever  such 
joists  or  girders  are  at  right 
angles  to  connecting  faces  of 
columns.  Where  connections  are 
oblique,  special  or  typical  details 
will  be  shown  on  the  drawings.  '  ' 
Fig.  126  illustrates  a  typical 
column  splice  in  the  Reliance 
Building,  at  a  point  where  the 
bay-window  framing  joins  the 
column. 

In  considering  the  subject  of 


FIG.  126. — Detail  of  Column 
Splice.     Reliance  Building. 


wind-bracing'  in  the  following  chapter,  it  will  be  seen  that 
rigid  connections  between  the  individual  columns  themselves 
and  between  the  columns  and  the  floor-girders,  contribute  an 
element  of  resistance  of  very  considerable  value  to  the  struc- 
ture, and  this  rigidity  of  the  joints  is  particularly  valuable  where 
no  special  system  of  trussing  is  provided  to  resist  the  wind 
strains.  If  complete  vertical  splices  are  used,  the  columns  are 
made  practically  continuous,  or  a  unit  from  foundation  to  roof, 
and  failure  can  only  occur  by  breaking  or  bending  ;  and  if  such 
splices  are  further  supplemented  by  web  connections  between 
the  columns  and  the  girders,  the  resultant  joint  or  assemblage 
of  joints  will  prove  as  simple  as  it  is  efficient.  Fig.  127  illus- 
trates these  connections,  as  used  in  the  American  Surety  Co.  's 
Building,  New  York.  This  figure  also  shows  the  connection 
of  the  sway  bracing. 

The  necessity  of  continuity  in  the  columns  and  web  con- 


COLUMNS.  223 

nections  for  the  girders  should  not  be  limited  to  cases  in  which 
no  additional  wind-bracing  is  provided,  nor  should  efficient 
wind-bracing  be  neglected  even  with  these  additional  factors, 
as  will  be  pointed  out  more  fully  in  Chapter  VIII. 

Advantages,  therefore,  as  regards  convenient  connections 
and  splices,  or  as  regards  efficient  connections  and  efficient 
splices,  are  found  to  result  principally  through  the  use  of 
rectangular  or  box-column  forms,  such  as  the  Z-bar  column, 
or  those  made  of  plates  and  angles  or  plates  and  channels. 
These  types  present  square  surfaces  for  connections  with  the 
girders,  thus  allowing  web  splices  if  desired ;  bracketing  for 
irregularly  placed  beams  can  be  easily  cared  for,  and  continuous 
vertical  splices  can  generally  be  arranged  for  all  ordinary  cases 
by  introducing  fillers  where  the  change  in  size  is  not  too  great. 
Under  these  considerations  the  Z-column  with  or  without 
cover-plates,  and  the  plate  and  angle  column  as  shown  in  Fig. 
127,  are  unsurpassed. 

Relation  of  Size  of  Section  to  Small  Columns. — It  is  not 
generally  desirable  in  building  construction  to  have  a  very 
small  column  in  the  upper  stories,  because  girder  loads  are  so 
much  heavier,  proportionately,  than  the  column  loads.  Some- 
times as  many  as  six  beams  must  connect  with  an  upper-story 
column  at  one  level,  and  in  such  cases  it  is  almost  impossible 
to  make  good  connections  with  a  small  column. 

It  is  therefore  advisable  to  use  some  type  of  column  which, 
under  these  conditions,  will  allow  of  sufficient  size  or  surfaces 
to  obtain  the  required  connections,  and  which  will  still  not 
require  excess  or  waste  material  through  providing  such  form. 
In  this  respect,  Z-bar  columns  are  often  undesirable,  as  a 
minimum  size  6-in.  column  may  be  insufficient  for  the  girder 
connections,  and  any  increase  in  size  is  attended  by  a  radical 
increase  in  weight.  A  thickness  of  metal  less  than  T5^  in. 
should  never  be  used,  and  a  minimum  thickness  off  in.  is  better 
for  conservative  practice.  Any  form,  therefore,  which  calls 


224  ARCHITECTURAL  ENGINEERING. 

for  any  amount  of  metal  at  or  near  the  centre  of  gravity  of  the 
section,  such  as  columns  of  the  I  form  and  Z-bar  sections,  is 
undesirable  under  these  conditions,  and  a  form  possessing  a 


FIG.   127. — Detail  of  Girder  and  Column  Connections.     American  Surety 
Co.'s  Building,  New  York. 

large  radius  of  gyration  for  a  minimum  of  metal  will  be  found 
preferable. 

Fireproofing  Capabilities  of  the  Section. — The  rectangular 
column  sections  will  not,  of  course,  fireproof  as  compactly  as 
the  circular  sections,  but  when  the  room  thus  lost  is  used  for 
"pipe-space,"  as  is  becoming  more  and  more  frequent,  this 


COLUMNS.  225 

point  has  great  value  in  the  estimation  of  architects.  In  the 
Columbus  Building,  Chicago  (1893),  a  square  hole  was  cut  in 
all  of  the  bed-plates  of  the  columns  to  allow  the  passage  of 
pipes  inside  of  the  column  areas.  Such  a  cutting  of  bed-plates 
cannot  be  too  severely  condemned.  The  increased  use,  how- 
ever, of  vertical  splices  in  columns,  instead  of  horizontal  bed- 
and  cap-plates,  allows  all  water-,  waste-,  and  vent-pipes  to  be 
carried  up  along  the  side  of  the  metal  columns,  and  inside  the 
fireproofing  slabs,  where  the  room  may  be  had  without  too 
much  waste.  It  is  not  advisable  to  place  any  piping  inside  of 
the  metal  columns,  and  hence  such  sections  as  the  Phoenix  and 
Keystone  Octagonal  offer  no  advantages  in  this  respect.  The 
columns  of  plates  and  angles,  channels,  Zees,  and  the  Gray 
column,  all  allow  considerable  pipe-space  within  the  minimum 
circular  or  rectangular  enclosure  for  fireproofing. 

It  would  seem,  however,  that  separate  ducts  in  the  walls 
or  along  the  sides  of  the  columns  for  all  piping  would  be  far 
better  than  such  concealed  risers.  Separate  ducts  would  result 
in  increased  outlay,  but  they  would  offer  the  great  advantage 
of  allowing  inspection  of  all  piping  whenever  and  wherever 
desired. 

It  sometimes  becomes  desirable,  for  architectural  effect,  to 
keep  the  column  sizes  within  very  limited  areas.  Figs.  128 
and  129  show  two  column  forms  which  were  used  in  the 
Waldorf-Astoria  Hotel,  New  York,  where  a  heavy  concentra- 
tion of  metal  was  required  within  a  minimum  circular  form  to 
allow  the  use  of  enclosing  shells  of  polished  stone.  The 
column  shown  in  Fig.  128  was  composed  of  2  13"  52-lb. 
channels,  2  plates  20"  X  i">  2  plates  12^"  X  i">  2  plates 
10"  X  f",  and  4  angles  6"  x  3i"  X  f".  That  shown  in  Fig. 
129  was  made  of  8  angles  5"  X  3i"  X  H"»  2  plates  9"  X  I", 
2  plates  1 6"  X  'I",  and  4  plates  5"  X  f". 

Summary. — From  a  careful  weighing  of  the  foregoing 
practical  considerations  in  column  design,  it  will  be  found  that 


226 


ARCHITECTURAL  ENGINEERING. 


no  more  satisfactory  type  can 'be  adopted  than  the  box  column 
of  plates  and  angles.     This  section  has  been  employed  in  some 


FIG.  128. — Column  Section  used  in 
Waldorf  -  Astoria  Hotel,  New 
York. 


FIG.  129. — Column  Section  used  in 
Waldorf  -  Astoria  Hotel,  New 
York. 


of  the  heaviest  building  columns  ever  designed,  and  in  many 
of  our  most  important  high  buildings.  Box  columns  were  used 
in  the  Masonic  Temple  in  Chicago,  as  has  before  been  stated, 
and  in  the  Ivins  or  Park  Row  Building,  New  York.  In  the 
latter  structure  the  heaviest  column  was  designed  for  a  load  of 
2,900,000  Ibs.,  and  was  composed  of  3  web-plates  24"  X  ii"> 
4  covers  48"  X  H''»  an^  8  angles  6"  X  6"  X  yt ">  as  shown 
in  Fig.  1 30.  In  the  Waldorf-Astoria  Hotel  a  column  was  used 


FIG.  130. — Heavy  Column  Section.     FIG.   131. — Heavy  Column  Section. 
Park  Row  Building,  New  York.  Waldorf-Astoria  Hotel. 

as  shown  in  Fig.  131,  this  probably  constituting  the  heaviest 
pillar  ever  used  in  building  construction.  This  was  required 
to  support  the  large  trusses  over  the  ball-room  in  the  first  story. 
The  load  carried  was  estimated  at  5,400,000  Ibs.,  and  to  obtain 
the  required  sectional  area,  10  web-plates,  4  covers,  and  12 


COLUMNS.  Wy 

angles  were  used.     The    length  was  30  ft.  4  ins.,  and  the 
weight  of  the  column  was  46,980  Ibs. 

.Columns  made  of  channels  and  plates,  and  the  standard 
Z-bar  columns,  rank  next  in  order  to  those  made  of  plates  and 
angles.  Channel  columns  are  more  limited  as  to  size  and 
area,  through  the  use  of  the  component  channel  members, 
while  very  heavy  Z-bar  columns  become  rather  complicated  in 
form,  as  shown  in  types  3  and  4  of  Fig.  1  13. 

The  largest  Z-column  section  in  '  '  The  Fair  '  '  Building, 
Chicago,  consists  of  4  Z-bars  6"  X  I",  2  webs  16"  X  £", 
6  covers  16"  X  If"*  aggregating  an  area 
of  142  sq.  ins.  and  carrying  a  load  of 
1,700,000  Ibs.  The  largest  Z-column  in 
the  new  Y.  M.  C.  A.  Building,  Chicago 
(see  Fig.  132),  was  a  two-story  column 
24  ft.  3  ins.  long,  composed  as  follows: 
4  Z's  6"  X  3"  X  |",  2  plates  24"  X  |", 
2  plates  1  6"  X  I",  I  plate  14"  X  £",  2  FlG-  132.—  Heavy  Col- 


plates     26"  xl",     4     angles    4"  X  4"     T°*'  ?'  "'    ' 

A.  Building,  Chicago. 


X  If",    4  angles  5"  X  4"  X  I"  -  total 
=  218  sq.  ins. 

Column  Bases  :  Cast  Plates.  —  As  the  concentrated 
column  loads  must  be  distributed  over  the  foundations  which 
receive  them,  some  form  of  distributing  base  or  shoe  is  necessary 
at  the  bearing  ends  of  all  the  lowest  tier  columns.  The  area 
and  character  of  such  bases  are  determined  by  the  amount  of 
the  column  load,  and  by  the  allowable  pressure  per  square 
inch  on  the  underlying  foundation.  If  the  shoe  or  base  is  to 
rest  on  grillage  beams,  or  on  some  special  form  of  distributing 
or  cantilever  girder,  at  least  one  dimension  of  the  base  is 
usually  fixed  by  such  conditions  ;  but  if  the  bearing  is  to  be  upon 
concrete,  brick  masonry,  or  dimension  stones,  the  required 
area  of  the  base  is  determined  by  dividing  the  total  column 
load  by  the  allowable  pressure  per  square  inch  on  the  founda- 
tion material.  The  quotient  will  give  the  required  number  of 


228  ARCHITECTURAL  ENGINEERING. 

square  inches  in  the  area  of  the  base.  The  unit  pressure  on 
various  classes  of  foundation  materials  are  usually  fixed  by  the 
municipal  building  laws.  If  timber  grillage  is  to  receive  the 
column  base,  distributing  beams  or  girders  will  usually  be 
required  between  the  base  and  the  grillage,  in  order  to  obtain 
the  requisite  bearing  areas. 

When  the  column  loads  are  small,  solid  cast-iron  base 
plates  may  be  employed.  These  are  usually  cast  with  a  bevel 

I ... — ,  or   wash,   and    the  column    may  be 

\-GOLUMN-lk—  I  ->|    secured  by  means  of  tap-bolts  through 
J  L          j    small  knees  attached  to  the  column 

^r~* ^v      !    shaft,  or  by  means  of  bolts  passing 

f  I       *f         ^\    through  ribs  or  flanges  cast  on  the 

JT»       plate,  as  shown  in  Fig.  133.     Such 

FIG.  i33.-Cast-iron  Base       base   Plates   are    proportioned  as  fol- 

Plate  lows : 

The  bottom  or  bearing  area  of  the  plate  is  determined  by 
dividing  the  total  column  load  by  the  allowable  bearing  per 
square  inch,  /,  upon  the  material  which  supports  the  base. 
The  size  of  the  plate  thus  found,  and  the  known  size  of  the 
column,  will  then  fix  the  projection  /.  To  determine  the 
thickness  d>  let 

M=  bending  moment  in  inch-pounds,  =/S, 
where  /  =  allowable  extreme  fibre  stress  per  square  inch  for 

tension  =  3,500  Ibs.  to  4,000  Ibs. ; 
5  =  section  modulus. 
Then,  for  the  projecting  portion  of  casting, 

PI 

M  =  —,  where  P  =  //. 

Hence  M  =  — . 

But   5  =  — g— »    where    b  =  I    for  a   section    I    in.    wide. 

Hence,  as  M '  =  fS 

fd*      pl*  ,       »       3//3 

6-=— ,     and     ^=-r, 


COLUMNS. 


229 


or 


-v* 


The  thickness  /  is  usually  made  about  equal  to  — . 

4 

Steel  Column  Shoes. — For  heavier  column  loads,  where 
simple  cast  plates  as  above  are  not  sufficiently  strong  to  act  as 
distributors,  steel  shoes  or  cast-iron  bases  or  column  stands 
will  be  required. 

Built-up  shoes  of  steel  plates  and  angles  are  considered  by 
many  to  distribute  the  loads  more  efficiently  over  rectangular 
base  areas  than  results  from  the  use  of  cast-iron  bases.  The 
latter,  however,  are  much  more  common  than  the  steel  bases. 

Steel  column  shoes  may  be  calculated 
as  follows: 

Referring  to  Fig.  134,  assume  a  12 -in. 
Z-bar  column,  carrying  a  load  of  344,000 
Ibs.  The  bed-plate  or  shoe  is  to  rest  on 
a  grillage  foundation,  the  top  layer  of 
which  is  composed  of  4  I5~in.  42-lb. 
I-beams.  Hence  the  shoe  is  made  24  ins. 
wide  to  span  these  I's. 

The  column  shaft  carries  one-fourth  of 
the  total  load  directly  to  each  of  the  two 
central  beams,  thus  leaving  the  shoe  to 
transmit  one-fourth  of  the  load  to  each  of 
the  two  outer  beams.  'The  total  load 
being  344,000  Ibs. ,  the  amount  transmitted 

by  the  shoe  on  either  side  is  ^—^ — -  = 


9 

9 

9 

9 

9 

9 

© 

9 

® 

9 

0 

9 

9 

9 

9 

9 

9 

9 

9 

9 

/ 

9 

9 

I 

/ 

9 

9 

\ 

/ 

9 

9 

9 

\ 

L 

© 

?  9 

© 

V> 

. 

I* 24 


86,000  Ibs.,  or  43,000  Ibs.  at  each  flange 

of  the  Column.  FIG.  134.— Steel  Column 

The  horizontal  distance  from  the  line  Shoe, 

of  vertical  rivets  in  the  column  shaft  to  the  centre  line  of  an 
outer  beam  is  4  ins.,  hence  the  bending  moment 
M=  43,000  X  4  =  172,000  in. -Ibs. 


» 23°  ARCHITECTURAL  ENGINEERING. 

The  section  modulus, 

M       172,000 

5=7  =  -76^r:=ia75- 

bh* 
But  5  =  -g-,  where   b  equals  the  thickness  of  the  gusset 

plate,  and  h  the  depth  of  the  gusset.  Assuming  a  gusset 
plate  12  ins.  deep,  we  have 

10.75  = z »   whence  b  =  .448  ins. 

The  gussets  should  therefore  be  £  in.  thick.  For  the  vertical 
lines  of  rivets  transmitting  the  loads  from  the  column  shaft  to 
the  gussets,  each  row  must  transmit  43,000  Ibs.  at  single  shear. 
The  value  of  a  f-in.  rivet  in  single  shear  at  10,000  Ibs.  per  sq. 
in.  is  4,420  Ibs.  Hence  the  number  of  rivets  required  in  each 

43,000 

line  is  —       —  =  10.      The  gusset  assumed  is  not  deep  enough 
4,420 

to  take  so  many  rivets,  so  that  it  becomes  necessary  to  use 
vertical  stiffeners  as  shown  in  Fig.  134,  these  being  "  milled  " 
or  planed  at  the  bottom  to  bear  upon  the  bottom  angle-foot, 
and  extended  up  the  column  shaft  a  sufficient  distance  to  take 
six  rivets  above  the  four  in  the  gusset. 

Cast-iron  Column  Bases. — The  most  ordinary  form  of  dis- 
tributor for  column  loads  over  foundation  areas  is  the  cast-iron 
column  stand  or  base,  also  called  shoe  and  stool,  though 
shoes  are  generally  taken  to  mean"  steel  bases  as  previously 
described.  The  proportioning  or  calculations  for  cast  bases 
vary  considerably  in  actual  practice — indeed,  it  is  more  than 
probable  that  a  very  large  proportion  of  cast  bases  are  never 
figured  at  all;  but,  even  when  figured  according  to  one 
method,  any  particular  casting  will  be  found  to  vary  very  con- 
siderably if  figured  by  other  methods  in  more  or  less  common 
use. 

In  designing  base  castings,  the  following  elements  of  the 
problem  are  fixed  by  the  conditions  of  the  foundation:  the 


COLUMNS. 


231 


column  load,  the  size  of  column,  and  the  character  of  founda- 
tion which  is  to  receive  the  base.     The  column  load  and  the 


FIG.  135. — Cast-iron  Column  Stand. 

foundation  material  will  at  once  fix  the  area  of  the  base,  and 
hence  the  actual  load  per  square  inch  reacting  on  such  base. 
The  height  of  base  casting  may  be  taken  at  from  one-third  to 


232  ARCHITECTURAL  ENGINEERING. 

one-half  the  side,  and  for  such  column  loads  as  may  not  be 
safely  supported  by  solid  base  plates,  a  minimum  thickness  of 
metal  should  be  i^  ins.  for  the  top  and  bottom  plates  and  for 
the  ribs.  The  dimensions  of  the  top  plate  are  determined  by 
the  column  size,  care  being  taken  to  provide  connection  holes  for 
bolts  connecting  the  base  casting  to  flanges  riveted  to  the  column. 

With  these  conditions  fixed,  a  trial  section  may  be  assumed, 
and  calculated  as  follows  : 

Referring  to  Fig.  135,  assume  a  column-load  of  980,000 
Ibs.,  a  column  section  as  shown,  and  a  cast  base  48  ins.  by 
42  ins.  The  load  per  square  inch  on  the  bottom  plate  is  then 


The  resultant  moment  of  the  external  forces  acting  on  the 
casting  must  equal  —  , 

y\ 

where  f  equals  the  allowable  extreme  fibre  strain  ; 

/  equals  the  moment  of  inertia  of  the  section  ; 
and    ^j  equals  the  distance  of  the  extreme  fibres  from  neutral 
axis  of  section. 

To  find  /,  consider  a  section  of  the  casting  on  the  line  AB 
(see  diagram  i).  The  position  of  the  neutral  axis  must  first 
be  found,  and  the  distance  G  of  the  neutral  axis  from  the 
bottom  of  section  will  equal 

I9J  X  I7J+72|X  9J  +  92  X  i 


_ 

A    ''  i9|  +  72^  +  92 

=  5.918  ins.,  or  call  6  ins. 

The  moment  of  inertia  of  the  entire  section,  /,  will  equal  the 
sum  of  the  moments  of  inertia  of  the  various  rectangles,  /", 
etc.,  plus  the  areas  of  the  several  rectangles  multiplied  by  the 
squares  of  the  distances  from  their  individual  centres  of  gravity 
to  the  neutral  axis  of  entire  section.  Or, 
1=  2(7"  +  Ad*}, 

and  remembering  that  I"  for  a  rectangle  is  —  ,  we  find  /  to 
equal  6,797  in.  -Ibs. 


COLUMNS.  233 

Then,  taking /"for  tension  at  4,000  Ibs., 

//      4,000  X  6,797 

J—  =-   ^—^— =  4, 5  30,000  in.-lbs. 

To  find  the  resultant  moment  of  the  external  forces  for  the 
portion  of  the  casting  on  either  side  of  the  centre  line,  AB,  we 
have  two  forces — one,  the  total  pressure  on  a  half  of  the  base, 

980,000 
or   ,  which  is  applied  at  a  point  midway  between  the 

centre  line  AB  and  the  edge  of  base-plate;  second,  one-half 
the  column-load  acting  on  the  top  flange  of  casting,  the  point 
-of  application  of  which  may  be  taken  at  the  centre  of  gravity 
of  one-half  the  column  section.  Computing  this,  by  the  same 
method  as  previously  used,  we  find  the  centre  of  gravity  of  the 
half  column  section  to  be  4  ins.  from  the  centre  line  of  column, 
or  line  AB. 

J/ therefore  equals 

980,000 
— X  (ioi  -  4), 

or  3,185,000  in.-lbs.,  and  as  this  is  considerably  less  than  the 
value  of  —  previously  found,  the  casting  is  amply  strong. 

y\ 

For  a  calculation  of  the  ribs,  consider  a  section  on  the  line 
CD  as  in  diagram  2. 

The  neutral  axis,  computed  as  before,  is  found  to  be  6  ins. 
oip  from  the  bottom  of  section. 

/,  calculated  as  previously,  equals  7,210;  hence 
f±=  4.000x7.2.0  =  4|8o6>666  .n  ^ 

The  moment  on  the  area  of  base  supported  by  the  ribs  in 
question  will  equal 

(486  X  14  X  48)  X  7,     or     2,286, 144  in.-lbs. ; 
hence  the  ribs  might  be  taken  of  a  lighter  section ;  but  due 
judgment  must  be  exercised  to  produce  a  casting  of  about  right 
proportions,  and  when  possible  internal  stresses  are  considered, 


&3*  ARCHITECTURAL  ENGINEERING. 

and  the  practically  indeterminate  solution  for  a  base-plate  of 
this  design,  it  is  .best  to  err  largely  on  .the  safe  side  in  all  cal- 
culations. 

Column-loads. — If  the  building  laws  under  which  the 
designer  is  working  allow  a  reduction  in  the  live-loads  assumed 
to  be  carried  by  the  columns  themselves  ,.as  in  the  New  York 
Building  Code,  or  a  reduction  in,  or  total  disregard  of,  the 
live-loads  upon  the  foundations,  as  is  the  case  in  the  Chicago 
ordinance,  the  dead-  and  live-loads  on  all  columns  should  be 
kept  separate  to  allow  the  proporitoning  of  the  columns  them- 
selves, or  of  the  foundations.  Several  examples  of  the  reduc- 
tion of  live-loads  upon  the  columns  or  footings,  or  both,  were 
given  in  Chapter  IV,  but  whatever  the  requirements  of  the 
building  laws  in  force,  the  column-loads  are  best  tabulated  by 
means  of  "  column-sheets."  These  vary  considerably  in  form 
and  completeness,  according  to  the  refinement  with  which  the 
various  classes  of  loads  are  treated. 

Column-loads  include  floor-  and  roof-loads,  wind-loads, 
spandrel-  and  pier-loads,  the  weights  of  the  columns  them- 
selves and  their  fireproof  coverings,  and  special  loads  such  as 
tanks,  vaults,  safes,  elevator-loads,  and  any  permanent 
machinery,  the  latter  class  of  loads  being  usually  treated  as 
concentrated.  Floor-  and  roof-loads  can  readily  be  taken 
from  the  floor  plans,  provided  the  end  reactions  of  all  floor- 
girders  are  marked  on  the  original  drawings,  as  the  girders  are 
calculated.  Wind-loads  are  determined  as  explained  in 
Chapter  VIII,  while  pier-  and  spandrel-loads  are  calculated 
as  described  in  Chapters  V  and  VI. 

Column-sheets. — As  soon  as  all  loads  in  the  structure 
have  been  definitely  settled,  the  column-sheets  may  be  started, 
thus  forming  a  tabulated  list  of  all  the  loads  transferred  to  the 
footings  through  the  columns.  From  these  sheets  may  be  seen 
the  approximate  load  that  each  column  must  carry  at  any 
floor,  starting  with  the  upper-story  columns,  supporting  the 
roof-load  only,  and  adding  in  the  loads  at  the  successive  floors 


COLUMNS. 


235 


down  to  the  foundations.    ;  The  column,  weight  itself  is  'first 
assumed,    and    then    corrected,    after    the    proper    section    is 

obtained. - 

*  '-The  column-sheet  used  in  the  Masonic  Temple  calculations 
was  as  follows: 


Colui 

nn  i. 

Colui 

nn  2. 

Load 
on  Column. 

Lpad 
on  Footing. 

,    Load 
on  Column. 

Load 
on  Footing. 

Floor  load      .          .... 

Cz< 

o 

Tank  loads 

,    - 

(Hi 

Weight  of  column  

Total  

2OTH  FLOOR. 

The  column-sheet  used  in  the  Venetian  Building  was  made 
as  in  the  accompanying  table: 


Column  i. 

Roof. 

Attic. 

i2th 
Floor. 

Estimated  weight  of  column  

Total  ... 

Wind  Loads. 

Total  wind  load 

Column  2. 

Etc. 

Total 


236  ARCHITECTURAL  ENGINEERING. 

The  following  column-sheet  is  to  be  recommended  as  com- 
bining all  requisites  in  a  tabulated  statement: 


Column  i. 

Column  a. 

Load 
on  Column. 
Concentric. 

Load 
on  Column. 
Eccentric. 

Load 
on  Footing. 

Floor  load        

Tank  loads,  etc  

ftu 

Weight  of  column  
Wind 

OS 

Total 

Area  required  for  col.  .  . 

sq.  in. 

sq.  in. 

Foot'g  area 

Load 
on  Column. 
Concentric. 

Load 
on  Column. 
Eccentric. 

Load 
on  Footing. 

Floor  load  

as 

1 

Etc. 

The  final  loads  on  the  basement  columns  taken  from  these 
sheets  will  show  the  loads  for  which  the  footings  themselves 
must  be  figured,  while  the  final  loads  on  the  footings  will  give 
the  weights  for  which  the  clay  areas  must  be  proportioned,  if 
the  foundations  are  on  yielding  soil. 

The  following  table  shows  the  column-sheet  loads  for  a  few 
of  the  columns  in  the  Fisher  Building,  Chicago.*  The  assumed 
roof-  and  floor-loads  for  the  same  building,  and  their  distribu- 


*  See  E.  C.  Shankland  in  Minutes  of  the  Proceedings  of  the  Institution 
of  C.  E.,  vol.  cxxviii. 


COLUMNS. 


237 


tion  on  joists,  girders,  columns  and  footings,   were  given  in 
Chapter  IV. 


No.  4. 

Nos.  9-1  3-31 
10-19-22 
11-20-23 

Nos.   28-31 
29-32 
30-33 

Nos.  34 
35 

Roof 

Ibs. 

Ibs. 

Ibs. 

Ibs. 

Attic. 

Tanks 

Total   

3O  OCX) 

10  230 

17  190 



Floor             

II  780 

17  670 

24  510 

Column  and  casing.... 

2,440 

78  7^0 

4,870 

4,870 

18 

Tanks  

I,7OO 

28,900 

5,OOO 

Total 



Ploor   

23  250 

32  250 

48  75O 

17 

Column  and  casing  

2,440 

21  580 

8,230 

4,870 

4,870 

Total... 

162.4.00 

104.110 

112.'!  00 

124  OQO 

Floor  

14  260 

21  390 

I 

Column  and  casing  
Spandrel-mullion  

2,840 
19,600 

12,000 

8,820 

5,670 

5,670 

Total  

,, 

910,  i  10 

Floor                      .       . 

Base- 

Sidewalk 

1     66 

4,000 

ment. 

Party-wall  

26  780 

9 

Total  

Foot- 

Live-load, deduct  

34.100 

51,150 

70,950 

107,250 

ing. 

Proportioning  Column- sizes. — There  have  been  few  ex- 
periments of  value  on  the  ultimate  strength  of  full-sized  steel 
columns  of  the  types  in  more  ordinary  use.  Building  operations 
have  to  be  conducted  too  quickly  to  allow  many  tests  on  the 
full-sized  columns  before  using.  Tests  have  been  made  on 
full-sized  Gray  columns,  and  also  on  the  Larimer  column,  but 


«38  ARCHITECTURAL  ENGINEERING. 

these  are  both  special  shapes,  and  the  tests  have  little  bearing 
upon  data  regarding  the  more  common  forms.  The  only  full- 
sized  tests  on  Z-bar  columns  were  made  by  C.  L.  Strobel, 
then  Chief  Engineer  of  the  Keystone  Bridge  Company,  (see 
Transactions  of  the  American  Society  of  Civil  Engineers,  April, 
1888),  who  introduced  this  shape  into  the  United  States.  But 
even  these  tests  are  hardly  fair  ones  for  present  comparisons,  as 
lattice  bars  were  used  instead  of  web  plates,  and  almost  all  the 
tests  were  for  a  much  higher  ratio  of  the  radius  of  gyration  to  the 
length  of  column  than  is  ordinarily  met  with  in  building  work. 
The  tests  were  also  for  iron  columns,  and  not  for  steel.  It 
seems  as  though  higher  breaking  loads  would  be  obtained  for  the 
majority  of  steel  columns  as  used  at  the  present  time.  Burr,  in 
his  ' '  Strength  and  Resistance  of  Materials, ' '  deduces  formulae 
for  the  Keystone  and  Phcenix  columns,  but  none  for  the 
Z-column  or  the  box  column  of  plates  and  angles.  The  latter 
type  was  used  in  the  Masonic  Temple  in  two-story  lengths, 
lattice  bars  being  used  instead  of  plates  in  the  lighter  columns. 
But  as  the  height  of  a  single  story  was  less  than  1 2  ft.  unsup- 
ported length,  a  uniform  unit-stress  of  12,500  Ibs.  per  sq.  in. 
was  used  without  reduction  by  the  radius  of  gyration,  for  all 
concentric  loading.  Columns  with  eccentric  loads  were  figured 
for  a  unit-stress  of  12,500  Ibs.  per  sq.  in.,  reduced  by  Rankine's 
formula  for  eccentric  loading. 

For  columns  of  ordinary  single-story  lengths,  this  practice 
of  proportioning  the  section  by  simply  dividing  the  total 
column-load  by  the  allowable  stress  per  square  inch,  will  serve 
all  practical  requirements,  as  previously  explained  in  the  dis- 
cussion of  Gordon's  formula. 

In  the  Venetian  Building  the  columns  without  strains  from 
wind-bracing  were  figured  at  15,000  Ibs.  per  sq.  in.  for  all 
concentric  dead-  and  live-loads,  with  an  extra  allowance  for 
eccentric  loads.  The  columns  carrying  strains  from  the  wind- 
bracing  were  figured  at  20,000  Ibs.  per  sq.  in.  for  all  concentric 


COLUMNS.  239 

loads, — dead,  live,  and  wind,— with  an  additional  allowance 
for  eccentric  loading.  In  these  columns  the  wind-strains 
amounted  to  from  35  to  40  per  cent,  of  the  total  load,  so  that 
this  mode  of  treatment  of  using  a  higher  unit-stress  gave  a 
much  greater  section  to  the  column  than  if  a  lower  unit-stress 
had  been  used  and  the  wind  forces  disregarded.  These  unit- 
stresses  have  been  used  in  a  number  of  high  buildings,  not- 
withstanding some  rather  severe  criticism. 

In  "The  Fair"  Building  (W.  L.  B.  Jenney,  architect), 
12,000  Ibs.  was  used  uniformly  on  all  columns,  with  no  allow- 
ance for  eccentric  loading.  This  building  is  one  of  the  heaviest 
in  the  city  of  Chicago,  being  figured  for  1 30  Ibs.  live-load  per 
square  foot  for  the  1st,  2d,  3d,  4th,  and  6th  floors,  200  Ibs.  for 
the  5th  floor,  100  Ibs.  for  the  /th  and  8th  floors,  with  the  rest 
at  75  Ibs.,  all  in  addition  to  dead-loads.  Great  care  was  taken 
in  providing  good  connections  throughout. 

In  the  Fort  Dearborn  Building,  by  the  same  architect,  a 
uniform  unit-stress  of  13,000  Ibs.  per  sq.  in.  was  used  on  all 
columns,  made  of  channels  and  plates,  with  a  proper  reduction 
for  eccentric  loading. 

The  writer  believes  that  with  the  use  of  a  mild  steel,  of  an 
ultimate  strength  of  from  65,000  to  68,000  Ibs.  per  sq.  in., 
15,000  or  16,000  Ibs.  per  sq.  in.  may  safely  be  used  for  all 
concentric  dead-,  live-,  and  wind-loads  combined  (with  an 
additional  allowance  for  eccentric  loading  as  before  described), 
provided  that  the  wind-pressure  is  taken  at  not  less  than  30 
Ibs.  per  sq.  ft.,  and  that  the  live-loads  on  the  floor  systems  are 
assumed  as  required  by  the  municipal  building  laws.  With 
careful  regard  for  all  connections,  and  remembering  that  the 
strength  of  a  structure  lies  in  its  weakest  point,  these  unit- 
stresses  would  seem  to  satisfy  both  the  conditions  of  proper 
economy  and  satisfactory  design. 

The  use  of  20,000  Ibs.  per  sq.  in.,  as  in  the  Venetian 
Building,  would  seem  too  high,  especially  when  the  live-load 


«40  ARCHITECTURAL  ENGINEERING. 

is  but  35  Ibs.  per  sq.  ft.  on  the  floor  systems,  and  when  but 
50  per  cent,  of  this  is  considered  as  transferred  to  the  columns. 
In  columns  of  long  length,  or  for  lengths  of  90  radii  and 
over,  calculation  by  the  radius  of  gyration  becomes  necessary. 
For  such  cases  the  standard  formula, 

/ 

/  =  17,100  -  57-, 

may  be  used,  where  /  equals  the  allowable  stress  per  square 
inch,  /  equals  the  length  in  inches,  and  r  equals  the  radius  of 
gyration  of  section  in  inches. 

This  formula  is  derived  from  the  tests  on  full-sized  Z-bar 
columns  before  referred  to,  and  gives  values  about  20  per  cent, 
in  excess  of  those  found  to  be  true  for  the  iron  columns  tested. 

Modern  building  design  has  rapidly  developed  the  necessity 
for  columns  of  extraordinary  lengths  and  areas.  In  the 
Schiller  Theatre  Building,  Chicago,  Phoenix  columns  were 
used  in  connection  with  the  trusses  over  the  auditorium  of  a 
length  of  92  ft.  10  ins.,  weighing  25,000  Ibs.  each,  while  in 
the  Chicago  Board  of  Trade,  12-section  Phoenix  columns, 
3  ft.  3  ins.  in  diameter,  were  employed  for  an  unsupported 
length  of  90  ft.  The  large  columns  in  the  Waldorf-Astoria 
Hotel  were  previously  mentioned. 

In  proportioning  the  sizes  of  material  for  columns  of  two- 
story  lengths,  no  change  in  section  need  be  made  provided  the 
difference  in  loads  is  slight.  It  will  often  be  more  economical 
to  proportion  the  member  for  the  heavier  load,  and  to  let  the 
required  section  continue  uniform,  rather  than  to  decrease  the 
section  slightly  and  thus  cause  the  splicing  or  rearrangement 
of  material.  If  the  difference  in  loads  is  considerable  for  a 
two-story  length,  additional  cover-plates  may  be  riveted  on  to 
the  lower  story  length  only,  thus  having  one  cover-plate  below 
and  none  above,  or  one  continuous  cover  for  the  two  stories 
and  an  additional  one  in  the  lower  section.  If  channel  columns 


COLUMNS.  241 

are  used,  the  same  size  and  weight  of  channel  section  may  be 
used  for  the  entire  length,  making  the  difference  in  area  in  the 
thickness  of  the  flange-plates,  or  the  same  sized  flange-plates 
may  be  used  throughout,  by  changing  the  weights  of  the 
channels  in  each  story. 

A  convenient  schedule  for  column  lengths,  splices,  and 
material,  may  be  made  as  shown  on  page  242. 

Column  Details  and  Splices. — The  details  or  shop  draw- 
ings for  columns  must  show  the  required  connections  or  shelf- 
angles  for  the  various  beams  and  girders  attaching  to  the 
column,  the  spacing  of  the  shaft-rivets  and  latticing  or  tie- 
plates  if  required,  besides  the  details  of  splices.  Fig.  136 
illustrates  a  shop  drawing  of  a  three-story  Z-bar  column,  with 
the  various  girder  connections  and  splices. 

The  details  employed  in  the  design  of  shelf-angles  or  sup- 
ports for  girders  carried  by  the  columns  will  vary  considerably 
with  the  different  types  of  columns,  but  in  general  it  may  be 
stated  that  where  a  sufficient  number  of  rivets  cannot  be 
obtained  direct  through  the  shelf-angle  into  the  column-shaft, 
the  additional  rivets  must  be  secured  by  means  of  stiffening 
angles.  Assuming  a  safe  shearing-stress  of  10,000  Ibs.  per 
sq.  in.  for  rivets,  and  f  in.  diameter  rivets  as  are  usually  em- 
ployed except  for  the  heaviest  work,  the  value  of  each  rivet  in 
single  shear  is  4,420  Ibs.  This  may  be  used  for  all  metal 
T5¥  in.  thick  or  over,  but  for  £-in.  metal  the  lesser  bearing 
value  of  3,750  Ibs.  would  have  to  be  used.  Taking,  then,  the 
shelf-angle  shown  in  Fig.  137,  the  safe  load  would  be  four 
times  4,420  Ibs.,  or  8.8  tons.  If  the  end  reaction  of  the  girder 
to  be  supported  is  greater  than  this,  stiffening  angles  must  be 
introduced  to  provide  the  additional  number  of  rivets,  as  in 
Fig.  138,  where  the  safe  load  becomes  double  the  former,  or 
17.7  tons.  The  stiffening  angles  are  placed  directly  against 
the  vertical  flange  of  the  shelf-angle,  and  fillers  are  inserted 
from  the  bottom  of  the  shelf-angle  to  the  lower  ends  of  the 


242 


ARCHITECTURAL  ENGINEERING. 


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Form  of  Schedule  for  Column  Lengths  and  Column  Material. 


COLUMNS. 


243 


J.3136   No.18 


FIG.  136.  — SHOP  DETAIL  OF  Z-BAR  COLUMN. 


244 


ARCHITECTURAL   ENGINEERING. 


stiffeners.  Where  large  loads  are  to  be  carried,  the  upper 
ends  of  the  stiffeners  should  be  "faced  "  or  planed,  to  insure 
a  full  bearing  for  the  seat. 

Column  sections  are  ordinarily  increased  from  story  to  story 
by  using  increasing  thicknesses  of  shapes  of  the  same  general 
sizes,  or  by  the  addition  of  reinforcing  cover-plates,  etc.  In 
such  cases  the  variations  in  the  principal  dimensions  of  the 


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FIG.  138. 


FIG.  137. 
Details  of  Splices  and  Beam  Connections  for  Z-bar  Columns. 

cross-sectioii  are  very  slight,  and  the  splices  may  be  made  by 
butt-joints,  thus  utilizing  the  direct  bearing  of  the  upper 
member  upon  the  lower  one.  The  splice-plates  are  therefore 
not  required  for  transferring  any  vertical  load,  but  as  shear, 
wind-strains,  and  rigidity  are  to  be  provided  for,  the  splice- 
plates  must  be  designed  accordingly,  and  good  practice  has 
made  three  lines  of  rivets  above  and  below  the  joint  a  mini- 


COLUMNS.  245 

mum.  Fig.  137  illustrates  a  column  splice  for  the  Z-section 
where  the  size  of  the  column  changes  only  in  the  thickness  of 
the  material.  The  slight  variations  usually  found  between 
the  two  sections  may  be  made  up  in  filler  plates  inserted 
between  the  Z-flanges  and  the  splice-plates. 

If  a  radical  change  is  made  in  the  dimensions  of  the  cross- 
section,  as,  for  instance,  in  changing  from  a  lo-in.  Z-column 
to  an  8-in.  Z-section,  a  horizontal  cap-plate  or  diaphragm 
must  be  inserted,  as  in  Fig.  138.  This  is  usually  riveted  to 
the  lower  column,  and  serves  to  provide  a  bearing  and  dis- 
tributing surface  for  the  upper  column.  But  as  explained 
previously,  continuous  vertical  splices  are  far  preferable  for 
many  reasons. 

If  direct  bearing  between  the  columns  cannot  be  utilized, 
on  account  of  differences  in  the  cross-sections,  and  it  is  not 
desired  to  use  horizontal  cap-plates,  vertical  splice-plates  may 
be  arranged  to  transfer  the  load,  in  which  case  the  number  of 
rivets  must  be  proportioned  to  transmit  the  entire  strain. 

Column  splices  are  generally  made  just  above  the  floor- 
beam  connections,  this  being  largely  for  aid  in  erection  as 
before  mentioned.  It  is  now  customary  to  "stagger"  the 
splices  in  adjacent  columns,  so  that  if  one  column  splices  at 
the  tenth  and  twelfth  floors,  those  on  either  side  should  splice 
at  the  eleventh  and  thirteenth  floors.  Column  splices  should 
always  be  riveted,  never  bolted. 

Column  ends  should  always  be  "faced  "  or  "milled  "  to 
a  true  surface  which  is  exactly  normal  to  the  column  axis. 
The  finished  length  from  end  to  end  must  be  exact,  and  the 
member  should  be  free  from  bends  or  buckels. 

Fireproofing  of  Columns. — As  the  columns  carry  the 
greatest  loads  found  in  modern  buildings  (some  over  3,000,000 
Ibs.),  the  proper  fireproofing  of  these  members  becomes  a 
most  important  subject  for  consideration.  In  only  too  many 
cases,  however,  is  this  slighted  even  to  a  very  dangerous 


246  ARCHITECTURAL  ENGINEERING. 

extent,  as  was  proven  by  the  Athletic  Club  Building  fire, 
before  referred  to. 

The  first  attempts  at  making  fireproof  columns  were 
through  the  use  of  a  double  column,  one  inside  the  other,  with 
the  intervening  space  filled  with  plaster.  This  idea  was 
patented,  and  reference  may  still  be  found  to  such  construction 
in  the  New  York  building  law,  as:  "The  said  column  or 
columns  shall  be  either  constructed  double,  that  is,  an  outer 
and  an  inner  column,  the  inner  alone  to  be  of  sufficient  strength 
to  sustain  safely  the  weight  to  be  imposed  thereon." 

The  scientific  fireproofing  of  columns  by  means  of  terra- 
cotta was  started  by  Mr.  P.  B.  Wight  in  1874,  and  the  Chicago 
Club  house,  designed  by  Treat  &  Foltz,  architects,  was  the 
first  instance  where  terra-cotta  gores  were  used  around 
columns.  Many  systems  have  since  been  introduced,  and  both 
the  hard  tile  and  the  porous  tile  have  been  used  extensively. 
The  cheapest  method  has  been  through  the  use  of  shells  of 
hard  terra-cotta  surrounding  the  column,  but  not  backed  up 
to  the  metal-work.  This  system  is  decidedly  faulty  in  placing 
so  much  reliance  in  the  joints  alone  for  stability,  as  the  blocks 
are  simply  cemented  to  one  another,  and  not  to  the  metal 
column. 

The  requirements  in  the  adequate  fireproofing  of  columns 
are: 

1 .  The  material  must  be  indestructible  by  fire  and  water. 

2.  The  material  must  be  non-heat-conducting. 

3.  The  material  must  be  so  secured  to  the  column  that  it 
cannot  be  dislodged. 

The  use  of  hard  fire-clay  tiles  is  only  to  be  recommended  when 
such  tiles  are  hollow,  with  a  proper  air-space  around  the  metal 
column,  and  even  then  experience  seems  to  show  that  the  hard 
tile  is  in  no  way  as  satisfactory  under  great  heat  as  the  more 
porous  kinds.  Applications  of  cold  water  in  combination  with 
heat  have  also  proved  the  hard  tile  far  less  reliable  in  case  of 


COLUMNS. 


247 


conflagration  than  the  porous  tile.  The  hard  tile  is  very  apt 
to  crack  off  under  such  conditions,  as  has  been  stated  in 
chapter  IV. 

The  use  of  hollow  blocks  of  porous  tile,  well  bedded 
against  the  metal  column,  has  proved  to  be  the  most  rigid  and 
efficient.  Here,  as  in  terra-cotta  floor-arches,  the  competition 


FIG.  139.  FIG.  140  FIG.  141. 

FIG.  139. — Method  of  Fireproofing  Phoenix  Columns. 
FIG.  140. — Method  of  Fireproofing  Channel  Columns. 
FIG.  141. — Method  of  Fireproofing  Z-bar  Columns. 

in  price,  which  places  the  better  article  or  method  at  a  dis- 
advantage, is  to  be  deplored.  Loosely  drawn  specifications 
are  also  responsible  in  a  great  measure  for  many  very  common 


FlG.  142. — Method  of  Fireproofing  Columns,  Monadnock  Building. 

defects.     Figs.  139,  140,  and   141   show  the  ordinary  methods 
of  placing  the  fireproof  furring  for  columns. 

The  Z-bar  columns  in  the  newer  portion  of  the  Monadnock 
Building  were   fireproofed  as   shown   in  Fig.    142  up  to  and 


248  ARCHITECTURAL   ENGINEERING. 

including  the  eighth  floor.  Hollow  bricks,  laid  in  cement 
mortar,  were  built  solidly  around  the  columns  to  a  line  distant 
4  ins.  from  the  extreme  points  of  the  metal-workx  and  a  2-in. 
coating  of  hollow  tile  was  then  laid  against  the  brick  backing 
extending  beyond  the  column  in  one  direction,  to  serve  as  a 
space  for  vertical  pipes.  The  columns  above  the  eighth  floor 
received  the  hollow-tile  protection  only. 

For  more  extended  data  regarding  the  use  of  metal  lath 
and  plaster,  concrete,  and  terra-cotta  as  fireproof  coverings  for 
columns,  the  reader  is  referred  to  the  chapter  on  Column  Fire- 
proofing  in  the  author's  "  Fireproofing  of  Steel  Buildings." 

Building  Laws  :  Fireproofing. — The  requirements  for  fire- 
proofing  the  interior  columns  of  office  buildings  are  thus  defined 
by  the  Chicago  ordinance : 

' '  The  coverings  for  columns  shall  be,  if  of  brick,  not  less 
than  8  ins.  thick ;  if  of  hollow  tile,  one  covering  at  least 
2 4  ins.  thick.  If  the  fireproof  covering  is  made  of  porous 
terra-cotta,  it  shall  be  at  least  2  ins.  thick.  Whether  hollow 
tile  or  porous  terra-cotta  is  used,  the  courses  shall  be  so 
anchored  and  bonded  together  as  to  form  an  independent  and 
stable  structure." 

' '  In  all  cases  there  shall  be  on  the  outside  of  the  tiles  a 
covering  of  plastering  with  Portland  cement  or  of  other  mortar 
of  equal  hardness  and  efficiency  when  set. ' ' 

Two  layers  of  any  covering  made  of  plastering  on  metallic 
lath  are  also  allowed  by  this  ordinance  in  office  buildings. 

The  New  York  law  requires  that  columns  in  fireproof  build- 
ings ' '  shall  be  protected  with  not  less  than  2  ins.  of  fireproof 
material,  securely  applied. ' ' 


CHAPTER   VIII. 
WIND-BRACING. 

A  CAREFUL  comparison  of  the  treatment  of  wind  forces  as 
applied  to  the  mercantile  buildings  of  to-day  leads  one  to  the 
conclusion  that  the  designers  differ  very  materially  in  regard 
to  the  forces  to  be  resisted,  the  strength  of  the  materials  em- 
ployed, and  the  most  efficient  details  of  construction.  Indeed, 
there  are  very  many  well-known  buildings  from  ten  to  sixteen 
stories  high  that  possess  absolutely  no  metallic  sway-bracing, 
and  others,  scarcely  better,  where  sway-rods,  as  wind-laterals, 
were  attached  to  pins  through  lugs  on  the  cast  columns,  which 
lugs  were  of  an  ultimate  strength  of,  perhaps,  25  per  cent,  of 
the  rods.  H.  H.  Quimby,  in  his  paper  on  "Wind-bracing  in 
High  Buildings,"  *  mentions  the  case  of  an  office  building  in 
New  York,  of  seventeen  stories,  or  200  ft.  in  height,  and  60  ft. 
wide;  13 -in.  walls  were  used  front  and  back,  broken  by 
windows  and  bay-windows,  with  wind-bracing  consisting  solely 
of  the  interior  partitions  of  8-in.  box  tile,  with  four  ribs  of 
$  in.  each,  or  2\  in.  thickness  of  tile  in  each  partition.  This 
building  towers  above  its  neighbors  of  five  or  six  stories  only, 
while  but  a  few  blocks  away  is  one  of  seventeen  stories,  also, 
but  150  ft.  wide,  or  2^  times  the  width  of  the  former,  with 
sway-bracing  consisting  of  I5~in.  cannel-struts  and  6-in.  eye- 
bars.  Such  is  the  diversity  of  practice. 

Some  architects  have  depended  solely  upon  partitions  of 
hollow  tile  for  the  lateral  stability  of  their  buildings,  weak  as 

*  Trans.  A.  S.  C.  E.,  vol.  xxvii.  No.  3. 

249 


••JO  ARCHITECTURAL   ENGINEERING. 

the  partitions  must  be  through  the  introduction  of  numerous 
doors  and  office  lights.  This  method  of  filling  in  the  rectangles 
of  the  frame  by  light  partitions  may  be  efficient  wind-bracing, 
but  the  best  practice  would  certainly  indicate  that  it  cannot  be 
relied  upon,  or  even  vaguely  estimated. 

A  building  with  a  well-constructed  iron  frame  should  be 
safe  if  provided  with  brick  partitions,  and  if  the  base  is  a  large 
proportion  of,  or  equal  to  the  height,  or  if  the  exterior  of  the 
iron  framework  is  covered  with  well-built  masonry  walls  of 
sufficient  thickness ;  for  the  rigidity  of  solid  walls  would  exceed 
that  of  a  braced  frame  to  such  an  extent  that,  were  the  build- 
ing to  sway  sufficiently  to  bring  the  bracing-rods  into  play,  the 
walls  would  be  damaged  before  the  rods  could  be  brought  into 
action. 

Hence  the  stability  must  depend  entirely  either  on  the 
masonry  or  on  the  iron  framing;  and  in  veneer  buildings, 
which  are  being  considered  here  in  particular,  the  latter  system 
of  bracing  the  metal-work  must  be  used,  with  the  walls  as  light 
as  possible,  simply  enclosing  the  building  against  climatic  and 
injurious  forces.  This  practice  has  been  adopted  quite  uni- 
formly by  all  conservative  architects  and  engineers,  and  will 
alone  be  considered  here  as  a  method  of  wind-bracing. 

Each  building  offers  its  own  peculiar  conditions  to  the 
carrying  out  of  proper  wind-bracing,  and  many  factors  must 
be  considered  for  a  judicious  solution.  The  height,  width, 
shape,  and  exposure  of  the  structure,  as  well  as  the  character 
of  the  enclosing  walls,  will  determine  the  amount  of  the  wind 
pressure  to  be  cared  for,  while  the  details  of  construction,  the 
internal  appearance,  and  the  planning  of  the  various  floors  will 
largely  influence  the  manner  in  which  this  bracing  is  to  be 
treated.  The  architectural  planning  of  the  offices,  rooms,  and 
corridors  often  raises  most  serious  obstacles  to  a  proper 
arrangement  of  wind-bracing,  and  the  engineer  is  frequently 
called  upon  to  make  most  generous  concessions  in  favor  of 


WIND-BRACING.  251 

doors,  windows,  passages,  and  even  whole  areas,  as  is  some- 
times demanded  in  banking-  or  assembly-rooms  and  the  like. 
Such  considerations  have  led  to  the  development  of  the  portal 
type  of  wind-bracing.  As  more  and  more  of  the  constructional 
work  of  large  buildings  is  placed  in  the  care  of  the  engineer, 
as  opposed  to  the  purely  architectural  or  decorative  draughts- 
man, just  so  will  the  iormer  insist  that  a  proper  regard  for 
construction  is  of  equal  value  with  the  artistic  portion  of  the 
work.  The  one  must  supplement  the  other,  instead  of  giving 
way  to  irrationalities  of  design. 

Intensity  of  Wind  Pressure. — The  intensity  of  wind  pres- 
sure which  should  be  calculated  for  in  the  design  of  high  build- 
ings varies  greatly,  as  has  before  been  stated,  according  to 
the  ideas  of  the  designer.  Many  architects  and  engineers  are 
content  to  provide  for  a  very  moderate  average  wind  pressure, 
on  the  assumption  that  extreme  pressures  are  of  very  rare 
occurrence,  and  of  very  short  duration.  Other  architects,  and 
probably  most  conservative  engineers,  believe  that  it  is  pre- 
cisely the  unusual  and  unlocked  for  emergency  which  should 
be  foreseen,  and  that  any  such  additional  security  should  be 
considered  not  as  a  useless  waste  of  expenditure,  but  in  the 
nature  of  insurance  upon  the  life  and  efficiency  of  the  structure. 

Statistics  as  to  severe  storms  or  tornadoes  show  that  such 
extreme  conditions  are  of  too  frequent  occurrence  to  be  ignored 
without  assuming  considerable  hazard.  The  reports  of  the 
U.  S.  Signal  Service  show  that  between  the  years  1889  and 
1896  great  tornadoes  averaged  about  three  per  annum,  the 
total  property  loss  being  about  $24,000,000.  The  most 
destructive  storms  were  those  in  Kansas  City  in  1886,  Louis- 
ville in  1890,  Little  Rock  in  1894,  and  St.  Louis  in  1896. 

The  relation  between  the  velocity  of  wind  and  the  pressure 
exerted  upon  surfaces  normal  to  its  direction  is  usually 
expressed  by  the  formula  P  =  cV*,  where  P  equals  the  pres- 
sure in  pounds  per  square  foot,  c  equals  a  constant,  and  V 


252  ARCHITECTURAL  ENGINEERING. 

equals  the  wind  velocity  in  miles  per  hour.  The  value  of  the 
constant  £,  depending  upon  experiment,  has  been  variously 
computed  by  different  authorities.  Some  experiments  have 
indicated  a  value  as  low  as  0.003,  others  place  it  at  0.005,  while 
the  United  States  Weather  Bureau  has  adopted  the  value  of 
0.004,  tnus  making  the  formula  P  =  O.OO4F2.  The  experi- 
ments made  to  determine  this  value  were  through  the  use  of 
gauges  with  surfaces  of  4  and  9  sq.  ft.  According  to  this, 
formula,  an  assumed  pressure  of  40  Ibs.  per  sq.  ft.  would 
correspond  with  a  velocity  of  100  miles  per  hour. 

Experiments  made  at  the  Forth  bridge  on  two  wind-gauges 
of  300  sq.  ft.  and  i£  sq.  ft.  respectively,  indicated  that  with 
an  increase  in  area  the  unit  of  pressure  decreased  in  a  very 
marked  degree;  but  regardless  of  experiments  with  gauges, 
there  is  sufficient  evidence  to  show  that  high  wind  pressures 
are  exerted  over  far  wider  areas  than  is  generally  supposed. 

The  extreme  velocity  in  the  St.  Louis  tornado  was  120 
miles  per  hour.  The  greatest  wind  velocity  ever  recorded  in 
New  York  City  was  75  miles  per  hour,  for  a  duration  of  twa 
minutes.  This  was  recorded  by  the  instruments  of  the  U.  S. 
Signal  Service  on  March  28,  1895,  and,  according  to  the 
formula  previously  given,  is  equivalent  to  a  pressure  of  22^  Ibs. 
per  sq.  ft. 

A  unit  of  30  Ibs.  should  serve  as  a  minimum  in  high  build- 
ings of  veneer  construction.  Mr.  Quimby,  in  the  paper  before 
alluded  to,  favors  provision  for  a  4O-lb.  pressure,  with  steel 
bracing  strained  not  over  one-third  of  the  ultimate  strength ; 
while  others,  in  a  discussion  of  the  article,  advocate  the  use  of 
30  Ibs.  Mr.  Guy  B.  Waite,  M.  Am.  Soc.  C.  E.,  states  that 
"  After  consulting  standard  authors,  reliable  data,  and  promi- 
nent engineers,  the  writer  is  unable  to  find  any  engineer  who 
is  willing  to  assume  the  responsibility  of  allowing  an  average 
of  less  than  30  Ibs.  per  sq.  ft.  horizontal  pressure  on  the 
exposed  windward  side  of  high  buildings." 


WIND-BRJCING.  253 

Probably  the  most  important  contribution  to  the  subject  of 
wind-pressure  up  to  the  present  time  is  the  paper  of  Mr.  Julius 
Baier  before  the  American  Society  of  Civil  Engineers.*  From 
this  paper,  which  gives  a  most  complete  discussion  of  tornadoes, 
and  their  causes  and  effects,  the  following  quotations  are 
taken : 

' '  The  St.  Louis  tornado  was  but  one  of  a  number  accom- 
panying a  general  storm  that  moved  through  Missouri  and 
Illinois.  As  far  as  known  it  was  not  more  violent  than  many 
others  that  have  been  observed.  Its  great  destructiveness  was 
merely  incidental  to  the  fact  that  its  path  crossed  a  territory 
embracing  a  large  and  closely  built  city.  It  gave  evidence 
that  wind  pressures  existed  at  least  equivalent  to  or  greater 
than  20  Ibs.,  60  Ibs.,  and  85  to  90  Ibs.  per  sq.  ft.  over  con- 
siderable areas.  Whatever  the  actual  distribution  may  have 
been,  the  effects  were  those  of  such  pressures  uniformly  dis- 
tributed over  the  areas  of  the  respective  structures.  These 
pressures  were  measured  by  their  results  in  exactly  the  same 
manner  in  which  they  are  ordinarily  assumed  to  act,  with  the 
consequent  elimination  of  all  uncertainties  usually  involved  in 
readings  of  pressure-gauges  or  deductions  from  anemometer 
records,  and  they  are  to  that  extent  positive  and  definite.  In 
addition,  there  were  indications  that  a  pressure  of  somewhere 
from  20  to  40  Ibs.  was  quite  general  over  a  comparatively  wide 
area  in,  or  adjacent  to  the  path  of  the  storm,  and  that  the 
pressures  at  higher  altitudes  were  more  severe  than  those 
measured. 

' '  In  view  of  these  facts  it  appears  to  the  author  rational  to 
assume: 

4 '  First.  That  the  safety  and  interests  of  the  community 
and  of  the  owner  of  the  building  require  a  recognition  of  a  wind 

*See  "Wind  Pressure  in  the  St.  Louis  Tornado,  with  Special  Reference 
to  the  Necessity  of  Wind-bracing  for  High  Buildings,"  Trans.  Am.  Soc. 
C.  E.,  vol.  xxxvii. 


254  ARCHITECTURAL   ENGINEERING. 

pressure  of  at  least  30  Ibs.  per  sq.  ft.  against  the  exposed  sur- 
face of  the  building,  with  an  additional  local  provision  of 
50  Ibs.  for  several  stories  near  the,  top;  and  that  this  amount 
should  be  safely  taken  care  of  by  some  positive  and  definite 
provision  in  the  construction  of  the  frame. 

' '  Second.  That  the  vast  interests  at  stake,  the  amount  of 
capital  invested  and  the  comparatively  small  additional  ex- 
pense necessary  would  suggest  to  the  owner  the  desirability  of 
increasing  the  provision  to  40  Ibs.  per  sq.  ft. 

"Third.  That  the  other  uncertain  elements  of  safety  due 
to  the  ultimate  strength  of  the  material,  the  inertia  of  the  mass, 
and  the  bracing  effect  of  walls  and  partitions,  should  be  recog- 
nized only  as  providing  against  the  uncertain  and  possible 
higher  pressure  of  the  wind  which  may  occur. 

4 '  The  chief  justification  of  much  that  seems  bold  or  ques- 
tionable in  the  construction  of  some  high  buildings  lies  in  the 
fact  that,  as  yet,  none  have  failed.  If  the  safety  of  such  great 
structures  is  to  be  determined  entirely  by  the  logic  of  the  fitness 
of  the  survivor,  based  on  a  brief  and  favorable  experience, 
rather  than  by  a  rigid  analysis,  by  tried  and  accepted  principles 
of  engineering  design,  it  may  ultimately  lead  to  some  very 
deplorable  results. ' ' 

Methods  of  Wind-bracing. — It  has  been  previously  said  that 
the  stability  of  a  building  must  depend  entirely  either  upon  the 
masonry,  that  is,  the  inertia  or  dead  weight  of  the  structure, 
or  upon  the  steel  framework.  A  free  standing  masonry  wall 
without  bracing  of  any  kind  will  resist  considerable  wind  pres- 
sure on  account  of  its  inertia  or  weight.  The  greater  the 
weight,  the  greater  the  resisting  moment,  and  in  this  way  it 
may  be  said  that  all  the  materials  entering  into  the  building 
act  in  some  degree  to  increase,  by  gravity,  the  static  conditions 
which  must  be  overcome  to  allow  failure.  In  buildings  of 
moderate  height,  with  solid  masonry  construction,  adequate 
resistance  to  lateral  deformation  may  be  secured  without  the 


WIND-BRACING.  255 

introduction  of  steel  bracing  members ;  but  in  veneer-construc- 
tion buildings  of  considerable  height,  in  which  thin  protective 
walls  only  are  used,  and  in  which  the  window  and  court  areas 
are  large,  and  the  partitions  thin  and  of  little  value,  the  lateral 
strength  of  the  materials  entering  into  the  construction  of  the 
building,  except  the  steel  frame,  cannot  be  counted  upon  as  of 
any  positive  value.  While  the  steel  frame  is  more  or  less 
reinforced  by  the  weight  and  stiffening  effects  of  the  other 
materials,  still  no  definite  or  even  approximate  values  can  be 
given  to  such  items,  except  their  purely  static  resistance  or 
weight. 

Mr.  Julius  Baier,  in  his  article  on  wind  pressure  in  the 
St.  Louis  tornado,  before  mentioned,  states  .as  follows  regard- 
ing the  necessity  for  some  efficient  system  of  metallic  sway- 
bracing: 

' '  The  effect  of  an  extreme  wind  pressure  on  a  high  office 
building  with  curtain  walls  must  depend  largely  on  the  extent 
to  which  the  frame  of  that  building  partakes  of  the  nature  of 
the  skeleton  type  or  the  cage  type  of  construction. "... 

"  If,  now,  the  building  is  of  the  pure  skeleton  type,  it  will 
have  only  the  elements  of  stability  " — given  by — "  its  weight 
above  the  floor  in  question,  and  possibly  some  additional  brac- 
ing of  a  more  or  less  uncertain  value  "  .  .  .  "  and  it  will  fail, 
just  as  the  elevator  failed;  it  will  topple  over  and  fall  to  one 
side  or  towards  one  corner  on  the  floor  below. "... 

' '  If  the  building  is  of  the  cage  type,  it  will  stand  safely 
under  a  wind  pressure  that  will  destroy  the  skeleton  building. 
While  the  failure  of  the  walls  at  any  story  may  reduce  the 
rigidity  somewhat,  it  cannot  affect  the  strength  of  a  framework 
designed  without  placing  any  dependence  on  the  covering. 
Such  a  framework  will  readily  carry  the  lateral  stresses  from 
the  upper  section  to  the  section  below."  .  .  . 

' '  The  St.  Louis  tornado  passed  within  less  than  a  mile  of 
the  office  buildings  in  that  city.  Fortunately  it  made  no  test 


256  ARCHITECTURAL  ENGINEERING. 

of  the  buildings,  but  it  has  left  some  definite  evidence  of  the 
possible  force  of  the  wind  and  of  the  action  of  this  force  on  the 
materials  of  construction.  While  it  raises  anew  the  question 
as  to  the  amount  of  wind  force  which  should  be  provided  for 
in  designing  high  buildings,  it  raises  with  more  emphasis  the 
question  as  to  the  method  of  providing  for  this  force  after  its 
amount  has  been  assumed.  Any  dependence  placed  on  curtain 
walls  and  partitions  for  lateral  strength  is  open  to  very  grave 
question.  The  rigidity  imparted  to  a  building  by  the  simul- 
taneous action  of  the  total  mass  of  material  under  ordinary 
conditions  is  no  indication  of  the  ultimate  strength  that  may 
be  developed  at  a  critical  moment,  and  the  very  general  failure 
of  the  walls  under  extreme  wind  pressure  further  destroys  any 
certainty  of  such  assistance  as  might  be  otherwise  relied  upon. 
The  elements  of  safety  against  wind  force,  exclusive  of  the 
strength  that  may  come  from  the  walls  and  partitions  where 
they  exist,  are  the  stability  due  to  weight  alone,  stability  due 
to  the  strength  and  stiffness  of  the  frame,  and,  when  the  force 
is  a  sudden  one,  the  inertia  of  the  mass  resisting  motion. "... 

' l  The  amount  of  metal  required  for  an  efficient  system  of 
wind-bracing  is  but  a  small  part  of  the  weight  of  the  metal  in 
the  entire  frame,  and  the  cost  of  the  latter  is  only  about  10  to 
20  per  cent,  of  the  expenditure  for  the  entire  building,  exclu- 
sive of  the  site.  The  cost  of  the  wind-bracing  can  represent, 
therefore,  only  a  very  small  proportion  of  the  total  capital  in- 
vested. When  it  is  considered  that  any  additional  metal  used 
to  strengthen  the  cage  as  a  precaution  against  wind  force  is 
equally  effective  against  possible  damage  due  to  earthquake 
shocks  or  to  the  unequal  settlement  of  the  foundations,  and  is 
also  an  additional  margin  provided  against  the  weakening 
effect  of  corrosion,  the  slight  increase  in  cost  must  appear 
trifling  as  compared  to  the  amount  of  the  entire  investment  and 
the  additional  protection  secured  for  the  property. ' ' 

"  It  is  somewhat  unfortunate  that  the  merits  of  the  design 


WMD-BRACMG.  257 

of  the  framework  are  not  so  readily  apparent  to  the  investor, 
and  that  this  part  of  the  structure  is  of  necessity  immediately 
covered  and  permanently  concealed  from  view.  If  the  differ- 
ence in  strength  and  security  due  to  the  construction  of  the 
frames  of  some  of  these  great  buildings  were  as  generally 
evident,  as,  for  instance,  the  difference  in  strength  due  to  the 
varying  thickness  of  solid  masonry  walls  was  in  older  forms  of 
construction,  there  would  probably  be  a  more  general  recogni- 
tion on  the  part  of  the  owners  of  the  need  of  securing  the  best 
type  of  framework. 

Full  reliance  must,  therefore,  be  placed  upon  some  form  of 
lateral  bracing  in  the  steel  frame.  This  may  be  obtained  by 
means  of  stiffness  in  the  connections,  and  through  the  intro- 
duction of  especial  bracing  members. 

The  lateral  strength  obtained  through  the  various  connec- 
tions of  the  steel  beams,  girders,  and  columns  is  largely 
proportional  to  the  details  employed  in  such  connections.  The 
difficulty  in  obtaining  proper  connections  in  cast  columns, 
either  between  themselves,  or  between  the  columns  and  the 
girders  or  bracing  members,  constitutes  one  of  the  principal 
objections  to  their  use.  Cast  columns  will  not  permit  of  the 
use  of  rivets,  nor  can  any  efficient  web  connections  be  obtained 
with  connecting  girders.  The  loose  bolts  destroy  the  neces- 
sary rigidity  of  the  bracing,  and  in  fact  the  entire  stiffness 
resulting  from  column  and  girder  connections  in  steelwork  is 
entirely  lacking  where  cast  columns  are  employed. 

No  great  rigidity  can  be  obtained  through  the  use  of  steel 
columns  which  are  joined  at  each  and  every  floor-level  by 
means  of  cap-plates.  Details  are  often  employed  wherein  the 
girders  rest  upon  the  cap-plates  of  the  columns,  being  secured 
by  means  of  rivets  in  the  lower  flanges  only  of  the  beams. 
Such  connections  are  worth  little.  A  better  detail  is  to  provide 
both  top  and  bottom  flange  connections,  using  an  angle  riveted 
to  the  column  for  the  top  connection,  with  a  leg  long  enough,. 


258 


ARCHITECTURAL   ENGINEERING. 


and  a  cap-plate  wide  enough,  to  secure  four  rivets  in  each 
flange.  A  still  better  detail  is  to  provide  special  brackets  on 
continuous  column  shafts,  so  that  the  girders  may  have  both 
top  and  bottom  flange  connections,  besides  web  connections 
directly  to  the  column. 

Considerable  stiffness  may  be  secured  by  means  of  using 
continuous  column  splices,  as  illustrated  in  Figs.  137  and  138, 
Chapter  VII,  where  the  columns  are  made  in  two-story  lengths, 
and  staggered  as  to  splices,  that  is,  adjacent  columns  breaking 
joints  in  alternate  floors.  If  this  method  is  employed  through- 
out the  building  it  will  add  materially  to  the  resultant  stiffness, 
but  no  very  definite  value  can  be  placed  upon  such  methods, 
.even  providing  efficient  web  connections  are  made  with  the 
igirders. 

Absolutely  positive  results  can  be  obtained  only  through 
the  use  of  some  definite  form  of  metallic  bracing.  This  may 
be  in  the  form  of  sway-rods,  portals,  or  deep  girders  between 
the  columns,  a  selection  depending  largely  upon  circumstances. 

Truss-rods,  portals,  or  lattice  or  plate  girders  constitute  the 
most  definite  types  of  wind-bracing  ordinarily  employed,  and 
one  of  these  systems  should  be  used  where  either  great 
strength  or  positive  assurance  is  desired. 


Q 
Q 


OOP 


KXXX 


FIG.  144.  FIG.  145.  FIG.  146. 

(2)  (3)  (4) 

Methods  of  Wind-bracing. 


FIG.  147. 
(s) 


Bracing  by  means  of  sway-rods  is  shown  in  Figs.  143  and 
144.  This  system  is  economical,  and  easy  of  erection,  the  only 
difficulty  lying  in  the  manner  in  which  the  sway-rods  require 


WIND-BRACING.  259 

a  wall  or  partition  to  contain  and  conceal  the  members.  The 
locations  of  doors,  etc.,  may  sometimes  be  arranged  to  better 
advantage  by  making  the  rods  pass  through  two  stories,  as  in 
Fig.  144. 

Portals,  as  in  Fig.  145,  can  be  used  in  place  of  sway-rods 
where  conditions  as  to  corridors,  doors,  etc.,  prohibit  the 
crossing  of  such  spaces.  In  this  system  the  transmission  of  the 
strains  in  the  portal  members  is  indirect,  and  their  use  is  not 
generally  considered  economical. 

Knee-braces,  as  in  Fig.  146,  may  only  be  considered  as  a 
partial  means  of  wind-bracing,  or  as  supplementing  the  stiff- 
ness in  connections  secured  elsewhere  in  the  structure.  These 
are  not  to  be  recommended  as  the  only  means  of  bracing  in 
any  important  work,  but  are  used  rather  as  an  act  of  necessity 
where  only  partial  bracing  is  required.  They  can  be  con- 
veniently arranged  in  the  exterior  walls  either  above  or  below 
the  girders,  or,  if  required,  both  above  and  below,  without 
interfering  with  the  architectural  requirements  as  to  windows 
or  other  openings.  Any  form  of  knee-bracing  requires  great 
exactness  in  manufacture,  and  care  in  erection. 

Lattice  girders,  as  in  type  (5),  Fig.  147,  now  constitute  a 
very  common  form  of  wind-bracing.  In  some  instances,  as  in 
the  Reliance  Building,  Chicago,  previously  illustrated,  plate 
girders  are  used  instead  of  latticed  members.  In  this  type  of 
bracing  the  wind  stresses  are  transferred  to  the  ground  on  what 
is  often  called  the  "table-leg  principle,"  that  is,  each  story  is 
made  rigid  in  itself,  the  columns  being  figured  as  vertical 
beams  to  resist  the  lateral  flexure  due  to  the  wind  forces. 

Wind-bracing  must  reach  to  some  solid  connection  at  the 
ground.  It  should  also  be  arranged  in  some  symmetrical 
relation  to  the  building  outlines.  If  the  building  is  narrow  and 
braced  crosswise  with  one  system,  the  bracing  should  be  mid- 
way, while  if  two  systems  are  employed,  they  should  be  placed 
equidistant  from  the  ends.  This  symmetry  is  necessary  to 


26o  ARCHITECTURAL  ENGINEERING. 

secure  the  equal  services  of  both  systems,  thus  preventing  any 
twisting  tendencies. 

Each  type  must  be  figured  properly,  as  the  strains  in  the 
horizontal  members  and  the  columns  are  essentially  concerned 
in  the  calculations.  The  problem  is  not  capable  of  exact  solu- 
tion, owing  to  several  indeterminable  factors  that  enter  into 
the  computations,  and  the  consequent  equal  number  of  assump- 
tions that  must  be  made.  The  stresses  in  the  wind-bracing 
will  be  maximum  when  the  direction  of  the  wind  is  normal  to 
the  exterior  wall,  or  parallel  to  the  plane  of  bracing.  This 
condition  is,  therefore,  assumed.  A  further  assumption  is 
made  that  the  floors  are  sufficiently  rigid  to  transmit  the  hori- 
zontal shears  due  to  wind. 

The  external  forces  will  be  the  same  whichever  of  the  five 
methods,  shown  in  the  figures  above,  is  used,  provided  the 
•exposed  areas,  panels,  etc.,  are  the  same.  The  horizontal 
external  force  at  any  panel  point  will  be  equal  to  the  distance 
between  the  systems  (at  right  angles  to  the  bracing)  times  the 
distance  between  floors  half-way  above  and  half-way  below, 
times  the  assumed  wind  pressure  per  square  foot.  The  total 
shear  at  any  point  equals  2,  or  the  sum  of,  the  forces  at  or 
above  the  point  taken. 

These  shears  are  undoubtedly  reduced  to  some  considerable 
extent  through  many  practical  considerations.  The  dead- 
weight of  the  structure  itself,  the  resistance  to  lateral  strains 
offered  in  the  stiff  riveted  connections  between  the  floor  systems 
and  the  columns,  the  stiffening  effects  of  partitions  (if  contin- 
uously and  strongly  built),  and  linings,  coverings,  etc.,  all  tend 
to  decrease  the  distorting  effects  of  the  wind  pressure.  But, 
in  view  of  the  uncertainty  in  regard  to  the  efficiency  of  these 
latter  considerations,  they  may  not  be  relied  upon,  and  are 
therefore  disregarded  in  the  calculations. 

Sway-bracing,  Analysis  of . — The  simplest  case  of  wind- 
bracing  is  shown  in  Fig.  143.  Considering  one  bay  alone  as 


H/IND-BRACING. 


261 


braced,  the  system  may  be  analyzed  as  follows:  Referring  to 
the  upper  story  of  a  framework,  as  shown  in  Fig.  148,  Pl  = 

Hoof. 


F& 


As 


± 


\ 


FIG.  148.  —  Figure  showing  Analysis  of  Sway-rod  Bracing. 

^L^  ,  where  Pl  =  resultant  wind  pressure  on  upper  story, 
p  =  unit-pressure,  and  Hl  and  Ll  equal  respectively  the  height 
and  width  of  the  area  affecting'the  bracing  in  the  panel  under 

p 
consideration.        ^-  must  then  be  the  horizontal  component  of 

the  stress  in  the   diagonal,  and  the  tension  in  this  diagonal, 
making  an  angle  0  with  the  horizontal,  must  be 


The  diagonal  tension  in  the  second  story  from  the  top  will  be 

Tz=  (--  -\-  P\    sec    t),    where    P  =  wind    pressure    on    any 

p 

single  story,  assuming  them  to  be  of  equal  height.      —  l  -j-  P  = 

compressive  stress  in  the  horizontal  strut  at  the  top-floor  level. 


In  like  manner,   T3  =  [—-  +  2P)  sec  6. 

The  tension  in  the  diagonal  rods  w 
loads  on  the  windward  columns,  and  an  equal  increase  in  loads 


3 
The  tension  in  the  diagonal  rods  will  cause  a  decrease  in 


*62  ARCHITECTURAL  ENGINEERING. 

on   the   leeward  columns.     Calling  this  increase     r  decrease 
Vl ,  we  have 

Vl  -  -^-,  where   ^  =  -^. 
In  a  similar  manner, 


2    -          /     »  3    -          f     ' 

Vz  must  equal  f^2  -f-  the  vertical  component  of  the  diagonal 
Ts,  or  Fg  =  — V2  -j"  jT3  sin  0.      This  will  serve  as  a  check  on 

the  calculations. 

These  wind  loads  Vlt  V2,  etc.,  must  be  added  to  all  the 
other  regular  loads  on  the  columns.  In  the  columns  i,  3, 
etc.,  the  direct  or  dead-loads  carried  by  the  columns  resist  the 
upward  vertical  components  of  the  stresses  in  the  rods  con- 
nected to  the  bottoms  of  these  columns.  Thus  the  dead-load 
in  column  3  is  reduced  by  the  full  amount  of  the  upward  com- 
pressive  strain  from  wind  in  that  column,  or  F2,  and  if  this 
amount  were  to  equal  or  exceed  the  dead- load  in  column  3, 
tension  would  occur  in  the  connection  of  this  column  to  the 
one  below. 

It  will  be  seen  that  the  increment  to  the  stress  V  at  each 
floor  may  be  eccentric,  as  shown  in  Fig.  155,  the  length  of  the 
arm  equalling  the  distance  from  the  point  of  attachment  to  the 
horizontal  strut,  to  the  centre  of  the  column  itself.  If  this 
connection  were  at  the  axis  of  the  column,  the  eccentricity 
would  be  reduced  to  zero,  and  the  eccentric  load  become  a 
dead-load. 

Take  the  case  of  a  typical  skeleton  building,  fourteen 
stories  in  height,  of  12  ft.  each,  24- ft.  front,  and  columns 
spaced  12  ft.  apart  in  the  depth  of  the  building.  Assuming 
that  stiffness  against  side-yielding  alone  is  necessary,  place 
diagonal  members  in  each  story,  as  in  Fig.  149,  utilizing  the 
floor-girders  as  struts,  with  the  columns  as  chords.  At  30  Ibs. 


WIND-BRACMG. 


263 


per  sq.  ft.  wind  pressure  the  panel-load  equals  4,300  Ibs. 
Considering  the  protection  afforded  by  neighboring  buildings, 
the  point  of  application  of  the  resultant  wind  pressure  will  be 
taker  at  two-thirds  of  the  height  of  the  structure  above  ground. 
^•^v^rfcT  The  total  shear  will  then  equal  about 
60,000  Ibs.,  or  30  tons.  In  the  basement 
panel,  then,  sec  0=  1.12,  giving  33.6 
tons  tension  in  the  cellar  diagonal.  The 
moment  of  the  resultant  wind  pressure 
=  30  X  n8  =  3,540  foot-tons,  and  this, 
divided  by  24,  gives  147 \  tons  compression  at 
the  leeward  foundation.  The  vertical  com- 
ponent of  the  basement  diagonal  =  15  tons, 
leaving  a  tension  of  132 £  tons  on  the  wind- 
ward column. 

The  dead  weight,  including  iron,  walls, 
floors,  filling,  etc.,  will  equal  about  250 
tons  for  one  foundation,  while  even  for  a 
building  with  no  filling  or  partitions  com- 
pleted, the  dead-weight  is  still  some  200 
tons,  thus  rendering  anchorage  unneces- 
sary. 

If,  in  the  same  cross-section  of  the 
building,  n  bays  not  adjacent  are  braced 
by  means  of  diagonal  rods,  the  tension  T 


-f* 

i 

i 

i 

i 

j 

1 

i 
\ 
\ 

\ 

^ 

t*t 

i 
\ 
\ 
i 
! 
i 
j 

^M 

* 

5 

<r> 

* 

\ 

i 
j 

X 

X 

^ 

X 

X 

X 

X 

X 

X 

X 

X 

\ 
4 

X 

i 

r—&j-'o"-* 

FlG.  149.  —  Figure 
showing  Typical 
Sway-rod  Bracing. 


P  f  rl 

becomes  7\  =  ^  sec  0,  and  Vl  =  -*£. 

The  bracing  in  Fig.  144  may  easily  be  analyzed  in  a 
manner  similar  to  the  above. 

Sway-bracing,  Examples  of. — One  of  the  highest  build- 
ings in  Chicago  is  the  Masonic  Temple,  273  ft.  10  ins.  from 
grade  to  top  of  coping.  A  cross-section  of  this  building  is 
shown  in  Fig.  150,  with  one  system  of  bracing-rods.  It  will 
be  seen  that  a  combination  of  forms  (i)  and  (2)  was  used,  the 


264 


ARCHITECTURAL  ENGINEERING. 


bracing  being  arranged  to  suit  halls  and  doorways.  In  this 
building  the  sway-rods  were  not  connected  to  the  floor-beams 
themselves,  but  to  special  I-beams  placed  between  the  columns 
and  just  below  the  floor  system. 

In  "The  Fair"  Building,  system  (i)  was  used,  but  with 
lattice  girders  from  column  to  column,  serving  as  struts  and 
floor-beams  at  the  same  time.  Gusset-plates  were  dropped 
below  the  girder  to  receive  the  pins  for  connection  with  the 
turnbuckle  rods. 

One  of  the  simplest  examples  of  system  (i)  of  wind-bracing 

was  described  by  Mr.  C.  T. 
Purdy    in    the    Engineering 
^    News,    vol.    xxvi.,    No.    52, 
•— f    the     example     referred      to 


FIG.  150. — Cross-section  of  Masonic  Temple, 
Chicago,  showing  Wind-bracing. 


FIG.  151.— Floor  Plan  of 
Venetian  Building. 


being  the  Venetian  Building,  Chicago.      The  floor  plan  of  this 
building  is  shown  in  the  accompanying  figure  (151),  the  four 


WIND-BRACING. 


sets  of  sway-rods  being  located  as  marked.  Each  set  of  brac- 
ing is  therefore  figured  to  resist  a  wind  pressure  for  an  area 
the  horizontal  width  of  which  is  equal  to  one-fifth  the  depth  of 
the  building,  and  the  height  of  which  is  the  height  of  the 
building.  The  area  tributary  to  each  floor  X  40  Ibs.  equals 
the  horizontal  shear  at  each  floor  or  panel -point,  while  the 
total  shear  at  any  floor  equals  the  sum  of 
the  shears  acting  on  the  panel-points 
directly  above,  as  we  have  seen  before. 
It  was  not  considered  necessary,  however, 
to  carry  the  whole  amount  of  this  shear 
into  the  steel  bracing.  The  practical  con- 
siderations which  tend  to  diminish  the  dis- 
torting effect  due  to  a  lateral  force,  decided 
that  but  70  per  cent,  of  these  shears  needed 
to  be  cared  for  by  the  bracing,  leaving  30 
per  cent,  to  be  taken  up  by  the  other 
factors.  The  strains  and  sections  for  one 
bay  are  here  given  (Fig.  152). 

All  the  columns  affected  by  this  brac- 
ing were  made  continuous  from  the  foun- 
dations to  the  second-floor  level,  and 
portals  were  used  to  take  the  place  of  the 
diagonal  rods  in  two  instances  v/here  rods 
were  out  of  the  question.  This  occurred 
on  a  main  floor  devoted  to  large  banking- 
rooms.  The  bending  moments  due  to 

FIG.   152.  —  Wind-brae-    , 
ing  in  Venetian  Build-  theSC  P°rtals  Were  taken  UP  in  the  Columns. 

ing.  In  the  case  where  the  rods  came  down  to 

the  first-floor  level,  the  bottom  strut  was  connected  to  the 
columns  so  as  to  take  both  tension  and  compression  horizon- 
tally, as  well  as  to  resist  the  component  of  the  rod  strains. 
This  insured  the  resistance  of  both  columns  to  the  horizontal 
thrust  of  the  strut,  whichever  pair  of  rods  was  strained,  and 


266  ARCHITECTURAL  ENGINEERING. 

the  columns  were  calculated  to  resist  the  bending  moment 
incurred,  as  well  as  to  carry  the  regular  column-loads. 

With  the  use  of  the  portals,  the  columns  were  designed  to 
resist  the  bending  moment  which  the  stopping  of  the  rods 
necessitated,  and  as  a  further  assurance  that  these  connections 
should  be  as  strong  as  the  rest  of  the  system,  the  top  connec- 
tions of  all  of  the  first-floor  beams  were  omitted,  and  the  clear- 
ance spaces  between  all  the  beams  and  columns  were  driven 
tight  with  thin  metal  wedges,  until  the  girders  and  beams 
passing  along  the  column  axes  were  continuous  and  in  com- 
pression out  to  the  sidewalk  walls,  which  latter  are  backed  by 
the  solid  street. 

The    horizontal    channel-struts    are    shown    in    Fig.    153. 


FIG.  153.— Detail  of  Channel-struts.     Venetian  Building. 

They  were  used  as  shown  up  to  and  including  the  seventh 
floor.  A  lighter  section  was  used  for  the  floors  above.  A 
slight  connection  only  was  made  between  the  channel-struts 
and  the  columns.  The  struts  were  planed  at  both  ends,  with 
no  clearance,  thus  making  butt  joints  with  the  columns.  A 
bent  plate  between  the  channels  provided  holes  for  four  rivets 
connecting  to  the  columns,  but  they  were  hardly  necessary. 
Underneath  the  ends  of  these  struts  a  cast-iron  block  was 
bolted  to  the  column  and  supported  by  two  bracket-angles 
beneath,  with  sufficient  rivets  to  resist  the  vertical  compression 
of  the  rods  in  this  direction  (see  Fig.  154). 

Above  the  ends  of  the  struts  other  cast-iron  blocks  were 
used,  planed  top  and  bottom,  thus  allowing  them  to  fit  in 


WMD-BRACMG. 


267 


tightly  between  the  tops  of  the  struts  and  the  cap-plates  of  the 
columns.  These  blocks,  therefore,  fitted  into  the  recesses 
made  by  the  flanges  of  the  Z-bars  so  closely  that  the  f-in. 
cap-plates  were  brought  into  direct  shear  entirely  around  three 
sides  of  the  blocks.  The  shear  resistance  of  the  plate, 
together  with  the  weight  of  the  beam  on  it,  was  more  than 
sufficient  to  resist  the  upward  vertical  component  of  the  rods. 
Such  cast-iron  blocks  in  this  connection  are  very  convenient 


FIG.  154.— Detail  of  Channel-Strut 
Connections.     Venetian  Building. 


FIG.    155.— Partial    Cross-section 
of  Venetian  Building. 


for  use,  for  it  often  happens  that  the  bracket-angles  cannot  be 
brought  directly  under  the  channels  of  the  struts,  and  the 
medium  between  the  strut  and  the  bracket-angles  must  act  as 
a  beam  as  well  as  a  filler.  Fig.  155  shows  a  partial  cross- 
section  of  the  building  with  doorway,  etc.  This  shows  the 
reason  for  placing  the  pin-points  so  far  from  the  column- 
centres.  The  channel-struts  are  reinforced  with  cover-channels 


268 


ARCHITECTURAL  ENGINEERING. 


to  resist  the  bending  moment  on  the  strut  caused  by  thus 
moving  the  pin-centres. 

The  diagonal  rods  in  this  building  were  proportioned  on  a 
basis  of  20,000  Ibs.  per  sq.  in.  All  rods  had  turnbuckles, 
and  no  rods  were  of  an  area  less  than  $  in.  square.  The 
Ashland  Block,  by  Burnham  &  Root,  Chicago,  has  longer 
struts  than  those  in  the  Venetian  Building,  15-in.  channels 
being  used  in  the  floors,  acting  both  as  struts  and  floor-beams. 

Portal  Bracing  (3),  Analysis  of  —  The  third  method  of 
wind-bracing,  called  the  portal  system,  may  be  analyzed  as 
follows  (see  Fig.  1  56)  :  Taking  the  upper  floor  first,  the 


K  ---  X  -- 


r—%4 


•Z, 


•& 


"77 

i 

i  J 


! 
I 

J_ 


cr 

FIG.  156. — Figure  showing  Analysis  of  Portal  Bracing. 

external  force  Pl  may  be  considered  as  producing  equal  hori- 
zontal reactions  at  the  bottoms  of  the  portal  legs,  or  at  the 


W1KD-BRACMG.  269 

p 

floor-level,  equal  to  —  each.     A  wind  moment  M  is  also  pro- 

duced at  this  floor-level,  or, 

TT 

M  =  P\h\  >   where  frl  =  —  -  . 

Owing  to  the  rigidity  of  the  framework,  this  wind  moment 
will  be  resisted  by  the  resisting  moment  of  the  column  sections, 
and  by  the  portal  connections  at  the  floor-line.  This  resisting 

moment  must  equal  —  ,  where  f  =  the  unit-strain  on  extreme 

fibres,  yv  =  distance  of  extreme  fibres  from  the  neutral  axis, 
and   /=  moment   of  inertia   of  the  section.      But  M=P1hl, 

hence/=  f 


/  will  be  slightly  different  on  the  two  sides  of  the  neutral 
axis.  On  the  compression  side  of  the  bay,  /  will  be  taken  as 
the  moment  of  inertia  of  the  section  of  the  column  and  the 
portal,  while  on  the  tension  side,  /  must  be  taken  for  a  section 
of  the  column  and  the  bolts  securing  the  portal  to  the  floor- 
beam  or  to  the  portal  below.  If  a  splice  occurs  in  the  column 
on  the  tension  side,  /  must  be  taken  for  the  sections  of  the 
bolts  connecting  the  cap-plates  of  the  column,  and  for  the 
bolts  through  the  portal  and  floor-beam. 

The  decrease  of  load  on  the  one  column,  and  the  equal 
increase  in  load  on  the  other  column  will  be  as  before,  or 


In  column  2,  the  vertical  column-load  Vl  due  to 

wind  must  be  added  to  the  regular  column-load,  the  same  as 
in  previous  discussion.  V^  must  also  equal  the  shear  on  all 
vertical  planes. 

The  horizontal  shear  along  the  line  aa  —  Pl  ,  while  the 
horizontal   shear  in  either  leg  or  portal  or  at  bottom  of  leg 

p 

=  —  .     These  shears  will  determine  the  thickness  of  the  webs. 
2 


270  ARCHITECTURAL  ENGINEERING. 

The  connections  of  the  portal  to  the  column  on  either  side 
must  equal  the  total  vertical  shear. 

Taking  moments  about  the  line  dd,  it  will  be  found  that 
2M  =  O.  That  is,  there  is  no  bending  moment  along  the 
line  dd,  and  neither  the  floor-beams  nor  portals  are  strained  by 
bending  moment  along  this  line. 

For  a  maximum  stress  in  the  flange  C  take  a  point  in 
flange  A,  distant  x  from  line  dd,  and  distant  j/,  at  right  angles, 
from  flange  C.  Then  x  times  the  vertical  shear  divided  by 

y  =  stress  at  section  taken,  and  this  is  maximum  when  —  has 

y 

its  maximum  value.  The  stress  in  the  flange  A  may  be 
obtained  in  a  similar  manner. 

The  leg  of  the  portal,   including  column  2,  may  also  be 

p 
taken  as  a  cantilever,  with  the  two  forces  —  and  Vv  acting  on 

it.  The  flange  C  will  be  in  compression,  the  column  itself 
acting  as  a  tension  chord.  Assume  a  point  on  the  centre  line 
of  the  column,  distant  xl  from  bottom  of  leg,  and  at  distance 

yl  from  the  flange  C,  at  right  angles.      Then  — — I  =  strain  in 

2y\ 

flange  C,  and  this  is  maximum  when  —  is  maximum.     There 

is  a  slight  error  in  this  treatment,  but  it  is  on  the  side  of  safety. 
If  the  flange  C  is  proportioned  for  these  maximum  stresses,  the 
requirements  will  be  fulfilled. 

In  the  second  story  from  the  top,  Vz  =  -~  ,  considering 

P2  =  2/\ ,  or  that  the  stories  are  of  equal  height.  The  con- 
centric load  Fj  in  column  2  from  the  column  above,  and  its 
equal  reaction,  may  be  omitted  in  a  calculation  of  the  strength 
of  the  portal-bracing  (as  they  are  applied  along  the  same 
straight  line),  as  may  also  the  equal  negative  effects  in 
column  i. 


WMD-BRACMG 


271 


The  vertical  shear  in  this  second-story  bracing  will  equal 
S2  =  Vz  —  Vr     The  horizontal  shear  across  the  top  of  the 

p 
portal  =  P2 ,  while  in  either  leg  the  shear  ==  — -. 

Portal-bracing,  Examples  of. — One  of  the  first  attempts 
at  a  portal  system  in  building  construction  was  through  the  use 
of  a  portal-strut  used  in  the  older  portion  of  the  Monadnock 
Building,  as  in  Fig.  157. 
I     f^._ 


FIG.  157. — Portal-strut  used  in  Monadnock  Building. 

The  portal  system  (3)  was  used  in  the  Old  Colony  Building, 

Chicago,   completed  in  1894.     The  portals  are  placed  at  two 

planes  in  the  building — a  cross-section  of  one  set  being  shown 

in  Fig.  158.     Wind  pressure  was  figured  at  27  Ibs.  per  sq.  ft. 


FIG.  158. — Cross-section  showing  Portals  in  Old  Colony  Building. 

on  one  side  of  the  building  at  a  time.      Each  portal  was  cal- 
culated independently  for  the  sections  of  both  top  and  bottom 


272 


ARCHITECTURAL  ENGINEERING. 


flanges,  thickness  of  web,  cross-shear  on  rivets  connecting  the 
curved  flanges,  and  for  all  splices  and  connections.  A  detail 
of  one  portal  is  shown  in  Fig.  159.  This  arrangement  of 


U 

FIG.  159. — Detail  of  Portal  in  Old  Colony  Building. 

wind-bracing  proved  very  satisfactory  in  all  respects,  and, 
according  to  the  designer,  was  cheaper  in  the  end  than  the 
sway-rods  provided  in  the  first  design ;  but  the  writer  would 
question  whether  portal-bracing  can  be  provided  cheaper  than 
tension-rods,  as  claimed.  With  good  details  in  connections 
and  proper  regard  for  their  location  in  the  original  planning  of 
the  building,  sway-rods  can  be  used  without  great  expense  or 
trouble.  The  portal  arrangement  certainly  makes  a  fine 
interior  appearance  if  the  arched  openings  are  given  a  slight 
decorative  treatment  in  plaster,  as  was  done  in  the  Old  Colony 
Building.  The  floor  plan  will  generally  govern  the  use  of 


W1KD-BRACMG. 


273 


either  one  or  the  other  system,  whether  the  rooms  are  to  be 
connected  by  large  openings  or  small  doorways. 

Knee-braces  (4),  Analysis  of.  —  The  system  of  knee- 
braces,  or  arrangement  (4)  for  wind-bracing,  is  not  an 
economical  method,  as  it  produces  heavy  bending  moments  in 
both  the  horizontal  struts  and  in  the  columns  themselves.  This 
system  may  be  analyzed  as  follows  (see  Fig.  160): 

6 


\  /i--*— 

*^f 

i 

t 

£•—* 

i 

\ 

i 

^JL.  > 

\ 

^ 

i 
A 

\ 

\ 

\            \ 

1 

.1.1 

FIG.  160.  —  Figure  showing  Analysis  of  Knee-bracing. 

p 

The  shear  at  the  top-floor  level  will  be  —  at  each  column. 

P  h 

Then  as  before,   V^  =  —  j-1. 

The  tension  in  the  brace  cb  is  nearly 


r  =     ff     =     . 

2  '     l  '  /j          2/j    ' 

There  will  be  an  equal  amount  of  compression  in  the  opposite 
brace.  This  suggests  the  use  of  knee-braces  capable  of  resist- 
ing both  compression  and  tension.  There  will  be  a  bending 

P      h 

moment  at  C  whose  value  is  approximately  M  =  —  •  .  —  = 
1  ".      The  factor  —  is  used,  as  the  column  is  considered  as 


274 


ARCHITECTURAL  ENGINEERING. 


square-ended  and  fixed  by  the  static  load  and  by  bolts.      This 
bending  moment  will  also  exist  at  d. 

Ph./ 

At  b  there  will  be  a  bending  moment  Ml  =  V^  =  — l~r^- 

Knee-braces,  Examples  of. — This  type  of  wind-bracing 
was  used  in  the  Isabella  Building,  by  W.  L.  B.  Jenney,  archi- 
tect, as  shown  in  Fig.  161. 


FIG.  161. — Detail  of  Knee-bracing.  Isabella  Building. 
A  modification  of  the  knee-brace  system  of  wind-bracing 
was  employed  in  the  new  Fort  Dearborn  Building  (1894-95), 
by  Jenney  &  Mundie,  architects,  Chicago.  In  this  case  a  wind 
load  of  40  Ibs.  per  sq.  ft.  was  taken,  and  the  assumption  made 
that  25  per  cent,  of  this  wind  load  would  be  resisted  by  the 
rigid  connections  provided  between  the  columns  and  the  floor 
system,  leaving  75  per  cent.,  or  30  Ibs.  per  sq.  ft.,  to  be  taken 
up  by  the  exterior  columns.  This  was  done  by  using  channel 
girders  between  the  columns  in  the  exterior  walls,  with  gusset- 
plate  connections  to  the  columns,  as  shown  in  Fig.  162,  lo-in. 
and  i2-in.  channels  being  used  generally.  In  the  lower  stories, 


WIND-BRACING. 


275 


where  the  wind  moment  necessitated  it,  a  double  system  of 
gusset  connections  was  used,  under  and  above  the  channel 
girders. 


MM1 


I 

FIG.  162. — Detail  of  Channel-struts  and  Gussets. 
Fort  Dearborn  Building. 

Lattice  Girders  (5),  Analysis  of. — Referring  to  Fig.  163, 
the  external  wind  pressure  for  the  panel  in  question  may,  as 
before,  be  represented  by  Pn ,  this  being  for  a  superficial  area 
extending  half  way  to  the  next  bracing  members,  both  hori- 

p 

zontally  and  vertically.       —  may  then  be  considered  as  applied 

in  a  line  with  each  chord  of  the  girder.  The  horizontal  shear 
due  to  the  force  Pn  must  then  be  resisted  by  the  two  columns 
at  any  and  all  points  between  the  lower  line  of  the  girder  and 
the  top  line  of  the  girder  below.  Hence  the  foot  of  each 

p 

•column  must  resist  the  shear  — -.     Also,  if  Ps  represents  the 


276 


ARCHITECTURAL   ENGINEERING. 


shear  from  all  the  stories  above  the  bracing  in  question,  — - 
will  equal  the  shear  at  the  foot  of  each  of  the  upper  columns, 

P    JL.p 

and will  be  the  total  shear  at  the  foot  of  each  of  the 

columns  in  the  story  under  consideration. 


n 


I 


c 


LT 1 iU 

FlG.  163. — Figure  showing  Analysis  of  Lattice-girder  Bracing. 
If  the  compression  in  the  leeward  column  or  the  decrease 
in  load  in  the  windward  column  is  called  V  as  formerly,  for 
the  story  in  question,  and  if  VH  represents  the  same  forces  in 
the  story  above,  then 


This  value  of  V  is  a  live  load  due  to  the  wind  forces,  and 
must  be  added  to  the  other  column  loads  as  in  previous 
examples. 


WMD-BRACMG. 


277 


The  compressive  stress  in  the  upper  flange  of  the  girder, 
or  member  ac, 


,,       ,  „ 

'       2     "' 


The  stress  in  the  lower  flange  of  the  girder,  or  member  bdy 
which  is  also  compression, 


Considering  the  columns  as  fixed  at  both  ends,  the  maxi- 
mum bending  moments  will  be  at  the  points  b  and  d,  and  will 
be  equal  to 

2    X    ~^~~  X  k*  = 

The  columns  must  be  designed 
to  resist  this  bending  moment  as 
well  as  the  vertical  loads.  This 
would  suggest  that  in  narrow  build- 
ings of  considerable  height,  the 
columns  be  made  of  such  form  as 
to  give  a  greater  width  or  depth  in 
the  narrow  direction  of  the  struc- 
ture than  is  provided  lengthwise, 
thus  providing  in  the  form  for  this 
additional  moment. 

The  values  V  previously  derived 
may  be  obtained  somewhat  more 
simply  by  using  the  notation  given 
in  Fig.  164. 

Let/  =  wind  pressure  per  lineal 

foot  Of  height;  riG.l64.-Analysi.of 

h^  =  distance    from    roof  to  girder  Bracing. 

foot  of  columns  of  story  in  question ; 
h  =  distance  from  foot  of  columns  in  question  to  line 

midway  between  girders  in  story  in  question  and 

story  below. 


4 

fly 

ffoof 

f^ 

2 

t 

z 

i 

3 

&+ 

4- 

4 

S 

6 

Pr 

—?f- 

r^i 

,._.j  , 

2  78  ARCHITECTURAL  ENGINEERING. 

Then  P7  =  p(h7  —  h),  and 


„ 

'    I  2l 

This  value  of  V  should  correspond  with  that  previously 
given. 

Lattice  Girders,  Examples  of.  —  Lattice  girders  as  here 
described  are  almost  invariably  used  in  supporting  the  floor- 
loads  for  the  tributary  areas,  the  floor-beams  being  carried  at 
the  panel-points  of  the  latticed  members.  Also,  when  located 
within  the  exterior  walls,  the  girders  serve  as  spandrel  sup- 
ports as  well,  thus  carrying  the  wall-loads  story  by  story. 
The  girders  consequently  perform  a  twofold  service  —  they 
support  vertical  floor-  and  wall-loads  and,  at  the  same  time, 
serve  as  struts  for  the  transmission  of  wind  strains. 

In  proportioning  such  members,  they  should  first  be  cal- 
culated for  the  vertical  loads  —  either  for  the  floor-  or  wall- 
loads,  or  both,  after  which  the  sections  of  the  upper  and  lower 
flanges  should  be  increased  to  provide  for  the  additional  wind 
strains  here  given.  The  diagonals  or  lattice  members  should 
also  be  somewhat  increased  in  section,  thus  providing  for  suffi- 
cient rigidity  between  the  flanges.  The  girders  are  usually 
made  the  full  depth  of  the  spandrel,  reaching  from  just  above 
the  top  of  one  window  to  immediately  below  the  sills  of  the 
windows  in  the  next  story  above. 

In  some  cases,  where  double-story  column  lengths  are 
employed,  lattice  girders  of  this  type  are  placed  at  the  column 
joints  only,  that  is,  in  alternate  stories.  In  the  intermediate 
stories,  the  usual  spandrel-beams  or  channels  are  inserted. 
This  practice  greatly  increases  the  bending  moments  on  the 
columns,  and  is  not  advisable  in  extremely  high  or  important 
work. 

Fig.  165  illustrates  a  diagram  elevation  of  the  framework 
of  the  south  wall  of  the  Park  Row  Building,  showing  the 


tWND-B&JCING. 


279 


combined  use  of  lattice,  plate,  and  box  girders,  angle-braces, 
and  sway- rods.  A  good  example  of  lattice  girders  was  also 
employed  in  the  Tract  Society  Building,  New  York  City. 

In  the  Reliance  Building,  Chicago,  55  ft.  wide  and  200  ft. 


FiG.i6s. — Diagram  Elevation  of  Park  Row  Building,  showing  Wind  Bracing, 
high,  24-in.  plate  girders  were  used  between  all  outside 
columns,  the  connections  to  the  columns  being  made  vertically 
to  the  webs  of  the  girders,  as  shown  in  Figs.  103  and  126. 

In  the  very  narrow  ic-story  Worthington  Building,  Boston, 
the  wind  strains  were  cared  for  without  the  aid  of  any  diagonals 
or  portals  by  making  the  corner  columns  of  two  heavy  web 
plates,  one  in  each  wall  plane,  which  thus  acted  as  vertical 


280  ARCHITECTURAL   ENGINEERING. 

plate  girders.  The  intermediate  wall  columns  are  also  built 
up  of  plates  and  angles,  but  of  large  superficial  areas.  The 
columns  are  united  by  continuous  lines  of  plate  girders,  serving 
as  both  wall-  and  floor-girders  as  well  as  for  the  transmission 
of  wind  strains,  the  total  wall  area  thus  appearing  much  like 
a  solid  metal  diaphragm  or  sheet,  perforated  by  window  areas. 

In  this  building  some  of  the  plate  girders  are  arranged  with 
sliding-shelf  seats  and  slotted  holes,  so  as  to  provide  for 
expansion  and  contraction  under  variations  of  temperature. 

Deflection  or  Vibration. — For  the  theoretical  limit  in  the 
height  of  a  building,  considering  the  wind  pressure,  we  may 
assume  that  the  wind  acts  against  the  building  in  a  horizontal 
direction,  so  that  the  structure  may  be  taken  as  being  under 
the  same  conditions  as  a  uniformly  loaded  beam,  fixed  at  one 
end  and  with  the  other  end  free.  If  this  were  actually  the 
case  with  a  steel  beam,  we  should  make  the  depth  of  the  beam 
such  that  it  would  deflect  less  than  the  amount  necessary  to 
crack  the  plaster.  If  the  beam  were  supported  at  both  ends, 
this  depth  would  be  one  twentieth  of  the  span. 

The  lengths  under  these  two  conditions,  to  secure  the  same 
deflections,  must  bear  the  relation  one  to  the  other  as  0.57 
to  i. 

If,  then,  we  have  an  office  building  or  any  skeleton  struc- 
ture 25  ft.  wide,  and  make  the  height  twenty  times  the  width, 
the  building  would  be  500  ft.  high,  and  reducing  this  in  the 
above  ratio,  we  have  285  ft. 

This  height  would  give  a  theoretical  deflection  of  some 
8  ins.  or  9  ins. ,  which  would  throw  the  centre  of  gravity  of  the 
upper  wall  beyond  the  outer  edge.  The  maximum  allowable 
deflection  would  be  about  2^  ins.  or  3  ins.,  and  this  would  give 
a  height  of  from  70  to  95  ft. 

The  load  effect  on  a  uniformly  loaded  cantilever  is  four 
times  that  for  a  uniformly  loaded  beam  supported  at  both  ends. 
If  we  work  on  the  assumption  that  the  building  is  analogous 


WIND-BRACING.  2  8 1 

to  the  cantilever  beam,  and  make  its  height  one  fourth  as  great 
as  we  would  if  it  were  supported  at  both  ends,  we  should  have 
the  depth  to  the  length  about  as  I  to  5.  This  would  give  a 
height  of  125  ft. 

Some  careful  experiments,  however  (see  Engineering 
News,  March  3,  1894),  on  the  deflections  of  tall  skeleton-con- 
struction buildings  in  Chicago,  tend  to  show  that  any  actual 
deflections  in  well  designed  and  carefully  constructed  buildings, 
under  very  heavy  winds,  are  far  less  than  any  theoretical 
assumptions.  Two  sets  of  tests  were  made,  one  on  the 
Monadnock  Building  of  seventeen  stories,  and  the  other  on 
the  Pontiac  Building  of  fourteen  stories.  Observations  were 
made  with  transits  set  in  sheltered  positions,  and  these  obser- 
vations were  checked  by  means  of  plumb-bobs,  suspended  in 
the  stair-wells  from  the  top  floor. 

The  vibrations  in  the  Monadnock  Building  from  west  to 
east,  or  in  its  narrow  direction,  were  from  J  in.  to  ^  in.  The 
plumb-bob  test,  however,  showed  the  greatest  variation  to  be 
in  a  north  and  south  direction,  or  longitudinally;  but  as  the 
walls  in  three  of  the  four  separate  divisions  of  this  building  are 
of  solid  brickwork,  from  3  ft.  to  6  ft.  in  thickness,  and  the 
length  is  several  times  the  breadth,  it  is  difficult  to  believe  that 
any  actual  longitudinal  deflection  could  be  detected. 

In  the  transverse  deflections  the  transits  showed  a  greater 
deflection  in  the  veneer  portion  of  the  building  than  in  the 
more  solid  parts,  as  would  very  naturally  be  expected.  The 
time  of  a  complete  vibration  was  two  seconds. 

The  experiments  on  the  Pontiac  Building,  which  is  of  the 
veneer  type,  compared  very  closely  with  those  on  the  Monad- 
nock Building,  except  that  the  amplitude  of  the  vibration  was 
less  in  the  former  building,  due  to  its  somewhat  more  sheltered 
position.  The  same  peculiarity  of  an  apparently  greater  longi- 
tudinal vibration  was  noticed  here  also.  The  wind  was  from 
the  northwest,  and  registered  eighty  miles  per  hour. 


282  ARCHITECTURAL  ENGINEERING. 

Veneer  or  skeleton  construction  has  been  adopted  in  San 
Francisco,  where  the  fear  of  earthquakes  has,  heretofore,  been 
sufficient  to  keep  investors  from  erecting  high  buildings.  The 
new  Chronicle  Building  and  the  Croker  and  Mills  buildings 
are  of  the  veneer  type,  twelve  stories  and  over  in  height,  and 
have  served  as  precedents  in  that  locality. 

In  1897,  a  still  higher  structure,  namely,  the  Spreckels 
Building,  was  erected  after  advanced  methods.  This  building 
is  for  office  purposes,  the  height  being  19  stories,  or  300  ft. 
above  the  sidewalk.  An  earthquake  shock  which  disturbed 
that  locality  in  the  spring  of  1 898  was  reported  to  have  caused 
the  building  to  rock  and  sway,  but  to  have  left  it  practically 
uninjured. 

Building  Laws. — The  building  laws  of  Greater  New  York 
require  the  following  provisions  as  regards  wind  forces: 

"  All  structures  exposed  to  wind  shall  be  designed  to  resist 
a  horizontal  wind  pressure  of  thirty  pounds  for  every  square 
foot  of  surface  thus  exposed,  from  the  ground  to  the  top  of  the 
same,  including  roof,  in  any  direction. 

"In  no  case  shall  the  overturning  moment  due  to  wind 
pressure  exceed  seventy-five  per  centum  of  the  moment  of 
stability  of  the  structure. 

4 'In  all  structures  exposed  to  wind,  if  the  resisting 
moments  of  the  ordinary  materials  of  construction,  such  as 
masonry,  partitions,  floors,  and  connections  are  not  sufficient 
to  resist  the  moment  of  distortion  due  to  wind  pressure,  taken 
in  any  direction  on  any  part  of  the  structure,  additional  bracing 
shall  be  introduced  sufficient  to  make  up  the  difference  in  the 
moments. 

"  In  calculations  for  wind-bracing,  the  working  stresses  set 
forth  in  this  Code  may  be  increased  by  fifty  per  centum. 

"  In  buildings  under  one  hundred  feet  in  height,  provided 
the  height  does  not  exceed  four  times  the  average  width  of  the 
base,  the  wind  pressure  may  be  disregarded." 


WIND-BRACING.  283 

The  Chicago  building  ordinance  makes  the  following 
requirements : 

"  In  the  case  of  all  buildings,  the  height  of  which  is  more 
than  one  and  one-half  times  their  least  horizontal  dimension, 
allowances  shall  be  made  for  wind  pressure  which  shall  not  be 
figured  at  less  than  thirty  pounds  for  each  square  foot  of 
exposed  surface.  In  buildings  of  skeleton  construction  the 
metal  frame  must  be  designed  to  resist  this  wind  pressure. ' ' 

The  building  laws  of  Boston  and  Philadelphia  contain  no 
reference  to  wind  pressures. 


CHAPTER   IX. 
FOUNDATIONS. 

No  part  of  the  architect's  or  engineer's  work  requires  more 
care  than  the  successful  planning  and  carrying  out  of  the  foun- 
dation design.  The  importance  of  an  adequate  foundation 
has,  fortunately,  been  pretty  generally  realized  at  all  times; 
but  where  the  architect  or  engineer  was  formerly  called  upon 
to  meet  only  comparatively  simple  conditions  in  building  prac- 
tice, namely,  the  designing  of  offset  masonry  foundations  for 
buildings  of  no  great  height  where  little  or  no  thought  for 
adjacent  work  was  required,  present  conditions  of  foundation 
design  in  large  cities  often  make  an  exceedingly  complex 
problem.  The  architect  must  now  deal  with  large  concen- 
trated loads  for  buildings  of  great  height  and  often  of  very 
small  area;  he  must  frequently  build  on  treacherous  soil,  and 
thus  be  required  to  find  expedients  to  supplement  the  natural 
weakness  of  the  foundation  bed  by  artificial  means ;  the  safety 
of  surrounding  structures  must  be  preserved  during  building 
operations ;  and  means  must  be  provided  to  guard  against  the 
undue  settlement  of,  and  consequent  damage  to  adjoining 
buildings. 

Foundation  design  for  important  structures  will  be  found 
to  differ  widely  in  various  cities  or  localities,  owing  to  the 
great  differences  in  the  character  of  the  underlying  material. 
Thus,  in  Chicago,  surface  foundations  predominate  in  high 
building  design;  in  Boston,  piles  are  used  very  extensively; 
and  in  New  York  City  pneumatic  foundations  to  bed-rock  or 
hard  pan  have  been  largely  used  since  the  introduction  of 
skeleton  methods.  All  of  these  types  will  be  explained  more 
or  less  fully  in  this  chapter,  but  successful  and  economical 

284 


FOUNDATIONS. 


285 


foundations  are  so  largely  matters  of  good  judgment  and 
experience,  that  general  descriptions  only  may  be  attempted 
as  guides  to  conditions  arising  in  actual  practice. 

Bearing-power  of  Foundation  Materials. — The  safe  loads 
which  may  be  applied  to  foundation  soils  naturally  vary  greatly 
according  to  the  character  or  composition  of  the  stratum  to  be 
built  upon,  or  upon  the  character  of  the  underlying  but  invisi- 
ble subs  oil.  It  will  not  be  sufficient  to  base  any  decided 
opinions  upon  what  may  be  seen  only.  An  examination 
below  the  surface  is  indispensable  for  all  materials  except  firm 
rock,  unless  precedent  has  unquestionably  established  safe 
•unit-loads. 

Foundation  materials  vary  in  reliability  from  rock  bottom, 
hard  and  compact  and  in  natural  bed,  to  poorer  or  "rotten  " 
rock  formations,  clayey  soils,  gravel,  or,  finally,  to  such 
unstable  bottoms  as  mud,  marshy  ground,  or  quicksand.  For 
complete  data  as  to  the  bearing  power  of  these  different 
materials,  and  for  a  great  range  of  valuable  information  per- 
taining to  foundations,  reference  may  be  made  to  "  A  Treatise 
on  Masonry  Construction,"  by  Prof.  I.  O.  Baker,  or  to 
"A  Practical  Treatise  on  Foundations,"  by  W.  M.  Patton. 
The  following  table,  giving  the  average  safe  bearing-powers  of 
soil,  is  taken  from  Prof.  Baker's  work: 


Kind  of  Material. 

Safe  Bearing  power 
in  Tons  per  Sq.  Ft. 

Min. 

Max. 

Rock  —  the  hardest  —  in  thick  layers,  in  native  bed  

2OO 
25 
15 

5 
4 
2 

I 
8 
4 

2 

0.5 

30 
2O 
IO 

6 
4 

2 
IO 

6 
4 
I 

"         ii      11     ii     brick           " 

Clay,  in  thick  beds,  always  dry  

"      clean    dry 

286  ARCHITECTURAL  ENGINEERING. 

For  ordinary  soils  it  is  therefore  generally  safe  to  assume  a 
capacity  of  from  2  to  4  tons,  or  4,000  to  8,000  Ibs.  per  square 
foot,  while  for  soft  or  treacherous  soils,  or  those  resting  on  soft 
strata,  the  load  should  not  exceed  I  to  2  tons,  or  2,000  to 
4,000  Ibs. 

In  building  a  structure  of  any  importance  upon  soft  or 
yielding  material,  either  because  of  the  difficulty  or  expense  in 
reaching  a  firm  bottom,  it  is  not  always  sufficient  that  the 
weight  upon  the  soil  should  cause  no  injurious  settlement;  for 
if  such  material  as  mud  or  fine  wet  sand  is  heavily  loaded  and 
not  confined,  the  lateral  escape  of  the  semi-fluid  mass  may  be 
permitted  by  near-by  excavations  or  building  operations,  or 
even  by  excavations  at  a  considerable  distance.  Such  lateral 
escapement  may  result  in  serious  settlement  to  the  structure, 
or  in  great  expense  and  trouble  to  adjacent  owners,  even 
where  the  building  laws  may  have  been  technically  complied 
with.  If  any  possibility  of  lateral  relief  exists,  equity  to  all 
should  dictate  the  use  of  deep  foundations  or  piles  to  solid 
material.  It  has  been  claimed  that  an  excess  of  settlement 
has  resulted  in  certain  structures  in  New  York  City,  lying  near 
the  water-front,  due  to  this  flow  of  underlying  soft  soil.* 

In  compact  clayey  soils,  the  large  experience  gained  on 
such  foundation  material  in  Chicago  goes  to  show  that  no  per- 
ceptible lateral  movement  occurs;  for  with  very  heavy  build- 
ings on  either  side  of  the  street,  the  soil  would  naturally  fol- 
low the  line  of  least  resistance,  and  show  upheaval  or  disturb- 
ance of  piping  and  pavements.  This  tendency  has  never  been 
noticed,  and  it  is  therefore  presumed  that  the  settlement  which 
does  occur  results  from  the  gradual  squeezing  out  of  the 
water  in  the  clay. 

Rock  foundation  is  seldom  loaded  to  the  full  capacity,  even 
under  greatly  concentrated  loads.  In  New  York  City,  the 

*  See  "Concerning  Foundations  for  Heavy  Buildings  in  New  York 
City,"  by  Chas.  Sooysmith,  Trans.  Am.  Soc.  C.  E.f  vol.  xxxv. 


FOUNDATIONS.  287 

hard  stratum,  where  not  rock,  is  usually  found  to  be  a  very 
firm  and  compact  mixture  of  silt,  clay,  and  gravel,  containing 
stones  of  various  sizes.  This  is  generally  called  hard-pan, 
but  is  sometimes  termed  rock  on  account  of  its  exceeding  hard- 
ness. The  safe  bearing  capacity  is  considerably  in  excess  of 
the  usual  pressure  per  square  foot  for  concrete  bases,  viz. ,  1 50 
Ibs.  per  sq.  in.,  or  10.8  tons  per  sq.  ft. 

Bearing  Pressures:  Building  Laws. — The  "Bearing 
Capacity  of  Soil  ' '  is  thus  specified  in  the  Greater  New  York 
Building  Code  : 

' '  Where  no  test  of  the  sustaining  power  of  the  soil  is  made, 
different  soils,  excluding  mud,  at  the  bottom  of  the  footings, 
shall  be  deemed  to  safely  sustain  the  following  loads  to  the 
superficial  foot,  namely: 

' «  Soft  clay,  one  ton  per  square  foot ; 

"Ordinary  clay  and  sand  together,  in  layers,  wet  and 
springy,  two  tons  per  square  foot; 

"Loam,  clay,  or  fine  sand,  firm  and  dry,  three  tons  per 
square  foot; 

"Very  firm,  coarse  sand,  stiff  gravel,  or  hard  clay,  four 
tons  per  square  foot,  or  as  otherwise  determined  by  the  Com- 
missioner of  Buildings  having  jurisdiction.  " 

The  Chicago  Building  Ordinance  requires  the  following: 

"  If  foundations  of  other  materials  than  piles  are  used,  they 
shall  be  so  proportioned  that  the  loads  upon  the  soil  shall  not 
exceed  the  limits  for  different  kinds  of  soil  than  those  hereafter 
given,  to  wit  : 

1 '  If  the  soil  is  a  layer  of  pure  clay  at  least  fifteen  feet  thick, 
without  admixture  of  any  foreign  substance  excepting  gravel, 
it  shall  not  be  loaded  more  than  at  the  rate  of  3,500  pounds 
per  square  foot.  If  the  soil  is  a  layer  of  pure  clay  at  least 
fifteen  feet  thick  and  is  dry  and  thoroughly  compressed,  it  may 
be  loaded  not  to  exceed  4,500  pounds  per  square  foot. 

' '  If  the  soil  is  a  layer  of  dry  sand  fifteen  feet  or  more  in 


288  ARCHITECTURAL  ENGINEERING. 

thickness,  and  without  admixture  of  clay,  loam,  or  other 
foreign  substance,  it  shall  not  be  loaded  more  than  at  the  rate 
of  4,000  pounds  per  square  foot. 

"Foundations  shall  not  be  laid  on  filled  or  made  ground, 
or  on  loam,  or  on  any  soil  containing  admixture  of  organic 
matter. 

"  If  the  soil  is  a  mixture  of  clay  and  sand,  it  shall  not  be 
loaded  more  than  at  the  rate  of  3,000  pounds  per  square  foot. ' ' 

The  Boston  Building  Law  leaves  the  determination  of  the 
bearing-power  of  soils  to  the  discretion  of  the  building  authori- 
ties. 

Examples  of  Foundation  Pressures. — The  following  data 
will  serve  to  show  the  actual  unit  pressures  on  the  soil  induced 
by  a  number  of  well-known  buildings.  These  are,  however, 
of  little  value  in  determining  the  allowable  pressure  for  other 
structures,  even  though  very  near  to  the  sites  mentioned,  as 
full  records  of  test  borings,  or  samples  of  the  actual  materials 
encountered  are  required  in  all  cases  for  a  proper  determina- 
tion of  bearing  values. 

As  examples  'of  bearing  on  rock  or  hard-pan  in  New  York 
City,  at  the  base  of  caisson  foundations,  the  Manhattan  Life 
and  the  Gillender  buildings  may  be  cited.  The  Manhattan 
Life  Building  is  seventeen  stories  high,  and  is  supported  on  1 5 
caissons,  the  pressure  per  square  foot  at  base  of  caissons  being 
calculated  at  10.8  tons  per  sq.  ft.  The  Gillender  Building, 
supported  on  caissons  sunk  to  bed  rock,  causes  an  estimated 
unit  pressure  of  12  tons  per  sq.  ft. 

For  bearing  on  sand,  the  New  York  "World"  Building 
resulted  in  a  load  of  4.7  tons  per  sq.  ft.,  some  of  the  resultant 
loads  being  considerably  eccentric.  The  foundations  consist 
of  inverted  arches  built  upon  continuous  concrete  footings,  thus 
resulting  in  broad  belts  of  bearing  areas.  The  material  of  the 
site  was  fine  dense  sand. 

The  St.  Paul  Building  (see  Frontispiece)  is  built  upon  an 


FOUNDATIONS.  289 

extremely  compact  sand,  overlaid  with  fine  sand.  The  foun- 
dations consist  of  a  steel  and  concrete  grillage  covering  the 
entire  lot  area,  the  resultant  pressure  being  3.2  tons  per  sq.  ft. 
The  Spreckels  Building,  San  Francisco,  310  ft.  high,  is  built 
upon  a  very  similar  grillage  covering  the  entire  foundation 
area,  the  pressure  being  4,500  Ibs.  per  sq.  ft.  on  a  dense  wet 
sand. 

"The  Washington  Monument,  Washington,  D.  C.,  rests 
upon  a  bed  of  very  fine  sand  2  ft.  thick  underlying  a  bed  of 
gravel  and  bowlders;  the  ordinary  pressure  on  certain  parts 
of  the  foundation  is  not  far  from  1 1  tons  per  sq.  ft. ,  which  the 
wind  may  increase  to  nearly  14  tons  per  sq.  ft."  * 

In  Chicago,  the  soil  underlying  the  city  consists  of  loam 
or  made  ground  to  a  depth  of  12  or  14  ft.  below  the  sidewalk 
grade,  below  which  there  is  a  layer  of  blue  clay,  sometimes 
termed  hard-pan,  from  6  to  10  ft.  thick.  Below  the  firm  layer, 
the  material  changes  to  different  grades  of  soft  and  saturated 
clay,  which  again  becomes  hard  and  firm  at  a  depth  of  50  to- 
60  ft.  Limestone  bed-rock  is  found  at  from  40  to  80  ft.  below 
the  street-level. 

The  upper  stratum  of  hard  clay  is  used  for  the  support  of 
the  grillage  foundations,  and  custom  has  established  a  unit 
pressure  of  from  3,000  to  4,000  Ibs.  per  sq.  ft.  From  3,000  to 
3,500  Ibs.  has  been  found  to  give  the  best  results.  "The 
Fair  "  Building  was  loaded  to  2,850  Ibs.  per  sq.  ft.  on  the  soil, 
this  being  more  conservative  than  average  practice.  The 
Y.  M.  C.  A.  Building  loaded  the  clay  to  3,500  Ibs.  per  sq.  ft, 
and  the  Monadnock  Building  to  3,750  Ibs.  per  sq.  ft. 

"  In  the  case  of  the  Congressional  Library,  the  ultimate 
supporting  power  of  <  yellow  clay  mixed  with  sand  '  was  13^ 
tons  per  sq.  ft. ;  and  the  safe  load  was  assumed  to  be  2\  tons 
per  sq.  ft. "  t 

*  See  "A  Treatise  on  Masonry  Construction,''  I.  O.  Baker,  page  192. 
\  Ibid.  ' 


290  ARCHITECTURAL   ENGINEERING. 

In  Boston,  dry  compact  clay  is  loaded  to  3  tons  per  sq.  ft. 

Test  Loads. — If  foundations  are  to  be  constructed  in  or 
upon  compressible  soil,  tests  of  the  bearing  capacity  of  the 
material  are  desirable  if  any  doubt  exists  as  to  safe  unit-loads. 
Such  tests  are  often  resorted  to  where  raft  or  grillage  founda- 
tions are  employed,  or  for  pile  foundations. 

Tests  to  determine  the  bearing-power  of  the  soil  at  the  site 
of  the  Chicago  Masonic  Temple  were  made  by  supporting  an 
iron  tank  on  a  plate  of  2  sq.  ft.  area.*  In  one  test  the  plate 
rested  directly  on  the  hard-pan,  and  in  the  second  test  it  was 
placed  at  the  bottom  of  a  hole  2  ft.  4  ins.  deep  in  the  hard 
pan.  The  tank  was  gradually  filled  with  water,  and  the  settle- 
ments were  noted  under  the  varying  loads.  The  time  of 
observations  extended  over  four  and  six  days,  respectively,  in 
the  two  tests.  These  tests  showed  that  it  is  safer  never  to 
descend  below  the  top  of  the  hard  pan  in  such  clayey  founda- 
tion material  as  exists  in  Chicago. 

Test  loads  to  determine  the  bearing  capacity  of  piles  are 
sometimes  made  by  loading  a  pile  or  a  group  of  piles  with  a 
box  of  sand  or  other  material,  and  noting  the  settlements. 
Groups  of  piles  were  thus  tested  on  the  sites  of  the  World's 
Fair  Buildings  at  Chicago,  the  piles  being  driven  to  different 
depths,  to  ascertain  the  differences  in  settlement  under  a 
uniform  load. 

The  Chicago  Library  foundations  are  among  the  most  care- 
fully executed  pile  foundations  in  Chicago.  Under  the  walls 
of  this  building  three  rows  of  piles  were  driven,  and  the  tests 
were  made  as  follows:  To  give  the  conditions  as  they  would 
be  in  the  final  structure,  three  rows  of  piles  were  driven  in  a 
trench,  and  the  middle  row  was  cut  off  below  the  other  two, 
thus  bringing  all  the  bearing  on  four  piles  only  (two  in  each 
outside  row),  but  thereby  allowing  the  outside  rows  to  derive 

*  See  E.  C.  Shankland  in  Minutes  of  the  Proceedings  of  the  Institution 
of  Civil  Engineers,  vol.  cxxviii. 


FOUNDATIONS.  291 

the  benefit  of  the  compression  of  the  earth  due  to  the  driving 
of  the  central  row.  The  work  was  done  by  a  Nasmyth 
hammer,  weighing  4,500  Ibs.,  falling  42  ins.,  and  having  a 
velocity  of  54  blows  per  minute.  The  last  20  ft.  were  driven 
with  an  oak  follower.  The  piles  were  driven  at  2£  ft.  centres 
to  a  depth  of  52  ft.,  27  ft.  into  soft  clay,  23  ft.  into  hard  clay, 
and  2  ft.  into  the  hard-pan.  Their  average  diameter  was 
13  ins.,  and  the  area  at  the  small  end  80  sq.  ins. 

The  bearing-power  of  the  hard-pan  was  taken  at  200  Ibs. 
per  sq.  in.  Rankine's  formula  gives  about  170  Ibs.  The 
extreme  average  frictional  resistance  per  square  inch  of  the 
sides  of  the  piles,  deduced  from  experiments  under  analogous 
conditions,  was  15  Ibs.  per  sq.  in.  The  extreme  resistance  at 
the  pile  point  was  200  Ibs.  X  80  =  1600  Ibs.  The  average 
external  surface  of  one  pile  equalled  (52  X  12  X  41)  =  25,000 
sq.  ins.  At  15  Ibs.  per  sq.  in.  this  gives  375,000  Ibs.,  or  195^ 
tons.  Disregarding  the  point  resistance,  the  bearing-power 
of  a  pile  would  be  about  187  tons. 

Assuming  the  ultimate  crushing  strength  of  wet  Norway 
pine  not  over  1,600  Ibs.  per  sq.  in.,  and  with  a  factor  of  safety 
of  3,  the  safe  load  will  be  not  over  533  Ibs.  per  sq.  in.  The 
piles  were  taken  at  an  average  area  of  1 1 3  sq.  ins. ,  which  gives 
not  over  60,230  Ibs.  per  pile,  or  about  30  tons.  This  gives  a 
factor  of  3  for  crushing,  and  a  factor  of  6  for  the  frictional 
resistance  of  the  soil.  If  the  timber  were  loaded  at  one  half 
its  ultimate  strength,  45  tons  could  be  used  per  pile. 

A  platform  to  hold  a  load  of  pig-iron  was  built  resting  on 
the  outside  rows  of  piles,  and  the  weight  was  gradually 
increased  until  at  the  end  of  eleven  days  the  mass  was  38  ft. 
high,  weighing  404,800  Ibs.  on  4  piles,  or  about  50^5-  tons  per 
pile.  Levels  were  taken  at  intervals  of  two  weeks,  and  as  no 
settlement  was  observed,  30  tons  per  pile  was  considered  a 
safe  load. 

Tests  were  also  made  of  drawing  piles  at  this  site,  and  an 


292  ARCHITECTURAL   ENGINEERING. 

ordinary  pile,  driven  in  clay  to  a  depth  of  45  ft.,  gave  45,000 
Ibs.  resistance. 

A  very  interesting  test  of  the  bearing  capacity  of  a  founda- 
tion soil  was  made  at  the  time  of  erecting  the  St.  Paul  Build- 
ing, New  York.  This  structure  is  25  stories  high,  and  the 
ratio  of  height  to  width  is  unusually  great,  as  may  be  seen  in 
the  Frontispiece  showing  a  view  of  Post-office  Square,  with 
the  St.  Paul  Building  to  the  right. 

The  character  of  the  foundation  material  was  found  to  con- 
sist of  bed-rock  (at  a  distance  of  about  86  ft.  below  the  street- 
level),  overlaid  with  a  fine  but  extremely  compact  sand  which 
was  considered  capable  of  sustaining  at  least  4  or  5  tons  per 
sq.  ft.  The  architect,  Mr.  Geo.  B.  Post,  therefore  decided  to 
excavate  to  the  fine  sand  found  just  below  the  water-level,  and 
to  cover  the  entire  site  with  a  solid  protective  layer  of  concrete, 
12  ins.  thick,  upon  which  the  grillage  footings  were  to  be 
placed.  These  steel  grillages  were  designed  to  distribute  a 
uniform  pressure  of  3.2  tons  per  sq.  ft.,  with  an  attendant 
uniform  settlement  of  -f  of  an  inch ;  and  as  pumping  tests  had 
failed  to  show  any  disturbances  in  the  adjacent  sand,  and 
furthermore,  as  both  the  ' '  Times  ' '  and  ' '  World  ' '  buildings 
had  been  founded  upon  practically  the  same  strata  of  sand 
nearby,  with  heavy  loading  and  satisfactory  results,  it  was 
thought  that  the  proposed  construction  would  prove  very  satis- 
factory. 

The  above  decision  of  the  architect,  however,  was  publicly 
questioned,  and  as  even  very  slight  inequalities  of  settlement 
might  prove  serious  in  so  high  and  narrow  a  building,  it  was 
decided  to  make  a  careful  experimental  test.  This  was  con- 
ducted by  Mr.  Theodore  Cooper  as  follows : 

On  the  sand  bottom  of  a  hole  cut  in  the  concrete,  a  12-in. 
by  12-in.  stick  was  placed  on  end  on  March  26,  1896,  and  this 
was  loaded  gradually  until,  on  April  8,  the  gauge  showed  a 
settlement  of  £J-  of  an  inch,  under  a  load  of  13,000  Ibs.  No 


FOUNDATIONS,  293 

additional  settlement  was  caused  by  pouring  water  into  the 
test-hole.  It  was  then  decided  to  examine  the  effects  of 
cutting  a  second  nearby  hole  in  the  concrete  bed,  so  a  new 
hole  was  made  4  ft.  6  ins.  from  the  first.  As  no  new  evidence 
of  settlement  occurred  under  the  new  conditions,  21  ins.  of 
water  was  poured  into  the  first  test-hole,  and  this  was  soon 
visible  in  the  second  opening  through  the  effects  of  moisture  in 
the  sand.  Both  holes  were  then  filled  with  water  and  allowed 
to  remain  until  the  following  day,  and  as  no  added  settlement 
resulted  to  the  test-load,  nor  any  uplifting  of  sand  in  the  second 
hole  occurred,  the  test  was  considered  as  warranting  the  archi- 
tect's design  in  all  particulars. 

Test  Borings. — Unless  repeated  precedents  of  identical 
conditions  exist,  an  accurate  knowledge  of  the  underlying 
foundation  material  is  plainly  a  requisite  of  the  utmost  impor- 
tance before  an  intelligent  foundation  design  can  be  even 
approximated.  A  sufficient  number  of  borings  or  soundings 
from  which  to  judge  existing  conditions  will  always  prove  both 
time  and  money  well  invested. 

The  number  of  test  borings  required  for  any  particular  site 
will  largely  depend  upon  the  nature  of  the  subsoil,  and  upon 
the  character  of  the  proposed  foundations.  If  the  underlying 
material  is  known  by  previous  experience  to  be  comparatively 
homogeneous,  and  if  the  character  of  the  foundations  is  such 
that  reasonable  variations  in  the  subsoil  are  no  particular 
obstacles,  a  few  borings  only  may  be  sufficient  to  give  a  com- 
paratively accurate  knowledge;  but  if  pneumatic  foundations 
are  to  be  employed,  or  if  the  character  of  the  substrata  is 
liable  to  considerable  variation  as  to  depth  or  composition, 
then  it  will  be  found  best  to  provide  borings  at  more  frequent 
intervals, — sometimes  several  borings  within  the  limits  of  each 
pier.  For  the  new  Post-office  and  Government  Building  in 
Chicago,  only  four  borings  were  made,  one  at  each  corner  of 
the  site,  and  as  these  were  found  essentially  alike  they  were 


294  ARCHITECTURAL   ENGINEERING. 

furnished  to  the  contractors  bidding  on  the  foundation  contract 
"as  general  and  not  specific  information,  the  contractor 
assuming  all  chances  as  to  the  formation  of  the  soil." 

Test  borings  may  be  made  in  a  comparatively  simple, 
inexpensive,  and  still  trustworthy  manner  as  follows : 

A  section  of  i£-in.  or  2-in.  iron  pipe  is  first  driven  into  the 
ground  as  far  as  possible.  A  length  of  f-in.  pipe  is  then  pro- 
vided with  a  wedge-shaped  end  or  cutting  edge,  about  12  ins. 
long,  this  being  attached  by  means  of  an  ordinary  threaded 
coupling.  Small  holes  are  provided  in  the  faces  of  the  wedge, 
and  the  section  of  smaller  pipe,  with  its  wedge  end,  is  then 
inserted  within  the  large  pipe  already  driven.  The  upper  end 
of  the  f-in.  pipe  is  provided  with  a  special  handle  or  with  a 
hammer  end,  this  being  usually  about  12  ins.  long  with  a  solid 
handle-bar  at  right  angles  to  the  line  of  pipe,  provided  hand 
pressure  is  to  be  used,  or  with  a  buffer  end  or  cap  in  case  a 
ram  or  weight  is  employed.  In  either  case,  connection  is 
made  for  water-supply  by  means  of  a  short  elbow  which  will 
connect  the  water-service  with  the  inside  of  the  f-in.  pipe,  the 
water  being  delivered  at  a  pressure  varying  from  50  to  100 
Ibs.,  depending  upon  the  service.  This  is  sometimes  obtained 
from  city  pressure,  sometimes  from  a  hand  force-pump,  or  even 
from  a  steam  pump,  if  upon  the  premises. 

Upon  starting  the  water-supply,  the  water  passes  down  the 
f-in.  pipe,  through  the  small  holes  in  the  wedge  end,  and  then 
upwards  between  the  two  pipes,  bringing  the  bottom  material 
with  it,  in  suspension,  and  discharging  over  the  top  of  the 
outer  tube.  As  the  water  scours  out  at  the  bottom,  the  small 
tube  may  be  gradually  lowered  into  the  subsoil  either  by 
constantly  turning  the  handle  at  the  top,  or  by  means  of  a  light 
iron  ram,  sliding  in  upright  guides  and  operated  by  a  windlass. 
In  silt  or  clay  it  will  not  generally  be  found  necessary  to  lower 
the  outside  pipe  with  the  f-in.  pipe,  as  the  hole  will  remain 


FOUNDATIONS.  295 

sufficiently  large  under  the  water  action  alone.  In  gravel  or 
sand  the  outer  pipe  should  generally  follow  the  inner  one. 

To  obtain  samples  of  the  material  being  penetrated,  the 
inner  pipe  is  lifted  out  at  intervals  of  several  feet,  the  wedge 
end  is  removed,  and  a  special  iron  or  brass  tube  is  attached, 
this  being  usually  about  12  ins.  long,  and  slightly  contracted 
at  the  lower  end.  This  is  then  lowered  to  the  bottom  and 
pressed  for  its  full  depth  into  the  material.  The  pipe  is  then 
raised,  and  the  sample  is  pressed  from  the  tube  and  placed  in 
bottles  or  jars  for  later  examination. 

Bowlders  or  bed-rock  can  be  told  by  the  sound  or  rebound 
of  the  pipe.  If  bowlders  are  encountered,  a  new  boring  must 
be  started  at  some  distance  from  the  first  position.  Bowlders, 
or  a  thin  layer  of  rock  underlaid  by  a  stratum  of  soft  and 
unreliable  character,  may  easily  be  mistaken  for  bed-rock. 

Adjoining  or  Party  Walls. — Where  modern  buildings  of 
considerable  height  are  built  next  to  older  structures,  the  foun- 
dations of  the  new  building  are  almost  invariably  placed  at  a 
lower  level  than  the  foundations  of  the  old  adjoining  building. 
This  is  because  of  the  present  necessity  for  sub-basements,  in 
which  to  place  the  mechanical  plant  of  the  modern  building, 
and  also  on  account  of  the  desirability  of  'carrying  the  founda- 
tions for  tall  and  important  structures  below  the  surface-soil, 
or  to  hard-pan  or  solid  rock.  Party  walls,  also,  where  utilized 
by  the  newer  building,  are  often  required  to  be  extended 
downwards,  to  provide  deeper  basement  and  sub-basement 
room  in  the  new  structure  than  exists  in  the  old. 

The  present  Building  Code  of  Greater  New  York  provides 
that  ' '  Whenever  an  excavation  of  either  earth  or  rock  for 
building  or  other  purposes  shall  be  intended  to  be,  or  shall 
be,  carried  to  the  depth  of  more  than  ten  feet  below  the  curb, 
the  person  or  persons  causing  such  excavation  to  be  made  shall 
at  all  times,  from  the  commencement  until  the  completion 
thereof,  if  afforded  the  necessary  license  to  enter  upon  the 


296  ARCHITECTURAL   ENGINEERING. 

adjoining  land  and  not  otherwise,  at  his  or  their  own  expense 
preserve  any  adjoining  or  contiguous  wall  or  walls,  structure 
or  structures  from  injury,  and  support  the  same  by  proper 
foundations,  so  that  the  said  wall  or  walls,  structure  or  struc- 
tures, shall  be  and  remain  practically  as  safe  as  before  such 
excavation  was  commenced,  whether  the  said  adjoining  or 
contiguous  wall  or  walls,  structure  or  structures,  are  down 
more  or  less  than  ten  feet  below  the  curb." 

If  license  to  occupy  the  premises  of  the  adjoining  basement 
space  is  not  accorded,  then  the  owner  refusing  to  grant  such 
license  is  obliged  to  make  his  own  walls  secure  by  proper 
foundations;  but  as  few  owners  would  deny  such  a  privilege 
when  the  cost  of  protecting  or  renewing  their  foundations  would 
fall  upon  themselves,  the  responsibility  for  adjoining  or  party 
walls  is  usually  upon  the  owners  of  the  new  structure. 

The  construction  of  the  older  existing  buildings  is  liable  to 
be  of  a  far  inferior  quality,  the  foundations  often  consisting  of 
rubble  or  dimension  stone  carried  down  a  short  distance  only 
below  the  basement  grade,  while  the  walls  which,  in  the  older 
construction,  almost  invariably  support  floor-  and  roof-loads, 
are  apt  to  prove  of  indifferent  quality  and  dangerous  to  alter 
in  any  way.  Great  care  is  therefore  necessary  in  the  protec- 
tion of  the  existing  work,  and  as  the  driving  of  new  pile  foun- 
dations close  to  the  old  wall  or  foundation  would  induce  jar  or 
settlement,  and  as  excavation  would  undermine  the  support, 
some  temporary  method  of  securing  the  original  walls  must  be 
resorted  to,  while  the  foundations  are  being  either  reinforced 
or  rebuilt.  This  must  almost  always  be  accomplished  without 
interruption  to  the  business  of  the  adjoining  tenants,  and  it  is 
not,  therefore,  usual  to  disturb  the  walls  above  the  basement 
area.  New  foundations  are  built  while  the  superimposed  walls 
are  supported  by  shoring  or  underpinning. 

Shoring. — Methods  of  shoring  will  depend  largely  upon 
the  loads  to  be  carried,  the  conditions  at  the  building  site,  and 


FOUNDATIONS.  297 

upon  local  custom  or  practice.  In  some  localities,  where  firm 
foundation  may  be  had  in  the  new  building  site,  and  where  the 
load  to  be  carried  is  not  too  great,  inclined  timber  shores  are 
used.  These  are  firmly  supported  and  wedged  at  their  lower 
ends,  and  leaned  against  the  wall  to  be  supported  at  an  angle 
of  10°  or  15°,  and  from  their  upper  ends  are  suspended  hanger- 
rods,  with  adjustable  turn-buckles,  and  with  large  flat  hooks 
or  arms  at  the  lower  ends  which  hook  through  slots  or  open- 
ings cut  in  the  wall  at  sufficient  intervals  to  provide  adequate 
support. 

Another  ordinary  method  is  through  the  use  of  needle- 
beams,  these  consisting  of  rails,  beams,  .or  wooden  girders, 
laid  through  openings  cut  in  the  wall  near  its  base.  The 
needle-beams  are  supported  at  either  end  on  cribs  or  blocking 
(usually  adjusted  by  means  of  jack-screws),  their  distance 
centre  to  centre  being  sufficiently  small  to  carry  the  wall 
safely  over  the  intervening  spaces.  The  wall  is  firmly  wedged 
over  each  beam,  so  that  it  is  properly  supported  while  the 
lower  portion  is  removed  to  permit  the  construction  of  the  new 
foundation.  The  new  wall  is  built  up  to  the  under  side  of  the 
supported  portion,  the  joints  being  well  wedged,  and  after  the 
mortar  has  well  set,  the  needle-beams  are  removed  and  the 
holes  are  filled  up. 

In  some  instances,  notably  in  the  building  of  the  founda- 
tions for  the  American  Surety  Co.  's  Building,  New  York, 
where  room  in  the  new  building  site  was  badly  needed,  the 
continuous  row  of  cribwork  or  blocking  under  the  needle-beams 
was  replaced  by  a  truss  built  directly  against  the  old  wall,  from 
which  truss  the  needle-beams  were  suspended  by  means  of 
adjustable  rods.  Each  end  of  the  truss  was  supported  on  crib- 
work  and  jacks,  but  the  intervening  space  was  thus  left  free 
and  open  for  work.*  In  later  cases,  small  groups  of  piles 

*For  complete  description,  see  Trans.  Am.  Soc.  C.  E.,  vol.  xxxvii.  p.  42. 


298 


ARCH  I  TEC  TURAL   ENGINEERING. 


which  occupied  very  little  ground  space  were  substituted  for 
the  cribwork,  thus  leaving  the  new  lot  comparatively  un- 
obstructed. 

During  the  construction  of  the  Standard  Oil  Co.  's  Building, 
New  York,  the  side  wall  of  a  five-story  building,  estimated  to 
weigh  about  9  tons  per  lineal  foot,  was  supported  by  means  of 
wooden  needle-beams  as  shown  in  Fig.  166.*  The  inner  ends 


O/d  Bu/i 


FIG.  166. — Needle-beams  used  in  Shoring  at  Standard  Oil  Co.'s  Building. 

rested  on  timber  blocking,  while  the  outer  ends  were  carried 
directly  on  clusters  of  piles  driven  within  the  site  of  the  new 
building;  but  as  it  was  necessary  to  leave  vacant  the  spaces 
for  new  pneumatic  caissons,  and  as  single  needle-beams 
between  these  spaces  would  be  too  far  apart  to  support  the 
intermediate  wall,  the  piles  were  arranged  as  shown,  capped 
with  timbers  parallel  to  the  wall,  and  supporting  radiating 
needle-beams. 

In  some  cases  the  shoring  of  the  old  building  which  was  to 
remain  has  been  started  before  the  demolition  of  the  buildings 
to  be  removed.  This  is  done  from  the  basement  of  the  build- 
ing to  be  torn  down,  and  is  a  saving  of  time,  often  of  consider- 
able importance. 

*See  the  Engineering  fiecord.  vol.  xxxviii.  No.  i. 


FOUNDS  TIONS.  299 

Underpinning.* — When  deep  excavations,  such  as  the 
pneumatic  type  or  heavy  piling,  must  be  conducted  for  a  new 
and  important  structure  alongside  an  adjoining  building  of 
great  weight  but  of  unsatisfactory  foundation  construction, 
unquestioned  support  from  either  hard-pan  or  bed-rock  is  often 
desired,  and  in  such  cases  the  ordinary  methods  of  shoring  are 
impracticable.  Underpinning  from  rock  or  other  reliable 
material  is  now  very  frequent  in  important  building  operations, 
•even  where  hard-pan  or  rock  is  found  only  at  very  considerable 
depths;  and  this  practice  has  served  greatly  to  lessen  the 
dangers  and  difficulties  of  placing  foundations  for  high  buildings 
under  the  very  severe  conditions  imposed  by  adjacent  struc- 
tures. 

The  method  of  underpinning  now  employed  insures  the 
rigid  support  of  the  adjoining  building,  "thereby  avoiding  the 
usual,  though  often  small  movements  which  follow  the  removal 
of  the  artificial  supports  used  during  the  period  of  construction, " 
and  also  the  freedom  from  obstruction  of  the  site  to  be  built 
upon. 

The  operation  of  underpinning,  as  employed  on  the  build- 
ings adjacent  to  the  Commercial  Cable  and  Queen's  Insurance 
buildings,  New  York,  maybe  briefly  described  as  follows:  (See 
Fig.  167.) 

Vertical  slots  are  first  cut  into  the  wall  to  be  supported, 
one  over  each  supporting  pipe,  the  length  being  usually  10  or 
12  ft.,  and  the  width  sufficient  to  receive  a  pipe  of  the  diameter 
calculated  as  necessary  for  support.  Transverse  or  cross  slots 
are  then  cut  at  the  top  of  each  vertical  slot,  into  which  one  or 
more  steel  beams  are  placed  and  firmly  wedged  to  support  the 
wall.  A  length  of  iron  pipe  is  then  placed  within  a  vertical 


*  For  a  complete  description  of  this  subject,  see  "The  Underpinning  of 
Heavy  Buildings,"  by  Jules  Breuchaud,  in  Trans.  Am.  Soc.  C.  E.,  vol. 


300 


ARCHITECTURAL  ENGINEERING. 


slot,  and  a  jack  and  blocking  are  inserted  between  the  top  of 
the  pipe  and  the  short  I-beams  already  inserted.  The  pipe  is 
then  driven  into  the  ground,  either  by  pressure  from  the  jack, 
or  by  aid  of  a  water-jet,  until  a  second  section  can  be  added 
on  top  of  the  first  by  means  of  screw  couplings,  or  interior 
bolted  flanges.  By  alternate  jacking  and  blocking,  this  opera- 


FIG.  167.— Underpinning  at  Commercial  Cable  and  Queen  Insurance  Co.'s 
Buildings. 

tion  is  continued  until  bed-rock  or  other  satisfactory  material 
is  reached. 

The  top  of  the  last  section  of  pipe  driven  is  left  at  about 
the  level  of  the  bottom  of  the  wall,  and  a  second  set  of  hori- 
zontal I-beams  is  then  placed  directly  on  top  of  the  pipe,  as 
shown  in  Fig.  167.  Vertical  beams  or  columns  are  then 
tightly  driven  between  the  two  sets  of  I-beams,  and  the  slot 
in  the  wall  is  filled  in  with  brickwork.  The  compression  of 


FOUND  A  TIONS.  301 

the  mortar-joints  in  the  brickwork  so  built  in  is  thus  avoided. 
One  or  two  pipes  only  are  driven  at  one  and  the  same  time. 

For  the  support  of  the  Western  Union  Building,  see  Fig. 
167,  nine  pipes  were  used  to  support  a  side  wall  57  ft.  long. 
The  pipes  were  heavy  steam-piping,  10  ins.  diameter  and  f-in. 
metal,  in  lengths  of  5  ft.,  and  connected  by  outside  couplings 
over  butt-joints.  Each  alternate  pipe  enclosed  a  smaller 
interior  one,  placed  so  as  to  break  joints,  the  space  between 
the  two  being  grouted  with  Portland  cement.  After  the  pipes 
were  driven  to  hard-pan  or  bed-rock,  they  were  filled  with 
Portland-cement  concrete. 

Two  distinct  systems  of  working  have  been  employed. 
First,  the  small-pipe  system,  in  which  the  diameter  of  the  pipe 
is  too  small  to  permit  of  an  inspection  of  the  bottom,  and  where 
the  tubing  is  driven  to  refusal,  or  until  the  pressure  exerted  by 
the  jack  is  greater  than  the  final  load  to  be  carried  by  the  pipe. 
This  method  can  only  be  used  under  favorable  conditions,  for 
small  pipes  are  only  reliable  when  driven  to  hard-pan  or  rock. 
The  striking  of  a  bowlder  might  indicate  a  sufficient  resistance, 
and  yet  quicksand  under  the  bowlder  might  be  drawn  off  under 
the  sinking  of  nearby  caissons,  and  allow  a  subsequent  settle- 
ment of  the  pipe.  To  be  sure  of  the  absence  of  bowlders, 
preliminary  test  borings  should  always  be  made. 

The  pipes  are  generally  made  strong  enough  to  support  the 
required  load  before  being  filled  with  concrete.  If  steel  or 
wrought-iron  pipe  is  used,  the  outside  surface  is  unprotected, 
and  ultimate  destruction  through  corrosion  cannot  be  pre- 
vented; while  cast-iron,  which  is  considered  less  liable  to  rust, 
is  more  unreliable  under  the  jack  pressure.  It  has  been  sug- 
gested first  to  force  down  a  thin  steel  pipe,  and  then  place  a 
cast-iron  pipe  within,  filling  the  intervening  space  with  grout. 

The  second  system  of  working  is  through  the  use  of  cylin- 
ders large  enough  in  interior  diameter  to  permit  of  reasonably 
comfortable  access,  both  for  working  and  for  examination.  If 


302  ARCHITECTURAL   ENGINEERING. 

the  final  load  on  the  cylinder  is  larger  than  can  be  exerted  by 
means  of  jacking,  or  if  test  borings  show  that  obstacles  exist, 
and  the  location  cannot  be  changed,  large  cylinders  must  be 
employed.  For  this  purpose  28-in.  and  33-in.  diameter  cast- 
iron  columns  have  been  used,  of  i^-in.  metal,  where  the  pipe 
was  extended  to  rock  bottom  or  below  a  stratum  of  hard-pan 
which  had  to  be  removed  by  excavating  the  hard-pan  from 
around  the  lower  edge  of  the  pipe.  Bowlders  were  also 
removed,  and  the  rock  surface  prepared  for  proper  bearing. 
In  such  cases,  work  is  usually  done  under  air  pressure,  an 
air-lock  being  attached  to  the  top  of  the  pipe,  and  sufficient 
air  pressure  supplied  to  keep  the  pipe  free  from  water. 

Cast  cylinders  of  this  type,  30  ins.  in  diameter,  with  a  sec- 
tional area  of  91  sq.  ins.  metal,  have  been  loaded  with  from 
200,000  to  380,000  Ibs.,  and  some  as  high  as  686,000  Ibs., 
thus  giving  loads  at  the  foot  of  the  cylinders  of  41,200  Ibs.  per 
sq.  in.  and  upwards,  the  metal  in  the  cylinders  being  in  general 
strained  by  a  compressive  force  of  not  over  4,000  to  5,000  Ibs. 
per  sq.  in. 

Settlement. — In  constructing  foundations  upon  compressi- 
ble soils,  great  care  must  be  given  to  the  question  of  settle- 
ment. If  piling  is  used,  driven  to  bed-rock  or  hard-pan,  or  if 
pneumatic  foundations  are  sunk  to  bed-rock,  no  special  thought 
need  be  given  to  settlement,  as  none  should  occur  if  the  foun- 
dations have  been  properly  designed  and  executed;  but  for  all 
forms  of  grillage  or  raft  foundations,  resting  directly  upon  earth 
or  clay,  the  question  of  settlement  is  very  important. 

The  danger  to  be  guarded  against  is  unequal  settlement, 
for  settlement  in  some  degree  is  sure  to  follow,  and  in  good 
design  this  is  anticipated  and  provided  for  in  fixing  the  original 
grades;  but  if  the  various  foundation  piers  settle  at  all  un- 
equally, the  cracking  and  separating  of  the  component  parts 
will  result  in  unsightly  blemishes,  if  not  in  dangerous  strains 
upon  the  masonry  or  steel  construction. 


FOUNDATIONS.  3°3 

The  evil  of  unequal  settlement  can  hardly  be  better  exem- 
plified than  in  the  case  of  the  former  United  States  Government 
Post-office  and  Custom-house  in  Chicago,  built  in  1877,  an<^ 
now  being  replaced  by  a  new  one.  The  foundations  consisted 
of  a  continuous  sheet  of  concrete,  made  in  different  layers,  but 
altogether  3  ft.  6  ins.  thick.  Some  portions  of  the  building 
were  extraordinarily  heavy,  others  comparatively  light,  but  the 
concrete  base  was  thought  to  be  sufficient,  even  though  there 
were  bad  sloughs  under  the  building.  But  it  proved  a  most 
dismal  failure,  and  even  a  menace  to  life  and  limb.  The 
building  settled  nearly  24  ins.  in  places,  and  a  dropping  of 
some  part  of  the  structure  was  no  unusual  occurrence.  After 
but  eighteen  years  of  service  this  example  of  government 
architecture  and  engineering  was  known  as  ' '  The  Ruin  ' '  in 
Chicago  and  vicinity. 

In  Europe,  numerous  examples  exist  of  a  similar  monolithic 
concrete  construction  under  heavy  buildings,  but  in  all  such 
cases  the  concrete  base  is  exceedingly  thick,  and  this  thickness 
is  relied  upon  to  resist  the  uneven  reactions  from  the  uneven 
pier-  and  wall-loads.  The  Nicolas  Church  in  Hamburg  is  said 
to  rest  upon  a  bed  of  concrete  8  ft.  thick,  while  under  the 
tower,  the  concrete  base  is  1 1  ft.  6  ins.  thick. 

When  a  load  is  applied  to  the  surface  of  a  clayey  soil  such 
as  exists  in  Chicago,  an  initial  settlement  occurs  at  a  pressure 
of  about  i  ton  per  sq.  ft.  Another  settlement,  which  ceases 
in  a  few  hours,  is  produced  under  an  increased  weight,  and 
further  settlement  will  not  directly  occur  even  with  a  load  of 
4,500  Ibs.  to  3  sq.  ft.  There  is,  however,  a  further  progressive 
settlement,  owing  to  the  gradual  pressing  out  of  the  water  from 
the  clay.  Baker  says:  "The  bearing-power  of  clayey  soils 
can  be  very  much  improved  by  drainage,  or  preventing  the 
penetration  of  the  water. ' '  That  the  water  is  pressed  from  the 
clay  was  shown  to  be  the  case  by  careful  observations  made 
at  the  Auditorium.  Wells  were  sunk  some  24  ft.  deep,  5  ft. 


3°4  .    ARCHITECTURAL  ENGINEERING. 

in  diameter,  and  4  ft.  6  ins.  from  the  foundations.  The  borings 
were  made  through  the  stratified  clay,  and  it  was  shown  that 
the  clay  became  more  and  more  compact  from  time  to  time, 
thus  proving  that  this  squeezing  process  does  take  place.  The 
settlements  were  here  carefully  watched  for  a  number  of  years, 
and  they  were  found  to  be  uniform — about  T^  in.  per  month. 

If  the  building  is  heavy,  an  immediate  settlement  of  from 
2£  ins.  to  4  ins.  is  noticed,  followed  by  a  gradual  progressive 
settlement.  The  Monadnock  Building,  200  ft.  high,  with 
3,750  Ibs.  per  sq.  ft.  on  footings,  settled  5  ins.,  while  6  ins. 
was  allowed  for.  The  Home  Insurance  Building  settled  |  in. 
under  two  stories  which  were  added  to  the  original  building. 
The  Y.  M.  C.  A.  Building,  with  a  foundation  load  of  3,500  Ibs. 
per  sq.  ft.  on  the  clay,  settled  2-\\-  ins.  in  two  years  ;  but  as 
this  building  was  erected  very  slowly,  covering  about  two  years 
from  start  to  finish,  the  settlement  was  no  doubt  considerably 
lessened. 

To  ascertain  the  settlement  of  the  Masonic  Temple, 
Chicago,  levels  were  taken  for  various  columns  in  this  struc- 
ture, the  readings  extending  over  a  period  of  five  years,  or 
from  1891  to  1895,  inclusive.  Some  of  these  settlements  have 
been  plotted  graphically,*  and  the  results  show  that  the 
"  curves  are  rapidly  approaching  a  horizontal  line;  the  amount 
of  settlement  since  the  last  levels  were  taken,  almost  two 
years  before,  is  nearly  the  same  in  each  case,  the  maximum 
variation  being  only  ^  in.,  although  they  had  varied  consider- 
ably before."  * 

The  four  exterior  corner  columns  in  this  building  showed 
total  settlements  after  five  years  of  /£  ins. ,  8T9F  ins. ,  1 1  ins. , 
and  8-y'g-  ins.,  respectively. 

In  good  design,  the  anticipated  settlement  is  provided  for 
in  the  start  by  raising  the  level  or  grade  of  the  footings  by  the 

*  See  E.  C.  Shankland  in  Proc.  of  the  Institution  of  C.  E.,  vol.  cxxviii. 
Part  II. 


FOUNDATIONS.  3°5 

amount  it  is  expected  the  structure  will  settle.  This  sometimes 
causes  the  sidewalks  to  slope  rather  steeply  from  building-line 
to  curb,  but  as  the  building  settles,  more  level  conditions 
obtain.  The  footings  of  the  Great  Northern  Theatre  (D.  H. 
Burnham  &  Co.,  architects)  were  raised  9  ins.  to  provide  for 
this  amount  of  settlement. 

It  must  not  be  forgotten  that  the  footings  are  designed  for 
the  final  loads  that  rest  upon  them,  and  at  all  stages  of  the 
construction  the  same  relation  must  be  maintained  between  the 
weights  on  the  various  piers  that  will  exist  in  the  completed 
state,  if  uniform  settlement  is  desired.  This  was  well  exem- 
plified in  the  case  of  the  Auditorium  tower,  which  extends 
many  stories  above  the  main  building,  thus  bringing  greater 
weights  on  the  tower  footings.  Here  the  tower  foundations 
were  loaded  with  varying  weights  of  pig-iron  at  the  different 
stages  of  construction,  in  order  that  the  proper  relative  excess 
on  these  piers  should  be  preserved  as  in  the  final  weight. 
Even  with  all  these  precautions,  and  after  most  careful  tests  of 
the  ground  beforehand,  this  tower  has  settled  more  than 
originally  allowed  for,  or  more  than  20  ins.,  but  this  was 
partly  due  to  adding  several  stories  to  the  height  of  the  tower, 
after  the  foundations  had  been  completed. 

Concrete. — The  employment  of  considerable  quantities  of 
concrete,  in  some  form  or  other,  is  now  so  general  in  founda- 
tion construction  that  the  proper  composition  and  method  of 
using  concrete  enter  into  nearly  all  large  building  operations. 

In  most  cases  of  grillage  foundations,  concrete  is  used  for 
the  bottom  or  bed-course,  as  shown  in  Figs.  171  and  174,  the 
thickness  generally  varying  from  I  to  2  ft. ;  but,  in  special 
cases,  concrete  has  been  applied  in  a  continuous  sheet  over  the 
entire  building  site,  as  a  protective  layer  or  covering  over  a 
less  reliable  material  below.  The  site  of  the  St.  Paul  Build- 
ing, New  York,  where  the  natural  surface  consisted  of  a  dense 
wet  sand,  was  thus  covered  with  a  uniform  layer  of  concrete 


306  ARCHITECTURAL  ENGINEERING. 

12  ins.  thick,  upon  which  were  placed  the  grillage  foundations 
of  steel  beams.  Concrete  is  also  sometimes  used  in  piers,  and 
for  the  encasement  or  protection  of  grillage  members,  cantilever 
girders,  etc.,  as  well  as  for  filling  the  interiors  of  pneumatic 
caissons  and  air-shafts. 

The  composition  of  concrete  is  sometimes  specified  by 
building  ordinance.  Thus  the  New  York  law  requires  foun- 
dation concrete  to  "be  made  of  at  least  one  part  of  cement, 
two  parts  of  sand,  and  five  parts  of  clean  broken  stone, ' '  or 
"good  clean  gravel  maybe  used  in  the  same  proportion  as 
broken  stone. ' '  The  Chicago  Ordinance  does  not  specify  the 
proportion  of  the  ingredients. 

In  general,  it  may  be  stated  that  the  best  results  are 
obtained  from  compositions  in  which  the  volume  of  the  mortar 
is  slightly  in  excess  of  the  voids  or  spaces  between  the  loose 
broken  stone  or  gravel  employed.  For  material  of  average 
uniform  size,  the  voids  will  run  about  40  to  50  per  cent,  of  the 
mass.  The  stone  should  be  clean  and  screened,  and  of  such 
size  that  it  will  pass  through  a  2 -in.  diameter  ring  in  any 
direction.  The  sand  must  be  sharp  and  clean,  and  the  cement 
fresh  and  dry,  these  materials  being  mixed  dry,  with  sufficient 
water  added  to  reduce  the  mass  to  the  consistency  of  mortar. 
The  concrete  should  be  laid  in  layers  not  over  6  or  8  ins. 
thick,  and  rammed  until  water  shows  at  the  surface. 

The  concrete  usually  specified  for  U.  S.  Government  work 
is  i  part  cement,  3  parts  sand,  and  5  parts  broken  stone. 
This  or  similar  mixtures  may  be  considerably  cheapened  with- 
out materially  affecting  the  strength  by  using  about  equal 
parts  of  broken  stone  and  clean  gravel  instead  of  the  5  parts 
stone.  Prof.  Baker  states  that  the  concrete  foundations  under 
the  Washington  Monument  were  made  of  I  part  Portland 
cement,  2  parts  sand,  3  parts  gravel,  and  4  parts  broken  stone, 
and  that  this  mixture  stood,  at  6  months  old,  a  load  of  2,000 
Ibs.  per  sq.  in.,  or  144  tons  per  sq.  ft.  The  concrete  used  in 


FOUNDATIONS.  307 

the  Masonic  Temple  foundations  was  made  of  I  part  Portland 
cement,  2  parts  clean  sharp  torpedo  sand,  and  3  parts  clean 
stone  broken  to  pass  a  2^-in.  diameter  ring. 

The  safe  bearing  loads  on  concrete,  not  reinforced  by 
metal  members,  is  limited  to  4  tons  per  sq.  ft.  by  the  Chicago 
Building  Law  (the  offsets  to  be  not  more  than  one-half  the 
heights  of  the  respective  courses),  and  by  the  New  York  laws 
to  15  tons  per  sq.  ft.  when  made  of  Portland  cement,  and 
8  tons  per  sq.  ft.  if  cement  other  than  Portland  is  used. 

The  crushing  strength  of  concrete  varies  greatly  with  the 
time  it  has  been  set,  as  the  strength  rapidly  increases  with  age. 
Average  ultimate  crushing  strengths  for  good  concrete  may 
be  placed  at  about  15  tons  per  sq.  ft.  for  I  month  old,  60  tons 
for  concrete  6  months  old,  and  100  tons  for  an  age  of  12 
months.  Assuming  a  safety  factor  of  six,  working  loads 
would  become  2£  tons  for  concrete  I  month  old,  10  tons  for 
concrete  6  months  old,  and  16  tons  for  concrete  I  year  old. 
These  strengths  would  suggest  the  desirability  of  placing 
concrete  foundations  as  early  in  the  building  operations  as 
practicable ;  but  the  superstructure  weights  are  increased 
gradually,  and  the  foundations  are  almost  invariably  in  place 
several  weeks  before  any  great  load  is  applied.  It  is  usually 
4  months  at  least  before  the  full  load  is  reached,  so  that  the 
concrete  has  ample  time  to  set. 

When  used  between  beams  of  grillage  foundations,  the 
stone  employed  must  be  broken  fine  enough  to  allow  of  ramming 
in  between  the  beam  webs  and  flanges.  For  such  cases,  the 
stone  is  usually  specified  to  be  broken  to  pass  through  a  f-in. 
ring,  or  broken  to  "  chestnut  "  size.  Crushed  granite  is  also 
used,  not  exceeding  £-in.  cube. 

Foundation  Loads. — In  all  cases  where  live-loads  have 
been  figured  on  the  columns,  consistency  requires  that  what- 
ever loads  have  been  figured  on  basement  columns,  must  be 
figured  in  the  calculations  of  the  foundations;  or  the  bearing 


308 


ARCHITECTURAL   ENGINEERING. 


areas  are  proportioned  for  dead-loads  only,  while  the  strengths 
of  the  foundations  themselves  are  figured  for  dead-  plus  some 
live-load.  But,  as  before  said,  live-loads  have  been  entirely 
disregarded  on  the  footings  of  many  of  the  best  buildings. 
W.  L.  B.  Jenney  advocates  as  follows:  In  hotels,  office  build- 
ings, and  retail  stores,  neglect  the  live-loads  on  the  footings, 
but  figure  them  in  heavy  warehouses,  machinery  plants,  etc. 
Where  much  pounding  occurs,  as  in  machinery  in  motion,  use 
double  the  weight  as  dead-load  that  is  figured  for  live-load, 

In  "The  Fair"  Building,  where  a  large  quantity  of 
merchandise  is  stored,  and  the  aisles  are  constantly  filled  by 
throngs  of  people,  the  following  system  was  used:  The  floor- 
beams  carry  all  the  dead-  plus  live-loads,  the  girders  carry  the 
dead-load  plus  90  per  cent,  of  the  live-load,  while  any  one 
column  carries  a  percentage  of  the  sum  of  the  live-loads  of  all 
the  stories  above  that  column  plus  the  total  dead-load.  The 
percentage  of  live-load  is  given  in  the  last  column  of  the 
accompanying  table: 


Column. 

Attic 

1 6th  story 
I5th     " 
I4th     " 
I3th     " 


6th  story 
Sth    «• 
Basement 


Live-load  on  beams. 

Per  cent 

.  for  column. 



IOO 

per  cent. 

75  Ibs. 

90 

<  «      « 

75   " 

87* 

«      <  < 

75   " 

77* 

<<      <  « 

75  " 

72* 

<•      t  < 

Decrease  of  24  per 

cent,  in  each  story. 

75  Ibs. 

55 

per  cent. 

130  « 

52£ 

«      « 

130  i( 

40 

«  «      « 

No  live-load  was  figured  on  the  clay  area,  but  the  allow- 
able pressure  per  square  foot  was  taken  at  a  very  conservative 
.figure — 2,850  Ibs. 


FOUNDATIONS.  309 

As  before  stated,  the  loads  to  be  used  in  proportioning 
foundations  are  often  specified  by  building  ordinance. 

The  New  York  code  provides  as  follows  for  loads  to  be 
used  in  designing  footings  in  buildings  more  than  three  stories 
in  height : 

' '  For  warehouses  and  factories  they  are  to  be  the  full 
dead-load  and  the  full  live-load  established  by  this  code. 

' '  In  stores  and  buildings  for  light  manufacturing  purposes 
they  are  to  be  the  full  dead-load  and  seventy-five  per  cent,  of 
the  live-load  established  by  this  code. 

"  In  churches,  schoolhouses,  and  places  of  public  amuse- 
ment or  assembly,  they  are  to  be  the  full  dead-load  and 
seventy-five  per  cent,  of  the  live-load  established  by  this  code. 

"  In  office  buildings,  hotels,  dwellings,  apartment  houses, 
lodging  houses,  and  stables,  they  are  to  be  the  full  dead-load 
and  sixty  per  cent,  of  the  live-load  established  by  this  code. 

"  Footings  shall  be  so  designed  that  the  loads  will  be  as 
nearly  uniform  as  possible  and  not  in  excess  of  the  safe  bearing 
capacity  of  the  soil,  as  established  by  this  code."  (See  Bear- 
ing Pressures,  Building-  Laws.} 

The  Chicago  ordinance  makes  no  specific  requirements  as 
to  foundation  loads,  but  states  that  "  foundations  shall  be  pro- 
portioned to  the  actual  average  loads  they  will  have  to  carry 
in  the  completed  and  occupied  building,  and  not  to  theoretical 
or  occasional  loads." 

For  working  under  such  requirements  as  the  New  York 
law,  methods  are  given  in  Chapter  VII.  under  a  discussion  of 
column  sheets,  etc.,  whereby  the  dead-  and  live-loads  may  be 
kept  separate,  and  hence  conveniently  selected  for  the  com- 
putations of  the  foundations. 

Present  Types  of  Foundations. — The  various  methods  of 
securing  adequate  foundation  areas  for  the  loads  to  be  sup- 
ported may  be  classified  as  follows  : 

i.   By  simply  building  the  walls  or  piers  upon  the  natural 


310  ARCHITECTURAL  ENGINEERING. 

soil,  the  necessary  base  being  secured  by  means  of  projecting 
courses  of  masonry.  This  method  is  only  applicable  to  build- 
ings of  very  moderate  height  and  load,  and  need  not  be  here 
considered  in  detail.  The  only  requirements  demanding 
special  attention  are  that  the  soil  must  be  of  the  required  bear- 
ing capacity,  that  the  bed  of  the  foundation  shall  be  below  the 
frost-line,  and  that  the  centre  of  pressure  must  always  coincide 
with  the  centre  of  base. 

2.  By  obtaining  the  necessary  bearing  area  by  means  of 
timber  platforms  or  grillage,  as  was  utilized  in  the  construction 
of  the  World's  Fair  buildings,  and  in  the  Chicago  Auditorium. 
This  method  will  be  more  fully  explained  under  a  following 
heading. 

3.  By  utilizing  a  grillage  composed  of  steel  rails,  beams, 
or  riveted  girders  in  combination  with  concrete.      This  type  is 
often  used  to  support  two  or  more  columns  upon  one  grillage, 
in  which  case  the  footing  is  termed  a  ' '  combined  footing. ' ' 

4.  By  driving  piles  to  some  hard  or  firm  material,  usually 
designated  hard-pan,  or  to  rock. 

5 .  By  sinking  steel  cylinders,  or  caissons  of  timber  or  steel 
(by  the  pneumatic  process  or  otherwise),  to  bed-rock,   or  to 
such  material  as  will  answer  the  purpose  of  bed-rock.      This 
system  is  also  used  to  support  either  a  single  column,   or  a 
number  of  columns. 

Types  3,  4,  and  5  will  each  be  considered  in  detail  in  fol- 
lowing paragraphs.  Forms  3  and  5  are  also  often  used  in 
connection  with  cantilever  girders,  but  the  introduction  of  such 
girders  makes  but  a  variation  in  the  detail  of  the  calculations. 

Proportioning  Grillage  Areas. — An  investigation  of  the 
compressibility  of  the  soil  leads  to  the  conclusion  that,  if  we 
wish  to  procure  uniform  settlement,  all  parts  of  the  foundation 
areas  must  be  exactly  proportioned  to  the  loads  they  have  to 
carry.  Examples  are  not  lacking,  in  Chicago  and  elsewhere, 
of  the  actual  crushing  of  light  piers,  when  alternating  with 


FOUND  A  TIONS.  311 

heavy  ones,  because,  proportionately,  the  lighter  piers  had  too 
great  a  footing  area.  In  the  Mills  Building  in  New  York  City 
the  mullions  in  the  lower  floors  of  the  building  and  over  the 
light  foundations  were  seriously  damaged  and  even  crushed, 
because  they  were  not  strong  enough  to  force  down  the  lighter 
piers  of  too  large  an  area,  as  fast  as  the  heavy  piers  were 
settling. 

It  is  the  judgment  of  the  best  engineers  that  the  areas  of 
foundations  on  compressible  soil  should  be  proportioned  to  the 
dead-loads  only,  and  not  to  theoretical  or  occasional  loads. 
Whenever  live-loads  have  been  figured  on  both  the  interior 
columns  and  on  the  columns  in  the  exterior  walls,  the  exterior 
columns  have  always  been  found  to  settle  more,  from  the  fact 
that  the  live-load  forms  a  larger  percentage  of  the  interior- 
column  loads  than  of  the  wall-column  loads. 

Thus  in  the  Marshall  Field  warehouse  in  Chicago,  designed 
by  an  eastern  architect,  the  live-load  of  75  Ibs.  per  square  foot 
on  every  floor  was  carried  down  to  the  footings,  according  to 
the  then-prevalent  custom  in  New  York  and  Boston,  the  result 
being  that  all  of  the  floors  have  risen  considerably  at  the 
centre. 

Experience  has  also  shown  that  after  the  clay  has  been 
compressed  by  a  load  of  3,000  Ibs.  per  sq.  ft.,  and  allowed 
several  months'  repose,  no  very  perceptible  addition  to  that 
compression  will  result  without  a  material  addition  to  the  load. 
It  is  therefore  good  practice  to  neglect  live-loads  on  the  clay 
for  hotels,  office  buildings,  or  lightly  loaded  retail  stores,  if 
permitted  by  the  local  building  laws.  In  warehouses,  how- 
ever, or  in  buildings  carrying  very  heavy  permanent  or  shifting 
floor-loads,  or  machinery  in  motion,  the  change  of  loads  and 
the  jarring  increase  the  compression  of  the  clay  very  largely. 
Hence  extra  allowance  must  be  made  in  such  instances.  This 
is  sometimes  done,  for  grillage  foundations,  by  proportioning 
the  foundation  area  for  the  pier  receiving  the  maximum  com- 


312  ARCHITECTURAL  ENGINEERING. 

bined  dead-  plus  live-loads,  for  the  allowable  unit  bearing 
pressure.  Then,  assuming  that  only  the  dead-load  acts  over 
the  area  so  found,  compute  the  resulting  unit  bearing  pressure, 
and  use  this  unit  in  proportioning  the  remaining  piers  for  dead- 
loads  only.  Thus,  assume  that  the  maximum  column  load  is 
400  tons  dead-load,  plus  240  tons  live-load,  or  640  tons  total. 
Assuming,  also,  a  unit  bearing  pressure  of  4  tons  per  sq.  ft., 
the  foundation  area  required  is  £|J-  or  160  sq.  ft.  Considering 
now  that  only  the  dead-load  acts,  the  foundation  area  will 
receive 'but  4^  tons  per  sq.  ft.,  or  2\  tons  per  sq.  ft.  The 
remaining  footings  may  then  be  proportioned  by  dividing  the 
dead-loads  only  by  the  unit  of  pressure,  2^-  tons  per  q.  ft. ,  as 
determined  above. 

The  method  of  proportioning  the  grillage  areas,  however, 
will  be  largely  governed  by  municipal  regulations,  as  explained 
under  the  heading  ' '  Foundation  Loads. ' ' 

Timber  Grillage. — For  temporary  work,  or  for  spread 
foundations  in  very  wet  soil,  timber  grillage  may  be  employed 
to  increase  the  bearing  areas  of  the  footings,  provided  the 
timber  employed  is  always  below  the  water-line.  The  use  of 
this  method,  however,  is  not  to  be  recommended  for  loads  of 
any  considerable  magnitude  in  permanent  structures,  as  steel 
and  concrete  grillage  may  be  substituted  to  advantage.  Steel 
grillage  will  permit  of  greater  offsets,  and  also  require  less 
thickness  for  the  footings,  than  may  be  obtained  through  the 
use  of  timber  construction.  Also,  steel  and  concrete  are  not 
dependent  upon  conditions  of  moisture  for  use,  while  timber, 
to  insure  preservation  against  rapid  decay,  must  be  kept  wet 
at  all  times. 

A  notable  example  of  temporary  timber  grillage  was  the 
use  of  this  system  in  the  buildings  of  the  World's  Columbian 
Exposition  at  Chicago.  It  was  first  intended  to  use  pile  foun- 
dations throughout,  but  at  the  same  time  as  driving  test  piles, 
test  platforms  of  3-in.  plank  were  constructed  and  placed  in 


FOUNDATIONS. 


313 


different  locations  upon  the  sandy  soil,  for  the  purpose  of  test- 
ing the  surface  bearing  capacity.  These  were  then  loaded 
with  pig-iron  to  about  2\  tons  per  sq.  ft.  This  load  was 
applied  gradually,  and  the  settlements  were  carefully  noted 
for  several  days.  It  was  found  that  under  the  maximum  load- 
ing the  settlement  was  very  slight,  about  f  of  an  inch,  and  very 
uniform.  It  was  therefore  decided  to  use  pile  foundations 
driven  to  hard-pan  in  certain  locations  where  quicksand 
existed,  but  to  use  platform  foundations  proportioned  for  a 
bearing  pressure  of  i^  tons  per  sq.  ft.,  where  the  ground  was 
favorable. 

The  general  design  of  these  platform  foundations  was  as 
shown  in  Fig.  168.     They  consisted  of  3~in.  pine  or  hemlock 


FIG.  168. — Timber  Grillage  Foundation,  Fisheries  Building,  World's 
Columbian  Exposition. 

planks,  with  blocking  on  top  to  distribute  the  load  uniformly 
over  all  the  planks.  This  blocking  also  served  as  a  support 
for  the  posts,  which ,  carried  the  caps  and  thus  the  floor-joists 
and  upright  posts  of  the  building.  The  blocking  was  well 
spiked  to  platform  planks  and  posts,  and  caps  and  sills  were 
drift-bolted.  For  bearing  of  vertical  posts  upon  underlying 
blocking  (end  fibre  upon  transverse  fibre),  a  unit  pressure  of 


314  ARCHITECTURAL  ENGINEERING. 

400  Ibs.  per  sq.  in.  was  allowed.  For  tension  in  extreme 
fibres  of  caps  and  joists,  a  unit  of  1,200  Ibs.  per  sq.  in.  was  used. 
The  footings  under  the  New  Orleans  Custom-house  are 
mentioned  by  Prof.  Baker  (see  ' '  A  Treatise  on  Masonry  Con- 
struction," p.  211),  as  an  example  of  timber  grillage.  Upon 
a  plank  floor  laid  7  ft.  below  the  street-level,  were  placed 
12-in.  diameter  logs,  side  by  side,  ®ver  which  similar  logs  were 
placed  transversely,  2  or  3  ft.  apart.  The  open  spaces  were 
filled  with  concrete,  and  a  continuous  layer  I  ft.  thick  was  then 
spread  over  the  entire  area.  The  settlement  has  been  very 
great,  and  far  from  uniform,  but  had  the  same  foundation 
materials  been  employed  in  independent  footings,  proportioned 
for  the  separate  pier-loads,  unequal  settlement  would  have  been 
avoided. 

For  allowable  offsets  in  timber  courses,  Prof.  Baker  gives 
the  following:  "  If  the  pressure  on  the  foundation  is  0.5  ton 
per  sq.  ft.,  the  safe  projection  is  7.5  times  the  thickness  of  the 
course;  if  the  pressure  is  I  ton  per  sq.  ft.,  the  safe  projection 
is  5.3  times  the  thickness  of  the  course;  if  the  pressure  is  2  tons 
per  sq.  ft.,  the  safe  projection  is  3.7  times  the  thickness  of 
the  course.  The  above  values  give  a  factor  of  safety  of  about 
10." 

Masonry  in  Foundations. — The  application  of  masonry  to 
foundation  design  will  usually  be  in  the  form  of  cap-stones 
over  piles,  as  in  Fig.  184,  or  as  masonry  piers  of  brick  or  stone 
over  pile  or  caisson  under-bearings,  as  in  Figs.  183  and  194. 

Data  as  to  the  compressive  strength  of  various  classes  of 
masonry,  also  unit-stresses  and  the  requirements  of  building 
laws  have  been  previously  given  in  Chapter  V.,  but  for  the  use 
of  masonry  construction  in  foundations,  it  will  be  necessary  to 
determine  the  allowable  batters  for  brickwork  or  masonry  of 
dimension-stones,  also  the  allowable  offsets  or  thicknesses  for 
dimension-stones  where  used  as  cap-stones  or  in  stepped-out 
foundations. 


FOUNDATIONS. 


3*5 


The  following  table  *  gives  the  safe  offsets  for  masonry 
footing  courses  in  terms  of  the  thickness  of  the  course  for  a 
factor  of  safety  of  I  o  : 


Offset   for    a  Pressure, 

in    Tons    per     sq.    ft., 
on  the    Bottom   of   the 

Kind  of  Stone. 

Course  of 

0.5 

1.0 

„ 

3  6 

6 

i  8 

Blue  stone     agging 

2.  7 

i  .  3 

2.6 

8 

i  .3 

siate                 

e    o 

6 

2.5 

2    7 

i  .3 

Hard  brick                     .  .              •  •                         

0.8 

i  i  part  Portland  cement  ) 

O   8 

o  6 

(  3     "     pebbles                    ) 
ii  part  Rosendale  cement} 

2     "     sand                           [•  TO  days  old  

0.6 

0.4 

0-3 

3     "     pebbles                      ) 

Results  given  by  the  above  table  are  correct  only  when  the 
footing  is  composed  of  entire  stones  for  each  course,  and  when 
the  projections  are  not  more  than  half  the  lengths  of  the  stones. 

"  The  preceding  results  will  be  applicable  to  built  footing 
courses  only  when  the  pressure  above  the  course  is  less  than 
the  safe  strength  of  the  mortar.  The  proper  projection  for 
rubble  masonry  lies  somewhere  between  the  values  given  for 
stone  and  those  given  for  concrete.  If  the  rubble  consists  of 
large  stones  well  bedded  in  good  strong  mortar,  then  the 
values  for  this  class  of  masonry  will  be  but  little  less  than  those 
given  in  the  table.  If  the  rubble  consists  of  small  irregular 
stones  laid  with  Portland  or  Rosendale  cement  mortar,  the 
projection  should  not  much  exceed  that  given  for  concrete. 
If  the  rubble  is  laid  in  lime  mortar,  the  projection  of  the  foot- 
ing course  should  not  be  more  than  half  that  allowed  when 
cement  mortar  is  used." 


*  See  Prof.  Baker's  "  Treatise  on  Masonry  Construction,"  p.  209. 


316  ARCHITECTURAL  ENGINEERING. 

For  offsets  in  brick  piers,  both  the  New  York  and  Boston 
building  laws  require  that  if  the  bricks  are  laid  in  single  courses 
the  offset  for  each  course  must  not  exceed  i£  ins.,  or,  if  laid 
in  double  courses,  then  each  offset  shall  not  exceed  3  ins. 

The  allowable  loads  and  offsets  for  concrete  piers  under 
the  Chicago  building  laws  are  given  under  the  preceding  head- 
ing "  Concrete. " 

The  Chicago  ordinance  specifies  that  the  offsets  in  dimen- 
sion-stones, where  two  or  more  layers  are  used,  "must  not 
be  more  than  three-quarters  of  the  height  of  the  individual 
stones,"  and  that  "dimension-stones  in  foundations  shall  not 
be  subjected  to  a  load  of  more  than  10,000  Ibs.  per  sq.  ft.  in 
piers.  If  the  beds  of  the  stones  are  dressed  and  levelled  off  to 
uniform  surface  and  the  stones  are  set  in  cement  mortar,  this 
strain  may  be  increased  to  14,000  Ibs.  per  sq.  ft." 

Comparison  of  Masonry  Offsets  and  Steel  Grillage. — The 
rapid  development  of  foundation  design  is  well  exemplified  by 
the  great  change  in  methods  employed  «tt  the  site  of  the 
Woman's  Temple,  Chicago.  In  1890  the  lot  where  this  build- 
ing now  stands  was  bought  by  the  present  owners.  Extensive 
masonry  foundations  had  been  built  here  a  few  years  before  for 
a  structure  that  was  never  erected,  and  upon  the  preparation 
of  plans  for  the  Temple,  the  first  thing  done  was  to  remove 
these  massive  masonry  piers  at  great  cost.  The  old  system 
consisted  of  stone  piers  made  of  successive  layers  of  large 
stones,  stepping  out  until  a  sufficient  base  was  obtained.  One 
of  the  newer  "raft"  footings  is  shown  in  Fig.  169,  and  also 
one  of  the  old  masonry  type,  in  Fig.  170. 

The  objections  to  these  old  piers  were  many:  they  were 
bulky,  occupying  too  much  space ;  they  were  heavy  and  costly 
as  regarded  the  time  necessary  for  building;  and  the  allowable 
offsets  of  the  masonry  work  seriously  limited  the  load-bearing 
surface  of  the  clay. 

These  piers  in  the  Woman's  Temple  were  all  underlaid 


FOUNDATIONS. 


317 


with  a  bed  of  concrete,  resting  on  the  clay  stratum  about  IO  ft. 
below  street-grade.     A  comparison  of  some  of  the  above  points 
may  be  made  as  follows: 
I.    Space. — 

1st.   Top  of  concrete  to  bottom  of  casting  =  i'  8". 
2d.       "     "        "         "        "       "      ."        =  7'o". 
Or,  comparing  the  parts  above  the  common  bed  of  concrete, 
1st  =217  cu.  ft.,     2d  =  691  cu.  ft. 


,  „ 

L_  //j'/T  M 

/O'U  -f\ 


FIG.  169.—  Detail  of  Rail-grillage  Footing. 
I 


FIG.  170. — Detail  of  Masonry-pier  Footing. 

This  point  of  space  is  a  very  important  one,  as  has  been 
before  mentioned,  since  basement-space  is  now  quite  as  valu- 


3*8  ARCHITECTURAL  ENGINEERING. 

able  as  any  office-space,  for  use  as  restaurants,  cafes,  or  for 
the  large  boiler  and  electric-light  plants  necessary.  It  is  even 
of  frequent  occurrence  to  extend  the  basement-space  out  under 
the  sidewalks  and  alleys.  Thus,  to  gain  cellar-room,  the 
foundation  must  either  be  lowered  or  made  thinner.  The  first 
has  been  ruled  out  of  Chicago  practice,  because  it  has  been 
clearly  demonstrated  that  the  less  the  clay  stratum  is  broken, 
the  more  uniform  and  satisfactory  the  settlement  will  be. 

II.  Weight. — Rating  the  masonry  at  150  Ibs.  per  cu.  ft., 
concrete  at  140  Ibs.,  and  allowing  44  cu.  ft.  for  the  steel  in 
No.  i,  the  weights  are: 

No.  I  =  103,000  Ibs. 

No.  2  =  261,000  Ibs. 

The  load  for  this  foundation  is  800,000  Ibs.,  and  the  saving  in 
weight,  through  the  use  of  the  raft  foundation,  is  thus  sufficient 
to  allow  an  additional  story,  without  adding  to  the  load  on  the 
clay.  On  large  foundations  this  difference  is  still  greater.  In 
the  case  here  assumed  the  103,000  Ibs.  is  about  13  per  cent, 
of  the  load  carried,  but  in  some  cases,  under  very  heavy  loads, 
it  has  been  found  to  run  as  high  as  20  per  cent,  (see  ' '  Steel 
Rail  Foundations,"  Engineering  News,  vol.  xxvi.  No.  32. 

This  saving  in  weight  is  one  of  the  factors  that  makes 
our  highest  buildings  possible,  and  fourteen  or  even  sixteen 
stories  are  not  loading  the  clay  as  severely  as  some  of  the 
older  structures.  Under  the  foundations  of  old  five-  or  six- 
storied  masonry  buildings,  which  were  torn  out  to  make  room 
for  new  office  buildings,  the  clay  has  been  found  loaded  to 
11,200  Ibs.  per  sq.  ft.,  while  "The  Fair  "  Building  is  loaded 
to  2,850  Ibs.  only,  for  a  sixteen-story  modern  structure. 

III.  Cost. — In  general,  the  cost  of  stone  foundations  will 
be  less  than  iron  ones,  but  considering  the  renting-space  in 
basements,  this  difference  will  be  quickly  made  up  where  the 
latter  are  used. 

IV.  Time. — In  the  time  required  for  building  operations 


FOUNDATIONS. 


the  new  foundations  are  greatly  superior,  as  rails  and  beams 
are  easily  obtained  and  cheaply  handled. 

V.  Load-bearing  Area. — As  to  the  fifth  point,  stone  foun- 
dations under  side  walls  frequently  cannot  step  out  sufficiently 
to  get  the  proper  bearing  area  without  projecting  into  the  next 
lot.  But  with  steel  we  can  combine  several  footings,  or  use 
cantilever  foundations,  thus  securing  the  desired  vesults.  For 
interior  footings,  also,  it  would  be  difficult,  ;n  fact  practically 
impossible,  to  obtain  sufficient  bearing  areas  for  great  loads 
through  the  use  of  masonry  offsets,  except  with  great  height 
and  attendant  bulk  of  material. 

Rail  Footings. — The  raft  footings  as  first  employed  were 
made  of  rails  only,  the  usual  method  of  figuring  being  as 
follows:  The  number  of  square  feet  of  footing  required  equals 

load  on  column 

~—p- —        — rr-     Multiply  the  result  by  2150  (equals 
pounds  per  sq.  ft.  on  earth 

approximate  weight  of  footing  per  square  foot),  add  to  the 
original  load,  and  refigure.  The  layers  were  then  laid  off,  the 
projection  of  any  layer  beyond  the  one  immediately  above 
being  always  3  ft.  or  less.  The  moments  on  the  projecting 
portions  of  the  layers  were  then  found,  and  these  moments, 
divided  by  the  allowable  bending  moment  per  rail,  usually 
taken  at  12,500  ft.-lbs.,  gave  the  number  of  rails  required  in 
the  different  courses.  One  extra  rail  was  usually  added  to 
each  layer  as  a  matter  of  safety. 

The  following  table  gives  the  properties  of  the  rails  from 
the  North  Chicago  Rolling  Mills.  The  75 -Ib.  rails  were  most 
commonly  used. 


No. 

Weight. 

He.ght. 

Base. 

u. 

'• 

* 

M. 

y  '=  16,000. 

6504 

65  Ibs. 

15-86 

6.86 

9.150 

7  01 

7503 

75 
75 

;f 

4*" 
4! 

«tr 

21.00 

21.66 

8.30 
9-37 

11,070 
12,500 

8001 

80 

5 

5 

2H 

26.36 

9-99 

13.320 

8501 

85 

5 

4f 

2* 

27-32 

10.41 

13.880 

8502 

85 

5 

2$ 

29.22 

11.13 

14,840 

8503 

85 

5 

5 

»tt 

25-38 

10.03 

i3.37o 

320 


ARCHITECTURAL  ENGINEERING. 


The  table  following  is  taken  from  the  footings  of  the  Great 
Northern  Hotel,  giving  the  loads  on  columns,  areas  of  footings, 
and  the  calculated  weights  per  square  foot  of  the  rails  and  the 
concrete  in  the  footings.  All  rails  were  75 -Ib.  rails,  No.  7503 
in  the  previous  table.  The  bottom  courses  of  all  footings  were 
of  concrete,  12  ins.  thick,  extending  6  ins.  beyond  the  lower 
course  of  rails,  but  the  weights  of  these  concrete  courses  are 
not  included  in  the  following.  Cast  shoes  4  ft.  X  4  ft.  were 
used  under  all  the  columns.  The  concrete  was  figured  as 
weighing  125  Ibs.  per  cu.  ft. 


Load  on  Col. 

Area  of  Footing,  sq.  ft. 

Weight  per  sq.  ft. 

Rails. 

Concrete. 

415.470 

12  X  n|  =  I41 

49 

83 

433,440 

10  X  I4i  =  146 

58 

60 

435.820 

9  X  i6i  =  146 

77 

83 

461,100 

12  X  13  =  156 

42 

80 

496,240 

10  X  i6£  =  163 

79 

91 

526,850 

I2f  X  14   =  178 

66 

82 

53L740 

13  X  I4i  =  185 

60 

78 

57L360 

I3i  X  I4i  =  192 

67 

74 

595,920 

I2£  X  l6  =200 

67 

88 

621,560 

13  X  16  =  208 

60 

94 

637,240 

13^  X  16  =  214 

68 

68 

666,000 

15  x  15  =  225 

66 

105 

672,000 

13  Xi?i  =  228 

67 

93 

Beam  and  Rail  Footings. — The  next  step  made  in  the 
development  of  raft  footings  was  in  the  use  of  I-beams  for  the 
upper  course  or  courses.  Fig.  171  shows  a  foundation  which 
was  figured  as  follows  (see  Engineering  News,  vol.  xxvi. 
No.  32): 

The  column  load  was  1,166,000  Ibs.  The  allowable 
pressure  per  square  foot  on  the  clay  was  taken  at  3,000  Ibs., 
giving  a  footing  22  ft.  8  ins.  X  17  ft.  3  ins.  The  lower  layer 
of  concrete  was  18  ins.  thick,  projecting  8  ins.  beyond  the 
lower  course  of  rails.  Fifteen-inch  steel  beams  were  used  in 
the  top  course,  weighing  50  Ibs.  per  ft.  The  allowable 


FOUNDATIONS. 


321 


moment  on  each  beam  equalled  117,700  ft.-lbs.     The  remain- 
ing courses  were  of  steel  rails,  4!  ins.  high  and  4!  ins.  base, 


FIG.  171. — Detail  of  Beam  and  Rail  Footing  in  "  The  Fair"  Building. 

75  Ibs.  per  yard  weight,  with  an  allowable  moment  of  12,100 
ft.-lbs.  per  rail. 

In  the  upper  course,  as  many  beams  are  used  as  the  space 
under  the  column  casting  will  allow.  The  projecting  arms 
must  therefore  be  determined.  The  total  length  of  the  I-beams 


322  ARCHITECTURAL  ENGINEERING. 

so  found  will  fix  the  width  of  the  second  course  from  the  top, 
and  the  projecting  arms  must  be  found  for  this  course  as  in  the 
first  case. 

The  arms  of  the  lower  two  courses  are  fixed  by  the  lengths 
of  the  upper  ones,  and  by  the  dimensions  of  the  clay  area; 
hence  the  question  is,  how  many  pieces  are  required  ?  The 
formula::  used  may  be  derived  as  follows: 


=  proecting  arm  in  any  course; 
a  =  width  of  supporting  area; 
P  =  total  load  on  footing; 
M  =  bending  moment  on  one  side  of  the  layer. 

Then  the   length   of  beam    or    rail   =  a-\-y-\-y  =  a-\-2y. 

Py 
The  total  load  on  y  =  —  -  --  ,  and  since  the  distribution  of  the 

*+2/ 

load  on  every  layer  is  uniform,  we  have 

Py  y  Py2 

M  =  -  -  —  X  lever  arm  —  =  —.  —  -  -  N  . 
a-\-2y*  2       2(0  +  2j/) 

In  calculating  the  lower  two  courses,  y  becomes  a  known 
quantity  and  M  an  'unknown.  In  the  upper  two  layers  M  is 
given  by  the  number  of  the  beams  used  and  y  is  unknown. 

Considering  now  the  top  course,  under  the  base  casting, 

5  ft.  X  5    ft.   in  area,  we  find  that  nine  beams  only  can  be 
placed  under  the  casting,   allowing  sufficient   space    between 
them  for  the  ramming  of  the  concrete. 

M  for  each  beam  =  117,700  ft.-lbs.  Hence  M  for  the 
whole  layer  =  9  X  1  17,700  ft.-lbs.  =  1,059,300  ft.-lbs.  Then 

1,166,000V3 

—.  -  —  =  1,059,300,  whence  y  =  5  ft.  4  ins.     The  length 

of  this  layer  then  becomes  5  -f  2  y  =  1  5  ft.  8  ins. 

For  the  second  course  we  find  that  31  rails  spaced  about 

6  ins.   centres  may  be  placed  under  the   15   ft.  8  in.  -beams. 
Closer  spacing  than  this  may  be  used  if  necessary.     The  load 


FOUNDATIONS.  323 

now  equals  1,166,000  Ibs.  -f-  the  weight  of  the  top  course 
(about  19,000  Ibs.).  Then  '  '  -  —  —  375>IO°;  whence 

y  =  2  ft.  5  ins.  The  length  of  the  rails  therefore  =5  ft.  -}- 
4  ft.  10  ins.  =  9  ft.  10  ins. 

For  the  calculation  of  the  lower  courses,  we  know  that  the 
area  covered  by  the  bottom  course  is  15  ft.  n  ins.  X  21  ft. 
4  ins.  This  leaves  a  projection  of  3  ft.  f  in.  for  the  bottom 
course,  and  a  projection  of  2  ft.  10  ins.  for  the  next  to  the 
bottom  layer. 

Then  for  the  third  or.  next  to  the  bottom  course,  we  have 


1,200,000  '_.  lbg 


a-\-2y  2i 

This  moment  requires  19  rails  to  be  used  in  the  layer. 
For  the  bottom  course, 

..a,o.ooo  lb..X3A  ft-  X 


>  - 

1  5  IT 

This  requires  29  rails,  30  being  used  for  safety. 

It  will  be  noticed  in  the  above  calculation  that  the 
moments  have  been  taken  for  the  projections  of  the  several 
courses  beyond  the  adjacent  supporting  layers  only.  Thus  in 
the  figures  for  the  next  to  the  bottom  course,  as  given  above, 
y  =  2  ft.  10  ins.  If,  however,  the  foundation  be  taken  as  a 
whole,  and  the  bending  moment  on  the  third  course  is  taken 
around  the  edge  of  the  cast  base,  the  same  as  the  top  course 
was  figured,  we  have  y  =  8^  ft.,  or, 

1,200,000  X  8i  X  4-rV 

M=  —  ?  -  ^-=-  =  1,920,000  ft.  -Ibs. 

2I| 

This  must  be  resisted  by  the  combined  moments  of  the  p-in. 
I-beams  in  the  top  layer,  and  the  19  rails  in  the  third  layer, 


324  ARCHITECTURAL   ENGINEERING. 

or  1,059,3004-229,900=  1,289,200  ft.-lbs.  This  assump- 
tion leaves  a  difference  of  630,800  ft.-lbs.  which  has  not  been 
cared  for. 

Both  of  the  above  methods  of  calculating  grillage  founda- 
tions have  been  extensively  employed.  Many  engineers  and 
architects  advocate  considering  each  layer  of  beams  separately, 
and  thus  taking  moments  for  each  layer  about  the  centre  of  the 
system.  This  method  requires  more  material  than  when 
moments  are  taken  about  the  edges  of  the  supporting  layers, 
but  the  excess  is  considered  to  offset  any  possible  corrosive 
tendencies.  If  the  individual  layers  were  piled  loose,  without 
being  embedded  in  concrete,  this  method  of  moments  about 
the  centre  for  each  layer  would  undoubtedly  be  theoretically 
correct,  but  the  action  of  the  concrete  filling,  with  its  tendency 
to  bind  the  beams  and  concrete  together,  causes  the  grillage 
to  act  largely  as  a  whole  and  thus  to  possess  a  moment  of 
resistance  much  greater  than  the  sum  of  the  resistances  of  the 
individual  layers.  This  latter  method  is  now  generally  em- 
ployed, and  will  be  used  in  the  following  calculations  for 
simple  and  combined  grillage  systems. 

The  use  of  rails  in  footings  has  now  been  succeeded  by  the 
employment  of  beams  throughout. 

Beam  Footings. — In  the  two  preceding  paragraphs,  the 
methods  of  calculation  employed  for  Rail  Footings  and  Beam 
and  Rail  Footings  have  been  described,  and  precisely  the  same 
procedure  may  be  followed  in  the  design  of  Beam  Footings  as 
now  employed  in  almost  all  cases  of  simple  grillage. 

In  determining  the  sizes  of  beams  in  any  layer,  care  must 
be  taken  to  leave  sufficient  clearance  between  the  flanges  to 
admit  the  concrete  which  must  be  rammed  in  place.  If  stone, 
crushed  or  broken  to  pass  a  f-in  ring,  be  specified,  I  in.  as  a 
minimum  between  the  flanges  will  answer. 

To  surround  and  protect  the  various  layers,  plank  frames 
or  open  boxes  are  made  for  each  course,  of  sufficient  size  to 


FOUNDATIONS. 


325 


permit  a  4-in.  concrete  covering  for  the  ends  and  sides  of  the 
beams,  and  a  i-in.  protective  layer  over  the  tops  of  the  courses. 
The  concrete  should  be  well  tamped 
between  the  beams,  and  the  whole 
exterior  is  then  plastered  with  pure 
Portland  cement  mortar,  so  that  no 
part  of  the  metal-work  is  exposed. 
A  bed  of  concrete  18  ins.  or  2  ft. 
thick  is  placed  under  all,  projecting 
6  ins.  to  12  ins.  beyond  the  beams. 
Fig.  172  shows  a  simple  beam 
footing  used  in  the  Marquette  Build- 
ing for  a  column  load  of  920,250  Ibs.  FIG  172<_simple  Beam  Foot. 

Formulas    applicable  to  this  type         ing,  Marquette  Building. 

of  footing  may  be  derived  as  in  the  following  paragraph. 

Simple  Beam  Footings,  are  those  which  receive  one  column 
only.  In  this  case  the  concrete  bed  is  made  symmetrical 
about  the  column,  in  order  that  the  centre  of  pressure  and 
centre  of  base  may  coincide. 

In  the  following  analyses  of  simple  and  combined  footings, 
let 

P  =  column  load ; 

a  =  width  of  column  base ; 

y  =  projection  of  beams  beyond  base  or  adjacent  layer ; 

/  =  length  of  beams  in  feet ; 

/=  allowable  extreme  fibre  stress; 

5  =  section  modulus. 

Referring  now  to  Fig.  173,  and  considering  the  upper 
course  of  beams  of  length  /,  the  load  per  lineal  foot  will  equal 

P  Py 

-T-,  and  the  load  at  the  centre  of  moments  c,  will  equal  —j-. 

The  bending  moment  at  c  will  equal 

Py  y  Py* 

—r  X  —  =  ---,-  foot-pounds. 


326 


ARCHITECTURAL   ENGINEERING, 


M 
But,  as  S  =  -j,  where  ^/"equals  the  bending  moment,  we 

have 

I2/V       6/V 

....     (i) 


i2/y  _  6/y 

2//     ~  IT' 


This  value  of  5  is  for  the  total  number  of  beams  in  the 
course.     The  required  value  of  5  for  one  beam  will  therefore 


P  *       "       rt 


FIG.  173. — Diagram  of  Calculation  of  Simple  Beam  Footing. 

be  obtained  by  dividing  5  as  found  by  equation  (i)  by  the 
number  of  I-beams  used  in  the  layer,  and  from  the  values  of  S 
given  in  the  mill  handbooks,  the  required  size  and  weight  of 
beam  may  be  readily  selected.  For  the  lower  course,  the 
calculation  may  be  made  in  exactly  the  same  manner,  remem- 
bering that  the  point  of  moments,  c,  is  taken  on  the  extreme 
edge  of  the  upper  course. 

Tabulated  sizes  and  weights  of  beams  for  simple  grillage 
foundations  may  be  found  in  the  handbook  of  The  Carnegie 
Steel  Co.  These  are  given  for  allowable  bearing  capacities  of 
from  i  to  50  tons  per  sq.  ft. ,  and  for  the  spacing  of  beams  9, 
12,  15,  1 8,  and  24  ins.  centres. 

In  order  that  perfectly  accurate  bearing  may  be  obtained 
between  the  various  layers  of  beams  composing  a  grillage 


FOUNDATIONS. 


327 


foundation,  some  engineers  and  architects  are  now  specifying 
that  all  bearing-surfaces  shall  be  faced  or  planed.  Thus  the 
top  and  bottom  flanges  of  the  I-beams  are  planed  where  re- 
ceiving a  layer  from  above,  or  where  bearing  upon  a  layer 
beneath.  In  such  cases  each  separate  layer  is  usually  made 
complete  in  the  shop,  the  beams  being  connected  by  special 
riveted  diaphragms,  instead  of  by  the  usual  cast  separators  and 
bolts. 

Combined  Footings.  —  In  proportioning  the  areas  for 
adjacent  grillage  footings,  they  are  often  found  to  overlap,  and 
in  such  cases  two,  three,  or  even  four  areas  may  be  combined 
as  one  footing.  When  this  is  done,  the  centre  of  gravity  of 
the  footing  area  must  coincide  with  the  centre  of  pressure  of 
the  loads  carried. 


FIG.  174.— Combined  Footing,  Old  Colony  Building. 


328  ARCHITECTURAL  ENGINEERING. 

Combined  footings  are  also  exceedingly  useful  where  access 
may  not  be  had  to  the  basement  of  an  adjoining  building  or 
buildings,  thus  precluding  the  construction  of  new  party-wall 
foundations  by  shoring  or  underpinning.  Recourse  may  then 
be  had  to  cantilever  construction,  in  which  a  combined  footing 
is  used  with  cantilever  girders  to  transmit  the  wall-loads  away 
from  the  lot-line,  and,  combining  with  the  other  column  loads, 
bringing  the  resultant  centre  of  pressure  over  the  centre  of 
base, 

The  first  cantilever  footings  introduced  were  those  in  the 
Manhattan  and  Rand  McNally  buildings  in  Chicago,  built  at 
about  the  same  time.  The  boilers,  etc.,  in  the  basements  of 
the  adjoining  buildings,  could  not  be  disturbed  to  allow  the 
introduction  of  new  party-footings,  so  the  cantilever  types  were 
adopted  for  the  new  structures,  and  the  foundations  of  the  old 
ones  were  not  interfered  with. 

Fig.  174  illustrates  a  combined  footing  and  cantilever 
girder  as  employed  in  the  Old  Colony  Building,  Chicago. 

Two  Equally  Loaded  Columns,  Area  Rectangular.  —  This 
case  may  sometimes  be  met  with  in  very  narrow  buildings, 
where  all  of  the  columns  become  outside  supports,  and  with 
practically  the  same  loads  at  either  side.  The  top  layer  beams 
then  become  uniformly  loaded  beams,  supported  at  each  end, 
and  the  moment  for  the  layer  becomes 


Jf=2Px  and>as     s 

84  / 

we  have 


The  lower  beams  are  calculated  by  equation  (i)  as  before. 

A  variation  of  this  case  is  shown  in  Fig.  175,  where  each 
footing  receives  four  columns,  supported  on  a  double  set  of 
cantilever  plate-  or  box-girders. 


FOUNDATIONS. 


329 


FIG    175. — Combined  Footing. 

Two  Unequally  Loaded  Columns,  Area  Rectangular. — 

This  is  one  of  the  most  ordinary  cases  in  practice.  Referring 
to  Fig.  176,  the  loads  Pl  and  P2  are  given,  also  the  distance 
x,  centre  to  centre  of  columns.  A  slight  inaccuracy  is  intro- 
duced by  considering  the  column  centre  Pl  as  the  end  of  the 
footing,  but  as  the  column  base  is  not  usually  over  24  ins. 
wide,  the  results  will  be  sufficiently  exact. 

To  find  the  centre  of  gravity  of  the  two  column  loads,  take 
moments   at  Pr      The   distance  g  from  Pl  to  the   centre  of 

gravity  will  then  equal  p-_?p,  and  as  the  total  length  of  the 
•*i    i    *-\ 


33°  ARCHITECTURAL   ENGINEERING. 


FIG.  176.  —  Diagram  of  Combined  Footing,  Two  Unequally  Loaded 
Columns,  Area  Rectangular. 

footing  must  equal  2g,  in  order  that  the  centre  of  gravity  and 
the  centre  of  pressure  may  coincide,  we  have 


The  uniform  pressure  per  lineal  foot  at  the  base  of  the  footing 
will  equal 


To  calculate  the  bending  moments,  it  is  first  necessary  to 
determine  the  points  of  no  shear,  as  the  bending  moment  will 
be  maximum  when  the  shear  =  o.  Moving  to  the  right  from 

p 
Pl  ,  the  first  point  of  no  shear,   a,   is  at  a  distance  of  ~  -  ft. 

The  second  point  of  no  shear  will  be  closely  to  the  left  of  P2  , 
or  such  a  distance  that  enough  of  P2  will  be  added  to  P,  to 
equal  px.  Sufficiently  accurate  results  will  be  obtained  if  this 
point  is  considered  to  coincide  with  the  column  centre,  b. 

Considering  now  all  of  the  forces  to  the  left  of  a,  we  have 
the  column  load  Pl  and  the  uniform  load  on  the  footing  base. 
The  bending  moment  will  equal  the  moment  of  the  column 
load,  minus  the  moment  of  the  uniform  load,  or 


FOUNDATIONS.  331 

Substituting  the  value  of/  previously  found,  we  have 


For  the  bending  moment  at  P2 ,  or  the  point  &,  take  the 
moments  of  the  forces  to  the  right  of  the  section.  The  result- 
ant moment  will  equal  the  moment  of  the  uniform  load  on  the 
footing  base,  minus  the  moment  of  one-half  the  column  load 
into  its  arm,  or  one-fourth  the  width  of  the  base  casting. 

Or,  M-- 

where  c  =  width  of  base  casting. 

••:*-.?-* 

and  substituting  the  value  of/,  as  before,  we  have 

M=       l   2/  2)       •-£ (4) 

i 

The  required  section  modulus,  or  5,  may  then  be  deter- 
mined by  substituting  the  greater  of  the  two  moments  thus 
found  by  equations  (3)  and  (4)  in  the  equation 

12M 

S  =  — j- ,  as  before. 

The  beams  in  the  lower  course  may  be  found  by  equa- 
tion (i). 

Two  Unequally  Loaded  Columns,  Trapezoidal  Area. — 

When  two  unequally  loaded  columns  are  to  be  supported  upon 
one  footing,  and  one  of  the  columns,  probably  the  heavier,  is 
a  wall  column  whose  foundation  may  not  extend  beyond  the 
lot-line,  a  trapezoidal  footing  area  can  be  used  instead  of  the 
rectangular  bed  previously  calculated. 

As  before,  the  centre  of  gravity  of  the  loads  must  coincide 
with  the  centre  of  pressure  of  the  base.  Referring  to  Fig.  176, 


332 


ARCHITECTURAL  ENGINEERING. 


=  the  distance  of  centre  of  gravity  of  area  from  the  lighter 
load,  Pr     Then 


g  — 


(5) 


This  distance  g  may  also  be  expressed  in  terms  of  /,  wl ,  and 
w2,  as  follows:   If  the  trapezoid  is  divided  into  two  triangles, 

w  I 
as  in  Fig.  177,  the  area  of  one  triangle  is  -^-,  and  of  the  other 

* /_. 


FIG.  177.— Diagram  of  Combined  Footing,  Two  Unequally  Loaded 
Columns,  Trapezoidal  Area. 

wl 

— .     The  centre  of  gravity  of  each  triangle   lies  on   a  line 

drawn  from  the  centre  point  of  the  base  to  the  opposite  angle, 
and   its   distance  from  either  base   equals   — .     Then,  taking 

moments  of  the  triangle  areas  about  the  shorter  side,  wl ,  and 
dividing  by  the  entire  area,  will  equal  the  distance  g,  or 


wJ       2l\ 

-    X 


x/ 


(6) 


The  area  of  the  trapezoid 


(7) 


FOUNDATIONS. 


333 


and  the  value  of  the  second  term  of  this  equation  can  be 
obtained  by  dividing  the  sum  of  the  two  loads,  />1,  and  P2, 
by  the  allowable  pressure  per  square  foot  on  the  soil.  The 
distance  centre  to  centre  of  columns,  /,  is  also  known,  so  that 
we  have  the  two  equations  (6)  and  (7)  containing  but  two 
unknown  quantities,  wl  and  w^.  Solving  for  these  we  have 


and 


2A 


(8) 


(9) 


Substituting  the  value  of  g  in  these  equations  as  found  pre- 
viously in  (5),  they  become 


and 


2A(2Pl  — 


2A(2P2  -  P,} 


(10) 


To  obtain  the  point  of  no  shear,  consider  Fig.  178,  with 


FIG.  178. — Diagram  of  Unit  Pressures  for  Footing,  as  in  Fig.  177. 

the  varying  unit  pressures  on  the  base.      Let  p2  represent  the 
maximum  unit  pressure  under  the  heavier  column,  and  p^  the 


334  ARCHITECTURE L   ENGINEERING. 

minimum  unit  pressure  under  the  lighter  column.     If/  denotes 
the  allowable  pressure  per  square  foot  on  the  soil,  then 

A.=  Pwi  »     and     A  =  Pwr 

The  pressure  due  to  the  load  Pl  will  vary  from  pl  beneath 
the  load,  to  o  at  the  other  extreme  end  B,  and  these  varying 
pressures  may  be  represented  by  vertical  ordinates  between  the 
base  AB  and  the  line  CB.  In  like  manner,  the  varying  pres- 
sures due  to  the  column  load  P2  may  be  represented  by  vertical 
ordinates  between  the  lines  CB  and  BD.  The  resultant  unit 
pressure  due  to  both  column  loads  will  be  represented  by  ver- 
tical ordinates  between  the  base  AB  and  CD. 

At  the  point  of  no  shear,  the  ordinate  at  that  point  will 
equal 


If  pQ  is  distant  q^  from  the  column  load  Piy   then,   from  the 
similarity  of  triangles, 


Taking   moments,    then,    to    the    left   of  this    point,    and 
remembering  that  pq0  =  P1  ,  we  have 

fJ  =  Plfl,-     .     .      (12) 


where  gx  is  the   distance   from  the  load  Pl  to    the  centre  of 
gravity  of  the  trapezoid  included  between  pl  and  p0. 

Changing  the  notation  in  equation  (6)  to  suit  this  trapezoid, 
we  have 

.r    -  il  X  A  +  2/0 

_  *l~  3  X  A+A'  __ 

*  For  the  proof  of  this  equation,  see  "  Stresses  in  Framed  Structures," 
P-  597.  Prof.  Du  Bois,  whose  method  of  calculation  of  this  case  is  here 
followed. 


FOUNDATIONS. 


335 


and  on  substituting  this  value  in  equation  (12),  M  is  deter- 
mined, and  consequently  S. 

As  the  lengths  of  the  lower  course  beams  vary,  and  as 
their  unit  pressures  vary  also,  calculations  must  be  made  for 
each  beam  separately.  If  the  centres  of  the  beams  are  plotted 
on  the  line  AB,  the  vertical  ordinates  between  AB  and  CD 
will  represent  the  unit  pressures,  and  the  total  load  distributed 
by  any  beam  will  be  the  product  of  its  ordinate  times  the  dis- 
tance centre  to  centre  of  beams.  The  load  so  found  should 
be  substituted  in  equation  (i). 

Limitation. — If  P2  =  2PX,  then  wl  in  equation  (10)  reduces 
to  o,  and  the  trapezoid  becomes  a  triangle.  Hence  if  either 
column  load  is  less  than  one-half  the  other,  this  method  is  not 
applicable. 

Three  Unequally  Loaded  Columns,  Area  Rectangular. — 
Considering  Fig.  174,  the  line  of  flexure  of  the  15 -in.  I-beams 


FIG.  179.— Line  of  Flexure  for  Continuous  Girder. 


F~*-jr  -        -  ^  -~**-  -  j£  "1 

i  ill  i  -  *  firTi.. 


T  t  T  T  T  T  \  T  ' 


FIG.  180.  —  Diagram  of  Combined  Footing,  Three  Unequally  Loaded 
Columns,  Area  Rectangular. 

will    be    as    in    Fig.    179.      To    find   the   maximum    bending 
moment  on  these  beams  we  must  compute  the  various  bending 


336  ARCHITECTURAL  ENGINEERING. 

moments  and  compare.  The  bending  moment  will  be  maxi- 
mum when  the  shear  =  o.  In  this  case  there  are  five  such 
sections,  as  shown  by  the  line  of  flexure  ;  hence  we  must  com- 
pute the  moment  at  each  point  to  find  the  greatest.  The 
moments  under  the  columns  will  be  positive,  causing  convexity 
downward,  while  the  moments  between  the  columns  are  nega- 
tive, causing  convexity  upward.  Fig.  180  may  then  be  used. 
To  find  the  distance  of  the  centre  of  gravity  of  the  loads 
from  the  left  end  we  have 


The  distances  from  the  left  end  of  the  beams  to  the  points 
where  S  =  o,  or  the  distances  xv  ,  x^  ,  xz,  x^  and  x6  ,  are  then 
found  to  be  as  follows: 

mp 
*i  A  =  (*i  -  W)A     or     ^  =  p_  p  ; 

P 

*      =  -P,     or    *=; 


or     x=  -— 


(m  +  a  +  n  +  at  +  g)p2  -  P  -  P, 

-jl-pr 

The  bending  moments  at  these  points  are  readily  found  by 
taking  the  moments  of  the  external  forces  on  one  side  of  the 
point  in  question ;  thus  M^  at  the  first  point  (remembering  that 

Wl 
M  =  — -  for  a  uniformly  loaded  cantilever)  is 


FOUNDATIONS.  337 


=  Pb-FZ*  =/>U--»j; 

2  \  2. 


c)  -  (P 

-b)-  Pl(*5  -b-c] 


2 

In  general  cases  M2  and  M4  will  be  small  except  where  the 
columns  are  very  far  apart,  and  the  maximum  bending  moment 
will  be  at  either  Ml  ,  M3  ,  or  M5  ,  according  to  which  column 
is  the  heaviest.  If  the  cast  bases  are  strong  enough  to  carry 
the  superimposed  loads  on  their  perimeters,  and  the  long 
beams  form  the  top  course,  the  values  of  M1  ,  M3,  and  M6  will 
be  reduced.  M2  and  M4  would  not,  however,  be  altered. 

Sufficient  deflection  could  hardly  take  place  to  increase 
materially  the  reaction  under  the  central  column,  if  figured  as 
a  continuous  girder;  but  if  so  calculated,  the  clay  reaction 
would  be  of  a  varying  intensity,  as  in  Fig.  181.  Thus,  from 


ft  jltMM 
u^-4  -----  .; 

1     rt,  %  H, 

FIG.  181.  —  Diagram  of  Unit  Pressures  for  Footing  as  in  Fig.  180. 
Clapyron's  formula,  we  have 


for  a  continuous  girder  of  two  equal  spans,  /.      But  in  the  case 
assumed 


and  *,=  -//'  +       .  or  *,=  _>,._ 


338  ARCHITECTURAL  ENGINEERING. 

Taking  now  the  shears  Sl  and  S2 ,  on  the  left  and  right 
respectively,  of  the  reaction  J?l ,  and  remembering  that 
Sl  -f-  S2  =  Rl ,  we  have 


Then 


where  f//  is  the  reaction  due  to  the  loads  on  the  two  spans  /, 
the  same  as  in  the  regular  formula  for  two  spans,  and  pj  is  the 


reaction  due  to  the  cantilever  load,  while  --  /-  is  the  effect  due 

4    / 

to  the  use  of  the  beam  as  a  continuous  girder. 
Also, 

' 


These  reactions  show  a  varying  tendency  in  the  unit  pres- 
sure on  the  clay,  as  in  Fig.  181. 

In  the  first  example  we  made  the  assumption  that  the 
reaction  from  the  clay  was  uniform  per  foot  of  length  of  the 
footing.  According  to  the  law  of  the  continuous  girder  this 
would  not  be  true,  as  we  have  seen  ;  but  when  we  consider 
that  the  beams  are  generally  of  sufficient  depth  to  prevent  any 
appreciable  deflection,  and  that  the  unifying  tendencies  of  the 
concrete  cause  the  footing  to  act  more  or  less  as  a  whole,  the 
assumption  is  undoubtedly  justifiable. 

Continuous  Grillage.  —  By  continuous  grillage  is  meant  the 
covering  of  the  entire  lot  area  with  a  platform  of  steel  beams 
and  concrete,  upon  which  the  individual  footings  of  the  columns 
rest.  This  method  has  been  employed  in  several  cases  of  high- 


FOUNDATIONS.  339 

building  construction,  the  idea  being  either  to  increase  the 
area  over  which  the  structure  is  supported,  thus  reducing  the 
unit  of  pressure  on  the  soil,  or  to  provide  a  rigid  layer  or  dis- 
tributing area  which  shall  take  up  the  strains  due  to  any  ten- 
dency toward  unequal  settlement,  thus  insuring  a  uniform 
settlement  of  the  whole,  rather  than  individual  settlements  of 
the  separate  concentrated  loads. 

In  the  St.  Paul  Building,  the  use  of  a  uniform  layer  of  con- 
crete over  the  entire  lot  area  has  been  previously  referred  to. 
This  would  hardly  be  considered  as  an  example  of  continuous 
grillage,  as  the  concrete  layer,  12  ins.  thick,  was  not  strength- 
ened by  any  steel  members.  The  concrete  was  rather  applied 
as  a  protective  layer  over  a  wet,  sandy  soil,  and  individual 
footings  were  used  upon  this,  as  though  upon  the  natural  sur- 
face. The  unit  pressure  was  6,000  Ibs.  per  sq.  ft.,  and  no 
appreciable  settlement  has  been  noticed. 

The  nineteen-story  Spreckels  Building  in  San  Francisco 
(Reid  Bros.,  architects)  is  supported  upon  a  continuous  grill- 
age as  shown  by  a  quarter  plan  of  the  footings  in  Fig.  182. 

"Although  the  main  building  is  but  75  ft.  square,  the 
excavation,  which  extends  underneath  the  adjacent  sidewalks, 
attains  dimensions  of  about  98  ft.  by  102  ft.,  and  was  carried 
to  a  depth  of  25  ft.  below  the  street-level,  where  a  concrete 
platform,  96  X  100  ft.  in  size  and  2  ft.  thick,  was  built  over 
the  entire  surface  of  the  dense  wet  sand  encountered.  Upon 
this  platform  was  set  a  layer  of  fifty-eight  15-in.  I-beams,  each 
composed  of  three  or  four  sections  web-  and  flange-spliced  to 
make  a  continuous  beam  96  ft.  long.  Concrete  was  filled  in 
level  with  the  top  flanges  of  these  beams,  and  another  tier  of 
sixty-three  15-in.  I-beams,  similarly  spliced  to  a  length  of 
91.5  ft.,  was  placed  about  equidistant  on  top  of  them  and  at 
right  angles  to  their  direction.  More  concrete  \vas  then  filled 
and  rammed  to  the  top  of  their  upper  flanges,  making  virtually 
a  solid  mass  of  concrete,  54  ins.  deep,  strengthened  by  the 


340 


ARCHITECTURAL  ENGINEERING. 


intersecting  grillages.  There  was  thus  formed  a  platform  con- 
centric and  parallel  with  the  walls  of  the  building,  and  project- 
ing beyond  them  about  9  ft.  on  each  side,  so  as  to  give  an 
extended  area  for  the  footing  upon  which  the  weight  is  aimed 
to  be  uniformly  distributed,  70  per  cent,  greater  than  the 
actual  floor  area  of  the  building.  This,  it  is  planned,  will 


FlG.  182.— Continuous  Grillage,  Spreckels  Building,  San  Francisco. 

bring  the  unit  pressure  down  to  4,500  Ibs.  per  sq.  ft.  on  the 
earth  surface,  and  insure  absolute  continuity  and  uniformity  in 
the  foundation,  that  it  may  have  sufficient  rigidity  to  take  up 
all  strain  and  insure  regular  and  uniform  settlement,  if  any 
should  occur.  On  top  of  the  concrete  footing  surface  are 


FOUNDATIONS.  341 

placed  twenty-eight  sets  of  distributing  girders,  each  formed 
of  five  or  six  parallel  2O-in.  rolled  steel  beams  bolted  together 
and  supporting  one  or  two  of  the  forty  main  columns  comprised 
in  the  framework  of  the  building.  Each  of  these  columns  is 
securely  anchored  by  bars  passing  through  its  pedestal,  and 
secured  by  keys  through  the  webs  of  the  lower  tier  grillage. ' '  * 

Fibre  Stresses  for  Foundation  Beams.  —  The  present 
Chicago  building  law  specifies  that  if  concrete  is  reinforced 
' '  by  iron  or  steel  beams  or  rails,  the  loads  and  offsets  in  the 
same  must  be  so  adjusted  that  the  fibre  strains  upon  the  metal, 
if  iron,  shall  not  exceed  12,000  Ibs.  per  sq.  in.,  or,  if  steel, 
that  the  fibre  strains  shall  not  exceed  16,000  Ibs.  per  sq.  in." 
The  same  extreme  fibre  stresses  are  specified  for  all  structural 
iron  or  steelwork. 

The  fibre  stresses  called  for  by  the  New  York  law  are 
identical  with  the  Chicago  requirements. 

As  high  as  20,000  Ibs.  have  been  used  for  fibre  stress  in  steel 
beams  and  iron  rails.  In  the  Old  Colony  Building  the  steel 
beams  in  the  foundations  are  strained  to  a  fibre  strain  of  14,000 
Ibs.  under  the  dead  weight  of  the  building  alone,  while  the 
maximum  dead-  plus  live-loads  induce  an  extreme  fibre  strain 
of  21,000  Ibs.  per  sq.  in.  The  Carnegie  strike  at  the  time  of 
building  precluded  the  possibility  of  obtaining  heavier  beams 
than  1 5 -in.  go-lb.  I-beams,  so  the  strain  was  allowed  under 
the  press  of  circumstances. 

Steel  Foundations,  Painting  of. — Protection  from  rust  by 
means  of  paint,  asphaltum,  concrete,  or  "by  such  materials 
and  in  such  manner  as  may  be  approved  by  the  commissioner 
of  buildings,"  is  specified  by  the  New  York  building  law  for 
metal  incorporated  in,  or  forming  part  of,  foundation  construc- 
tion. 

The  Chicago  law  does  not  require  the  painting  of  metal- 

*  See  the  Engineering  Record,  April  9,  1898. 


342  ARCHITECTURAL  ENGINEERING. 

work  embedded  in  concrete,  thus  recognizing  the  fact  that 
concrete  is,  in  itself,  a  better  preservative  than  paint.  Beams 
or  rails  must  be  entirely  enveloped  in  concrete,  the  mass  to  be 
free  from  cavities,  with  all  exposed  surfaces  coated  with 
cement  mortar  at  least  I  in.  thick. 

Pile  Foundations. — The  question  of  pile  foundations  vs. 
grillage  methods  to  secure  adequate  support  for  a  building  is  a 
matter  of  considerable  difference  of  opinion  among  many  archi- 
tects and  engineers.  There  are  those  who  consider  spread 
foundations  entirely  reliable,  and  who  show  their  faith  by 
using  this  type;  while  others,  who  question  the  advisability  of 
using  surface  foundations  for  important  structures,  advocate 
piling  to  hard-pan.  Each  type  undoubtedly  has  its  favorable 
conditions  and  limitations,  and  the  question  would  therefore 
seem  to  be  to  define  such  conditions  of  use. 

First,  as  to  the  nature  of  the  soil  to  be  builded  on,  the  suc- 
cessful use  of  spread  foundations  requires  a  uniform  material : 
' '  uniform  in  character,  in  compressibility,  in  softness  and  in 
depth."  Without  any  and  all  of  these  characteristics,  the 
material  is  not  adapted  to  the  uniform  settlement  which  must 
accompany  grillage  design.  These  conditions  are  fully  met 
in  such  subsoil  as  is  encountered  in  Chicago,  where  tests  and 
repeated  trial  have  shown  that  practically  uniform  settlement 
may  be  attained  without  resorting  to  the  necessity  for  deep 
foundations.  Very  few  office  buildings  in  Chicago  have  been 
built  on  any  other  than  grillage  footings,  except  the  heavy 
public  buildings  or  warehouses,  grain  elevators,  etc.,  along  the 
river  fronts  or  near  Lake  Michigan. 

When,  however,  considerable  variation  occurs  in  the  char- 
acter of  the  material  underlying  the  site,  as  is  especially  true 
in  the  lower  portion  of  New  York  City,  or  where  the  substrata 
are  of  a  yielding  or  quicksand  nature,  the  method  of  spread 
foundations  must  be  used  with  great  caution.  Even  assuming 
that  there  is  never  any  question  as  to  the  possible  outflow  of 


FOUNDATIONS.  343 

such  unstable  material,  as  might  result  from  relief  caused  by 
future  building  operations,  the  possibility  and  indeed  probability 
of  unequal  settlement  would  require  the  use  of  piles  unless  the 
importance  of  the  work  would  warrant  the  still  greater  expense 
and  security  of  pneumatic  foundations.  Grillage  foundations 
have  been  used  for  several  very  high  buildings  in  lower  New 
York,  notably  in  the  St.  Paul  Building  before  referred  to,  but 
in  all  such  cases  the  character  of  the  ground  has  been  found 
to  be  very  uniform  and  stable.  By  far  the  larger  number  of 
New  York's  important  structures  are  founded  either  on  piles, 
or  on  caissons  to  bed-rock. 

' '  The  first  method  that  naturally  comes  to  mind  for  pro- 
viding a  better  foundation  than  can  be  done  by  simply  spread- 
ing the  bearings  on  the  earth  at  customary  depths,  is  that  of 
driving  piles;  and  where  there  is  reasonable  certainty  that 
these  will  always  remain  wholly  submerged,  this  is  generally  the 
best  possible  foundation,  considering  its  cost,  for  buildings  of 
considerable  but  not  of  the  greatest  weight. ' '  *  But  unless 
the  driving  of  piles  can  be  accomplished  without  injury  to 
adjacent  buildings,  and  without  question  as  to  the  permanency 
of  the  piles  themselves,  the  use  of  piling  in  preference  to  gril- 
lage may  be  very  questionable.  Their  use  will  avoid  danger 
through  possible  excavations  in  adjoining  lots,  and  greater 
loads  may  generally  be  carried  over  a  given  area;  but  great 
care  is  necessary  to  see  that  the  piles  are  not  badly  injured  in 
driving,  and  that  the  upper  portions  are  never  exposed  to 
alternate  wet  and  dry  conditions. 

Test  Loads  on  Piling. — The  most  satisfactory  bearing 
values  for  piles  can  be  obtained  through  the  use  of  test  loads 
as  described  in  connection  with  the  Chicago  Public  Library 
under  the  previous  paragraph  "  Test  loads. "  Patton  states 
that  experience  and  experiment  are  of  most  value  in  determin- 


See  Charles  Sooysmith  in  Trans.  Am.  Soc.  C.  E.,  vol.  xxxv. 


344  ARCHITECTURAL  ENGINEERING. 

ing  the  bearing-power  of  piles,  and  even  with  experience, 
experiment  is  much  the  safer  rule  for  any  other  than  very  well- 
known  conditions. 

Test  loads  for  piling  may  be  obtained  by  driving  a  cluster 
of  piles  at  the  required  site,  as  nearly  under  the  actual  condi- 
tions to  be  fulfilled  in  the  completed  structure  as  may  be 
possible.  They  are  loaded  as  for  the  Chicago  Public  Library 
test,  and  settlements  noted.  For  working  values,  a  factor  of 
safety  of  from  2  to  4  is  used,  depending  upon  the  thoroughness 
of  the  test,  the  number  of  tests,  and  the  character  of  the  build- 
ing. If  not  driven  closer  than  30  ins.  centres,  a  cluster  of 
piles  will  usually  bear  a  greater  load  than  the  summation  of 
the  loads  determined  for  individual  piles.  This  is  due  to  the 
consolidation  of  the  soil  around  each  pile,  thus  giving  more 
and  more  resistance  to  the  remaining  piles  as  driven.  This 
increase,  however,  in  the  sustaining  power  due  to  compacting 
the  earth  is  limited  in  extreme  cases,  as  will  be  pointed  out 
under  the  heading  on  pile  formulae. 

Test  loads  should  not  be  applied  to  piles  until  twenty-four 
hours  or  more  after  they  are  driven,  in  order  to  permit  the  filling 
in  or  compacting  of  the  soil  around  the  shaft. 

Formulae  for  Bearing-power  of  Piles. — When  not  specified 
by  building  law,  or  fixed  by  test  loads,  the  safe  bearing  values 
of  piles  must  be  determined  by  formulae.  Of  these,  a  great 
number  has  been  devised  by  different  authorities,  and  Mr.  J. 
Foster  Crowell  *  shows  that  "  fourteen  different  values  for  the 
extreme  sustaining  power  of  the  same  pile,  driven  under  pre- 
cisely similar  conditions,  range,  in  a  typical  case,  all  the  way 
from  96,000  to  600,000  Ibs." 

A  great  deal  has  been  written  concerning  pile-driving  and 
pile  formulae,  and  for  extended  information  on  these  subjects 


*  See  "  Uniform   Practice  in  Pile-driving,"  J.   Foster  Crowell,   Trans. 
Am.  Soc.  C.  E.,  vol.  xxvii. 


FOUND  A  TIONS,  345 

reference  may  be  made  to  Prof.  Baker's  "  Treatise  on  Masonry 
Construction,"  Patton's  "Practical  Treatise  on  Foundations," 
the  paper  by  Mr.  Crowell,  before  referred  to,  and  other  articles 
and  books  on  the  same  subject.  Two  formulae  only  will  here 
be  given,  as  constituting  about  the  most  satisfactory  ones  which 
have  yet  been  employed. 

The  formula  originally  proposed  by  Mr.  A.  M.  Welling- 
ton, and  since  called  the  "Engineering  News"  formula,  is 
considered  by  many  as  more  reliable  and  decidedly  more  con- 
venient than  most  others  of  any  extended  use.  This  is  of  the 
form 

fwh 
-,  +  ,' 

where  P  =  safe  bearing  resistance  of  pile ; 

f  •=.  factor,  varying  from  12  to  I,  and  recommended  to 

be  taken  at  2 ,  thus  giving  a  factor  of  safety  of  6 ; 
w  =  weight  of  the  hammer,  in  pounds; 
h  =  height  of  hammer  fall,  in  feet; 
s  =  penetration,    in    inches,    under   the    last  blow   of 

hammer ; 
c  =  constant  to  provide  for  the  increased  resistance  to 

moving  at  moment  of  impact,  taken  equal  to  I . 

The  following  table  gives  the  safe  loads  in  tons,  according 
to  the  above  formula,  for  piles  driven  with  a  i-ton  hammer. 
For  a  hammer  of  different  weight,  multiply  the  safe  load  given 
in  table  by  the  weight  of  the  hammer  in  tons. 

A  complete  discussion  as  to  the  merits  of  the  above  formula 
maybe  found  in  the  Engineering  News,  vol.  xxix.  No.  8,  and 
from  the  views  expressed  on  this  subject  by  many  well  qualified 
to  judge,  it  will  be  seen  that  the  varying  conditions  of  pile- 
driving,  including  the  great  range  of  material  to  be  penetrated, 
the  loss  of  energy  due  to  broomed  heads,  and  many  other 
conditions  of  a  practical  nature,  make  it  impossible  to  even 


346 


ARCHITECTURAL  ENGINEERING. 


approximately  fix  the  ultimate  bearing-power  of  piles  in  terms 
of  the  weight  and  fall  of  a  hammer,  and  the  attendant  penetra- 
tion. 


Last 
Penetra- 
tion of 
Pile,  in 

Height  of  Fall  of  Hammer,  in  Feet. 

0.25 

4.8 

6.4 

8.1 

9-7 

12.9 

16.1 

19.4 

22.5 

25-8 

29.1 

32.3 

O.5O 

4.0 

5-3 

6.7 

8.0 

10.7 

13-3 

16.1 

18.7 

21.3 

24.0 

26.6 

3V3 

•  75 

1-4 

4.6 

5-7 

6.9 

q.2 

II.  5 

13.8 

16.1 

18.4 

20.7 

23.0 

28.8 

34-5 

.00 

3.0 

4.0 

5-o 

6.0 

8.0 

IO.O 

12.  0 

14.0 

16.0 

iS.Oj  20.  o 

2<>.0 

30.0 

•  25 

$.6 

4-5 

5-4 

7-i 

8.9 

10.7 

12.5 

14-3 

16.1 

17.9 

22.  S 

26.7 

•  50 

3.2 

4.0 

4.8 

6.4 

8.0 

9.6 

II.  2 

12.8 

14.4 

16.0 

2O.  0 

24.0 

•  75 

3-6 

4-4 

5-8 

7-3 

8.8 

IO.2 

ii.  7 

I3-I 

14-6 

18.2 

21.9 

2.00 

3-3 

4.0 

5-3 

6-7 

8.0 

9-3 

10.7 

12.0 

13-3 

16.7 

20.  0 

2-50 

3.4 

4.6 

5-7 

6.9 

8.0 

Q.I 

10.3 

11.4 

14.3 

I7.I 

3-00 

3-0 

4.0 

5-o 

6.0 

7-0 

8.0 

9.0 

IO.O 

12.5 

15-0 

3-50 

3-6 

4-4 

5-3 

6.2 

7-i 

S.o 

8.9 

II.  I 

13-3 

4.00 

3-2 

4.0 

4.8 

5-6 

6.4 

7-2 

8.0 

IO.O 

12.  0 

5-00 

3-3 

4.0 

4-7 

5-3 

6.0 

6.7 

8.3 

IO.O 

8.6 

Prof.  Patton  *  states  that  "  after  a  period  of  rest  it  is  evident 
that  piles  support  their  loads  by  the  upward  pressure  at  the 
point  of  the  pile,  and  by  the  frictional  resistance  on  the  surface 
of  the  pile  in  contact  with  the  soil,"  and  he  therefore  considers 
that  both  the  best  and  simplest  way  of  determining  the  safe 
bearing-power  of  a  pile  is  in  terms  of  the  bearing-power  of  the 
point  and  the  frictional  resistance  against  the  surface  of  the 
pile,  or 

P  =  P  + A 

where  P  =  safe  bearing-power  of  pile ; 

/  =  safe  resistance  to  settling,  determined  by  the  bear- 
ing-power of  the  soil ; 
/=  factor  depending  upon  the  frictional  resistance  of 

the  soil  upon  the  surface  of  the  pile; 
s  =  number  of  square  feet  of  pile  surface  in  contact  with 
the  soil. 


1  See  "  A  Practical  Treatise  on  Foundations,"  p.  220. 


FOUNDATIONS.  347 

For  value  of/,  Prof.  Patton  gives  from  5,000  to  6,000  Ibs, 
per  sq.  ft.  for  safe  load  on  sand,  gravel,  and  clay,  while  in  silt 
the  value  would  be  o. 

For  values  of/,  take 

100  Ibs.  per  sq.  ft.  for  the  softest  semi-fluid  soils; 
200  Ibs.  per  sq.  ft.  for  compact  silt  and  clay; 
300  to  500  Ibs.  per  sq.  ft.  for  mixed  earths  with  con- 
siderable grit,  and 
400  to  600  Ibs.  per  sq.  ft.  for  compact  sand  or  sand  and  gravel. 

When  piles  are  driven  by  water-jet,  instead  of  by  hammer 
blows,  such  formulae  as  the  Engineering  News  form  could  not 
apply,  and  it  would  be  necessary  to  use  some  such  form  as 
Patton 's,  or  else  to  determine  the  bearing-power  by  test  loads. 
Prof.  Patton  recommends  the  use  of  his  formula,  as  above,  but 
supplemented  by  tests  where  possible. 

In  determining  the  resultant  bearing-power  of  a  large 
number  of  piles  driven  close  together,  Mr.  Sooysmith  has 
pointed  out  *  that  the  value  of  the  total  number  may  be  only 
the  safe  bearing-power  of  the  underlying  stratum  supporting 
the  pile-points.  For,  while  a  single  pile  or  a  few  piles  may 
rely  on  both  the  resistance  at  the  point  and  the  friction  upon 
the  sides,  many  piles  driven  closely  together  and  to  a  material 
at  all  yielding  may  be  considered  as  simply  replacing  com- 
pressible material  and  as  transferring  the  load  to  the  layer 
receiving  the  points.  The  bearing-power  of  the  foundation 
then  becomes  the  safe  bearing-power  of  the  stratum  below  the 
piles,  plus  the  frictional  resistance  of  the  side  walls  or  outer 
surfaces  of  the  site,  or  of  the  mass  filled  with  piles.  It  is, 
therefore,  quite  possible  to  overload  the  substratum  by  driving 
the  piles  too  close  together. 

*  See  Trans.  Am.  Soc.  C.  E.,  vol.  xxxv.  p.  464. 


348  ARCHITECTURAL  ENGINEERING. 

Specifications  for  Piles. — The  specifications  for  piles  and 
pile  platforms  in  the  Chicago  Post-office  and  Government 
Building  were  as  follows : 

Piles. — All  piles  are  to  be  of  the  same  kind  of  wood,  but 
may  be  of  any  one  of  the  following:  Hard,  yellow,  first-growth, 
untapped,  Southern  pine,  or  oak,  or  Norway  pine.  They  must 
be  not  less  than  10  ins.  diameter  at  the  small  end  and  not  less 
than  1 6  ins.  or  more  than  23  ins.  at  the  butt.  Each  pile  must 
be  sound  throughout,  of  natural  growth,  reasonably  straight 
and  true  along  its  entire  length,  properly  trimmed,  and  the 
small  ends  sawed  off  to  a  plane  normal  to  the  axis  of  the  pile. 

The  piles  are  to  be  driven  with  a  steam  hammer,  the 
machine  to  be  placed  in  the  trench  or  on  a  level  with  the 
general  excavation,  as  the  contractor  may  choose.  Should 
the  latter  method  be  adopted,  the  guides  must  be  lengthened 
to  reach  within  4  ft.  of  the  bottom  of  trench  or  pit,  and  if  a 
follower  is  used  the  head  of  the  pile  shall  be  properly  protected 
from  injury  by  a  suitable  iron  ring.  The  heads  of  all  piles 
must  be  sawed  off  accurately  on  a  horizontal  plane  true  to  the 
required  level.  All  piles  must  be  driven  until  they  reach  and 
fetch  up  hard  on  the  very  hard-pan  underlying  the  clay,  and 
the  pile  shall  not  sink  more  than  \  in.  for  the  last  six  blows  of 
a  2,ooo-lb.  steam  hammer  with  full  force.  All  piles  must  be 
of  sufficient  length  to  fulfil  the  above  conditions  whatever  the 
soil  may  be.  The  average  depth  of  hard-pan  is  assumed  to 
be  72  ft.  below  the  inside  sidewalk  grade,  and  is  to  be  taken 
as  a  basis  of  length  of  pile.  Should  any  portion  of  the  ground 
require  piles  exceeding  48  ft.  in  length  when  cut  off  to  the 
required  level  figured  on  the  drawings,  the  contractor  is  to 
receive  an  additional  amount  per  foot. 

Platform. — After  the  heads  of  the  piles  have  been  sawed 
off,  the  earth  around  them  is  to  be  thoroughly  tamped,  well 
rammed  and  smoothed  off  to  the  level  even  with  the  top  of  the 
piles.  The  piles  are  then  to  be  capped  by  white-oak  caps* 


FOUNDATIONS.  349 

14  X  14  ins.,  of  lengths  shown  on  the  drawings.  The  caps 
shall  be  fastened  to  the  pile-heads  by  means  of  i-in.  wrought- 
iron  drift-bolts  24  ins.  long,  one  in  each  end  of  each  cap- 
timber.  All  joints  and  ends  of  all  timbers  are  to  be  sawed 
square,  and  joints  properly  broken  so  that  no  two,  as  far  as 
practicable,  will  come  on  the  same  line,  and  all  butt-joints  are 
to  come  directly  over  centre  of  pile-heads  or  cross-caps.  The 
caps  are  to  project  over  the  outer  edge  of  the  top  of  the  outside 
pile.  On  top  of  these  cap-timbers  a  platform  will  be  laid  con- 
sisting of  white-oak  timbers  12  X  12  ins.,  closely  laid  in 
random  lengths,  no  timber  being  less  than  12  ft.  long.  The 
outside  timbers  of  each  platform  to  be  bolted  to  each  cap- 
timber  on  which  they  rest  with  one  i-in.  wrought-iron  drift- 
bolt  20  ins.  long. 

Water-level. — Wherever  piles  are  employed  for  founda- 
tions, it  is  obviously  of  the  utmost  importance  to  establish  the 
permanent  water-level,  in  order  that  the  piles  may  be  always 
below  this  line.  This  may  be  ascertained  by  means  of  test- 
pits,  dug  to  below  the  water-level,  in  which  the  water  is  per- 
mitted to  remain  for  as  long  a  time  as  may  be  allowed  by  the 
building  operations.  The  water-level  may  then  be  measured 
at  stated  intervals,  care  being  taken  to  prevent  any  unusual 
local  disturbances,  such  as  the  inflow  of  rain-water  or  water 
from  pipes,  springs,  or  sewers.  The  line  finally  determined 
on  should  be  low  enough  to  provide  for  some  reasonable 
lowering  of  the  observations. 

The  removal  of  a  building  in  New  York  City  which  had 
been  built  on  piles  driven  some  ten  or  twelve  years  previously, 
and  the  seriously  decayed  condition  of  the  piles  has  been  cited 
by  Mr.  Sooysmith  as  showing  the  danger  attending  the  use  of 
piles  when  not  driven  below  the  water-line.*  Mr.  Sooysmith 
further  adds  that,  owing  to  the  number  of  springs  and  driven 

*  See  Trans.  Am.  Soc.  C.  E.,  vol.  xxxv.  p.  465. 


35°  ARCHITECTURAL  ENGINEERING. 

wells  throughout  lower  New  York,  "the  water-level  at  any 
one  point  may  be  materially  lowered  at  any  time  by  pumping 
from  a  driven  well  in  the  vicinity  or  from  the  constant  drainage 
of  some  leaking  basement  or  other  excavation.  Thus  it  would 
seem  that  the  permanence  of  any  given  water-level  in  the  city 
can  rarely  be  relied  upon." 

Pile  Foundations  in  Chicago. — Pile  foundations  were  used 
in  Chicago  for  many  years  previous  to  the  introduction  of  the 
isolated  pier  method,  and  some  of  the  oldest  and  heaviest 
buildings  are  founded  on  them ;  notably  the  grain  elevators 
along  the  Chicago  River,  which,  in  spite  of  their  constantly 
varying  loads,  have  so  far  maintained  their  integrity,  though 
few  buildings  could  be  more  trying  on  any  type  of  foundations. 

Some  years  ago  the  use  ot  piles  in  Chicago  was  decried  in 
consequence  of  the  very  careless  methods  and  designs  used  in 
the  City  Hall  Building.  And  as  we  look  back  upon  the  results 
of  this  work,  it  is  hardly  surprising  that  piles  should  have  been 
viewed  with  suspicion  for  some  time  after  by  those,  at  least, 
who  looked  no  deeper  than  the  effect,  without  considering  the 
cause.  In  this  building  the  piles  were  driven  so  near  together 
that  when  a  new  one  was  driven  its  neighbor  was  raised  up. 
The  foundations  were  put  in  uniformly,  although  the  weight 
was  far  from  being  uniform  on  the  different  piers;  and  even  at 
the  time  the  floors  were  placed  a  variation  of  7^  ins.  had 
resulted  in  the  settlement. 

Another  example  of  poor  pile-driving  at  about  the  same 
time  was  the  foundations  for  the  Chicago  water-works  tower. 
The  surface  material  consisted  of  about  17  ft.  of  pure  lake- 
shore  sand,  and  during  the  later  blows  a  very  heavy  hammer 
was  needed  to  drive  a  pile  even  J  in.  by  measurement.  But 
the  specifications  as  to  depth  were  to  be  complied  with  rather 
than  any  regard  as  to  resistance,  and  the  piles  were  hammered 
and  rehammered  until  the  sand  was  pierced,  and  a  drop  of 
1 1  ins.  into  soft  material  was  suddenly  noticed. 


FOUNDATIONS.  351 

After  these  and  other  failures  the  stone  and  concrete  foun- 
dation was  used,  until  the  introduction  of  the  "raft  "  method, 
which  was  almost  universally  approved,  and  so  extensively 
used  that  the  pile  method  was  for  a  time  quite  dispensed  with. 
But  in  1889  Mr.  S.  S.  Beman  revived  the  use  of  piles  in  the 
Wisconsin  Central  Depot,  under  trying  circumstances.  The 
building  itself  is  only  eight  stories  high,  while  the  tower, 
carried  on  piles  at  20  tons  and  more  per  pile,  is  240  ft.  high. 
There  has  been  no  appreciable  unequal  settlement. 

Another  firm  advocate  of  the  pile  foundation  was  Mr.  Felix 
Adler  of  the  firm  of  Adler  &  Sullivan.  The  Schiller  Theatre 
Building,  by  these  architects,  was  built  on  piles,  "as  the 
enormous  concentrations  of  loads,  next  to  adjacent  walls,  made 
it  seem  almost  impossible  to  use  iron  and  concrete  foundations 
without  an  expense  almost  prohibitive."  It  was  therefore 
decided  to  use  piles,  driven  50  ft.  below  datum,  loaded  at  55 
tons  per  pile,  and  cut  off  at  datum,  with  oak  grillage  on  top 
and  a  solid  bed  of  concrete  spread  over  the  entire  area. 

The  work  in  question,  however,  was  not  at  all  successful 
as  regards  the  adjacent  property,  and,  indeed,  such  damage 
was  done  by  the  pile-driving  that  suit  was  instituted  against 
the  owners  of  the  Schiller  Theatre  by  the  owners  of  the 
adjacent  Borden  Block,  as  a  result  of  damage  sustained.  A 
similar  suit  was  brought  against  the  proprietors  of  the  Stock 
Exchange  Building. 

Later  examples  of  the  use  of  pile  foundations  in  Chicago 
are  described  in  the  following  paragraph,  and  under  the  head- 
ing "  Combined  Grillage  and  Piling." 

Pile  Foundations  in  Chicago  Post-office  and  Government 
Building.* — The  new  Chicago  Post-office  and  Government 
Building  is  a  heavy  masonry  structure,  supported  on  pile  foun- 
dations carried  down  through  the  overlying  clay  generally 
found  in  that  locality,  to  the  hard-pan  which  lies  at  an  average 

*  See  Engineering  News,  vol.  xxxix.  No.  4. 


352 


ARCHITECTURAL   ENGINEERING. 


depth  of  about  72  ft.  below  the  street-grade.  The  borings 
made  at  this  site  were  previously  referred  to  under  the  heading 
"Test  Borings."  About  5,000  piles  were  used  in  all,  these 
being  driven  in  rows  for  the  exterior  walls,  and  in  clusters  of 
varying  size  for  the  independent  piers,  etc.,  distributed  over 
the  site.  They  were  spaced  about  3  ft.  to  3  ft.  6  ins.  centres, 
the  specifications  for  the  pile  material  being  as  given  in  a 
previous  paragraph. 

The  details  of  a  pier  are  shown  in  Fig.  183.     The  bottom 


FIG.  183. — Pile  Foundations  in  Chicago  Post-office, 
of  the  trench  is  about  28  ft.  below  the  street-level,  and  as  the 
piles  averaged  48  ft.  in  net  length,  this  made  about  76  ft.  from 
the  street-grade  to  foot  of  piles.  White-oak  capping,  14  x 
1 4  ins.,  was  placed  upon  the  pile-tops  after  the  heads  had  been 
cut  off  to  a  uniform  grade,  and  a  close  flooring  of  12-in.  by 
1 2 -in.  white-oak  timbers  was  then  laid  to  support  a  3-ft.  bed 
of  concrete.  Upon  this  concrete  the  masonry  piers  were  built 
up  to  the  required  grade,  the  material  being  limestone,  laid  in 
courses  about  12  ins.  thick. 

The  pile-driving  was  done  with  a  steam  pile-hammer 
weighing  4,400  Ibs.,  and  making  60  blows  per  minute. 

Pile  Foundations  in  Park  Row  Building.  —  The  total 
weight  of  this  building  was  estimated  at  65,200  tons,  56,200 
tons  being  for  the  weight  of  the  structure,  including  wind 


FOUNDATIONS. 


353 


pressure,  but  exclusive  of  steel  frame,  which  latter  portion  was 
estimated  at  9,000  tons.  The  area  covered  is  about  15,000 
sq.  ft.,  and  some  3,900  foundation  piles  were  used,  thus  giving 
about  1 6  tons  per  pile.* 

Test  borings  indicated  an  underlying  bed  of  uniform,  fine 
wet  sand,  extending  some  95  ft.  to  hard-pan  or  bed-rock,  and 
this  material  proved  so  firm  and  solid  that  but  few  of  the  piles 
could  be  driven  lower  than  15  or  20  ft.  The  piles  were  there- 
fore driven  until  the  last  blow  showed  a  refusal  of  I  in.  fall 
under  a  2,ooo-lb.  hammer  with  a  drop  of  20  ft. 

Under  the  various  piers  the  piles  were  driven  in  rows,  the 


FIG.  184.— Pile  Foundations  in  Park  Row  Building,  New  York, 
piles  being  18  ins.  centres,  in  rows  24  ins.  apart.  After  the 
tops  had  been  cut  off  below  the  permanent  water-level,  the 
heads  were  surrounded  to  a  depth  of  16  ins.  with  a  solid  mass 
of  concrete,  composed  of  I  part  sand,  2  parts  Portland  cement, 
and  5  parts  2|-in.  stone.  A  lo-in.  granite  capping  course  was 
then  laid,  upon  which  brick  piers  were  built,  loaded  to  1 5  tons 
per  sq.  ft.,  and  a  12-in.  granite  course  was  last  applied  to 
receive  the  grillage  beams.  (See  Fig.  184.) 

The  steel  grillage  beams  were  grouted  in  a  £-in.  bed  of 
Portland    cement    mortar,    and    where    irregularities    existed 

*  For    a    detailed    description    of    this    building,    see    the    Engineering 
Record,  vol.  xxxviii.  No.  7. 


354 


ARCHITECTURAL  ENGINEERING. 


between  the  beams  and  the  granite  capping  of  more  than  £  in., 
thin  flat  bars  of  steel,  bedded  in  grout,  were  employed  as 
packing. 

Where  two  or  more  columns  were  combined  as  one  pier, 
heavy  box  girders  were  used  to  distribute  the  loads. 

These  foundations  were  executed  with  considerable  diffi- 
culty, as  the  walls  and  foundations  of  the  adjoining  buildings 
were  not  suitable  to  resist  the  vibrations  caused  by  pile-driving. 
Underpinning  by  means  of  needle-beams  and  pipe  supports 
was  therefore  rendered  necessary  while  the  adjacent  foundations 
were  removed  and  replaced  by  new  brick  walls  and  footings, 
carried  down  somewhat  below  the  level  of  the  new  excavation. 
Combined  Grillage  and  Piling. — For  the  purpose  of  com- 
pressing the  clay  and  thereby 
permitting  a  greater  bearing 
unit  per  square  foot,  piles  have 
been  used  in  combination  with 
ordinary  grillage  foundations, 

Jl  .  /  •••  *  •  •  .*.-  •-.... vi ..  va.n.u)h  as  in  the  case  of  the  Fisher 
Buitding,  Chicago,  ,896.  In 
this  instance,  the  piles  were  dis- 
regarded as  to  direct  bearing 
capacity,  and  the  footings  were 
designed  as  purely  spread  foun- 
dations. 

On  account  of  there  being 
no  party-wall  contract,  and  also 
on  account  of  the  high  resultant 
pressures  per  square  foot  for 
ordinary  spread  footings  along 
the  party-line,  Mr.  Shankland 
decided  to  drive  short  piles  into 


FIG.  185. — Pile  Foundation  in 
Fisher  Building,  Chicago. 


the  clay,  thereby  compressing  the  material  and  making  it  of  the 
same  condition  before  the  building  was  commenced  as  ordinarily 


FOUNDATIONS. 


355 


obtains  after  the  erection  of  a  heavy  building  upon  it.* 
Twenty-five-foot  piles  were  therefore  driven  about  3  ft.  cen- 
tres under  the  footings,  and  it  required  from  four  to  eight  blows 
of  a  2,50O-lb.  hammer,  falling  20  to  24  ft.,  to  drive  the  piles 
the  last  foot.  It  was  therefore  considered  perfectly  safe  to 
load  the  piles  to  25  tons  each,  or  rather,  as  the  piles  were 
practically  disregarded,  to  load  the  9  sq.  ft.  of  clay  around 
each  pile  to  nearly  6,000  Ibs.  per  sq.  ft.,  or  almost  double  the 
usual  allowance.  A  single  column-footing  for  this  building  is 
shown  in  Fig.  185. 

Another  very  interesting  combination  foundation  by  the 
same  designer  was  utilized  for  an  office  building  40  ft.  wide 
and  165  ft.  long,  where,  owing  to  the  absence  of  party-wall 
contracts,  the  footings  were  required  to  be  entirely  within  the 
lot-lines,  and  shoring  or  underpinning  would  have  been  costly 
and  dangerous.  It  was  therefore  decided  to  drive  piles  in  the 
central  portion  of  the  lot,  while  preserving  a  minimum  distance 
of  6  ft.  from  either  side  wall,  as  in  Fig.  186.  Plate  girders, 


FIG.  186. — Combination  Grillage  and  Piling. 

spanning  the  entire  lot  width,  were  then  placed  over  each  row 
of  piles,  upon  which  girders  the  cross-beams  and  column-shoes 


*  See   E.    C.   Shankland  in   Minutes  of   Proceedings  Inst.   C.    E.,  vol. 
cxxviii.  p.  20. 


356  ARCHITECTURAL  ENGINEERING. 

rested.  Concrete  was  used  to  cover  the  pile-tops,  and  to  sur- 
round the  metal-work  as  shown  in  the  illustration. 

Use  of  Piles :  Building  Laws. — The  laws  of  New  York 
specify  that  no  pile  shall  be  loaded  in  excess  of  20  tons.  The 
spacing  shall  be  not  less  than  20  ins.  nor  more  than  36  ins.  on 
centres,  while  the  size  must  be  not  less  than  5-in.  end  and 
lo-in.  butt  for  piles  20  ft.  or  less  in  length,  or  5-in.  end  and 
20-in.  butt  for  piles  more  than  20  ft.  in  length.  For  the  sus- 
taining power  of  piles,  Mr.  Wellington's  formula  is  specified. 
The  tops  of  all  piles  must  be  cut  off  below  the  lowest  water- 
line. 

The  Chicago  building  law  requires  that  piles  be  driven  to 
rock  or  hard-pan  bearing,  the  safe  load  to  be  according  to 
approved  formulae  for  pile-driving,  but  not  exceeding  25  tons 
per  pile.  A  capping  of  oak  grillage  is  specified,  the  extreme 
fibre  stress  not  to  exceed  1,200  Ibs.  per  sq.  in.,  the  top  of  such 
oak  grillage  to  be  at  least  I  ft.  below  city  datum  or  I  ft.  below 
the  bottom  of  any  adjacent  sewer  which  may  be  below  city 
datum. 

The  Boston  law  does  not  specify  any  unit  loads  for  piles, 
the  requirements  being  that  the  piles  shall  be  not  more  than 
3  ft.  apart  on  centres  in  the  direction  of  the  wall,  "and  the 
number,  diameter,  and  bearing  shall  be  sufficient  to  support 
the  superstructure  proposed. ' '  The  walls  of  buildings  over 
70  ft.  in  height  must  rest,  where  possible,  upon  at  least  three 
rows  of  piles,  all  to  be  capped  with  block-granite  levellers. 

Foundations  to  Bed-rock. — Foundations  to  bed-rock  have 
always  been  recognized  as  particularly  desirable  for  any  and 
all  forms  of  heavy  building  construction,  but  open  excavations 
(such  as  were  secured  before  the  introduction  of  modern 
methods)  become  impracticable  under  the  present  conditions 
obtaining  in  large  cities,  owing  to  the  safety  which  must  be 
accorded  adjacent  structures. 

The    greatly    increased    height    and    consequent    weight 


FOUND/1  TIONS.  357 

-developed  in  modern  buildings  have  required  a  corresponding 
extension  or  development  of  foundation  methods,  and  as  great 
security  and  absolute  integrity  have  been  demanded  of  the 
designer,  even  when  building  upon  soft  or  treacherous  soils, 
the  necessity  for  reaching  bed-rock  has  had  to  be  met,  and 
often  under  conditions  so  difficult  that  the  proceeding  would 
have  been  impossible  under  former  methods. 

When  bed-rock  is  to  be  found  at  no  great  depth,  there  can 
be  little  question  as  to  the  desirability  of  securing  rock  founda- 
tion for  any  structure  of  importance,  provided  the  cost  of  such 
foundation  be  not  disproportionately  large.  The  added  security 
would  warrant  a  reasonable  increase  in  cost,  and  this  added 
outlay  becomes  a  smaller  percentage  on  the  entire  work  as  the 
total  cost  and  importance  of  the  structure  is  increased. 

If  rock  bottom  is  at  great  depth,  and  the  soil  presents 
uniform  conditions  suitable  for  grillage  design,  there  can  be  no 
good  reason  for  incurring  the  increased  expense  of  caissons ; 
nor,  if  the  driving  of  piles  seems  expedient,  should  caissons  be 
preferred  at  largely  added  cost.  But  if  bed-rock  is  fairly 
accessible,  or  if  at  considerable  depth  and  overlaid  with  quick- 
sand or  soil  containing  water-bearing  strata,  recourse  must  be 
had  to  some  form  of  deep-foundation  design.  This  is  now 
accomplished  by  means  of  caissons,  of  which  two  types  have 
been  extensively  used — hydraulic  caissons  or  open  cylinders, 
and  pneumatic  caissons. 

Open  Cylinders  or  Hydraulic  Caissons. — Open  cylinders 
to  bed-rock  are  only  applicable  where  sand  or  earthy  soils  free 
from  bowlders  or  other  obstructions  are  to  be  penetrated,  and 
where  the  extensive  pumping  and  jetting  of  water  made  neces- 
sary by  this  process  will  not  cause  undermining  tendencies  in 
soft  or  unstable  soil  under  adjoining  buildings. 

This  method  consists  of  sinking  steel  or  wood  cylinders, 
either  circular  or  rectangular  in  cross-section,  from  the  surface 
to  the  rock  bottom.  The  cylinders  are  usually  made  of  f-in. 


358 


ARCHITECTURAL   ENGINEERING. 


i     " — •  * — *  •     ^ 

Hm 


steel  plates,  in  sections  about  3  ft.  long  and  from  6  to  10  ft, 
in  diameter,  according  to  the  bearing  area  required  in  the  pier. 
For  moderate  depths  the  cylinders  are  often  delivered  at  the 
site  completely  riveted  up,  but  for  any  great  depths  the  sec- 
tions are  field  riveted  as  fast  as  the  shell  is  sunk.  The  connec- 
tions between  the  several  sections  are  made  by  means  of 
lap-joints,  with  f  in.  field  rivets,  pitched  about  5  ins.  Wooden 
cylinders  are  also  employed,  as  in  the  new  Stock  Exchange 
Building  in  New  York. 

.     The  bottom  edge  of  the  cylinder  is  fitted  with  a  cast-iron 
nrrnj]  or  steel   cutting-edge,    which    is 

provided    with     nozzle     attach- 
/Tr—i  J— -t\  ments,  so  that  water-jets  at  about 

/  \  100  Ibs.  pressure  may  be  delivered 

through  orifices  in  the  cutting- 
edge.  The  first  section  is  started 
in  a  pit  dug  to  the  water-line, 
and  then  by  loading  the  tops  of 
the  cylinder,  and  by  starting  the 
water  pressure  through  the  cut- 
ting-edge, the  earth  is  scoured 
out  below  the  shell  and  so  softened 
that  the  applied  load  gradually 
sinks  the  cylinder  through  the 
soft  material  to  a  rock  bearing, 
but  still  leaves  a  vertical  earth 
core  within.  The  cylinder  is 
then  excavated,  and  either  filled 
with  concrete,  or  a  bed  of  Con- 
crete some  4  or  6  ft.  thick  is  placed 
at  the  bottom,  upon  which  brick  piers  are  started  of  the  full 
size  and  height  of  the  pier.  Grillage  beams  are  then  applied 
to  receive  the  column-stands,  as  illustrated  in  Fig.  187. 

Pneumatic  Caissons,  Use  of. — This  method  of  securing 


FIG.  187. — Open  Cylinder 
Foundation. 


FOUNDATIONS.  359 

deep  foundations  in  water,  quicksand,  or  unstable  soils,  has 
been  very  extensively  developed  in  bridge  building,  and  by  far 
the  larger  number  of  masonry  piers  for  important  railroad 
bridges  has  been  founded  on  caissons  driven  to  bed-rock  or 
hard-pan  by  the  pneumatic  process.  In  general  principles  and 
even  in  details  the  pneumatic  caissons  employed  in  building 
construction  differ  but  slightly  from  those  used  in  bridge  work, 
and  for  extended  information  on  this  subject  reference  may  be 
made  to  Prof.  Baker's  "Treatise  on  Masonry  Construction, " 
to  Prof.  Patton's  work  on  "Foundations,"  or  to  any  of  the 
detailed  reports  submitted  or  published  by  the  chief  engineers 
of  prominent  bridge  work. 

Pneumatic  caissons  have  been  and  are  now  being  employed 
in  many  of  the  most  important  high  buildings,  especially  in 
New  York  City.  The  process  has  been  found  most  reliable 
under  the  severest  conditions.  The  advantages  secured  by  this 
process  are,  first:  excavations  maybe  carried  on  under  a  suffi- 
cient air  pressure  to  insure  the  holding  back  of  any  inflowing 
outside  and  unstable  material ;  second,  obstructions  encoun- 
tered in  sinking  the  piers,  such  as  logs  or  bowlders,  may  be 
removed;  third,  the  rock  bottom  may  be  examined  and,  if 
necessary,  levelled  off  or  stepped  to  secure  a  firm  bearing; 
fourth,  the  piers  can  be  built  while  the  caissons  are  being  sunk, 
so  that  the  piers  are  completed  as  soon  as  the  bed-rock  is 
reached. 

Regarding  the  proportional  cost  of  this  type  of  foundations, 
Mr.  Charles  Sooysmith  states  as  follows :  *  "  The  pneumatic 
process  is  the  one  safe  and  sure  method  for  deep  excavations 
by  which  all  dangers  of  quicksand  or  other  difficulties  can, 
with  certainty,  be  quickly  overcome  and  a  perfect  foundation 
constructed ;  and  this,  too,  at  a  cost,  where  the  conditions  are 
determined,  which  can  generally  be  estimated  with  compara- 

*  See   ''  Concerning   Foundations   for    Heavy  Buildings    in    New   York 
City,"  Trans.  Am.  Soc.  C.  E.,  vol.  xxxv.  p.  468. 


360  ARCHITECTURAL  ENGINEERING. 

tive  certainty."  .  .  .  "  It  is  probable  that  a  sum  not  exceeding 
3  or  4  per  cent,  of  the  cost  of  the  entire  building,  added  to 
what  the  cheapest  possible  shallow  foundation  would  cost  for 
one  of  the  very  high  buildings,  would  cover  the  extra  cost  of 
carrying  its  foundations  to  the  solid  rock,  when  this  is  within 
70  or  80  ft.  of  the  surface.  In  many  cases  this  extra  cost  would 
be  more  than  offset  by  the  value  of  the  additional  story  or 
stories  that  could  be  provided  beneath  the  surface." 

Pneumatic  Caissons,  Design  of. — A  pneumatic  caisson 
consists  of  a  circular  or  rectangular  box  of  wood  or  steel,  with 
flat  top  and  vertical  sides,  but  open  at  the  bottom.  A  cross- 
section  of  an  ordinary  form  is  shown  in  Fig.  188.  The  top  or 
roof  is  sometimes  constructed  of  solid  layers  or  courses  of 
timbers,  and  sometimes  by  alternate  courses  with  spaces 
between  the  timbers.  In  the  latter  form,  the  voids  are  filled 
with  concrete.  The  side  walls  are  usually  made  solid,  of  about 
12-in.  by  12-in.  timbers,  while  the  lower  edges  or  "cutting- 
edges  ' '  are  provided  with  a  steel  plate  or  shoe  of  some  form 
to  act  as  a  cutting-  or  penetrating-edge  into  the  underlying 
material.  The  whole  construction  is  designed  to  be  air-tight. 

The  interior  or  working  chamber  is  connected  with  the 
exterior  by  means  of  "air-shafts,"  which  consist  of  vertical 
circular  shafts  extending  through  the  roof  and  up  through  the 
pier,  these  being  extended  by  means  of  successive  sections,  as 
the  chamber  descends.  Two  or  more  of  these  shafts  are 
usually  provided  for  the  use  of  the  workmen  and  for  the  carry- 
ing of  the  earth  or  other  excavated  material  from  the  inside  to 
the  surface  for  carting  away. 

Each  air-shaft  is  provided  at  its  upper  end  with  an  ' '  air- 
lock," consisting  of  a  small  steel  chamber  which  has  two 
doors — one  connecting  with,  the  vertical  shaft  leading  to  the 
working-chamber,  and  the  other  connecting  to  the  outside  air. 
As  the  inside  chamber  is  filled  with  compressed  air,  the  two 
doors  to  the  air-lock  may  never  be  opened  at  the  same  time — 


FOUNDATIONS. 


361 


otherwise  the  compressed  air  would  escape,  and  the  working- 
chamber  would  quickly  fill  with  water,  if  below  the  water-line. 
For  the  passage  of  materials,  the  air-locks  are  operated  as 
quickly  as  possible,  both  to  save  time,  and  to  cause  the  least 
possible  escape  of  compressed  air;  but,  for  the  passage  ofwork- 


FIG.  188. — Section  through  Pneumatic  Caisson. 

men,  the  transition  from  one  atmosphere  to  the  other  must  be 
made  more  gradually,  in  order  that  injury  to  the  inmates  may 
not  be  caused  by  the  sudden  increase  or  diminution  of  pressure. 
Caissons  may  be  built  in  position  or  delivered  at  the  site 
ready  for  use,  according  to  the  size  and  facilities  for  handling. 
When  exactly  located  upon  the  surface  material  where  the  pier 


362  ARCHITECTURAL   ENGINEERING. 

is  to  be  sunk,  the  men  in  the  working-chamber  start  excavat- 
ing the  underlying  soil,  and  undermining  the  cutting-edges, 
so  that  the  caisson  gradually  sinks  under  the  superimposed 
load.  This  may  be  started  with  open  air-shafts,  but  as  soon 
as  the  water-level  is  reached,  and  water  becomes  troublesome 
in  the  working-chamber,  the  locks  must  be  closed  and  air 
pressure  turned  on  of  a  sufficient  pressure  to  keep  the  chamber 
free  from  water.  Compressed  air  is  furnished  by  means  of 
compressors  located  at  the  site.  The  excavated  material  is 
hoisted  to  the  surface  by  means  of  buckets  working  in  the 
material  shafts,  but  if  sand  or  fine  soil  is  encountered,  the 
material  is  discharged  at  the  surface  by  means  of  the  sand- 
pump,  which  consists  of  a  vertical  pipe,  open  at  the  surface, 
but  sealed  at  the  lower  end  by  means  of  a  puddle  of  water 
maintained  below  the  level  of  the  caisson  bed.  The  fine 
material  held  in  suspension  is  drawn  up  by  the  suction 
obtained  by  discharging  compressed  air  around  the  discharging 
nozzle  of  the  sand-pipe. 

Water-tight  coffer-dams  are  usually  extended  above  the 
roofs  of  the  caissons,  so  that  the  caissons  maybe  sunk  without 
necessarily  waiting  for  the  starting  of  the  masonry  piers.  Time 
will  be  saved,  however,  if  the  piers  are  built  while  the  caisson 
is  being  sunk,  and  the  added  weight  of  the  piers  is  often  valu- 
able in  causing  the  caisson  to  follow  the  excavation.  In  small 
caissons  with  vertical  sides,  such  as  are  often  employed  in 
building  work,  the  friction  of  the  sides  often  becomes  so  great 
that  a  temporary  loading  of  pig-iron  is  necessary,  even  in 
addition  to  the  masonry  pier,  in  order  to  sink  the  caisson 
against  the  friction  and  the  upward  pressure  of  the  compressed 
air. 

When  the  caisson  has  reached  the  required  level,  the  bed- 
rock is  levelled  or  stepped  off,  as  may  be  necessary,  the  surface 
is  carefully  cleaned,  and  the  working-chamber  and  air-shafts 
are  filled  with  concrete. 


FOUND  A  TIONS.  363 

Caissons  are  now  lighted  by  electricity  and  telephone  com- 
munication with  the  surface  is  sometimes  provided.  Bowlders 
.are  removed  by  blasting  with  dynamite. 

First  Use  of  Pneumatic  Caissons. — Pneumatic  caissons 
were  first  employed  in  building  construction  in  the  Manhattan 
Life  Insurance  Building,  New  York  City.  The  building  proper 
is  seventeen  stories  high,  with  a  tower  on  top  terminating  in 
a  dome.  The  main  roof  is  at  an  elevation  of  242  ft.  from  the 
sidewalk,  and  from  sidewalk  to  base  of  flagstaff  =  347  ft. 
6  ins. ,  and  from  base  of  foundations  to  top  of  dome  =  408  ft. 
This  makes  the  dome  61  ft.  higher  than  the  neighboring  spire 
of  "  Old  Trinity." 

The  area  of  the  lot  is,  approximately,  120  ft.  deep  X  67  ft. 
frontage,  or  8,000  sq.  ft.,  which,  with  the  estimated  total 
weight  of  the  building  of  some  30,000  tons,  would  give  a  load 
of  7,500  Ibs.  per  sq.  ft.  of  lot  area. 

The  natural  soil  at  the  site  consisted  of  mud  and  quicksand 
to  a  depth  of  some  54  ft.,  down  to  bed-rock.  Had  piles  been 
used,  as  close  together  as  the  New  York  building  law  allows, 
or  30  ins.  centre  to  centre  over  the  entire  area,  some  1,323 
piles  could  have  been  driven,  with  an  average  load  of  45,300 
Ibs.  each.  This  was  inadmissible,  as  the  building  law  limited 
the  load  per  pile  to  40,000  Ibs.  each,  when  driven  2  ft.  6  ins. 
centres. 

A  new  departure  in  foundations  was  therefore  necessary, 
especially  as  the  surrounding  buildings  were  built  on  the 
natural  earth,  making  them  particularly  liable  to  injury  in  case 
of  any  increase  of  pressure  on  the  soil  from  additional  loading, 
or  decrease  in  pressure  through  deep  excavations  or  trenches 
for  piles  or  concrete  piers  below  the  adjacent  footings. 

Pneumatic  caissons  were  thus  adopted,  and  this  was  the 
first  example  of  the  pneumatic  system  as  applied  to  buildings, 
although  the  same  architects  (Messrs.  Kimball  &  Thompson1* 
had  before  used  smaller  caissons  in  the  Fifth  Avenue  Theatre 


ARCHITECTURAL   ENGINEERING. 


T 


FIG.  189. — Plan  of  Caissons  in  Manhattan  Life  Insurance  Co.'s  Building, 
New  York. 


FOUNDATIONS. 


365 


Building  in  New  York  City,  but  without  the  use  of  compressed 
air. 

Fifteen  caissons,  varying  in  size  from  9  ft.  9  ins.  in  diameter 
to  25  ft.  square,  supported  the  thirty-four  cast-iron  columns. 
These  caissons  were  sunk  to  an  average  depth  of  about  3 1  ft. 
6  ins.  below  the  bottoms  of  the  excavations  at  the  site.  After 
the  caissons  were  sunk  to  bed-rock,  the  rock  surface  was  dressed 
and  stepped  as  required,  and  the  chambers  and  shafts  were 
then  rammed  with  concrete,  composed  of  I  part  Alsen  cement, 
2  parts  sand,  and  4  parts  broken  stone.  The  superimposed 
piers  were  biiilt  of  hard-burned  brick  laid  in  cement  mortar. 
About  eight  days  were  required  to  sink  each  caisson.  The 
locations  of  the  several  caissons  are  shown  in  Fig.  189. 

A  very  elaborate  system  of  cantilever  girders  was  used  to 
transfer  the  loads  on  the  columns  in  the  side  walls  to  proper 


FIG.  190.— Cross-section  of  Caissons  in  Manhattan  Life  Insurance  Co.'s 
Building,  New  York. 

concentric  bearings  over  the  caisson  piers.  From  these  bear- 
ings the  load  was  distributed  over  the  whole  masonry  work  by 
means  of  targe  steel  bolsters,  thus  diminishing  and  equalizing 
the  unit-pressure.  A  cross-section  of  the  caissons  and  canti- 
lever girders  is  shown  in  Fig.  190. 


366 


ARCHITECTURAL  ENGINEERING. 


Pneumatic  Caissons,  Gillender  Building. — This  building, 
shown  in  Fig.  28,  is  310  ft.  high  from  the  top  of  the  grillage 
beams  to  the  top  of  the  dome.  The  narrow  width  of  the 


DgG 


cj/vmive/t 


DSDJ 


OBI 


FIG.  191. — Plan  of  Caisson,  Gillender  Building. 

building  permitted  all  of  the  columns  to  be  located  within  the 
exterior  walls,  and  six  columns  were  placed  on  each  side,  as 
shown  by  the  framing  plan,  Fig.  60. 

The  foundation  material  consisted  of  fine  loose  wet  sand, 
and  it  was  found  that  it  would  be  impracticable  to  support  the 


FOUNDATIONS. 


367 


structure  on  any  form  of  grillage  or  spread  foundations,  even 
though  the  entire  site  area  (viz.  1,852  sq.  ft.),  were  covered, 
as  the  estimated  load  and  the  pressures  developed  by  wind 


f 

FIG.  192. — Detail  of  Caisson,  Gillender  Building. 

strains  would  exceed  the  permissible  bearing.  Pneumatic 
caissons  were  therefore  adopted,  covering  about  three-fifths  of 
the  area  of  the  site.  Each  caisson  supports  four  columns,  or 
two  on  either  side  of  the  building,  as  shown  in  Fig.  191. 


368 


ARCHITECTURAL   ENGINEERING. 


These  were  proportioned  to  distribute  the  loads  at  12  tons  per 
sq.  ft. 

The  general  details  of  the  caissons  are  shown  in  Fig.  192, 
while  Fig.  193  shows  a  large  section  through  a  side  wall  and 
cutting-edge. 


T! 

FIG.  193. — Detail  of  Caisson  Cutting-edge,  Gillender  Building. 

Permanent  coffer-dams  were  extended  above  the  tops  of  the 
caissons,  thus  forming  vertical  continuations  of  the  caisson  sides 
for  the  enclosure  of  the  brick  piers  which  were  started  upon 
the  decks  of  the  caisson  chambers.  These  brick  piers  were 
about  1 8  ft.  high.  The  total  depth  from  cellar  floor-line  to 
bottom  of  cutting-edges  was  about  42  ft. 

The  caissons,  as  in  Figs.  192  and  193,  were  built  of  yellow 
pine,  with  a  steel  plate  cutting-edge  as  shown.  The  timber 
used  was  planed  on  all  sides,  and  the  outside  planking  was 
placed  vertically  to  reduce  the  skin  friction.  The  actual  time 
required  for  sinking  was  seven  days  for  the  centre  caisson, 
15  ft.  X  24  ft.,  and  four  days  each  for  the  end  caissons,  12  ft. 
X  24  ft.  each. 

Over  the  brick  piers,  which  were  laid  in  Portland  cement 
mortar,  a  12-in.  layer  of  concrete  was  placed  to  receive  the 
grillage  beams  and  cantilever  girders.  These  were  first  painted,. 


FOUNDATIONS. 


369 


then  coated  with  coal-tar,  and  then  surrounded  by  a  solid  mass 
of  concrete,  the  minimum  thickness  of  which  was  12  ins.  The 
interior  spaces  of  the  box  girders  were  filled  with  Portland 
cement  grout,  to  guard  against  corrosion. 

Pneumatic  Caissons,  American  Surety  Building. — A 
framing  plan  of  this  building  is  shown  in  Fig.  61.  The  struc- 
ture is  about  85  ft.  square,  and  twenty-one  stories  high,  or 


FIG.  194. — Foundation  Piers,  American  Surety  Co.'s  Building,  New  York. 

290  ft.  from  sidewalk  curb  to  roof.  The  estimated  maximum 
weight  of  the  building  was  some  26,000  tons,  and  this  was 
transmitted  to  bed-rock  about  72  ft.  below  the  sidewalk-grade 
by  means  of  brick  piers  and  pneumatic  caissons.  Thirteen 
steel  caissons  were  employed,  with  a  total  distributing  area  of 
3' 5 75  scl-  ft-»  the  pressure  per  square  foot  thus  being  about 
14,500  Ibs.  All  of  the  caissons  were  rectangular,  the  largest 
being  1 1  ft.  by  42  ft.  in  area,  and  9  ft.  high,  supporting  four 


37°  ARCHITECTURAL  ENGINEERING. 

columns.  The  brick  piers  are  about  30  ft.  high,  with  steel 
grillage  beams  on  the  tops  for  the  support  of  the  column  bases. 
On  two  sides  of  the  building,  the  wall  columns  are  located 
very  near  the  building-line,  and  as  the  caissons  underneath 
these  columns  could  not  be  extended  up^n  tbi  adjacent 
property,  it  became  necessary  to  devise  means  tor  overcoming 
the  heavy  eccentric  loading  which  would  have  resulted  in 
applying  the  column  loads  direct  to  the  caissons  in  the  lines  of 
the  column  axes.  This  was  accomplished  by  connecting  inner 
and  outer  piers  by  means  of  heavy  box  girders,  which  rested 
on  grillage  beams  over  the  centres  of  the  piers  as  shown  in 
Fig.  194.  The  girders  projected  at  each  end  beyond  the 
grillage  supports,  the  outer  or  wall  ends  forming  cantilevers 
to  carry  the  wall  columns,  and  the  interior  overhanging  ends 
forming  anchorage  ends,  which,  by  anchoring  down  to  the 
brick  piers,  served,  with  the  interior  columns  applied  centrally 
over  the  inner  piers,  to  counterbalance  the  wall  column  loads. 
The  walls  were  carried  on  plate  girders  running  between  the 
cantilever  girders. 


CHAPTER   X. 
SPECIFICATIONS— INSPECTION. 

ADEQUATE  specifications  as  to  character  of  materials  and 
workmanship,  and  competent  inspection  to  provide  for  the 
enforcement  of  such  specifications,  are  quite  as  important  as 
intelligent  and  economical  design.  Much  thought  may  be 
expended  in  preparing  careful  plans  and  details  of  the  work, 
the  execution  of  which  may  largely  be  rendered  nugatory 
through  loosely  drawn  specifications  or  through  the  lack  of 
enforcement  of  carefully  specified  requirements. 

As  the  steel  frame  for  any  building  constitutes  by  far  the1 
most  important  portion  of  the  structure,  the  specifications  and 
provisions  for  the  inspection  of  this  part  of  the  building  should 
be  most  clearly  and  carefully  stated.  Specifications  in  suffi- 
cient detail  must  also  be  furnished  for  all  of  the  classes  of  work 
which  enter  into  the  building's  construction,  but  as  these  are 
more  architectural  than  engineering  in  character,  no  attempt 
will  be  made  here  to  cover  other  than  the  steelwork. 

It  may  be  noted,  however,  that  specifications  covering 
fireproof  floor-arches,  roofs,  partitions,  column  protections, 
etc.,  are  generally  totally  inadequate  in  comparison  to  the 
great  importance  of  these  features.  In  the  report  of  the  board 
of  engineers  who  examined  the  effects  of  fire  upon  the  Home 
buildings  in  Pittsburg,  it  was  recommended  that  the  insurance 
companies  undertake  the  preparation  of  standard  specifications 
governing  the  character,  construction,  and  methods  of  apply- 
ing all  fireproofing  materials,  and  requiring  all  owners  either 

37i 


37 2  ARCHITECTURAL  ENGINEERING. 

to  use  such  fireproofing  materials  subject  to  these  specifications 
and  careful  inspection,  or  else  to  be  subjected  to  higher  rates 
of  insurance, — in  other  words,  to  vary  the  cost  of  insurance 
according  to  the  character  of  the  fireproofing  used.  Such 
practice  would  certainly  lead  to  a  decided  improvement  in  our 
fireproofing  methods. 

For  specifications  regarding  masonry  walls,  piers,  etc., 
reference  may  be  made  to  Prof.  Baker's  "  Treatise  on  Masonry 
Construction,"  or  to  Kidder's  "Building  Construction  and 
Superintendence,"  vols.  i.  and  ii.  The  latter  treatise  also 
includes  much  information  concerning  such  specifications  as 
Carpentry,  Plastering,  Painting,  etc.,  etc.  For  more  extended 
data  regarding  fireproof  floors,  roofs,  column  casings,  and 
partitions,  besides  a  consideration  of  the  elements  of  general 
fireproof  design  and  equipment  for  fire  resistance,  see  "The 
pireproofing  of  Steel  Buildings, ' '  by  the  author. 

Specifications  for  Structural  Steel. — These  should  fully 
and  carefully  cover  all  of  the  requirements  of  the  architect  or 
engineer  in  regard  to  the  steel  framework  during  its  manufac- 
ture, fabrication,  and  erection — thus  embracing  the  questions 
of: 

1 .  Quality  of  material. 

2.  Shop- work  and  painting. 

3.  Inspection. 

4.  Erection. 

Some  of  the  points  requiring  especial  emphasis  under  these 
various  headings  will  be  considered  before  detailed  specifica- 
tions are  quoted. 

Quality  of  Material  should  include  requirements  cover- 
ing chemical  constituents,  physical  properties,  and  the  general 
finish  of  the  plain  material. 

Quality.  Chemical  Constituents. — The  desired  results 
should  be  clearly  specified,  rather  than  processes  or  details  of 
attaining  results;  and  it  will  generally  be  found,  for  any  ordi- 


SPECIFICATIONS-INSPECTION.  373 

nary  work,  that  commercial  grades  of  material  of  known 
uniformity,  in  ample  and  usual  sections  which  can  be  purchased 
of  several  different  makers  and  furnished  in  prompt  deliveries, 
are  generally  preferable  to  special  grades  of  material  or  special 
sections. 

The  fact  that  results  have  been  attained,  or  the  prevention 
of  serious  delays  if  they  have  not,  should  be  determined  by 
prompt  testing  and  inspection,  for  which  facilities  should  be 
definitely  specified. 

The  chemical  composition  of  the  steel  should  not  be  speci- 
fied, other  than  possibly  to  limit  the  quantity  of  deleterious 
constituents,  such  as  phosphorus,  sulphur,  manganese,  etc., 
while  all  other  elements,  except  carbon,  are  to  be  entirely 
absent  or  merely  traceable  in  quantity.  "  No  engineer  should, 
unless  he  be  an  expert  steel-maker,  attempt  to  specify  an 
exact  chemical  formula  and  a  corresponding  physical  require- 
ment; in  doing  so  he  would  probably  make  two  requirements 
Avhich  could  not  be  obtained  in  one  piece  of  steel,  and  so 
subject  himself  to  a  back-down  or  to  ridicule,  or  both.  On 
the  other  hand,  he  may  properly,  and  he  should,  fix  a  limit 
beyond  which  the  hurtful  elements  would  not  be  tolerated."* 

All  steel  should  be  specified  of  open-hearth  manufacture 
and  of  uniform  quality.  Rivets  to  be  of  "  soft  "  steel,  all  other 
steel  to  be  of  ' '  medium  ' '  grade,  as  specified  under  the  require- 
ments for  physical  tests.  Chemical  analyses  should  show  not 
more  than  the  following  quantities  of  phosphorus  and  sulphur : 

Phosphorus.  Sulphur. 

Acid  steel 08  per  cent.          .06  per  cent. 

Basic  steel 06        "  .05       " 

There  has  been  much  recent  discussion  about  these  limits, 
but  the  above  percentages  will  give  a  thoroughly  satisfactory 
material  which  will  still  come  easily  within  the  practice  of  a 

*See  "A  Manual  for  Steel-users,"  by  Wm.  Metcalf,  p.  157. 


374  ARCHITECTURAL  ENGINEERING. 

good  rolling-mill.  The  elements  mentioned  should  be  deter- 
mined by  chemical  analyses,  made  and  furnished  by  the  rolling- 
mill  and  checked  by  the  inspecting  engineer.  Analysis  should 
be  made  for  each  original  furnace  heat. 

Physical  Properties  should  cover  ultimate  tensile  strength, 
elastic  limit,  elongation,  and  reduction  in  area,  and  these  can 
best  be  specified  by  calling  for  certain  physical  tests  for  which 
the  manufacturer  should  be  required  to  prepare  test  specimens, 
and  to  furnish  the  use  of  testing-machines  and  the  necessary 
labor  for  making  tests,  without  additional  charge. 

For  steel,  specimens  should  be  cut  from  the  finished 
material  for  each  original  furnace  heat,  and  for  each  different 
section  of  material;  for  wrought-iron,  from  each  section  of 
material  and  for  every  certain  number  of  tons;  for  cast-iron, 
from  each  cupola  or  furnace  charge,  and  cut  from  or  attached 
to  the  castings  to  be  used,  or,  if  this  is  not  practicable,  they 
should  be  cast  separately  from  the  same  pour. 

Test  specimens,  where  possible,  should  be  of  sufficient 
length  to  permit  the  elongation  to  be  measured  in  8  ins. ,  but 
specimens  representing  pins,  small  special  castings,  etc.,  may 
be  slotted  out  and  turned  down  for  3  ins.  clear,  or  less,  and 
measured  for  elongation  in  2  ins., or  less,  and  their  required 
elongation  percentage  should  be  more  than  for  8  ins.  length. 
All  turned  specimens  should  have  easy  fillets.  Test  specimens 
with  sharp  fillets  will  often  fail  more  readily  at  less  tensile 
strength  than  specimens  with  easy  fillets. 

In  specifying  the  physical  requirements  for  ultimate 
strength  in  steel  where  two  or  more  grades  are  called  for,  as 
"  medium  "  and  "  soft  "  steel,  the  limits  for  ultimate  strength 
should  not  overlap,  otherwise  the  rolling-mills  are  very  apt  to 
attempt  the  furnishing  of  one  grade  for  both  requirements,  and 
thus  frequently  fail  to  get  good  results  within  the  narrow  limits. 
The  specifications  must  then  be  waived,  or  many  apparently 
unreasonable  condemnations  made.  It  is  better  to  allow 


SPECIFIC  A  TIONS— INSPECTION.  375 

liberal  limits,  and  to  hold  to  them.  Mr.  Waddell,  in  his 
treatise  "  De  Pontibus,"  recommends  ultimate  tensile  strengths 
per  square  inch  as  follows: 

Soft  steel 50,000  Ibs.  to  60,000  Ibs. 

Medium  steel 60,000  Ibs.  to  70,000  Ibs. 

High  steel 70,000  Ibs.  to  80,000  Ibs. 

It  will  be  noticed  that  none  of  these  limits  overlap. 

The  elastic  limit  is  usually  specified  to  equal  at  least  one- 
half  of  the  ultimate  strength,  the  elongation  not  less  than  24 
per  cent,  or  25  per  cent,  in  8  ins.,  and  the  reduction  in  area 
not  less  than  about  40  per  cent. 

Bending  and  drifting  tests  are  confirmatory  of  tensile  tests, 
and  if  specified,  should  be  required  to  be  made.  Not  one 
inspector  in  ten  does  make  them.  Drifting  tests  are  best 
accomplished  by  punching  a  hole,  as  in  ordinary  riveted  work, 
and  increasing  the  size  with  a  drift-pin.  For  medium  steel 
the  diameter  should  be  increased  one-half  without  cracks  at 
periphery  of  hole  or  edge  of  piece. 

Forging,  annealing,  or  any  similar  treatment  of  test  speci- 
mens should  be  prohibited. 

General  Finish  of  Material. — Excellence  of  finish  in  the 
plain  material  before  fabrication  includes  surface  perfection,  or 
the  exclusion  of  defects  or  unsoundness  in  the  metal  or  of 
material  with  "wind,"  and  undue  variations  in  the  cross-sec- 
tion or  weight. 

For  variations  in  weight,  the  usual  clause  about  "  2£  per 
cent,  variation  from  required  weight  or  section  being  cause  for 
rejection"  is  adequate,  except  that  wide  plates  should  be 
shown  on  plans  by  thickness  on  the  edge  or  by  weight  per 
lineal  foot.  See  Standard  Specifications  of  Association  of 
American  Steel  Manufacturers  for  allowances  for  overweight 
of  wide  plates  rolled  to  gauge. 

Shop-work  can  best  be  controlled  by  placing  orders  with 


376  ARCHITECTURAL  ENGINEERING. 

shops  which  are  well  equipped  to  perform  the  class  of  work 
desired,  and  which  are  not  too  busy  with  other  contracts. 
There  is  much  difference  in  the  character  of  workmanship  due 
to  detail  shop  management.  Poor  shop-.work  can  be  dis- 
covered and  prevented  by  inspection. 

Several  points  worthy  of  especial  emphasis  in  shop-work 
or  shop-inspection  are  as  follows: 

Plans. — All  working  plans  or  details  made  by  the  shop 
should  be  required  to  bear  the  signature  of  approval  of  the 
engineer  or  architect  of  the  structure.  Said  engineer  or  archi- 
tect should  keep  an  original  approved  blue-print  on  file,  as 
tracings  may  be  changed. 

Punching. — The  diameter  of  die  should  not  exceed  the 
diameter  of  the  punch  by  more  than  T\  in. 

Assembling. — Material  should  be  straight  before  laying 
out,  and,  if  necessary,  straightened  after  punching.  Small 
shops  without  facilities  for  straightening  heavy  angles  and 
shapes  are  at  a  disadvantage  for  heavy  riveted  work,  as  such 
material  is  always  more  or  less  distorted  by  punching.  Mem- 
bers should  be  straight,  not  in  wind,  before  riveting,  and  a 
sufficient  number  of  temporary  holding-bolts  should  be  used. 

Reaming,  which  is  often  required  for  important  connections 
in  building  construction,  as  in  column  splices,  is  rarely  clearly 
specified. 

There  are  three  kinds  of  reaming  and  two  kinds  of  drilling, 
(i)  Reaming  may  be  a  removal  of  material  distressed  by 
punching,  when  specifications  should  provide  for  the  holes  to 
be  punched  of  less  diameter  than  the  finished  size  of  hole,  and 
reamed  to  full  size.  This  is  done  under  a  drill-press  on  indi- 
vidual pieces  of  material  and  does  not  necessarily  give  holes 
that  match  or  insure  good  riveting.  (2)  Reaming  may  be 
specified  as  "fairing"  the  holes,  and  is  done  by  a  portable 
reamer  at  assembling  when  the  various  pieces  of  a  member  are 
brought  together.  It  does  not  necessarily  remove  distressed 


SPECIFICATIONS -INSPECTION.  377 

material,  but  tends  to  improve  the  riveting,  and  this  is  gen- 
erally done  by  all  good  shops.  (3)  Reaming  may  be  speci- 
fied so  as  to  improve  both  material  and  riveting  by  means  of 
strict  specifications  regarding  the  considerably  smaller  size 
of  punched  holes  and  their  exact  matching,  or  by  requir- 
ing the  holes  to  be  reamed  at  assembling,  with  all  pieces  in 
position. 

The  drilling  of  pieces  separately  does  not  necessarily  im- 
prove the  riveting. 

Reaming  should  either  be  clearly  specified  or  not  specified 
at  all. 

Riveting  is-  generally  clearly  covered  in  standard  specifi- 
cations, but  the  calking  of  rivets  with  a  chisel,  or  by  squeezing 
the  heads  cold  with  a  smaller  die,  or  striking  them  on  the  sides 
with  the  machine  when  cold  should  be  unquestioned  cause  for 
condemnation.  These  last  two  methods  have  superseded  the 
clumsier  use  of  a  chisel,  and  are  apt  to  escape  an  inexperienced 
inspector. 

Painting-. — In  no  detail  of  manufacture  are  more  sins  com- 
mitted than  in  painting.  Rust  should  not  be  permitted ;  scale 
should  be  removed;  paint  should  be  well  brushed  on  under 
cover  when  temperature  is  above  freezing,  and  on  dry  surface ; 
paint  should  be  allowed  to  dry  between  coats  and  before  ship- 
ment, preferably  for  48  hours.  There  should  be  no  opportunity 
for  water  to  collect  or  to  start  rust  at  any  point.  Paint  should 
be  carefully  identified  as  the  brand  specified,  and  chemical 
analysis  can  be  made  with  advantage.  There  are  many  cases 
of  adulteration  or  substitution  of  paint;  i.e.,  a  substitute 
colored  with  aniline  instead  of  red  lead,  with  a  difference  of 
cost  of  about  $1.00  per  gallon;  a  similar  substitution  for 
graphite,  at  a  difference  in  cost  of  about  50  cents.  Linseed 
oil  is  rarely  used  as  specified,  and  many  of  the  substitutions  for 
and  adulterations  of  both  paints  and  oils  can  only  be  discovered 
by  analysis. 


378  ARCHITECTURAL  ENGINEERING. 

For  a  more  extended  discussion  as  to  paints  and  painting, 
see  Chapter  III,  pages  82  to  88,  inclusive. 

Erection. — It  is  desirable  to  have  .an  inspector  or  super- 
intendent at  the  building  site,  who  shall  be  capable  of  super- 
vising the  erection  in  all  its  details.  He  must  see  that  all 
pieces  are  erected  in  their  proper  places ;  that  riveted  or  bolted 
connections  are  made  as  specified  ;  that  the  painting  is  properly 
done;  that  floors  are  not  overloaded;  and,  generally,  that 
plans,  specifications,  and  good  practice  are  followed.  A  good 
man  will  also  greatly  assist  the  foreman  of  erection  in  securing 
the  correct  placing  of  pieces,  and  in  intelligently  directing  any 
necessary  changes  or  corrections. 

Specifications. — The  following  general  specifications  for 
structural  iron  and  steel  are  from  the  practice  of  Hildreth 
&  Co.,  Inspecting  and  Consulting  Engineers. 

Specifications  for  Structural  Iron  and  Steel. 

General — All  structural  iron  or  steel  shall  be  the  best 
of  its  kind,  both  as  regards  quality  of  material  and  manu- 
facture, and  shall  strictly  comply  with  plans  as  regards  dimen- 
sions. 

Deliveries  shall  be  made  in  the  order  required  for  con- 
struction, and  at  the  time  specified  in  the  contract,  If  shipment 
of  material  from  the  foundries  or  rolling-mills  or  finished  work 
from  the  shop  is  not  made  at  the  time  agreed  upon,  the  archi- 
tect may  purchase  materials  in  the  open  market  at  such  terms 
and  for  such  deliveries  as  in  his  opinion  shall  meet  the  require- 
ments of  construction,  and  the  cost  of  such  material  so  pur- 
chased shall  be  deducted  from  the  amount  due  under  the 
contract. 

Weights. — A  variation  of  two  and  one-half  per  cent.  (2^) 
for  steel  and  three  per  cent.  (3$)  for  cast-iron  from  the 


SPECIFICATIONS— INSPECTION.  379 

estimated  weights  will  be  allowed  in  the  finished  material. 
Any  individual  member  or  piece  of  material  which  weighs  less 
than  the  estimated  weight  and  this  allowance,  may  be  con- 
demned at  the  discretion  of  the  architect,  and  any  classification 
of  material  which  exceeds  the  estimated  total  weight  of  such 
class  by  more  than  the  variation  allowed  will  not  be  paid  for. 

CASTINGS. 

Quality. — All  castings  shall  be  of  tough  gray  iron,  free 
from  all  shrinkage-cracks,  blow-holes,  cold-shuts,  sand,  cinder, 
or  other  defects,  clean,  true  to  pattern,  and  neat  as  to  finish. 
Only  such  scrap  iron  as  may  be  approved  by  the  architect  or 
his  inspector  shall  be  mixed  with  the  metal  used  for  casting. 
Castings  shall  be  allowed  to  cool  slowly  in  the  sand  to  avoid 
shrinkage-strains. 

Tests. — Two  specimens,  each  I  in.  square,  shall  be  cast 
for  each  furnace  heat  as  runners  on  different  castings  or  from 
separate  parts  of  the  pour,  and  shall  be  capable  of  sustaining  a 
central  load  of  2,500  Ibs.  when  set  on  knife-edge  supports 
12  ins.  apart,  with  a  deflection  not  less  than  T3F  of  an  inch,  and 
when  turned  to  a  diameter  of  about  J  of  an  inch  for  a  distance 
of  4  ins.  shall  develop  a  tensile  strength  of  at  least  18,000  Ibs. 
per  square  inch.  A  blow  from  a  hammer  upon  the  rectangular 
edge  of  any  casting  shall  result  in  an  indentation  without  flaking 
the  metal.  Castings  shall  not  break  when  struck  with  a  sledge. 

Columns. — The  thickness  of  any  part  of  the  shell  shall 
not  vary  more  than  T\  in.  from  any  other  part,  nor  more  than 
^  in.  less  than  the  thickness  specified. 

Fillets. — Brackets  and  flanges  shall  be  boldly  filleted,  and 
in  no  case  with  fillets  of  less  than  £  in.  radius. 

STEEL. 

Quality. — All  steel  shall  be  uniform  in  quality,  and  manu- 
factured by  the  open-hearth  process.  Chemical  analyses  for 


380  ARCHITECTURAL   ENGINEERING. 

each  original  furnace  heat  shall  be  made  and  furnished  by  the 
rollling-mills  and  checked  by  the  inspectors. 

Steel  shall  not  contain  more  than  .08  per  cent,  of  phos- 
phorus, nor  .06  per  cent,  of  sulphur. 

Rivets  shall  be  "soft"  steel,  and  all  other  steel  shall  be 
of  "  medium  "  quality  as  specified  below. 

Tests. — Rolling-mills  rolling  the  steel  shall  furnish  two 
test  specimens  cut  from  finished  material  of  each  original  fur- 
nace heat,  to  identify  which  all  material  shall  be  marked  with 
the  number  of  the  original  furnace  heat  from  which  it  is  rolled, 
One  specimen  for  each  heat  shall  be  broken  by  tension  in  a 
testing-machine,  and  shall  show  in  pounds  per  square  inch  an 
ultimate  strength  of  from  60,000  to  68,000  Ibs.  for  "  medium  " 
steel  and  52,000  to  60,000  Ibs.  for  "soft"  steel;  an  elastic 
limit  of  at  least  one-half  the  ultimate  strength ;  and  an  elonga- 
tion in  8  ins.  of  at  least  25  per  cent.  If  the  first  specimen  fails 
to  fulfil  the  above  requirements,  four  other  specimens  may  be 
tested  at  the  discretion  of  the  inspector,  and  if  two  also  fail,  all 
material  rolled  from  such  furnace  heat  shall  be  condemned. 
The  second  specimen  shall  be  tested  by  bending  one  end  cold, 
and  the  other  end  shall  be  heated  cherry-red  and  quenched  in 
water  and  bent;  both  bends  shall  be  180°  flat  without  flaw. 

Finish. — Finished  material  shall  be  straight,  true  to  sec- 
tion, with  smooth  clean  surface,  and  free  from  cracks,  seams, 
buckles,  or  other  defects. 

Inspection. — The  rolling-mills  shall  furnish  all  test  speci- 
mens and  the  use  of  testing-machine,  together  with  all  labor 
necessary  for  handling  material  for  inspection,  without  charge. 
No  shipment  shall  be  made  without  at  least  two  days'  notice 
to  the  architect  or  his  inspector,  and  in  the  event  of  shipment 
from  mills  without  such  notice,  or  without  proper  facilities  for 
inspection,  the  cost  of  subsequent  inspection  at  the  shops  of 
material  so  shipped  shall  be  paid  by  the  rolling-mills,  if  so 
required  by  the  architect. 


SPECIFICATIONS— INSPECTION.  381 

WORKMANSHIP. 

General. — All  workmanship  shall  be  first-class  in  every 
particular,  and  in  accordance  with  the  best  modern  shop-prac- 
tice. 

Plans. — All  working  shop-plans  shall  conform  to  the  plans 
furnished  by  the  architect,  and  must  -bear  his  signature  of 
approval  before  work  commences.  Such  approval,  however, 
shall  not  relieve  the  shop  from  the  responsibility  of  correcting, 
without  charge,  any  errors  in  not  following  the  architect's 
plans,  or  errors  of  "  clearance  "  or  "  connections  "  which  can 
be  discovered  by  examination. 

At  least  two  sets  of  working  plans  and  two  copies  of  order 
lists  of  material  shall  be  furnished  the  architect. 

Foundry -work. — All  machined  surfaces  of  castings  shall 
be  accurate  and  smooth.  Columns  shall  be  of  exact  height, 
with  bearing  surfaces  at  right  angles  to  the  axis  of  the  column. 
Connection-holes  shall  be  accurately  spaced  and  drilled  to 
exact  position,  if  necessary  to  an  iron  template,  in  order  to 
provide  for  tight-fitting  turned  bolts.  The  depth  of  bracket- 
webs  shall  be  twice  the  horizontal  projection. 

Punching. — All  rivet-holes  shall  be  accurately  spaced  in  a 
true  line,  and  laid  out  by  template.  The  clearance  between 
die  and  punch  shall  not  exceed  -£%  in.  for  material  £  in.  thick, 
nor  -/%  in.  for  thicker  material.  Holes  shall  be  clean-cut  with- 
out cracks,  and  burrs  shall  be  removed  by  a  countersinking 
reamer. 

Built  girders  shall  have  rivet-holes  punched  £  in.  small,  and 
holes  shall  be  reamed  to  full  size  with  parts  in  position. 

Straightening. — The  material  for  all  built  members  shall 
be  straightened  after  punching. 

Assembling. — At  assembling,  and  before  riveting,  built 
members  shall  be  truly  straight  and  out  of  "wind,"  held  by 
a  sufficient  number  of  bolts  to  prevent  warping  or  bending 


382  ARCHITECTURAL   ENGINEERING. 

under  handling  and  riveting.  No  drifting  of  holes  shall  be  done 
under  any  circumstances  in  any  class  of  work,  but  failure  of 
holes  to  match  shall  be  corrected  by  new  material  or  by 
reaming,  at  the  discretion  of  the  architect  or  his  representative. 

Rivets,  shall  be  of  soft  steel  driven  by  machine  wherever 
practicable.  They  shall  completely  fill  the  holes  and  be  tight 
with  neat  cup-shaped  heads  concentric  with  the  holes  and  free 
from  cracks  at  edges.  Rivets  showing  evidences  of  burning 
will  be  rigidly  condemned.  In  removing  defective  rivets,  any 
injury  to  the  material  will  be  cause  for  condemnation  of  injured 
parts. 

Connections. — All  joints  shall  be  fully  spliced. 

All  framed  beams  shall  be  secured  in  position  by  angle- 
brackets  and  standard  connections. 

Connections  shall  be  made  by  rivets  or  turned  bolts  fitting 
tight,  as  shown  on  plans. 

Any  beam  or  girder  that  is  longer  or  more  than  £  in. 
shorter  than  required  for  its  special  place  shall  be  rejected. 
The  accurate  adjustment  of  the  lengths  of  framed  beams  shall 
be  made  by  reaming  connection-holes  and  setting  out  angle- 
brackets  at  their  ends  to  correct  length. 

Painting. — All  metal-work  shall  be  free  from  dust,  dirt, 
and  scale;  no  painting  shall  be  done  in  wet  or  freezing 
weather.  Except  for  cast-iron,  all  surfaces  in  contact  and  all 
places  inaccessible  at  erection  shall  be  painted  one  coat  of 
paint  at  assembling,  and  finished  members  shall  be  painted 
one  coat  before  shipment.  After  erection,  all  surfaces,  includ- 
ing cast-iron,  shall  be  painted  one  thorough  coat.  The  paint 

used  shall  be  the made  by ,  and 

it  shall  be  well  brushed  on  and  worked  over  the  entire  surface. 

Anchors. — All  beams  resting  on  walls  are  to  be  securely 
anchored  by  approved  T  anchors  built  into  the  wall. 

Inspection. — The  rolling  and  manufacture  of  iron-  and 
steel- work  will  be  inspected  at  foundries,  mills,  and  shops  by 


SPECIFICATIONS— INSPECTION.  383 

inspectors  appointed  by,  and  responsible  to,  the  architect.  The 
general  contractor  shall  include  an  amount  of  80  cents  per  net 
ton  of  iron-  and  steel-work  to  meet  the  cost  of  such  services, 
and  the  inspectors  shall  jointly  represent  the  architect  and  the 
general  contractor  at  the  places  of  manufacture,  and  shall 
report  the  progress  of  the  work,  and  otherwise  facilitate  the 
prompt  and  orderly  delivery  of  satisfactory  materials.  The 
inspection,  acceptance,  or  failure  to  inspect  shall  in  no  way 
relieve  the  general  contractor  or  the  foundries,  mills,  or  shops 
from  their  responsibility  to  furnish  satisfactory  materials  strictly 
in  accordance  with  the  contract,  plans,  and  specifications. 

Miscellaneous. — This  specification  is  intended  to  provide 
for  complete  work,  including  all  necessary  connections  and 
details  requisite  for  erection,  and  to  develop  the  full  strength 
of  the  structure.  Such  details  are  to  be  considered  as  specified, 
and  are  to  be  provided  by  the  contractor  without  additional 
charge. 

Apparent  discrepancies  in  plans  or  specifications  must  be 
referred  to  the  architect,  whose  decision  shall  be  final,  and 
work  done  without  such  decision  shall  be  at  the  contractor's 
risk. 

The  architect  reserves  the  right  to  reject  any  and  all 
materials  or  work  at  any  time  before  the  completion  of  build- 
ing, if  in  his  judgment  either  do  not  comply  with  the  terms  of 
these  specifications  and  good  practice,  and  his  decision  as  to 
the  true  intent  of  plans  and  specifications  shall  be  final. 

The  following  clauses,  applying  exclusively  to  building 
practice,  are  extracted  from  the  specifications  for  structural 
steelwork  used  by  Messrs.  Purdy  &  Henderson,  Consulting 
Engineers. 

Connections. — All  connections  of  beams  to  beams,  beams 
to  columns,  columns  to  columns,  and  other  important  connec- 
tions shall  be  riveted  wherever  the  character  of  the  connec- 


384  ARCHITECTURAL  ENGINEERING. 

tions  will  permit.  Where  rivets  cannot  be  used,  tight-fitting 
bolts  may  be  substituted. 

Character  of  Materials. — All  beams  and  channels  and 
all  the  column  material  shall  be  of  steel  as  hereinafter  specified. 
All  connecting  angles  and  plates  shall  be  of  steel.  All  rivets 
shall  be  of  steel.  Tie-rods,  bolts,  anchors,  and  lateral  ties 
shall  be  of  wrought-iron.  Bearing-plates  for  beams  in  masonry, 
except  as  specified,  bases  under  the  columns,  separators,  and 
filler-blocks  more  than  i£  ins.  thick,  shall  be  made  of  cast- 
iron. 

Beams. — In  general,  not  more  than  one-eighth  (£)  of  an 
inch  will  be  allowed  for  clearance  at  each  end  of  beams  con- 
necting to  beams,  and  one-fourth  (^)  of  an  inch  at  the  ends  of 
beams  connecting  to  columns.  In  all  cases  where  possible, 
the  connecting  angles  used  shall  be  of  the  same  size  as  those 
recognized  as  standard  by  the  Carnegie  Handbook,  and  having 
the  same  number  of  rivets.  Beams  and  girders  connecting  to 
columns  shall  have  eight  (8)  rivets  at  each  end,  four  (4)  in  the 
top  flange,  and  four  (4)  in  the  bottom  flange,  wherever  the 
details  of  the  columns  will  permit  of  that  number.  In  all  cases 
the  beams  must  extend  as  closely  as  possible  to  the  axis  of  the 
columns.  The  finished  floor-line  in  all  cases  will  be  3  ins. 
above  the  tops,  and  the  ceiling-line  i£  ins.  below  the  bottoms, 
of  the  12-in.  floor-beams.  The  height  and  position  of  the 
wall-beams  are  noted  on  the  sections.  Unless  otherwise  par- 
ticularly noted,  all  beams  or  other  long  pieces  of  iron  are 
indicated  to  their  approximate  lengths  by  a  single  line  on  the 
floor-plans. 

Columns. — Columns  shall  be  made,  in  general,  in  double 
lengths  reaching  through  two  floors  as  indicated  by  the  section 
sheet.  In  general,  columns  must  be  connected  to  columns  by 
splice-plates  on  the  side,  riveted  to  the  flanges  of  the  channels 
with  twelve  (12)  rivets  in  each  column.  These  plates  must  be 
£  in.  thick,  except  where  the  metal  of  the  columns  connected 


SPECIFICATIONS-INSPECTION.  385 

is  f  in.  thick  or  more,  in  which  case  the  splice-plates  must  be 
£  in.  thick.  Where  the  outside  measurement  of  one  column 
is  less  than  the  other  a  clearance  of  more  than  ^  in.  must  be 
taken  up  with  fillers  made  of  bars  3  ins.  X  ^8  "*•»  punched  the 
same  as  the  splice-plates.  All  columns  will  have  £  in.  cap- 
plates.  All  columns  shall  be  milled  at  each  end  to  a  smooth 
bearing-surface  at  right  angles  to  the  columns.  The  point  at 
which  the  change  in  section  is  made  is  in  general  18  ins.  above 
the  top  of  the  12 -in.  beams.  The  contractor  will  be  required 
to  furnish  the  architect  with  a  drawing  or  schedule  showing 
the  heights  at  which  he  desires  to  make  these  cuts,  showing 
the  length  of  each  column  and  the  relation  of  each  cut  to  the 
bottom  of  the  regular  floor-beams  of  the  floor  at  the  same  level, 
for  his  approval.  The  number  of  rivets  required  in  connec- 
tions supporting  beams  must  be  calculated  on  a  basis  of  a 
floor-load  of  ....  Ibs.  per  square  foot  of  floor,  or  on  the  basis 
of  the  full  capacity  of  the  beam  carrying  an  evenly  distributed 
load,  whichever  may  require  the  larger  number. 

Separators. — Separators  must  be  provided  for  all  double 
beams;  and  unless  measurements  given  make  it  impossible,  all 
separators  must  be  standard. 

Tie-rods. — Tie-rods  %  in.  in  diameter  must  be  provided  on 
all  floors,  and  £  in.  diameter  in  roof,  as  shown  on  plans. 
These  rods  must  be  made  with  two  nuts. 

Bolts  and  Rivets.  —  Rivets  must  be  calculated  for  shear  at 
not  more  than  9,000  Ibs.  per  square  inch  of  section.  All  rivets 
must  be  accurately  spaced,  and  drifting  that  will  be  liable  to 
injure  the  material  will  not  be  allowed.  Rivet-heads  must  be 
located  centrally  concentric  with  the  neck,  and  rivets  when 
driven  must  completely  fill  the  holes.  Wherever  possible  the 
rivets  must  be  machine-driven.  Rivets  must  be  used  in  all 
field  connections  where  riveting  is  possible,  and  such  work 
must  be  done  to  the  entire  satisfaction  of  the  superintendent  in 
charge.  Both  bolts  and  rivets  must  be  £  in.  in  diameter 


386  ARCHITECTURAL  ENGINEERING. 

throughout  the  building,  except  in  special  cases  where  it  is 
necessary  to  use  other  sizes. 

Bases. — Cast-iron  bases  must  be  provided  for  all  columns. 
These  bases  must  conform  to  the  accompanying  drawings,  and 
must  be  planed  smooth  on  top  and  to  the  dimensions  given  for 
height.  The  ribs  must  be  spaced  and  arranged  in  each  case 
so  that  the  entire  cross-section  of  the  column  shall  have  a 
direct  support  from  the  bottom  of  the  base.  The  holes  for  the 
bolts  connecting  the  columns  to  the  bases  must  be  drilled, 
after  the  bases  are  cast,  to  exact  measurements,  which  must  be 
obtained  when  the  columns  are  detailed.  These  bases  must 
be  set  by  the  contractor  to  exact  centre  and  to  exact  height, 
and  a  variation  in  height  of  over  y1^  in.  will  not  be  allowed. 
They  will  be  bedded  in  position  by  the  contractor  for  the 
masonry. 

Temporary  Bracing. —  If  for  any  reason  the  masonry  in  the 
exterior  wall  does  not  follow  closely  upon  the  erection  of  the 
ironwork,  the  contractor  must  put  temporary  timber  braces  in 
to  keep  the  construction  of  the  steelwork  plumb  until  the  walls 
are  in  place.  This  must  be  done  to  the  entire  satisfaction  of 
the  architects. 

Painting. — The  covered  surfaces,  surfaces  in  contact,  and 
surfaces  enclosed,  of  all  parts  of  riveted  members  must  receive 

one  good  coat  of paint,  after  the  pieces  are  punched 

and  before  they  are  assembled.  All  finished  members  must 
receive  one  complete  coat  of  paint  before  they  are  taken  from 
the  shop  or  exposed  to  the  weather.  All  surfaces  that  can  be 

reached  must  have  two  coats  of paint  after  erection. 

All  bolts  remaining  permanently  in  the  building  must  be  dipped 

in paint  before  being  placed  in  position.  All  paint 

must  be  done  on  dry  surfaces,  and  preferably  warm  ones.  All 
dirt  or  foreign  matter  of  any  kind  must  be  removed  from  the 
iron  before  painting.  All  scale  must  be  removed  from  finished 
members  before  painting  the  first  coat  in  the  shop.  All  rust 


SPECIFICATIONS— INSPECTION.  387 

that  has  accumulated  on  the  material  must  be  removed  before 

painting.  The  paint  used  must  be  the prepared  and 

mixed  by  the Company,  of ,  ,  and 

the  second  coat  must  have  an  entirely  different  color  from  the 
first  and  third  coats. 

Erection. — Use  of  iron  hammers  in  driving  and  bending 
iron  will  not  be  allowed  where  it  can  possibly  be  avoided. 
Wooden  mauls  must  be  used  wherever  their  use  is  possible, 
and  care  must  be  exercised  to  prevent  the  beams  and  columns 
from  falling  in  order  to  protect  the  metal  from  heavy  shocks. 

The  structural  iron  must  not  be  set  in  advance  of  the 
masonry  covering,  to  exceed  three  stories,  unless  specifically 
allowed  by  the  architects.  Especial  care  must  be  exercised 
to  keep  all  the  columns  plumb  and  in  proper  line  during  the 
erection. 

Inspection.* — The  use  of  steel  in  buildings  of  ten  or  more 
stories,  or  in  manufacturing  plants  where  the  floor-loads  are 
heavy  and  frequently  "  live  "  in  the  sense  of  causing  vibration, 
has  led  to  more  careful  specifications  as  to  the  quality  of 
material  and  character  of  workmanship,  to  assure  which  it  is 
the  practice  of  the  leading  engineers  or  architects  to  have  the 
structural  frame  inspected  and  tested  during  manufacture  at  the 
foundries,  rolling-mills,  and  shops.  This  work  is  generally 
performed  by  a  firm  of  engineers  who  make  a  specialty  of 
inspection,  and  who  have  a  number  of  trained  employees  per- 
manently located  at  the  principal  manufacturing  centres,  and 
who,  through  long  experience  and  working  for  a  number  of 
clients  at  the  same  time,  are  able  to  perform  such  inspection 
efficiently  and  economically. 

It  is  not  feasible  for  an  architect  to  attempt  a  similar  inspec- 

*  For  much  valuable  information  on  the  subjects  of  Mill,  Shop,  and 
Field  Inspection,  see  Chapter  XXI,  "Inspection  of  Materials  and  Work- 
manship,"  in  Waddell's  "  De  Pontibus." 


388  ARCHITECTURAL   ENGINEERING. 

tion  at  the  building  site,  because,  while  he  can  inspect  as  to  the 
workmanship,  he  can  form  no  opinion  as  to  the  quality  of 
material.  Further,  the  delays  and  cost  occasioned  by  errors 
which  have  to^be  corrected  at  the  building  are  such  as  to 
warrant  inspection  at  as  early  a  date  as  possible  in  order  to 
avoid  them.  It  is  also  not  feasible  for  an  architect  to  attempt 
inspection  at  the  mills  and  shops  himself  unless  he  is  prepared 
to  employ  several  men  or  else  have  the  inspection  incomplete 
and  perfunctory. 

The  cost  of  inspection  by  a  responsible  and  well-equipped 
firm  is  not  great,  and  will  run  from  60  cents  to  $1.00  per  net 
ton,  depending  upon  the  character  and  weight  of  the  various 
members.  Such  cost  is  properly  met  by  the  owner,  and  may 
be  either  provided  for  directly  or,  as  is  frequently  done,  by  a 
clause  in  the  specifications  about  as  follows: 

' '  The  structural  iron  and  steel  framework  shall  be  inspected 
and  tested  during  its  manufacture  at  foundries,  rolling-mills, 
and  shops  by  a  competent  firm  of  inspecting  engineers,  who 
shall  be  appointed  by  the  architect  and  be  responsible  solely 
to  him,  but  who  shall  also  represent  the  owner  and  the  con- 
tractor with  the  view  of  securing  the  prompt  and  orderly 
delivery  of  materials  in  accordance  with  the  contract  and  speci- 
fications. The  contractor  shall  include  in  his  bid  an  amount 
equivalent  to  eighty  cents  per  net  ton,  which  shall  be  paid 
monthly  for  such  services. ' ' 

It  is  a  mistake  to  sanction  cheap  terms  for  inspection.  If 
it  is  worth  doing  at  all  it  is  worth  doing  well,  and  it  is  better 
to  pay  a  fair  price  and  have  reliable  service  than  to  pay  less 
and  have  the  inspection  incomplete  and  slipshod. 

Well-performed  inspection  should  include  the  inspection  of 
all  castings  at  foundries  and  plates,  shapes,  etc.,  at  rolling- 
mills.  The  inspectors  should  personally  identify  the  test  speci- 
mens and  conduct  the  making  of  tests.  Each  piece  of  rolled 
material  should  be  examined  for  surface  defects,  straightness, 


SPECIFICATIONS— INSPECTION.  .  389 

and  section,  and  if  acceptable  should  be  marked  with  a  special 
brand — generally  a  die  on  a  stamping-hammer— and  sur- 
rounded by  a  circle  of  white  paint.  There  should  also  be 
resident  inspectors  located  at  the  manufacturing  shops  during 
the  entire  progress  of  the  work,  the  theory  being  that  the 
greatest  value  of  the  system  is  to  prevent  mistakes  and  facilitate 
the  work,  rather  than  merely  discover  errors  when  it  is  too  late 
to  accomplish  satisfactory  correction  without  important  delays. 
Without  going  into  too  great  detail,  shop  inspectors  should  see 
that  all  material  is  straight  before  and  after  punching;  that 
holes  are  reamed  where  required;  that  material  is  assembled 
correctly  before  riveting,  so  that  errors  in  not  following  plans 
may  be  easily  corrected ;  that  riveting  is  tight  and  of  neat 
appearance,  and  that  all  machine-work  is  accurate  and  work- 
manlike. Painting,  including  the  thorough  removal  of  scale 
and  freedom  from  rust,  should  receive  particular  attention. 
Paint  should  be  known  to  be  the  brand  specified,  and  can  be 
analyzed  with  advantage.  Any  good  paint  with  pure  oil 
properly  applied  will  prove  satisfactory,  but  there  are  many 
methods  of  adulteration  and  slighting  of  work  in  connection 
with  painting.  Shop  inspectors  should  make  a  final  inspection 
of  all  members  and  see  that  the  marking  is  clear  and  adequate, 
and  should  keep  record  of  the  actual  weights  for  comparison 
with  estimated  weights.  Reports  of  progress  of  work  should 
be  made  weekly,  and  a  final  report  on  completion  of  manufac- 
ture. 

With  such  inspection  under  intelligent  direction  much  can 
be  done  to  further  the  work,  not  only  in  preventing  and  intelli- 
gently correcting  errors,  but  in  securing  the  orderly  delivery 
of  work  as  required  at  the  building  site.  As  the  steel  frame  is 
generally  the  part  of  an  important  building  upon  which  all 
other  work  depends,  the  saving  of  a  few  days'  delay  represents 
a  saving  of  interest  charges  which  will  more  than  cover  the, 
cost  of  inspection. 


39°  ARCHITECTURAL  ENGINEERING. 

The  following  clauses  relating  to  inspection  should  be  dis- 
tinctly specified  in  addition  to  the  matter  previously  quoted  in 
the  forms  of  specifications  given : 

Inspection. — Manufacturers  should  give  notice  before  the 
commencement  of  rolling  or  casting,  and  reasonable  informa- 
tion thereafter;  they  should  give  opportunity  for  inspection  by 
daylight  during  the  regular  course  of  handling  of  material,  or 
by  special  handling,  and  all  material  should  be  turned  to  per- 
mit examination  on  all  sides. 

Identification. — Each  piece  of  material  should  be  branded 
with  the  number  of  the  original  furnace  heat,  except  in  the 
case  of  pieces  which  will  not  be  under  important  strain  in  the 
structure,  when  the  requirements  for  such  branding  may  be 
waived  by  the  inspector.  Material  from  stock  should  not  be 
used  to  meet  important  strains  in  members  in  the  structure 
unless  identified  as  above  and  tested,  or  the  quality  assured  by 
undoubted  records. 

Records. — Manufacturers  should  furnish  the  inspectors  with 
records  of  chemical  analyses  and  press  copies  of  shipping 
invoices.  All  records  or  books  giving  information  as  to  the 
quality  of  material  should  be  open  to  the  inspectors. 

Shipments  without  Inspection. — Shipments  made  without 
inspection  should  be  at  the  risk  of  the  shipper,  and  if  reason- 
able facilities  for  the  inspection  were  not  provided,  the  addi- 
tional cost  of  subsequent  inspection  should  be  borne  by  the 
shipper.  Any  material  found  to  be  defective  should  be  imme- 
diately replaced,  and  the  engineer  or  architect  may  properly 
reserve  the  privilege  of  purchasing  such  material  in  the  open 
market  at  the  expense  of  the  shipper.  To  those  who  have 
been  kept  waiting  for  material  for  weeks  while  an  interminable 
correspondence  was  carried  on,  and  finally  forced  to  accept 
unsatisfactory  material  rather  than  a  greater  evil  of  continued 
expensive  delay,  this  suggestion  should  appeal  strongly. 
Shops  usually  deal  with  one  or  two  mills  with  whom  they  have 


SPECIFICATIONS— INSPECTION.  391 

credit.     They,  therefore,  are  not  inclined  to  buy  in  the  open 
market. 

Relative  Value  of  Detailed  Inspection. — The  following 
table  *  will  serve  to  show  the  relative  values  of  the  details  of 
thorough  inspection  at  rolling-mills  and  shops,  as  taught  by 
experience : 

Percentage 
Mill  Inspection.  Values. 

(1)  Examination  of  rolling-mill  stock  and  supervision  of  methods. ...      3 

(2)  Identification  of  test  pieces  with  furnace  melt  and  material  from 

which  it  is  supposed  to  be  cut 8 

(3)  Tests  made  personally  by  inspectors,  including  not  only  tensile 

tests,  but  bending  and  drifting  tests  ;  record  of  latter  made  by 
outlining  on  back  of  tensile-test  blank 8 

(4)  Chemical  analyses  investigated  and  checked 2 

(5)  Surface  inspection  of  each  and  every  piece  of  material  with  iden- 

tification of  accepted  material  by  brand  and  complete  records 
of  accepted  and  rejected  material  with  description,  heat  num- 
bers and  weight 2O 

Shop  Inspection. 

(6)  Drawings  checked  for  clearance  and  compared  with  lists  of  ma- 

terial...        3 

(7)  Weights  estimated 3 

(8)  Shop-work  supervised  during  the  entire   progress,  including  re- 

inspection  of  material  and  detailed  inspection  of  all  portions  of 
the  work,  including  patterns  and  templates,  punching,  reaming, 
assembling,  riveting,  with  tests  of  rivets,  machine-work,  finish- 
ing, painting,  marking,  weighing,  loading,  and  shipment 25 

(9)  A  thorough  final   inspection  covering  all  important  dimensions, 

matching  of  field  connections,  clearances,  and  all  details  which 
will  affect  the  strength  or  the  ease  of  erection  of  the  structure.  10 

Inspection  from  Main  Office. 

(10)  Weekly  reports  showing  progress  of  work 5 

(n)  Final  report,  a  concise  summary  of  weekly  reports,  with  re- 
arrangement of  test  results  suitable  for  file,  being  a  demon- 
stration of  exhaustive  testing  and  thorough  inspection 10 

(12)  Personal  general  supervision  by  heads  of  inspecting  firm 3 


The  foregoing  branches  of  inspection  work  are  valuable  and 
necessary.     Items  6  and  7  can  properly  be  omitted  when  the 

*  From  Hildreth  &  Co.,  Inspecting  Engineers. 


39 2  ARCHITECTURAL  ENGINEERING. 

checking  of  drawings  and  estimating  of  weights  is  done  by  the 
architect  or  engineer.  Otherwise  no  modification  is  to  be 
recommended,  although  the  prices  of  inspection  could  possibly 
be  reduced  if  'it  were  considered  advisable  to  omit  any  of  the 
other  details. 

Cheap  and  poor  inspection  usually  omits  items  I,  2,  3  in 
part,  4,  5  in  whole  or  part,  6,  7,  8,  n,  and  12,  and  includes 
only  9  and  10  of  an  unreliable  character.  The  percentage 
value  of  such  cheap  and  poor  inspection  will  vary  from  10  to 
30  as  compared  to  the  value  of  good  work. 


INDEX. 


PAGE 

American  Surety  Co.'s  Building,  columns  in 197 

column-splices 222 

pneumatic  caissons  in 369 

shoring  of  foundations 297 

spandrels  in 175 

Anchorage  of  spandrels 171 

of  walls 161 

Anchors  for  terra-cotta 171 

specifications  for 382 

Ashland  Block,  spandrel  sections  in 168 

Atlantic  Building,  erection  of 78 

Base-plates  for  columns 227 

Bases  for  columns 230 

Bay  windows,  construction  of 179 

floors  and  ceilings  in 184 

Gillender  Building , 184 

Masonic  Temple 180 

Reliance  Building 182 

Beam-facings,  terra-cotta 96 

footings,  calculation  of  simple 325 

three    unequally   loaded   columns,   area 

rectangular 335 

two  equally  loaded  columns,  area  rect- 
angular  328 

two    unequally    loaded    columns,    area 

rectangular 329 

two   unequally   loaded   columns,    trape- 
zoidal area 331 

combined 327 

with  piling 354 

design  of 324 

393 


394  INDEX. 

MCE 

Beam-footings,  painting  of 341 

proportioning  areas  for    310 

stresses  in 341 

Beams.     See  Beam-footings. 
Floor-beams. 
Spandrel-beams. 

Bearing-power  of  foundation  materials 285 

building  laws 287 

Bolted  connections 68,  137,  140 

for  cast  columns 192 

Borings  for  foundation  tests 293 

Boston  Building  Laws,  bearing-power  of  soils 288> 

live-loads  on  floors 121 

masonry  walls 165 

pile-foundations 356 

Box  columns.     See  Plate  and  Angle  Columns. 

Brick,  fire-resisting  qualities  of 24,  150 

hollow 248 

Brick  arches 89 

Brickwork,  allowable  pressures  on ; 165 

Broadway  Chambers,  description  of 42 

erection  of  steelwork 63 

spandrels  in 178 

Building  Laws.     See  Boston  Building  Laws. 
Chicago  Building  Laws. 
New  York  Building  Laws. 
Philadelphia  Building  Laws. 

Cable  Building,  lintels  in .' 178 

Cage  construction,  definition  of 10 

rigidity  of 255 

Caissons,  open  or  hydraulic 357 

pneumatic.     See  Pneumatic  Caissons. 

Cast-iron  column-bases 230 

specifications  for 386 

plates 227 

columns,  connections  for 257 

eccentric  loading  of 212 

method  of  figuring 193 

tests  of 194 

types  of 192 

use  of 191 

specifications  for 379 

unreliability  of 4,  192 

Ceilings,  flat 102 

suspended 105,  108,  nc» 


INDEX.  395 

PAGB 

Cement,  preserving  qualities  of 80,  81,  159 

Chamber  of  Commerce  Building,  columns  in 209 

Champlain  Building,  floor  plan  of 63 

Channel  columns,  forms  of 196 

limitations  of 209 

See  also  Columns. 

Chicago  Athletic  Club  Building,  fire  in 15 

fireproofing  of 28 

Auditorium,  foundations  for 305 

test-wells  in 303 

Building  Laws,  bearing-power  of  soils 287 

fibre  stresses  for  foundation-beams 341 

fireproof  construction 14 

fireproofing  of  columns 248 

floor-arches in 

foundation-loads 309 

live-loads  on  floors 121 

pile-foundations 356 

protection  of  external  steelwork 160 

skeleton  construction 9 

stone  in  walls 165 

City  Hall,  foundations  for 350 

construction 149 

Library,  tests  on  pile-foundations 290,  343 

Post-office,  foundation  borings  for 294 

pile-foundations  in 351 

settlement  of 303 

specifications  for  piling 348 

Stock  Exchange,  data  about 34 

Water-works  tower,  foundations  for 350 

Clearance  for  floor-beams,  girders,  etc 142,  384 

Coffer-dams 362 

Columbian  floor 106 

Column-bases,  alignment  of 63 

method  of  calculating 228,  230 

types  of 227 

Columns,  cast-iron.     See  Cast-iron  Columns, 
channel.     See  Channel  Columns. 

choice  of 225 

cost  of 204 

design  of ,, 200,  204 

details  and  splices 241 

eccentric  loads  on 203,  210,  213 

erection  of 68 

fireproofing  of 27,28,  224,  245 

flexure  of 202 


396  INDEX. 

PAGE 

Columns,  forms  of 195 

formulae  used  in  calculating 201 

girder  connections  to 214 

Gray.     See  Gray  Columns. 

in  walls 156,  158 

Keystone.     See  Keystone  Octagonal  Columns. 
Larimer.     See  Larimer  Columns. 

loads  on 119,  234 

in  Fisher  Building 125,  236 

Fort  Dearborn  Building 124 

Marshall  Field  Building 122 

Old  Colony  Building 123, 

"The  Fair"  Building 3o5 

locations  of , 126 

Phoenix.     See  Phoenix  Columns. 

plate  and  angle.     See  Plate  and  Angle  Columns. 

proportioning  of  sizes 237 

protection  of  interiors  of. 161 

shopwork  and  workmanship 206 

specifications  for 384 

splices  for 217,  220,  258 

tabulation  of  loads  on 234 

two-story  lengths 240,  258 

unit  stresses  for 23$ 

Z-bar.     See  Z-bar  Columns. 

Column-sheets,  for  Fisher  Building 237 

Masonic  Temple 235 

Venetian  Building 235 

recommended  form  for 236 

use  of ,. 234 

Combination  end-  and  side-construction  terra-cotta  arches 100 

Combined  footings.     See  Beam-footings. 

Commercial  Cable  Building,  traveller  used  on 56 

underpinning  of  foundations  in 299 

Composition  floors,  Metropolitan 109 

Concrete  floors,  Columbian 106 

Expanded  Metal  Co.'s 107 


forms  of. 


103 


Roebling IO4 

for  U.  S.   government  work 306 

foundations 305 

Congressional  Library,  foundation-loads  on 289 

Connections,  bolted  vs.  riveted 138 


for  cast  columns. 


192 

girders  and  columns 241 

specifications  for 382,  384 


INDEX,  397 

PAGH 

Connections,  standard,  for  beams 138,  139 

Coping  of  floor-beams 142 

Corrosion  of  steelwork 78,  80,  81,  159 

Corrugated-iron  arches 89 

Court  walls,  construction  of 178 

Dead-loads,  on  columns 234 

in  Fisher  Building 125,  236 

Marshall  Field  Building 122 

on  floors 122 

in  Fisher  Building 125 

Fort  Dearborn  Building 124 

Marshall  Field  Building 122 

Old  Colony  Building 122 

foundations 308 

Deflection  of  floor-beams 135 

Derricks,  used  in  erection 56 

Detailing  of  steelwork 140 

Deterioration  of  steelwork 78,  80,  81,  159 

Dun  Building,  columns  in 198,  218 

Earthquakes,  effects  of 282 

Eccentric  loading  on  columns 210 

Ellicott  Square  Building,  columns  in 209 

End-construction  terra-cotta  arches 98 

Erection  of  steelwork,  derricks  for 56 

for  Atlantic  Building 78 

Broadway  Chambers 63 

New  York  Life  Building 77 

Reliance  Building 63 

inspection  of 378 

methods  of 50 

rapidity  of 59,  77 

specifications  for 387 

Expanded  Metal  Co.'s  floors „ 107 

Field-riveting 68,  77 

Fire  loss  in  U.  S 12 

Fireproof  construction,  defined. 14 

doors 29 

floors,  building  laws  regarding in 

See  Composition  floors. 
Concrete  floors. 
Terra-cotta  arches. 

selection  of no 

windows 29 


398  INDEX. 

PACK 

Fireproofing  of  columns 27,  28,  224,  245 

requirements  for 25 

Fire-resisting  design , 26 

materials 24,  151 

Fires,  Chicago  Athletic  Club  Building 15 

Home  Insurance  Building 18 

Home  Buildings,  Pittsburg 16 

Fisher  Building,  column-loads  in 236 

columns  in 209 

erection  of  steelwork 63 

floor-loads  in 125 

foundations  for 354 

Floor-arches.     See  Composition  Floors. 
Concrete  Floors. 
Terra-cotta  arches. 

beams,  calculation  of 129 

deflection  of 135 

shop  details  of 142 

spacing  of 129,  134 

framing,  methods  of 126 

marking  for 143 

girders.     See  Girders. 

loads,  building  laws  regarding 120 

dead 122 

in  Fisher  Building 125 

Fort  Dearborn  Building 123 

Marshall  Field  Building 122 

Mills  Building 116 

Old  Colony  Building 123 

Venetian  Building 116 

live 114 

Fort  Dearborn  Building,  column-loads  in 124 

column-stresses  in 239 

description  of 42 

floor-loads  in 123 

spandrels  in 169 

wind-bracing  in 274 

Foundations,  adjoining  or  party  walls 295 

beam.     See  Beam-footings. 

bearing-power  of  soils 285 

concrete 305 

continuous  grillage 338 

fibre-stresses  for  beams  in 341 

importance  of 284 

loads  on 288,  307 

masonry  in 314 


INDEX.  399 

PAGE 

Foundations,  pile.     See  Pile-foundations. 

pneumatic.     See  Pneumatic  Foundations. 

present  types  of 309 

pressures  on 288 

proportioning  of  grillage  areas 310 

rail.     See  Rail-footings. 

settlement  of 302 

shoring 296 

steel,  painting  of 341 

test  borings 293 

loads 290 

timber.     See  Timber-grillage. 

to  bed-rock 356 

underpinning 299 


Gillender  Building,  bay  windows  in 184 

data  on , 47 

foundation  pressures  in 288 

pneumatic  caissons  in 366 

spandrels  in 175 

Girders,  calculation  of 136 

connecting  to  columns 214,  241 

early  forms  of 2 

types  of 135 

Gray  columns,  disadvantages  of 204,  209 

eccentric  loading  on 214 

form  of 199 

specifications  for 221 

Great  Northern  Hotel,  rail-footings  in 320 

settlement  of 305 

Grillage,  beam.     See  Beam-footings. 

continuous 338 

over-piling *. 348 

proportioning  areas  for 310 

rail.     See  Rail-footings, 
timber.     See  Timber-grillage. 

Grouting 67 

Guaranty  Building,  columns  in 209 


Harrison  Building,  columns  in 196 

Home  Insurance  Building,  Chicago,  design  of 6 

,  settlement  of 304 

New  York,  fire  in 18 

Hooks,  ties,  etc 156 

Home  Buildings,  Pittsburg,  fire  in 16 


400  INDEX. 


I-beams,  introduction  of 4 

See  Floor-beams. 

Inspection,  cost  of. 388 

detailed 391 

importance  of 387 

of  erection 378 

specifications  for 380,  382,  390 

Iron  construction,  early  forms  of 2 

Isabella  Building,  wind-bracing  in 274 

Jewellers'  Building,  description  of 42 

Keystone  octagonal  column,  description  of 199 

disadvantages  of 204 

Knee-braces,  analysis  of 273 

examples  of 274 

use  of 259 

Larimer  column,  description  of 199 

details  of 207 

disadvantages  of 204,  208 

eccentric  loading  of 216 

splicing  of 217 

Lattice-girders  for  wind-bracing,  analysis  of 275 

examples  of 278 

use  of 259 

Lime,  action  on  steelwork. . 79 

Lintel  protections 180 

Lintels,  beams  for 188 

calculation  of  cast-iron 188 

Live-loads,  on  columns 234 

floor  system 114 

foundations 120,  307 

Loads,  dead.  See  Dead-loads, 
floor.  See  Floor-loads, 
live.  See  Live-loads. 

Mabley  Building,  columns  in 209 

Manhattan  Life  Building,  columns  in 197,  198 

foundation  pressures  in 288 

.     pneumatic  caissons  in 363 

Marquette  Building,  beam-footings  for 325 

data  on 34 

spandrels  in 172 

Marshall  Field  Building,  floor-loads  in 122 

spandrels  in 173 


INDEX.  401 

PAGE 

Masonic  Temple,  bay  windows  in 180,  182 

columns  in 197 

column-sheets  for 235 

column-stresses  in 238 

mechanical  plant  in 37 

piers  in . ..   148 

settlement  of 304 

test  loads  on  foundations 290 

wind-bracing  in 263 

Masonry,  in  foundations 314,  316 

piers,  materials  for 152 

objections  to 145 

See  also  Stone-masonry.  ' 

Metropolitan  floor 109 

Mill  construction,  defined 25 

Mills  Building,  floor-loads  in 116 

Monadnock  Building,  columns  in 219 

fireproofing  of  columns 247 

foundation  pressures  for 289 

settlement  of 304 

walls  in 144 

wind-bracing  in 271 

vibrations  under  wind-pressure 281 

Montauk  Block,  foundations  in 5 

Mortars,  action  on  steelwork 81,  159 

Mullions 182 

New  Orleans  Custom  House,  foundations  for 314 

New  York  Building  Law,  bearing-power  of  soils 287 

fireproofing  of  columns 248 

floor-arches 112 

foundation  concrete « 306 

live-loads  on  columns 120 

floors 121 

loads  on  foundations 309 

painting  of  iron  and  steelwork 87 

steel  foundations. 341 

party-wall  foundations 295 

pile-foundations . 356 

protection  of  steelwork 160 

stone  in  walls 166 

wind  forces 282 

Life  Building,  erection  of — ^.. ....      77 

Insurance  Building,  description  of 41 

Old  Colony  Building,  combined  footings  in 328 


402  INDEX. 


Old  Colony  Building,  fibre-stresses  in  foundation-beams  for 341 

floor-loads  for 122,  123 

wind-bracing  in 271 

Pabst  Building,  column-connections  in 221 

Painting,  cost  of 87 

field 77,  84 

for  foundation-beams 341 

New  York  Building  Law 87 

of  Congressional  Library  steelwork 85 

references  on 82 

requirements  for 82,  83,  84 

specifications  for 377,  382,  386 

Paints,  adulteration  of 86 

cost  of 87 

value  of 84 

Park  Row  Building,  columns  in 197 

description  of 42 

pile-foundations  in 352 

wind-bracing  in 278 

Partitions,  fireproof 28 

Party  walls 162 

foundations  for 295 

Philadelphia  Building  Law,  live-loads  on  floors 121 

Phoenix  columns,  connections  to 216 

disadvantages  of 204,  208 

form  of 199 

splicing  of 217 

Pile-foundations,  building  laws  regarding 356 

combined  with  grillage 354 

formulae  for  bearing-power  of 344 

in  Chicago  buildings 350 

Library 290 

Post-office 351 

Park  Row  Building 352 

specifications  for 348 

test  loads  on 290,  343 

use  of 342 

water-level  of 349 

Piping,  installation  of 29 

Plate  and  angle  columns,  advantages  of 223,  226 

forms  of 197 

Pneumatic  caissons,  design  of 360 

first  use  of 363 

in  American  Surety  Building 369 

Gillender  Building 366 


INDEX.  403 


Pneumatic  caissons  in  Manhattan  Life  Insurance  Building 363 

use  of 358 

Portal  wind-bracing,  analysis  of 268 

examples  of 271 

use  of 259 

Rail-  and  beam-footings 320 

footings,  calculation  of 319 

compared  with  masonry 316 

origin  of 5 

proportioning  areas  for 310 

Reaming,  specifications  for 376 

Reliance  Building,  bay  windows  in 182 

columns  in 209,  221 

data  on 34 

erection  of  steelwork 63 

spandrels  in 168 

wind-bracing  in - 279 

Riveted  connections 138,  140 

Rivets,  specifications  for 385 

Roebling  floors 104 

Roofs,  live-loads  on 121 

raised  skew-backs  for 102 

Rookery  Building,  foundations  in 7 

Schiller  Theatre  Building,  columns  in 240 

foundations  for 351 

Segmental  terra-cotta  arches 102 

Separators,  specifications  for 385 

Settlement  of  foundations 302 

Shoes,  steel,  for  columns 229 

Shop-work,  specifications  for 375 

Shoring  of  foundations 296 

Side-construction  terra-cotta  arches 97 

Siegel-Cooper  Building,  erection  of  steelwork 56 

Skeleton  construction,  defined 9 

development  of 7 

origin  of 6 

permanency  of 78 

stability  of 255 

Slow-burning  construction,  defined 25 

Soils,  bearing-power  of 285 

Spandrel-beams,  calculations  of 186 

loads,  table  of  weights  of 190 

sections,  American  Surety  Co.'s  Building ..    175 

Ashiand  Block i6& 


404  INDEX. 

PAGfc 

Spandrel  sections,  bay  windows. 179 

Broadway  Chambers 178 

court  walls 178 

Fort  Dearborn  Building 169 

Gillender  Building • 175 

Marquette  Building 172 

Marshall  Field  Building 173 

Reliance  Building , 168 

Spreckels  Building 175 

Spandrels,  denned 167 

Specifications  for  castings 379 

finish  of  material 375 

shop-work 375 

structural  iron  and  steel 378,  383 

steel 372 

workmanship 381 

importance  of 371 

Splices  for  cast  columns 192 

steel  columns 217,  220,  258 

Spreckels  Building,  effect  of  earthquake  on 282 

foundation  pressures  in 289 

foundations  for 339 

spandrels  in 175 

Standard  connections 138,  139 

Standard  Oil  Co. 's  Building,  shoring  of  foundations 298 

Steel,  chemical  constituents  of . . . 372 

physical  properties  of 374 

specifications  for 379 

Steelwork,  detailed  specifications  for 378,  383 

detailing  of.     See  Detailing. 

deterioration  of 78,  80,  81,  159 

erection  of.     See  Erection. 

inspection  of 387 

painting  of.     See  Painting. 

protection  of,  in  walls 160 

shop-work  on 375 

. ..,       specifications  for 372 

Stone  masonry,  allowable  pressures  on 165 

in  foundations 314,  316 

St.  Paul  Building,  columns  in 197 

foundation  pressure  in 288 

grillage  foundations 339 

tests  of  soil 292 

Sway-rod  wind-bracing,  analysis  of 360 

examples  of 263 

use  of 258 


INDEX.  405 

PAGE 

Tacoma  Building,  construction  of ;... »-....;.  7 

Terra-cotta,  anchors  for 171 

column  protections 246 

filler-blocks 103 

.     for  wall  construction 151,  155 

introduction  of 23 

manufacture  of 94 

raised  skew-backs 102 

Terra-cotta  arches,  choice  of 103 

combination  end-  and  side-construction too 

construction  of 96 

early  forms  of 91 

end-construction 98 

introduction  of 90 

manufacture  of 94 

present  types  of 97 

segmental 102 

side-construction 97 

tests  of 93 

Tests,  borings  for  foundation 293 

Denver 93 

floor-arches,  New  York  Building  Laws 112 

for  structural  steel 380 

of  cast  columns 194 

foundation-loads 290 

on  piling 343 

Tie-rods,  specifications  for 385 

use  of 135 

"  The  Fair  "  Building,  column-stresses  in 239 

foundation  pressures  in 289 

loads  in 308 

wind-bracing  in 264 

Timber-grillage 312 

in  New  Orleans  Custom  House 314 

World's  Fair  Buildings 313 

offsets  for 314 

on  piling 348 

Underpinning  of  foundations .' 299 

Unit-stresses  for  columns 238 

- '        foundation  beams 341 

masonry. 164 

wind-bracing . . 268 

Unity  Building,  erection  of  steelwork 60 

Veneer  construction 149 

Venetian  Building,  column-sheets  for 235 


4°6  INDEX. 

PACK 

Venetian  Building,  column-stresses  in 238 

floor-loads 116 

wind-bracing  in 264 

Vibrations  under  wind-pressure 280 

in  Monadnock  Building 281 

Pontiac  Building 281 

Waldorf-Astoria  Hotel,  columns  in 225 

Walls,  anchorage  for 161 

building  laws  regarding 160,  165 

columns  in 156,  158 

construction  of 144 

hooks  and  ties  for 156 

load-supporting ' 145 

materials  used  in 150,  155 

party 162 

self-supporting 147 

thickness  of 162 

unit-stresses  for 164 

veneer-construction*. 149 

weights  of 190 

Washington  Monument,  foundation  pressures  under 289 

Water-level  for  pile-foundations 349 

Weights  of  brick  walls 190 

materials 190 

Western  Union  Building,  underpinning  of  foundations 301 

Wind-bracing,  Chicago  Building  Law 282 

diversity  of  practice  in 249 

in  Fort  Dearborn  Building 274 

Isabella  Building 274 

Masonic  Temple 263 

Monadnock  Building 271 

Old  Colony  Building 271 

Park  Row  Building 278 

Reliance  Building 279 

"  The  Fair  "  Building 264 

Venetian  Building 264 

Worthington  Building 279 

knee-braces.     See  Knee-braces, 
lattice-girders.     See  Lattice-girders. 

methods  of 254 

New  York  Building  Law 282 

portals.     See  Portals, 
sway-rods.     See  Sway-rods. 

pressure,  deflections  under 280 

intensity  of 251 


INDEX.  407 

PACE 

Wisconsin  Central  Depot,  foundations  for 351 

Workmanship,  specifications  for 381 

"  World  "  Building,  columns  in 218 

foundation  pressure  in 288 

walls  in 148 

World's  Fair  Buildings,  foundations  for 312 

test  loads  on  foundations 290 

Worthington  Building,  columns  in 198 

wind-bracing  in 279 

Y.  M.  C.  A.  Building,  Chicago,  foundation  pressure  in 289 

settlement  of 304 

Z-bar  columns,  advantages  of 209,  223 

connections  to ......    ..   216 

forms  of 198 

full-sized  tests  of 238 

in  "  The  Fair"  Building 227 

Y.  M.  C.A.  Building 227 

splices  for 245 

Standard  dimension • 209,  2l6 


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