GIFT OF
MICHAEL REESE
Frontispiece.
New Half,
Veneer Construction.
THE MONADNOCK BUILDING.
Old Half,
Solid Masonry
Walls.
- ARCHITECTURAL ENGINEERING;
WITH SPECIAL REFERENCE TO
HIGH BUILDING CONSTRUCTION,
INCLUDING MANY EXAMPLES OF
CHICAGO OFFICE BUILDINGS.
BY
JOSEPH KENDALL FREITAG, B.S., C.E.
n
FIRST EDITION.
FIRST THOUSAND.
OF THE
"
NEW YORK:
JOHN WILEY & SONS.
LONDON: CHAPMAN & HALL, LIMITED.
1895.
T HI toll
COPYRIGHT, 1895,
Bi
JOSEPH K. FREITAG.
ROBERT DRUMMOND, ELECTROTVPER AND PRINTER, NEW YORK.
^>X
TT)
J
L-— -^
PREFACE.
THE author has attempted, in the following- pages, to
define and illustrate, in a manner as practicable as possible,
such of the fundamental principles in the design of the
modern high building as may prove useful to architects
and engineers alike.
vWhile the technical press of the country has devoted
considerable attention to many of the individual subjects
here considered, yet the realisation of a want of collective
data on the subject of Architectural Engineering has
induced the writer to present this volume.
As more and more of the principles of construction are
being added to the curricula of our architectural schools,
and as many of our engineering students are adopting
building construction as a specialty, it is hoped that this
effort will serve to unite still more closely the work of the
one with that of the other.
The author would mention the efforts of one highly
esteemed and dearly beloved in the engineering profession,
Mr. E. L. Corthell, who has been striving for several years
to see the two professions united by establishing an Inter-
national Institute of Engineers and Architects, as well as a
technical School of Architecture and Engineering at the
new University of Chicago. The writer would also
acknowledge the warm interest displayed in this work by
his former professor of engineering, Prof. C. E. Greene, of
the University of Michigan.
iii
IV PREFA CE.
The following chapters are arranged in the order in
which the calculations for such structural work must pro-
ceed, starting with the load-bearing floor system, thence
through the successive stages to the foundations. The
latter would seem to require the first attention ; but as they
are the last to be calculated, being dependent on all other
considerations, they have here been placed last. The illus-
trations 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.
JOSEPH KENDALL FREITAG.
CHICAGO, MAY, 1895.
CONTENTS.
CHAPTER I.
PAGE
INTRODUCTORY i
CHAPTER II.
FIRE PROTECTION 9
CHAPTER III.
SKELETON CONSTRUCTION— EXAMPLES— ERECTION, ETC 24
CHAPTER IV.
FLOORS AND FLOOR FRAMING 54
CHAPTER V.
EXTERIOR WALLS— PIERS 88
CHAPTER VI.
SPANDRELS AND SPANDREL SECTIONS— BAY WINDOWS 100
CHAPTER VII.
COLUMNS 113
CHAPTER VIII.
WIND BRACING 136
V
VI CONTENTS.
CHAPTER IX.
PARIITIONS— ROOFS— MISCELLANEOUS 163
CHAPTER X.
FOUNDATIONS •. 171
CHAPTER XL
UNIT-STRAINS—SPECIFICATIONS 201
CHAPTER XII.
BUILDING LAWS.. 216
LIST OF ILLUSTRATIONS.
FIG. PAGE
1. Reliance Building, Chicago - 17
2. Arrangement for Pipe-space in Halls 22
3. Chicago Stock Exchange Building. Perspective 25
4. Chicago Stock Exchange Building. Basement Plan 27
5. Chicago Stock Exchange Building. Ground Floor Plan 28
6. Chicago Stock Exchange Building. Typical Office Floor Plan. 29
7. Marquette Building, Chicago. Perspective 30
8. Marquette Building, Chicago. Typical Office Floor Plan 31
9. Reliance Building. Typical Office Floor Plan „ . 32
10. Masonic Temple, Chicago 34
1 1 . New York Life Insurance Building. Perspective 35
12. New York Life Insurance Building. Plan of Banking Floor. .. 36
13. New York Life Insurance Building. Typical Office Floor
Plan 37
14. Fort Dearborn Building. Perspective 38
15. Fort Dearborn Building. Typical Office Floor Plan 40
16. Champlain Building. Typical Office Floor Plan 41
17. Old Colony Building. Perspective 42
18. Typical Framing Plan of Fort Dearborn Building 43
19. Typical Framing Plan of Reliance Building 44
20. Reliance Building during Construction 48
21. Reliance Building during Construction 49
22. Brick Arch Construction 55
23. Corrugated Iron Arch , 55
24. Tile Arch used in Equitable Building, Chicago (1872) 55
25. Tile Arch used in Montauk Building, Chicago (1881) 56
26. Tile Arch used in Home Insurance Building, Chicago (1884) . . 56
27. Arch showing Tile Filling Blocks used in Woman's Temple,
Chicago 57
VI 1 1 LIST OF ILL US TRA TIONS.
FIG. PAGE
28. Panelled Beam, Fire-proofed 58
29. Fire-proofed Girder 58
30. The Lee Flat Arch 59
31. The Johnson Type of Flat Arch . 61
32. The Austria Tile Arch 65
33. The Melan Arch, Short Span .. : 67
34. The Melan Arch, Long Span 67
35. Arch of Metal Straps and Concrete 69
36. Arch of Wire and Concrete, Panelled Soffit 69
37. Arch of Wire and Concrete, Flush Soffit 70
38. Elliptical Concrete Arch 71
39. Segmental Tile Arch 72
40. Segmental Tile Arch used in Sibley Warehouse, Chicago 72
41 . Standard Connection-angles 85
42. Standard Connection-angles 86
43. Isometrical View of Connection of Floor-beam to Girder 87
44. Detail of Terra-cotta Front. Reliance Building 93
45. Section through Wall at Main Entrance to Masonic Temple. . . 94
46. Detail of Corner Pier for Reliance Building 97
47. Detail of Wall Girders in Reliance Building 98
48. Diagram of Thickness of Walls for Buildings Devoted to Sale
and Storage of Merchandise 99
49. Diagram of Thickness of Walls for Hotels and Office Buildings
other than Skeleton Construction 99
50. Diagram of Thickness of Walls for Office Buildings carrying
Wall Weight only 99
51. Spandrel Section. Ashland Block 101
52. Spandrel Section. Reliance Building 101
53. Connection of Cast Mullions. Reliance Building 101
54. Spandrel Section, nth floor. Fort Dearborn Building 102
55. Spandrel Section, I2th floor. Fort Dearborn Building 103
56. Spandrel Section, ist floor. Fort Dearborn Building 103
57. Spandrel Section, Roof and Cornice. Fort Dearborn Building. 104
58. Spandrel Section. Marquette Building 105
59. Spandrel Section. Marshall Field Building 106
60. Spandrel Section. Marshall Field Building 106
61. Spandrel Section through Court Wall of Marshall Field Building 107
62. Spandrel Section through Typical Court Wall 108
•LIS T OF IL L US TRA T1ONS. 1 X
FIG. PAGE
63. Spandrel Section through Bay Window. Masonic Temple .... 109
64. Spandrel Section at Bottom of Bay Window. Masonic Temple. 109
65. Half Plan of Metal-work in Bay Window. Reliance Building. . no
66. Half Plan through Bay-window Walls. Reliance Building.... no
67. Spandrel Section through Centre of Bay. Reliance Building. . in
68. Spandrel Section at Side of Bay. Reliance Building 1 1 1
69. F'loor and Ceiling Supports in Bay Window. Reliance Building 112
70. Details of Joints for Cast Columns 114
71. Detail of Larimer Column 122
72. Detail of Larimer Column 122
73. DetalTof Gray Column and Connecting Girders 125
74. Detail of Phcenix Column 125
75. Detail of Z-bar Column. Monadnock Building 127
76. Detail of Phcenix Column 128
77. Detail of Phcenix Column used in Old Colony Building 129
78. Detail of Box Column 129
79. Section of Z-bar Column used in " The Fair " Building 130
80. Method of Fire-proofing Phcenix Column 134
81. Method of Fire-proofing Box Column 134
82. Method of Fire-proofing Z-bar Column 134
83. Method of Fire-proofing Columns in Monadnock Building. . . . 134
84. Diagram of Wind Bracing by means of Sway-rods 139
85. Diagram of Wind Bracing by means of Sway-rods 139
86. Diagram of Wind Bracing by means of Portals 139
87. Diagram of Wind Bracing by means of Knee-braces 139
88. Figure showing Analysis of Sway-rod Bracing 141
89. Figure showing Typical Sway-rod Bracing 143
90. Wind Bracing used in Masonic Temple 144
91. Floor Plan of Venetian Building 144
92. Wind Bracing in Venetian Building 145
93. Detail of Channel-struts. Venetian Building 146
94. Detail of Cast Blocks. Venetian Building 146
95. Partial Cross-section of Venetian Building 147
96. Figure showing Analysis of Portal Bracing 149
97. Portal-strut used in Monadnock Building 151
98. Cross-section showing Portals in Old Colony Building 151
99. Detail of Portal in Old Colony Building 152
100. Figure showing Analysis of Knee-bracing 153
X LIST OF ILLUSTRATIONS.
FIG. PAGE
101. Detail of Knee-bracing used in Isabella Building 154
102. Channel-struts and Gussets used in Exterior Walls of Fort
Dearborn Building 155
103. Detail of Column Joint in Pabst Building, Milwaukee 158
104. Detail of Column Splice in Reliance Building 159
105. Detail of Book Tile 164
106. Hall and Main Entrance to Marquette Building 166
107. Hall and Main Entrance to New York Life Insurance
Building 167
108. Hall and Main. Entrance to Fort Dearborn Building 168
109. Rail Footing 174
1 10. Masonry Footing 174
in. Beam and Rail Footing 181
112. Beam Footing used in Marquette Building , 184
113. Double Footing used in Marquette Building 184
1 14. Plan of Cantilever Footing 1 86
115. Elevation of Cantilever Footing 186
116. Line of Flexure for Continuous Girder 187
117. Figure showing Analysis of Cantilever Footing , 187
118. Figure showing Analysis of Continuous Girder 189
119. Plan of Foundations. Manhattan Life Insurance Building,
New York 199
120. Cross-section showing Foundations of Manhattan Life Insur-
ance Building, New York 200
ARCHITECTURAL ENGINEERING.
CHAPTER I.
INTRODUCTORY.
AMONG the most noteworthy examples of Architectural
Engineering in recent years, " Le Tour Eifel " stands unique
— a most perfect expression of this recently coined term,
signifying a complete union of the great art of architecture
and the science of engineering. While universally accepted
as distinctly an engineering feat, this tower possesses such
perfect structural beauty that it may well lay claim to the
eulogies of architectural critics — eulogies that should be all
the more emphatic when we stop to consider how few and
far between, in modern times, are the creations of the engi-
neer that can, at the same time, appeal to the architectural
artist or designer, as embodying the beauty of form with
the excellence of construction ; while the reverse may truly
be said of modern architecture. For who may claim justly
that our present architectural efforts are true, characteristic
expressions of modern life, or reflections of the progress
that has characterized our age — as classical architecture
embodied classical life and mediaeval architecture expressed
mediaevalism ?
The science of engineering has, at least, been progress-
ive, keeping pace with modern developments, while archi-
tecture, for the most part, has been stationary, content to
2 ARCHITECTURAL ENGINEERING.
copy the original form of a civilization whose substance
has undergone ages of evolution. Hence arise the causes
for the present antagonism in these two closely related pro-
fessions. There should be none, but that there is, no one
will deny. One of the most prominent engineers of the
United States has been heard to characterize architects as
" milliners/' and their work as " millinery " or " gingerbread
decoration "; while the architect, on his own little pedestal of
pure art, scorns the engineer as incapable of producing the
beautiful. There is, doubtless, partial justice in each of
these criticisms; the architect's blind devotion to classic
forms becoming as much of a hindrance to the practical
aims of the engineer, as the barren stamp of utility, glaring
from a purely engineering work, is an offence to the eye of
the artistic designer. But the keynote has already been
sounded for a more perfect union between these two pro-
fessions, each of which is the necessary complement of the
other.
Although the term architectural engineering has but
recently sprung into use, the perfect union of the two arts
is as old as the arts themselves. Pyramids, obelisks,
temples, palaces, and sepulchres, all show that the architects
of early days were the engineers as well. Vitruvius, the
only ancient whose ideas on architecture have' been pre-
served for us, established three qualities as indispensable
in a perfect building : stability, utility, and beauty,— the first
two of which certainly lie within the range of the science
of engineering. As a proof that those early architects
were governed by the laws of Vitruvius, we have but to
look upon the pyramids of Egypt, the vast monoliths of
Rome, the temples of Sicily, or the massive Parthenon.
Their graceful proportions and harmony of design have
for centuries made of the architect an admiring copyist,
while their massiveness and stability suggest to the en-
IN TR OD UCTOR Y. 3
gineer the possibilities of human power. Take lor example
one of the largest pyramids not far from the city of Cairo.
This rough, awe-inspiring mass of masonry covers 11 acres
of the sands of the Nile, while its height is but little less
than our Washington Monument, or nearly 500 feet.
Again, consider the temple of Babylon, 660 feet in height,
built of blocks of stone 20 feet long, used in a brick-like
fashion, some of them being 15 feet broad and 7 feet thick ;
or the massive remains of an Egyptian temple, the walls
of which were found to be 24 feet thick; while at the gates
of Thebes the foundation walls were 50 feet thick and per-
fectly solid.
The ethnologist tells of an age of clay, then stone in
the rough and, later, polished ; an age of bronze, then iron ;
and now we add steel and the newer materials. Architec-
ture, as represented in the temples, tombs, palaces, and
habitations of man, has always been, like literature, the
surest indication of the customs, arts, and needs of the
people who produced it — in fact, a perfect reflection of the
civilization in which it is found. " Cain, the son of Adam,
builded a city," — the rude mud hut or the flimsy structure
of reeds serving as man's habitation in primitive times, imi-
tating the nests of birds, of which modifications still exist
in China and other Eastern countries, as well as in many
parts of dark Africa. The later days of clay and straw and
then burned brick were succeeded by the age of stone,
reaching such a height of excellence in the works of the
Greeks and Romans, and the castles and cathedrals of the
middle ages. The temple of Solomon, rebuilt by Herod
at Jerusalem, was, so the Bible states, 46 years in erection,
with stones 46 feet long, 21 feet high, and 14 feet thick,
while some were of the great length of 82 feet. Would it
not tax the ingenuity of an engineer in our own advanced
age to handle such masses of stone ? Architecture and en-
4 ARCHITECTURAL ENGINEERING.
gineering certainly worked in harmony in these examples,
which must ever rank with the greatest creations of man.
Now, with the hurrying strides of civilization, comes a
demand for a cheaper and quicker construction, a medium
capable of being more easily handled than the huge blocks
of stone of early ages; while the principles of statics and
the economics of construction present themselves with
ever increasing clamor for solution and application, until
we boast that our age is one of specialties, involving an
exactness hitherto unknown in the observance of all the
laws of nature formulated, as they are, into exact sciences.
It was but natural, in the examples we have considered,,
that architecture should go hand in hand with engineering,
for the architect was the engineer, employing rule of thumb
methods, to be sure, and knowing little of the laws of
statics or dynamics. Indeed it was not till the thirteenth
century that the solution of the theory of arches and vaults
was attempted. Old, old indeed, is the relation of friend-
ship that has existed between the naturally allied arts of
architecture and engineering — a mutual bond, which will,
we believe, give us still more perfect examples of the
strength and beauty that architectural engineering makes
possible : architectural, in reference to the expression and
beauty of the edifice — engineering (perhaps partially, if not
wholly, hidden from the eye), in construction, durability, and
magnitude that result from the possibilities which open up
before the mind accustomed to dealing with the matter
and forces of nature, and adapting them to the ever-increas-
ing wants of an exacting public. The materials of nature
assume higher and higher planes in the fulfilment of man's
needs, as he constantly overcomes more of the natural de-
structive elements and agencies by applying himself with
scrupulous exactness to every detail of work. Considering
the present tendency to specialization, it seems absurd to
IN TROD UCTOR Y. 5
suppose that the architect may eventually be employed
simply as an ornamental draughtsman by the engineer, or
that the engineer may become subservient to the architect.
Either profession is too noble and comprehensive in itself
to permit of such absorption. It is but a natural prejudice
to give first importance to one's own branch of work ; and,
indeed, the engineer quite justly claims a prerogative, since
upon the accuracy of his calculations depend the stability
of the structure and the safety of the tenants. But, on the
other hand, one cannot severely censure the architect for
ridiculing such work as many of our best engineers send
forth, as devoid of beauty or even harmony of line. It is
apparent, therefore, that the truest expression of our life
and civilization must be found in a more perfect harmony
of these two professions. The architect of early days was
enabled by rule of thumb methods, good judgment, and a
knowledge of past examples to produce the structures he
built; but with the exactness of our professional work at
the present time, and the multifold necessities of our com-
prehensive civilization, the architect who endeavors to
compass the sphere of the trained engineer will find the
longevity of Methuselah desirable for his education. Let
the engineer know more of art and appreciate its value, and
let the architect know as much as possible of construction
and the laws of the forces of nature. But that either may
fully grasp the details of both professions seems well-nigh
impossible.
The architect has been accustomed to say that such a
perfect union is impracticable, but the architectural critics of
to-day are demanding it, as is shown by the following : " In
art, as in nature, an organism is an assemblage of interde-
pendent parts, of which the structure is determined by the
function, and of which the form is an expression of the
structure." Again : " That form is pleasing to good taste
ARCHITECTURAL ENGINEERING.
which shows and reveals its use. That form reveals the
use most successfully whose surface and outlines and whose
skeleton or frame speak for themselves, and are not ob-
scured by misplaced ornament."
If these quotations from purely architectural critics,
without reference to engineering, are to be given value,
then surely a more rational union of excellent structural
design on economic principles, with perfect architectural
expression of the underlying organism, is not only possible
but necessary for a proper reflection of our civilization.
The people of our country have demanded " sky-scrapers,"
in accordance with the strong tendency to centralization.
Newr problems have been created and new necessities im-
posed, and the engineer has come to the front with the
steel and terra-cotta of the "Chicago construction," as the
means of solution on his part ; but it remains for the archi-
tect to give true expression and permanent form to what
the engineer has evolved. It is from the union of the
results obtained by a rational division of labor in the art of
building that we hope for the perfect architecture of the
present age.
It has been said that our civilization has demanded a
medium of construction more in accord with the push and
hurry and economy of our day than is found in the mas-
sive masonry construction ; a substance combining the
strength, durability, and adaptability required by the de-
mands of commerce and rapid progress. In the architec-
tural history of our own country we have not confined
ourselves to any one material long enough to develop for
it a unique, characteristic style of representation. Our
architectural form has, rather, been a series of rapid
changes. The refined and sober examples of our colonial
forefathers rapidly gave way to the more ostentatious
efforts of the jig-saw in our frame construction, and this
IN TR OD L/C TOR Y. 7
period of the shingle and fretwork gave place to the rows
of red brick, and later the brown-stone front, with all its
attendant horrors in galvanized iron. Cast iron, too, has
held its sway for its own little period, only to be displaced
by its more refined and enduring successor, steel. Our
present epoch has been characterized so often as one of
steel and terra-cotta that the subject is becoming trite
indeed ; but only through the combination of these ma-
terials have the huge frame-works which now mark our
large American cities become possible. And as the " sky-
scraper " office buildings present interesting problems in
architectural engineering, which are being constantly dis-
cussed in the technical press of to-day, some of the con-
structional points involved will be considered here with
special reference to " Chicago construction," a construction
which has almost universally been attributed to the skill
of the architect, though in only too many cases the archi-
tect, who has designed, as it were, the sugar coat, to make
the exterior palatable to the public, reaps all the reward
for what the engineer has made possible.
The fact that in our large cities it is found most advan-
tageous as to time and convenience for business transac-
tions, to have our commercial headquarters and office-build-
ing district concentrated within a limited area, has caused
the adoption of buildings numbering from 16 to over 20
stories. Increased floor-space must be obtained to realize
on the investment, and it is evident that these tower-like
structures must continue to increase in numbers, when we
note the abnormally enhanced prices to which the value
of land is rising. The American Surety Company in New
York City might be mentioned as paying the sum of
$1,500,000 in 1894 for a piece of property about 85 feet
square, which would be at the rate of $8,000,000 per acre.
The continued development, however, of this centrah-
8 ARCHITECTURAL ENGINEERING.
zation of business operations is attended by many vexing-
difficulties, the attempted solution of which has caused a
number of clauses of restriction to appear in the municipal
building laws. Considerable discussion has been going on
about the sanitary aspect of this question ; the damp, un-
wholesome, and microbe-laden air which must lurk in the
deep valleys or streets between mountainous structures on
each side ; the dark and uninviting offices of the lower
stories, which would soon become vacant ; and the con-
gested condition of our sidewalks when our vertical carry-
ing capacity is greater than our horizontal or street
capacity — ail are considerations of grave importance.
But that the proper regulation of building operations,
with their attendant difficulties and future possibilities of
development and style, may be successfully accomplished
by general municipal ordinances is very doubtful. The
building laws of many of the larger cities already prescribe
a maximum height for all structures; but considering high
buildings,/^ se, it is evident that it is not so much legisla-
tion limiting the possibilities of design that is needed, as it
is laws compelling the appointment of competent engineers
to supervise the designs, specifications, and execution of
large buildings, and possibly a competent board of archi-
tects to pass on the proposed location of an extraordinarily
high structure. It would be well if we adopted more of
the European practice, giving harmonious appearance to
our thoroughfares and considering the specific conditions
of each new structure of monumental pretensions, instead
of binding all through an inflexible law. Edifices fronting
on parks or open spaces might then be treated in more
heroic proportions than those of narrow by-ways, and the
incongruous mixture of ups and downs, side by side, might
give place to some semblance of harmony between
neighbor and neighbor.
CHAPTER II.
FIRE PROTECTION.
BEFORE considering the details of skeleton construction
it will be well to consider the general subject of fire-proof-
ing, 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
necessary 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 pre-
vented, a proper treatment of the fire problem certainly be-
comes 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.
The old adage of an ounce of prevention being better than
a pound of cure is slowly but surely demonstrating its
truth as applied to the ravages of fire, as well as of disease,
and the specialist who enters this broad field of research
and improvement must meet causes and effects with a pre-
9
10 ARCHITECTURAL ENGINEERING.
cision not less exact than does his medical brother. Con-
flagration has formerly been looked upon as an inevitable
calamity, inflicted by a supernatural agency ; and property-
owners have been content, year after year, to pay enormous
insurance rates, suffering with resignation the destruction
of their property and the annihilation of their business.
Add to these the loss of articles of peculiar associations, —
heirlooms and treasures of art and science,— and the possi-
bility of relief from this Damoclean sword of conflagration
is a liberation indeed. And that this 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 palatial office buildings, stores, and mag-
nificent residences, but also by people of limited means, as
is evidenced by the start already made in fire-proofing the
ordinary city house, at a figure not exceeding the cost of
present methods. It was found recently, in taking figures
for a building in Philadelphia to cost $125,000, that a thor-
oughly 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.
The tide has turned, and nothing can stay the flood of
progress in this direction. The dawn of the twentieth cen-
tury will undoubtedly see nearly all of our mercantile,
manufacturing, and even dwelling houses, except those of
FIRE PROTECTION. II
the very cheapest description, built according to fire-resist-
ing principles. Steel, the clay products, and cement or
concrete are the" materials of the future, permanent, fire-
resisting, of ready adaptability, and of remarkably low cost.
The fire-trap timber construction, threatening the exhaus-
tion of our vast forestry resources, accompanied by its
susceptibility to dampness, drought, heat, and cold, involv-
ing dry-rot, as shown by the collapse some years ago of a
prominent hotel in Washington, must give way to new con-
ditions, and further improvement in a field of such promise.
The insurance burden will be gradually lightened, and
human life be better protected.
While buildings could be erected with absolutely no
inflammable material in their construction, there would
still remain the furniture and property of the tenants to
feed possible fire. This element of danger cannot be elimi-
nated ; and added to this are the dangers that come from
without as well as from within. For as long as highly in-
flammable buildings surround even the most excellent of
modern fire-proof structures the term is but mockery.
Fire-proof structures must stand in fire-proof cities. Hence
the word " fire-proof," as applied to modern structures, does
not mean one that claims immunity from all danger of fire,
for considerable 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
12 ARCHITECTURAL ENGINEERING.
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 struc-
tural members are protected against the effects of fire by
coverings of a material which must be entirely incom-
bustible 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; fourth, three layers of plastering on metal lath,
so applied upon metal furring that there shall be a solid
layer of mortar at least one-half inch thick between the
metal to be covered and the metallic lath, and then two air-
spaces of at least three-fourths of an inch in the clear be-
tween the first-mentioned layer of plastering and the outer
surface of the finished covering."
There are many materials quite satisfactory as fire-
proofing mediums for the constructional parts of a building,
but the inventor has yet to supply an acceptable incom-
bustible material for the interior finish. The best that can
be done, at present, is to reduce the inflammable elements
to a minimum, and endeavor to confine the fire by means of
fire-proof floors and partitions, so that it may do no injury
beyond the consumption of local woodwork and furnish-
ings. This may be accomplished largely by means of
floors of concrete or terra-cotta with I-beams, using mosaic
or marble tile instead of wood flooring, partitions of
plaster board, cement or metallic lath, or terra-cotta blocks,
and bases and wainscoting of marble. The possibility of
FIRE PROTECTION. 1 3
using frames and casings for doors and windows made
either of metat^o^ sheet metal over wood, and doors
covered with sheet metal, seems but a question of short
time in adding further efficiency to high-class fire-proof
structures. A metal-covered door has lately been intro-
duced in this country, giving a well-appearing, light, and
incombustible contrivance, and serving as an effectual
barrier against the spread of flames. The success that has
attended the use of wire glass in skylights has also
prompted the suggestion to reduce the exterior hazard by
protecting all windows, which offer the most vulnerable
points of attack, by using a plate glass with silvered or
gilded wires imbedded therein, in graceful patterns or net-
work, serving the purpose of additional fire protection, as
well as architectural effect. The planning of the building,
and the proper location and installation of the various
power plants and mechanical features, also become vital
problems in fire-proofing.
The success that has attended past efforts in this direc-
tion may be judged by such examples of fire as have been
afforded in protected structures. The largest and most
interesting of such tests of the new methods was the burn-
ing of the Chicago Athletic Club building while under
construction. Though not entirely satisfactory as a test of
present building methods, u this building furnishes an assur-
ance 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 conflagration, if
the quantity of combustible materials the building contains
is not greatly in excess of that which enters into the con-
struction of the building itself."
This extract from 'the report of experts employed to
investigate this fire and its effects, emphasizes two very
important facts, namely, the danger of the indiscriminate
14 ARCHITECTURAL ENGINEERING.
use of combustible 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
tc be fully fire-proof where the loss to the insurance com-
panies 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 distributed) to have produced suffi-
cient 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 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 unpro-
tected ; 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.
It is not advocated that fire-proofing as efficient (or in-
efficient when the preservation of human life is considered)
as the foregoing example is sufficient for present needs-
it certainly is not. But certain underlying facts have been
clearly proved by this test, and taking these essential points
FIRE PROTECTION. 15
as a basis, and using the utmost care and judgment in the
matter of details, it must be admitted that the use of terra-
cotta, as seen in the better examples of recent fire-proof
buildings, goes a long way in the successful solution of one
of the most important problems of modern times.
The method of fire-proofing now employed consists of
a vital skeleton or frame-work of wrought iron or mild
steel, enclosed in a continuous sheathing of terra-cotta.
Every square inch of the metal-work must be protected by
means of the various shapes made by the terra-cotta com-
panies, thus avoiding all direct transfer of heat.
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 out-
come 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
fire-proofing at that date, both in the exterior walls and in
floor arches, and the peculiar advantages of terra-cotta
caused it to undergo many improvements in rapid succes-
sion, effecting 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 weight, its great fire-resisting quali-
ties, its peculiar adaptability to all conditions of position
and form, its susceptibility to modelling, and its readiness
of manufacture in shapes convenient 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.
l6 ARCHITECTURAL ENGINEERING.
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 almost
more general than stone, appearing in entire fronts, as a
bold-faced impersonation of solidity itself.
The field of architectural expression in terra-cotta has
recently been widened to a still more remarkable degree
by the successful completion in enamelled terra-cotta of
the fa£ades of the Reliance Building, Chicago, supplied by
the Northwestern Terra-Cotta Co. (see Fig. i). Should
this material successfully withstand our severe climatic
changes, and undergo the same course of rapid improve-
ment as did the ordinary terra-cotta used in exteriors, a
vast field for more extensive coloring effects would then be
opened up to the architect who strives to create " a thing
of beauty forever" in the smoke and soot-laden air of our
American cities. The underlying idea of enamelled ex-
teriors is, of course, that they may be readily washed down
and cleansed of the soot which so soon destroys any at-
tempts at light coloring.
With this general review of the fire problem, and terra-
cotta as a weapon of defence, it becomes evident that a fire-
proof structure must possess :
1. General excellence of design.
2. All floors of fire-proof construction.
3. All columns of masonry or steel, protected from fire.
4. All outside piers and walls of masonry or steel, pro-
tected from fire.
5. All partitions and furring of fire-proof 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 "fire-proof construction."
The term " slow burning construction " is applied to build-
FIRE PROTECTION.
FIG. i. — The Reliance Building. D. H. Burnham & Co., architects.
1 8 ARCHITECTURAL ENGINEERING.
ings in which the structural members, carrying the floor
and roof loads, are made of combustible material, but
protected throughout from injury by fire, by means ol
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 I j- inches of mortar or incombustible deaden-
ing is required above the joists. Columns, if of oak, with
a sectional area of 100 square inches or over, need not have
special fire-proof coverings. Partitions and elevator en-
closures must be wholly of incombustible material, and no
wood furring is allowed.
Buildings of " mill construction " are those in which all
floor and roof joists and girders have a sectional area of at
least 72 square inches, with a solid timber flooring not less
than 3f inches in thickness. Columns of wood need not be
protected, but they should have a sectional area of at least
100 square inches. Partitions and elevator enclosures are
of incombustible material, and no wooden furring or lath-
ing is used.
" Fire-proof 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 suppression of the conflagration. These types are
peculiarly adapted to large mills, warehouses, and the like.
The scientific fire-proofing of a building does not con-
sist in a proper selection of materials alone, for a structure
may be reasonably secure against accidental fire, or the
extension of fire, even when built of combustible materials ;
nor does it lie merely in guarding against the causes of
fire. It can be secured only by a thorough acquaintance
FIRE PROTECTION. 19
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 communi-
cation 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 con-
fining 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
must 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 importance
equal to that of fire. This threatening possibility has not
yet verified itself, and it is to be hoped that it will be
denied the opportunity.
No less important is the cutting oft of all communica-
tion between pipe- and air-passages. Piping and passages
of all kinds should be carefully considered as a part of the
fundamental design, for they not only become great eye-
sores from their exposed positions in offices, but they also
serve to make many of our fire-proofing endeavors quite
useless.
The architect or engineer must finally be well informed
in regard to the details and varied uses of approved fire-
proofing 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 neces-
sary, so that the most practicable form may be chosen to
secure the desired end.
20 ARCHITECTURAL ENGINEERING.
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 bug-bear 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 fire-proof slabs of the column, thus forming
one long continuous flue from basement to roof. The
finished line of the fire-proofed and plastered column is
often not more than 2 in. from the extreme points of the
metal-work, and then, deducting £ in. or £ in. for plaster,
little enough is left for the fire-proofing proper. The
various pipes before mentioned will very often project
even farther than the column itself, thereby tempting the
fire-proofer to trim and shave till the original little has be-
come still less.
In the Athletic Club Building fire some of these points
were illustrated with glaring prominence. A steel frame-
work and fire-proof covering having been used as the
main elements of construction, further consideration of fire
hazards were apparently slighted. In no case did the fire-
proofing extend more than 2 in. from the outermost edge
of the ironwork, while wooden nailing-strips were em-
bedded in the tile at intervals of about 3 ft. starting from
the floor (a 4-in. face exposed), making successively 3 ft. of.
FIRE PROTECTION. 21
tile and 4 in. 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 panel-
ling, 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 fire-proofing fall in 3-foot
sections. 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 un-
certain conjecture.
The proper installation and distribution of the mechani-
cal features in a modern office building have been given
considerable attention by John M. Carrere (see Eng. Mag.,
October, 1892), and the system proposed by him will un-
doubtedly add greatly to the efficiency of fire-proofing, and
remedy many of the weak details just considered. In
order to avoid chases, or continuous flues, the lowering of
the hall ceilings is suggested, " thereby obtaining a hori-
zontal space under the floors of the halls at each story,
lined and fire-proofed, where all the mechanical features
except steam heat can be placed " (see Fig. 2). An arrange-
ment of this 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, pip-
ing, and ventilating air-ducts, either exhaust or indriven.
22
ARCHITECTURAL ENGINEERING.
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 fire-proof blocks or brick from
cellar to roof, and connected at each floor with the hori-
OFFICE
OFFICE
OFFICE
FIG. 2.
zontal leads, but still partitioned off at each floor 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.
The growing importance of adequate fire protection
may be judged from the care displayed in the encasing of
the large girders at the new Tremont Temple in Boston.
These girders carry columns of great load, and any warp-
ing tendency from great heat would be attended by most
serious results. The steel girders were first surrounded
by blocks of terra-cotta on all sides, and these blocks
were then bound by iron bands. Over these blocks was
stretched expanded metal lathing with a heavy coat of
FIRE PROTECTION. 2$
Windsor cement. Iron furring was next placed on all sides
to receive a second layer of expanded metal lath, on which
was placed the finished plaster. The covering thus con-
sisted of a dead air-space, terra-cotta blocks, a coating of
cement, a second air-space, and an external coating of
cement.
CHAPTER III.
SKELETON CONSTRUCTION— EXAMPLES, ERECTION, ETC.
MANY of the details which will be discussed in the fol-
lowing 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 considered are, rather, those of
construction pure and simple. But the comprehensive
view of the subject necessary to the architect or architec-
tural engineer may only be obtained through an accurate
knowledge of the manifold items which become a part of a
successful plan. These accessories to the mere frame-work
lie within the province of the engineer as well as of the
architect, and here, as in the execution of the external ex-
pression 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 real-
ized when the self-sufficiency of a modern office building,
containing all modern improvements, is considered. Elec-
tric light, the telephone, mail-chutes, and well-appointed
toilet-rooms are already demanded as absolute necessities,
while late examples provide telegraph and messenger ser-
vice, cigar- and news-stands and barber-shops, besides
24
SKELETON CONSTRUCTION. 2$
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 condi-
tions, imposed on the designer of the foundations of office
buildings, that produced the successful development of the
so-called raft or floating foundations, in order that the base-
ments might be unencumbered by the large pyramidal
FIG. 3.— Chicago Stock Exchange. Adler & Sullivan, architects.
masses -of stone previously used as footings, and the base-
ment 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.
Some examples of office buildings recently constructed
in Chicago will here be given.
26
ARCHITECTURAL ENGINEERING.
THE CHICAGO STOCK EXCHANGE.
A perspective of this building by Adler & Sullivan,
architects, is shown in Fig. 3. The facades are constructed
of a yellow-drab terra-cotta, with white enamelled brick in
the interior court.
Fig. 4 shows the basement plan, containing the boiler-
and engine-rooms, restaurants, etc.
Fig. 5 is a plan of the ground floor, showing the en-
trance vestibules, elevators, store areas, etc.
Fig. 6 gives a plan of 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 BUILDING.
This office building (see Fig. 7), designed by Messrs.
Holabird & Roche, architects, has but just been completed.
The exterior walls are built mainly of a dark red brick, with
terra-cotta base, cornice, and trimmings.
A typical floorplan, showing possible sub-divisions, is
given in Fig. 8. Many of the floors in the larger office
buildings are never subdivided until rented, in order that
the arrangement of offices may be made to suit the tenant.
RELIANCE BUILDING.
Fig. 9 gives a typical floor plan of this building by
D. H. Burnham & Co., architects. 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
SKELE TON CONS TR UCTION.
Dd
28
ARCHITECTURAL ENGINEERING.
SKELETON CONSTRUCTION.
29
f ---•--.
3O ARCHITECTURAL ENGINEERING.
FIG. 7. — The Marquette Building. Holabird & Roche, architects.
SKELETON CONSTRUCTION.
ARCHITECTURAL ENGINEERING.
FIG. 9. — Typical Office Floor Plan of the Reliance Building.
SKELETON CONSTRUCTION. 33
supplied to support the elevator sheaves, and water-tanks
located to supply the hydraulic cylinders.
If the basement, as in Fig. 4, lies below the sewer level,
and it is to be occupied by stores, cafes, or by the boiler-
and engine-rooms, an ejector pit will be necessary to raise
the sewage to the proper level. Pumps for water-supply,
dynamos for electric 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. 10.
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
suspended from the basement ceiling.- The remainder of
the risers, and all drainage from the boiler-room and base-
ment 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, were carried in fire-proof 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 7000
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 2000 to 3800 gallons per minute.
34
ARCHITECTURAL ENGINEERING.
FIG. io.— The Masonic Temple. Burnham & Root, architects.
SKELE TON CONS TR UCTION.
35
Each office and store has a private wash-basin, with gen-
eral toilet-rooms and barber-shop on the nineteenth floor.
The main toilet-room contains 64 closets, besides addi-
tional rooms on the third and twelfth floors and in the base-
ment, with from 8 to 18 closets each.
FIG. ii.— The New York Life Insurance Building. Jenney & Mundie, architects.
Forty thousand square feet of radiation surface are re-
quired, all in direct radiation. The steam is supplied on the
" overhead " system through i6-in. mains running directly
ARCHITECTURAL ENGINEERING.
to the attic, thence around the exterior walls and down.
Six dynamos supply 7000 i6-candle-power lamps. For the
power and steam plant eight horizontal tubular boilers are
used, with a total of 1000 horse-power.
There are several features in the Masonic Temple de-
sign worthy of especial note. Several of the upper floors
FIG. 12. — Banking Floor, New York Life Insurance Building.
are 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 special features in the galleries provided at each
SKELE TON CONS TR UCTION.
37
story for the lower ten floors. This plan was intended to
attract small storekeepers and the like as occupants of the
adjoining stores or offices, thus concentrating many trades-
o <5 /£ reef
FlG. 13.— Typical Office Floor Plan, New York Lhe insurance Building.
men under one roof. The scheme has not proved a success.
The roof of the Masonic Temple is covered by an en-
closure of glass, serving as a summer-garden and place of
observation.
NEW YORK LIFE INSURANCE BUILDING.
A perspective of this building, designed by Jenney &
Mundie, architects, is shown in Fig. n. The lower three
38 ARCHITECTURAL ENGINEERING.
floors are built of granite, with brick and terra-cotta above.
The plan of the first floor, devoted to banking purposes, is
shown in Fig. 12, while the typical office plan is shown in
Fig. 13.
FIG. 14. — The Fort Dearborn Building. Jenney & Mundie, architects.
FORT DEARBORN BUILDING.
This building, shown in Fig. 14, is but just completed.
It was designed by Jenney & Mundie, architects, and a
number of the details used in its construction will be
SKELETON CONSTRUCTION. 39
given later. The typical office floor plan is given in
Fig. 15.
A floor plan of the Champlain Building, Holabird &
Roche, architects, is shown in Fig. 16.
Fig. 17 gives a perspective of the Old Colony Building,
by the same architects.
These examples of floor plans will serve to show the
general arrangement of offices, halls, and entrances in build-
ings very recently erected, and the conditions which deter-
mined the general features of construction will be apparent,
in so far as the plan may affect the locations of the columns,
etc. " The framing plans" must now be worked out, one
for each floor, showing the location of all piers, columns,
girders, beams, etc., in their proper positions, with all the
necessary dimensions and sizes.
Fig. 1 8 shows a framing plan of the third floor of the
Fort Dearborn Building.
Fig. 19 is a framing plan for the sixth, seventh, and
eighth floors of the Reliance Building.
The increased use of structural steel, as indicated in
these framing plans, has found the architects, to a great
extent, unprepared to solve in detail many of the prob-
lems imposed on them. They have been forced, in work
of any magnitude, to turn the details, if not the entire
constructional scheme, into the hands of the engineer,
either as an employe or co-partner. The ignorance which
the average architect displays in connection with struc-
tural iron details is proverbial, and contractors for steel-
work especially have long indulged in considerable sar-
casm at the expense of the architect and his plans.
When, however, this work is intrusted to the engineer, it
becomes a question as to how far the actual work of detail-
ing needs to be carried, after the computations and general
framing plans are made.
ARCHITECTURA L ENGINEERING.
FIG. 15.— Typical Office Floor Plan, Fort Dearborn Building.
SKELE TON CONS TR UCTION.
ARCHITECTURAL ENGINEERING.
FlG. 17. — The Old Colony Building. Holabird & Roche, architects.
SKELETON CONSTRUCTION.
43
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,
L/N£
FIG. 18. — Typical Framing Plan of the Fort Dearborn Building.
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>
44
ARCHITECTURAL ENGINEERING.
leaving the details to be worked out by the contractor with
the approval of the architect.
The trained engineer, however, is not usually satisfied
i --[
FIG. 19. — Typical Framing Plan of the Reliance Building.
with such license on the part of the contractor, and the
best classes of work are made in accordance with definite
details furnished by the engineer, after a careful considera-
SKELETON CONSTRUCTION. 45
tion 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 par-
ticular attention. The balance of the detailing may be
made to suit the contractor, with the approval of the en-
gineer, in conformity with the sizes of material marked on
the plan, and the carefully drawn specifications.
The idea of allowing the manufacturer to prepare com-
plete details after his own general scheme, and following
specifications 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 furnish the
moving-load diagram, and allow the bidders to design the
structure as they saw fit, so long as it fulfilled all require-
ments 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 advantage. Such
a practice, however, in building work will require a very
careful supervision of the work by the engineer, 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
framing plans, sufficient spandrel sections and any special
details, with all sizes and dimensions of material, will insure
46 ARCHITECTURAL ENGINEERING.
rapid and satisfactory work on the part of the iron con-
tractor. The shop drawings may then be examined, and
stamped with the approval of the engineer as received.
ERECTION.
In skeleton construction, the erection of the framework
progresses very rapidly after the material is once delivered
on the ground. All punching and riveting of the members
is done at the shop, leaving only the assembling and field-
riveting to be done on the ground, besides the adjustment
of the laterals. Field-riveting has entirely superseded the
use of bolts in the best class of work. Bolt connections
were tried, but were soon discarded on account of the
cracks which developed in the plastered ceilings, radiating
from the column connections with the floor system. This
was due to the play of the bolts in the holes.
Steam cranes built expressly for the purpose have been
used in some cases in Chicago. They were operated on
tracks which were quickly laid over the floor system, and
these cranes would pull themselves up an incline, from
story to story, as fast as erected. The crane boom and en-
gine platform revolved on a pivot, so that the members
required very little handling. The old-fashioned derricks
or gin-poles are, however, generally used, some contractors
preferring the short gin-pole, erecting one story at a time,
while others use a large boom derrick, setting several
stones in place before shifting the derrick. The erection
of ironwork costs from $6 to $8 per ton.
Two stories can generally be erected in six days of ten
hours each. In the Unity Building of seventeen stories the
metal-work, from the basement columns to the finished
roof, was accomplished in nine weeks.
The following data Avill give a better idea of the ra-
pidity of building operations in Chicago as shown in the
erection of the New York Life Building :
SKELETON CONSTRUCTION. 47
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 lajdng terra-cotta facing.
September 29. All steel set.
November 9. Tile floors all set.
November n. Terra-cotta all set.
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 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 Manhattan 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.
Several gangs of men may frequently be seen at dif-
ferent levels on a single front of a building, and laying
pressed-brick by electric light was even tried on the Ash-
land Block, Chicago, in an endeavor to complete the build-
ing by May i : and the intention was to make up for this
extra expense of night-work by time gained through leases
signed earlier than would otherwise have been possible.
48
ARCHITECTURAL ENGINEERING.
SKELETON CONSTRUCTION.
49
FIG. 21. — The Reliance Building during Construction, August I, 1894.
5O ARCHITECTURAL ENGINEERING.
Figs. 20 and 21 show the Reliance Building during con-
struction.
PERMANENCY OF SKELETON CONSTRUCTION.
Aside from the question of fire resistance, considerable
discussion has arisen of late concerning the permanency of
skeleton construction. This controversy between friends
and indifferent observers of skeleton methods has been
aggravated by the reluctance of the supervising architect
of the Treasury seriously to consider such construction as
worthy the dignity and solidity of government edifices—
notably in the proposed new Post-Office building for
Chicago. While the architectural pros and cons of terra-
cotta and steel, or concrete and steel, versus solid masonry
construction may not here be gone into, the engineering
side of this matter beer nes one of great importance.
Serious as it is, it must still be admitted as depending
largely on personal views, for the want of reliable data
under present conditions. Many 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. The divergence of present
opinion was well shown in a recent 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 condi-
tions. The point would then seem to be to define these
conditions. Prominent Chicago architects and engineers
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 knowl-
edge of wrought iron or steel, therefore, under definite
SKELETON CONSTRUCTION. 5 I
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. Chicago engineers and builders show their
daily faith in such comDinations 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 limestone, as a corrosive factor in connection
with ironwork seem to depend very largely upon the
peculiar conditions 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 pres-
ence 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 foundations, as found in build-
ing practice. Dry air and pure water produce but slight
oxidizing effects on iron or steel ; " but when the former
becomes moist, and the latter impure or acidulated, oxida-
tion of the material is speedily set up, and when once com-
menced, unless the process is arrested, its ultimate destruc-
tion 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 dampness 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 mois-
ture, we have : all exterior walls, piers, etc., and the base
ment members, including foundations. From the foregoing
it would seem that lime mortar should not be used in any
52 ARCHITECTURAL ENGINEERING.
of these positions. 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 penetrating 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 per-
fect conservator of metal-work, and instances are recorded
of iron found in perfect condition after a 4OO-years' entomb-
ment 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 em-
bedded 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
temperature, aad protected from the exterior dampness.
Interior columns, the floor system, and wind bracing
would, therefore^ 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 through-
out. Cement has rapidly cheapened 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 build-
SKELETON CONSTRUCTION. 53
ing work a perfect union between the cement mortar and
metal-work can never be attained at all points, and a
thorough coating of paint must largely be relied upon.
All constructive ironwork should, therefore, be well
coated with either lampblack mixed with oil, or red lead
and linseed-oil. The very best of materials should be em-
ployed. The oxide of iron or mineral paint which has
generally been specified for all painting of the metal-work
has been found to separate from the steel, and form an
oxidation of the metal behind the paint. A mixture of red
lead and linseed-oil is now considered as the best protec-
tive coating for iron or steel. A careful inspection of all
painting, both at the shop and in the field, should be rigidly
enforced.
The following are the requirements of the New' York
building law in regard to the protection of iron or steel
work against rust, etc :
" All ironwork and steelwork used in any building
shall be of the best material and made in the best manner,
and properly painted with oxide of iron and linseed-oil
paint before being placed in position, or coated with some
other equally good preparation or suitably treated for
preservation against rust."
The Chicago ordinance makes no mention of paint or
coatings to prevent rust in the metal framework except as
specified for fire-proofing purposes as follows ; " In all
cases the brick or hollow tile shall be bedded in mortar
close up to tne 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 metal-work in foundations are
given in Chapter XII.
CHAPTER IV.
FLOORS AND FLOOR FRAMING.
THERE is scarce a subject or detail in the present field
of architectural engineering that has provoked such wide-
spread attempts at improvement and perfection as the
question of fire-proof floor systems. The present day is
especially prolific in new patents and systems, all claiming
a complete revolution in existing methods, until both
architect and engineer alike are well-nigh bewildered in
their endeavors to keep track of the novelties that are con-
tinually being presented as the " cheapest and best " solu-
tion of a much-discussed problem.
A proper solution cannot be realized by either architect
or engineer working independently of each other, and per-
fection in present attempts must result from legitimate
criticism on the part of the architect as to the adaptability
of the material to exterior form, as well as from the appli-
cation of the laws of statics as demanded by the engineer.
Before investigating present methods and future prob-
abilities it will be profitable to examine earlier systems,
with their weak points and causes of failure.
The oldest so-called fire-proof arches consisted of I
beams, placed about 5 feet centres, with 4-inch 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 still be seen in
some of the more substantial buildings ot that epoch, which
54
FLOORS AND FLOOR FRAMING.
55
have survived to the present time. This construction 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.
This unsatisfactory and weighty construction, shown in
Figs. 22 and 23, gave way, as has been said, to the superior
FIG. 22.
FIG. 23.
advantages of terra-cotta or tile — superior in fire-resisting
qualities, as well as in greater lightness.
Hollow tile is made from fire-clay, moulded by dies into
the various hollow forms required for commercial use.
The clay is subjected during its manufacture to a high
pressure while in a moist or damp state, which accounts
for its great strength, and after drying is burned, like terra-
cotta, in a kiln.
FIG. 24.
The clay used in the manufacture of fire-proofing ma-
terial must be of a refractory nature — as plastic fire-clay,
semi-fire-clay, or fire-clay mixed with plastic clay or shale.
But few clays have been found that are practicable of
56 ARCHITECTURAL ENGINEERING.
manufacture into a floor of the required strength, and relia-
bility against fire.
TILE ARCHES.
The earlier forms of tile arches were made as in Fig. 24,
which shows the arch used in the Equitable Building in
Chicago (1872), and Fig. 25, which shows tile arch in the
FIG. 25.
Montauk Building, Chicago (1881). The latter may be said
to have been the first building of modern design in Chicago.
The arches were 6 inches deep, with a span of 3 to 4 feet.
But as these forms still left the lower flanges of the I beams
unprotected, they were soon superseded by the type shown
«. $0*-.
FIG. 26.
in Fig. 26. This arch was used in the Home' Insurance
Building, Chicago (1884), the tile being 9 inches deep and
6 foot span. This was the first instance in which the beam
soffits were protected against fire by anything more than
plaster ; and as many of the features in this arch are essen-
tially the same as in the types of tile arches as found in
present practice, a brief description will here be in place.
The pieces form radial joints, as in any segmental arch,
or are key-shaped with a centre " key." The arches are set
on " centres " of plank, hung from the beams by hook-bolts,
and these centres should remain in place at least twenty-
FLOORS AND FLOOR FRAMING.
57
four hours after the arches are set. The " skew-backs,"
or butment pieces of the arch, take the shape of the I beam
against which they bear, setting firmly and squarely on the
beam flanges. Different sized skew-backs are at hand for
use with different sized beams, as arches are often sprung
between beams of different depths. The soffit of the tile
arch extends about one inch below the bottoms of the beams,
and the skew-back pieces are made in such a manner that
a piece of fire-proofing tile may be slipped in and sup-
ported directly underneath the beam flange, to complete
the fire-proofing, as shown in Fig. 26. A coat of plaster
or cement is then given the whole surface, after which it
is read}7 for such decorative treatment as may be desired.
A concrete filling is placed over the arch, to distribute
the load from block to block, and to receive and embed
the wooden nailing-strips which take the finished flooring.
The metal beams are thus entirely surrounded by fire-clay,
concrete, and cement.
The depth of the tile arch depends upon the span, and
the load to be carried. The maximum spans of the various
2 CONCRETE-
TILLING
FIG. 27.
depths are generally furnished by the manufacturer of the
type in question, but such data should be fully established
by adequate tests, as will be pointed out later. Slight
variations in the span from centre to centre of beams are
made by using " half intermediate " tile, and different-sized
keys. The tile blocks are laid with lime mortar or cement
58 ARCHITECTURAL ENGINEERING.
joints, and in no case should the joint exceed \ inch in
thickness.
In many cases, where the panel length required beams
of a considerably greater depth than the tile arch itself,
tile filling-blocks were used, as being lighter than the
ordinary concrete filling — as shown in Fig. 27, taken from
the Woman's Temple, Chicago. Special shapes for skew-
backs, panelled beams, etc., made in this character of tile,
are shown in Figs. 28 and 29.
FIG. 28. FIG. 29.
The best semi-porous tile used in these types was made
from clay found at Chaska, Minn., at Brazil, Ind., and in
parts of eastern New Jersey.
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
a few years ago, known as the " Lee " arch, in which
the voids ran parallel to the line of thrust, or at right
angles to the supporting beams. One of these arches is
shown in Fig. 30, and it will be seen that the effective
area now comprises the vertical webs, as well as the hori-
zontal ribs; in other words, all of the material performs
useful work as an arch. A further improvement was
attempted by the use of a porous terra-cotta, made from
FLOORS AND FLOOR FRAMING. 59
a fire-clay which, before it is burned, is mixed with saw-
dust and finely cut straw. These ingredients are con-
sumed during the firing, leaving the material in a very
porous condition, and thus greatly reducing the dead
i "^i A.... I. £ — / r
FIG. 30.
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 "
15" " 40 "
Another step of progress lay in the skew-back or but-
ment 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.
Some very interesting and valuable tests of fire-proof
floor arches built after the Pioneer and Lee methods were
published in No. 796 of the American Architect and Build-
ing News — undoubtedly forming one of the most satisfac-
tory and extensive series of public tests yet attempted on
such construction. The trials were made in Denver, Col.,
1892, 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. 30,
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 grad-
6O ARCHITECTURAL ENGINEERING.
ually under the increased weights to .065 of a foot, sustain-
ing a final load of 15,145 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' o". The Pioneer arch was shat-
tered at the first blow, while the Lee arch, under the same
test, stood up to the eleventh drop, the former blows shat-
tering but parts of the arch.
In the fire and water tests, three applications of water
combined 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 con-
tinuously 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' o" 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 5' o '
Ibs.
603
•760
Ibs.
1670
1008
Assumed load per square foot as occurring in practice. . . .
l^O
ICQ
Coefficient of safety
2.4
6.7
This certainly shows a great step of advancement for
the Lee arch, but, assuming a factor of safety of 8, as
recommended by Rankme, and a total load of 165 Ibs. per
square foot (85 Ibs. dead + 80 Ibs. live), a uniform break-
ing-load of 1320 Ibs. per square foot is needed before the
tile arch can be considered fully acceptable.
Tests of the 12" blocks of the Empire Fire-proofing
Company might also be mentioned, made in 1891 by the
city engineer of Richmond, Va. A variation in the break-
FLOORS AND FLOOR FRAMING.
6l
ing-load was recorded of from 554 to 1057 H>s. Per square
foot. But it must be remembered that too much impor-
tance must not be placed on these maximum figures. The
average breaking-loads of such tests must be considered a
fair figure at which to judge the general run of arches as
placed in actual use by these companies; and in this light
the room and actual necessity for still further improve-
ment becomes self-evident.
A still later patent known as " Johnson's patent flat
arch," (see Fig. 31), is the one used most extensively in the
FIG. 31.
buildings of late erection. It is made of hard terra-cotta
with thinner webs than were formerly employed, and is of
the " end construction," thus utilizing all of the material as
in the Lee arch. This type seemed to meet with much
favor at first, and it was used in quite a number of
Chicago's best buildings, but experience would seem to
point to the porous tile as being far more satisfactory in
its fire-resisting qualities than the hard tile. A test by
fire and water of a wall of hard tile blocks occurred some
time ago in the rear of the Schiller Theatre Building,
Chicago. The combined action of heat and cold water
caused the blocks to crack to such an extent that they soon
fell from the metal uprights in considerable areas.
Soft tile or porous terra-cotta has been specified for all
fire-proofing work in the latest buildings designed by Mr.
W. L. B. Jenney, notably the New York Life Insurance
and the Fort Dearborn buildings.
62 ARCHITECTURAL ENGINEERING.
Tie-rods are necessary in all these forms of arches, to
take up the horizontal thrusts without dependence on the
adjoining- arches. Such rods are generally f inch diameter,
and spaced from 5 to 7 feet apart. All tests of tile arches
should require the tie-rods to be without initial strain ; for
if the rods be screwed up sufficiently to give an initial
strain equal to the tensile strength of the tile or cement-
ing material between the blocks, then is the tensile
strength of the arch for the breaking-load reduced to o,
and the beam may be reloaded to the same amount.
Reference to the Appendix table giving the principal
points of construction in the notable office buildings in
Chicago will show that either the " Pioneer," " Lee," or
" Johnson's " type of floor arch is used in nearly every
case, although it must be admitted that such a general use
of tile construction is far from being a guarantee of its per-
fection. Indeed, it is no exaggeration to say that there is
scarcely a single material used in constructional work in
regard to which we have as limited a knowledge of its
general or specific properties of resistance as is found in
terra-cotta or tilework ; and yet, in the modern building
the use of this style of floor has become so widely ex-
tended that terra-cotta or hollow tile has become one of the
most ordinary materials of construction. Its functions are
no less positive than those of the structural steelwork or
masonry-work, forming, as it does, the supporting area for
all dead and live loads coming on the floor system — crowds
in halls, theatres, and other places of public gathering, as
well as small safes, desks, and the many articles forming
concentrated loads.
Any failure in the hollow tile would be apt to result
in quite as great disaster or loss of life and limb as would
proceed from any failure in the iron or steel skeleton. It
is apparent, therefore, that the sustaining power of hoi-
FLOORS AND FLOOR FRAMING. 63
low-tile work should be absolutely definite, and that its use
should be governed by well-defined tests, or rules based
on such tests.
Some attempts on the part of the writer to secure reli-
able facts pertaining to tests on some of the newer tile
floor arches in almost daily use. developed the fact that
the fire-proofing companies had no data " in shape to be
made public," although the very types of arches about
which information was asked, had already been used in a
number of prominent buildings. This leads to the opinion
that architects and owners are too free in accepting the
alleged results of tests, or in accepting some general style
of arch because it has been used elsewhere. When iron
and steel specifications require severe tests from the fin-
ished material, representing each blow or cast, it would
hardly seem more unreasonable to require actual tests for
the style of arch used before accepting such arches for any
particular building. It is only by such repeated tests, and
competition based on actual results in each instance, that
the most economical designs for floors can be obtained,
consistent with good engineering principles ; and it is cer-
tain that such tests and open competitions would lead to
better quality, if not to better forms and details. Both
concentrated and uniform loads should be considered, as
occurring in actual circumstances.
The most satisfactory set of public tests on tile arches,
in which quality and not price has determined the award
of the contract, were those made for the Equitable Life In-
surance Building in Denver, Col., already referred to. A
load of 1008 Ibs. per square foot equally distributed was
carried in this instance, and though even higher figures are
claimed for later patent arches, the prime consideration of
price in the usual letting of contracts will soon tempt the
less reliable fire-proofing companies either to juggle their
64 ARCHITECTURAL ENGINEERING.
figures into deceiving records of tests, as is often done, or
to furnish poorer and poorer material as competition in-
creases and searching inquiry decreases.
Rankine advises the use of % to \ the ultimate strength
in metals, \ to -^ in wood, and \ to \ in masonry. Consider-
ing hollow tile as coming under the head of the poorest
class of masonry, an ultimate strength should therefore be
required of eight times the allowable stress, if it is wished
to procure uniform safety in a floor of steel beams and tile
arches. Assuming an arch carrying a live load of 80 Ibs.
per square foot, a dead load of 85 Ibs. per square foot (or 165
Ibs. total), the manufacturer should be required to show by
tests on the site that the type submitted is able safely to
stand a load of 1320 Ibs. per square foot, and this before
being allowed to compete in the question of cost. The
writer is aware of the objections of time and cost to such
methods, but in this way only can the excellence be main-
tained, and assurance be provided that the floor arch is
what it should be.
The unusual interest which is being displayed in the
subject of fire-proof floors, of tile and other materials, is
evidenced by the series of articles but lately begun in a
periodical devoted to the interests of the clay products.
This series of articles contemplates a complete record, as
far as possible, of all tests on fire-proof arches of ordinary
patterns, up to present date, with comments on the causes
of failure and possibilities of improvement. Such work
cannot fail to be productive of the most beneficial results.
The writer believes that the section devoted to the arch-
like action in present tile floors is still too small. This is
indicated by the sudden collapse of many arches at the
haunches while under test. It would also seem, through
past tests, that too much reliance has been placed in the
use of strong cementing materials between the blocks, thus
FLOORS AND FLOOR FRAMING. 65,
making the arch act as a monolithic piece. Hollow tile
blocks, as used in present forms of arches, cannot be con-
sidered as a beam, even with the best of cement joints.
They must still form a flat arch, whose line of resistance
must be determined precisely the same as in any segmental
arch. The fact that the arch blocks are of a uniform depth
cannot in any way change the mechanical conditions under
which the loads and supporting forces act.
Present types of tile arches do not admit of a proper
calculation of their dimensions according to the loads for
which they are designed ; the horizontal bearing-ribs are
still relied upon to help make up the required section, and
the height of the section as well as the thickness of the
tile webs, under different spans and loads, is left entirely
to the option of the manufacturer. None of the building
laws prescribe any conditions for the proper calculation of
floor arches under varying spans and loads, except to
define a minimum depth of arch blocks.
The depth of the tile arch should be nearly equal to the
depth of the supporting I beams, in order to secure the
most economical results, for this arrangement will be the
cheapest in the cost of the floor per square foot, consider-
ing tile and concrete filling, and the lightest, considering
the dead load.
An arch has been patented as shown in Fig. 32, but it is
evident that the concrete or cinder filling at the haunches
•
FIG. 32.
will cause the arch to weigh more than if the tile blocks
extended up to the tops of the beams ; while the mere fact
66 ARCHITECTURAL ENGINEERING.
of the arch being made with a segmental top adds nothing
to the strength.
CONCRETE ARCHES.
As has been stated before, the widespread interest dis-
played in the subject of fire-proof floors is indicated by the
numerous types which have entered the field in competi-
tion with the hollow-tile flooring. It is certainly no diffi-
cult problem to design and construct a floor which will be
of sufficient strength and of satisfactory fire-resisting proper-
ties out of fire-clay, cement, or concrete. But when the
elements of minimum cost and minimum weight must be
considered with maximum efficiency, the solution is not so
apparent.
Up to the present day fire-proof floors have been enor-
mously heavy, consisting largely of dead weight in the
most literal sense of the word. Such weights add greatly
to the cost of a building, and yet serve to little or no pur-
pose in strengthening or stiffening the structure. Hence
the endeavor to provide a substitute for the hollow-tile
floor which shall yield an increase in unit strength, and
thus decrease the dead weight and consequent cost.
A variety of combinations of iron or steel and concrete
as applied to floorings has lately been employed, and
would seem to possess features of great merit and of wide-
spread application. Floors constructed of concrete and
steel, with the latter thoroughly protected against corro-
sion, would certainly possess the great advantages of in-
combustibility and durability. It has long been claimed
that the unequal rates of expansion and contraction of iron
and concrete or cement under thermic changes would soon
destroy such a combination, but experiments have been
made which show that these rates are so nearly the same
that they may properly be considered identical. The re-
FLOORS AND FLOOR FRAMING.
67
cent tests of such flooring at Trenton, N. J. (see Engineering
Record, December 22, 1894), would also seem to point to
the successful fire endurance of such combinations.
The weakest points against fire would appear to be the
thin coating of cement plaster directly underneath the
beam flanges, where a stream of cold water applied to the
highly heated cement would probably cause it to crack off,
and leave the metal-work exposed.
It is of great importance to ascertain these points by
means of actual tests before final adoption, the same as
in the case of tile arches ; while the most judicious form of
the metal-work, and the shape and character of the moulded
concrete to develop the. maximum resistance with the least
weight, must also be determined by repeated tests.
The different character of the metal-work in combina-
tion with the concrete, presents three varieties : floors
using curved I beams, those using steel straps, and those
using wires.
i. Curved I Beams. — This system, shown in Figs. 33 and
34, is called the Melan system, from the inventor, J. Melan,
/•CONCRETE
. rp
vPILLIING
FIG. 33.
FIG. 34.
who has constructed many bridges of this type in Europe.
It consists of bent I beams, spaced about 5 ft. centres, with
68 ARCHITECTURAL ENGINEERING.
concrete body or slabs between. A filling of cinders or
other light material is then used to level up the surface
and receive the nailing-strips, as in other floors. A great
saving in dead weight and cost is claimed for this system,
but it still possesses great disadvantages which, in the
opinion of the writer, will seriously restrict its use.
The concrete must perform a twofold duty. It helps
to take up the compression of the arch, and at the same
time must act as a beam between the curved ribs. The
fibres are then brought under maximum strain in two direc-
tions, and if we adhere to the usage of allowing no cement
in tension, this combination becomes poor engineering
practice.
In most cases where appearances are considered, a sus-
pended ceiling will be necessary. Tenants and owners
desire a ceiling of unbroken plane, for the sake of light as
well as appearance. If such a suspended ceiling is to be of
fire-proof construction, it will necessarily add materially to
the weight and cost ; or, if it is not of fire-proof material, a
large amount of combustible material is added in a very
dangerous position.
Exposed tie-rods are necessary, unless a suspended ceil-
ing be used.
The workmanship must be of the most careful charac-
ter, to insure the proper results from these concrete beams.
2. Concrete and Steel Straps. — Concrete floors in com-
bination with steel straps have been used in the follow-
ing buildings : Drexel Institute, American Philosophical
Society Building, and Academy of Natural Sciences, in
Philadelphia, and in the Alumni Building of Rensselaer
Polytechnic Institute at Troy. This form of flooring,
shown in Fig. 35, consists of I-beam girders spaced
S' o" to 1 8' o" centres as may be required, between
which are hung steel straps at intervals of from 12" to 24",
FLOORS AND FLOOR FRAMING.
69
with their ends bent or hooked over the top flanges of the
girders. The straps curve downward, and midway in their
length hang close to the ceiling-line. A concrete or
jSigp^p^p^l^
FIG. 35-
cement filling is used, embedding the straps and girders.
If the beams are of considerable depth, the soffit of the
arch may show the panelled beams, as in Fig. 36. The
FIG. 36.
upper layer of cement may be laid in colored geometrical
patterns, or, if a wood floor is used, this upper layer of cement
is made but i" in thickness, with nailing-strips embedded.
The following table gives data from two of the build-
ings before mentioned :
Centre to
Thickness
Building.
Span.
Straps.
Centre
of Straps.
of
Concrete.
Assumed Load.
American Philosophical J
Society Building ")
8'
1 6'
16'
1" x |"
2^ ' x r
2 " x r
24"
24"
12"
$
8"
80 Ibs. live load.
80 " " "
210 " total "
Academy Natural Sciences
18'
H" x f"
18"
8"
100 " live "
3. Concrete Floors with Twisted Wires or Rods (see Fig. 36).
— This method is very similar to the previous type, except
that wires are used instead of straps. The wires are
secured to the beams by means of hooks, 3" long, made of
ARCHITECTURAL ENGINEERING.
y square iron. The wires are of twisted double strand,
No. 12 gauge, with a length of gas-pipe laid on them at the
centre of the span to give them a uniform sag. The filling
consists of five parts by weight of plaster of Paris, and one
part of wood shavings, mixed with sufficient water to bring
the mass to the consistency of a thin paste. This filling is
laid on a level centering, as in the previous type. The dis-
tance between the wires is varied, according to the load
to be provided for.
Where a flat ceiling surface is desired, this type is modi-
fied, as shown in Fig. 37. The floor-plate is constructed on
VFLAT5
FIG. 37.
wires as before, while the ceiling-plate is made of the same
composition, but with flat bars embedded therein, resting
on the lower flanges of the I beams.
Tests of this flooring under static loads have been made
as follows :
Distance
between
Beams,
Centre to
Centre.
Clear
Span be-
tween
Flanges.
Length
of
Section
Tested.
Area
Tested,
Square
Feet.
Total
Load in
Lbs.
Load
per
Sq Ft.
in Lbs.
Remarks.
4' 7"
4'2"
i' o"
4.166
5,630
1,351
Did not fail. Test made
in building under con-
tract.
5' 5"
5'o"
o' 9i"
3.958
7,600
1,920
Two cables on one side
broke, others u n -
broken.
4' 6"
4' or
2' 6"
10.105
15,682
1,551
Failed by breaking of
cables on one side.
4'6"
4( or
5' or
20.38
29.314
1,438
Adjoining sections, be-
ing without load, lifted.
No wires broken.
FLOORS AND FLOOR FRAMING. 71
The fire and water tests also proved very satisfactory ;
indeed, plaster of Paris or gypsum has been used in Europe
for many years as a fire-proof material.
The greatest objections to these arches lie in the dis-
coloration of the plastered ceiling, due to the rusting of
the wires, and the excessive amount of water retained for a
long time by the sawdust. Galvanized wires should be
used, and some material substituted for the sawdust.
Another form of concrete arch which has been used in
California (see Engineering Record, March 24, 1894) depends
-7-4"
T
on twisted iron rods ij" X ij" for support (see Fig. 38),
The concrete arches are f 4" centre to centre of columns
without the aid of any metal-work. The columns are
placed 25' o" centres longitudinally, with 4 twisted rods act-
ing as supports between. The concrete slabs are joined by
a lap joint, with a lead strip embedded to prevent the pas-
sage of water. This type was tested to 390 Ibs. per square
foot. The arches deflected £" at the centre and remained
uninjured. Such construction is hardly applicable to office
buildings on account of the curved soffit, and small trans-
verse space between columns, but modifications of this
form would seem to offer many advantages in roof con-
struction.
72 ARCHITECTURAL ENGINEERING.
SEGMENTAL ARCHES OF TILE.
For long spans in buildings where a flat ceiling is not
necessary, as in warehouses, etc., a segmentalarch is often
used, following the curve of pressure, as shown in Fig. 39.
FIG. 39.
The tie-rods, spaced equally, are encased in tile to give a
panelled effect. The arch shown in Fig. 40 was used with
FIG. 40.
extra heavy tiles in the Sibley Warehouse, Chicago.* The
use of such segmental arches for office buildings has been
abandoned after a trial in the Rand-McNally Building,
Chicago. A ceiling of flat tile was there suspended under
a segmental arch, but it did not prove successful, and has
not since been used.
The floor of N. Poulson also deserves special notice,
but the use of these particular arches seems somewhat
limited up to the present time to public buildings, libraries,
etc., where the groined arch is more suitable than in office
structures. There is no example of the Poulson arch in
Chicago, to the writer's knowledge. The system may be
described as follows : The total floor-space is divided into
panels of about 25' each way by the columns, with con-
~p
* Tests at Washington, D. C., March 26, 1894, on a segmental arch 15' 4"
span, -fa" rise, and using blocks 8" at the haunches and 6" at the centre, de-
veloped a safe capacity of 1000 Ibs. per square foot of bearing surface.
FLOORS AND FLOOR FRAMING. 73
necting lattice girders. These panels are spanned by a
system of arched flats, generally 3"x i " , with a rise of
1 8". The thrust of the arches is taken up by an octagonal
frame of angle irons in each panel. All arch intersections
are bolted. . These flats are built into the lower parts of
concrete beams, which carry the floor on their upper
edges, and curved .plaster soffits on the under sides, form-
ing the ceiling ribs. A rubber bag, held up by an umbrella
scaffold, is pressed up into the triangular space formed by
the intersecting ribs, and a plaster of Paris or cement soffit
is formed with the curved bag for support. Heavy steel
wires are then stretched over the system, which wires, in
turn, support galvanized wire cloth. A 3" cement filling is
then placed on top to hold the nailing-strips.
"GUASTAVINO" ARCH.
The peculiar strength of the egg-shell, or of any con-
tinuous layer of material, flat, curved, or dished, like the
buckle-plate for example, undoubtedly suggested the form
of the Guastavino arch. Arch or dome shells are built of
small rectangular tiles of hard terra-cotta, three or four
layers being used, of \" thickness each, laid together in
either square or herring-bone bond. Portland cement is
used for the joints and between the concentric layers or
shells. The great strength of these arches lies in the fact
that they follow closely the curve of pressure, thus avoid-
ing tension in the voussoirs, and in the fact that the suc-
cessive layers break joint so perfectly that to open any
joint several tiles must be sheared off. The great dis-
advantage in the use of this type in mercantile or office
buildings lies in the curved soffit, and the necessary use
of exposed tie-rods where several spans occur side by side.
In solid masonry construction, as in libraries, public build-
ings, etc., where the walls or piers are capable of resisting
ARCHITECTURAL ENGINEERING.
the horizontal thrusts, and where a curved soffit is in
keeping, this type possesses great advantages.
It will be noticed that little has been said as regards
the comparative cost of the types of flooring here men-
tioned. This question will undoubtedly serve as a prime
factor in making a choice between the various methods,
but, as stated before, the question of expense should be
held entirely subservient to that of safety, both present and
future. Two different types of floor construction, with a
considerable variance in the ultimate capacity, cannot prop-
erly be compared in the question of cost. If all methods
meet the maximum requirements, the conditions are equal,
and the cost may be considered as the determining factor.
The following table gives the comparative costs of the hol-
low-tile and Melan floors.*
Material.
Hollow-tile Floor
(see Fig. 30).
Total load = 150
Ibs. per sq. ft.
Melan.
Total load = 150 Ibs. per sq. ft.
6' 8" Span
(see Fig. 33).
20' Span
(see Fig. 34).
Beams, connections, tie-rods,
etc
Cts.
j 11.44 Ibs. ®
I 3 c. = 34.3
Cts.
I 10.12 Ibs. ©
I 3 c. = 30.4
1.8 Ib. @3ic. = 6.3
14
16 " @ 2 c. = 32
6
92.7
Cts.
j 4.95 Ibs. ®
\ 3 c. = 14.9
2.25lbs.@3*c.= 7.9
20
13 " @.2C.= 26
75-8
Arching
26
2
16" @,2 C. = 32
Depth
Cost, cents per sq. ft
94-3
CHICAGO BUILDING LAWS— FLOOR ARCHES.
The following requirements are specified in the Chicago
building ordinance, Section 117 : " The filling between the
individual iron or steel beams supporting the floors of
fire-proof buildings shall be made of brick arches, or con-
crete arches, or hollow-tile arches, or Spanish tile arches.
Brick arches shall not be less than 4 inches thick, and shall
have a rise of at least i^ inches to each foot of span between
the beams. If the span of such arches is more than 5 feet,
the thickness of the same shall not be less than 8 inches. If
* See Transactions Am. Soc. Civil Engineers, vol. xxxi. No. 4.
FLOORS AND FLOOR FRAMING. 75
hollow-tile arches having a straight soffit are used, the
thickness of such arches shall not be less than at the rate of
\\ inches per each foot of span. If Spanish tile arches are
used, they are to be made as per the published formulas of
the Guastavino Construction Company, subject to the verifi-
cation and approval of the Commissioner of Buildings. If
concrete arches are used, the concrete in the same shall not
be strained more than 100 pounds per square inch, if the
concrete is made of crushed stone, nor more than 50 pounds
per square inch, 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 cover-
ing of beams and girders."
Again, Section 88 : " 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 i^ inches for each foot of span. The arches must be
so constructed that the joints of the same point to a com-
mon centre ; the butts of the arches shall be carefully fitted
to the beams supporting them ; and there shall be a cross-
rib for every 6 inches or fractional part thereof in
height ; and in addition to these there shall also be diag-
onal ribs in the butts. Floor arches made in the form of a
segment of a circle or ellipsis must be constructed upon the
same principles, but in such cases the individual voussoirs
forming the arch shall not be less in height than one thir-
tieth of the span of the arch. Such arches, whether flat or
curved, shall have their beds well filled with mortar, and the
centres shall not be struck until the mortar has been set."
Before leaving the subject of fire-proof floors it will be
well to mention the test of hollow-tile arches provided in
the case of the Chicago Athletic Club Building, before
76 ARCHITECTURAL ENGINEERING.
mentioned. The steel beams where not fire-proofed were
badly bent where the ends were not held, but the metal
portions were in perfect condition where the fire-proofing
remained intact. Not a single floor arch fell, and " tests
since made on the worst-looking ones have developed a
sustaining capacity of 450 Ibs. per square foot without
sign of rupture."
The arches treated of in this article, as affecting the
method of design of the floor-beams, girders, and columns,
are the ordinary tile arches — be they of the older Pioneer
construction, the Lee form, or the newer arches similar to
the Johnson type.
FLOOR LOADS.
Before considering the most economical arrangement
of floor-beams, the question of loads, which will largely
govern the design of the floor system, must be examined.
The loads in building construction may be classified as
dead, live, wind, and eccentric loads. These will all be
considered in their proper places in these pages. The prin-
cipal loads affecting the floor system are :
Dead Loads, comprising all of the static loads due to the
constructive parts of the building, stationary machinery,
water-tanks, and any other permanent loads.
Live Loads, comprising the people in the building, office
furniture, movable stocks of goods, small safes (large safes
require special provision), or varying loads of any character.
The maximum live load per square foot is usually as-
sumed as follows:
For crowd of people 80 Ibs.
For floors of houses 40 "
For theatres and churches 80 "
For ball-rooms or drill-halls 90 "
For warehouses, etc from 250 " up.
For factories 200 to 450 Ibs.
FLOORS AND FLOOR FRAMING. 77
While 80 Ibs. is the maximum possible live load per
square foot from a crowd of people (unless dancing be con-
sidered), 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, per-
haps, 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.
Prof. Baker, in his " Treatise on Masonry Construction,"
gives 10 Ibs. per sq. ft. movable load for dwellings, 20 Ibs.
for large office buildings, 100 Ibs. for churches, theatres,
etc., and from 100 to 400 Ibs. for stores, warehouses, and
factories, according to contents.
A 2O-lb. unit load in office buildings, as recommended
by Prof. Baker, might be seriously questioned, and late
experiments in this direction would seem to sustain the
criticism. While 20 Ibs. per square foot may be amply suf-
ficient 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 ex-
tremes, either present or future. An article in the Ameri-
can Architect, August 26, 1893, gives the results of some
experiments 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 con-
sidered 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 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
7$ ARCHITECTURAL ENGINEERING.
and 16.2 Ibs. for the Adams Building. The greatest moving
load in any one office in the three buildings 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 circum-
stances, 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 foun-
dations, as well as on the columns of the lower stories."
With a proper provision, then, for maximum loads in
the floor system, the 20 Ibs. recommended by Prof. Baker
is not enough, though safe, perhaps, for an average. But, as
remarked before, the use of averages is dangerous, and it be-
comes a very nice problem to balance present economy with
maximum present requirements or future possibilities ; for
the present weight per square foot may not safely be taken
as the maximum occurring during the life of the building.
The municipal laws of New York and Boston provide for
a moving load of 100 Ibs. per sq. ft., while those of Chicago
require 70 Ibs. live load per. sq. ft. on the floor system, with
proper reductions for the columns and footings. With a
proper regard for economy 100 Ibs. per sq. ft. would cer-
tainly seem too large ; So Ibs. for the lower and busier floors,
and 40 Ibs. for the upper or office floors, are certainly safe,
and good averages, considered in all lights. These loads,
used in all calculations affecting the metal framing, must
not be confounded with the required loads for the strength
of the individual tile arches. While the live load per
square foot may be reduced over large areas in proportion-
ing the metal-work, the maximum possible live load must
FLOORS AND FLOOR FRAMING. 79
still be used when any single floor arch is considered by
itself, or subjected to tests to determine its strength. Some
further data on live loads are given later under a discussion
of the building laws of New York, Boston, and Chicago.
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
The practice in Chicago seems to be pretty well denned
in the matter of decrease of live loads per sq. ft., as they
are transferred from beams to girders, from girders to
columns, and thence down the columns to the footings.
This practice is founded on the supposition that it is quite
possible that the beams may sometime have to carry their
full capacity in live loads, while the chances are increas-
ingly 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 struc-
ture, is also gradually lessened, as the vibration is taken up
in the transfer of the load from member to member, so that
by the time it reaches the footings or foundations 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.
In the Venetian Building in Chicago the beams were
calculated for the following live loads :
8o
ARCHITECTURAL ENGINEERING.
Upper floors 35 Ibs.
Second, third, and fourth floors 60 "
First floor 80 "
Girders carry 80 per cent, columns 50 per cent.
The dead loads to be considered in the floor system in-
clude 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 sq. ft. of floor surface. This is abso-
lutely necessary in regard to partitions in office buildings,
as they are constantly being changed to suit the conven-
ience 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, 1-inch maple 4 Ibs.
Deadening 9 "
1 5-inch tile arch 45 "
Iron 12 "
Plaster 5 "
Partitions, 3-inch mackolite 20 "
Total 95 Ibs. dead load.
We have, therefore, for live and dead loads as follows :
Beams.
Girders.
Columns.
Footings.
Offices •
Ljve
8*
65
45
Dead
QX
OS
95
95
Total . .
180
160
140
95
Store floors : Live. ....
95
75
55
Dead
95
95
95
95
Total...
190
170
150
95
FLOORS AND FLOOR FRAMING.
8r
The dead loads assumed in the Old Colony Building,
Chicago (1893), comprised :
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 160 140 130 90
The floors for the Fort Dearborn Building were calcu-
lated in accordance with the following data :
Dead Load
Live Load.
Beams.
Girders.
Beams.
Girders.
1st floor
85
75
40
140
50
85
75
40
140
50
50
125
70
40
200
2OO
40
70
IIO
60
40
1 80
1 80
40
60
2<i to 1 3th floors .
Roof . . .
Skvliffht
Stairs
50
The live load on the beams from the second to thir-
teenth floor inclusive was taken at 70 Ibs. per sq. ft., and
an additional 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.
The girders were figured for partition loads at 20 Ibs.
82
ARCHITECTURAL ENGINEERING.
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
4O
I3th floor
• L^\J
50
40
40
1 2th
45
85
nth
41
126
loth
35
161
gth
3i
192
8ih
25
217
7ih
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 fol-
lows, a 9" porous end-construction arch having been used :
9" arch 26 Ibs. per sq. ft.
9" 2i-lb. I beams 4 " " " "
6 to i cinder concrete 30 ". " " "
Mosaic and wood floors, average.. 10 " " " "
Plaster 6 " " " "
Total 76 " " " "
FLOOR FRAMING— BEAMS.
The distance centre to centre of the floor-beams must
be determined with reference to the type of floor arch
used. Ordinary practice in Chicago skeleton construction
has made from 5 to 6 feet the usual span for tile arches, in
FLOORS AND FLOOR FRAMING. 83
panels 01 ordinary lengths ; but in cases where the columns
are spaced a considerable distance apart the floor-beams are
placed nearer together. Reference to Figs. 18 and 19 will
show the practice in beam-spacing in late examples of
skeleton buildings in Chicago.
The most economical arrangement of floor-beams has
had little investigation, and there seems to be no uni-
formity 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 ex-
ample, a framing plan calling for a bending moment in a
floor-beam of 65,000 foot-pounds. This would require a
moment of resistance of 48.72, The moment of resistance
for a 12" 4o-lb. beam is only 46.9, while R for a 15" 4i-lb.
beam is 56.6. The latter would have to be used, with an
excess in strength of some 16 per cent; and if such panels
occurred frequently in a floor system, an excess of 16 per
cent would therefore occur throughout. Hence an eco-
nomical 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.
Again, it is seldom economical to use the heaviest
weight of any depth of beam, if a deeper beam can be used.
There is necessarily 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 moment of resistance for a 12"
32-lb. beam is 37, while the 10" 33-lb. beam has R — 32.3.
The former is lighter, and far stronger. A 20" 64-lb. beam
is also stronger than a 15" 80 Ib. beam.
84 ARCHITECTURAL ENGINEERING.
The coefficient for a 15" 5o-lb. beam is 753,000.
" " 15" ss-lb. " " 792,000.
" " i5"6o-lb. " " 916,300.
Hence the use of a 15" 55-lb. beam is not economical, as the
coefficient does not vary between the 50- and 6o-lb. limits
in proportion to the weight. For a uniformly distributed
load these coefficients are obtained by multiplying the
load, in pounds uniformly distributed, by the span length
in feet. If the load be concentrated at the centre of the
span, multiply the load by 2, and then consider it as uni-
formly distributed. The maximum coefficients of strength
for I beams of different depths and weights are usually
given in the pocket companions issued by the various steel
companies. The handbook of Carnegie, Phipps & Co. is
generally used by architects and engineers. In that book
the maximum permissible coefficients are given for all of
the ordinary rolled shapes, on a basis of 16,000 Ibs. per
square inch fibre strain, and also on a basis of 12,500 Ibs.
per square inch fibre strain. The former is generally used
in building work.
The distribution of the material in the cross-section
affects the moment of inertia, and hence R. The sections
from some mills will be found better than those from
others in this respect.
Care must be taken in figuring floor-beams to see that
the length of clear span is not too great, giving a deflection
sufficient to crack the plaster ceiling beneath. A deflec-
tion of about ffa of the clear span, or -fa of an inch per
foot, has been found by experiment and practice to be the
maximum permissible deflection — or d — L X 0.33, where
d = greatest allowable deflection in inches, at centre of
beam, and L — length of span in feet. This safe deflection
limit is also indicated for each size and weight of beam
FLOORS AND FLOOR FRAMING. 85
given in the tables for uniformly loaded I beams in the
handbook of Carnegie, Phipps & Co.
Lateral stiffness may also need consideration in some
cases. Where the floor-beams are of the same depth as the
girders, "coping" is necessary, or a cutting away of the
ends of the floor-beams to fit against the flanges of the
girders. About -J inch clearance is usually allowed be-
tween floor-beams and girders, and \ inch between columns
and girders. This is sufficient for easy erection.
The standard connection-angles manufactured by Car-
negie, Phipps & Co. are generally used whenever prac-
ticable, as connections between floor-beams and girders.
These connection-angles are given for the various depths
and weights of steel and iron beams in the handbook.
They are designed on a basis of 10,000 Ibs. allowable
shearing-strain, and 20,000 Ibs. bearing on rivets or bolts
per square inch, and are usually of sufficient strength for
regular details as found in practice. The adoption of such
FIG. 41.
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 element of weakness. From careful observation of
building methods as practiced in Chicago, the writer is
convinced that faulty details constitute an even greater
part of the defects in the general run of buildings, than
86 ARCHITECTURAL ENGINEERING.
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.
H_°LE5
I . •*!*•
3T/}NDARD CONNECTION L.
r°R
FIG. 42. »
Figs. 41 and 42 show standard connection-angles for the
beams as given.
GIRDERS.
The girders, running from column to column, support the
floor-beams, and transfer their loads directly to the columns.
As before mentioned, it is often necessary to use two I beams
side by side as a girder, or even plate or latticed girders
in longer spans or under special loads. Separators should
always be used in the case of double beams, in order to
equalize the loads on the two beams, and also to act as
spacers, keeping them a proper distance apart. Carnegie's
separators are generally taken as standard.
It is quite impracticable to make any comparisons as to
the relative economy of short spans for girders with many
columns, and fewer columns with longer girders. Both
types are to be found in Chicago, even to extremes, but
they are usually the results of conditions, rather than at-
tempts at economy. The conditions governing the design
of any particular building are usually so potent that the rule
in one case might prove the exception in the next. The
arrangement of the exterior piers, the architectural effect
striven for, the arrangement and proper planning of the
FLOORS AND FLOOR FRAMING. 8?
interior for the uses intended, all govern, in a great meas-
ure, the placing of the supporting columns, and hence the
girder lengths. Thus in Fig. 18, showing the framing plan
of the new Fort Dearborn Building, two Q-inch beams or two
lo-inch beams are generally used as girders, while in Fig. 19,
of the Reliance Building, single beams are used as girders
in all cases. In the Woman's Temple, Chicago, Burnham
£ Root, architects, the floor-beams are nearly all 30 feet
long, and the girders likewise, i5-in. I beams having been
used throughout ; while in the new Marshall Field Build-
ing, by the same architects, a 2o-foot panel was used.
In office buildings the panels are often made of such
dimensions as to give two suitable office widths from centre
to centre of piers. Thus the practice of Holabird & Roche,
architects, is to space the exterior and interior columns 23
feet centres where possible, making two offices of n ft.
6 in. in each bay (see Fig. 16).
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, re-
sulting in a much greater bend-
ing moment. If but two beams
are used, 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 ar-
ranged as to be flush on the under FIG. 43.
sides, as shown in Fig. 43. This is to provide for the
plastered ceiling. The inequalities in the arch depths are
made up in the concrete filling.
CHAPTER V.
EXTERIOR WALLS—PIERS.
THE subject of the exterior piers which carry their
tributary floor and roof loads, besides the weight of the
walls themselves, is capable of three separate treatments,
each of which is used under its own peculiar circumstances.
First. Where the outside piers are constructed entirely
of masonry, carrying all of the wall-, floor-v and roof-loads
which come on them, by means of masonry alone. Such
construction is used in buildings of moderate height, and
constitutes the ordinary type of building. But in the
higher structures of from sixteen to twenty stories, which
are here being considered in particular, it is the rare excep-
tion, at the present time, to rely entirely on masonry piers.
The objections to such piers of solid masonry are three-
fold :
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 Chicago and elsewhere, in which the ex-
terior walls carry their proper share of all loads ; but a
little observation will show that in high buildings of this
type the comforts of the tenants have, in a large measure,
been sacrificed for architectural effect.
b. The second objection to such large masonry piers is
EXTERIOR WALLS— PIERS. 89
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 the clay or foundations that
many of the most remarkable examples of architectural
engineering would be well-nigh impossible.
In the new Marshall Field Building in Chicago, masonry
piers were used to carry all exterior loads, but a mercan-
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.
Second. The second treatment of which the exterior
piers are capable is that in which metal columns, carrying
the tributary floor and roof loads, are placed inside the
masonry piers, while the latter support themselves 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 much
faster than will the metal columns under the gradual settle-
ment of the whole structure. As an example of initial com-
pression in freshly laid mortar, Mr. Geo. B. Post, archi-
tect of the New York Produce Exchange building, states
that a measured height of 9' 6" at the time of building,
compressed about J" under a maximum pressure of 62 Ibs.
per square inch of base, induced by the finished wall. The
whole wall was built very rapidly.
9O ARCHITECTURAL ENGINEERING.
If, then, the masonry bears on rivet-heads, plates, or
connections on the columns, a heavy strain is produced
which has not been provided for. Great care is necessary
in such combinations 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. This was the case in the
old portion of the Washington Monument.
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 maxi-
mum allowable pressure of 12 tons per square foot on brick-
work, as used by the engineer, would be reached at the
level of the fifth floor ; hence below that level the load ex-
ceeded 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 ex-
pedient 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 con-
sist of three separate columns cf masonry, and the one
continuous metal column.
Third. The third method of constructing the exterior
piers is the one more approved at the present stage of
architectural engineering — 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
EXTERIOR WALLS— PIERS. 91
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 fast and remarkably during the
past ten years of Western architecture, while the height of
municipal buildings has been increasing steadily from ten
to twenty stories. The increasing value of ground-space,
the demands for rapid construction, and the necessity for
the lightest possible loads on the subsoil, have all con-
tributed to the success of this type.
Chicago 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
brickwoik, enclosing the steel columns and filling the span-
drels 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 build-
ing construction, now fulfils simply a decorative and pro-
tective function. The great possibility 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
special 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 architectural and protective wrapper of terra-cotta,
tile, or brickwork, inside and outside. The terra-cotta
92 ARCHITECTURAL ENGINEERING.
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 wires or clamps to the concealed beams- or
girders which really support the loads.
Brick and terra-cotta are generally preferred to other
building materials for the exterior walls of a tali building,
on account of the ease with which they may be handled
as well as for the facility with which they may be built
into and about the forms of beams and columns. Stone
has gradually been driven from the field of skeleton con-
struction in exterior walls, except as used in the lower
stories only, as a base for the superimposed brick or terra-
cotta work. This has been due to the difficulty experi-
enced in properly attaching the masses of stone to the
metal framework. Stone has also 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 en-
closed in ornamental frames or grilles of metal-work sur-
rounding the columns, as shown in lower part of Fig. 44.
Fig. 45 shows the girder over the main entrance to the
Masonic Temple.
In order to render the exterior impervious to moisture,
and thus protect the metal framing against corrosion, only
the very hardest and most thoroughly burned brick should
be used. Portland cement mortar is also specified in the
best classes of work, with well-filled joints and careful
bonding and anchoring. In other words, less is now re-
quired of the brick wall as a supporting member than
formerly, when the walls fulfilled the function of bearing
dead loads only ; but much more is now demanded of it as
to quality and perfection of workmanship, and hence a
better constructed and more thoroughly knit wall has re-
sulted in the best examples of Chicago construction.
The Chicago building ordinance defines skeleton con-
EXTERIOR WALLS— PIERS.
93
FIG. 44.— Detajl of Terra Cotta, Reliance Building.
94
ARCHITECTURAL ENGINEERING.
struction as follows : " The term ' skeleton construction '
shall apply to all buildings wherein all external and internal
loads and strains are transmitted from the top of the build-
ing to the foundations by a skeleton or framework of metal.
In such framework the beams and girders shall be riveted
SJ.X
_^r±....L
FIG. 45. — Section over Main Entrance, Masonic Temple.
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 connections to unite
EXTERIOR WALLS— PIERS. 95
them with the pillars. ... If buildings are made fire-proof
entirely, and have skeleton construction so designed that
their enclosing walls do not carry the weight of floors or
roof, then their walls may be reduced in thickness one
third from the thickness hereinafter provided for walls of
buildings of the different classes, excepting only that no
wall shall be less than 12 inches in thickness; and pro-
vided, 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 reli-
ance upon the walls below them. But if walls of hollow
tiles are used as filling between the members of the skeleton
construction, they shall be of the full thickness specified for
non-skeleton buildings."
The requirements for protecting external structural
members of iron and steel are defined as follows : " All iron
or steel used as a supporting member of the external con-
struction of any building exceeding 90 feet in height shall be
protected as against the effects of external changes of tem-
perature 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
inches thick. If of hollow tile, it shall be not less than 6
inches thick, and there shall be at least two sets of air-
spaces betweeft 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.
" Where skeleton construction is used for the whole or
part of a building, these enveloping materials shall be inde-
pendently supported on the skeleton frame for each indi-
vidual story.
9 ARCHITECTURAL ENGINEERING.
" If terra-cotta is used as part of such fire-proof en-
closure, 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 back-
ing.
" If hollow tile alone is used for such enclosure, the
thickness of the same shall be made in at least two courses,
breaking joints with and bonded into each other."
The New York law prescribes the following: " Where
columns are used to support iron or steel girders carrying
curtain-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 4 inches in thickness and bonded
into the brickwork of the curtain-walls, or the inside sur-
faces of the said columns may be covered with an outer
shell of iron having an air-space between ; and the exposed
sides of the iron or steel girders shall also be similarly cov-
ered in and tied and bonded."
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 horizontal 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^-inch wall of enamelled brick. The inner sup-
ports consisted of I beams placed between the columns,
supporting a 4-inch wall of hollow tile. Thus the wall
was formed of two layers or "skins" held together by the
window-frames, etc. To Mr. W. L. B. Jenney belongs the
credit of having designed the first skeleton building erected
EX TERIOR WA LL S— PIERS.
97
in Chicago; the Home Insurance Building-, built in 1883.
This structure also contained the first Bessemer steel beams
used in building construction.
To avoid any injury to the walls or piers in skeleton
construction through the expansion and contraction of the
tall columns of steel, the masonry or envelope must be so
constructed as to be independent for each story length.
This is provided by means of shelf-angles or brackets at
each and every floor level, thus allowing the entire front
of the building to be built in such a manner that any or
all of the envelope or masonry facing may be removed with-
out injury to the load-bearing members. In the Home
Insurance Building just mentioned, cast lintels were used
to form the soffits of the windows at each floor, and de-
signed to carry the walls for the story above.
Fig. 46 shows a corner pier from the Reliance Building,
"T
FIG. 46. — Detail of Corner Pier, Reliance Building.
and Fig. 47 is a plan of the supporting framework for
same.
A striking example of what has been made possible in
the construction of exterior piers by skeleton methods is
98
ARCHITECTURAL ENGINEERING.
shown in the difference between the old and new portions
of the mammoth Monadnock Building in Chicago (see
frontispiece). At the time of designing the older portion
of this building, the owner, in spite of the protests of the
architects, insisted on having the conservative practice of
solid masonry piers, which, for a height of sixteen stories,
resulted in walls some 6 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 the walls of
this new building were built in the veneer pattern, which
had previously been rejected by the owner of the other
portion. It doubtless proved an expensive lesson for the
first investor.
A brick wall carried to the height of the Manhattan
Life Insurance Building in New York City (241') would,
according to the building laws of most cities, have to be
about 6 feet thick. Through the use of skeleton construc-
tion the enclosing walls in this building were made only 12
and 16 inches thick.
Fig. 48 shows the required thickness of walls under the
Chicago ordinance for buildings devoted to the sale,
storage, and manufacture of merchandise. Fig. 49, is for
EXTERIOR WALLS— PIERS.
99
the walls of hotels, apartments, and office buildings of
construction other than the skeleton type. Fig. 50 shows
i
J
*?
•i-
i
%i
FIG. 48.
r
t
4~
|
j
|
4- HI
i
J
i- I
—
FIG. 49.
"T
U
FIG. 50.
the requirements for masonry walls (in office buildings)
which carry their own weight only.
CHAPTER VI.
SPANDRELS AND SPANDREL SECTIONS— BAY WINDOWS,
THE spandrels constitute those portions of the exterior
walls, either on the street fronts or in the interior court,
which lie between the piers and between the window-spaces
of successive 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 con-
templated by the designer in his arrangement of the ma-
terial, 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
construction, 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 em-
barrassments in the irregular bracketing from the columns,,
100
SPANDRELS AND SPANDREL SECTIONS.
IOI
which becomes necessary in the support of the spandrel-
beams where the spandrel- or curtain-walls are recessed.
Fig. 51 shows a very simple form of spandrel section
FIG. 51.
FIG. 52.
from the Ashland Block, Chicago, where flush walls were
used. The veneer wall is but 9 inches thick.
The use of plate girders, as the main spandrel supports,
is shown in Fig. 52, which is a section
taken from near the corner of the Re-
liance Building. The connections of
these plate girders to the Gray columns
used, are shown in Fig. 104, Chapter VII.
The connections of the cast uprights
to support the terra-cotta mullions be-
tween the windows, are shown in Fig.
53. Figs. 54 and 55 are taken from
the eleventh- and twelfth-floor levels re-
spectively of the Fort Dearborn Build- FIG. 53.
ing. The section given in Fig. 56 is taken at the first-floor
102
ARCHITECTURAL ENGINEERING.
or sidewalk level, and shows the prismatic lights in the
sidewalk, as well as the small windows which help to light
the basement restaurant space. Fig. 57 is a section taken
at the attic floor, showing the main cornice and roof con-
struction.
FIG. 54.
•
The materials generally used for veneer buildings con-
sist, 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
fronts, as seen in the Stock Exchange Building, or in the
Reliance Building of enamelled terra-cotta.
The brick or tile work of the piers is usually supported
by bracket-angles, attached to the columns, as has been
described in Chapter V, while the body or backing of the
SPANDRELS AND SPANDREL SECTIONS.
103
-4- —
FIG. 55.
FIG. 56.
IO4
ARCHITECTURAL ENGINEERING.
spandrel-walls is supported directly by the main spandrel-
beams, as indicated in the previous figures.
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
FIG. 57-
blocks either to the brick backing or to the metal-work
itself. These anchors are usually made of ^ inch square or
round iron rods, which are hooked into the ribs provided
in the terra-cotta blocks, and then drawn tight to the brick-
work or metal-work by means of nuts and screw-ends.
SPANDRELS AND SPANDREL SECTIONS.
105
Such anchors are shown in Fig. 59. Hook-bolts are also
largely used, as in Fig. 55, 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. 59. The
many possible methods which may be employed in secur-
ing proper anchorage cannot always be shown by draw-
ings, and a proper execution of the work can only be
FIG. 58.
secured by most careful superintendence, and study in the
field. The general scheme, however, must always be indi-
cated on the sprandrel 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.
Fig. 58 shows a sprandrel section from the Marquette
Building, at the fifteenth-floor level. Heavy separators
io6
ARCHITECTURAL ENGINEERING.
FIG. 60.
SPANDRELS AND SPANDREL SECTIONS.
ID/
were used between the I-beam girder and the outside
spandrel-channel.
A rather complicated spandrel section is that indicated
in Fig. 59, taken from the Marshall Field retail store
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. 60 is from the same building, taken at the level
where the granite facing stops and the brick and terra-
cotta work begins.
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 de-
crease in thickness as compared 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. 61.
A simple court-wall spandrel sec-
tion is shown in Fig. 62.
FIG. 61.
BAY WINDOWS.
With the introduction of the steel
construction came the possibility and demand for the bay
io8
ARCHITECTURAL ENGINEERING.
window, a feature which has certainly become very promi-
nent in modern office-building and hotel design.
As in the ordinary spandrel section, the material for
FIG. 62. — Typical Court Wall. Practice of Jenney £ Mundie, Architects.
each story must be carried in such a manner as to make it
independent 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
SPANDRELS AND SPANDREL SECTIONS.
109
walls must be constructed as light as possible. No yielding
or deflection is permissible in these brackets, and if the
FIG. 63.
<J
FIG. 64.
supporting member is a floor-beam or floor-girder, as in
Fig. 63, taken through a bay window of the Masonic
no
ARCHITECTURAL ENGINEERING.
Temple, the girder should be rigidly connected to the
floor system, to prevent any twisting tendency due to the
weight of the bay. This is accomplished, as in the above-
FIG. 65.
FIG. 66.
mentioned figure, by means of the top and bottom tie-
plates shown.
Fig. 64 shows a section at the bottom of a bay window
in the Masonic Temple.
Fig. 65 shows a half plan of the metal framing for the
State Street bay window in the Reliance Building.
SPA ND REL S A ND SPA ND REL SEC T1ONS.
-x
FIG. 67.
FIG. 68.
112
ARCHITECTURAL ENGINEERING.
The terra-cotta mullions of the bay and the pier are
shown in plan in Fig. 66.
The column bracket in the bay is given in Fig. 67, while
Fig. 68 is a section at the side bracket.
The method of supporting the floors and ceilings in the
bays is shown in Fig. 69.
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 enthusiasts, 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 gen-
eral and specific cases may then be selected, as combining
the features desired.
A discussion as to the relative values of cast versus
wrought 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
shown by their use in the new 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 new pretty generally con-
fined to buildings of very moderate height or to special
"3
114
ARCHITECTURAL ENGINEERING,
cases where advantages are to be gained, as in the use of a
number of ornamental cast columns. The great uncer-
tainty as to the uniformity of cast metal led to the use of a
very low unit-strain, while in the case of steel the unit-
strains can be assumed on a very definite reliance on the
trustworthiness of the metal. Among our more progres-
sive 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. 70), it will be seen that these
splices cannot result in as rigid
a framework as the riveted
joints in steel-work. The col-
umns in the modern design
must be capable of affording
stiff connections so as to with-
stand both the direct dead
and live loads transferred from
the floor system, as well as
sufficient connections for the
wind bracing. These cannot
be secured well by means of
bolts 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 constantly employed to plumb the
columns. These constitute elements of weakness which
may easily allow considerable distortion. The girder
connections to the columns, resting on cast brackets, and
bolted through the flanges, are bad in the extreme, espe-
FIG. 70.
COL UMNS. 1 1 5
cially for cases of eccentric loading and the irregular plac-
ing of beams.
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 consider-
ing 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, break-
ing 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 more prominent forms of American wrought
columns include the Phoenix, Keystone octagonal, latticed
angles, channels and lattice, plates and angles, Z-bar
columns, and the newer Larimer and Gray types. The
relative advantages of these various sections are of the
greatest importance, as affecting economical and successful
design. In actual practice the treatment 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, the
formulas differ greatly, not in fundamental principles, per-
haps, 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 no or very few
Il6 ARCHITECTURAL ENGINEERING.
full-sized tests have ever been made on the effects of eccen-
tric loading. Indeed, the 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.
Burr, in his " Strength and Resistance of Materials,"
states that " The general principles which govern the re-
sistance 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 Burr would seem to indicate
that a closed column is stronger than an open one, due to
the fact that the edges of the segments are mutually sup-
porting when held in contact by complete closure. From
a theoretical standpoint, therefore, the Phoenix column is
undoubtedly the most 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 maxi-
mum 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
COLUMNS. 117
in connection with the judicious choice of a section. In-
deed, we shall see that several practical considerations in
the use of columns in buildings call for a form very differ-
ent 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.
In the column formula,/ — — — ^ (the form
, ^ i x*x\
2 + "-* + -^-
of Gordon's formula, including the effect of eccentric
loading), there are expressions for the three kinds of
stresses in a column under compression — that due to the
flexure of the column, that due to eccentric loading, and
that due to the uniformly distributed load. The term of
eccentric loading does not occur in the so-called Gordon's
formula, or in those derived from it, but in building con-
struction this term must not be omitted. The placing of
columns centrally over one another necessitates the applica-
tions of loads to the sides of the columns, and unless the
loads are equal, and on opposite sides of the column, the
effect is to increase the stress on the side where the greater
load occurs.
/2
The second term in the denominator, a — , is usually so
small that it really makes this term of the least importance
in the above equation, due to the ordinarily short length of
columns in buildings, and to their usual broad flat bases.
Hence in one-story columns (unless in long first-story col-
umns), where the length is usually under 90 radii, the differ-
ence in the strength of the various sections tends to disap-
pear, and almost any of the sections will answer with the
Il8 ARCHITECTURAL ENGINEERING.
ordinary unit-strains, if the columns are well made and the
loads are not eccentric. Eccentric loading will be consid-
ered later, under a general discussion of the various
sections.
In longer columns, however, where the length is greater
than 90 radii, calculation by the radius of gyration becomes
necessary. In the new Schiller Theatre Building, Chicago,
Phcenix columns were used, of a length of 92 ft. 10 in.r
weighing 25,000 Ibs. each. Modern building methods have
rapidly developed the necessity for columns of extraordinary
length, carrying loads hitherto considered visionary. It is
not uncommon to have 800 tons and even more on a single
column with a sectional area of 158 sq. in. The Edison
Electric Illuminating Company of New York City used
columns of the Phcenix type, having loads of 600 net tons,
35 ft. 4 in. over all in length, weighing 15,000 Ibs. each. As
vibration occurred in the building, very low unit:strains
were allowed, the columns being further strengthened by
disregarding the increment to the least radius of gyration
caused by using eight fillers, each ^f in. thick.
The formula used was one deduced from the experi-
P 42,000
ments at the Watertown Arsenal, namely, -~ =•
O
/_!_ ^'Y
\ 50,000 X f%)
for the crushing strain per sq. in.
Twelve-section Phcenix columns were also used in the
Chicago Board of Trade, 90 ft. unsupported length, 3 ft,
3 in. diameter, fire-proofed.
But by far the larger number of columns used in modern
building construction are, as has before been stated, under
90 radii, being used in single-story lengths of from 10 to 14
feet. The determining factors are, therefore, such practical
considerations as affect columns of these lengths; so that
the ideal disposition of the metal must be considered in con-
COLUMNS. 119
nection with other very important requirements. The fol-
lowing points of the problem are important, in a discussion
of which the writer partly follows the points enumerated by
Mr. C. T. Purdy, in the Engineering News, December 5, 1891:
1. Cost, availability.
2. Shopwork, and workmanship of column.
3. Ability to transfer loads to centre of column — eccen-
tric loading.
4. Convenient connections of floor system.
5. Relation of size of section to small columns.
6. Fire-proofing 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 considera-
tion, while point 6 is of chief interest to the architect and
decorator.
i. 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 break in the combine which formerly existed on
I beams and channels has reduced the price on these sections
from the former combine price of $3.20 to about $1.50, or to
a price uniform with that for plates and angles. Indeed the
price of iron and steel shapes has never been so low in the
history of this country as at the present time, and were such
prices to continue, they would doubtless prove a tremendous
stimulus to steel construction even in dwellings.
All of the " patent " columns, such as Z-bar, Phoenix,
Keystone octagonal, Larimer, and Gray forms, have the
great disadvantage of being rolled or manufactured by cer-
tain mills only, and in this age of push and hurry the quick
delivery of material is a very essential point. The demands
for structural steel at good seasons of trade in this country,
are so great that it is next to impossible to secure such a
I2O ARCHITECTURAL ENGINEERING.
prompt delivery of material as is required for the comple-
tion of a large building within the contract time. The con-
tracts that have been executed in the city of Chicago dur-
ing the last three or four years have undoubtedly shown
the most wonderful construction in points of excellence and
time that the world has ever seen ; while 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 patent on the more important of the
patent sections has, however, recently expired, so that now
the Z section is being roiled by several mills, and it is not
only cheaper than formerly, but much more available,
being rolled even on the Pacific coast. The Phoenix shape,
although the patent has long since expired, is rolled by but
one mill in this country, the Phcenixville, and by one other
mill in England. The Keystone column is but little used.
Columns of plates and angles, or channels, .possess this ad-
vantage of availability in a greater measure than any of the
other sections, the parts being obtainable at any mill, if not
in stock.
2. Shopwork and Workmanship. — With the present uni-
form low price per pound of most of the column sections,
the items of shopwork and workmanship become of far
greater importance in the cost of the completed column
than the cost of the section at the mill — assuming the sec-
tional 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 section, and must there-
fore 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 punching operations, as well as the ex-
pense of rolling the sections employed, will need to be con-
sidered as affecting the cost of shopwork. Thus in the
COLUMNS. 121
Gray column no less than sixteen operations of punching
are required for four rows of rivets, with the additional
expense of hydraulic pressed bent plates, connecting the
angles. This will materially increase the cost of manufac-
ture. (See following table.)
Larimer column, i row of rivets.
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.
Keystone octagonal column, 4 rows.
Z-bar column, with single covers, 6 rows.
Box column of plates and angles, 8 rows.
Latticed angle column, 8 rows.
8-section Phcenix column, 8 rows.
Z-bar column with double covers, 10 rows.
The new Larimer column, but recently placed on the
market 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 1 8 in. from each end of the column, and then 5 in.
centres.
122
ARCHITECTURAL ENGINEERING.
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. 71). Where
FIG. 71.
FIG. 72.
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 octagonal 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 sheet to conform in the lower
part to the shape of the outside of the flanges of the column
(Fig. 72). In this way not only the upper flange, but the
vertical flange too, is made continuous around the top of
the column. Also the thickness of the horizontal flange is
retained uniform, the thickness of the vertical flange being
somewhat tapered.
This column is one of the cheapest on the market at the
present time, but it 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 o-in. column, where 5-in. I beams are used, or
in smaller columns, it is often very difficult on account of
COLUMNS. 123
interference to drive the rivets through the holes, unless the
rivets are driven in a slanting direction. This often re-
sults in weak connections. Jones & Laughlins, the manufact-
urers of this column, have made a large number of tests of
built columns, showing a marked gain in ultimate strength
over the Z-bar column tests published by C. L. Strobel.
Comparing a 7" Larimer column (6" I beams, I2f Ibs. per
foot, of sectional area of 9.261 a", total length 120", gauged
length 100") with a 6" Z-bar column (6" X 3" Z's, \" metal,
area = 9.32 a " , total length = 1 19.88", gauged length = 80"),
the Larimer shows an ultimate strength of 346,300 Ibs., or
37>393 Ibs. per sq. in., as compared with an ultimate
strength of 293,200 Ibs., or 31,460 Ibs. per sq. in. for the Z
column. The Z-bar column failed through the buckling of
the Z's, and twisted in a spiral direction between the two
ends. The Larimer column deflected in an oblique direc-
tion. Larger Larimer columns also showed a greater ulti-
mate strength per sq. in. than the Z-bar columns.
A point that has always been made much of in the
claims for the Z-bar column is that but two rows of rivets
are required, and those near the centre of the column ; for
it is reasonable to suppose that punching in the outer por-
tions of a column tends to weaken the member, even when
the riveting is most carefully done ; and this is even more
important in small columns, where the ratio of the radius of
gyration to the length of the column is greatest, and where
we desire the greatest efficiency of the material used. But
is this claim of two rows of rivets founded on fact? If Z-bar
columns were used without cover-plates, the claim would
indeed be true, but take, for instance, the large Z-bar col-
umns in the Venetian Building, quoted by Mr. Purdy in the
article named. No less than ten rows of rivets are required
with the heavy cover-plates used, and, indeed, when we
stop to consider the large proportion of Z-bar columns
124 ARCHITECTURAL ENGINEERING.
which liave covers, the claim of only two rows of rivets
assumes but little value, and the section proves less desira-
ble than the box column of plates and angles, — inasmuch
as the material of the Z's, near the centre of the column, is
practically wasted, though adding so materially to the
weight. It can hardly be denied, even by the most enthu-
siastic supporters of the Z section, that the use of this shape
has really been thrust upon the Chicago builders during
the last few years far more than its merits would warrant.
A glance at the Appendix table shows that twenty-two out
of a total of forty buildings in Chicago have used the Z-
bar column. Its use in Eastern cities has been far more
limited.
It is hard to see, therefore, where the Z-bar column
possesses any decided advantage so far as shopwork is con-
cerned, unless used without cover-plates. The columns of
plates and angles and the Z sections are about on a par in
these respects, while the channel columns are more favora-
ble than either. The channel columns are, however, some-
what limited as to section, while plates and angles can be
increased to any desired area. The latter section was used
in the highest steel building in Chicago, the Masonic Tem-
ple, latticing being used on two sides of the columns in the
upper stories.
The character of ^vorkmanship will vary with the differ-
ent shops, as well as with the different sections used. The
reputation of the shop, aided by careful inspection, will de-
termine the excellence of the workmanship.
3. Ability to Transfer Loads to Centre of Column — Eccen-
tric Loading. — It will be seen at a glance that many of the
sections under consideration are totally unfitted for the
transfer of loads to the centre of the column. The condi-
tions in designing a framework are seldom so favorable as
not to require many of the columns to be loaded unsym-
COL UMNS.
125
metrically, and this point has been carefully considered in
the details of the best modern structures, in order to obtain
the highest possible efficiency in the material used. Every
step in this direction will certainly add to the capacity of
the column, for an eccentric load will necessitate the use of
a much less mean unit-strain than where the force can be
applied directly to the axis. Fig. 73 shows the connection
between beams or girders and
the Gray column. It is evi-
dent that, unless the top of the
column is very rigidly bound
FIG. 73.
FIG. 74.
together by outside plates or angles, the girder loads, if
eccentric, are borne mainly by the T shape to which the
girder is connected, and not by the whole column. This
lack of latticing to transmit shear may constitute a very
serious disadvantage in cases of heavy eccentric loading.
The use of Phcenix plates with pintle connections, as
advocated by Foster Milhken, would certainly seem to
126 ARCHIJ^ECTURAL ENGINEERING.
possess the greatest advantages under this heading (Fig.
74). There is no leverage in this method to tear the joint
asunder, as there is in any flange joint. This system was
recently used in the large power-house of the Broadway
cable road in. New York, with pintle-plates over eight feet
deep. Unless pintle-plates can be used, however, any form
of closed column is bad under this consideration of central
loads, and here the practical method of loading columns
conflicts seriously with the use of an ideal closed section.
The Z-bar column possesses advantages here, too, over
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. (But Z-bar columns without covers fail by
wrinkling, and under this condition they are the weakest
of any of the sections.) The box column of plates and
angles, however, possesses this same advantage, though not
to as great an extent in the lighter sections. The possi-
bility of changing the section of a column so that the
radius of gyration shall be greater or less in either direc-
tion 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.
The calculation for eccentric loading should be treated a
follows :
(a) Determine the section required for the total load, both
eccentric and concentric, the whole considered as concen-
tric.
COL UMNS.
127
(b) Find y^ or half the width of the column.
(c) Find the radius of gyration in the plane of eccentric
loading.
(d) Find the area of section required to resist the
bending moment arising from the eccentric loading, using
radius of gyration and ^, as in the assumed section. The
moment due to eccentric loading will equal the eccentric
load X its distance of application from the axis of column, or
//
M,—~=
y,
y,
«
whence A =
— -.
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 j, are changed
materially, in providing for the new area required, then
a new assumed sectional area is
taken, radius of gyration and yl
found for it, the solution proceed-
ing as before.
4. Convenient Connections. — This
feature in column construction is
a very important one. Satisfac-
tory details can easily be made
for almost any of the sections,
where the beams are symmetri-
cally placed and loaded, and where
all occur at the same elevation ;
but when the irregular placing
of beams is necessitated, as re-
gards position, load, and height, FIG- 75-
it is important that the character of the column afford
as great an opportunity as possible for the connection of
128 ARCHITECTURAL ENGINEERING.
plates and angles. The connection in Z-bar columns forms
one of the greatest advantages in the use of this section ;
and in the smaller columns without covers, where the con-
nections are generally the most difficult, the advantages
are the greatest. The general system of connections is
shown in Fig. 75, taken from the Monadnock Building.
Angle-brackets are riveted to the column, on which is
placed a plate £ in. to I in. in thickness, on top of which come
the girders, the column of the next floor setting centrally
over the one below. The girders are riveted or bolted
through to the bed-plate below, by the flanges, and through
an angle above, as shown in Fig. 75. A small wrought-iron
" gib " or wedge is dropped in between the top end of
the girder and the web, to take up any possible compressive
strains. If the girders are all to be brought to one level,
cast-iron bolsters are used.
The system followed in the Phoenix column is as shown
in Fig. 76, 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 load-
ing a considerable tilting movement
occurs in this column, unless used
with pintle-plates, as before sug-
gested. Connections were made with bent plates in the
Old Colony Building, Chicago, as shown in Fig. 77.
Box columns of plates and angles offer quite as many
advantages as regards connections, if not more, than any
other section. The details are really the simplest of all,
when we consider columns of a single floor height only
(Fig. 78), but the joint is not a desirable one, nor is any where
a horizontal plate separates the two columns ; for it prevents
COL UMNS
129
efficient splicing, as well as good girder-connections. This
point will be taken up later under the head of " Column
Joints."
tip >
m
Xii*.. \\ // .:~l'>'<.*
-L&zrZ Ctf££l~
e%... rf^
>v •"- '. I- f /
•^f^r^-
• "^ •
FIG. 78 -
FIG. 77.
5. 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.
6. Fire-proofing Capabilities of the Section. — The rectangular
column sections will not, of course, fire-proof as compactly
as the circular sections, but when the room thus lost is
used for " pipe-space," as is becoming more and more fre-
quent, this 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 area.
Such a cutting of bed-plates cannot be too severely con-
demned. The increased use, however, 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 fire-proofing slabs,.
13° ARCHITECTURAL ENGINEERING.
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 Key-
stone-octagonal offer no advantages in this respect. The
columns of plates and angles, channels, Z's and the Gray
column, all allow considerable pipe-space within the mini-
mum circular or rectangular enclosure for fire-proofing.
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.
The largest Z-column section in " The Fair " building,
Chicago, consists of 4 Z bars 6" X f", 2 webs 16" X f", 6
covers 16" X yf", aggregating an area
H B of 142 sq. in. and carrying a load of
1,700,000 Ibs. The largest Z column in
the new Y. M. C. A. Building, Chicago
(see Fig. 79), was a two-story column
24' 3" long, composed as follows: 4 Z's
6" X 3" X £", 2 plates 24" X f> 2
plates 1 6" X J", i plate 14" X f", 2
plates 26" X £", 4 angles 4" X 4' X |f", 4 angles 5" X 4"
X I" — total — 218 sq. in. The minimum Z section gener-
ally used is 4 Z's 3" X •£*", i web 8" X Ty = 12.4 sq. in.
Metal less than •£$" in thickness is never used in the best
practice.
The calculations of the strengths of wrought columns,
in accordance with the building laws of New York, Boston,
and Chicago, are given in Chapter XII; and the unit-
strains used in several prominent buildings are given in
Chapter XI.
It is apparent, therefore, that each of the types of
COLUMNS. 131
columns considered, has its own good points, but the choice
of one, as decidedly superior to all others, would be well-
nigh impossible. The Larimer column may lead in cheap-
ness, the Z or box columns are superior for connections,
the material, in the Phoenix or Keystone columns is placed
most advantageously from a theoretical standpoint. The
choice, then, must depend on the personal views of the de-
signer, as well as on the local conditions as to cost, manu-
facture, and the details employed in the problem at hand.
The writer favors the box column of plates and angles. It
is easily obtained, cheap, good for connections, possesses a
minimum and maximum radius of gyration, which can be
utilized under eccentric loading, and it offers the greatest
advantages for continuous columns, a point which will be
considered later in connection with wind bracing.
A discussion on columns would hardly be complete
without some reference to the views expressed on this sub-
ject by Gen. Wm. Sooysmith. He advises the use of
limestone pillars instead of steel columns, declaring that the
action of the metal-work under heat would be dangerous in
the extreme. To quote : " There may be steel buildings in
which the fire-proofing has been so well done that they will
pass through an ordinary fire without such failure. But if
the steel becomes even moderately heated, its stiffness will
be measurably diminished, and the strength of the upright
members so reduced as to cause them to bend and yield."
While acknowledging the great experience and ability of
Gen. Sooysmith in constructive work, and especially in foun-
dations, the writer would seriously question the authority
for such an apparent reflection on fire-proofing methods.
There not only may be buildings which are sufficiently fire-
proofed, but it is a well-established fact that builders, archi-
tects, and engineers can and do fire-proof their buildings
sufficiently to guard against all possible heat arising from
132 ARCHITECTURAL ENGINEERING.
the material used in the building, or from the burning of
surrounding structures. And that there is almost no limit
to the possibility of protection from heat by fire-clay is
shown in the immense converters in use by the large steel
companies. They are made of steel, protected by fire-clay,
and in spite of a temperature of 2000° night and day, these
furnaces last even as long as four years before renewal.
Again, limestone (CaCo3) is friable under the action of
heat, decomposing into lime (CaO) and carbon di-oxide
(CO,) at a temperature of 600°. Hence the limestone pillars
would require quite as much protection by fire-proofing
as the steelwork. Gen. Sooysmith claims a safe load of 500
tons for a column of limestone 2' X 2' in area and 9' high.
This equals 576 sq. in., or at 5500 Ibs. per sq. in. given by
Rankine, gives an ultimate compressive resistance of 1584
tons. Allowing the factor of safety of 8, recommended by
Rankine, we have even less than 200 tons, while Baker
recommends but 20 or 25 tons per sq. ft. for the best
ashlar masonry (10 tons was the maximum pressure in the
Brooklyn bridge, and 19 tons in the St. Louis bridge), or
100 tons for this limestone column. This same load of
200 tons would be carried by a 12" Z-bar column of 4 Z's
3" X 6" X f ", and i plate 8" X f " = 42 sq. in. area, at
10,000 Ibs. per sq. in. The economy of space in this latter
column is at once apparent, even disregarding the fire-
proofing necessary to a limestone pillar.
THE FIRE-PROOFING OF COLUMNS.
As the columns carry the greatest loads found in modern
buildings (some over 1,500,000 Ibs.), the proper fire-proof-
ing of these members becomes a most important subject for
consideration. In only too many cases, however, is this
slighted even to a very dangerous extent, as was proven by
the Athletic Club Building fire, before referred to.
COLUMNS. 133
The first attempts at making fire-proof 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 con-
struction in the New York building laws, 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 im-
posed thereon."
The scientific fire-proofing 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, archi-
tects, was the first instance where terra-cotta gores were
used around columns. Many systems have since been in-
troduced, 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 fastened 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
hooked to one another, and not to the metal column.
The requirements in the adequate fire-proofing of col-
umns are :
1. The material must be indestructible by fire.
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 conflagration than the porous
134
ARCHITECTURAL ENGINEERING.
tile. The hard tile is very apt to crack off under such
conditions, as has been stated in the chapter on Floors.
The use of solid blocks of porous tile, well bedded
against the metal column, seerns to be the one most highly
recommended. Here, as in terra-cotta floor arches, the
competition in price, which places the better article or
method at a disadvantage, is to be deplored. Loosely
drawn specifications are also responsible in a great measure
for many very common defects. All wiring of the indi-
vidual blocks either to the columns or to one another
FIG 8a
FIG 81.
FIG. 82.
should be made by means of copper wire. Figs0 80, 81, and
82 show the ordinary methods of placing the fire-proof
furring for columns.
The Z-bar columns in the newer portion of the Monad-
nock Building were fire-proofed as shown in Fig. 83 up to
M0LL0W ffft/CK.S
FIG. 83.
and including the eighth floor. Hollow bricks, laid in
cement mortar, were built solidly around the columns to a
COLUMNS. 135
line distant 4 in. from the extreme points of the metal-work,
and a 2-in. coating of hollow tile was then laid against the
brick backing extending beyond the column in one direc-
tion, to serve as a space for vertical pipes. The columns
above the eighth floor received the hollow-tile protection
only.
The requirements for fire-proofing the interior columns
of office buildings are thus defined by the Chicago ordi-
nance :
" The coverings for columns shall be, if of brick, not less
than 8 inches thick; if of hollow tile, one covering at least
2\ inches thick. If the fire-proof covering is made of
porous terra-cotta, it shall be at least 2 inches 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."
u 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."
" If plastering on metallic laths be used as fire-proofing
for columns, it shall be in two layers, of which the first
shall be applied in such manner that the mortar will cover
the entire external surface of the column, while the space
between the two layers shall be not less than i in. thick."
" The metallic lath shall in each case be fastened to
metallic furrings, and the plastering upon the same shall be
made with cement. Protection for the lower five feet shall
be required in this case the same as where porous terra-
cotta or hollow-tile covering is used."
CHAPTER VIII.
WIND BRACING.
A CAREFUL comparison of the treatments 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 employed, and the most efficient details of con-
struction. Indeed, there are buildings from ten to sixteen
stories high in the city of Chicago, 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 Build-
ings," * mentions the case of an office building recently
erected, of seventeen stories, or 200 ft. in height, and 60 ft.
wide ; 13-in. walls were used front and back, broken by win-
dows and bay windows, with wind bracing consisting solely
of the interior partitions of 8-in. box tile, with four ribs of
-ft 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 2j times the width of the
former, with sway-bracing consisting of i5-in. channel-struts
and 6-in. eye-bars. Such is the diversity of practice.
Some architects depend solely upon the partitions of
hollow tiles for the lateral stability of their buildings,
* Trans. A. S. C. E., Vol. XXVII, No. 3.
136
WIND BRACING. 137
weak as 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 cer-
tainly 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 building 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 uniformly by the best Chicago archi-
tects 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
1 38 ARCHITECTURAL ENGINEERING.
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 doors, win-
dows, passages, and even whole areas, as is sometimes
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 draughtsman, just so will the former 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.
Two distinct corps of workmen are found in the offices
of the more prominent architects of the day : the archi-
tectural draughtsmen, for all decorative design and
work, and the engineers, who have charge of the con-
structional problems, as indicated in this outline. In such
an office the two kinds of work can be carried on simul-
taneously, concessions made on both sides, and a satisfac-
tory medium reached.
Quimby, in his article on wind bracing, favors the pro-
vision of a 4O-lb. wind pressure, with iron or steel bracing
strained not over J of the ultimate strength ; while George
A. Just, in a discussion, advocates the use of 30 Ibs. Cir-
cumstances must to a great extent govern the choice of
the designer. The shape and exposure of the structure,
and the solidity of the enveloping walls, will, as said above,
largely determine the amount of wind pressure to be car-
ried by the metallic bracing ; but if such bracing be relied
upon entirely, a unit of 30 Ibs. should serve as a minimum.
The following was adopted by E. C. Shankland, Chief En-
gineer of the World's Columbian Exposition : For roof
trusses, 40 Ibs. per horizontal sq. ft. of roof taken vertical,
WIND BRACING.
139
or 25 Ibs. per sq. ft. taken vertical in addition to the effect
of 30 Ibs. wind acting under an angle of 20° with the
horizon, whichever will give the largest result. On pur-
lins and jack rafters take 30 Ibs. per horizontal sq. ft; on
gallery floors take 80 Ibs. per horizontal sq. ft; on main-
floors take loo Ibs per horizontal sq. ft. A horizontal wind
pressure of 30 Ibs. per sq. ft. shall be taken care of unless
otherwise decided by the Engineer of Construction. All
details must be carefully calculated both for bearing and
shear.
Many and many are the architects who have used cast-
iron columns piled story on story, with tile partitions only
as a wind-resisting medium, and their structures stand, to
become a source of wonder to the engineering profession.
But in a field of such great uncertainty any judicious in-
crease in safety is in the nature of insurance, and must not
be regarded as wasted, simply because never destroyed.
Wind bracing must reach to some solid connection at
the ground. It should also be arranged in some symmet-
rical relation to the building outlines. If the building
is narrow and braced crosswise with one system, the brac-
ing should be midway, while if two systems are employed,
\
\ XI
FIG. 84.
(i)
FIG. 87.
(4)
they should be placed equidistant from the ends. This
symmetry is necessary to secure the equal services of both
systems, thus preventing any twisting tendencies.
140 ARCHITECTURAL ENGINEERING.
The more common forms in ordinary practice are shown
in Figs. 84, 85, 86, and 87.
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 solution, owing to several indeterminable factors
that enter into the computations, and the consequent equal
number of assumptions 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 suffi-
ciently rigid to transmit the horizontal shears due to
wind.
The external forces will be the same whichever of the
four methods, shown in the figures above, is used, provided
the exposed areas, panels, etc., are the same. Th.e hori-
zontal external force at any panel point will be equal to the
distance between the systems (at right angles to the brac-
ing) times the distance between floors half-way above and
half-way below, times the assumed wind pressure per sq.
ft. The total shear at any point equals 2 forces at or
above the point taken.
These shears are undoubtedly reduced to some con-
siderable 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 stiffen-
ing effects of partitions (if continuously and strongly built),
and linings, coverings, etc., all tend to decrease the distort-
ing effects of the wind pressure. But, in view of the un-
certainty in regard to the efficiency of these latter con-
siderations, they may not be relied upon, and are therefore
disregarded in the calculations.
WIND BRACING.
141
SWAY-RODS (l).
The simplest case of wind bracing is shown in Fig.
84. Considering one bay alone as braced, the system may
be analyzed as follows: Referring to the upper story
of a framework, as shown in Fig. 88, Pt =^HJLl where
Pl = resultant wind pressure on upper story,/ = unit-press-
ure, and H^ and Ll equal respectively the height and width
of the area affecting the bracing in the panel under con-
p
sideration. — must then be the horizontal component of
Hoof.
p
N
\A/
"vi
t
'Pa <"7
JCt ur i
1
2\
1
^
ft Aa ,
^
\/
a
»^J
f+
rs?
i ^ ..
<xj
/ \
|
4r
USj
\/
te
1
KSX§
^s^i
1
1
/\
^
\ 7
C^
%.^l
_.i
FIG. 88.
the stress in the diagonal, and the tension in this diagonal,
making an angle Q with the horizontal, must be
Tt = y sec 0.
The diagonal tension in the second story from the top will
be T^— I -— + Pj sec 0, where P= wind pressure on any
single story, assuming them to be of equal height. ~ + P =
compressive stress in the horizontal strut at the top-floor
ip \
level. In like manner, Tt = ( — + 2 P) sec 0.
The tension in the diagonal rods will cause a decrease
I42 ARCHITECTURAL ENGINEERING.
in loads on the windward columns, and an equal increase
in loads on the leeward columns. Calling this increase or
decrease F,, we have
V, = -', where *, =
/ 2
In a similar manner,
Fs must equal F, -f- the vertical component of the diagonal
P h
T9, or F3 = — Y^ -}~ 7~, sin & This will serve as a check
on the calculations.
These wind loads F,, F, 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
connected to the bottoms of these columns. Thus the
dead load in column 3 is reduced by the full amount of the
upward compressive strain from wind in that column, or
F,, 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 F at
each floor may be eccentric, as shown in Fig. 95, 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 o, and the
eccentric load become a dead load.
Take the case of a typical skeleton building, fourteen
stories in height, of 12 feet each, 24 foot front, and
columns spaced, 12 feet apart in the depth of the build-
ing. Assuming that stiffness against side-yielding alone is
necessary, place diagonal members in each story, as in
Fig. 89, utilizing the floor-girders as struts, with the
WIND BRACING.
143
X
X
X
X
X
X
X
X
X
columns as chords. At 30 Ibs. per square foot wind press-
ure the panel load equals 4,300 Ibs. Con-
sidering the protection afforded by neigh-
boring buildings, the point of application
of the resultant wind pressure will be
taken at two thirds of the height of the
structure above ground. The total shear
will then equal about 60,000 Ibs., or 30
tons. In the basement panel, then, sec 6 =.
1.12, giving 33.6 tons tension in the cellar
diagonal. The moment of the resultant
wind pressure = 30 X 1 18 = 3, 540 foot-tons,
and this, divided by 24, gives 147^ tons ten-
sion at the windward foundation. The
vertical component of the basement di-
agonal = 16.8 tons, leaving a compression
of about 131 tons on the leeward 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 render-
ing anchorage unnecessary.
If, in the same cross-section of the building, n bays not
adjacent are braced by means of diagonal rods, the tension
P P h
T becomes T, = — sec 6, and V, = — V*
272 nl
The bracing in Fig. 85 may easily be analyzed in 3
manner similar to the above.
The highest building in the city of Chicago is the
Masonic Temple, 273' 10" from grade to top of coping. A
cross-section of this building is shown in Fig. 90, with one
system of bracing-rods. It will be seen that a combination
of forms (i) and (2) was used, the bracing being arranged to
X
FIG. 89
144
ARCHITECTURAL ENGINEERING.
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 connec-
tion with the turnbuckle rods.
One of the best examples of system (i) of wind bracing
in Chicago, the writer found
to be that described by Mr.
C. T. Purdy in his article
in the Engineering News of
^!%!;%%%^;^%%^^/
FIG. 90.
FIG. 91
December, 1891. This building, the Venetian, is of the
veneer type, and contains some excellent details. The
floor plan is shown in the accompanying figure (91) with the
WIND BRACING.
145
/'-fi' a/'-6"
four sets of sway-rods given. Each set of bracing is there-
fore 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 2ffoos
height of the building. The area tribu-
tary to each floor X 40 Ibs. equals the
horizontal shear at each floor or panel- 2
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 brac-
ing. The practical considerations which
tend to diminish the distorting 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. 92).
All the columns affected by this brae-
FIG. 92.
ing were made continuous from the foundations to the
second-floor level, and portals were used to take the place
of the diagonal rods in two instances where rods were out
of the question. This occurred on a main floor devoted to
large banking-rooms. The bending moments due to these
portals were taken up in the columns. 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 ten-
sion and compression horizontally, 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,
146
ARCHITECTURAL ENGINEERING.
whichever pair of rods was strained, and 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
FJG. 93.
to resist the bending moment which the stopping of the
rods necessitated, and as a further assurance that these con-
nections should be as strong as the rest of the system, the
FIG. 94.
top connections of all of the first-floor beams were omitted,
and the clearance spaces between all the beams and
WIND BRACING.
columns were driven tight with thin metal wedges, until
the girders and beams passing along the column axes were
continuous and in compression out to the sidewalk walls,
which latter are backed by the solid street.
The horizontal channel-struts are shown in Fig. 93.
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 sup-
ported by two bracket-angles beneath, with sufficient rivets
to resist the vertical compression of the rods in this direc-
tion (see Fig. 94).
Above the ends of the struts other cast-iron blocks were
used, planed top and bottom, thus allowing them to fit in
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" 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 com-
ponent of the rods. Such cast-iron
blocks in this connection are very
convenient for use, for it often hap- FIG. 95.
pens that the bracket-angles cannot be brought directly
148 ARCHITECTURAL ENGINEERING.
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. 95 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 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 \" square. The
Ashland Block, by Burnham & Root, Chicago, has longer
struts than those in the Venetian Building, 15" channels
being used in the floors, acting both as struts and floor-
beams.
PORTAL BRACING (3).
The third method of wind bracing, called the portal
system, may be analyzed as follows (see Fig. 96) : Taking
the upper floor first, the external force Pt may be considered
as producing equal horizontal reactions at the bottoms of
p
the portal legs, or at the floor level, equal to -J each. A
wind moment M is also produced at this floor level, or,
M = PJi, , where h, = -.
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
y\
unit-strain on extreme fibres, y^ = distance of extreme fibres
WIND BRACING.
149
from the neutral axis, and / = moment of inertia of the
P h v
section. But M — PJi, hence /= '*rj*
/ will be slightly different on the two sides of the neutral
axis. On the compression side of the bay, / will be taken as
4^1
i
i
-i-
«*
f
i
i
^
I
*r
Y
I -r-
IT
\\
FIG. 96.
the moment of inertia of the section of the column and the
portal, while on the tension side, / must be taken for a sec-
tion 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
15° ARCHITECTU&AL ENGINEERING.
P h
V, = -y2. 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. Vl must also equal the shear on
all vertical planes.
The horizontal shear along the line aa = Plt while
the horizontal shear in either leg or portal or at bottom
p
of leg = — '. These shears will determine the thickness of
the webs. 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
^M = 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 y, at right
angles, from flange C. Then x times the vertical shear
divided by y = stress at section taken, and this is maximum
x
when — has its maximum value. The stress in the flange A
y
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 Vl 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 x^ from bottom of leg,
and at distance y^ from the flange C, at right angles. Then
P x x
— -— = strain in flange (7, and this is maximum when — is
* y, y,
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.
WIND BRACING. 151
Ph
In the second story from the top, F, = ~T~?, considering
P2 = 2Plt or that the stories are of equal height. The con-
centric load F, in column 2 from the column above, and its
equal reaction, may be omitted in a calculation of the
•i
HIM
, /£ —
FIG. 97. — Portal-strut used in the Monadnock Building.
strength of the portal bracing (as they are applied along the
same straight line), as may also the equal negative effects in
column i.
The vertical shear in this second-story bracing will
FIG. 98.
equal 5, = F2 — V,. The horizontal shear across the top
p
of the portal = P9, while in either leg the shear = — -.
One of the first attempts at a portal system in building
152
ARCHITECTURAL ENGINEERING.
construction was through the use of a portal-strut used in
the older portion of the Monadnock Building, as in Fig. 97.
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. 98. Wind pressure was figured at
27 Ibs. per square foot on one side of the building at a
time. Each portal was calculated independently for the
sections of both top and bottom flanges, thickness of web,
cross-shear on rivets connecting the curved flanges, and for
FIG. 99. — Detail of Portal, Old Colony Building.
all splices and connections. A detail of one portal is shown
in Fig. 99. This arrangement of 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
WIND BRACING.
153
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 either one or the other system, whether the
rooms are to be connected by large openings or small
doorways.
KNEE-BRACES (4).
The system of knee-braces, or arrangement (4) for
wind bracing, is not an economical method, as it produces
|
i
4
i
/ j
£.!> ~
"T
i
^
FIG. 100.
heavy bending moments in both the horizontal struts and
in the columns themselves. This system may be analyzed
as follows (see Fig. 100)
154
ARCHITECTURAL ENGINEERING.
The shear at the top-floor level will be -- at each column.
Then as before, F, =
/ '
The tension in the brace cb is nearly
There will be an equal amount of compression in the oppo-
site brace. This suggests the use of knee-braces capable
of resisting both compression and tension. There will
be a bending moment at C whose value is approximately
P h Ph h
M= — l . — — = — L -. The factor — — is used, as the column
224 2
is considered as square-ended and fixed by the static load
FIG. ioi. — Knee-bracing used in the Isabella Building.
and by bolts. This bending moment will also exist at d.
At b there will be a bending moment M^ = Fj/a = ' .' a.
This type of wind bracing was used in the Isabella
WIND BRACING.
155
Building, by W. L. B. Jenney, architect, as shown in
Fig. 101.
A modification of the knee-brace system of wind brac-
ing 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
FIG. 102. — Gusset-plate Bracing used in Fort Dearborn Building.
the exterior walls, with gusset-plate connections to the
columns, as shown in Fig. 102, 10 in. and 12 in. channels
being used generally. In the lower stories, where the
wind moment necessitated it, a double system of gusset
connections was used, under and above the channel girdersr
156 ARCHITECTURAL ENGINEERING.
A somewhat similar method was used in a building in
New York City, 120 ft. in height and 24 ft. frontage,
designed by L. de C. Berg. The Z columns were used,
spaced 12-ft. centres, and anchored to foundations. At
three levels in the building occur riveted girders in the
exterior walls ; the girders connect to the columns by
large gusset-plates. At these levels, diagonal ties of flats
are also run horizontally over the floor system. An addi-
tional load of 15 Ibs. vertically was figured in the columns
and girders for the effect of the wind. A similar system
of horizontal flats was also used in the old Monadnock
Building, Chicago. In the Reliance Building the wind
strains were transferred from story to story on the table-leg
principle. 24-in. plate girders were used in the exterior
walls at each floor level, as in Fig. 73.
The effects of earthquakes would scarcely seem to war-
rant much consideration in our latitude, though Quimby
and those who discuss his article, give considerable promi-
nence to it. " The only safeguard against an earthquake is
a system of bracing with some elastic material of positive
strength, that will so unify a structure that it will hold
together, even to the point of overturning bodily."
The Chicago skeleton construction has been adopted in
San Francisco, where the fear of earthquakes has, hereto-
fore, been sufficient to keep investors from erecting high
buildings. The new Chronicle building and the Croker
and Mills buildings are of the Chicago type, twelve stories
and over in height, and nave served as precedents in
that locality.
From a consideration of the wind strains in a building
it would seem that a seventh point should be added to the
list of headings under the discussion of columns, namely :
7. Column Joints. — "The stability of the individual
columns in a framed structure is an element of resistance of
WIND BRACING. 157
considerable value if the connections are rigid," and
" wherever adequate rod-bracing is not provided, join the
columns by complete splices, making them continuous, each
column a unit, to fail only by breaking or bending."
Although Quimby seems to limit the necessity of such
continuity to cases in which no wind bracing is provided,
the writer believes that the method of column joints at
each and every floor level is wrong, whether wind bracing
be provided or not, and that the tendency should rather
be toward design with continuous columns, and riveted
members for the main girders and spandrel sections in the
walls. Nor should efficient wind bracing be neglected
even with these additional factors.
Columns have generally been of single floor lengths,
with J" cap-plates on top, with the beams connected
to the columns by rivets through both top and bottom
flanges, those through the bottom flange passing also
through the bed-plate and the angle riveted to the column
beneath (see Fig. 78). Connections to the bed-plate only
should always be avoided, as the lateral strain to be re-
sisted should go to the column and not to the bed-plate.
The columns are usually connected to each other by at
least four rivets, spaced on opposite sides, as far from
the centre of the column as possible, and passing through
the cap-plate and connection-angles of each column. If
this is done, every rivet driven tends to stiffen the connec-
tion of the columns. If the girder loads are heavy, bracket
angles must be provided in the lower column to take the
shear off the cap-plate. At least 3J-in. bearing in full is
given to each beam, and the columns should be carefully
planed on the ends, and at true right angles to the column
axes.
This method of bracketing the tiers of columns together
by means of angles or bent plates, gives a detail that is
158
ARCHITECTURAL ENGINEERING.
sufficient to prevent lateral displacement, but because of
the elasticity of the brackets in bending, and the large
ratio of the height of the column to the base, contributes
very little to the rigidity of the structure. The overturn-
ing 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 the writer believes can be obviated by
continuous columns.
In the Masonic Temple, the use of columns of two-
storied lengths was tried, as an additional factor of stiff-
ness in so high a building, with the joints "staggered,"
FIG. 103.
or each column breaking joints with its neighbor. The
next step was to discard the bed-plates entirely, using
vertical connection-plates for all column splices. Fig. 103
WIND BRACING.
159
shows a column splice with connections for the floor-
girders and wind bracing, used in the new Pabst Building,
Milwaukee, by S. S. Beman, architect. The floor-girders
are made of latticed channels, and the sway-rods are con-
nected to the vertical splice-plates of the columns much as
the laterals in bridge-work are connected to the chords.
The following clauses relating to the splicing of the
Gray columns used in the Reliance Building are from the
specifications 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 longitud-
inal axis of the column, and the greatest care must be used
in making this work exact.
The columns will be con-
nected, one to the other, by
vertical splice-plates, sizes of
which, with number of rivets,
are shown on the drawings.
The holes for these splice-
plates in the bottom of the
column shall be punched J- in.
small. After the splice-plates g
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."
*•>*•
JED
.0:
QiiiiO
ribl
•I
FIG. 104.
l6o ARCHITECTURAL ENGINEERING.
Fig. 104 shows a typical detail of a column splice in
the Reliance Building, where the framing for a bay win-
dow joins the column.
Foster Milliken, in his discussion of Quimby's article,
classifies the .points constituting a perfect joint as follows :
1. Continuity of column from cellar to roof.
2. Proper connections for load and proper distribution.
3. Facility of connections for wind bracing.
4. Ready alignment.
5. Simplicity of design, facilitating erection.
He adds that the ideal column would be one tapering
uniformly, with the section varying from floor to floor with
the loads, advocating the continuous Phcenix column with
pintle-plate connections, as before described. Any such
system as this, demanding built sections of plates and angles
for girders, instead of the conventional rolled beams, would
certainly give much more efficient connections with the
columns; and joints may be designed adding greatly to
the rigidity of the structure, even where the regular trans-
verse bracing is omitted, or where it interferes seriously
with the necessary openings in the partitions.
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.
WIND BRACING. l6l
If, then, we have an office building or any skeleton
structure 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 in. or 9 in., which would throw the centre of gravity of
the upper wall beyond the outer edge. The maximum
allowable deflection would be about 2\ in. or 3 in., and this
would give a height of from 70 to 95 feet.
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 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 feet.
Some recent experiments, however (see Engineering
News, March 3, 1894), on the deflections of tall skeleton
construction buildings in Chicago, tend to show that any
actual deflections in well-designed and carefully con-
structed 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 posi-
tions, and these observations 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 \ 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 thick-
ness, and the length is several times the breadth, it is diffi-
1 62 ARCHITECTURAL ENGINEERING.
cult 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
Monadnock Building, except that the amplitude of the
vibration was less in the former building, due to its some-
what more sheltered position. The same peculiarity of an
apparently greater longitudinal vibration was noticed here
also. The wind was from the northwest, and registered
eighty miles per hour.
CHAPTER IX.
PARTITIONS— ROOFS— MISCELLANEOUS.
PARTITIONS.
MOST of the partitions now placed in Chicago office
buildings are made from the same character of hollow tile
as is used in the floors and around the columns, except that
a soft tile is almost invariably used to allow the driving of
nails in placing the door-frames and transom-lights. Tile
blocks are used in this construction, varying in thickness
from 2 in. to 6 in., but the 4-in. blocks are generally used.
They may be either square or brick-shaped, and are fre-
quently clamped together, but are always laid to break
joint, At all openings in the partitions wood frames are set
to stiffen the jambs, and to afford grounds for the plastering,
as well as to serve for the attachment of the architraves.
The plastering is applied directly to the tile surface.
These partitions may be readily torn down and shifted
to suit the tenant, without injuring the construction of the
floors or walls. They are never used to sustain loads.
An effective partition which has been used quite exten-
sively, consists of metallic lathing wired to light channel-
irons, spaced as studs. Each side is then plastered, making
a partition only 2 in. thick. This type of partitions was
adopted in the Armour school and in the Dexter office
building in Chicago.
Another method is to use i^-in. I beams spaced as studs
2 ft. on centres. The spaces between these supports are
163
164 ARCHITECTURAL ENGINEERING.
filled in with scratch-coat mortar, and a coat of plaster-
ing may then be given each side. II either of these systems
of metal studs is used, a strong solution of alum-water
should be given the rough coat of plastering to prevent the
staining of the finished plaster.
ROOF CONSTRUCTION.
The roof construction in such classes of buildings as are
here being considered, should be as thoroughly fire-proof as
any other part of the structure. This is secured through
the use of tile arches, as in the floors, or by means of book-
tile supported on T irons, placed about 18 in. centres. The
T irons are supported on I-beam purlins, and if this type is
employed care must be taken to see that such a form ol
book-tile is used as will effectually protect the under sur-
faces of the T irons. A common method has been to place
the book-tile on the flanges of the T irons, thus leaving the
lower surface of the T's with a coating of plaster only.
Book-tile are now made which project below the metal
work, as do the floor arches, thus offering a coating of clay
as protection against heat (see Fig. 105).
V- 16" * 16" •• * '6" *
FIG. 105.
Tile arches of the segmental pattern are often used in
roof construction, and the whole is then covered with a
layer of concrete which receives the composition roofing
(see Fig. 57). The supporting girders and purlins should
also be covered, either with special forms of tile blocks or
slabs, or else with expanded metal lath to receive a thick
coat of cement plaster.
Great care should be taken to see that all spaces between
PA R Tl TIONS— ROOFS— MISCELLA NEO US. 1 6$
roofs and suspended ceilings are rendered fire-proof in all
their parts, that the spread of unseen fire may be made im-
possible. Much may be done through a judicious use of
metallic lath secured to a light iron framework, in the
innumerable instances where a masonry or tile protection
becomes impossible.
SUSPENDED CEILINGS.
Such ceilings are usually made of book-tile or of a thin
fire-clay tile supported by light T irons. Ceiling tile is often
made not over % in. in thickness, with grooved edges that
fit into i X i inch T irons, spaced 12 inch centres, which are
supported in turn by 3 in. T's hung irom the roof purlins.
FURRING TILE,
to take the place of the wood and lath furring used in ordi-
nary construction, is employed to prevent the penetration
of the moisture through the exterior walls. These tiles are
made similar to the partition tile, and should always be pro-
vided with an air-space, to insure a circulation of air, that
the injurious effects of damp walls upon the interior finish
may be overcome.
FIRE-PROOF VAULTS.
The old system of building brick vaults in tiers is not
followed in the modern office building. The vaults are now
built of tile and placed as may be desired according to each
floor plan, much as the tile partitions. They are not
usually shifted, but should it be required, the operation,
would in no way affect the floor or load-bearing construe-,
tion. The tile walls should be of considerable thickness,
with at least two air-spaces, and the top should also be
made of two thicknesses of tile in case the vault does not
run to the ceiling.
1 66
ARCHITECTURA L ENGINEERING.
STAIRWAYS AND ELEVATOR ENCLOSURES.
The stairways are usually made of cast risers, strings,
and newel-posts, with wrought railings and wooden or
polished bronze or brass hand-rail. All exposed parts of
the risers and strings are generally specified to be panelled
FIG. 1 06.— Main Entrance and Elevator- hall, Marquette Building.
and ornamented as per detail drawings, and provided with
lugs and flanges to receive the marble treads and plat-
forms. The metal-work for the stairways and the elevator
PAR TIT IONS— ROOFS— MISCELLA NEO US.
i67
guards or enclosures are heavily electroplated in brass, cop-
per, or bronze. An aluminium finish was tried in the newer
portion of the Monadnock Building. Chicago, but it has
tarnished very badly. Fig. 106 shows the main entrance-hall
to the Marquette Building, serving as a good illustration, of
the decorative treatment which may be given the columns
and exposed or sunken girders in the ceiling. Fig. 107
FIG. 107.— Entrance-hall, New York Life Insurance Building.
shows the main entrance to the New Vork Life Insurance
Building, with the walls, ceiling, and stairs finished in
Italian marble and the floor of mosaic.
1 68
ARCHITECTURAL ENGINEERING.
The main stairway and entrance-hall to the Fort Dear-
born Building are given in Fig. 108.
EfflBAflCE ^ELEWOR HALL - -TO BANK
• , JE/WEY &MUM)IE -ARCHITECT.?
FIG 108.— Entrance-hall, Fort Dearborn Building.
COLUMN-SHEETS.
Before the column-sheets may be started it is necessary
that all loads occurring in the structure be definitely settled.
These loads include, as suggested in the previous chapters,
the weights of all structural material (floors, roof, piers,
spandrels, and the like), besides wind, snow, elevator, and
tank loads. The column-sheets may then be started, 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
down to the foundations. The column weight itself is first
PA JK TIT IONS— ROOFS— MIS CELL A NEO US.
169
assumed, and then corrected, after the proper section is
obtained.
The column-sheet used in the Masonic Temple calcula-
tions was as follows :
Column i.
Column 2.
Load
on Column.
Load
on Footing.
Load
on Column.
Load
on Footing.
to
8
&
Floor load
Masonry piers
Spandrels
Elevators
Tank loads
Weight of column
Total
«'
£
s
The column-sheet used in the Venetian Building was
made as in the accompanying table :
Column i.
Roof.
Attic.
1 2th
Floor.
Load from column above. ..... .
Floor load live ....
Spandrels
Estimated weight of column
Total
Wind Loads.
Concentric wind loads
Total wind load
Column 2.
Etc.
[ Base-
\ aient.
Total.
ARCHITECTURAL ENGINEERING.
The following column-sheet is to be recommended as
combining all requisites in a tabulated statement:
Column i.
Column 2.
Load
on Column.
Concentric.
Load
on Column.
Eccentric.
Load
on Footing.
Masonry piers
Elevator loads
Tank loads etc . . .
fa"
o
Weight of column
Wind
0
&
Total
Area required for col. . .
sq. in.
sq. in.
Foot'g area
Material of column
sq. ft.
Load
on Column.
Concentric.
Load
on Column.
Eccentric.
Load
on Footing.
t£
fe
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 propor
tioned.
CHAPTER X.
FOUNDATIONS.
No part of the work of the engineer requires more care
and skill than the design and execution of the foundations.
" Where it is necessary, as so frequently it is at the present
day, to erect gigantic edifices — as high buildings or long-
span bridges — on weak and treacherous soils, the highest
constructive skill is required to supplement the weakness of
the natural foundation by such artificial means as will enable
it to sustain such massive and costly burdens with safety "
(Baker). And nowhere is this more true than in Chicago,
where it is almost impossible to penetrate to bed-rock with
any degree of practicability, and where the soil underlying
the city consists of blue clay (below a soft loam or quick-
sand) at about 12 or 14 feet below the sidewalk grade, and
thence down to a bed-rock of limestone from 40 to 80 feet
below the street level. The clay is hard and firm in the
upper strata, but becomes soft and yielding as it descends,
often containing pockets of spongy material, thus necessi-
tating borings for reliable information of particular locali-
ties. Borings have been extensively made, both by private
parties and by the government, resulting in an allowance of
from i£ to 2 tons per sq. ft. on the clay, with due consider-
ation for proper settlement. Baker states as follows on
this subject : " The stiffer varieties of what is ordinarily
called clay, when kept dry, will safely bear from 4 to 6 tons
per sq. ft., but the same clay, if allowed to become saturated
with water, cannot be trusted to bear more than 2 tons per
171
I72 ARCHITECTURAL ENGINEERING.
sq. ft. At Chicago the load ordinarily put on a thin layer of
clay (hard above and soft below, resting on a thick stratum
of quicksand) is \\ to 2 tons per sq. ft., and the settlement,
which usually reaches a maximum in a year, is about i in.
per ton of load."
Unequal settlement is thus the great evil that must be
guarded against, for settlement will come, slowly but surely,
and in all good designs it is provided for in the start by
making the structure some 3 in. to 5 in. higher than its final
level. The evil of unequal settlement can hardly be better
exemplified than in the case of the United States Govern-
ment Post Office and Custom House in Chicago, built in
1877, and now about to be replaced by a new one. The
foundations consist of a continuous sheet of concrete, made
in different layers, but altogether 3 ft. 6 in. thick. Some
portions of the building were extraordinarily heavy, others
comparatively light, but the Washington architects thought
the concrete sufficient, even though there were bad sloughs
under the building. But it has proved a most dismal
failure, and even a menace to life and limb. It has settled
nearly 24 in. in places, and a dropping of some part of the
structure is no unusual occurrence. After but eighteen
years of service this example of government architecture
and engineering has been known as " The Ruin " in Chi
cago and vicinity.
The investigation of the compressibility of the soil leads
to the conclusion that, if we wish to procure uniform settle-
ment, all parts of the foundation areas must be exactly pro-
portioned to the loads they have to carry. Examples are
not lacking, in Chicago and elsewhere, of the actual crush-
ing of light piers, when alternating with heavy ones, be-
cause, proportionately, the lighter piers had too great a foot-
ing area. In the Mills Building in New York City the
mullions in the lower floors of the building and over the
FO UNDA TIONS. 1 7 3
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.
The footings themselves must be of sufficient strength
to distribute the applied loads over the requisite area ; in
this way only can satisfactory results be obtained.
The arrangement of independent piers was first advo-
cated in Chicago by Frederick Bauman, in a pamphlet
published by him in 1872, entitled " The Method of Con- o
structing Foundations on Isolated Piers," and this method
has certainly been brought to a high degree of perfection
by the engineers of Chicago. The rapid development of
foundations is well exemplified by the great change in
methods employed at the site of the Woman's Temple. In
1890 the lot where this building now stands was bought by
the present owners. Extensive masonry foundations had
previously been built here 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 a cost of many thousands of dollars. The old sys-
tem consisted of stone piers made of successive layers of
large stones, stepping out until a sufficient base was ob-
tained. One of these newer " raft" footings is here given/
and also one of the old masonry type (Figs. 109, 1 10).
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
with a bed of concrete, resting on the clay stratum about
10 ft. below street grade. A comparison of some of the
above points may be made as follows:
1/4 ARCHITECTURAL ENGINEERING.
I. Space.
i st. Top of concrete to bottom of casting — i' 8".
2d. « " « = 7'o".
Or, comparing the parts above the common bed of concrete,
ist = 217 cu. ft., 2d = 691 cu. ft.
This point of space is a very important one, as has been
before mentioned, since basement-space is now quite as valu-
FIG. no.
able as any office-space, for use as restaurants, cafes, or for
the large boiler and electric-light plants necessary. Indeed,
it is of frequent occurrence to extend the basement-space
FO UNDA TIONS. 1 7 5
out under the sidewalks and even 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. Hence the present details.
II. Weight. — Rating the masonry at isolbs. 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," Engineer-
ing News, August, 1891).
This saving in weight is one of the factors that makes
our highest buildings possible, and even the " sky-
scrapers " are not loading the clay as severely as some of
the older structures. When the foundations of the old
masonry building were torn out to make room for the new
Reliance office building, the clay was found to be loaded
to 2 tons and over per sq. ft. for a five-story building,
while " The Fair " Building is loaded to 2850 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.
176 ARCHITECTURAL ENGINEERING.
IV. Time. — In the time required for building opera-
tions 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
foundations under side walls frequently cannot step out
sufficiently to get the proper bearing area without project-
ing into the next lot. But with iron we can combine
several footings, or use cantilever foundations, thus secur-
ing the desired results.
As may be seen by Fig. 109, the new type of founda-
tions consists first of a layer of concrete, about 2 ft. thick,
upon which come layers of I beams or rails, each layer
laid transversely to those just below or above. The spaces
between the rails are rammed tight with concrete, which
preserves the iron from the action of air and water.
It is the judgment of the best engineers that the area
of the foundations on the clay 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 per-
centage of the interior-column loads than of the wall-
column loads. Experience has also shown that after the
clay has been compressed by a load of 3000 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. So that it is good practice to neglect
live loads on the clay for hotels, office buildings, or lightly
loaded retail stores. In warehouses, however, or in build-
ings 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
FO UNDA TIONS. 1 7 7
largely. Hence we must make extra allowances in such
instances.
In all cases where live loads have been figured on the
columns, consistency requires that whatever loads have been
figured on basement columns, must be figured on the
metal in the foundations ; or the clay areas are proportioned
for dead loads only, while the strengths of the foundations
themselves are figured for dead + some live load. But, as
before said, many of the best buildings have entirely dis-
regarded live loads on the footings. W. L. B. Jenney
advocates as follows: In hotels, office buildings, 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 we figure for live load.
In " The Fair " Building, where a large quantity of mer-
chandise is stored, and the aisles are constantly filled by
throngs of people, the following system was used : The
floor-beams carry all the dead + live loads, the girders
carry the dead load + 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 -f- the total
dead load. The percentage of live load is given in the
last column of the accompanying table :
Column. Live load on beams. Per cent for column.
Attic 100 per cent.
i6th story 75 Ibs. 90 "
1 5th " 75 « 87* «' «
I4th " 75 " 77^ " "
1 3th " 75 " 72 J " "
Decrease of 2J- per
cent in each story.
6th story 75 ibs. 55 per cent.
5th - 130 " 524 " "
Basement 130 l- 40 " "
178 ARCHITECTURAL ENGINEERING.
No live load was figured on the clay area, but the
allowable pressure per square foot was taken at a very con-
servative figure — 2850 Ibs.
The first use in Chicago of iron rails, in connection with
masonry or concrete footings, occurred in the Montauk
Block, by Burnham & Root, architects. The old method
of pyramidal foundations of dimension stones was used
with a concrete base 18 in. thick. Iron rails were built into
this concrete to obtain a larger offset than could otherwise
have been obtained.
At first old rails were employed in these foundations,
but now practice demands as reliable material in this por-
tion of the metal-work as in any other. Steel rails at 75 Ibs.
per yd. are generally used unless steel beams are required.
Ordinarily, rails are cheaper than beams ; more iron is
required, but at less cost than in beams. The concrete, too,
is easier to ram between the rails, and the webs are always
thick.
Under very heavy loads, or long spans, beams become
necessary, 10 in. to 20 in. I beams being frequently used.
Only the projecting portions are strained as beams, hence
the place for beams is at the top of the pile— the larger the
proportion of iron or steel uncovered the more economical
the foundation. 20,000 Ibs. and 16,000 Ibs. have been used
for fibre strains in steel beams and iron rails, though the
new Chicago ordinance limits the fibre strain to 14,000 Ibs.
and 11,000 Ibs. per square inch. In the Old Colony Build-
ing 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 a
fibre strain of 21,000 Ibs. per sq. in. of extreme fibre. The
Carnegie strike at the time of building precluded the possi-
bility of obtaining heavier beams than I5~in. QO-lb. I beams,
so the strain was allowed under the press of circumstances.
FOUNDATIONS.
179
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
—T-. Multiply the result by 250
pounds per sq. ft. on earth
(equals approximate weight of footing per square foot), add
to the original load, and refigure. The layers are then
laid off, the projection of any layer beyond the one imme-
diately above being always 3' o" or less. The moments on
the projecting portions of the layers are then found, and
these moments, divided by the allowable bending moment
per rail, usually taken at 12,500 foot-lbs., give the number
of rails required in the different courses. One extra rail
is 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-lb. rails are
most commonly used.
No.
Weight.
Height.
Base.
u.
/.
R.
M.
f— 16,000.
6504
65 Ibs.
15-86
6.86
9,150
7501
75
4f"
4|"
21.00
8.30
11,070
7503
8001
75
80
4f
5
5
¥
21.66
26.36
9-37
9.99
12,500
I3>320
8501
85
5
4f
2f
27.32
10.41
13,880
8502
85
5A
5
2f
29.22
11.13
14,840
8503
85
5
5
aft
25.38
10.03
13,370
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-lb. rails, No. 7503 in the previous table. The bottom
courses of all footings were of concrete, 12" thick, ex-
tending 6" beyond the lower course of rails, but the
weights of these concrete courses are not included in the
i8o
ARCHITECTURAL ENGINEERING.
following. Cast shoes 4' o" X 4' o" were used under all the
columns. The concrete was figured as weighing 125 Ibs.
per cubic foot.
Load on Col.
Area of Footing, sq. ft.
Weight per sq. ft.
Rails.
Concrete.
415,470
12' 'X llf = 141'
49
83
433,440
JO X I4i = 146
58
60
435,820
9 x 16} = 146
77
83
461,100
12 X 13 = 156
42
80
496,240
10 X i6| = 163
79
91
526,850
I2| X 14 = 178
66
82
531,740
13 X Mi = 185
60
78
57L360
I3i X I4i = 192
67
74
595,920
12^ X 1 6 = 200
67 88
621,560
13 x 16 = 208
60 94
637,240
13* X "i 6 = 214
68 68
666,000
15 X 15 = 225
66 105
672,000
13 X 17! = 228
67
93
BEAM AND RAIL FOOTINGS.
The next step made in the development of the raft foot-
ings was in the use of I beams for the upper course or
courses. Fig. 1 1 1 shows a foundation which was figured as
follows (see Engineering News, August, 1891)'-
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' S" X if 3". The lower layer of con-
crete was 1 8" thick, projecting 8" beyond the lower course
of rails. Fifteen-inch steel beams were used in the top
course, weighing 50 Ibs. per mot. The allowable moment
on each beam equalled 117,700 ft.-lbs. The remaining
courses were of steel rails, 4f" high and 4f " base, 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 project-
ing arms must therefore be determined. The total length
of the I beams so found will fix the width of the second
FOUNDATIONS.
181
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 bv the
K yj--// :
FIG. in. — Beam and Rail Footing from "The Fair" Building.
lengths of the upper ones, and by the dimensions of the clay
area; hence the question is, how many pieces are required?
The formulae used may be derived as follows :
Let y = projecting arm in any course ;
a = width of supporting area ;
1 82 ARCHITECTURAL ENGINEERING.
I — 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.
ly
The total load on y = — : , and since the distribution of
« + 2/
the load on every layer is uniform, we have
ly v Iv*
M = — ~- - X lever arm 4 = -,— -
2~2(a+2y)'
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/ is unknown.
Considering now the top course, under the base casting,
5'o" X 5' o" in area, we find that 9 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 117,700 ft.-lbs. = 1,059,300 ft.-lbs. Then
*2K -f*2y) = I'°59»300f whence y = 5' 4". The length of
this layer then becomes 5 + 2 y — 15' 8".
For the second course we find that 31 rails spaced about
6" centres may be placed under the 15' 8" beams. Closer
spacing than this may be used if necessary. The load now
equals 1,166,000 Ibs. -f- the weight of the top course (about
19,000 Ibs.). Then - = 375, 100; whence y = 2' 5" '.
The length of the rails therefore = 5' o" + 4' IO// = 9' IO//-
For the calculation of the lower courses, we know that
the area covered by the bottom course is 15' 11" X 21' 4".
This leaves a projection of 3'OiJ-" for the bottom course, and
a projection of 2' 10" for the next to the bottom layer.
Then for the third or next to the bottom course, we have
1.200,000 Ibs. x *| ft. X iA = =
21$ S>/
FO UNDA TIONS. 1 8 3
This moment requires 19 rails to be used in the layer.
For the bottom course,
. i ,220,000 Ibs. X 3rfr ft- X iji
M = - = 343,ooo ft-lbs.
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' 10". 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-J- ft, or,
1,200,000 X 8| X4TV
M=- — — 1,920,000 ft.-lbs.
2lj
This must be resisted by the combined moments of the 9" I
beams in the top layer, and the 19 rails in the third layer, or
1 ,059,300 + 229,900 = 1,289,200 ft.-lbs. This assumption
leaves a difference of 630,800 ft-lbs. which has not been
cared for.
The practice in regard to the calculation of such foot-
ings is still an unsettled question. Those who used the first
method claimed that the action of the concrete filling, with
its tendency to bind the iron and concrete together, caused
the foundation to act as a whole, and thus possess a
moment of resistance much greater than the sum of the
resistance of the individual layers. But in view of the
uncertainty of any such assumption-, the other method of
calculating all moments about the edge of the casting
would seem more logical, as well as being on the safe side.
Both methods are now being used in Chicago buildings.
The use of rails in footings has been succeeded almost
entirely by the use of I-beams throughout.
1 84
ARCHITECTURAL ENGINEERING.
Fig. 112 shows a footing used in the Marquette Building
for a column load of 920,250 pounds.
5-2Q*J'totoaarfoi'
n ii nil LI ii n ii H •
T
4*'
4.
*w<
_.i-
C0t../Vo. 29 -1,0*0=320.250*63.
C/967- &/)££• 3J 6 "x 4-J0 "
FIG. 112.
> 730 tas.
FIG. 113.
Fig. 113 is taken from the same building, and is figured
for loads of 406,340 Ibs. on column 32, and 561,790 Ibs. on
column 44.
In determining the sizes of the beams or rails in any
layer, care must be taken to leave sufficient clearance be-
tween the flanges to admit the concrete which must be
rammed in place. If stone, broken to pass a f-" ring be
specified, i" as a minimum between the flanges will answer.
In covering these rails with concrete 4 inches of con-
crete should be left at the ends and sides of the rails, and i
inch on the tops. A plank frame is made of the same size
as the concrete bed, and at the proper height by the aid of
levels. After this is filled another frame is made for the
next, course, and so on. The concrete is made of the best
Portland cement, usually i part cement to 4 parts of broken
stone and 2 parts of coarse sand. The concrete must be
well tamped between the beams, and the whole exterior
FO UND A TIONS. 1 8 5
plastered with pure Portland cement mortar, so that no
metal-work is exposed. A bed of concrete 18" or 2' o"
thick comes under all, projecting 6" to 12" beyond the rails.
COMBINED FOOTINGS.
The raft foundation is particularly valuable where the
positions of loads in reference to each other are bad. We
may then use compound foundations, combining several by
means of long beams— as under smokestacks, party-walls, etc.
One of the most delicate problems is the construction of
a very heavy building by the side of one already completed,
so that the latter will not suffer by settlement, due to the
additional weight of the new building.
Such settlement was shown to a remarkable degree in
the Studebaker Building, next to the Auditorium, Chicago.
The former settled from 10" to 12" from the weight of the
latter. To obviate such settlement the old wall is carried
on timbers, supported at either end by jack-screws. The
new wall is then put in, and, with the new foundation which
is provided, settles gradully. The jack-screws under the
old building are turned as occasion requires, to keep the
old wall at its proper level. This is continued until all
settlement ceases, when the jack-screws are removed, one by
one, and a new wall is substituted under the old building.
If access cannot be had to the basement ot the old
building, or underpinning, in the manner above described,
is impossible, cantilever foundations must be employed.
The old foundations must not carry any additional weight,
and we cannot substitute new footings ; hence the usual
type of raft footing is used, but several are combined, and
the centre of gravity of the combined area coincides with
the centre of gravity of the loads. On these footings come
high cast-iron shoes, supporting cantilever girders which
carry the columns and wall of the new building, immedi-
1 86
ARCHITECTURAL ENGINEERING.
ately next to the old one, and yet transferring all the load,
with the attendant settlement, away from the lot-line. The
first cantilever footings introduced in Chicago were used
in the Manhattan and Rand-McNally buildings 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 disturbed. This method was em-
ployed in the Western Union Building in New York, where
FIG. 114.
•
a load of 286 tons was transferred from a corner to more
secure footings.
Such a combined footing maybe analyzed as follows:
FO UNDA TIONS.
I87
Taking Fig. 114 as a plan, and Fig. 115 as an elevation, the
line of flexure of the 15" I beams will be as in Fig. 1 16. To
find the maximum bending moment on these beams we must
FIG. 116.
compute the various bending moments and compare. The
bending moment will be maximum when the shear — o. In
this case there are five such sections, as shown by the line
of flexure ; hence we must compute the moment at each
point to find the greatest. The moments under the
columns will be +, causing convexity downward, while
the moments between the columns are — , causing con-
vexity upward. Fig. 117 may then be used.
\>-m
IJjil/
---- or-
li
H f I t
ft 1 1 tt 1
T t nt t
i
^__ ! „„
pzzz -/-. H
FIG. 117.
To find the distance of the centre of gravity of the loads
from the left end we have
Pb + Ptf + c
P
P
,
=?,, and
- = A-
a I
The distances from the left end of the beams to the points
1 88 ARCHITECTURAL ENGINEERING.
where 5 = o, or the distances xl , x^, *,, *4) and x^, are then
found to be as follows :
mp
*..=*= -*)ft or *'=;
_
A -A
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 (remember-
Wl
ing that M= -- for a uniformly loaded cantilever) is
Mt =
- OT — a — n — a.
2
In general cases 7I/., and jW, will be small except where
FO UNDA TIONS. 1 89
the columns are very far apart, and the maximum bending-
moment will be at either Ml , Mt, or Mt , 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 Mlt M3,
and M6 will be reduced. M9 and J/4 would not, however,
be altered.
Sufficient deflection could hardly take place to in-
crease 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. 118.
JIT/
FIG. 118.
Thus, from Clapyron's formula, we have
for a continuous girder of two equal spans, /. But in the
case assumed
2 o 2 o _t
Taking now the shears 5, and 53, on the left and right
respectively, of the reaction R1 , and remembering that
Sl + S\ = RI , we have
5, = — L~7"~J)+ ~> and 5, =//,.
Then
19° ARCHITECTURAL ENGINEERING.
where f/>/ is the reaction due to the loads on the two spnas
/, the same as in the regular formula for two spans, and//
is the reaction due to the cantilever load, while -^~- is the
4 I
effect due to the use of the beam as a continuous girder.
Also,
r, 5 . , i pl?
These reactions show a varying tendency in the unit
pressure on the clay, as in Fig. 118.
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 con-
sider 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.
SETTLEMENT.
It must not be forgotten that the footings are designed
for the final loads that rest on 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 com-
pleted state, if uniform settlement is desired. This was well
exemplified in the case of the Auditorium tower, which
extends many stories above the main building, thus bring-
ing 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
FO UND A TIONS. 1 9 1
most careful tests of the ground beforehand, this tower has
settled more than originally allowed for.
When a test load is applied to the surface, an initial set-
tlement occurs on the surface at a pressure of i ton per sq.
ft. Another settlement is produced under an increased
weight, which ceases in a few hours, and further settlement
will not directly occur even with a load of 4500 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' o"
deep, 5r o" in diameter, and 4' 6" 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 TV' per month.
If the building is heavy, an immediate settlement of
from 2\" to 4" is noticed, followed by a gradual progres-
sive settlement. The Monadnock Building, 200' high,
with 3750 Ibs. per sq. ft. on footings, settled 5", while 6" was
allowed for. The Western Banknote Building, eighteen
stories high, built on quicksand over clay, with solid
masonry walls and fire-proofed, settled 2J-". The Home
Insurance Building settled £" under two additional stories,
and "The Fair" Building settled only i".
PILE FOUNDATIONS.
It is this uncertainty of settlement, and limit to the
bearing capacity of the clay, which would seem to make
192 ARCHITECTURAL ENGINEERING.
the pile the best foundation, if its use can be effected with
consistent economy.
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 build-
ings could be more trying on any type of foundations.
Some twenty years ago the use of piles in Chicago was
decried in consequence of the very slipshod 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
by the time the floors were placed a variation of 7%' had
resulted in the settling.
Another very good example of poor pile-driving at
about the same time were the foundations for the Chicago
water-works tower. The surface material consisted of about
if of pure lake-shore sand, and a very heavy hammer was
needed to drive a pile even J" by measurement, the hammer
rebounding three and four times. But the specifications
as to depth had to be complied with, and the piles were
hammered and hammered until the sand was pierced
through, and a drop of u" was suddenly noticed.
After these and other failures the stone and concrete
foundation was used, until the introduction of the " raft "
method, which was almost universally approved, and so
FO UND A TIONS. 1 93
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 ap-
preciable unequal settlement.
Another firm advocate of the pile foundation is 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." So it
was 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. Mr. Adler, who is one of the best authorities on
pile foundations in Chicago, states as follows on this case :
" As the tendency in pile-driving was to raise the sur-
rounding earth, \ve watched the adjacent buildings care-
fully. It was found on driving the piles in the first lot that
an adjacent building had settled 6 in., and had to be raised on
screws ; and throughout the pile-driving these settlements
were noticed, requiring the greatest care. Another sur-
prise was that of the four surrounding buildings the one
with the least efficient foundations was the only one not
requiring such attention, and the piles were driven right up
to the building-line without movement of the walls. Un-
der the Borden Block, the heaviest of the adjoining build-
ings, the movement was such as to require holding up, and
inserting new foundations.
" Another peculiarity, which seemed to be a legitimate
outcome of the pile-driving, was the apparent readjustment
of the particles of clay and sand into the condition of jelly,
IQ4 ARCHITECTURAL ENGINEERING.
thus destroying the resisting qualities. The water in the
soil is not thoroughly mixed, but occurs in strata or
pockets ; hence the jar of the driving caused the sand, clay,
and water to mix, forming a jelly. The water also rushed
into the Schiller site from under the Borden Block, un-
doubtedly explaining some of the settlements."
These remarks of Mr. Adler certainly show that the
work in question was not at all successful as regards the
adjacent property, and, indeed, such damage was done by
the pile-driving in the case of the Schiller Theatre that suit
was instituted against the owners of that building, by the
owners of the adjacent Borden Block, as a result of damage
sustained. A similar suit was brought against the proprie-
tors of the Stock Exchange building, and the results of the
suits now pending must largely settle the foundation ques-
tion in Chicago. The outcome is awaited with much in-
terest by all of the architects interested in high-building
methods.
The new Chicago Library foundations are perhaps the
most carefully executed pile foundations in Chicago, being
designed and executed by Gen. Sooysmith. 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 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 4500 Ibs., fall-
ing 42 in., 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.
FO UND A TIONS. 1 9 5
Their average diameter was 13 in., and the area at the
small end 80 sq. in.
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 sq. in. of the
sides of the piles, deduced from experiments under analo-
gous conditions, was 15 Ibs. per sq. in. The extreme resist-
ance 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. in. 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 113 sq. in.,
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 5OT7Q- tons
per pile. Levels were taken at intervals of two weeks, and
as no settlement was observed, 30 tons per pile was consid-
ered a safe load.
Tests were also made of drawing piles at this site, and
an ordinary pile, driven in clay to a depth of 45 ft, gave
45,000 Ibs. resistance.
In localities where bed-rock itself cannot be reached
with economy, piles will undoubtedly give the most satis-
factory results, it they can be driven to bed-rock or hard-
I96 ARCHITECTURAL ENGINEERING.
pan. the tops cut off below the water-line, and all this with-
out damage to surrounding property.
A prominent point in the criticisms of Gen. Sooysmith
on Chicago high-building methods is his recommendation
of deep piling to bed-rock, with the tops cut off 1 5 ft. below
datum. While this would doubtless be a good thing, it is
entirely unnecessary in the opinion of the writer, and far
too expensive, Some reasons for this difference of opinion
are the following : A number of high buildings supported
on piles driven to hard-pan only, with the tops cut off at
datum, are proving very satisfactory. Among others may
be mentioned the Home Insurance Building, which has
settled so uniformly that the greatest variation in levels
throughout the whole is but three-fourths of an inch.
Piling to bed-rock would necessarily be very expensive in
many localities, and in parts of Chicago this would mean
80 ft. below the sidewalk level ; and if the piles were driven,
from a sub-basement, as proposed by Gen. Sooysmith, the
trouble and expense of draining this area below the sewer
level would be very great. If piles are to be used at all, a
proper penetration of the hard dry clay would seem suffi-
cient, with the tops cut off at datum. The large grain ele-
vators along the Chicago River, with their constantly vary-
ing loads, which prove a most severe test, have stood with-
out blemish, as before said.
And that such piling is the only system of foundations
to be recommended, as Gen. Sooysmith thinks, might be
questioned. There can be no doubt that proper piling, or
caissons sunk to bed-rock, must be employed where room
cannot be had for steel foundations proportioned at 3000
Ibs. per sq. ft. of clay area, but some of the disadvantages
of piling have already been pointed out. The general law
of damage to adjacent property includes the driving of
pile foundations, and the difficulty encountered in caring
FO UN DA TIONS. 1 97
for surrounding buildings must certainly not be overlooked.
Where all buildings are built on piles, the adjacent prop-
erty need not be injured.
Another objection to piling next to buildings supported
on steel foundations lies in the difficulty of supporting the
walls on screws to allow for additional settlement during
and after the placing of the new foundations. This can
always be done when new steel foundations are used, but
it becomes much more difficult and dangerous with the use
of piles.
The method of independent piers and raft foundations
has certainly proved quite satisfactory in its very extensive
use in Chicago, and, with such uniform settlement as has
resulted, on account of the care that was taken beforehand,
it answers all the requirements made of it. The writer
has a preference for pile foundations, but the many advan-
tages that attend the other kind must be freely acknowl-
edged.
PNEUMATIC FOUNDATIONS.
Pneumatic caissons have lately been employed in a
notable example of high building construction in New
York City, namely in the Manhattan Life Insurance Build-
ing. 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' o" from the widewalk, and from side-
walk to base of flagstaff = 347' 6", and from base of foun-
dations to top of dome = 408' o". This makes the dome
6if o" higher than the neighboring spire of " Old Trinity."
The area of the lot is, approximately, 120' o" deep X 67'
o" frontage, or 8,000 square feet, which, with the estimated
total weight of the building of some 30,000 tons, would
give a load of 7,500 Ibs. per square foot of lot area.
The natural soil at the site consisted of mud and quick-
198 ARCHITECTURAL ENGINEERING.
sand to a depth of some 54' o", down to bed-rock. Had
piles been used, as close together as the New York build-
ing law allows, or 30" centre to centre, over the entire
area, some 1323 piles could have been driven, with an
average load of 45,300 Ibs. each. This was inadmissible,
as the building law limits the load per pile to 40,000 Ibs.
each, when driven 2' 6" centres.
A new departure in foundations was therefore neces-
sary, especially as the surrounding buildings were built on
the natural earth, making them particularly liable to in-
jury 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, the work being
executed by Sooysmith & Co. This was the first example
of the pneumatic system as applied to buildings, although
the same architects, Kimball & Thompson, had before used
smaller caissons in the Fifth Avenue Theatre building in
New York City, but without the use of compressed air.
Fifteen caissons, varying in size from 9' 9" in diameter
to 25' o" square, supported the thirty-four cast-iron columns.
These caissons were sunk to an average depth of about
31' 6" 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, 4 parts broken stone.
The superimposed piers were built 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. 119.
A very elaborate system of cantilever girders was used
to transfer the loads on the columns in the side walls to
FOUNDATIONS.
199
FIG. 119.
2OO
ARCHITECTURAL ENGINEERING.
proper concentric bearings over the caisson piers. From
these bearings the load was distributed over the whole
masonry-work by means of large steel bolsters, thus
FIG. 120.
diminishing and equalizing the unit-pressure. A cross-
section of the caissons and cantilever girders is shown in
Fig. 120.
CHAPTER XL
UNIT-STRAINS—SPECIFICATIONS.
THE question of unit-strains will naturally vary to a con-
siderable extent with the personal opinions of the designer
— the more conservative his views the lower his allowances.
But, whatever the preferences of the engineer or architect,
he is, to a large measure, limited by the city building laws
with which he is required to conform. A comparison be-
tween the building ordinances of New York, Chicago, and
Boston, given in the next chapter, will show the wide diver-
gence which exists in their respective requirements.
A few unit-strains will here be mentioned as having been
employed in Chicago skeleton buildings before the adoption
of the present ordinance. Cast iron and timber will not be
considered as entering into modern high-building construc-
tion.
BRICKWORK.
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 Chicago architects :
10 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.
201
2O2 ARCHITECTURAL ENGINEERING.
He shows, however, that these figures are very conserva-
tive, as his tables of the ultimate strength of best brickwork
give from no tons with lime mortar to 180 tons with Port-
land cement mortar per square foot. So while the 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."
COLUMNS.
We have few experiments of value on the ultimate
strength of full-sized columns of the type most used at
present. Building operations have to be conducted too
quickly to allow many tests on the full-sized columns before
using. Tests have been made on the full-sized Gray columns,
and on the Larimer column, as before referred to. 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 Engineers, April,
1888), who introduced this shape into the United States.
But even these tests are hardly fair ones for present com-
parisons, 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. It seems as though higher
breaking loads would be obtained for the majority of
columns as used at the present time. Burr, in his " Strength
and. Resistance of Materials," deduces formulas for the Key-
stone and Phoenix 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 the plates in the lighter columns. But
as the height of a single story was less than 12' o" unsupported
length, a uniform unit-strain of 12,500 Ibs. per sq. in. was
UNIT-S TjRA INS—SPECIFICA TIONS. 203
used without reduction by the radius of gyration, for all
concentric loading. Columns with eccentric loads were
figured for a unit-strain of 12,500 Ibs. per sq. in. reduced by
Rankine's formula for eccentric loading.
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 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-strain
gave a much greater section to the column than if a lower
unit-strain had been used and the wind forces disregarded.
These unit-strains have .been used in a number of Chicago
high buildings, notwithstanding some rather severe criti-
cism.
In " The Fair" Building, by 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 130 Ibs. live
load per square foot for the ist, 2d, 3d, 4th, and 6th floors, 200
Ibs. for the 5th floor, 100 Ibs. for the 7th 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-strain of 13,000 Ibs. per sq. in. was used on all
columns, made of channels and plates, with a proper reduc-
tion 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
204 ARCHITECTURAL ENGINEERING.
additional allowance for eccentric loading as before de-
scribed), 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-strains 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
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.
SPECIFICATIONS FOR STRUCTURAL STEELWORK.
Material and Workmanship. — The entire structural frame-
work, as indicated by the framing plans, or sp^ified, is to
be of wrought steel, of quality hereinafter designated, all
material to be provided and put in place by this contractor
unless specifically stated to the contrary. All work to be
done in a neat and skilful manner, as per detail or specified,
and if not detailed or specified, as directed by the superin-
tendent to his entire satisfaction.
Quality and Material. — Steel may be made by either the
Bessemer or open hearth process. It shall be uniform in
quality, and must not in any case contain over o.io of i per
cent of phosphorus.
The grade of steel used (except for rivets) shall fill the
following requirements when tested in small specimens:
Ultimate tensile strength : 60,000 to 68,000 Ibs. per sq. in.
Elastic limit : Not less than one half the ultimate strength.
Elongation : Not less than 20 per cent in 8 in.
Reduction in area : Not less than 40 per cent at point of
fracture.
UNI7^-S TRA INS—SPECIFICA TIONS. 2Q$
Bending Test. — Duplicate specimens will be required to
stand bending 180° around a mandrel, the diameter of which
is equal to one and a half times the thickness of the specimen,
without showing signs of rupture on either concave or con-
vex side. After being heated to a dark cherry red, and
quenched in water at 180° Fahr., the specimen must stand
bending as before.
Inspection. — All steelwork is to be inspected front the
melt to final delivery of finished material on board cars.
The inspection will include surface, mill, and shop inspec-
tion by an inspector satisfactory to the engineer, to whom
all reports are to be made. No work shall be delivered
until approved and stamped by the inspector. All inspec-
tion shall be at the expense of this contractor.
Tests. — A test from the finished material will be required
representing each blow or cast. In case the blows or casts
from which 'the Blooms, slabs, or billets in any reheating
furnace charge are taken, have been tested, a test represent-
ing the furnace heat will be required, and must conform to
the requirements as before specified.
The original blow or cast number must be stamped on
each ingot from said blow or cast, and this same number,
together with the furnace heat number, must be stamped on
each piece of the finished material from said blow, cast, or
furnace heat.
Rivet Steel. — The steel used for rivets shall fulfil the fol-
lowing requirements:
Ultimate tensile strength : 56,000 to 62,000 Ibs. per sq. in.
Elastic limit : Not less than 30,000 Ibs. per sq. in.
Elongation : Not less than 25 per cent in 8 in.
Reduction of area at point of fracture shall be at least
50 per cent.
Specimens from the original bar must stand bending
1 80° and close down on themselves without sign of fracture
206 ARCHITECTURAL ENGINEERING.
on convex side of curve. Specimens must stand cold
hammering to one third the original thickness without flay-
ing or cracking, and must stand quenching as heretofore
required for rolled specimens.
Cast Iron—Mi cast iron shall be of the best quality of
metal for the purpose intended. Castings shall be clean and
free from defects of every kind, and boldly filleted at all
angles.
The cast iron must stand the following test :
A bar i" square, 5' o" long, 4' 6" between bearings, shall
support a centre load of 550 Ibs. without sign of fracture.
Drawings. — All copies of architects' drawings, shop draw-
ings, templates, patterns, models, etc., and all necessary
measurements at the building, shall be made by this con-
tractor at his own expense. All shop drawings must be
submitted for the approval of the architects, and such
changes or additions shall be made as are required by said
architects or their agent.
Painting. — No material shall be painted until approved
by the inspector, nor shall any painting be done when
material is exposed to rain, or in otherwise improper con-
dition. No material shall be shipped until the paint is
thoroughly dry.
All iron and steel shall receive one coat of best red lead
ground in linseed-oil before leaving the shop. When the
framework is completed, all exposed portions are to be
touched up with paint as specified, and the whole shall then
receive a second coat of best red lead mixed with linseed-
oil.
Beams. — All floor, roof, and other beams shown on fram-
ing plans to be of size and weight shown, and accurately
located according to plan. Where two or more beams are
shown side by side, they shall be provided with cast separa-
tors at least every 8' o" apart, but with never less than three
UNIT-S TRA INS—SPE CIFICA TIONS. 2OJ
in each span. Each separator to be at least £" thick, and cast
to fit the profile of the beam exactly. Separators must be
provided at each and every bearing. Where the distance
centre to centre of beams -is not given in the drawings, they
shall be set. at the minimum distance given in Carnegie's
table of separators.
Girders. — All plate and lattice girders to be proportioned
to the following stresses per square inch :
Extreme fibre stress 12,000 Ibs.
Compression 10,000 "
Tension 12,000 "
Shearing 6,000 " for webs, 9,000 for rivets.
Direct bearing, including rivets, 15,000 Ibs.
In all built girders the flanges alone are to be considered
as resisting the bending moments. Both flanges to be of the
same section, the net section to be figured in all cases. No
angles to be used smaller than 2\" X 2\" X •£%", and no webs
to be of a thickness less than •§". Wherever the distance
between the flange-angles is greater than 70 times the thick-
ness of the web, stiffening angles shall be used not farther
apart than the total depth of the girder. Stiffeners must be
provided at all bearings and at points of concentrated load-
ing. All stiffeners to be placed over filler plates, and ends
of stiffeners, top and bottom, to fit closely against the flange-
angles.
Columns. — The maximum strain upon the metal in col-
umns shall not exceed 12,000 Ibs. per sq. in. for a length less
than or equal to 90 radii of gyration. For columns of a
greater length the metal shall be proportioned by the
formula 17,000 , / to be taken in inches. No column
to have an unsupported length of more than 30 times its
least lateral dimension. The least radius of gyration shall
be used.
208 ARCHITECTURAL ENGINEERING.
All columns, where possible, shall be made in two-story
lengths, breaking joints alternately. Columns to be built
with vertical connection-plates or splice-plates, all joints to
be equal in strength to the column itself. Bearing-surfaces
must be " finished " and protected by white lead and tallow.
All columns must be perfectly true and tested at frequent
intervals. " Shimming" will not be allowed.
Castings. — Cast iron used in the shape of lintels, corbels,
or brackets shall be so proportioned that the compressive
strain does not exceed 13,500 Ibs. per sq. in., nor the tensile
strain exceed 3,000 Ibs. per sq. in. Cast-iron plates may be
loaded to 15,0x30 Ibs. per sq. in. Cast-iron column bases may
be strained to 6,000 Ibs. fibre strain. They shall not give a
pressure of more than 15 tons per sq. ft. on brickwork, nor
more than 30 tons per sq. ft. on granite.
Plates. — Cast-iron plates shall be set under ends of all
beams and girders, resting on masonry, so proportioned as,
not to exceed a load of 1 5 tons per sq. ft. on brickwork, nor
more than 30 tons per sq. ft. on stone.
Connections — Splices. — All field-connections and splices to
be riveted with hot rivets. Where girders or beams rest
on brackets attached to the columns, such beams or girders
shall be riveted through the bottom flanges to the bracket,
and also have connection-angles connecting the top flanges
to the column. The ends of all girders or beams resting on
masonry walls or piers to have anchors securely embedded
in the masonry-work.
Rivets. — All rivets to be of mild steel, as before specified.
The pitch of rivets shall never be less than \\" nor more
than 6", while the minimum distance from the centre of any
rivet to the edge of material shall be i J". No rivets to be
used in tension. An excess of 25 per cent shall be allowed
in proportioning field-rivets. Rivet-holes may be punched
or drilled, but must not be more than -fa" larger than
UNIT-STRAINS— SPECIFICA TIONS. 2OQ
diameter of rivet. Rivet-holes must be accurately spaced,
as drift-pins will be allowed for assembling only. The rivets
shall completely fill the holes, with full heads concentric
with the rivets, and in full contact with the surface of the
material.
SPECIFICATIONS FOR BRICKWORK, ETC.
(Extracts from Masonry Specifications for the Fort Dearborn Building. Jenney
& Mundie, Architects.)
This contractor will furnish and set all that part colored
red on the drawings, and not shown or specified for
pressed brick or terra-cotta ; to be the best character of
common brickwork, laid up with the best merchantable,
good, sound hard bricks, acceptable to the architects, to
lines and levels on all sides, in lime mortar, all joints being
carefully filled and the bricks rubbed well into place and
pounded down to make a small solid joint. When laid in
dry, warm weather, bricks will be laid wet. The joints of
all outside common brick, and of all interior brickwork not
to be plastered, shall be neatly struck and cleaned down.
Pressed-brick Work. — The contractor will furnish and set
all that part colored red on the drawings and marked or
shown to be pressed-brick work, to include all returns into
openings, with the best character of pressed-brick facing of
even color and of the kind and character hereinafter speci-
fied. All exposed brickwork of areas and entrances in
fronts marked to be finished in pressed-brick work shall be
faced with the same character of pressed brick as used in
the adjacent parts. All joints in the pressed-brick work to-
be neatly rodded. All pressed-brick work to be laid from
an outside scaffold in mortar the color of the brick. All
courses to be gauged true. In laying pressed brick each
edge and down the middle is to be buttered and all vertical
joints to be filled from front to back. The returns of pressed-
210 ARCHITECTURAL ENGINEERING.
brick work must be carefully dovetailed into the common
brickwork or banded by solid headers.
In the piers only solid headers must be used. A sample
of pressed brick is to be deposited with the architects.
This contractor will furnish and set the terra-cotta or
salt-glazed tile copings to all masonry walls not covered by
stone or metal copings. The copings are to be 2 inches
wider than the wall and to have lapped joints. Copings to
be set in Portland cement.
Concrete. — This contractor will furnish and set all concrete
foundations or concrete filling shown on the drawings. All
concrete shall consist of equal parts of Portland cement,
mortar, and broken stone. The size of broken stone is to
be that of small egg coal. The mortar is to be thoroughly
mixed, and the stone to be wet before mixing with mortar.
The concrete to be cut over twice. No more water to be
used than is necessary to moisten every particle of cement.
All concrete to be used immediately after mixing, and shall
be pounded hard in place until the water stands on the top
of the concrete.
Cement Plastering. — The outside of all masonry walls that
will come in contact with the earth shall be smooth plas-
tered by this contractor with a surface coat of Portland
cement mortar of an average thickness of £ inch from the
lower footings to the top of finished grade.
Protection. — This contractor will carefully protect his
work by all necessary bracing, and by covering up all walls
at night, in bad weather, and at all times when work is
liable to be interrupted either by storms or cold. He will
protect all masonry-work from frosts by covering with
manure or other material satisfactory to the architects.
The top of all walls injured by the weather shall be taken
down by this contractor at his expense before recommenc-
ing work.
UNIT-S TRA INS—SPE C I PICA TIONS, 2 1 1
Footings. — Concrete footings shall be enclosed by 2-inch
plank curb, said plank to be left in place. All water is to
be baled out of trenches before the concrete is put in.
SPECIFICATIONS FOR FIRE-PROOFING.
(Extracts from Fire-proofing Specifications for the Fort Dearborn Building.
Jenney & Mundie, Architects, Chicago.)
The following- specifications include the fire-proofing of
all the steel in the building, the filling in between the beams
forming floors, and the concreting over the same to the top
of the floor-strips, and the projections of the beams below
the arches.
Also the covering of all columns, both those standing
clear and those partly incased in the walls.
Also the building of all tile partitions and the tile vaults.
Also the building of the party-walls over the present old
brick walls. Also the tile floor of the roof and pent-houses
on the roof.
All work shall be laid in mortar composed of 3 parts of
best fresh lime mortar and i part best Louisville cement,
thoroughly mixed together at time of using. Said lime
mortar shall be composed of fresh burned lime and clean
sharp sand in proportions best suited to this work.
This contractor shall furnish all material, including the
mortar for setting the same, and will do all his own hoisting
and set all the work in a thoroughly substantial and work-
manlike manner to the satisfaction of the superintendent
Floors. — All floors shall be supported on flat arches set
in between the beams and of a shape that shall give a uni-
form flat ceiling in the rooms below.
The bottoms and projections of all beams and girders
shall be protected by projecting parts of tile or by separate
beam slabs. In laying the floor arches every joint shall be
filled full over its entire surface, from top to bottom.
212 ARCHITECTURAL ENGINEERING.
Floor arches, ten days after they are laid and before they
are concreted, shall stand a test of a roller, 15 inches face,
and loaded so as to weigh 1500 pounds, rolled over them in
any direction.
All columns shall be covered with column tile held by
metal clamps both in horizontal and vertical joints. These
column protections shall be so made as to conform with the
city ordinance.
Roof. — The roof shall be supported in the same way as
the floors, only the soffits may be segmental.
Partitions. — All the partitions shown in the several plans
are to be built including all cross and subdivision partitions.
All are to be of hollow tile 4 inches thick in the first and
second stories, and 3 inches thick in all other stories for
cross-partitions. All hail partitions to be 4 inches thick.
In glazed partitions the lower parts and all parts other
than the sash and frames shall be of tile.
The tiles shall be set breaking joints, and be tied with
metal ties or clamps.
All vaults shown on plans above second story to be
built with vestibules, as shown.
Furring. — The outside walls in the basement, in the part
for rent, will be furred with 3-inch tile, so as to form a ver-
tical and true surface for plastering.
All tile work shall be straight and true.
All tilework shall be thoroughly burned and free from
serious cracks or checks or other damages, and shall be laid
in a proper and workmanlike manner.
No centres to be lowered until the mortar has set hard.
All structural steel on which the strength of the building
depends in any way, including wind bracing, shall be pro-
tected by fire-proof covering.
Concreting. — This contractor shall fill in on top of the tile
arches with dry cinder concrete, composed of reasonably
UNIT-S TRA INS—SPECIFICA TIONS. 2 1 3
clean soft-coal cinders, to be levelled off at the top of the
highest beams or girders, and after the floor-strips are set
to be filled in between said strips with said dry cinders,
pressed down hard and leaving- a surface reasonably uniform
\ inch below the tops of the strips, so that the floor can be
laid without disturbing the cinders.
All damages to tilework to be repaired before the cin-
ders are laid.
Party-ivalls. — Above the present walls on the west and
south sides this contractor shall furnish and lay in the afore-
said cement and lime mortar hard-burnt wall tile. Said
wall to be composed of two 6-inch tile between columns,
and elsewhere three thicknesses of 4-inch tile clamped to-
gether both in the length and across the wall. The face of
the outside tile shall be guaranteed to stand weather for five
years, dating from the completion of said wall ; the contrac-
tor agreeing to replace any tile injured by the weather
either in winter or summer during said period.
Every joint in this wall, both vertical and horizontal,
shall be thoroughly filled over its entire surface with the
mortar before mentioned. All outside joints to be struck
in a neat and workmanlike manner.
TERRA-COTTA SPECIFICATIONS.
Material. — This contractor shall furnish and set wherever
called for on drawings terra-cotta to exactly match in color
the sample submitted, all in strict accordance with detail
drawings. Material for ail terra-cotta to be carefully selected
clay, left in perfect condition after burning, and uniform in
color. All pieces to be perfectly straight and true, and with
mould of uniform size where continuous. No warped or dis-
colored pieces will be allowed. This contractor to furnish
a sufficient number of over-pieces, so as to avoid all delay.
Modelling. — All work shall be carefully modelled by skilled
214 ARCHITECTURAL ENGINEERING.
workmen, in strict accordance to detail drawings, and
models shall be submitted for architects' approval before
work is burned. No work burnt without such approval
will be accepted by the architects unless perfectly satisfac-
tory.
Mortar. — All mortar used for exposed joints in terra-
cotta work shall correspond in every particular with mortar
used for pressed-brick work. It shall be composed of lime
putty, colored with " Pecora " or " Peerless " mortar stains ;
colors to be selected by the architects.
Ornamental Fronts, Belt Courses, Bands. — This contrac-
tor shall furnish and set all ornamental terra-cotta, belt
courses, and bands, as shown on elevations or sections, or
where otherwise indicated, in strict accordance with detail
drawings. All terra-cotta work to be secured to the iron-
work in the most approved manner, with substantial w rough t-
iron or copper anchors, and thoroughly bedded in cement
mortar. All horizontal courses to have lap joints. All pro-
jecting courses to have drips formed on the under side.
Caps and Jambs, Sills. — All caps and jambs where indi-
cated as terra-cotta will be constructed in strict accordance
with detail drawings. All sills and belt courses to have
counter-sunk cement joints as directed by the superintend-
ent. All projecting sills to have drips formed on under
side, and all sills shall be raggled for hoop iron, which shall
be bedded by this contractor in cement mortar.
Terra-cotta Mullions. — All ornamental mullions of terra-
cotta to be secured to metal uprights in approved manner,
and well bedded and slushed with cement mortar.
Cornice. — This contractor shall construct cornice in strict
accordance with detail drawings, with sufficient projection
through walls and approved anchorage to the metal-work to
make same thoroughly secure, this contractor to furnish all
necessary anchors. Form raggle in cornice as shown for
UNIT-STRAINS— SPECIFICA TIONS. 21 5
connection of gutter, this raggle to be on face of terra-cotta.
Leave openings in cornice for down-spouts as shown.
Anchors. — This contractor shall furnish all anchors, of
substantial wrought iron or copper, for the proper support
and anchoring of all terra-cotta used in his work. All
terra-cotta to be drawn to tight and accurate joints, to entire
satisfaction of the superintendent. All terra-cotta must fit
the supporting metal-work exactly.
Cutting and Fitting. — This contractor shall do all cutting
and fitting necessary to make his work perfect in every par-
ticular, all possible cutting and fitting to be done at the
factory before delivery.
Protection of Terra-cotta. — All projecting terra-cotta shall
be protected with sound plank during the erection of the
building by terra-cotta contractor, said protection pieces to
be removed on cleaning down of building.
Cleaning Down. — This contractor shall carefully clean
down all terra-cotta work at completion of building, when
directed by the superintendent, and shall carefully point up
all joints before leaving work.
CHAPTER XII.
BUILDING LAWS.
THE building ordinances of the cities of New York,
Chicago, and Boston are all of comparatively recent adop-
tion, and though perhaps no one of them may lay claim to
being a model building law, still one might expect to
find much of the best practice and experience in building
construction incorporated in one or all of these laws.
Some of the more important subjects coming under the
head of Architectural Engineering may be compared as
follows :
FLOOR LOADS.
The requirements for live loads per square foot on the
floor-beams, over and above the dead weight of the floor
itself, are:
New York.
Chicago.
Boston.
i Dwellings (a) . ...
7O
70 )
7O
2 Office buildings (3)
IOO
70 >• (e)
/u
IOO
1 20
70 )
TCP)
4. Stores, warehouses, factories,
150
150 minimum
o CQ
and upward.
Posted notices of
Allowable Load.
Posted notices in
Bldgs. for Me-
chanical or Mer-
cantile Purposes.
(a) Includes hotels and apartments in New York.
(d) Includes apartments and boarding and lodging-houses in Chicago.
(<:) Called <l places of public assembly" in New York.
(d) Includes stables in Chicago.
(e) Allowances may be made for reduction in these loads on columns and
foundations.
It will be seen that these three laws agree in a live
load of 70 Ibs. per square foot for private dwellings. This
is undoubtedly high, 40 Ibs. per square foot being about
216
BUILDING LAWS. 217
the average in use by the best engineers and consulting
architects. This requirement, taken with the value given
for the strength of wooden beams in the Boston law, necessi-
tates timbers of far larger size than has been the practice of
the best architects, or as used in houses which have been built
and occupied from thirty to fifty years. Kidder shows that
actual loads in parlors (including piano), dining-rooms, etc.,
average only 14 to 23 Ibs. per square foot of the whole area.
The excessiveness of the load of 70 Ibs. for dwellings would
seem to be further indicated by the use of the same load in
the Chicago laws for classes 2 and 3. New York and Bos-
ton are about alike for these two classes ; but if 70 Ibs. is
sufficient for office and public buildings, why require it for
lighter private dwellings?
In class 4 each city law requires that all floors for ware-
houses, etc., must be carefully computed, according to the
intended use, and the capacity of such floors be posted in
conspicuous places about the building. The New York and
Chicago laws are much more explicit on this point than is
the Boston law, while the Chicago ordinance leaves the re-
quired load to the judgment of the architect or engineer with
the approval of the Building Commissioner. The minimum
load of 1 50 Ibs. in the New York law is far too small in many
cases, but the loads for these types of buildings are hard to
classify, and are best left to the care of competent designers
under the approval of the building departments. Mr. W.
L. B. Jenney had occasion to estimate the loads in the whole-
sale warehouse of Marshall Field & Co. in Chicago, and the
surprisingly low average of 50 Ibs. per square foot was found
for the total floor area, including all passage-ways. The
maximum load on limited areas was found to be 57 Ibs.
The writer sees no reason for changing the previous
recommendations of live loads, as given under a discussion
of the floor system, namely :
218
ARCHITECTURAL ENGINEERING.
40 Ibs. per square foot for dwellings ;
80 to 90 Ibs. for places of public gatherings, devotional,
educational, or amusement ;
40 Ibs. for the upper floors of office buildings ;
80 Ibs. for the lower floors of office buildings ;
and from 150 to 450 Ibs. for places of manufacture, storage,
machinery, etc.
WROUGHT IRON: STRESSES IN POUNDS PER SQUARE INCH.
New York.
Chicago.
Boston.
Extreme fibre stress, rolled beams
I2,OOO
11,000
beams or rails in
foundations.
I2,OOO
I2,OOO
Tension .
12 OOO
12 OOO
Compression in flanges, built
12 OOO
IO OOO
IO,OOO
9,000 rivets.
7, 500 shop rivets
6 ooo field rivets
Q OOO
Direct bearing, including pins
6,000 webs.
15,000
6,000 webs.
I5,OOO
Bending on pins
l8,OOO
Modulus of elasticity. .
27,000,000
STEEL: STRESSES IN POUNDS PER SQUARE INCH.
New York.
Chicago.
Boston.
Extreme fibre stress, rolled beams
15,000
14,000
in foundations.
l6,OOO
16,000
l6,OOO
15,000
Compression in flanges, built
beams
15 ooo
I^.^OO
I2,OOO
9,000 rivets.
9,000 shop rivets
7, 500 field rivets.
IO,OOO
Direct bearing, including pins
and rivets . . .
7,000 webs.
15,000
10,000 webs.
18,000
22,500
Modulus of elasticity . ...
29,000,000
As may be seen from these tables, the Boston law is the
most comprehensive, while the Chicago ordinance is singu-
larly deficient in unit-stresses, and even somewhat contradic-
tory in some of the few values given. Thus under the head-
BUILDING LAWS.
ing of plate girders, fibre stresses of 13,500 Ibs. per square
inch for steel and 10,000 Ibs. for wrought iron are allowed,
while in a preceding section " all girders, beams, corbels,
brackets, and trusses " are allowed fibre stresses of 16,000 Ibs.
for steel, and 12,000 Ibs. for wrought iron. This latter sec-
tion does not limit the use of these unit-stresses to either
rolled or built members, thus clashing with the require-
ments for plate girders. Still different fibre stresses are
called for under the requirements for rail or beam founda-
tions, 14,000 Ibs. per square inch for steel, and 11,000 Ibs. for
wrought iron. No values are given for bearing.
The New York law, under the provisions for plate gird-
ers, specifies that " no part of the web shall be estimated as
flange area, nor more than J of that portion of the angle-iron
ivhich lies against the web'' As the effective depth of the
girder is limited to the distance between the centres of
gravity of the flange areas, this requirement would seem
quite unnecessary. If the web be neglected as affecting the
flange area, and proper deductions made for rivet-holes, the
whole angle areas can very properly be used.
COLUMNS.
The New York and Boston laws both call for com-
putations by Gordon's formula, using the constants of
12,000 Ibs. per square inch for steel, and 10,000 Ibs. for
wrought-iron columns. No column is to have an unsup-
ported length of more than 30 times its least lateral dimen-
sion, nor to have metal less than £" in thickness.
The Chicago law allows the use of the constant of 12,000
Ibs. per square inch for wrought-iron columns, or
5 = i2,ooo# -f- ( i -J- -g ija, /, and r all in inches.
For steel columns two formulae are given :
22O ARCHITECTURAL ENGINEERING.
S = 17,000 — \—) for columns more than 60 radii in length,
and S=: 13,5000 for columns under 60 radii in length (/ and
r both in inches). The formula for columns over 60 radii in
length gives about 13,000 Ibs. per square inch for a column
in which - = 66.
CAST COLUMNS.
The New York law specifies that the computations for
cast columns shall be made by the use of Gordon's formula,
with the constant of 16,000 Ibs. per square inch. All cast
columns to have a minimum average thickness of £", with
an unsupported length of not more than 20 times their least
lateral dimensions.
The Chicago law gives formulas for both round and rec-
tangular cast columns. For round cast columns :
(I* \ / = length of column in in.;
I 4- ^— TT2 ) d-= diam. of columns in in.;
^^ / a = sectional area col. in in.
For rectangular cast columns :
/ and a as before ; d = the side
c _ / , /' \ of square column, or the least
' V 55577 horizontal dimension of other
columns.
The Boston law provides tables for both round and
square cast columns.
STONE.
THE USE OF STONE FOR WALLS, FACINGS, PIERS, RCHES, ETC., is THUS
SPECIFIED, IN TONS PER SQUARE FOOT.
New York.
Chicago.
Boston.
)
f 3^ of the ultimate
j strength derived from
60 1 First quality,
Marble and limestone. .
Sandstone
( Not
f specified.
j tests, approved by Com-
1 missioner of Buildings.
| dressed beds,
* (laid solid in
cement mor ar.
l_ Portland cement.
The safe loads given in the Boston law are about double
those recommended by Baker, while the Chicago require-
BUILDING LAWS. 221
ments, using -fa of the average ultimate strengths given
by Prof. Baker, allow 38 tons on granite, 30 tons on lime-
stone, and 24 tons on sandstone per square foot.
The use of ashlar masonry in wall facings is limited as
follows : Boston law : " In reckoning the thickness of walls
ashlar shall not be included unless it be at least 8" thick. In
walls required to be 16" thick or over the full thickness of
the ashlar shall be allowed ; in walls less than 16" thick, only
half the thickness of the ashlar shall be included. Ashlar
shall be at least 4" thick, and properly held by metal clamps
to the backing, or properly bonded to the same."
Chicago la w : " Stone may be used as facing for brick walls
under the following conditions : If the facing is ashlar, with-
out bond courses, and the individual courses thereof meas-
ure 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, and reaching at least 8" 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 six 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", then such ashlar
facing shall be counted as forming part of the wall,
and the total thickness of wall and facing shall not be re-
quired to be more than herein specified for walls of the
different classes of buildings."
New York law : " All stone used for the facing of any
building, and known as ashlar, shall not be less than 4" thick.
222
A R CHITECTURA L ENGINEERING.
Stone ashlar shall be anchored to the backing, and the back-
ing 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."
Dimension stones, as specified in the Chicago ordinance
for foundations, shall not be subjected to a load of more
than 10 tons per square foot. If the beds of the stones are
dressed and levelled off to uniform surface, and the stones are
set in Portland cement mortar, this load may be increased
to 25 tons per square foot.
BRICKWORK: ALLOWABLE PRESSURES IN TONS PER SQUARE
FOOT.
New York.
Chicago.
Boston.
Brickwork laid in cement
mortar
It; "I
15 tons with Port-"]
Tr "\
Brickwork laid in cement
and lime mortar
u4- \.(a\
12 tons with or- 1 ,,*
1
TO \.(f\
Brickwork laid in lime
mortar .
8
8 tons with lime 1
i£ r\c)
Q 1
0 )
8 J
(a) Isolated brick piers shall not exceed 12 times their least dimensions.
(b) The loads permitted for brick piers shall be 25 per cent less than in
walls.
In walls an additional 25 per cent may be allowed if brickwork is thor-
oughly grouted or " shoved."
A further 20 per cent additional allowance may be made if walls are built
of sewer brick only, or, if vitrified paving bricks are used, this allowance may
be made 30 per cent.
(c) In brick piers in which the height is from 6 to 12 times the least dimen-
sion, these pressures are reduced to 13, 10, and 7 tons respectively for the
mortars as above given.
BEARING POWER OF PILES AND SOILS.
GIVEN IN POUNDS PER PILE, OR PER SQUARE FOOT ON FOOTINGS.
New York.
Chicago.
Boston.
Piles
40 ooo
50 ooo
1
Pure clay, at least 15 ft. thick. . .
Dry sand, at least 15 ft. thick. . .
Clay and sand mixture
I Not
f specified.
4,000
3.500
•3 OOO
Not
[ specified.
" Good solid, natural earth "...
8,000
I
It would certainly seem quite remarkable that a city of
the size of Boston should fail to specify any unit loads for
BUILDING LAWS. 22$
foundations. For ordinary footings the only requirements
are that " the foundation, with the superstructure which it
supports, shall not overload the material on which it rests."
Piles are specified for use " where the nature of the ground
requires it," and " the number, diameter, and bearing of such
piles shall be sufficient to support the superstructure pro-
posed." All piles must be capped with block granite level-
lers, and must not be over 3' o" centres in the direction of
the wall.
It is to be hoped that the building department of the
city of Boston is less of a political organization than is the
case in most large American cities, or that the contractors
of that city are more conscientious than the average. The
New York laws, in the requirements for pile foundations,
permit a 5" point, while no mention is made of the butt end.
Piles are usually specified with 8" points and 14" butts, and
for such piles the allowable pressure of 20 tons under the
New York law is certainly very conservative ; 30 tons are
very commonly used for piles of 6" to 8" point, and 12" to
1 6" butt.
The New York laws also require that " if, in place of a
continuous foundation wall, isolated piers are to be built to
support the superstructure where the nature of the ground
and the character of the building make it necessary, inverted
arches shall be turned between the piers at least 12" thick
and of the full width of the piers." This practice has long
since been condemned in Chicago, as in no way satisfactory
or desirable.
The Chicago building ordinance is certainly far superior
to those we have just mentioned, as regards the subject of
foundations, and the following quotations would seem to
recommend themselves for general application.
" Foundations shall be proportioned to the actual average
224 ARCHITECTURAL ENGINEERING.
loads they will have to carry in the completed and occupied
building, and not to theoretical or occasional loads."
" Foundations shall be constructed of either of the fol-
lowing : Portland cement concrete, or Portland cement con-
crete and steel or iron, or dimension stone, or sewer or pav-
ing brick, or timber piles covered with grillage of oak tim-
ber, or a grillage of oak timber alone ; it being, however,
provided that timber shall not be used in connection with
any foundation at a level higher than city datum."
" Where pile foundations are used, borings of the same
shall first be made to determine the position of the under-
lying stratum of hard clay or rock, and the piles shall be
made long enough to reach to hard clay or rock, and they
shall be driven down to reach the same, and such piles shall
not be loaded more than 25 tons to each pile. The heads of
the piles are to be protected against splitting while they are
being driven, and after having been driven the piles are to
be sawed off to uniform level and covered with an oak tim-
ber grillage, so proportioned that in the transmission of
strains from pile to pile the extreme fibre strain in the tim-
bers composing the grillage shall not be more than 1200 Ibs.
to the square inch."
The bearings on other materials than piles are then given,
as in previous table. The cement to be used in concrete
footings "shall not be less than 90 per cent fine on 8o-mesh
sieve, and when mixed one part of cement to one part of
clean, sharp sand, moulded into briquettes of one square inch
cross-section, shall not break when seven days old at less
than 225 Ibs. tensile strain, nor at thirty days at less than
275 Ibs. tensile strain."
In view of the many discussions at the present day it
will be interesting to note the requirements for the coating
or painting of rails or beams in foundations.
The Boston law requires that "all metal foundations and
BUILDING LAWS. 22$
all constructional ironwork underground shall be protected
from dampness by concrete, in addition to two coats of red
lead, or other material approved by the inspector."
New York law : " When crib footings of iron or steel are
used below the water-level, the same shall be entirely coated
with coal-tar, paraffine varnish, or other suitable preparation
before being placed in position. When footings of iron or
steel for columns are placed below the water-level, they
shall be similarly coated for preservation against rust."
The Chicago ordinance requires a perfect covering of
concrete only : " If steel or iron rails or beams are used as
parts of foundations, they must be thoroughly embedded in
a concrete, the ingredients of which must be such that after
proper ramming the interior of the mass will be free from
cavities. The beams or rails must be entirely enveloped in
concrete, and around the exposed external surfaces of such
concrete foundations there must be a coating of Portland
cement mortar not less than one inch thick.
WIND PRESSURE.
No mention is made of the wind pressure to be figured in
either the New York or Boston law, except that the former
law requires a live load of 50 Ibs. per square foot to be taken
for all roofs.
The Chicago law provides as follows : " In the case of
all buildings the height of which is more than i| times their
least horizontal dimension, allowances shall be made for
wind pressure, which shall not be figured at less than 30 Ibs.
for each square foot of exposed surface. The precautions
against the effects of wind pressure may take the form of
any one or all of the following factors of resistance to
wind pressure :
" First. Dead weight of structure, especially in its lower
parts.
226 ARCHITECTURAL ENGINEERING.
" Second. Diagonal braces.
" Third. Rigidity of connections between vertical and
horizontal members.
" Fourth. By constructing iron or steel pillars in such
manner as to pass through two stories with joints breaking
in alternate stories."
ALLOWABLE HEIGHT OF BUILDINGS.
The New York law sets no limitation on the height of
buildings in that city.
Boston law : " No building or other structure hereafter
erected, except a church spire, shall be of a height exceed-
ing 2£ times the width of the widest street on which the
building or structure stands, whether such street is a
public street or place or a private way existing at the
passage of this act or thereafter approved as provided by
law, nor exceeding 125 feet in any case; such width to
be the width from the face of the building or structure to
the line of the street on the other side, or if the street is
of uneven width, such width to be the average width of
the part of the street opposite the building or struc-
ture."
Chicago ordinance : " No building shall be erected in the
city of Chicago of greater height than 160 feet from the
sidewalk level to the highest point of external bearing,
walls. And the height of no building of skeleton construc-
tion shall be more than three times its least horizontal
dimension. And no building of masonry construction shall
be more than four times as high as its least horizontal
dimension."
The buildings which have been termed " sky-scrapers "
in Chicago were all built before the passage of this ordi-
nance, or on building permits which were issued before the
law went into effect.
APPENDIX TABLE.
227
undations.
k IshJ
- s«e«^ ^
c ipi:,;,
c <S^'S^0«0tl
ind beams on
Df concrete.
on 12" of
rete.
oo
WJ 3 2 3
§= S * «
§
rt
'rt
jf
nd beams.
i
N
•o
e
rt
CO
' o
4
)
Oy ^ «^ S^SSu
02 pi Di CC 03
V Q3
/ * .
a^ w
4)-
n
-|s
H
£
J3
! *
•" *O C
I p
j ^ *v?
>
?§ ^ 8-3
en y O - 0 O
s.s rt ^ *
u
" \
Channels in
exterior walls
Gusset-plate
knee-bracing
in the exterior
walls
Cross-walls
Rods
1 "
-••v
Walls only -j
£
1
6
c
o
55
None — solid
walls only
Exterior
Walls.
1 » . .
u
>
3 3
r
» --»!*§
gi
Veneer
I
."2 v
Veneer
JO
)
. ' C
tl
|
^55"
(i
«
V
H "
"o
CO
H::: ||
H- -
^
S ^-
H
I **»
> M
; frs
CX!
4) *Q ^ W
: 3
"o
co
P— '
333
3
D
3T
H
concrete
arches
used
Hard tile
Kind of Columns.
•U.^, OT <-v~
lii
(U Q « *J «- -^ »-
ys^
( Box column of )
•< plates and >
/ anerles i
j Channels and |
1 plates \
!-•
Z bar and Phcenix
Zbar
3
I Z bar and I
f Phce.iix f
r
— > '
1
N
3
4 *t* W3
O t>
ii ii
ii ii
J o o
II
03H
;
&
~* *-
^
>*2*2
5 «
' §
H '3
"5 X
o o o vo o
$ 0 %l
0
r?K J
fti
ii N
II II
^
o
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INDEX.
PAGE
Anchors for terra cotta work 104
specifications for 215
Ashland Block, data about 228
wind-bracing in 148
Athletic Club Building, data about 228
fire in . . .- 13, 75
fire-proofing of columns 20
Auditorium, data about 227
foundations of 190
settlement of 191
Auditorium Annex, data about 228
Bay windows, construction of 107
floors and ceilings in 112
framing of, for Reliance Building 109
Masonic Temple 109
spandrel sections, Reliance Building 112
Beam footings, calculation of „ 180
foundations 178
Beams in floor system 82
spandrel loo
specifications for 206
Book-tile 164
Borings for foundations 171
Boston Building Law — allowable height of buildings 226
floor loads 216
foundations 222
loads on brick- work 222
loads on masonry 220
strength of columns 219, 220
wrought-iron and steel 218
Box columns 124, 126, 131
fire-proofing of 134
Boyce Building, data about 228
Brackets for bay windows 108
Reliance Building H2
229
230 INDEX.
PAGE
Brick, hollow, used for fire-proofing 134
Brick-work — allowable pressure on 201
building laws 220
specifications for 209
Building Laws 216
brick-work 222
cast columns 220
columns 219
foundations 222
height of buildings 226
stone, walls, piers, etc 220
wind pressure 225
wrought-iron and steel 218
Built sections vs. rolled beams 160
Caissons— pneumatic 198
Cantilever girders 186, 198
Cast columns— building laws 220
disadvantages of 114
joints for 114
Castings— specifications for 208
Cast-iron — specifications for 206
Caxton Building — data about 227
Ceilings — suspended. . . 165
Cement plastering — specifications for 210
Champlain Building — data about 227
floor-plan of 39
Chicago Building Law — allowable height of buildings 226
fire-proof construction defined 1 1
fire-proofing of exterior columns 95
interior columns 135
floor arches 74
floor loads 216
foundations 222
loads on brick-work 222
masonry 220
mill construction defined 18
skeleton construction defined 94
slow-burning construction defined 16
strength of columns 219, 220
wind pressure 225
wrought-iron and steel 218
Chicago Construction 91
Chicago Library — pile foundations 194
Chicago Office Buildings— data about 227, 228
Chicago Stock Exchange — data about 227
description of 26
Clearance between floor-beams, girders and columns 85
Columbus Building — data about 228
INDEX. 231
PAGE
Column-brackets for bay windows 112
-connections ... 127
Pabst Building, Milwaukee 159
-formula 117
-joints 156
-loads, in Fort Dearborn Building 82
-loads in "The Fair" Building 177
-sheets 168
Columns — building laws 219
capabilities of fire-proofing 129
cast vs. wrought 113
choice of 131
cost of 119
details in Venetian Building 145
eccentric loading 124
examples of great length 181
expansion and contraction of 97
fire-proofing of 132
Athletic Club Building 20
Chicago Law 135
New York Law 96
Gray type 125
joints for cast-iron 114
Larimer type * 121
limestone pillars 131
patent 119
Phoenix type with pintle-plates 125
placed in exterior walls 89
plates and angles 124
practical considerations 119
principles of resistance 1 16
requirements for fire-proofing 133
riveting of 121
Schiller Theater Building 118
shopwork and workmanship 120
specifications for 207
splices in Reliance Building 159
tabulation of loads 169
theoretical form 116
two-story lengths 158-
types of, for building work 115
unit strains on 202
used for pipe-space 129
vertical splices 157
Z-bar sections used in "The Fair" Building 130
Y. M. C. A. Building 130
type 123
Combined footings i8s
232 INDEX.
PAGE
Combined footings, calculation of 186
Compression of clay under foundations 176
Concrete floor-arches 66, 69, 71
in foundations 184
specifications for. . . 210
Connection-angles — standard 85
Connections — specifications for 208
Court walls 107
Dead loads 76
on floor system go
of Fort Dearborn Building 82
on foundations 176
Deflection of floor-beams 84
framework, due to wind 160
Detail plans for steelwork 43
Drawings — specifications for 206
Earthquakes — provisions for 156
Eccentric loading — calculation of 126
on columns 124
Elevator enclosures 166
Erection of steel-work 46
cost of 46
cranes used in 46
time required for 46
Field connections 46
Fire loss in United States g
Fire-proof construction — comparative cost of 10
definition of u
Fire-proof ducts for piping 21
structures — requirements of 16
vaults 1 65
Fire-proofing, efficiency of . 131
in Tremont Temple, Boston 22
materials for 12
methods of -., , 15
of columns 20, 132
of stairways and elevator shafts. . . ., 19
specifications for 211
Fire test of fire-proof building 13
Floor arches, brick 54
Chicago Building Law for 74
comparative costs of 74
corrugated iron 54
Guastavino type 73
hollow tile 54
in Equitable Building 56
in Home Insurance Building .... 56
in Montauk Building 56
INDEX. 233
PAGE
Floor arches, Melan system 67
segmental 72
steel straps and concrete 68
test by fire 75
test of Metropolitan system 7°
.wire mesh 69
Floor-beams, calculation of 84
Chicago practice 82
connections for 85
deflection of . . 84
economical arrangement of 83
necessary clearance 85
Floor-girders •- 86
length of 86
Floor-loads.. 76
Fort Dearborn Building 81
Marshall Field Building 80
Old Colony Building 81
requirements of Building Laws 216
"The Fair" Building 177
Floors, specifications for 211
Fort Dearborn Building — data about 227
description of 38
floor and column loads 81, 82
unit strains on columns 203
wind-bracing 155
Foundations i ?i
Auditorium 190
beam 1 78
Building Laws 222
calculation of beam footings 180
combined footings 186
rail footings 179
Chicago Library 194
combined footings 185
concrete in 184
Great Northern Hotel 179
independent piers 173
loads on 176
Manhattan Building , 186
Life Insurance Building, New York 197
Marquette Building 184
masonry -vs. raft 173
Old Colony Building 178
pile 192
pile vs. raft 196
pneumatic 197
rail.. 178
234 INDEX.
PAGE
Foundations, Rand-McNally Building 186
Schiller Theater Building 193
settlements of I9i
"The Fair" Building 177
Wisconsin Central Depot 193
Framing plans . 39
economical ; 83
Furring, specifications for 212
tile 165
Girder loads — Fort Dearborn Building 82
Girders, cantilever 186, 198
for floor system 86
spandrel 101
specifications for 207
Gray column, details of 125
Great Northern Hotel, data about 228
, foundations of 179
Guastavino floor arches 73
Hartford Building, data about 228
Height of buildings — building laws 226
Hollow tile 54
advantages of 15
floor arches 56
sustaining power 62
used for furring 165
used in partitions 163
Home Insurance Building 97
data about 227
settlement of 191
Inspection, specifications for 205
Iron, wrought, building laws 218
Isabella Building, data about 227
wind-bracing 154
Jackscrews used in foundations 185
Johnson's patent tile-arch 61
J oints, open 90
Knee-braces, calculation of , 153
Knee-bracing — Fort Dearborn Building 155
Isabella Building 154
Larimer columns — connections 121
tests of 1 23
Lee tile-arches 58
Leiter Building, data about 227
Lime vs. cement 50
Limestone pillars vs. steel columns 131
Live loads — Chicago practice 79
defined 76
discussion of, for office buildings 77
INDEX. 235
Live loads on foundations 176
in Mills Building, San Francisco 79
in Venetian Building 79
Manhattan Building, data about 227
foundations of 186
Life Insurance Building, New York, foundations of 197
Marquette Building, data about 227
description of 26
foundations of 184
Marshall Field Building, data about 228
floor loads 80
Masonic Temple, box columns in 124
column-sheets in 169
data about 228
mechanical plants in 33
piers in 90
special features in 36
two-story columns in 158
unit strains on columns 202
wind-bracing in 143
Masonry — building laws 220
piers 88
Mechanical features, installation of 21
Melan floor-arches 67
Metropolitan floor-arches 69
Mill construction 18
Monadnock Building, data about 227, 228
settlement of igi
vibrations due to wind. 161
wind-bracing in 152
Mortar, colored 214
Mullions, connections of lor
specifications for 214
Newberry Library, data about 228
New York Building Laws — fire-proofing of columns 96
floor loads 216
foundations 222
loads on brick-work 222
masonry 220
protection of steel-work 53
strength of columns 219, 220
wrought-iron and steel 218
New York Life Insurance Building, data about 227
description of 38
time required for erection 46
Old Colony Building — column connections 128
data about 227
floor loads 81
236 INDEX.
PAGE
Old Colony Building — foundations 178
wind-bracing 152
Owings Building, data about 228
Pabst Building — column connections 159
Painting of metal work , specifications for 206
Panelled beams 58
Partitions — load per square feet on floor system 80
specifications for 212
types of 163
used in wind-bracing 136
Permanency of skeleton construction 50
Phoenix Building, data about 228
columns, connections of 128
fire-proofing of 134
with pintle-plates 125
Piers — exterior — Chicago type 91
Marshall Field Building 89
Masonic Temple 90
Monadnock Building 98
treatment of 88
Pile foundations 192
Chicago Library 194
tests of 194
Piles — building laws 222
Pioneer tile-arches 58
Plaster used as fire-proofing 135
Plates, specifications for 208
Pneumatic caissons 198
foundations 197
Pontiac Building, data about 227
deflections due to wind 162
Porous tile in fire-proofing 134
Portal bracing, calculation of 148
Old Colony Building 152
Poulson floor-arches 72
Pressed-brick work, specifications for 209
Rail footings, calculation of 1 79
foundations 178
Rails, properties of 179
Rand-McNally Building, data about 228
foundations of 186
Reliance Building, data about 228
description of 26
splices in columns . 159
wind-bracing of 156
Rivets, specifications for 208
steel, specifications for 205
Rods for wind-bracing 148
INDEX. 237
Roof construction 164
Roofs, specifications for 212
Rookery Building, data about 227
Schiller Theater Building, data about 227
foundations of 193
Security Building, data about 228
Segmental floor-arches 72
Separators 86
Settlement, allowance for 172
Chicago Post Office 1 72
of exterior walls 89
of foundations 191
use of jackscrews in 185
Skeleton construction, defined 94
earliest example of 96
permanency of 50
Skew-backs in tile-arches 57, 58
Slow-burning construction 16
Spandrel sections — Ashland Block 101
bay windows 108
for Reliance Building 112
Fort Dearborn Building 101
Marshall Field Building 107
Marquette Building 105
Masonic Temple, bay windows 109
through court walls 107
Spandrels, defined 100
Specifications for brick-work 209
fire-proofing 211
structural steel-work 204
terra-cotta 213
Stairways 166
Steel — requirements of building laws 218
Steel-work, deterioration of 50
in walls, protection of 95
painting of 53
protection of 51
Boston law 53
Chicago law 53
New York law 53
specifications for 204
time required for erection 46
with cement mortar 52
with lime mortar 50
Stone — building laws 220
Struts — wind-bracing in Venetian Building 147
Sway-rods, calculation of, for wind-pressure 140
typical calculation of 143
238 INDEX.
PAGE
Tacoma Building, data about. ... 227
Terra-cotta, anchors for 104
enamelled 16
for exterior walls 91
specifications for 213
used for column fire-proofing , 133
Tests of steel-work, specifications for 205
Teutonic Building, data about 228
" The Fair" Building, data about 227
foundations 177
floor loads 177
loads on columns 177
settlement of 191
unit strains on columns 203
wind-bracing in 144
Tie-rods for floor-arches 62
Tile-arches for roofs 164
necessary tests for 63
tests of 59
types most used 61
weights of 59
Tile floor-arches, construction of 56
Tile floors, calculation of 64
Tile, hard vs. porous 133
Title and Trust Building, data about 228
Tremont Temple, Boston, fire-proofing in 22
Unit strains 201
on columns 202
Unity Building, data about 228
erection of steel-work 46
Vaults, fire-proof 165
Veneer construction 102
Venetian Building, column sheets in 169
data about 227
floor loads 79
unit strains on columns 203
wind-bracing 144
W ills, allowable pressure on 201
compression of 89
exterior 88
Chicago type 91
thickness of . 98
with spandrel girders 101
court 107
settlement of exterior 89
solid masonry, objections to 88
Western Bank-note Building, settlement of 191
Wind-bracing — calculation of knee-braces 153
INDEX. 239
PAGE
Wind-bracing — calculation of portal-bracing 148
sway-rods 141
Chicago practice 137
diversity of practice in 136
in Ashland Block 148
Fort Dearborn Building 155
Isabella Building 154
Masonic Temple 143
Monadnock Building .... 152
Old Colony Building 152
Reliance Building 156
" The Fair " Building 144
Venetian Building 144
types of 139
Wind-pressure — building laws 225
calculation of sway-rods 140
experiments on deflection 161
Fort Dearborn Building 155
limiting height of building , 160
practical considerations 140
unit loads 138
World's Columbian Exposition 138
Wisconsin Central Depot, foundations of 193
Woman's Temple, data about 228
foundations of 1 73
World's Columbian Exposition — wind-pressure 138
Y. M. C. A. Building, data about 227
Z bar columns, fire-proofing of 134
Monadnock Building 134
objections to 123
large sections of • 130
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