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UC-NRLF
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EXCHANGE
UNIVERSITY OF ILLINOIS BULLETIN
PUBLISHED WEEKLY BY THE UNIVERSITY
Vol. X JANUARY 13, 1913 No. 16
[Re-entry at the Post Office at Urbana, III., as second-class matter under Act of Congress of July 16, 1£94, pending]
BULLETIN NO. 64
TESTS OF REINFORCED CONCRETE
BUILDINGS UNDER LOAD
BY
ARTHUR N. TALBOT
AND
WILLIS A. SLATER
UNTVEKSITY OF ILLINOIS
ENGINEEKING EXPEKIMENT STATION
URBANA, ILLINOIS
PEJCE: FIPTY CENTS
EUROPEAN AGENT
CHAPMAN AND HALL LTD., LONDON
THE Engineering Experiment Station was established by act
of the Board of Trustees, December 8, 1903. It is the purpose
of the Station to carry on investigations along various lines of
engineering and to study problems of importance to professional engi-
neers and to the manufacturing, railway, mining, constructional, and
industrial interests of the State.
The control of the Engineering Experiment Station is vested in the
heads of the several departments of the College of Engineering. These
constitute the Station Staff, and with the Director, determine the
character of the investigations to be undertaken. The work is carried
on under the supervision of the Staff, sometimes by research fellows
as graduate work, sometimes by members of the instructional staff of
the College of Engineering, but more frequently by investigators belong-
ing to the Station corps.
The results of these investigations are published in the form of
bulletins, which record mostly the experiments of the Station's own staff
of investigators. There will also be issued from time to time in the
form of circulars, compilations giving the results of the experiments of
engineers, industrial works, technical institutions, and governmental
testing departments.
The volume and number at the top of the title page of the cover
are jnerely qjjbjticajy; numbers and refer to the general publications of
itjridf Illinois; above the title is given the number of the En-
zperi'/neflt' Station bulletin or circular which should be used
to 'th^e 'publications.
For copies of bulletins, circulars or other information address the
Engineering Experiment Station, Urbana, Illinois.
UNIVERSITY OF ILLINOIS
ENGINEERING EXPERIMENT STATION
BULLETIN No. 64 JANUARY, 1913
TESTS OF REINFORCED CONCRETE BUILDINGS
UNDER LOAD
BY ARTHUR N. TALBOT, PROFESSOR OF MUNICIPAL AND SANITARY
ENGINEERING AND IN CHARGE OF THEORETICAL AND APPLIED
MECHANICS, AND WILLIS A. SLATER, FIRST ASSISTANT
IN ENGINEERING EXPERIMENT STATION
CONTENTS
I. INTRODUCTION
PAGE
1 . Preliminary 5
2. Scope of Bulletin 6
3. Acknowledgment 6
4. Comment 7
II. THE TESTING OF BUILDINGS
5. Building Tests Made 7
6. Definitions 10
7. General Outline of Method of Testing 11
8. The Planning of a Test 12
9. Preparation for the Test 17
10. Loading 21
1 1 . Extensometers 25
12. Standard Bar 28
13. Deflection Instruments 30
14. Extensometer Observations 32
15. Observation of Cracks - 35
16. Accuracy of Deformation Measurements ' 35
17. Effect of Changes in Temperature on Accuracy of Results. ... 39
18. Records and Calculations 43
19. Test Data 44
20. Cost of the Tests 46
III. THE WENALDEN BUILDING TEST
21. The Building 46
22. Method of Testing 48
264347
2 CONTENTS
PAGE
23. Method of Loading 49
24. The Deformations and Stresses 51
25. Test Cracks 57
26. Deflections 58
27. Wall Panel '. 59
28. Examination of Floor after Test 60
IV. THE TURNER-CAKTER BUILDING TEST
29. The Building 61
30. Method of Testing 63
31. Preparation for the Test 66
32. Method of Loading 67
33. Making the Test 69
34. Deformations and Stresses 73
35. Beams 76
36. Girders 79
37. Decrease in Compression with Distance from Support 80
38. T-beam Action 81
39. Floor Slab 82
40. Bond Stresses 82
41. Web Deformations 83
42. Deflections 84
43. Effect of Number of Panels Loaded 84
44. Effect of Time on Stresses Developed 86
45. Columns 87
46. Test Cracks 87
V. THE DEERE AND WEBBER BUILDING TEST
47. The Building 88
48. Method of Testing 89
49. Loading and Testing 91
50. Deflections 96
51. Stress in Reinforcement at Center 97
52. Stress in Reinforcement at Column Capital 99
53. Stress in Concrete at Edge of Capital 99
54. Summary of Stresses 101
55. Cracks 102
56. Comments 103
VI. GENERAL COMMENTS
57. General Comments . . 103
CONTENTS 3
LIST OF TABLES PAGE
1. Probable Error of the Average of any Group of Five Consecutive Readings 39
2. Form Showing Method of Reducing Deformation Data 42
3. General Data of Tests 45
4. Schedule of Loading Operations: Wenalden Test 52
5. Stress Indications in Wenalden Building Test 54
6. Maximum Stresses and Moment Coefficients in Wenalden Building Test 54
7. Schedule of Loading Operations in Turner-Carter Building Test 74
8. Stress Indications in Turner-Carter Building Test 76
9. Maximum Stresses and Moment Coefficients in Turner-Carter Building Test 76
10. Data on Position of Rods on which Deformations were Measured in Deere and Webber
Building Test 91
11. Deflection of Slab (in inches) at Points Midway between Columns in Deere and Webber
Building Test 94
12. Unit-Deformation in Reinforcement at Center of Span between Columns in Deere and
Webber Building Test 98
13. Unit Deformation in Reinforcement over Capital in Deere and Webber Building Test 99
14. Unit Deformation in Concrete at Edge of Capital in Deere and Webber Building Test 100
15. Stress Indications in Deere and Webber Building Test 101
LIST OF FIGURES
1. Drawing Showing Relative Sizes of Tests 8
2. Carleton Building Test; Plan Showing Position of Gauge Lines 12
3. Powers Building Test; Load-deformation Diagrams for Series of Gauge Lines on Rein-
forcing Bar 14
4. Powers Building Test; Location of Series of Gauge Lines 15
5. Powers Building Test; Data of Fig. 3 Plotted as Distance-deformation Curves 15
6. Franks Building Test; Observation Platform and Deflection Framework 18
7. Turner-Carter Building Test ; Photograph showing Variation in Height of Gauge Lines 19
8. Turner-Carter Building Test; Interior of Office 20
9. Barr Panel Test; Sand in Sacks as a Loading Material 22
10. Franks Building Test; Pig-iron as a Loading Material 22
11. Moment and Shear Curves for Three Arrangements of Load 24
12. Illinois Type of Berry Extensometer 25
13. Original Berry Extensometer in Use 27
14. New Berry Extensometer 27
15. Extensometer Designed by F. J. Trelease 28
16. Turner-Carter Building Test; Taking an Observation on a Standard Gauge Line 29
17. (a.) Deflectometer; University of Illinois Type; (b.) Deflectometer Used in Corrugated
Bar Company's Tests 31
18. Turner-Carter Building Test; Instruments and Tools 32
19. Position and Finish of Gauge Holes . . 33
20. Powers Building Test ; Load-deformation Curves of Two Observers 37
21. 4-in. x 4-in. Timber Beam Test; Load-deformation Curves of Observations made to Com-
pare Instruments 37
22. Probable Error; Diagram Showing Values Calculated from Data of Four Building Tests ... 38
23. Barr Panel Test; Diagram Showing deformation along Bottom Reinforcing Bar 38
24. Diagram Showing Change in Length of Instruments Due to Change in Temperature 40
25. Diagram Showing Change in Length of Steel Bar Due to Change in Temperature 41
26. Form for Records of Original and Calculated Notes 44
27. The Wenalden Building 47
28. General Position of Reinforcement in Wenalden Building 48
29. Plan Showing Location of Gauge Lines on Upper Side of Floor 49
30. Plan Showing Location of Gauge Lines on Under Side of Floor 49
31. View of Test Load in Wenalden Building . 50
32. Load-deformation Diagrams for Under Side of Girder at Middle 51
33. Load-deformation Diagrams at End of Girder 51
34. Load-deformation Diagrams for Upper Side of Beams at End 56
35. Location of Deflection Points in Wenalden Building 58
36. Diagrams Showing Deflection of Intermediate Beam 58
4 CONTENTS
PAGE
37. Wall Panel Test; Plan Showing Location of Gauge Lines 59
38. Wall Panel Test; Load-deformation Diagram 60
39. Wall Panel Test; Diagram Showing Deflection of Intermediate Beam 61
40. The Turner-Carter Building 62
41. Sketch Showing Reinforcement of Beams and Girders at Supports 63
42. Plan Showing Location of Gauge Lines on Under Side of Floor '. . . . 64
43. Plan Showing Location of Gauge Lines on Upper Side of Floor 65
44. Location of Sand Boxes and Floor Cracks 66
45. View of Sand Boxes 67
46. View of Test Load in Turner-Carter Building 68
47. Load-deformation Diagrams for Under Side of Beams at End 69
48. Load-deformation Diagrams for Under Side of Beams at End 70
49. Load-deformation Diagrams for Under Side of Beams at End 71
50. Load-deformation Diagrams for Upper Side of Beams at End 72
51. Load-deformation Diagrams for Under Side of Beams at Middle 73
52. Load-deformation Diagrams for Upper Side of Beams at Middle 75
53. Load-deformation Diagrams for Under Side of Girders at End 75
54. Load-deformation Diagrams for Upper Side and Under Side of Girders at Middle 77
55. Load-deformation Diagrams for Concrete on Under Side of Slab 77
56. Load-deformation Diagrams for Concrete on Upper Side of Slab 78
57. Load-deformation Diagrams for Bent-up Bars and Stirrups 79
58. Diagram Showing Distribution of Compressive Deformation in Bottom of Column Beam . 80
59. Diagram Showing Distribution of Compressive Deformation in Intermediate Beam 80
60. Diagram Showing Distribution of Compressive Deformation Across Flange of T-beams 81
61. Arrangement of Gauge Lines to Test for Movement of Bar Relative to Concrete 82
62. Load-deflection Diagrams 85
63. Cabinet Projection Showing Beams and Girders and Position of Test Cracks 87
64. Deere and Webber Building at the Time of Test 88
65. Plan of Floor Showing Location of Panels Tested 89
66. Arrangement of Reinforcement and Location of Observation Points 90
67. Falsework for Instruments and Observers 92
68. Deflectometer in Place 92
69. Wissler Dial for Measuring Deformation in Reinforcement 93
70. View of Maximum Test Load 93
71. Diagram of Deflections 95
72. Diagram Showing Stress in Reinforcement at Center of Span 96
73. Diagram Showing Stress in Reinforcement over Capital 97
74. Diagram Showing Stress in Concrete at Edge of Capital 100
75. Location of Cracks Traceable at Load of 350 Ib. per sq. ft 102
TESTS OF REINFORCED CONCRETE BUILDINGS UNDER
LOAD
I. INTRODUCTION.
1. Preliminary. — In the development of the newer types of build-
ing construction, the need of further information on the action of the
structure in its various parts has been felt. Analysis gives methods of
calculation of stresses and laboratory tests give data on the action of
individual members; but the truth of the assumptions used in analysis
may be questioned, and because of the method of fabrication or the in-
fluence of one part on another the action of the structure may not be
in exact accord with the conclusions derived from analytical considera-
tions. It is especially important that knowledge on the amount and dis-
tribution of deformations and stresses actually developed in structures
be extended, and every effort may well be made to determine these
stresses by tests of structures themselves. Many load-deflection tests of
structures have been made, and such tests are required by city building
departments as a condition of acceptance for allowable loading, and these
tests have been used by construction companies and engineers to dem-
onstrate the adequacy of various designs. Load-deflection tests are of
value in judging of the quality of the workmanship and in giving con-
fidence in the structure, but they throw little light on the stresses devel-
oped in the different parts or upon their distribution. The deflections
observed in such tests constitute a very inadequate measure of the stresses
and may even be misleading in this respect. Slight deflections, which
have been taken to indicate low stresses in steel and concrete, may actu-
ally be accompanied by high stresses. In the matter of design there has
been a divergency of views on the relation between the bending moment
at a section at the support and that at the middle of the beam, on the
distribution of stresses across a flat slab acting as the flange of a T-beam,
on the restraint of girders and beams, and on the stresses developed in
the flat slab type of floor construction. It is evident that measurements
of the deformation in structures may be expected to greatly assist the
settlement of such questions as these.
The measurement of deformation in the various parts of a structure
by a field test is a recent development in testing work. It may be ex-
pected that in the early stages of the development of such field tests
difficulties will be encountered and that experience will bring out the
6 ILLINOIS ENGINEERING EXPERIMENT STATION
methods which are most satisfactory and will indicate the precautions
which must he observed to insure accurate and trustworthy results. The
statement of the requirements for such a test will be of value in making
other tests, and the methods of course should be carefully stated with the
record of such tests.
2. Scope of Bulletin. — This bulletin records the results of three
field tests made on reinforced concrete floor systems in which the meas-
urement of deformations or strains in the parts of the structure was an
important feature. As these tests comprise the earliest known measure-
ments of this kind made upon reinforced concrete buildings and as the
writers have been connected with the development of this method
of testing, it has seemed proper to include a discussion of the method of
testing — the use of the instruments, the methods of observation, the
precautions to be taken, the accuracy of the results and the methods of
loading. The bulletin then gives a record of the results of the tests on
the floor systems of two buildings of the beam and girder type and of one
building of the flat slab type, and contains discussions of the stresses
developed and the general phenomena observed.
3. Acknowledgment. — The technical part of making the tests was
done as the work of the Engineering Experiment Station of the Uni-
versity of Illinois. The first building test in which deformations of steel
and concrete were measured was made on the Deere and "Webber Build-
ing in November, 1910. This test was under the direct supervision of
Mr. Arthur K. Lord, then Kesearch Fellow in the Engineering Experi-
ment Station. Mr. Lord is entitled to much credit for his work in
directing this test and for the initiative, foresight and care used in
developing methods and in making the test. The report of the test on
the Deere and Webber Building and the discussion of the results were
prepared by Mr. Lord and with his permission are included in this
bulletin. Mr. W. A. Slater was in direct supervision of the test of the
Wenalden Building and the Turner-Carter Building, and has been inti-
mately connected with the other tests of the kind named in this bulletin,
and to him credit is due for many of the methods and details of the
testing work and for formulating the provisions and precautions neces-
sary to give accuracy and trustworthiness to the results.
The tests were undertaken as co-operatove work. The tests on the
Wenalden Building and the Turner-Carter Building were made in con-
nection with the Committee on Reinforced Concrete and Building Laws
of the National Association of Cement Users, and the president and the
treasurer of the Association raised the funds to defray expenses of the
test. The contractors who erected the buildings also assisted in these
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 7
tests. The expense of the Deere and Webber test was borne by the build-
ing contractor, to whom especial credit should be given for very active
interest and co-operation in initiating a new line of tests.
The tests were conducted by members of the staff of the Engineering
Experiment Station of the University of Illinois. These included Messrs.
H. F. Moore, W. A. Slater, A. R. Lord, D. A. Abrams, N. E. Ensign
and H. F. Gonnerman. The observers on the Deere and Webber Building
test were Messrs. Moore, Slater and Lord; on the Wenalden Building
test, Messrs. Moore, Slater and Ensign ; and on the Turner-Carter Build-
ing, Messrs. Moore and Slater. Professor Talbot was in charge of the
work. Papers covering much of the ground of this bulletin have been
presented before the National Association of Cement Users and pub-
lished in Vols. VII and VIII of the Proceedings of the Association.
4. Comment. — A few words on tfie basis and limitations of such tests
may not be out of place here. It must be borne in mind that the meas-
urements and observations are subject to some uncertainty as compared
with certain laboratory tests; they are not exact or precise, and some
erratic readings may be expected. The measuring instrument is used
under unfavorable conditions. The gauge holes are deep in the concrete
and the measurements may be interfered with by dust or other obstruct-
ing matter. It is evident that great care and much skill is necessary
in making observations. Each test made has shown advances in accuracy
and certainty, and further experience ought to show additional progress.
Besides, it must be understood that the structure itself is not entirely
homogeneous and that all parts of it do not act alike. Further, the struc-
ture itself is tied together so closely that stress in one portion may be
modified or assisted in an unknown amount by another portion, which
may not be thought to affect it. The modulus of elasticity of the con-
crete in the structure is not easily determined. The load-deformation
diagrams may be irregular and imperfect. This all means that care
must be taken in the interpretation of results and that some irreg-
ularities and uncertainties must be expected. With careful work im-
portant information will be brought out, as these tests show, and an
accumulation of data on the action of structures, and tests of special
features of construction will advance knowledge of structural action and
be worth many times the cost of the work.
II. THE TESTING OF BUILDINGS.
5. Building Tests Made. — The number of building tests in which
deformations have been measured is comparatively small. A list is here
given of all known tests on reinforced concrete building floors in which
ILLINOIS ENGINEERING EXPERIMENT STATION
deformations in the steel and the concrete have been measured. The
methods used in all these tests are essentially the same ; they have been
developed at the University of Illinois Engineering Experiment Station.
Fig. 1 shows the range in size of the test areas in the buildings tested.
Deere and^ Webber
Building
Borr
Pane/
Powers
Bu//d/ng
Larkfn
Bui/ding
Wena/cfen Bui/ding
CarJeton Bui /ding
FIG. 1. DRAWING SHOWING RELATIVE SIZES OP TESTS.
Tests have been made on steel structures by the U. S. Bureau of Stand-
ards using methods somewhat similar to those here described, but as this
bulletin is concerned primarily with the results of tests on reinforced
concrete floor systems specific mention of the tests by the Bureau of
Standards is omitted.
Test No. 1. Deere and Webber Building, Minneapolis, Minnesota,
October and November, 1910. Flat slab floor with four-way reinforce-
ment, built by Leonard Construction Company of Chicago, and tested
by co-operation between the contractors and the Engineering Experiment
Station of the University of Illinois.
Test No. 2. Wenalden Building, Chicago, Illinois, June and July,
1911. Beam and girder building constructed by Ferro-Concrete Con-
struction Company of Cincinnati, and tests made by co-operation between
the National Association of Cement Users, the construction company,
and the Engineering Experiment Station of the University of Illinois.
Test No. 3. The Powers Building, Minneapolis, Minnesota, July and
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 9
August, 1911. Flat slab floor with two-way reinforcement, built and
tested by Corrugated Bar Company of St. Louis.
Test No. 4. Franks Building, Chicago, Illinois, August, 1911. Flat
slab floor with four-way reinforcement, built and tested by Leonard Con-
struction Company of Chicago. Prof. W. K. Hatt of Purdue Univer-
sity was employed as consulting engineer for this test.
Test No. 5. Turner-Carter Building, Brooklyn, New York, Septem-
ber, 1911. Beam and girder floor, built by Turner Construction Company
of New York ; test made by co-operation between National Association of
Cement Users, the construction company, and the Engineering Experi-
ment Station of the University of Illinois.
Test No. 6. Carleton Building, St. Louis, Missouri, October, 1911.
Flat slab floor with two-way reinforcement, built and tested by Corru-
gated Bar Company. *
Test No. 7. Barr Building, St. Louis, Missouri, December, 1911.
Full size test panel (25 x 26 ft. 9 in.) ; terra-cotta tile used to lighten
construction ; consists of two-way T-beams with web between tile on ten-
sion side and concrete flange above the tile on the compression side.
Panel built by the Corrugated Bar Co. to demonstrate efficiency of
design proposed for Barr Building in St. Louis ; test made by Corrugated
Bar Company.
Test No. 8. Ford Motor Building, Detroit, Michigan, February and
March, 1912. Flat slab floor, built and tested by the Corrugated Bar
Company.
Test No. 9. Larkin Building, Chicago, Illinois, August, 1912. Flat
slab floor, built and tested by Leonard Construction Company.
The Deere and Webber Building test was undertaken to learn of the
general action of the flat floor slab. The tests on the Wenalden Building
and the Turner-Carter Building were made to find the general action of
the beam and girder type of construction. The tests made by the Corru-
gated Bar Company were for their own information but the results of
the tests on the Powers Building and on the Barr Building test panel
were presented before the Eighth Annual Convention of the National
Association of Cement Users. Those of the Carleton Building and the
Ford Motor Building were in the nature of investigation of special
features of design. The Franks Building test made by the Leonard
Construction Company was an investigation to obtain a basis for making
provision in the Chicago building code for this form of construction.
The Larkin test was the most extensive of those enumerated and was
made with the object of furnishing the Leonard Construction Company
with additional information for the design of flat slab floors.
10 ILLINOIS ENGINEERING EXPERIMENT STATION
6. Definitions. — In the following descriptions of tests, many terms
will be used for which somewhat arbitrary definitions will need to be
made. These definitions are given here :
Gauge Hole: A small hole (0.055 in. is here recommended) drilled
into the steel bar or into the plug inserted in the concrete has been termed
a gauge hole. It is for the admission of the point of a leg of the ex-
tensometer.
Gauge Line: The gauged length connecting a pair of gauge holes is
termed a gauge line.
Reading: A reading is a single observation on any gauge line.
Observation: An observation as here used is the average of a number
of readings.
Correction : A correction is the amount which if added algebraically
to the observation will give the observation which would have been ob-
tained if the instrument had not changed from its reference length.
Series of Observations: A set of observations on all gauge lines or
on a selected number of gauge lines at a given load and taken in an estab-
lished order is termed a series of observations.
Interval: An interval as used here is the time elapsing between con-
secutive observations, and all intervals in any series are (for lack of more
exact information) assumed to be equal. For this purpose the average
of two consecutive observations on standard gauge lines is considered
a single observation.
Standard Gauge Line : Changes in the temperature of the instrument
always occur in the course of a test. Frequently these changes are suf-
ficient to cause an appreciable change in the length of the instrument.
These and other small changes (usually unaccounted for) in the length
of the instrument will introduce errors into the results unless the nec-
essary corrections are applied to the observations. For the purpose of
determining what these corrections should be, it is necessary to have
reference to the standard bar may be understood to signify the standard
constant as possible. This gauge line is termed a standard gauge line.
Usually it is placed on a steel bar separate from the structure, and this
has given rise to the term standard bar. In several of the tests, however,
the standards have consisted of gauge lines placed in the steel and con-
crete of the structure remote from the area affected by the load. Stand-
ard gauge line is adopted, therefore, as the more general term and any
reference to the standard bar may be understood to signify the standard
gauge line on a bar separate from the structure.
Reference Length and Reference Observation: In order to deter-
mine changes in length of instrument it is necessary to make comparison
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 11
of all observations on the standard gauge line. To facilitate this com-
parison the length of the instrument at the time of some reference
observation on the standard may be chosen as a reference length. A
comparison of all other readings on the same standard gauge line with
the reference observation chosen will show whatever variation there is in
the length of the instrument. For convenience the first observation on
the standard gauge line has been assumed as the reference observation.
The length of the instrument at the time of this observation will then
be known as the reference length.
7. General Outline of Method of Testing. — After determining what
measurements will best give the information desired from the test, the
gauge lines are laid off on the surface of the concrete and small holes
are cut or drilled in the concrete at a predetermined distance apart in
order to expose the steel or allow a metal plug ""to be inserted, according
as the measurement is of steel deformation or concrete deforma-
tion. The metal plugs used are securely held in place by embed-
ment in plaster of paris. The gauge holes having been carefully
prepared, a set of zero observations is taken on all gauge lines,
an increment of the loading material is then applied and a sec-
ond series of observations on the gauge lines is taken. The differ-
ence between the two observations on the same gauge line represents
the deformation in that gauge line. It is possible that this appar-
ent deformation may be due partly to temperature changes in the instru-
ment instead of stress changes of the material by reason of applied load.
For this reason reference measurements are made on standard un-
stressed bars made of invar steel which has a very low coefficient of ex-
pansion and whose change in length due to change in temperature would
therefore be very slight. From these readings on the standard bar, tem-
perature corrections are computed as shown in a later paragraph and
applied to the observations in order to determine the actual change in
length of the gauge line. Another increment of load is then applied and
another series of observations taken.
Floor deflections also have been measured in all of these tests, but
they have been considered as of secondary importance. They have been
used to throw light on the correctness or incorrectness of the deformation
readings and to gain some idea of the general distribution of stresses
throughout a floor. Apparently they can be depended upon to show with
considerable accuracy the proportional rate of increase of stress, but
deflection formulas are so imperfect that measurements of deflections can
not be depended upon to give actual values of stresses.
Measurements of dimensions such as span, depth of beams, location of
12
ILLINOIS ENGINEERING EXPERIMENT STATION
PL AN SHOW/M eL OCATJOM
or PO/WTS ON TOP OF SLAB
® Def/ect/on point
<*> Ppmf on $•/<?<:•/
*« rb/nr on concrgre.
Gauge /enpf ft 3 /n
6 LOCAT/ON
OF Po/wrs o/*\8orroM OF SLA &
FIG. 2. CARLETON BUILDING TEST; PLAN SHOWING POSITION OF GAUGE LINES.
observation points, weight of loading material, location of cracks and
any other measurements which are of value in working up results are
carefully taken.
The gauge lines are usually distributed over and under the surface
of the floor tested in order to gain an idea of the changes occurring in
different parts of the structure. The statements in the preceding para-
graphs give in general terms the features of a field test. There are
many difficulties to be overcome and many chances for error. The meth-
ods of overcoming the difficulties and avoiding the errors will be dis-
cussed in the following pages. Host of the statements there made rep-
resent the results of experience on building tests.
8. The Planning of a Test. — Each test made will involve individual
consideration of the choice of area to be loaded, the number and loca-
tion of gauge lines and deflection points, the number of laborers re-
quired, the loading material to be used and its distribution, and the
provisions for storage of the loading material near the test area without
appreciably affecting the stresses which are to be measured. Other mat-
ters will come up for consideration but generally different solutions will
be required for each test.
The area to be loaded should be chosen so as to fulfill the following
conditions as completely as possible.
(a) It should be so located as to give conditions in the beams, slabs,
columns, etc., as severe as will be found anywhere in the building when
in use.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 13
(b) It should be free from irregularities of construction.
(c) It should be as free as possible from disturbances by workmen.
(d) It should be as easily accessible to the loading material as
In most cases some limitation is found on part or all of the conditions
named. For example, in the test of the Wenalden Building it was im-
possible to find an area entirely free from irregularities of construction.
An industrial track crossed one of the panels chosen, and the floor was
thicker immediately under this track than at other places. On the edge
of one or two of the panels tested, beams about an inch deeper than the
regular beams were located. However, none of the measurements as-
sumed to give typical results were taken in these panels, and it is believed
that the stresses in the other panels were not affected appreciably by the
irregularities. Again, in the test of the Franks Building it was not
possible to choose a lower floor convenient to the loading material. The
choice of an upper floor fulfilled one of the conditions mentioned — it
gave a much more severe test of the columns than a test on a lower floor
would have done. Also, in the test of the Carleton Building at St. Louis
the area to be tested was specified by the city building department, and
there was no choice as to location, on the part of those making the test.
The number of measurements to be taken will depend upon the na-
ture of the test, the number of observers, and the number of laborers.
If the test is a part of a series by which it is expected to gain scientific
information which will afford a basis for design, it is likely that it will
be made deliberately enough that a large number of measurements may
be taken. Such tests were those of the "Wenalden Building, the Franks
Building, the Turner-Carter Building and the Barr test panel. If, on
the other hand, the test has more of a commercial nature or is a utiliza-
tion of the opportunity offered by the acceptance test to take some meas-
urements which will show actual stresses, or if for any other reason the
test is hurried, the number of measurements will necessarily be rather
small. Of this class, the tests of the Carleton Building in St. Louis and
of the Ford Motor Building in Detroit, Michigan, are good examples.
Notice was given the engineers only about one day in advance that a test
would be made on the Carleton Building. Permission was obtained from
the contractor to expose bars for measurement in various places and to
erect the necessary scaffolding. The measurements were made more for
the purpose of checking the analysis upon which the design was based
than to form in itself a basis of design. Therefore comparatively few
observation points were used. It is believed that this test is representa-
tive of the type of test which is practicable on a commercial basis, hence
14
ILLINOIS ENGINEERING EXPERIMENT STATION
'
2/4
^
2sl
Deformation per Unit of Length.
FIG. 3. POWERS BUILDING TEST; LOAD-DEFORMATION DIAGRAMS FOR SERIES
OF GAUGE LINES ON REINFORCING BAR.
(by courtesy of the Corrugated Bar Company) a plan is given in Fig. 2
showing the points where measurements were taken.
The principal subjects for investigation in any test will determine
the arrangement of observation points. Whatever the subject of
study may be, the observation points should be arranged in such a
way that a curve of deformations may be plotted against distance,
showing a gradual progression from the condition at one part of the
structure to the condition at another, for it is found that even under
the most careful work there are inconsistencies which will make the.
results look doubtful if standing by themselves. The points so ar-
ranged should be numerous near the place where the measurements of
greatest importance are to be taken, so that the results will not de-
pend upon measurements at a single point, or upon the average at
portions of the structure supposed to be similarly situated but in dif-
ferent parts of the building where unknown conditions actually may
cause a large variation in the phenomena of the test. It will not be
possible to carry out this plan for all subjects of investigation, as the
number of observations required usually would be impracticably large.
Such provisions may be made to cover the main lines of investigation,
and isolated observation points may be used to gain information as to
tendencies of other portions of the structure, but of course less reliance
must be placed on the results of the latter measurements than where the
larger number of observations is made. It would be advantageous, as
was done in the Powers Building test and also in the Barr panel test, for
two observers to check measurements on the same points. One or both of
these checks is very valuable in establishing the correctness of observa-
tions. Fig. 3, 4, 5, and 58 illustrate the former method. Fig. 3 gives
the load-deformation diagrams for a series of gauge lines in the test of
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS
15
FIG. 4. POWERS BUILDING TEST; LOCATION OF SERIES OF GAUGE LINES.
the Powers Building. Fig. 4 shows the location of these gauge lines with
reference to the wall and a column. Fig. 5 shows the same data plotted
as deformation against distance from the column instead of against load.
It may be seen that the correctness of the load-deformation curve for one
of these points, if standing hy itself, might be doubted because of the
complete change in the character of the curve at a load of 200 lb.
per sq. ft. But when these deformations are plotted against dis-
tance, the results look so consistent that it is scarcely conceivable that
they are seriously incorrect. In the test of the Wenalden Building very
high compression deformations were observed in the beams near the sup-
.OOOQ
.OOO6^
^.0004
FIG. 5.
O /O 20 30 40
D/srartce from Capirai in Inches.
POWERS BUILDING TEST; DATA OF FIG. 3 PLOTTED AS DISTANCE-
DEFORMATION CURVES.
16 ILLINOIS ENGINEERING EXPERIMENT STATION
ports. As this was the first test of a beam and girder floor it was con-
sidered especially important that in the next test, that on the Turner-
Carter Building, evidence be obtained which would give additional
information bearing on this high compression in the concrete; accord-
ingly the method of placing observation points at frequent and regular
intervals along the ends of the beams was used. The deformations meas-
ured are plotted in Fig. 58, p. 80, against the distance from the supporting
column, and the results not only tend to show the correctness of these
measurements but also to indicate that the high stresses observed in the
beams of the Wenalden Building were actually present.
The subjects for investigation will vary largely in different tests. In
the tests discussed in this bulletin deformations have been measured
with a view to obtaining information on each of the following subjects :
. (a) The values of the coefficients of bending moment at the center
of the span and at the support of the beam or slab under investigation.
(b) Eelative moments at support for various conditions of fixedness.
(c) The extent to which the floor slab acts as a compression flange
of the floor beam to produce T-beam action.
(d) Bond stresses.
(e) Diagonal tension.
(f) Stresses in columns.
(g) Time effect under constant load.
(h) The lateral distribution of stress to parts of the structure en-
tirely outside of the loaded area.
(i) The extent to which steel stresses are modified by errors in the
assumption that no tension is carried by concrete.
(j) Stresses in slabs of beam-and-girder floors.
(k) Kelative stresses in short and long directions of rectangular
panels.
Other subjects of investigation have received attention but those men-
tioned above are the most important ones. Some phenomena have been
observed which bring out additional problems. Of these the determina-
tion of the amount of arch action present is probably the most important.
It is not to be expected that the moment coefficients can be determined
with absolute accuracy. The method used has been to measure deforma-
tions on both steel and concrete at the center and supports of the beams
and from these measurements to determine the total resisting moment
developed at the given section. Equating this resisting moment to the
bending moment kWl (where k is the bending moment coefficient), a
solution is made for the value of k. Arch action, tension in the concrete
and the sharing of bending moment by adjacent beams complicate the
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 17
problem. It is suggested that the amount of arch action may be deter-
mined in any case by making a special study of the deformations in a
cross-section at the mid-span of each beam and on the floor slab across
an entire panel. In this study, deformations should be observed on the
steel and at various elevations on the concrete so that the position of the
neutral axis and of the center of gravity of tensile and compressive
stresses respectively may be accurately determined. By this means it
should be possible to determine if the sum of the compressive stresses is
in excess of that of the tensile stresses. If so, the difference apparently
must be the direct thrust due to arch action. A second section may
profitably be taken at or near the point of inflection. The same study
can be made, though not so satisfactorily, at the ends of the beams. The
measurements for thrust will require observations on an extremely large
number of gauge lines, and the observations must be expended far enough
into the adjacent panels to determine the extent to which they share in
carrying the load.
9. Preparation for the Test. — In all of these tests it was necessary
to cut holes in the concrete in order to expose the steel. Fig. 4
shows holes cut in the concrete of the Powers Building where a series of
measurements was taken on a rod which passed through a column. This
cutting has been best accomplished by the use of a cold chisel with a
very gradually tapering point. This work is a task for common laborers
and a long one for inexperienced men. It has been found that a great
deal of speed can be developed by practice, hence the importance of com-
pleting this part of the work with a single set of workmen.
A saving in mutilation of floors often can be effected by planning the
test ahead of time and inserting plugs in the concrete during construction
in the proper position for the gauge lines. Removal of the plugs after
the concrete has set exposes the steel without the use of a cold chisel.
Likewise metal plugs may be set in the concrete at the proper positions
for the measurement of concrete stresses and thus save cutting into the
concrete to place compression plugs. The point has been raised that by
preparation of this kind a chance is given to the contractor to know what
panels are to be tested and thus to make the construction of that panel
better than others. For this reason there is room for question as to the
advisability of using this method. Its employment will depend largely
on the purpose of the test and on the conditions under which it is made.
In most of the tests under consideration this point has been taken care
of by the fact that it was not known until shortly before the test what
area was to be loaded.
Drilling of the gauge holes will be discussed in article 14.
18
ILLINOIS ENGINEERING EXPERIMENT STATION
An elevated platform which will enable the observer to get close
enough to the floor above to take observations of deflection and deforma-
tion is necessary. This should be supported at such a height that
when the observer stands upon it the points where measurements of
deformation are to be taken will be about one inch above his head. For
flat slab construction this condition is easily obtained (see Fig. 6),
FIG. 6.
FRANKS BUILDING TEST; OBSERVATION PLATFORM AND DEFLECTION
FRAMEWORK.
but with beam and girder construction where there are measure-
ments on beams, girders and the floor slab, the heights of different gauge
lines vary so much that arrangement will need to be made for building
certain parts of the platform higher than others (see Fig. 7).
It is important that the elevation of the platform should be such that
the observer can stand erect while taking the readings, and yet such that
the instrument will not be too high for convenient and accurate
observation.
Another framework for the purpose of supporting deflection appa-
ratus under the points where measurements of deflection are to be taken
is also necessary. In order that the movements of the observers upon the
observation platform may not jar the deflection apparatus, the two frame-
works must be built independently of each other. In all the tests which
have been made, these deflection frames have stood on the floor and have
been braced from one to the other in order to make a comparatively rigid
framework. Fig. 6 shows scaffolding and deflection frames for the
Franks test.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 19
FIG. 7.
TURNER-CARTER BUILDING TEST; PHOTOGRAPH SHOWING
VARIATION IN HEIGHT OF GAUGE LINES.
The equipment necessarily will consist of the following : cutting and
drilling tools, portable lamps for throwing light into observation holes,
note books and facilities for doing drafting and for reducing data.
The cutting and drilling tools are sufficiently described in other
paragraphs.
Some kind of a portable light is a necessity as gauge lines are often
located in dark corners and as observations may be taken at any hour of
the day or night. The lamp shown in the photograph of Fig. 16, p. 29,
is a hunter's acetylene lamp and is quite satisfactory. The lamp is at-
tached to the forehead and light may be thrown in various directions
according to the setting of the clamp attachment. The acetylene tank
may be attached to the belt or carried in the pocket.
Loose leaf note books should be provided in which the sheets are as
large as conveniently can be handled and filed. The data sheets shown
20 ILLINOIS ENGINEERING EXPERIMENT STATION
in Fig. 26, p. 44, are very conveniently ruled in hectograph ink and
copied by means of a hectograph. Printed forms might be used, de-
pending on whether the number required would justify the expense of
having them printed.
For the most efficient work in computing results and making sketches
for records, it is important that an adequate place be provided where
quiet may be had, where benches and drafting tables may be used and
where instruments and other equipment may be kept. The photograph
in Fig. 8 shows the temporary office which was provided in the
FIG. 8. TURNER-CARTER BUILDING TEST; INTERIOR OF OFFICE.
Turner-Carter Building test. This is one of the portable office shanties
which the company moves to places where work is being done. The
photograph shows the interior of the office with the observers and re-
corders at work reducing the data of the test. This added equipment will
add only slightly to the cost of the test but very greatly to the efficiency
of the work. Special attention is called to it because the office is an im-
portant piece of equipment and it has not always been provided.
10. Loading. — In the tests which already have been made, the fol-
lowing loading materials have been used: brick, cement in bags, loose
sand in boxes or bins, sand in sacks and pig iron. The material used
will almost always be that which is most easily available, because the
moving of loading material from any distance adds very greatly to the
cost of the test. Leaving consideration of cost out of the question, sand
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 21
in sacks seems to be the most satisfactory of the materials above men-
tioned for loading purposes. Some of the qualities of the materials
mentioned are as follows :
(a) Brick: Brick spalls and chips in handling, covering the floor
with dust and jagged particles which cause discomfort to the observer in
kneeling to take observations. It is important to avoid this because dis-
comfort necessarily decreases the accuracy of his observations. This
might be avoided by sweeping, but in sweeping it is difficult to avoid
getting dirt into holes where observations are to be taken, and this is
just as troublesome as having the dirt on the floor. Fig. 31, p. 50, a
photograph of the Wenalden test, shows the use of both brick and cement
in the same test. Attention is called to the proximity of the cement sacks
to the beams and girders of the floor above. In some cases if cement and
brick were used the intensity of the load would be limited by. the height
of the ceiling.
(b) Cement : Cement sifts through the sacks and the sacks become
untied, scattering cement on the floor, filling observation holes and caus-
ing much dust in sweeping or cleaning up. The dust is injurious to
delicate instruments and annoying to observers and recorders.
(c) Loose Sand in Small Boxes : As sand is usually damp, it does
not have the fault of causing dust, and consequently is more easily
cleaned up than the other materials mentioned. There are, however,
other objections to it. In filling boxes it is difficult to avoid spilling the
sand around and between the boxes, and consequently filling the observa-
tion holes. On account of the great difficulty in removing loose sand
without spilling a great deal of it, it is impracticable to take observa-
tions as the load is being removed, therefore it is necessary to remove in
one increment the whole load from a given panel. Fig. 46, p. 68, is a
photograph of the Turner-Carter test and shows this method of loading.
(d) Sand in Sacks: Sand in sacks constitutes a very satisfactory
loading material. An example of its use is shown in Fig. 9, a photo-
graph of the test of the Barr Building test panel. It was piled up
to a height of about nine or ten feet, and very little inconvenience was
caused by the sacks coming untied or by spilling the sand. The worst
difficulty encountered, and this exists with all materials handled in sacks,
is that of the sliding of sacks on themselves when the load is piled high.
It can be seen in Fig. 9 that bracing was necessary to prevent the sand
from sliding together and filling up the aisles. It is a source of danger
to those taking observations as, if a slide should occur, it probably would
give very little warning and might catch the observer while in such a
position that he could not escape. However, this objection would hold
22
ILLINOIS ENGINEERING EXPERIMENT STATION
FIG. 9. BARR PANEL TEST; SAND IN SACKS AS A LOADING MATERIAL.
with any material when piled as high as was that in this test. Under
any circumstances it is necessary that care be taken and undue risks
avoided.
(e) Pig Iron: Pig iron was used as loading material in the test of
the Franks Building (see Fig. 10). From the standpoint of the
making of the test, the worst objection to it is that, as with the brick,
small particles break off and cause annoyance to observers. This is
FIG. 10. FRANKS BUILDING TEST; PIG-IRON AS A LOADING MATERIAL.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 23
less troublesome than with brick and in other ways pig iron is clean. It
possesses the great advantage that with its use a very heavy load can
be applied without piling the load extremely high.
Tin plate in boxes two feet square, each weighing 200 pounds, was
to have been used in a building test. A more nearly ideal loading ma-
terial would probably be hard to find, but unfortunately this test could
not be carried out.
The intensity of the loading will depend mainly on the load for
which the building was designed. It will not be possible to make the
load absolutely uniform, as aisles usually will be necessary for the pur-
poses of (a) convenience in placing the load, (b) access to gauge lines
for the taking of observations, and (c) the prevention of arching in the
loading materials. It has been found that it is difficult to cover more
than about 75% of the actual area of the floor, and in manj cases less
than this will be covered. Hence in computing the probable height of
the load this fact must be taken into consideration.
Aisles should be so placed that the load, even though partly carried
by arching of the material, will cause stresses in the floor v which approx-
imately are equal to, and always as severe as, those caused by an
actual uniform load. Fig. 11 shows the moment and shear diagrams
which would be obtained by loading a simple beam with a total load W
distributed over the span in three different ways, as follows :
(a) Solid Line : Total load W, uniformly distributed over full span.
(b) Broken Line : Same load W distributed over one-half of span,
giving aisles of equal width at center and support.
(c) Heavy Dotted Line: Same load W distributed over one-half
span, half of load being carried by arch action to ends of boxes (shown
W
here as concentrated loads, ~o~), and the other half being uniformly dis-
tributed over the half span.
It will be possible in almost any test to arrange the loading ma-
terial in such a way as to come within the limits outlined by the three
arrangements of load assumed in the preceding illustration, and it is
seen that if this is done, the presence of the aisles or of arching to the
sides of the boxes or piers, while not affecting the amount of the maxi-
mum moment and the maximum shear, would tend to cause them to
exist over greater portions of the span than would be the case with an
equal uniform load. In this figure aisles equal to one-quarter of the span
have been assumed. In no case would they be as large as this, and
therefore the moment and shear diagrams actually should conform even
more nearly to those for uniform load than is shown in the figure.
24
ILLINOIS ENGINEERING EXPERIMENT STATION
Arrangement should be made, if possible, to store the loading ma-
terial near the test area in order to hasten, the work of applying the load
after the test begins. The general rule has been to allow loading material
to be stored as close as one full panel length from the test area, but the
intensity of the storage load has been kept down as much as possible.
The number of laborers which can be used advantageously will de-
pend upon the distance of the point from which the loading material is
FIG. 11. MOMENT AND SHEAR CURVES FOR THREE ARRANGEMENTS OF LOAD.
to be transferred, upon the size and accessibility of the tested area, upon
the amount of work which can be done by them during the intervals be-
tween increments of load while observations are being taken, and upon
the length of time required to take a series of observations. The direc-
tion of the labor should not be left to the one in charge of the test, if it
can be avoided, since proper attention to the conduct of the test demands
all of his time. In the tests included in this bulletin the number of la-
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS
25
borers has varied between wide limits, from 5 or 6 in the Powers test to
30 or 35 in the Deere and Webber test.
* 11. Extensometers. — In the past the great obstacle to the measure-
ment of deformations in building tests has been the difficulty of attaching
the measuring instruments to either the steel or the concrete on the flat
surface of a floor, and recent tests show the necessity of making measure-
ments of steel deformation directly on the steel. A satisfactory method
of accomplishing this has been provided by the introduction of the ex-
tensometer invented by Professor H. C. Berry of the University of
Pennsylvania and adapted to this work by modifications and improve-
ments made at the University of Illinois. T^nis instrument is similar in
some respects to the strain gauge designed and used as long ago as 1888
by James E. Howard, Engineer-Physicist of the Bureau of Standards,
and until recently Engineer of Tests at Watertown Arsenal.
The great value of this instrument in building tests lies in the Tollow-
ing facts: (a) Its use makes it possible to take measurements directly
upon the surface of the steel and concrete, (b) With its use there is no
apparatus left in place to be damaged or disturbed during loading,
(c) Due to the fact that it is portable, measurements may be taken in a
large number of places with a single instrument. Measurements have
been taken at as many as 268 points in a single test. If fixed instruments
were used this would call for an outlay of from $2500 to $5000 for
instruments and the impossibility of keeping so many instruments in
adjustment under testing conditions would render their use im-
practicable.
Fig. 12 shows the Illinois extensometer in its present form.* Any
Gauge length adjustable
from 6 "to//*
FIG. 12. ILLINOIS TYPE OF BERRY EXTENSOMETER.
*Another form has been devised since the manuscript for this bulletin was prepared and this*
newer extensometer is now in use in laboratory tests.
26 ILLINOIS ENGINEERING EXPERIMENT STATION
movement of the point B due to a change in the length of the gauge line
is transmitted to the Ames gauge through vertical movement of point C,
by means of the leg BD and the arm DC pivoted at D. The Ames gauge
is sensitive to a movement at C of .0001 inch. The ratio of the length
CD to the length BD is approximately five and the Ames gauge is thus
sensitive to a movement at B of .00002 in. (.0001 inch -4-5). How-
ever, this must not be taken to mean that the extensometer possesses this
degree of accuracy in measuring stresses, since ^some movement of the
point of the leg at B is certain to result from variation in the handling
of the instrument.
To obtain the exact ratio between movements at points B and C the
instrument is calibrated by means of a Brown and Sharpe screw mi-
crometer. For known movements of the point B readings of the Ames
gauge are taken and a calibration curve plotted for the entire range of
the instrument.
The first instrument of this type built by the Engineering Experi-
ment Station of the University of Illinois was made for the Deere and
Webber test. It was designed by Professor H. F. Moore and Mr. A. R.
Lord, and was like the instrument in use at present except that it had a
15 in. gauge length and was made entirely of steel. Later on in making
the instrument for general use aluminum was substituted for steel in
order to reduce its weight and the gauge length was made variable from
6 in. to 11 in. Since then several minor changes have been made. The
legs have been made stiffer in order to reduce the error due to uncon-
sciously applied longitudinal thrust and the points have been made
sharper in order to reduce the pressure required in seating the instru-
ment. These improvements have considerably reduced the probable error
of observation.
The extensometer loaned by Professor Berry to the University of
Illinois in 1910 for use as one of the instruments in the Deere and Webber
test is shown in Fig. 13. It differed from the Illinois instrument in that
the movement of the multiplying arm was measured by means of a screw
micrometer instead of the Ames gauge head, the point of contact of the
micrometer plunger and the lever arm being determined by means of a
telephone apparatus. The screw micrometer and the frame of the ex-
tensometer were insulated from each other and were connected with the
poles of a small battery by means of copper wires. A contact between
the plunger of the screw micrometer and the multiplying lever completed
the circuit and the current set up produced a vibration of the diaphragm
of the telephone apparatus carried on the head. This method of observa-
tion was very slow and the electrical connection got out of order very
easily.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS
27
FIG. 13. ORIGINAL BERRY EXTENSOMETER IN USE.
The use of the Ames gauge head (instead of the screw micrometer
and telephone apparatus) adopted by Professor Moore in the instrument
used in the Deere and Webber test has greatly facilitated the use of the
extensometer. The legs of this instrument also were made longer in order
to adapt it to the measurement of deformations of steel embedded in con-
crete. Both of these modifications later have been used by Professor
Berry in instruments which he has put upon the market.
The extensometer more recently designed by Professor Berry is shown
in Fig. 14. It is not different in principle from the one just described.
FIG. 14. NEW BERRY EXTENSOMETER.
It differs from the Illinois instrument in the following details: (a)
Instead of having a uniformly variable gauge length ranging from 6 in.
to 11 in., it has two fixed gauge lengths of 2 in. and 8 in. respectively,
(b) The instrument shown here has a multiplication ratio of two be-
28
ILLINOIS ENGINEERING EXPERIMENT STATION
tween leg and arm, and in order to make this ratio five (as in the Illi-
nois type) it is necessary to use a leg which is only one inch long. With
this arrangement the instrument cannot usually be used for measuring
deformations in reinforcing bars in place, owing to their depth of em-
bedment, (c) The framework of this instrument is of invar steel or of
aluminum. While invar steel makes the weight somewhat greater than
that of the aluminum instruments, it has the advantage of reducing the
dependence on an invar steel standard bar and the study of the effect of
temperature changes in the steel and concrete of the structure is accom-
plished with greater ease.
Mr. F. J. Trelease of the Corrugated Bar Company has designed an
instrument of the Berry type and has used it in at least one test. This
instrument, shown in Fig. 15, also has as its main feature a multiplying
FlG. 15. EXTENSOMETER DESIGNED BY F. J. TRELEASE.
lever which actuates the plunger of an Ames gauge head. The prin-
cipal difference between this instrument and the one shown in Fig. 12
is that the multiplying lever is vertical instead of horizontal. Eesults
have been obtained with it which do not differ much as to accuracy
with those of the Illinois type of instrument.
12. Standard Bar. — The necessity for a standard bar was first found
in the test of the Deere and Webber Building. Variation in tempera-
ture was sufficient to cause a change in the length of the instrument as
great in many cases as that in the reinforcing steel due to the applied
load. Hence it was found necessary to make observations on an un-
stressed standard bar to show any temperature changes in the length
of the instrument. In this test a bar of about §^-in. steel was used
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS
29
as a standard. It was protected from rapid temperature changes by
embedment in plaster of paris, and was kept on the floor where the test
was being made. In this way it was expected to make the change in
the length of the standard bar due to temperature variations about
equal to the change in length of the reinforcing steel due to the same
cause. To some extent this purpose was accomplished, but as the plaster
covering was thin and not very dry, the change in the standard bar must
have been much more rapid than that in the reinforcing steel. In the
test of the Wenalden Building and of the Barr test panel, precautions
were taken to embed a standard bar in concrete. This was done also in
the tests of the Powers Building and of the Franks Building, and in
addition standard gauge lines were established in parts of the floor not
affected by the load. In the Turner-Carter test only the latter method
was used. These standard gauge lines have been placed both on the r£-
inforcing steel and in the concrete. Fig. 16 shows the taking of an
FIG. 16. TURNER-CARTER BUILDING TEST; TAKING AN OBSERVATION ON A
STANDARD GAUGE LINE.
observation during the Turner-Carter test on a standard gauge line. The
standard gauge line is located in a part of the floor entirely away from
the loaded area.
30 ILLINOIS ENGINEERING EXPERIMENT STATION
The greatest development in the use of the standard gauge line has
been in the frequency of reference to it and in the development of an
exact system for the calculation of temperature corrections. It was
noted previously that a steel extensometer was used in the Deere and
Webber test but that in the subsequent tests an aluminum instrument
was used. Since the coefficient of expansion for aluminum is almost
twice that for steel, it is apparent that dependence on a standard must
have been of still greater importance in the later tests. Difficulty was
found in interpreting the notes taken on the Wenalden test, but the
greater dependence on the standard gauge line and the more systematic
use of it since then has very largely overcome this difficulty. In the test
of the Larkin Building standard bars of invar steel were used. Invar
steel has a very low coefficient of expansion and its use as a standard
bar makes it possible to eliminate from the measurements almost all
the effects of temperature variation in the extensometer. If it is desired
to determine how great are the temperature effects, a standard gauge line
can be placed in the floor as before in such a position as not to be
affected by the floor load.
It has been the practice in the more recent building tests for each
observer to make observations regularly on two standard gauge lines.
This is done in order that one may form a check on the other. If only
one standard were used, a large accidental change in the readings due
for instance to sand in the gauge holes might be mistaken for a tempera-
ture effect. If two standards are used, such an accidental change as the
above seldom would be the same in both, and the error would be de-
tected. An accident to the instrument would probably cause the same
change on both standard gauge lines and the use of the two standards
would not help to detect this kind of an error. However, such errors
are usually so large as to be apparent in a reading of the standard gauge
line and are infrequent as compared with errors due to dirt in the
gauge holes.
13. Deflection Instruments. — In the building tests referred to in this
discussion deflection instruments of two types have been used, one being
that used by the Illinois Engineering Experiment Station and the other
that used by the Corrugated Bar Company. The former consists of a
screw micrometer head of 1-in. travel, connected in tandem with
an Ames gauge head micrometer of ^-in. travel. The screw micrometer
is designed to cover large variations in deflections and the Ames gauge
head small ones. The Ames gauge head shows an increase in reading
for a decrease in length of the deflection instrument, and a screw mi-
crometer head, as ordinarily constructed, would show a decrease in read-
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS
31
ing for a decrease in length. Thus to obtain an observation which in-
volves the readings of both the Ames gauge head and the screw microme-
ter head it is necessary to take the difference of these readings, but in
making calculations a sum is much more easily and accurately handled
than a difference. To permit addition, the graduation on the screw
micrometer head used in this deflection instrument has been reversed
so that it shows an increase for a decrease in length, just as with the
Ames gauge head. Fig. 17a shows this deflection instrument and also
Concrete floor
FIG. 17. (a) DEPLECTOMETER; UNIVERSITY OF ILLINOIS TYPE.
(b) DEFLECTOMETER USED IN CORRUGATED BAR COMPANY'S TESTS.
the method of using it. A plate having a 5/2-in. steel ball attached is
plastered to the surface, deflections of which are to be measured. A ^$-in.
bolt, which has a steel ball inserted into its upper end, is set into a
wooden block (part of the deflection framework) in such a way that
its elevation can be adjusted to give any desired zero reading of the
deflectometer. Thus at the beginning of a test all the zero deflection
readings can be determined, so that for a considerable length of time
all the change in deflection will be shown on the Ames gauge without
any change of the screw micrometer. As larger changes take place, a
second setting of the screw micrometer will probably be necessary. The
32
ILLINOIS ENGINEERING EXPERIMENT STATION
great advantage of this instrument is the rapidity with which it can
be used. It has been found to work very satisfactorily in most respects.
, The deflection instrument used by the Corrugated Bar Company is
shown in Fig. 17b and consists of a screw-micrometer depth-gauge by
means of which distances for varying loads are measured between the
stationary frame and a point on the beam or floor slab. It has the ad-
vantage of a much larger range of measurement than is found in the
Illinois instrument. In the Barr panel test a gross deflection of more
than 3 in. took place. As the Illinois type of deflectometer has a range
of only 1^4 in-? it could not have been used in this test. This amount of
deflection, however, is more than would be likely to occur in the test
of a building. The disadvantage of the Corrugated Bar Company in-
strument is that it requires a longer time to make an observation than
does the deflectometer previously described.
14. (JExtensometer Observations. — In obtaining good results with
this type of extensometer, a great deal depends upon careful manipula-
tion. Two things which are of great importance in this respect are (a)
the preparation of the gauge holes, and (b) care and experience in the
use of the instrument. \
FIG. 18. TURNER-CARTER BUILDING TEST; INSTRUMENTS AND TOOLS.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 33
The placing of the gauge holes so they will come within the range
of the extensonieter is hest accomplished by the use of some kind of gauge
marker such, for instance, as is shown in Fig. 18. In the work of the
Illinois Engineering Experiment Station the holes are drilled with a
No. 54 drill (.055 in. in diameter). At the beginning of the use of the
Berry extensonieter a number E countersink drill (approximately
3/:i2 in. in diameter) was used; but a smaller one seems to be better,
because it is easier to get the properly finished hole, because a slight
eccentricity of the gauge holes on the reinforcing rod (see Fig. 19)
causes less error in manipulation of the extensonieter when a small
drill is used, and because, in the case of measurements on small rods,
tne 3/32~in- drill cuts awav a large percentage of the steel in the rods.
A breast drill geared so that one revolution of the crank gives about
4=%- revolutions of the drill had been used previously. In the hands of
a skilled workman very satisfactory work can be done in this way, but
where, as quite frequently will be the case, the drilling has to be done by
persons not familiar with this kind of work something better is needed.
A drill driven by a flexible cable attached to a small electric motor giving
a speed of rotation of 400 r.p.m. or more does better and more rapid
work. Where high carbon steel is encountered fewer drills are broken,
and when a hole is drilled a better job is usually the result.
£ After drilling the holes, the edges should be finished to remove the
burr and to round off the sharp corners.] The tool shown in Fig. 19 is
£ccerjfr/c tfo/e Centra/ Ho/e
FIG. 19. POSITION AND FINISH OF GAUGE HOLES.
designed to accomplish this purpose. Such a (tool should not be a cutting
tool but rather a wearing or polishing tool. A pointed magnet to remove
steel dust and small fragments of steel torn off in drilling, would be of
34 ILLINOIS ENGINEERING EXPERIMENT STATION
use. It is harxl to place too much emphasis on the proper preparation
of gauge holes/
/Observers should be experienced in the use of the Berry extensom-
etef before undertaking work on a field test. The chances of error in
the manipulation of the instrument are large. As a rule the deforma-
tions measured are small so that the error is likely to be quite a large
proportion of the total measurement, hence it is important to reduce
errors to the lowest possible limit.)
(If the observations at zero are as reliable as other observations, a
curve may be drawn through all the points of any load-deformation
diagram, weighting the zero observations equally with the others; the
zero point shown by the intersection of the most probable curve should
then be used as the origin. This method involves waiting until the com-
pletion of the test to draw these curves. It would be much better to
repeat the observations at zero load several times and to give more care
and time to their determination than is given at any other load. By
this means a check can be had upon the action of the structure as the
test progresses, and the construction of the most probable curve will be
made more simple. To obtain a satisfactory zero point, then, it is
essential that several complete series of observations should be taken with
no load on the Boor) and it would be well to repeat this through con-
siderable range of temperature to study temperature effect on the steely
and on the concrete. This study was attempted in the Deere and Web-
ber test, but the changes both in instruments and in reinforcement were
included in the measurements and could not be separated, so no definite
conclusions could be drawn. However, with an invar steel standard bar
or with an instrument made of invar steel these two sorts of changes
can be separated and to some extent at least the effect of temperature
determined.
fin taking an ordinary observation about five readings should be
averaged. In most of the building tests which have been made, indi-
vidual extensometer readings were recorded, but in certain laboratory
testsjand in the test of the Larkin Building/the practice of averaging the
results mentally v as followed. This has given very satisfactory results
and saves a great deal of time on a test, and with a good recorder the
calculations can be kept up with the observations ; but the practice should
be adopted with caution and only after some experience in this kind of
work. In the more recent building tests where individual readings were
recorded, the practice followed in making an observation has been to
reject all readings until five consecutive readings have been obtained
which agree within .0004 in. T^feese five consecutive readings then are
averaged to form an observation. .)
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 35
Deflectometer observations have been sufficiently discussed in the de-
scription of the deflectoineter and will not be considered here again.
15. Observation of Cracks.— Up to very recently the observation of
cracks has been considered one of the most important features of a test.
Although it is not considered so important as formerly when strains
were not measured, if carefully done it may form a valuable check on
the measured deformations. These observations should be made and
recorded for zero load and at each increment of load. This is one of
the most tedious parts of the test, and to carry it out faithfully requires
a great deal of patience. The examination should be minute and very
thorough. One who is not familiar with this kind of work will be likely
to miss important indications, and careful supervision should be main-
tained over this part of the investigation.
Special attention has been called to observation of cracks because
of incorrect ideas which apparently prevail with regard to them. It
seems to be the opinion of some engineers that the type of construction
advocated by themselves is immune from cracks. When it is remembered
that plain concrete fails in tension at a unit deformation of about .0001,
it is apparent that cracks must form when the stress in the steel is such
as to correspond with this deformation, or at about 3000 Ib. per sq. in.
At this stage the cracks are often too small for detection with the
unaided eye, but with care in observation almost always very fine cracks
can be seen at stresses ranging between 3000 and 10000 Ib. per sq. in.
Thus to report for a floor loaded to twice the design load that no cracks
were observed is to admit one of three things; that an excess of steel
was used, or that sufficient care in taking observations was lacking, or
that not -all the facts of the case were reported. It should be borne in
mind that the cracks referred to in this discussion are often extremely
minute and usually are not visible to a casual observer. Frequently
cracks have been traced with a lead pencil to make them distinct for
the purpose of sketching, and it seems apparent that some persons visit-
ing the test have mistaken these pencil marks for large cracks. At any
rate reports have been circulated as to the existence of large cracks in
a test where, to the writers' personal knowledge, there were none but
minute cracks. /
16. Accuracy of Deformation Measurements.— (The ratio of multi-
plication in the Berry extensometer is not exactly equal to the ratio of
the length of the arm to the length of the leg, the error being due to
the fact that the plunger of the Ames gauge head does not always travel
in a line perpendicular to the multiplying lever. However, calculations
show that this approximation results in an error in the measurement of
36 ILLINOIS ENGINEERING EXPERIMENT STATION
steel stresses equal to only about one-quarter of one per cent for an ex-
treme case. It may be seen Aaterjthat errors of observation are so large
in proportion that this error can be neglected.)
In forming a basis for a conclusion as to 'the accuracy of the figures
given out as results of tests, use has been made of the check readings
taken by two observers on the same gaij^e lines and of calculated prob-
able error of the mean of five readings. jWhile it is possible to calculate
with some accuracy the probable error of replacing the instrument on
the same gauge line time after time at one sitting, it is very difficult to
determine the error caused by gradually cramping the quarters of the
observer as the loading material piles up. Consequently ^he probable
error calculated from a number of readings taken on the same gauge
line at different sittings will in general be larger than that calculated
from the same number of readings if taken at a single sitting. How-
ever, as experience develops skill in replacing the instrument at a single
sitting, experience will also increase the consistency of results obtained
at widely different times, and the calculated probable error will be a
measure of relative, but not of the actual, accuracy of observation. A
determination of errors based on independent checking by a second ob-
server should be expected to eliminate to a large extent errors of all kinds
and the greatest dependence should be placed on this kind of results. )
In the test of the Powers Building most of the observations taken
were checked by a second observer and some of the results are shown
in the load-stress curves of Fig. 20. The values shown in solid circles
were observed by Mr. F. J. Trelease and those in open circles, by Mr.
Slater. The zero reading for the latter is in each case at a load of 50
Ib. per sq. ft., and in order to make a direct comparison of results, all
these curves must be set over so that their zeros coincide with the stress
values at 50 Ib. per sq. ft. of Mr. Trelease's curves. Having made this
correction the average variation between all the comparable points is
about 670 Ib. per sq. in. (.0000223 unit deformation), which amounts
to a probable error of approximately ±340 Ib. per sq. in. '(±.000011
unit deformation).
Fig. 21 shows the results of a series of measurements taken in the
same way on the upper and lower surfaces of a 4-in. by 4-in. timber beam
loaded with sacks of sand on a 12-ft. span. The points in open circles
represent measurements on the top surface and those in crosses on the
bottom surface. Determined in the same way, these measurements show
an average probable error of approximately ±.000017 unit deformation.
In Fig. 22 is given a curve which shows for each of four building
tests the probable error of the average of five readings. Each plotted
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 37
point is the average of the probable errors calculated for six different
gauge lines at a given load. What this diagram may be expected to
200\
m
O
o o
Stee/ Stress in Pounds per Square Inch
FIG. 20. POWERS BUILDING TEST; LOAD-DEFORMATION CURVES OF Two
OBSERVERS.
?//• Deformation.
/
/
/
/
/
' /
^./
/
fk/
/;
&
f
&
w
Y
V
° .0004
X
X
OOO2
/
/
0
/
/
ZOO 4OO 6OO
L oacf in Pounds.
QOO
FIG. 21, 4 x 4-iNCH TIMBER BEAM TEST; LOAD-DEFORMATION CURVES OF
OBSERVATIONS MADE TO COMPARE INSTRUMENTS,
38
ILLINOIS ENGINEERING EXPERIMENT STATION
/ a 3 +
Orc/er of Tests
FIG. 22. PROBABLE ERROR; DIAGRAM SHOWING VALUES CALCULATED FROM
DATA OF FOUR BUILDING TESTS.
show is the improvement in results with increased experience rather than
the actual value of the probable error. The marked improvement in re-
sults shown here is due in part to increased skill in the observer and in
part to improvement in the instrument itself. Fig. 23 gives a curve show-
ing deformations in steel in a bottom bar of the Barr test panel as shown
.0005
^.0004
^.0002
$ .ooo^
^.0003
TT
Distance in Inches from Edge of Beam.
FIG. 23. BARR PANEL TEST; DIAGRAM SHOWING DEFORMATION ALONG BOTTOM
REINFORCING BAR.
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 39
in the sketch. The points shown as open circles are for a load of 590 Ib.
per sq. ft. and solid circles are for a load of 615 Ib. per sq. ft. This
is the best curve the writers have been able to obtain on any building
test, and it can not be taken as representative, but rather to illustrate
what may be obtained under the best conditions. The regularly vary-
ing differences for a small difference of loads indicate that the stresses
must have been determined correctly within a very small range.
A study of probable error was made in the Turner-Carter test by
the use of a series of 100 observations taken by each of the two observ-
ers on two gauge lines selected as likely to give the most and the least
accurate results. The results of this study are given in Table 1.
TABLE 1.
PROBABLE ERROR OF THE AVERAGE OF ANT GROUP OF FIVE
CONSECUTIVE READINGS.
'
Gauge Line
1
2
Average
Unit deformation
H. F. Moore
W. A. Slater
.00000687
.0000043
.0000106
.000014
.00000873
.0000091
Stress in steel in
Ibs. per sq. in.
H. F. Moore
W. A. Slater
206
130
318
435
262
282
While these measurements were not all on steel, the probable error
has been reduced to terms of stress in steel for convenience of interpre-
tation. It is very interesting to note that the average probable error of
±282 Ib. per sq. in. agrees very well with that for the Turner-Carter
test as shown in the curve of Fig. 22. The same observer took the data
in both .cases, but the data for the value shown in Fig. 22 are taken
directly from the records of the test and represent the conditions on six
typical gauge lines.
From the data in hand it seems safe to conclude that under difficult
conditions stresses in steel can be determined with ±500 Ib. per sq. in.
and that under favorable conditions with careful work it may be de-
termined within ±200 or ±100 Ib. per sq. in. The advantage of further
increase in accuracy of results lies in the determination of the relations
between stresses in different parts of the structure.
17. (Effect of Changes in Temperature on Accuracy of Results. —
Changes of temperature will give measurable changes of length in/re-
inf or cing( steel,/ in concrete ^nd in instruments made of ordinary ma-
terials. In most of the building tests, corrections have been made for
the changes in the instrument due to changes in temperature by means
of observations on standard unstressed gauge lines chosen to represent
40
ILLINOIS ENGINEERING EXPERIMENT STATION
as nearly as possible the conditions of the steejjand the concrete^! the
part of the structure tested. The method of calculating this correction
will be described in a later paragraph. It is there mentioned that in
distributing the corrections found by reference to the standard bar, a
linear variation from the time of one standard observation to the time
of the next standard observation was assumed. Some observations have
been made to determine the correctness of this assumption.
To determine the amount of change in length of an aluminum ex-
tensometer covered and uncovered, a test was made in which the two
instruments were suddenly exposed to a change of temperature of
60° F. A covering which consisted of a double layer of rather heavy
felt protected one of the instruments from a sudden change in tempera-
ture. The other instrument was entirely unprotected. The results of
this test are shown in Fig. 24 with the change of length of the instru-
•S
I
FIG. 24.
O05
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./n/oo
A-/C/^_
A?/
0
a^
~>TT
. —
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men
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fair
y
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V
IO 20 30 40
Length of Exposure in Minutes
DIAGRAM SHOWING CHANGE IN LENGTH OF INSTRUMENTS DUE TO
CHANGE IN TEMPERATURE.
ment plotted as ordinates against time as abscissas. For these measure-
ments a standard bar of invar steel was used. The coefficient of expan-
sion of this being very small, the change of length measured must have
been almost entirely that in the instrument. The curve shows that for
an instrument not insulated from temperature changes, only about five
minutes is required for the instrument to come to the temperature of the
air. For the insulated instrument about 20 minutes was required. This
may be interpreted to mean that if an unprotected instrument is used,
readings on the standard bar should not be more than five minutes apart.
TALBOTM3LATER TE STS OF REINFORCED CONCRETE BUILDINGS 41
With an instrument protected as was this one, intervals of 20 minutes
would not be too much. The amount of change for the case shown here
is "extreme, as the instrument was suddenly exposed to a change in
temperature of about 60° F. This change would seldom be found, and
the length of time required to make the change for a smaller difference
of temperature may be less, but probably would not vary much for other
ranges of temperature. It may be concluded that the method used for
distributing the correction is justifiable, since the instrument was pro-
tected from sudden change of temperature and the observations on stand-
ard bars were usually at intervals not greater than 20 minutes.
The above test shows the effect on the instrument of change in
temperature. Another test was made to determine the effect of change
in temperature on steel embedded in concrete and on steel exposed to the
air. A ^-in. square bar of steel entirely unprotected from temperature
changes and a % in. round bar embedded in 1 in. of concrete were ex-
posed to a sudden change of temperature of about 43° F. Measurements
were taken on a 6-in. gauge length of each bar at very short intervals
of time. The results are shown in Fig. 25. The results of this single
"K
Ol § oo/S
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\^ aoas
Q JDOGO
jjX-*-
o
n
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r
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Q -3/3 "Square Bar:
b - 3/8" Round Bar.
Embedded /n
Concrete.
<? /C7 2O JO 40 SO
7~ime /n Minutes.
FIG. 25. DIAGRAM SHOWING CHANGE IN LENGTH OF STEEL BAR DUE TO
CHANGE IN TEMPERATURE.
test must be used with caution as the total measured change in length
was very small and a small error would show up very plainly. How-
ever, the curve for the embedded bar agrees in its general characteris-
tics with some of the results obtained by Professor Woolson on "Effect
of Heat on Concrete" reported in the 1907 Proceedings of the American
Society for Testing Materials. The test indicates that for this range
of temperature rather rapid changes may be found in the steel, corre-
sponding to stresses of about 9000 Ib. per sq. in. and 3000 Ib. per
sq. in., respectively, for exposed steel and steel protected as in this case.
The range of temperature is extreme and the size of bars smaller than is
42
ILLINOIS ENGINEERING EXPERIMENT STATION
i
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TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 43
often found in floor construction; therefore the results found in tests
would probably be less extreme. However, this indicates the necessity
of attempting to eliminate from the results of the test the effect of
temperature changes, especially if ttye stresses measured are small.
18. Records (jn^ f!/t1-/""l/t-tiinnn -L-Ri™* the beginning of the use of
the Berry extensometer for testing purposes, as much development has
been made in the keeping of notes as in the use of the instrument. Be-
cause of a lack of completeness of notes the advantages of the use of the
standard bar were not fully realized for some time. Only after the
method of keeping notes had been highly systematized was it possible to
make properly the corrections which observations on the standard bars
indicated should be madeJ During the time of placing an increment of
load the recorder will have considerable time in which to be working
up results of the series of observations taken at the previous increment
of load, and as the method of making these calculations is quite intri-
cate, a man is required for this work who has ability to do more than
merely record.
It is very important on account of the great number of observations
taken (about 12000 in. the Turner-Carter test) that all records be ar-
ranged systematically. (The following points are mentioned as being im-
portant in this connection: (1) In the field test individual readings
should be recorded and their average used as a single observation unless
it appears that the proposed abridgment of this procedure (see page 35)
may be used safely. (2) Recording readings in the order of their size
will assist the recorder in obtaining the correct readings and in rapidly
obtaining the average. (3) The exact sequence of observations should
be maintained in the record as the calculations of corrections depends
largely on this.]
Fig. 26 is a sheet for the record of original readings and the results
calculated from them.
Calculating corrections and applying them to the results make the
reduction of data rather intricate. This work has been reduced to a
definite system indicated by the form shown in Table 2. In this system
the first observation on the standard bar is used as the reference obser-
vation (see definition, p. 10). The corrections are distributed among
the gauge lines as though the change in the length were a linear function
of the time from one standard bar observation to the next one. These
assumptions do not entirely accord with the facts but have been found
satisfactory as a working basis. Any other standard bar observation
than the first one would do as well for a reference observation except
for matters of convenience. It is important that calculations should be
44
ILLINOIS ENGINEERING EXPERIMENT STATION
kept up as the work progresses, because it can be done with less labor
then than at any other time and because it will be of value to know as
the test progresses what results are being secured.
19. Test Data.— Table 3 gives general data of the tests referred to
in this discussion. The figures giving area of test show the total area
^ TE573 OF BUILDING, Observer Sheet
^ Gauge Line
1
2
3
+
3
6
7
8
9
10
II
/2
/3
l±
/S
16
tSSBEta
Readings
Uncor^ A«
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Readings
Upcor-r Diff.
CorrrctMn
Corr. Diff
Readings
/ncarr Diff
Correction
Readings
Urtcorrr Av
'Jncorr Di/f
Correcfton
Corn 0,ff.
FIG. 26. FORM FOR RECORDS OF ORIGINAL AND CALCULATED NOTES.
of the floor covered, and do not count any area twice, even though
loaded twice as was done in the Wenalden Building test. They do in-
clude the area of separate single panel tests which were made in the
Wenalden and Franks tests.
The maximum test load in Ib. per sq. ft. is given in the column under
that caption. In some cases this was over only a part of the test
area. The part upon which the maximum load was applied bore the
following ratios to the total test area: Wenalden 80 per cent, Powers
50 per cent, Franks 40 per cent, Larkin 40 per cent, all others 100 per
cent.
The column giving the amount of load handled includes the rehand-
ling due to change of position of loads. The proportionate parts of the
loads rehandled in this way were : Wenalden 40 per cent, Powers .50 per
cent, Franks 80 per cent, Larkin 73 per cent. In all the other tests no
load was rehandled.
The column giving the number of observers includes only those read-
ing deformations. In the Wenalden', Powers and Larkin tests another
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 45
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46 ILLINOIS ENGINEERING EXPERIMENT STATION
observer took deflection readings. In the Powers test and the Barr test,
almost all the deformation readings were taken by each of two observers,
giving a larger number of gauge lines per observer than appears in the
table.
20. Cost of the Tests. — An effort was made to learn the cost of
making the building tests in which the stresses in the structure were
observed, but difficulty was found in separating the items connected with
the tests from those incidental to the building construction. The ex-
pense of such a test depends upon the size of the test area as well as
upon the number of gauge lines used. The loading of a single panel
gives little information, and this information may be misleading in re-
gard to the maximum stresses which will be developed in such a panel
when the adjacent panels also are loaded. A test of a floor system
should involve the loading of as many as five panels ; a greater number
would be more representative of full loading. The application and re-
moval of 600 000 Ib. of load involves considerable expense, especially if
this material has to be brought to the building and later taken away.
This item may be from $300 to $700 depending upon the distance the
loading material is conveyed. The cost of building the platforms and
drilling and cutting the holes for the gauge points may be counted to
be about $100. A thorough test will take a week's time of the observers
and two weeks' time of the one in charge of the test even though the test
itself may not run over five days. A well organized party of three ob-
servers and three recorders was able to take the observations on 268
gauge lines and record and work up the data as the test progressed.
This involved placing the load in four increments and removing it in two
increments and the test itself covered a period of six days. To make
an adequate report of such a test is itself quite a task, and the expense
of this item is considerable. A much smaller amount of work will give
special information on a few matters. The data at hand indicate that
a thorough test may cost as much as $1500 for all items and in one
test mentioned the total cost was more than $2000.
III. THE WENALDEN BUILDING TEST.
21. The Building. — The Wenalden Building, Fig. 27, is a ten-story
reinforced concrete structure at 18th and Lumber streets, Chicago. It
was built by the Ferro-Concrete Construction Company, Cincinnati,
Ohio, in accordance with the plans and specifications of Howard Chap-
man, architect. It is now occupied by Carson, Pirie, Scott and Com-
pany, dry goods merchants, as a warehouse. The building is of the
beam and girder type. The floor panels are 15 ft. by 20 ft. The gird-
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS
47
E£ EE SI EE HE EE EE EE HI HHTir
E- E— £Z 25 22 EsEI!E EE IE! BE ir
[SI EE! ES E2 EE EE £!E EE
IBS pyg Fin HPI no nn nn mi gn jjn gr rr
^ im gm |m gn lEEEEBlT
pm mi HH im fin im nra mi nn mi nn IT
it r
*«•*»>••-»
^IG. 27. THE WENALDEN BUILDING.
ers are placed between columns in the short direction. Floor beams ex-
tend the long way of the panel, there being two intermediate beams
built into and supported by the girders and a column beam built into
and supported by the columns. The floor, 3% in. thick (including the
top finish), was built continuously with the beams and girders.
The reinforcement is of the form used by the Ferro-Concrete Con-
struction Company. The main reinforcing bars (twisted bars) are car-
ried along the bottom of the beam from the end of a panel to a point
beyond the middle of the panel, where they are bent up to the top of the
beam and carried horizontally to a corresponding point on the other side
of the support, then bent down and continued along the bottom of the
beam to the end of the next panel, these reinforcing bars thus having a
length of two panels. In the intermediate beams at the bottom and
middle there are four rods % in. square and in the side beams one rod
% in. square and three rods % in. square. In the girders there are four
rods 7/s in- square, the disposition of which is similar to that in the
beams. • By this plan there is twice as much of the main reinforce-
ment in the bottom of the beam or girder at the middle of the span as
there is at the top over the supports, except that four % in. square rods
placed in the floor slab are also available for end reinforcement of the
intermediate beams. The beams are G1^ in. and the girders 7% in. wide.
The general position of the reinforcement is shown in Fig. 28. The posi-
tion of the vertical stirrups is not shown.
The contractors report that the concrete was composed of one part
Portland cement, 2 parts torpedo sand, and 4 parts crushed limestone.
48
ILLINOIS ENGINEERING EXPERIMENT STATION
Although the building was not fully completed when the test was made,
the floor tested had been built more than 12 months at the time of
the test. The work of cutting the floor and beams for inserting points of
measurement proved to be very difficult and showed the concrete to be
very hard and of excellent quality.
22. Method of Testing. — The test was made on the first floor of the
building. This was the only one which could be reached with the loading
material. The space chosen was one freest from openings and other
£/e\/afion of /n^ermed/ofe Beam
r-
*-"*&
•^l '
^
^
\
-
*J
\
siglaS •<-:-:°Jim-.--j, &
Jbl>
!?
L
E/eval/on of Co/umn
View of Gf refer
FIG. 28. GENERAL POSITION OF REINFORCEMENT IN WENALDEN BUILDING.
irregularities of construction. At various points at the top and bottom
of beams, holes were cut into the concrete until the reinforcement was
bared and gauge holes were drilled in the bars 6 in. or 10 in. apart for
use in inserting the instruments with which the measurements of elonga-
tion were made. Where stresses in the concrete were to be measured,
holes were cut in the concrete and short pieces of steel were set in plaster
of par is. Gauge holes were drilled in these steel inserts in such a way as
to give gauge lines 6 in. or 10 in. long. The position of these points is
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 49
shown in Fig. 29 and 30. For the work of measuring deflections, steel
bajls were affixed to the under side of beams and girders at various places
and other balls were placed about 7 in. lower on supports which had been
FIG. 29. PLAN SHOWING LOCATION OF GAUGE LINES ON UPPER SIDE OF FLOOR.
built up independently of the observing platforms. A number of these
points of deflection were used to determine the inflection points of the
beams.
For any observation several instrument readings, usually five, were
taken on each gauge line and these were averaged. Measurements were
FIG. 30. PLAN SHOWING LOCATION OF GAUGE LINES ON UNDER SIDE OF FLOOR.
made on the standard bar before and after each series of observations to
permit corrections for instrumental changes.
23. Method of Loading. — The floor was designed for a live load of
200 Ib. per sq. ft. and the test load was made 400 Ib. per sq. ft. over
the panels loaded.
50
ILLINOIS ENGINEERING EXPERIMENT STATION
The loading was done by piling brick and bags of cement in piers
separated by aisles in such a way as to give access for points of measure-
ments and to prevent arching effects influencing the tests. The load was
put on in increments of about 80 Ib. per sq. ft. of the total panel area,
and a set of observations was taken at each increment of load. Brick
was used in the first part of the loading and cement in the later work.
The average weight of the brick was determined by weighing a con-
siderable number, and such care was given to determine the number of
brick and sacks of cement that it is believed the weights are accurately
known.
The following is the general plan of the test. A single panel (B,
Fig. 29) was first loaded. This load was then removed. The load was
then applied on three panels in tandem (ABC, Fig. 30). These three
panels are termed area M in the load-deformation diagrams. Then,
leaving this load on, a load was applied along three adjacent panels
(DEF) covering two-thirds of the width and making in all the equivalent
of five loaded panels. This portion of these three panels is termed area
FIG. 31. VIEW OF TEST LOAD IN WENALDEN BUILDING.
N in the load-deformation diagrams. The load was then taken off by in-
crements. The total weight of the load used was 600 000 Ib. Fig. 31
is a view of the test load.
A further test was made by loading a single panel at the end of the
building, a so-called wall panel.
The loading was begun Monday, July 10, 1911, the loading of five
panels was finished at noon on the following Friday, and unloading was
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 51
completed on Monday, July 17. The schedule of loading is given in
Table 4. The wall panel was loaded on Friday and Saturday, July 14
and 15. The unloading of this panel was finished August 1.
24. The Deformations and Stresses. — The results of observations
for various gauge lines are plotted in Fig. 32, 33 and 34. From a
400
320
/eo
80
O
M 250, A/250
o
0
0
0
0
o,/y o
<
3
f
&L
Q
Deformation per Unit of Lenyfh
FIG. 32. LOAD-DEFORMATION DIAGRAMS FOR UNDER SIDE OF GIRDER AT MIDDLE.
8°o
M250,M250
M4OO.W60
0
0
0
0
o
o,/y o
Deformation per (Jn/'f of Length
FIG. 33. LOAD-DEFORMATION DIAGRAMS AT END OF GIRDER.
52
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 4.
SCHEDULE OF LOADING OPERATIONS.
Day
Date
Observations
Loading
Observations
Load
Ib. per
sq. ft.
Hours
Ib. per
sq. ft.
Hours
Load
Ib. per
sq. ft.
Hours
Sunday ....
7-9-11
0
5.45 P. M.
Monday ....
7-10-11
0
7.00
to-
8.00 A. M.
SOB
160 B
8.00
to
8.50 A. M.
SOB
160 B
8.50
to
A. If.
10.25
to
A. M.
to
10.25 A. M.
2405
A. M.
to
12.10 P. M.
240 B
12.10
to
P. M.
320 B
to
3.00 p. M.
320 B
3.00
to
P. M.
400 B
to
5.10 P. M.
400 B
5.10
to
P. M.
Tuesday
7-11-11
400
6.00
to
8.00 A. M.
240 B
8.00 A. M.
to
240 B
11.00 A. M.
to
OB
12.30
to
3.30 P. M.
OB
3.30
to
4.00 P. M.
Wednesday .
7-12-11
0
6.45
to
A. M.
80 A, B
andC.
8.00
to
10.00 A. M.
80 A, B
andC.
10.00
to
10.45 A. M.
160 A, B
andC.
10.45 A. M.
to
1.00 P. M.
160 A, B
andC.
1.00
to
P. M.
240 A, B
and C.
1.30
to
P. M.
240 A, B
andC.
to
2.45 P. M.
320 A, B
andC.
3.20
to
5.00 P. M.
320 A, B
andC.
5.00
to
6.30 P. M.
Thursday. . .
7-13-11
320 A, B
andC.
6.30
to
7.45 A. M.
380 A, B
andC.
8.00
to
9.45 A. M.
380 A, B
andC.
9.45
to
10.30 A. M.
400 A, B
andC.
10.30
to
11.15 A. M.
400 A, B
and C.
11.15 A. M.
to
12.00 M.
400 M
160 N
11.30 A. M.
to
400 M
160 AT
3.15
to
3.45 P. M.
400 M
3.45
to
4.30 P. M.
Friday
7-14-11
320 N
8.00
to
9.30 A. M.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 53
TABLE 4.
SCHEDULE OF LOADING OPERATIONS — Continued.
Day
Date
Observations
Loading
Observations
Load
Ib.per
sq. ft.
Hours
Ib. per
sq.ft.
Hours
Load
Ib.per
sq.ft.
Hours
Friday
7-14-11
400 M
400 N
10.30
to
11.30A.M.
400 M
400 N
11.30 A. M.
to
12 M.
80 G
2.00
to
3.00 P. M.
80G
3.40
to
P. M.
x
160 G
to
5.00 P. M.
160 G
5.00
to
5.30 P. M.
Saturday . .
7-15-11
250 M
250 N
8.00
to
A. M.
250 M
250 N
11.40 A. M.
to
1.30 P. M.
p
240 G
8.15
to
9.00 A. M.
240 G
9.00
to
A. M.
320 G
8.40
to
A. M.
320 G
9.50
to
10.00 A. M.
380 G
to
10.45 A. M.
380 G
10.45
to
11.15 A. M.
400 G
to
11.40A.M.
400 G
A. M.
to
12.00 M.
study of these it is readily seen that there are irregularities in the meas-
urements and that the general trend of some of the lines must be taken
rather than absolute values.
In translating from unit-deformation to unit-stress the modulus of
elasticity of steel has been taken at 30 000 000 Ib. per sq. in. and that
of the concrete has been assumed to be 3 000 000 Ib. per sq. in. For sim-
plicity the straight-line stress-deformation relation for concrete has been
assumed, though it is evident that this relation does not hold for the
higher stresses and that calculated stresses based upon this assumption
are in excess of the actual stress. The interpreted stress for a number of
gauge lines is recorded in Table 5.
Table 6 gives calculated stresses and calculated bending moment co-
efficients. The first line of each set gives the calculated stresses in the
reinforcement and in the concrete based upon the value of the bending
moment quite commonly assumed in design calculations, 1/12 Wl, where
W is the total distributed load on the beam and I is the span length.
These are printed in italics. In these cases the span length was taken as
54
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 5.
STRESS INDICATIONS IN WENALDEN BUILDING TEST.
Stresses are given in pounds per square inch.
Gauge
Line.
Single Panel.
Three Panels.
Five Panels.
Reinforcement at end of girder. .
208
8000
7 000
209
202
7000
12000
13000
9 000
Reinforcement at middle of girder
115
10 000
11 000
Concrete at end of girder
120
121
119
210
8000
6000
1 100
14000
16000
1600
9 000
17000
17 000
2200
10 000
Reinforcement at middle of intermediate beam. .
Concrete at end of intermediate beam .
211
212
213
214
216
109
111
113
114
110
2000
9000
9000
11 000
13000
' 8 666
' e'666
9000
14000
16000
13000
13000
14000
7000
16000
11000
14000
14000
16000
13000
14000
16000
11000
16000
11000
1 300
Concrete at middle of intermediate beam
112
217
1500
Low
1700
Low
2000
Low
222
229
TABLE 6.
MAXIMUM STRESSES AND MOMENT COEFFICIENTS IN WENALDEN
BUILDING TEST.
Stresses are given in pounds per square inch.
Member
Reinforcement
Concrete
Stress
Coefficient
Stress
Coefficient
Girder End
44000
13000
19000
17000
36000
16000
22000
16000
69000
15000
26000
11000
1/12
0.024
1/12
0.075
1/12
0.037
1/12
0.06
1/12
0.018
1/12
0.035
1 700
2200
420
1 900
2000
440
1/12
0.106
1/12
I/ IS
0.088
1/12
End.....
Middle.
Middle
Intermediate Beam, End
End..
Middle
" Middle
Column Beam, End
End ..
Middle...
Middle .
3 in. longer than the clear span. Measurements had been made upon the
position of the bars and the depth of the reinforcement, which were not
always exactly according to the plans, and the calculations have been
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 55
based upon the dimensions found. In the second line of each group the
maximum stress obtained by the measurements is given in the column of
stresses, and the bending moment coefficient (the coefficient of Wl)
corresponding to these stresses is recorded in the adjacent column. In
these calculations the common assumptions of design calculations (in-
cluding the neglect of the tensile strength of the concrete) are followed
except that the width of T-beam is taken as equal to the distance from
center to center of beams. In calculating the bending moment coefficient
from the measured stress, the position of the neutral axis and the value of
the moment arm are assumed to be the same as given by the ordinary
assumptions. Although the stress in the reinforcement is measured at
the surface of a bar of the outer layer, this stress is considered as -being
the same as that acting at the center of gravity of the group of bars, for
the actual variation in the group is unknown and this method will give
a bending moment coefficient larger than that found by considering that
the stress in the bars of the other layer is smaller.
In the calculations for compressive stresses, the compression rein-
forcement was considered to take its proportion of the compressive stress
though there may be a question whether the embedment in such designs
is sufficient to insure this condition.
It will be seen that in the tests with three and five panels loaded the
highest stress observed in the reinforcement in the middle of the inter-
mediate beams was 16000 Ib. per sq. in. and the highest stress observed
at the ends of the beams was 16000 Ib. per sq. in. The stresses observed
in other bars having similar positions were lower, and probably the high-
est stress is not representative of the general stresses. However, it may
be best to compare on the basis of the highest stresses. The bending mo-
ment given in the table as derived from the measured stresses is .06 Wl at
the middle of the beam and .037 Wl at the end of the beam. Measurement
of the compression of the concrete in this test was less satisfactory than
the measurement of the reinforcement deformations, and considerable
variation was found at the different points of observation. Not enough
gauge lines gave satisfactory measurements to warrant making quantita-
tive conclusions, but the indications of the action of the concrete may be
useful. The value of the resisting moment which corresponds to the
concrete stresses, on the assumptions made, is .088 Wl for the end of the
beam. For the middle of the beam the stresses were small and the in-
dications so irregular that no value of resisting moment can be given.
In the beams at the sides of the panel (column beams) the stresses
were in general somewhat lower, but with a full loading a stress of 15000
Ib. per sq. in. at the middle of the beam was observed and 11000 Ib. per
sq. in. at the end.
56
ILLINOIS ENGINEERING EXPERIMENT STATION
Deformation per Un/'f of Length- '
FIG. 34. LOAD-DEFORMATION DIAGRAMS FOR UPPER SIDE OF BEAMS AT END.
Fewer measurements were made on the reinforcement of the girder.
A stress of 17 000 Ib. per sq. in. was observed at the middle of the girder
and 13 000 Ib. per sq. in. at the end. On the same assumptions these
values correspond to bending moments of .075 Wl and .024 Wl, re-
spectively. The stress in the concrete at the end of the girder was also
very high, but the corresponding bending moment (.106 Wl) is not far
from the calculated moment for a restrained beam with concentrated
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 57
load. It should be noted in this connection that the reinforcement is
bent down rapidly into the beam from the face of the column, see Fig. 28.
• Calculating with the usual assumptions of beam formulas, the total
compressive stress in the concrete at the end of the beam is greater than
the total tensile stress in the reinforcement. Two elements probably
enter into the results, the tensile strength of concrete, which may be con-
siderable as distributed over the width of the floor, and an arching action
of the structure. However, it should be noted that the value of the
bending moment coefficient derived from the reinforcement stresses at
the middle of the beams and girder is not much less than values com-
monly used and also that the calculated resisting moment developed at
the end of the beam based on the concrete stresses is not far from the
amount usually assumed.
Attention should be called to the fact that the compressive stress in
the concrete, both that calculated from an assumed bending moment co-
efficient and that calculated from the measured deformation, is much
higher than that to be found by the use of the parabolic stress deforma-
tion relation and the actual stress will be less than that given in the
table.
Measurements were made on the concrete at the top of the floor slabs
in a direction parallel with the beams to find the distribution of compres-
sive stresses between beams. These measurements were not fully satis-
factory, but within the limits of accuracy of the measurements, no dif-
ference in the amount of shortening over the beam and at points between
beams could be determined, and the whole floor evidently acted as a part
of the compression member of the T-beam so formed.
25. Test Cracks. — The surface of the beams and girders had re-
ceived a white coat, which permitted very fine cracks to be detected, much
finer than may be observed on uncoated concrete. In the test, as the load
was applied, fine tension cracks in the concrete through the middle of the
length ffef the beam were observable at stresses in the reinforcement corre-
sponding to the stresses at which load cracks are detected in the tests of
beams in laboratory work. To an experienced observer development of
the cracks was confirmation of the measurements of the low stresses de-
veloped in the reinforcement. Upon removal of load most of these
cracks closed until they were not visible to the eye.
As the calculated reaction on the end of a girder was upward of
40000 lb., it will be seen that the vertical shearing stresses were very
high. Diagonal tension cracks developed in these girders just outside
the junction with the intermediate beams, making an angle of nearly
45° with the horizontal. These cracks did not entirely close on the
58
ILLINOIS ENGINEERING EXPERIMENT STATION
removal of the load. No measurements were taken to determine the
diagonal deformations. It seems probable that the restraint at the end
of the girder and the tensile strength of the concrete acted to prevent the
fuller development of these cracks.
No diagonal cracks were observed in the beams.
26. Deflections. — Fig. 35 gives the location of the points at which
the deflections were measured. Fig. 36 shows the deflections with a load
36
31
32
35
Panel A 30
B
C
39/0 If 1? 13 14 15 16
55i_
29
38
23,
tt
F
FIG. 35. LOCATION OF DEFLECTION POINTS IN WENALDEN BUILDING.
\fOOlAferS?. Ft. on Fbnel B on/y
WENALDEN TEST-,- DEFLECT ION OF/NTERMEDI/ITE BEAM-
FIG. 36. DIAGRAMS SHOWING DEFLECTION OF INTERMEDIATE BEAM.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 59
of 400 lb. per sq. ft. for points along an intermediate beam, (1) with
one panel loaded (panel B, Fig. 29) and (2) with three panels loaded
(aTea M, Fig. 30), and (3) with five panels loaded (areas M and N,
Fig. 30). As may be expected, the deflection in the middle panel is
greater for one panel loaded than when three panels are loaded.
27. Wall Panel. — A single wall panel was loaded and observations
were taken on the gauge lines which are shown in Fig. 37. No meas-
i f
307
v:
304-
I I
J05J l_
Wall F>anel of
302
FIG 37. WALL PANEL TEST; PLAN SHOWING LOCATION OF GAUGE LINES.
urements of the compression in the concrete were made. On the
reinforcement only a few gauge lines were used. The observed values
are plotted in Fig. 38 and Fig. 39. Because of the small number of
gauge lines and because of some of the conditions of the test which were
not entirely favorable, the results may not be trustworthy quantitatively
as compared with the other tests, but the indications are of interest.
There is considerable restraint shown at the ends of the beams, that at
the pilaster being about the same as that at the column end and that at
the wall being greater than that at the girder end. All of these are
nearly as large as the values found in the interior panels. The stress in
the middle of the beams is considerably greater than that found in the
middle of the beams in an interior panel. The deflections are also
greater than for interior panels and the deflection curves are of a differ-
ent character. It is recognized that there are some apparent inconsisten-
60
ILLINOIS ENGINEERING EXPERIMENT STATION
400
3SO
240
/60
60
0
320
240
/6O
<30
3O6
3C4-
* *
^ftlC^^
i 1 1 1
§ §
Deformation per Uff't of Length.
FIG. 38. WALL PANEL TEST; LOAD-DEFORMATION DIAGRAM.
cies in these statements, and the action of wall panels is a matter which
should receive full investigation in the future.
28. Examination of Floor after Test.— An. examination of the floor
was made May 6, 1912, to ascertain whether the cutting of the concrete
for purposes of observation had caused any permanent disfigurement.
On the under surface of slabs and beams where the chances would be
greatest for material used for filling the test holes to fall out of place,
the concrete was intact. It seems probable that if the surface had been
painted over after the repairs were made the patched portions could not
have been detected without a minute examination. Although the base-
ment was well lighted in the vicinity of the main test the only indica-
tions of the location of cracks were pencil marks where the cracks had
been traced to secure ease in sketching their position. These pencil
marks had been painted over but showed through the thin coat of white.
It is probable that a more minute examination would have detected
cracks, but the fact that after removal of the test load not even the diag-
onal tension cracks were plainly visible bears out the conclusions that the
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 61
FIG. 39. WALL PANEL TEST; DIAGRAM SHOWING DEFLECTION OF
^ INTERMEDIATE BEAM.
steel stresses caused by the test load were light. The basement under that
part of the floor where the wall panel test was made was not so well
lighted, hence the examination here was not so significant. On the upper
surface of the floor tested, there were cracks which were distinct, but not
more so than many which were observed before the test had been made.
The area on which the wall panel test was made was inaccessible, being
completely covered with merchandise.
IV. THE TURNER-CARTER BUILDING TEST.
29. The Building.— The Turner-Carter building (see Fig. 40) is an
eight-story reinforced concrete building 60 x 200 ft., located at Wil-
loughby Avenue and Walworth Street, Brooklyn, New York. It was
constructed by the Turner Construction Company for the Turner-Carter
Company (manufacturers of shoes) in accordance with the plans and
specifications of Frank Helmle, architect.
The building is of the beam and girder type. The panels are 17 ft.
4 in. by 19 ft. 6 in. The floor was built continuously with the beams
and girders. The girders are 10 in. wide and 24 in. deep including the
finished floor. Each panel has two intermediate beams 7 in. wide with a
total depth of 18 in. The column beams are the same size as the inter-
62
ILLINOIS ENGINEERING EXPERIMENT STATION
FIG. 40. THE TURNER-CARTER BUILDING.
i
mediate beams. The columns below the test floor are octagonal and are
30 in. from face to face. The position of reinforcement of the beams
and girders is shown in Fig. 41. The beams and girders were designed
as simple beams, but reinforcement is supplied for continuity, and the
construction is such as to give continuity in the beams and girders. The
structure was designed for a live load of 150 Ib. per sq. ft.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS
63
The aggregates were an excellent grade of sand and gravel obtained
from the sand banks in Hempstead Harbor on the north shore of Long
Island. The gravel ranged in size from ^ to % in. For the beam and
girder reinforcement bars having an elastic limit of about 50000 Ib. per
sq. in. were used. The beams have one 1-in. square bar and two %-in.
square bars at the middle and one 1-in. square bar over the support car-
ried about 15 in. beyond the center line of the girder. Ten ^-in. round
bars placed in the slab are also available for tension reinforcement in the
end of the intermediate beams, as is also one T-bar used for supporting
the slab reinforcement during construction. The girders have two 1-in.
square and three %-in. square bars at the middle, placed in two layers,
and two 1-in. square bars over the support carried nearly to the farther
face of the column.
The floor tested was constructed July 25 so that at the time of the
test, September 10 to 20, 1911, the work was about fifty days old.
30. Method of Testing.— The feature of the test, as of the Wen-
alden test, was the measurement of the deformations in the reinforce-
1^7 / ion o f Co/vmn Beam
E/evaf/or? of Intermediate Beam J?ecf/o/?LL
View o-F &//-c/er Sect /'on
FIG. 41. SKETCH SHOWING REINFORCEMENT OF BEAMS AND
GIRDERS AT SUPPORTS.
64
ILLINOIS ENGINEERING EXPERIMENT STATION
ment and in the concrete at various points in the girders, beams and
slabs. The most important determinations undertaken in the test were
the measurement of the compressive deformations in the concrete at and
5/2« ~%Z/I.
I I
?30D/«aA.236E— 2*6 240ft
§ I M
\\*\ \ !l '
I
i,
?SV- b-f-SA"— (J-sf-J
Ik
51
1— -11-
____ l ____ l_
'
H
u
_M^
nr
j L
u u u u u u u
FIG. 42. PLAN SHOWING LOCATION OP GAUGE LINES ON UNDER
SIDE OF FLOOR.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 65
near the supports of the beams, the compressive deformations of the con-
crete at the middle of the beam, and the distribution of these compres-
sive stresses across the top of the slab between beams to determine the
extent of T-beam action. The deformation in the reinforcement was
i
FIG. 43.
U HJ IF U U U U
PLAN SHOWING LOCATION OF GAUGE^LINES ON UPPER SIDE OF FLOOR.
66
ILLINOIS ENGINEERING EXPERIMENT STATION
measured at the centers of the spans and at the ends and also on the in-
clined portions of the bent-up bars. Various other measurements which
it was thought would throw light upon the action of the structure were
taken.
31. Preparation for the Test. — A week was used in preparing for
the test. Platforms supported by scaffolding for the use of observers
were built on the second floor. Independent of this was a framework,
which was supported by the second floor, for use in making measurements
of deflection. The boxes for holding the sand were constructed, this
being facilitated by a power saw located on the second floor. Consider-
able time was consumed in drilling holes in the concrete to bare the rein-
FIG. 44. LOCATION OF SAND BOXES AND FLOOR CRACKS.
forcement. In some cases this was found to be at a considerable depth
from the surface. In all nearly two hundred holes were cut in the con-
crete. Holes were drilled in the reinforcing bars, as heretofore de-
scribed, for use as gauge points. The gauge length was made 8 in. The
position of the gauge lines for the reinforcing bars is shown on Mg. 42
and 43 by the even numbers. For use in the measurement of deforma-
tions of the concrete, holes about J/£ in. in diameter and 1 in. deep were
drilled in the concrete and steel plugs were inserted and set in plaster of
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS
67
paris. Gauge holes for receiving the points of the extensometers were
drilled in these plugs with a No. 54 drill. The position of the gauge
lines is shown in Fig. 42 and 43 by the odd numbers. The gauge
length was 8 in.
The deflections were measured between a steel ball set in the under
surface of the beam and a ball attached to the framework previously de-
scribed. The measurements were made as described in Art. 13.
32. Method of Loading. — The test area was on the third floor. The
loading material was damp sand which was placed in bottomless boxes.
These boxes were of various sizes and were placed in such a way as to
give a well distributed load. The general size of the box was 4 ft. 6 in.
wide, 8 ft. long and 4 ft. 6 in. deep. Fig. 44 shows the position of the
boxes and the test area. Fig. 45 is a view with the sand boxes ready for
FIG. 45. VIEW OP SAND BOXES.
loading. The boxes were made small enough to permit a good distribu-
tion of load even though part of the weight of the sand might be carried
by arching and friction down the sides. The test area covered three full
panels and parts of four others, in all equivalent to five panels. A load-
ing space was chosen which it was thought would give the fullest stresses
over the girders and beams on which the principal measurements were
made. In removing the load the outer panels were unloaded first in an
68
ILLINOIS ENGINEERING EXPERIMENT STATION
attempt to determine the relation between single panel loading and group
loading. The load applied was the equivalent of 300 Ib. per sq. ft.,
double the design live load.
Before beginning the test, a calibration of the heaviness of the sand
was made by weighing the sand which had been shoveled into a box of
16 cu. ft. capacity placed on the scales. It was found that there was a
difference of about 10 per cent in the weight of sand which had been
FIG. 46. VIEW OF TEST LOAD IN TURNER-CARTER BUILDING.
thrown in loosely and sand which was packed somewhat. During un-
loading, the entire contents of three of the sand boxes (about 500
cu. ft.) were weighed. This gave an average of 88.6 Ib. per cu. ft., agree-
ing closely with the weights of the unpacked sand previously weighed,
and this value was used in the calculation of loads.
On a part of the area where the boxes were not carried to a sufficient
height and where the space was not covered adequately by them, cement
in sacks was used as loading material.
The supply of sand for the loading had previously been delivered on
the same floor, the piles being kept at least one panel away from the
location of the test area, and this was distributed over sufficient floor
space that the stresses in the beams of the test area could not be affected.
In applying the load the sand was wheeled in barrows and dumped into
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 69
the boxes. As the sand was placed, the sides of the boxes were rapped
to break the adhesion of the sand. Some leveling of the sand in the boxes
was done, but there was little compacting by tramping or otherwise.
33. Making the Test. — A very important element of a test of this
kind is the initial observation for fixing the zero point of the test read-
ings. Three sets of observations for a number of gauge lines were made
Alone O
FIG. 47. LOAD-DEFORMATION DIAGRAMS FOR UNDER SIDE OF BEAMS AT END.
before the beginning of the test, on the afternoon of September 10 and
the forenoon of September 11. Where discrepancies were found new ob-
servations were made. Even with this number of observations there are
uncertainties in some initial readings. Experience confirms the view
that before any load is placed the initial readings which have been taken
should be worked up and observations repeated until all discrepancies and
uncertainties have been removed.
Headings were taken immediately after the completion of each incre-
ment of load and again immediately before the beginning of placing an-
other increment of load. This usually corresponded with evening read-
ings and morning readings. A series of readings was also taken with the
full test load on. These extended over a period of 48 hours. A similar
method was used in the process of removing the load.
70
ILLINOIS ENGINEERING EXPERIMENT STATION
None
0
\DEFHI ^0
^ All
/00
A/one ^
\DErHI ^300
^300
§/(7^
A^/?e ^ 0
E ^300
*
A/I ^30O
All
AH ^
^
\
1
\
\
\
^
j
/
><
X
\
^
V
/^
\^
\
S»
20
V
24.
}/
5>S
2t
A
T|
\
\
\
/
\
\
\
I
/
/
V
\
v
\
\
\
\
2±
\^
20
^
2+
A
2.
*A
\
\
/
^
^
\
^
/
\
\
\
\
\
\
\
2
37
M
-P
^N
V
\
\
\
/
]
/
/
\
1
>
^
f^
/
/
>
\
\
^s
\
gi
7^
^
9.«9
\
PP
\
\
N
\
V
?8§§§§^§§s§§i§i
Ue formation perL/ni+ of* Leng+h.'
FIG. 48. LOAD-DEFORMATION DIAGRAMS FOR UNDER SIDE OF BEAMS AT END.
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 71
Atone . O\
Dffll 300
x;// fyoo
Nl
Hone 0
zz
za
\
'-<
ZZi
2
233
\
£3'
<\4 -s. 0}
g
. . . . . .
De formation per Unii- of Length.
FIG. 4Q. LOAD-DEFORMATION DIAGRAMS FOR UNDER SIDE OF BEAMS AT END.
72 ILLINOIS ENGINEERING EXPERIMENT STATION
None „ O
* " \
^
MffHt
r^/3
A/
None
/00
/fc/7<? ^ 0
^ ^5^6?
J^2
None
None ^ 0,
\
J<?^
^ ""^ ^Vj N"j
O C> <^ Qs
o q o ^
308
32
-c
'3*2-
\
zee
(\j r^
^ Cb
'?.?•
S'8 8
£// orUnfM '
FIG. 50. LOAD-DEFORMATION DIAGRAMS FOR UPPER SIDE OF BEAMS AT END.
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 73
2*Q
^?6
234
\
"\
36
J\J ^ <0 ^ <M ^ O
^ ^ ^ ^i ^ O O
b^^c^cioooS
:><^<^Q>C>OQ>OO
De-formation per Unit of Leng+h
i
\
& §
FIG. 51. LOAD-DEFORMATION DIAGRAMS FOR UNDER SIDE OF BEAMS AT MIDDLE.
Table 7 shows the loading schedule. The load was applied in incre-
ments of 100 Ib. per sq. ft. based upon the whole test area. The applica-
tion of the load consumed three days. The full load was left on 48
hours. The unloading schedule is shown also in Table 7. In the unload-
ing, the load on panels B and C was first removed, then the load on
panel D, F and I, followed by the removal of the load on panel H.
Fig. 46 is a view at a load of 300 Ib. per sq. ft. over the test area. The
total load was over 500000 Ib.
34. Deformations and Stresses. — The results of observations on vari-
ous gauge lines for the beams and girders are plotted in Fig. 47 to 54.
Fig. 55 gives the deformations in the concrete on the under side of the
\
74 ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 7.
SCHEDULE OF LOADING OPERATIONS IN TURNER-CARTER
BUILDING TEST.
Day
Date
Observations
Loading
Observations
Load
Ib. per
sq. ft.
Hours
Ib. per
sq. ft.
Hours
Load
Ib. per
sq. ft.
Hours
LOADING SCHEDULE.
Sunday. . . .
9-10-11
0
12 M.
to
2 P. M.
Monday. . . .
9-11-11
0
7.20 A. M.
to
12 M.
100
1.30
to
6.00 P. M.
100
6.10
to
8.00 P. M.
Tuesday
9-12-11
100
6.30 A. M.
to
8.15 A. M.
200
10.30 A. M.
to
3.00 P. M.
200
3.10
to
5.30 P. M.
Wednesday .
Thursday. . .
9-13-11
9-14-11
200
300
6.20
to
8.20 A. M.
8.00
to
8.30 A. M.
300
9.00 A. M.
to
3.30 P. M.
300 3.50
to
5.50 P. M
300 10.30
to
11.30 P. M.
300 3.00
to
| 3.30 P. M.
UNLOADING SCHEDULE.
Friday
9-15-11
300
7.30
to
9.30 A. M.
300 on Z>,
E, F, H
and/.
3.30
to
7.30 P. M.
300 on D,
E, F,H
and/.
8.00
to
8.30 P. M.
Saturday. . .
9-16-11
300 on D,
E, F, H
and/.
7.20
to
9.15 A. M.
300 on E
andH.
9.30
to
11.45 A. M.
300 on E
and H.
6.30
to
8.00 P. M.
Monday ....
9-18-11
300 on E
and H.
6.15
to
9.20 A. M.
300 on E
only.
9.30 A. M.
to
12.00 M.
300 on E
only.
12.15
to
1.50 P. M.
4.15
to
8.00 P. M.
Tuesday 9-19-11
i 300 on E 4.50
only. to
6.50 P M.
Wednesday .
9-20-11
300 on E
only.
8.30 A. M.
to
12.30 P. M.
Zero. 1.00 Zero on
to all panels.
3.40 P. M.
4.00
to
5.40 P. M.
floor slab and Fig. 56 those on the upper side. Fig. 57 records measure-
ments made on the bent-up bars and stirrups.
As already stated, the location of the gauge lines is shown on Fig. 42
and 43, the odd numbers referring to measurement on the concrete, the
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 75
even numbers to measurement on the reinforcement. The numbers in the
two hundreds are gauge lines on the under side or second story side, and
the numbers in the three hundreds are on the upper side or third story
side.
Stresses and bending moment coefficients are tabulated in Tables 8
None
300
§#77// §300
***// ^300
%*'/ §200
§
Hone % 0
£ ^300
^300
A/I ^30O
>
x 1
/
J
/
1
\
/
\
\
\
X
k
A
31
d
31
A
J<
>7J
30
\
\
I
\
1
/
/
/
7
/
t
1
x
|
\
\
\
I
1
Jt
7JT
3
3
?9\
30
\
' — r
\
§§§§
8 S
S Q ^>
5> ^) ^> Ci Q)
<^ <^> Q. O Cb _
per Unit of Length.
FIG. 52. LOAD-DEFORMATION DIAGRAMS FOR UPPER SIDE OF BEAMS AT MIDDLE.
VJ VJ
§ §
E ^300
100
245
n per Unit of Length
FIG. 53. LOAD-DEFORMATION DIAGRAMS FOR UNDER SIDE OF GIRDERS AT ENP.
76
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 8.
STRESS INDICATIONS IN TURNER-CARTER BUILDING TEST.
Stresses are given in pounds per square inch.
Member
Gauge Line
Reinforce-
ment
Gauge Line
Concrete
End of girder
269
900
Middle of girder
220
8000
311
Little
244
9000
End of beam ....
304
8000
265
1 100
318
8000
267
1 100
«
310
4000
281
1 000
it
293
800
Middle of beam
202
7000
301
350
206
11 000
305
350
it
230
9000
313
200
••
234
8000
315
300
14
236
8000
«
238
11000
II
240
5000
Bent up bar in girder
222
5000
224
5000
Bent up bar in beam
214
— 3 000
TABLE 9.
MAXIMUM STRESSES AND MOMENT COEFFICIENTS IN TURNER-CARTER
BUILDING TEST.
Stresses are given in pounds per square inch.
Member
Reinforcement
Concrete
Stress
Coefficient
Stress
Coefficient
Girde
Inten
ColuE
r, End...
31 000
1/12
1/12
0.05
1/12
0.03
1/12
0.05
1/12
l'/12
0.05
1 200
900
300
Little
1 SOO
1 100
S80
350
1 200
950
S60
225
1/12
0.06
1/12
1/12
0.07
1/12
0.077
1/12
0.064
1/12
0.054
End
Middle. . .
12600
8000
SI 600
8000
18600
11000
19600
Middle
nediate Beam, End
End..
Middle
" Middle
an Beam. End
End
" Middle
17000
10000
Middle
and 9. The stresses calculated on the basis of a bending moment co-
efficient of 1/12, the more usual one in designing are printed in italics.
The suggestions given for caution and care in interpreting measure-
ments should be applied to this test.
35. Beams. — For the tensile stresses in the reinforcement at the
middle of the intermediate beams at the full load of 300 Ib. per sq. ft.,
the highest stress observed was 11000 Ib. per sq. in. and the average
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 77
stress recorded may be said to be 8500 Ib. per sq. in. At the ends of the
intermediate beams, the highest stress observed in the reinforcement was
None O
f? L 3 nn
\
1
/
\
/
§DFfM ^3Off
I
f
NXJ ^^
\
/
(
"5 AH ^?nn
4
/
/
\
^AJI ^\IOO
>
/22
O
/
24
4
i
3^
Hi 5
None ^ 0^
/
/
5
i ^
5 s
n.
!J
ii
M
~4-,
II
T~^
\\
4 N
y
n
^ Q
- fj.
^
n
. cv
i Q
»^
i i
) Q
> c
! §
ii
. ^
ii
K
ii
> >
> Ci
> <i
> o
FIG. 54. LOAD-DEFORMATION DIAGRAMS FOR UPPER SIDE AND UNDER
SIDE OF GIRDERS AT MIDDLE.
Mane
None ^ 0
F ^.300
200
None
/SI
\
/^O5
^
S § §
/2O3
±
^ ^ ^ ^ O ^ O ^ ^
O O C> Q O O O ^ ^b
Unit of Length-
FIG. 55. LOAD-DEFORMATION DIAGRAMS FOR CONCRETE ON UNDER
SIDE OF SLAB.
78
ILLINOIS ENGINEEEING EXPERIMENT STATION
8000 lb. per sq. in., and the general value may be said to be 7500 Ib.
per sq. in. Using the assumptions for resisting moment ordinarily taken
in design calculations, these stresses may be considered to correspond to
a bending moment coefficient of .05 Wl for the maximum stress at the
middle of the beam and .03 W I for the maximum stress at the end of
the beam, if the tensile strength of the concrete be not considered.
0
~>0
J300
None 0
£ '"
Atl ^30O
\AH
^//
/Vone ^ 0^—jL
1
I
1
I
/
(
V
f
J
1
1
\
\
\
\
3c
A
32
A
3?
\
*3/<l
A
^^
\,
^f —
/
J
I
/
1
\
\
3/'t
\
30,
A
> ^ ^
§
//.
mciTion per Unit o
FIG. 56. LOAD-DEFORMATION DIAGRAMS FOR CONCRETE ON UPPER
SIDE OF SLAB.
Assuming a modulus of elasticity for the concrete of 2500000 lb.
per sq. in., the concrete on the compression side of the beams at the mid-
dle showed a compressive stress of 350 lb. per sq. in. and at the end of the
beam 1100 lb. per sq. in. It is apparent that the total compressive stress
in the concrete is greater than the total tensile stress in the reinforce-
ment of the beams. A possible explanation is that end thrust exists, in-
volving so-called arch action in the beams and floor structure, and that
the tensile stress is relieved by the presence of this thrust. The tensile
strength of the concrete must have a large effect on the resisting moment.
The coefficient for Wl in the expression for bending moment, necessary to
give a compressive stress equal to the maximum measured in the con-
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 79
^^
J
^ , (
N/V/7// <h ?/*)/)
§£/:/-/// ^300
^ >*// ^Ci Q/l/O
\
y
^
/
/
xj .£
\
/
/
ft x^/7 X 7/9/7
^
/^
\
2
^
2/4
A
2/4
A
\
\
\
^.
"t) £-/*, LJ C/v?/?/7
I
/
I
\
S/7T/"/// « ?/9/7
\
1
)
.
V
^ /I// r^^/7/7
/
/
\
2
w
/4
?2
22
*&
^ ~
<5
<$ §
r
s
/
>
b -
b <;
•* i
> S
^4 x
:> ^
N t;
^ S
* ;
^ *
M >
x C
i C
i ^
5 «C
\
(N
i c
. c
1 1
^ s
\ ;
x ^
5 C
. s § § , , , , ,
De /b/-/77c7//o/7 pet- Unit o
FIG. 57. LOAD-DEFORMATION DIAGRAMS FOR BENT-UP BARS AND STIRRUPS.
crete, on the assumptions made, is .077 for the middle of the beam and
.07 for the end of the beam. These coefficients are lower than the value
of 1/12 usually assumed in design of such beams.
36. Girders. — For the tensile stresses at the middle of the girders
the observations showed about 8000 Ib. per sq. in. in the reinforcement
at the middle. This corresponds to a bending moment coefficient of .05,
again neglecting the tensile strength of the concrete. The reinforcement
at the end of the girder was inaccessible.
Assuming a modulus of elasticity of 2500000 Ib. per sq. in., the con-
crete on the compressive side of the beam at the support showed a com-
pressive stress of 900 Ib. per sq. in. The reading at the middle of the
beam showed very little compression. Assuming that the loads on the
girder are concentrated at the points where the intermediate beams are
connected, and making the same assumption of distribution of stress as
before, the coefficient of bending moment was .06. It seems probable that
the compression at the middle of the span must be distributed over a
considerable width of floor, or larger readings of compression would have
been obtained.
80
ILLINOIS ENGINEERING EXPERIMENT STATION
3 00/6. per
200/b.
£er_
^/sfance
OOO4 <f\-^.0004
fc Q
'ir
,0002 \ ^.0002
\
N\
8 5 * *
* ^ JJ SI * %
O/sfance fro/77co/t//r?s7-/s?ches
FIG. 58. DIAGRAM SHOWING DISTRIBUTION OF COMPRESSIVE DEFORMATION
IN BOTTOM OF COLUMN BEAM.
> "UvJ8 <-^ y^
D/sr&/7ce from j/rde/ —
FIG. 59. DIAGRAM SHOWING DISTRIBUTION OF COMPRESSIVE DEFORMATION
IN INTERMEDIATE BEAM.
37. Decrease in Compression with Distance from Support. — In four
beams measurements of compressive deformations were taken at a series
of gauge lines from the support to a location near the point of inflection.
The position of these points is shown in Fig. 42. The gauge lines
No. 223, 225, 227, 229, 231 and 233 are on one side of column No. 6,
and 281, 283, 285, 287, 289 and 291 are on the other side of column
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 81
No. 6. It may be expected that there will be full restraint for the end
of the beams. Gauge lines 243, 241, 239, 237 and 235 are on one side
of a girder and 293, 295, 297, 299 and 1201 are on the other side. The
unit-deformations for these gauge lines at loads of 200 Ib. per sq. ft. and
300 Ib. per sq. ft. are plotted in Fig. 58 and 59.
The measurements recorded for the column beams show considerably
more compressive stress than do those for the intermediate beams, per-
5=3
ro-j1-"
o
— ,
\
)
, —
3E
1
f
• '
Secf/os? Mtf
FIG. 60. DIAGRAM SHOWING DISTRIBUTION OF COMPRESSIVE DEFORMATION
ACROSS FLANGE OF T-BEAMS.
haps one-third more. This difference in stress may be due partly to the
deflection of the girder, and to the deflection of the intermediate beam
between its support and a point opposite the end of the column beam,
which would permit a larger part of the load to be carried by the column
beam. It may be due somewhat to the fact that reinforcing bars are
bent down from a point at the end of the column beam, while in the
intermediate beams the bars run horizontally for a foot from the face
of the girder.
The direction of the lines in Fig. 58 and Fig. 59 indicates a zero
stress at about 45 in. from the face of column in the column beams and at
about 50 in. from the face of the girder in the intermediate beams. In
both cases the results locate the point of inflection at about 0.22 of the
clear span.
38. T-beam Action. — The distribution of compressive stresses in the
T-beam formed by a beam and the floor slab (which involves the dis-
tances away from the beam for which compressive stresses are devel-
oped) has been a fruitful source of discussion. Measurements parallel
to the axis of the beam were taken on the upper surface of the floor slab
immediately above beams and at intervals between them. These gauge
lines are No. 315, 317, 319, 321, 323, 325 and 327 (see Fig. 42). The
deformations are shown in Fig. 52 and 56. The amount of these def-
ormations at points across the slab for loads of 200 Ib. and 300 Ib. per
sq. ft. is shown in Fig. 60. It is apparent that a somewhat higher stress
existed in one beam than in the other. Taking this into consideration,
82 ILLINOIS ENGINEERING EXPERIMENT STATION
the compressive stress varies quite uniformly from one beam to the
other, and the full width of the floor slab may be said to be effective in
taking compression. The overhang (counting to the mid-point between
beams) is 6^2 times the thickness of slab. It will be noticed that the
conclusions are the same as given for the Wenalden building test.
Readings were also taken on the under side of the floor slabs parallel
to the beams at three places (No. 1205, 1211 and 1213), but the condi-
tions attending the location of these points do not permit conclusions to
be drawn.
FIG. 61. ARRANGEMENT OP GAUGE LINES TO TEST FOR MOVEMENT OF BAR
RELATIVE TO CONCRETE.
39. Floor Slab. — Measurements were taken on the floor slab in the
direction of its span at three places on the under side and at one place
on the upper side immediately above one of the lower measurements.
These gauge lines were No. 277 on the under side of the slab close to a
girder (Fig. 42), No. 279 on the under side of the slab 5 ft. from the
edge of the girder, No. 309 (Fig. 43) on the upper surface immediately
above No. 279, and No. 1203 (Fig. 42) on the under side half way be-
tween girders. The measurements are plotted in Fig. 55 and 56. As
might be expected from being close to the girder and near the level of
its neutral axis, No. 277 showed little deformation. The pair of gauge
lines (No. 279 and 309) shows less deformation than would be calculated
by the ordinary beam formula, but perhaps not less than would be the
case if the tensile strength of the concrete is considered to be quite ef-
fective. The reading of No. 1203 was even smaller than No. 279. All
the stresses found in the floor slab were low. The deformations parallel
to the beams were discussed under T-beams.
40. Bond Stresses. — At the ends of the beams the reinforcing bars
lapped over the center line of the girder a distance of 15 in. An effort
was made to determine whether there was a movement of one of these
bars with reference to the adjoining concrete and with reference to the
adjoining bar ; also whether the deformation in the stub end of the rein-
forcing bar was the same as in the adjoining bar. Fig. 61 shows the
location of the reinforcing bars with reference to each other, and the
position of the gauge lines. No. 312-14 in comparison with No. 312
and 314 will indicate any relative movement of one bar with respect to
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 83
the other, and No. 312c and 314c in comparison with ]STo. 312 and 314,
respectively, will indicate any movement of the bars with respect to the
concrete.
It appears possible that the initial reading of No. 314 is slightly in
error, and the remarks already made about quantitative interpretation of
results and the chances for variations in stresses in adjacent bars or in
adjoining concrete should be borne in mind in studying the results. It
seems evident that No. 314 (on the lapped bar) records considerably less
stress than (Fig. 50, p. 74) No. 312. The measurements indicate a possi-
bility that the right-hand point of gauge line No. 314 has moved to the
right relatively to the right-hand point of No. 312, though this amount
may not be more than the amount of initial slip necessary to develop the
requisite bond stress. The measurements taken have no bearing on
whether the left-hand point of No. 314 has moved. The measurements
also indicate that there was no motion of the left-hand point on the rein-
forcing bar (No. 312 gauge line) relatively to the concrete at its side,
though it must be borne in mind that the point taken was so close to the
bar that only slip and not distortion of concrete could be measured.
41. Web Deformations. — No diagonal tension cracks were visible on
any of the beams or girders.
In girder 4 measurements were taken on the diagonal portion of a
reinforcing bar, one of the bars which is provided to take negative bend-
ing moment. This is shown in Fig. 42, Section K-K. The gauge lines
are No. 222, 224 and 226. The position of the gauge lines is also shown
in Fig. 41. The measurements are plotted in Fig. 57. It was impracti-
^ble to measure the deformation at a point closer to the support. The
measurements show about the same stress at No. 222 and 224, perhaps
5000 Ib. per sq. in. The stress at No. 226 is materially less. It is not
improbable that there was tension in this rod throughout its length. As
there was considerable compression measured in the gauge lines on the
bottom of the girder below No. 222, it seems probable that a crack was
formed in the top of the floor slab somewhere above No. 222, but as this
space was filled in with bags of cement no observation was made during
the test, and inspection of this space after the load was removed seems to
have been overlooked. At the other end of the girder, near column 6, a
fine test crack was found on the upper surface of the floor 2 in. from the
face of the column extending across the width of the girder and beyond.
This extended through the floor. A similar crack was observed on girder
3 near column 15.
Gauge line No. 228 is on a stirrup (see Fig. 41). This stirrup is in
an inclined position. It is not known what bar it is intended to be
84 ILLINOIS ENGINEERING EXPERIMENT STATION
connected with, nor whether there is connection with a tension bar. The
gauge line is in a region of the beam where horizontal compressive
stresses may be expected. The measurement in the stirrup at the first
increment of load shows tension (see Fig. 57) and subsequent increments
give compression. It should be noted that readings could not be taken
on the upper end of the stirrup. If the upper ends are merely bent out
into the floor slab it is hard to see that the stirrup may be expected to be
useful in transmitting web stresses.
In beam 9 (see Fig. 42, section L-L, gauge line No. 218) measure-
ment was taken on the diagonal portion of a reinforcing bar which is
carried through the girder at its top and a few inches beyond. See also
Fig. 41. This shows a tension of 3000 to 5000 Ib. per sq. in. (See
Fig. 57.) This bar was inaccessible from the top of the floor, but the
gauge lines on the companion bar (No. 324 and 318) show about 5000
and 9000 Ib. per sq. in. Measurements in the diagonal portion of a
single-bend bar (gauge lines No. 216 and 214, Fig. 42) which extends
only to the center of the supporting girder indicate a small compression
in the bar (see Fig. 57). A stirrup, which like the one in the girder
was close to the end of the beam and was inclined so that its lower end
was nearer the support than its upper, showed shortening of the stirrup
(see gauge line No. 212, Fig. 41, 42 and 57). In both cases, the ar-
rangement was such that the stirrup could hardly be effective.
The amount of the vertical shear in the beams and girders was such
that diagonal tension cracks might be expected except for the small tensile
stresses in the top of the girder and the end constraint which seems to
have been developed in both beams and girders.
42. Deflections. — The deflections of the beams (including that due
to deflection of girder) and the deflections of girders are given in Fig. 62.
The location of the deflection points is shown in Fig. 44. The effect of
time upon the deflection is shown by the increase in deflection under con-
stant load. The change when portions of the load had been removed may
be due in part to the time element and in part to the effect of location
of the load on the panels. The deflections seem relatively small, especially
when compared with deflections obtained in laboratory tests of beams
carrying the same loads. The conditions were such that the supports
were subject to possible displacement by workmen.
43. Effect of Number of Panels Loaded. — In taking off the load,
the outer panels were unloaded first, and observations were taken on the
remaining panels in an attempt to determine the relation between single
panel loading and group loading. Panels B and C were first unloaded
(see Fig. 42), then panels D and F, then panels H and I, and finally
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 85
None . Orr
JU// %/QO
H. XJ
Hone 0
£ ^300
DEFHI ^00
^ All ^300
^200
None 0
£ 300
^300
^300
A/one 0
E ^300
/7
/9
15
20
Def/ecf/ons /n /nc/ies
FIG. 62. LOAD-DEFLECTION DIAGRAMS.
86 ILLINOIS ENGINEERING EXPERIMENT STATION
panel E. The deformations at each of these stages are shown in the
load-deformation diagrams. If at each stage of the loading the average
of the deformations at all the points having a similar location (say the
points on the under side of the beams at the south end of the test area)
be taken the effect of area loaded may be judged by the ratios of these
values to the corresponding ones at full load. If the beams be considered
as freely supported (without restraint) and their weight be neglected,
and if it be assumed that no time is required for adjustment of members
to the load coming upon them, it should be possible in many cases to
forecast the effect of a change in the area loaded. Comparing the ratios
referred to above (no diagrams reproduced here) with what might be
expected on the basis of the above assumptions, it is found that in most
cases the direction of the changes in stress agrees with predictions. The
amount of change to be expected can not be predicted because of com-
plications in the division of load between elements of the structure. A
point worthy of note is that the stresses at the center of the panel E
are 30 per cent less when only panel E is loaded than when the whole
test area is loaded. This must be due to the fact that with the removal
of the load which rested on the side panels F and D the column beams
at the edge of panel E recover a considerable part of their deflection,
and because of their smaller deflection they will receive the effect of a
greater proportion of the panel load than taken before, thus relieving
the interior beams somewhat. The stresses were decreased at this stage
more than they were increased later by the removal of the load in the
end panel H. This indicates that the stiffness of the floor system per-
mits considerable lateral distribution of the load-carrying stress. The
removal of the load in panel H increased the stress in the beams at the
center of panel E much as though the beams were continuous and freely
supported. This would indicate that the most severe condition of load-
ing affecting the center of the beams is brought about by loading several
panels which lie side by side and are not separated by girders.
44. Effect of Time on Stresses Developed. — To determine the effect
of time-under-load on the amount of deformation developed, observa-
tions were taken at each stage of the loading after the load had been in
position for from 8 to 12 hours and also at intervals of 8 to 16 hours
when all panels were fully loaded. The latter investigation continued
over 48 hours. The results found during the loading seem to indicate
in a general way a tendency for the deformations at the ends of beams
both above and below to increase and also those at the centers of the
beams above, but on the lower surface of the beams at the center the
tendency was to decrease. ISTo reason is apparent why the changes on the
TALBOT-SLATER— TESTS OF REINFORCED CONCRETE BUILDINGS 87
compression and tension surfaces at the center of the beam should be in
opposite directions and it is probable that this result is erratic. With
full load the time effect at only a few gauge lines was observed ; only two
of them were at the center of the beams, both being below and none
above. These measurements also indicate an increase in deformation at
the ends of beams both above and below. At the center of beam below,
one gauge line shows an increase and the other a decrease in deformation
thus giving no results.
45. Columns. — Headings were taken on the four faces of column
No. 5 just below the girders, but the results are not consistent enough to
warrant attempting to draw conclusions.
46. Test Cracks. — Fine tension cracks were observed in the lower
part of the beams and girders. The location of the observed cracks is
shown on Fig. 63. The appearance of these fine cracks is similar to those
Pane/ C
Ovrt/'ne of loaded ^
Panel F
Panel B
Outline of loaded area-
Panel A
Panel £
Pane/ I
Panel D
fa Panel H
loxled area
Panel 0
FIQ. 63. CABINET PROJECTION SHOWING BEAMS AND GIRDERS AND POSITION
OF TEST CRACKS.
observed in laboratory tests. They would not be noticed without
specially careful examination.
The floor cracks already mentioned indicate the development of the
tensile stresses in the beams and girders at the support.
It was not possible to give full attention to every feature upon which
information was sought, and in some cases isolated points were used
with a view of determining tendencies, and in these naturally there is
less certainty in the indications.
88
ILLINOIS ENGINEERING EXPERIMENT STATION
V. THE DEERE AND WEBBER BUILDING TEST.
47. The Building. — The Deere and Webber Building is an eleven-
story and basement warehouse at Minneapolis, Minnesota, owned by the
Deere and Webber Company. It was built by the Leonard Construction
Company of Chicago. Fig. 64 is a view of the building at the
time of test. Fig. 65 shows the floor plan of the building and the loca-
tion of the panels loaded. The dimensions of the panels are 18 ft. 8 in.
by 19 ft. 1 in. A 1-2-4 mixture was used, the slab thickness measuring
9 3/16 in. The floor was designed by the Concrete Steel Products
Company for a live load of 225 Ib. per sq. ft., and the details of the
reinforcement are shown in Fig. 66. The floor tested was the fourth
from the ground and the conditions were not such as to make a high
showing of strength. Owing to a failure in the supply of aggregates
during the construction of this floor, an abnormal number of bulkhead
separations occur in the slab, as is shown in Fig. 65. Such separations
FIG. 64. DEERE AND WEBBER BUILDING AT THE TIME OF TEST.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 89
A/>7/4 /4 venue North.
I
r
s
FIG. 65. PLAN OF FLOOR SHOWING LOCATION OF PANELS TESTED.
occur in every panel under load except one. The concrete was only 40
days old at the beginning of the test. In general the conditions were such
as to give slightly higher stresses than would be expected had the slabs
been well seasoned and normally poured.
48. Method of Testing. — Fig. 66 and Table 10 show the position
of points at which measurements of deformation were made. The num-
bers given are those used in recording and plotting the data in the tables
and diagrams. The total number of readings was in excess of 3300.
The falsework for instruments and observers is shown in Fig. 67. For
measuring deflections the instrument shown in Fig. 68 was used. A pol-
ished steel ball was attached to the ceiling, another was carried on an
upright, and the instrument was inserted between them. Measurements
were made in this manner to the nearest .001 inch with accuracy. For
measuring the deformation in the reinforcement at the center of the
span a clamp was rigidly attached to the slab rod (the concrete being
removed at one point for this purpose), and a Wissler dial was carried
90
ILLINOIS ENGINEERING EXPERIMENT STATION
\
-r\
mm"
mmm\
4fl
77/J I
^
y /// / *
37 //'// *
yfafcw*
NI
m
/ /?a/
viiK %
?4 \Cfr*
'4 \G
LEGEND-. |/j
— Tens. Reading \>n Steel over Capita/.
— " • I' ' x,/ Center.
1\ ' I x/7" Temperature \Reac//ny.
E3I rJ^~ "7R~
FIG. 66.
ARRANGEMENT OF REINFORCEMENT AND LOCATION OF OBSERVATION
POINTS.
on the clamp (Fig. 69). A fine silk-covered copper wire was attached
to the rod at a distance of 15 in. from the clamp and passed imme-
diately helow the rod, over an idler on the clamp, and then over the
drum of the dial. As this wire was 1/16 in. below the under surface of
the slab rod, the deformations observed were only slightly in excess of
the deformation in the rod. The wire was placed in this position be-
cause experience in the laboratory has demonstrated that measurements
taken below the slab depending upon the position of the neutral axis for
correction, are subject to considerable error. By this arrangement the
deformation was measured to an indicated .0002 in. on a gauge length of
15 in. The measurement was less responsive to slight changes than were
the other measurements made.
For measurements of deformation in the reinforcement over the
column capital the University of Illinois type of Berry extensometer
built for this test (Article 11) was used. A gauge length of 15 in., was
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 91
TABLE 10.
DATA ON POSITION OF RODS ON WHICH DEFORMATIONS
WERE MEASURED.
Gauge Line
Band
Position in Band
Embed-
ment
inches *
Layer of Steel over
Column
3
7
12a
14
14a
39
40
108
109
110
111
112
202
203
204
207
205
206
208
209
Diagonal
Cross
;;
Diagonal
Cross
3d rod from center
tt
"H
"a
"H
"«
"»
2H
'04
'iy*.
'in
2d layer from top
3d
H
2d
A
Outer rod of band
2d rod from center
M
Outer rod of band
3d rod from ™»pt«r
H
Outer rod of band
3d rod from center. .
K
5th rod from center •
Outer rod of band
A
5th rod from center
2A
3d " " "
1st " " .. . .
2*A
Outer rod of band
3d rod from nentpr. . ,
3
Outer rod of band . . . .
3d rod from center
2H
*Measurement from surface to center of rod.
used. For measuring deformations in the concrete the original Berry
6-in. extensometer (Fig. 13) was used.
49. Loading and Testing. — In applying the load care was taken that
no serious arch action in the load be possible. In the earlier stages
brick were piled in piers, as shown in Fig. 65 and in Fig. 70, with open
aisles from 8 in. to 16 in. wide between the piers. For the later loading,
cement in bags was used as loading material, the piers being kept sep-
arate as before. The load given in the tables is in all cases the total load
on the panel divided by the area of the panel, the intensity of the load
under the pier being greater. The aisles gave an opportunity for making
observations upon the concrete and reinforcement.
To correct for temperature variations one entire day was spent in
observing effects due to temperature alone, and the large Berry exten-
someter was read on a standard bar before and after each series of slab
readings.
The test continued for six days from October 30 to November 4, in-
clusive, 1910. Eight panels were loaded. First readings were taken
on all instruments with the floor unloaded and then a load equal to 75 Ib.
per sq. ft. was applied over the entire eight panels. Another series of
observations was taken and the load increased to 150 Ib. per sq. ft. In
this manner alternate observations and loadings were continued for three
92
ILLINOIS ENGINEERING EXPERIMENT STATION
FIG. 67. FALSE WORK FOB INSTRUMENTS AND OBSERVERS.
FIG. 68. DEFLECTOMETER IN PLACE.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 93
FIG. 69. WISSLER DIAL FOR MEASURING DEFORMATION IN REINFORCEMENT.
FIG. 70. VIEW OF MAXIMUM TEST LOAD.
ILLINOIS ENGINEERING EXPERIMENT STATION
, I
^ 5
T-rT O
PQ
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I
§
11
Ococo
§»^
d
>.-n^03 -Hcoiot^cN KI t^ a> a> <=> *-< c<\ ooo-<co
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:KRgS K3$%
88
r
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d
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d
cocococo<
t^0003O3<
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CNCOCOCO»0
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g^^c
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O3 CO CO TJ< Tt< Tj< •
rH CN CN CN CN CN <
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COt^i-l
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COCOO<N<
CM •<* 00 Tt< i
d
1003OOO • •
CNCNCOCOCO : '
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CN Tj«i-l ^H
COCNi-n-H
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rH^^Mc^
d
)T-lT}t 1OOO Tfl OOI
ICOt^ OOO3CNCOI
O Tj< t^ O CO Tf< t^
00 CN i-i CN CN CN CN
*-* CN<N CN CN CN CN
d
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C«CN COOO
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O iO iO »O >O iO iO IOOO
o o o o o
>O iO U5 >O IO »
CO CO CO CO CO C
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS
95
330
300
^ 73
M
.<: o
73
350
300
&
0
W
I
FIG. 71. DIAGRAM OF DEFLECTIONS.
days. Over-night readings were taken on one or two occasions in the
evening, about midnight and in the morning. The maximum load of
350 Ib. per sq. ft. was allowed to remain on the floor about 22 hours,
readings being taken at frequent intervals during that time. In the
process of unloading the outer panels were first cleared, and finally the
load was removed from the center panel. Readings were taken at in-
tervals during the progress of the unloading. The data obtained are
presented in Tables 10-15 and plotted in Tig. 71-74.
96
ILLINOIS ENGINEERING EXPERIMENT STATION
50. Deflections. — Fig. 71 shows graphically the deflections at sixteen
points, the same data being recorded in Table 11. On the second dia-
gram of Fig. 71 note the comparison between readings 5 and 11, where
bulkheads existed, and readings 17 and 42, where no bulkheads were
present. Other instances of the marked effect of bulkheads on the
stiffness of the slab may be seen in the plotted data. It may also be
said in general that the deflections were greater in the outer panels
than in the center panels, in part due to the bulkheads in these outer
panels, and in part to the tendency to higher stresses and deflections
350
300
/SO
7S
'^ 350
300
%*<">
i? o
^Ss ^
^ ^}
Q Q
l«
10 1
fle former f/ort /rt inches or
^ !S
/rr Sfae/ tn Lbs. per- 5<y. /n.
FIG. 72. DIAGRAM SHOWING STRESS IN REINFORCEMENT AT CENTER OF SPAN.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 97
in end panels. The deflections probably would have been smaller
with well cured concrete and in considering deflections it must be re-
membered that this slab was only 43 days old when the maximum load
was placed upon it. The maximum deflection found was .32 in., which
is 1/1000 of the span. This was at a bulkhead in an outer panel. In
the center panel the deflection for all eight panels loaded, was .227 in.,
or 1/1400 of the span, which increased to .274 in. or 1/1200 of the span,
when the load was removed from the outer panels.
51. Stress in Reinforcement at Center. — Fig. 72 and Table 12 give
the data on the measured deformations in the reinforcement at the center
of the spans. The table is reduced to unit deformations while the dia-
grams show total deformation over the lengths gauged. The stresses ob-
served at the center were very low. On the upper diagram in Fig. 72
are shown deformations in the center panel and it is to be noted that
these are, in general, smaller than those in the outer panels. This
would seem to indicate that the reinforcement at the center of the span
should be designed for one panel loaded, as this apparently gives a worse
condition at the center than full loading. The observed stresses indicate
that the diagonal and cross band rods took practically the same stress.
350
500
X
TTT
Y\
7
7T
.-*
1*<&
,.'•
1M.
>r
•n
:0-
£
I I
Inches orer-
§ 8 .8 _ 55
//7 5 tee/ /n Lbs. per Sa. /r?.
FIG. 73. DIAGRAM' SHOWING STRESS IN REINFORCEMENT OVER CAPITAL.
98
ILLINOIS ENGINEERING EXPERIMENT STATION
02
fc
I
o
O
O
Oil O
<-H CO •**< 00 t- 00 00 b-<
d d
t^ OS OS O5 OS t^ O5
JrHCOrH t~(NC<INiO I-H T-I O O O OS OS Ot^i
O rH ,-H rH rH <N C<| <N <N <N rH .-H (N rH
> I I d d d
I rH r>-OOO5rHOO CO CO (N CO IM rH OS OS (N 1C
Oil O
ITjirH rHTfOSCOCO rH^lCCOt
d i f
IrHCOOO rH
•* CO CO CO C
CM Ol <N (N (
) CO CO CO CO CO CO CO CO i
I
SI
35
g o
d i d
Oil O
rH rH O rH Tt< »O rH O(
(N (M iM (M (N N <M C<> i
d d
CO CO CO CO CO CO CO
^ t>-"3 (
rnS 22^;
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS
99
52. Stress in Reinforcement at Column Capital. — Table 13 and
Fig. 73 give the data on the stress in the reinforcement over the column
capital. The upper diagram covers diagonal rods, the lower diagram
cross band rods. Among the diagonal rods it may be noted that the
stress in rod No. 207 was measured over the edge of the capital while
that in No. 203 and 204 was measured opposite the center of the col-
umn. The higher stress in No. 207 would seem to indicate that the
stress in these rods decreases, passing from the critical section at the
TABLE 13.
UNIT-DEFORMATION IN REINFORCEMENT OVER CAPITAL.
Load in Ib. per
sq. ft.
Gauge Line
Center
Panel
Outer
Panels
202
203
204
207
205
206
208
209
0
0
.00000
.00000
.00000
.00000
.00000
.00000
.00000
.00000
75
75
14
8
7
6
4
11
2
2
150
150
24
22
19
25
18
22
19
14
187.5
187.5
29
28
. 30
33
24
26
23
18
187.5
187.5
.00035
.00022
.00028
.00030
.00022
.00023
.00022
.00018
225
225
30
31
38
37
26
29
28
23
262.5
262.5
44
44
48
58
42
42
45
52
300
300
47
50
50
63
50
42
50
50
300
300
49
54
54
63
50
42
49
34
300
300
.00053
.00058
.00057
.00067
.00059
.00047
.00054
.00040
350
350
52
60
58
72
62
48
57
39
350
350
54
59
56
73
62
47
61
45
350
350 55
60
58
75
64
47
60
40
350
350 53
58
57
75
62
45
58
40
350
350 52
60
57
72
68
47
59
40
350
350 54
61
56
76
67
48
61
41
350
350
.00056
.00061
.00056
.00078
.00064
.00049
.00063
.00041
350
187.5
53
55
54
80
64
48
60
41
350
0
50
48
51
77
62
48
55
39
edge of the capital to any section nearer the center of the column. This
is as would be expected. The stresses found from these readings indicate
clearly that the slab should be designed for a maximum moment over the
support and not at the center. In the design of this building some 75%
more reinforcement was provided over the support than was used at the
center.
53. Stress in Concrete at Edge of Capital. — Fig. 74 and Table 14
give deformations observed in the concrete at the edge of the column
capital. Owing to the fact that when the slab was poured there was no
intention of testing, no specimens of the concrete were available from
which to determine the modulus of elasticity. Hence it is necessary
to assume a value for concrete about 40 to 45 days old cured in fall
weather at Minneapolis. From experiments made at the University of
100
ILLINOIS ENGINEERING EXPERIMENT STATION
TABLE 14.
UNIT-DEFORMATION IN CONCRETE AT EDGE OF CAPITAL.
Load in Ib.
Gauge Line
per sq. ft.
Center
Panel
Outer
Panels
102
103
104
105
106
107
0
0
0.00000
0.00000
0.00000
0.00000
000000
0.00000
75
75
11
17
9
7
8
7
150
150
21
28
21
22
17
20
187.5
187.5
24
30
24
16
18
20
187.5
187.5
0.00015
0.00021
0.00018
0.00013
0.00015
0.00012
225
225
15
25
20
17
14
20
262.5
262.5
28
37
31
28
25
31
300
300
36
43
38
36
32
34
300
300
39
44
38
33
30
33
300
300
0.00032
0.00038
0.00033
0.00029
0.00024
0.00031
350
350
41
47
40
38
32
38
350
350
43
47
42
39
33
38
350
350
43
49
43
42
35
39
350
350
44
45
44
42
34
37
350
350
47
48
46
42
34
40
350
350
49
50
48
41
36
40
350S
350
0.00047
0.00045
0.00046
0.00040
0.00034
0.00040
350
187.5
47
49
44
36
31
37
350
0
44
44
38
23
22
30
Illinois concrete of the same age cured under laboratory conditions
showed a modulus of 1875000 Ib. per sq. in., and in Table 15 this
modulus has been used as giving the value for the concrete stress. In
Fig. 74 a stress of 100 Ib. per sq. in. corresponds to a deformation of
.00032 in. if a modulus of 1 875 000 be assumed.
An interesting feature shown in the curves is the falling off in
the concrete deformation when the load was allowed to remain over
night. The decrease is less marked at higher loads than at low loads,
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FIG. 74. DIAGRAM SHOWING STRESS IN CONCRETE AT EDGE OF CAPITAL.
TALBOT-SLATER TESTS OF REINFORCED CONCRETE BUILDINGS 101
while readings taken at very frequent intervals while the maximum load
was on the floor showed that at first the stress steadily increased and
the decrease did not begin until some time after the load was applied.
The phenomenon is of interest as showing the readjustment in stresses
which takes place under load even in the least plastic constructions.
In general the concrete stresses checked those found in the reinforce-
ment over the support.
54. Summary of Stresses.— Table 15 gives a summary of the
stresses found at various points under the design load of 225 Ib. per
sq. ft. and also under the maximum load applied of 350 Ib. per sq. ft.
TABLE 15.
SUMMARY OF STRESSES.
Stresses are given in pounds per square inch.
^
Design Load — 225 Ib.
per sq. ft.
Maximum Load — 350 Ib.
per sq. ft.
L. L.
D. L.
Total
L. L.
D. L.
Total
REINFORCEMENT OVER HEAD:
3
Diagonal Band. Maximum. .
Average ....
13800
11 000
6900
5500
20700
16500
24200
18800
6900
5500
31 100
24300
Cross Band. Maximum. .
Average ....
10000
9000
5000
4500
15000
13500
18800
17200
5000
4500
23800
21700
REINFORCEMENT AT CENTER:
Diagonal Band. Maximum. .
Average
2400
2000
1200
1000
3 600 4 800
3000 4800
1 200
1000
6000
5800
Cross Band. Maximum. .
Average. . . .
2800
2500
1400
1 300
4200
3800
8000
6600
1400
1300
9400
7900
Outer Panels. Maximum. .
Average
4600
3800
2300
1900
6900 10400
5700 i 8000
2800
1 900
12700
9900
CONCRETE AT CAPITAL:
Diagonal Direction. Maximum. . 530
Average \ 500
265
250
795 800
750 750
265
250
1065
1000
Cross Direction. Maximum. . 500
Average 468
250
234
750 800
700 750
250
234
1 050
984
Concrete Stresses based on Ec = 1,875,000 Ib. per sq. in.
In making up this table the dead load stresses have been taken as one-
half the indicated live load stress at the design load (the dead weight
of the slab being half this load). This is a maximum assumption and
probably is somewhat in excess of the true value, as the concrete was not
broken in tension until after a live load of 75 Ib. per sq. ft. was ap-
plied.
102
ILLINOIS ENGINEERING EXPERIMENT STATION
55. Cracks. — Very careful observations were made to discover and
record all cracks. A reading glass was used to aid the eye, and dust
was removed by means of bellows. It is easy not to discover cracks in
such a test, and with casual observations very likely but few of these
cracks would be noted. In fact all of them were very fine. At a
load of 262.5 Ib. per sq. ft. a crack was observed at the bulkhead where
two days had elapsed between the pouring of the adjacent floor sec-
tions.
At 300 Ib. per sq. ft. cracks appeared at the other bulkheads. Very
fine cracks were also found in the center panel where no bulkhead
existed and over the edge of the capital at column ISTo. 41, these being
very faint and hard to trace for any distance. At 350 Ib. per sq. ft.
there could be traced out the cracks shown in Fig. 75 in which the
dotted lines represent cracks in the ceiling below. The cracks about
the column head are of interest as indicating the position of the critical
FIG 75. LOCATION OF CRACKS TRACEABLE AT LOAD OF 350 Lu. PER SQ. FT.
TALBOT-SLATER — TESTS OF REINFORCED CONCRETE BUILDINGS 103
section for which moments should be figured in analyses. These aver-
aged about 2 or 3 in. outside the edge of the capital.
At column No. 51 the position of the crack would seem to indicate
that for a single panel loaded the critical section moves nearer the sup-
port, resulting in higher stresses at the center. This crack and similar
ones, as at columns ISTo. 49, 39 and 21, were very faint, indicating a lower
stress in the reinforcement over the support at such points. The cracks
shown running diagonally near columns No. 21 and 51 were in all cases
directly beneath slab rods.
Another set of cracks which developed only under the maximum load
of 350 Ib. per sq. ft. is significant. These cracks ran along the center line
of the cross bands, being easily traced in the portion about half way be-
tween columns, growing fainter toward the columns, and disappearing en-
tirely in most cases before reaching the crack over the edge of the capital.
Evidently there is negative bending moment at these sections. These
cracks, we believe, had not been observed before, probably because other
building tests have not been so extensive, and because cracks have not
ordinarily been vopy carefully observed.
56. Comments. — The most important result of the Deere and Webber
Building test lay in the demonstration that a field test of a reinforced
concrete building may be made with the reasonable expectation of secur-
ing reliable and useful data on the stresses developed in the steel and in
the concrete. The test gives certain well-defined indications. It shows
that the bending moment at the support is much greater than that at the
center of the span. It indicates, by the position of the cracks, a critical
section for which moments should be calculated. It indicates that the
stresses at the center of the span are lower than analyses would lead one
to expect. It indicates that bulkheads act to increase deflections and
stresses. It indicates that the reinforcement at the center receives its
maximum stress for the condition of load on one panel only.
VI. GENERAL COMMENTS.
57. General Comments. — The tests described in the bulletin are of
such a nature and cover so much ground that it is impracticable to sum-
marize results or to formulate specific conclusions in any brief way. In
the body of the text, the results of tests have been stated and described
in detail, the action of structures discussed and conclusions drawn. The
data are given in full in the tables and diagrams. In general the conclu-
sions may be considered to be applicable to structures of similar construc-
tion. Possibly some of the conclusions, easily recognized in the text,
will require further tests to determine whether they are generally appli-
104 ILLINOIS ENGINEERING EXPERIMENT STATION
cable. The information obtained in these tests will be found of value
in the settlement of a number of questions which are in dispute, and
the results when taken in connection with other tests may be expected
to be of considerable assistance in developing analyses and deter-
mining constants for use in the design of reinforced concrete structures.
Many of the results of the tests have a bearing upon the unsettled prob-
lems and even on matters which many have considered to be not open
to question.
The tests here recorded have shown the practicability of measuring
the deformations or strains in critical parts or members of a reinforced
concrete structure when subjected to load. Methods have been developed
for making measurements and tests in a way that will give trustworthy
data. Difficulties have been overcome, and many of the precautions
found necessary have been formulated. Skill and experience are essen-
tial in making such tests, and the difficulties encountered are of a wider
range than those met in the best laboratory practice. As in other tests,
caution must be exercised in drawing conclusions, and judgment must be
used in interpreting results. The presence of low stresses should not be
taken as being conclusively indicative of low bending moments ; and the
action of tension in the concrete, of horizontal thrust distributed over
large distances, and of other agencies may need consideration. Action
under partial load, as when a single panel is loaded, must be recognized
to differ from that under full load.
Such problems as the distribution of bending moments along the
length of the beam, the distribution of stresses over areas outside of those
usually assumed as forming the beam, the presence of secondary stresses
and of web stresses in structures as they are fabricated, will be solved
only when adequate field tests have been made. The analysis of struc-
tures and the determination of the resistance of individual members or
parts require the making of assumptions and the choice of constants, and
the proper determination of these may be made only with full knowledge
of the properties of the materials found by laboratory tests and of the
action of the fabricated structure as shown in adequate field tests.
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The Library contains 200,000 volumes.
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For catalogs, and information address
C. M. McCONN, Registrar,
Urbana, Illinois.
UG 13 1937
18 1942
LOAN
JUN 26 1978
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