EXCHA1 132
\IOWA STATE COLLEGE
OF AGRieWTTURE AND MECHANIC ARTS
OFFICIAL PUBLICATION
Vol. XXI November 29, 1922 No. 26
PRELIMINARY IMPACT STUDIES SKUNK RIVER BRIDGE
ON THE LINCOLN HIGHWAY NEAR AMES, IOWA
By
ALMON H. FULLER
%
BULLETIN'S
Preliminary Report to
UNITED STATES BUREAU OF PUBLIC ROADS
IOWA STATE HIGHWAY COMMISSION
IOWA ENGINEERING EXPERIMENT STATION
ENGINEERING EXPERIMENT STATION
AMES, IOWA
Published weekly by Iowa State College of Agriculture and Mechanic Arts, Ames, Iowa.
Entered as Second-class matter, and accepted for mailing at special rate of postage pro-
vided for in Section 429, P. L. & R., Act August 24, 1912, authorized April 12, 1920.
PURPOSE OF THE STATION
The purpose of the Engineering Experiment
Station is to afford a service, through scientific
investigation, evolution of new devices and
methods, and tests and analyses of materials:
For the manufacturing and other engineer-
ing population and industries of Iowa;
For the industries related to agriculture, in
the solution of their engineering problems;
For all people of the state in the solution of
the engineering problems of urban and rural
life.
IOWA STATE COLLEGE
OF AGRICULTURE AND MECHANIC ARTS
OFFICIAL PUBLICATION
Vol. XXI November 29, 1922 No. 26
PRELIMINARY IMPACT STUDIES SKUNK RIVER BRIDGE
ON THE LINCOLN HIGHWAY NEAR AMES, IOWA
By
ALMON H. FULLER
Consulting Bridge Engineer
IOWA STATE HIGHWAY COMMISSION
and
Professor of Civil Engineering
IOWA STATE COLLEGE, AMES, IOWA
BULLETIN 63
Preliminary Report xu
UNITED STATES BUREAU OF PUBLIC ROADS
IOWA STATE HIGHWAY COMMISSION
IOWA ENGINEERING EXPERIMENT STATION
ENGINEERING EXPERIMENT STATION
AMES, IOWA
Published weekly by Iowa State College of Agriculture and Mechanic Arts, Ames, Iowa.
Entered as Second-class matter, and accepted for mailing at special rate of postage pro-
vided for in Section 429, P. L. & R., Act August 24, 1912, authorized April 12, 1920.
STATE BOAED OF EDUCATION
Members
Hon. D. D. Murphy, President Elkader
Hon. George T. Baker Davenport
Hon. Chas. E. Brenton Dallas Center
Hon. P. K. Holbrook Onawa
Hon. Edw. P. Schoentgen Council Bluffs
Hon. C. H. Thomas Creston
Hon. Pauline Lewelling Devitt Oskaloosa
Hon. W. C. Stuckslager Lisbon
Hon. Anna B. Lawther Dubuque
Finance Committee
Hon. W. E. Boyd, Chairman Cedar Eapids
Hon. Thomas Lambert Sabula
Hon. W. H. Gemmill, Secretary Des Moines
E\<;i\EEIM.\<: EXI'EIMMENT STATION
Station Council
(Appointed by the State Board of Education)
R.-iymond A. Pearson, LL. D President
Anson Marston, C. E Professor
Louis Bevier Spinney, B. M. E Professor
Warren H. Meeker, M. E Professor
Fred Alan Fish, M. E. E. E Professor
Allen Holmes Kimball, M. S Professor
O. E. Sweeney, M. S., Ph. D Professor
Fred E. White, B. C. E Chief Engineer, Iowa Highway Commission
"*" Station Staff
Raymond A. Pearson, LL. D President, Ex-officio
Anson Marston, C. E Director and Civil Engim-.T
H. E. Pride, B. S. in C. E Mullet in Editor
Warren H. Meeker, M. E Mechanical Engineer
Fred Alan Fish, M. E. E. E Electrical Engineer
Allen Holmes Kimball, M. S Architectural Engineer
O. E. Sweeney, M. S., Ph. D Chemical Engineer
Charles S. Nichols, C. E Sanitary Engineer
Louis Bevier Spinney, B. M. E Illuminating Engineer and Physicist
William J. Schlick, *C. E Drainage Engineer
T. E. Agg, C. E Highway Engineer
John Edwin Brindley, A. M., Ph. D Engineering Economist
Max Levine, S. B Bacteriologist
Lulu Soppeland, M. S Assistant Bacteriologist
J. H. Griffith, M. S Structural Materials Engineer
D. A. Moulton, B. S. in Cer. Eng Ceramic Engineer
A. K. Friedrich, E. M Mining Engineer
G. W. Burke, B. S. in Chem. Eng Chemist
C. H. Giester, B. S Assistant Chemist
Clyde Mason, B. S. in E. E., B. S. in C. E Engineer
C. J. Myers, B. S. in M. E Mechanical and Electrical Engineer
F. W. Hallgren Mechanician
CONTENTS
Page
Preface 4
Introduction 5
Organization 5
Loads 5
Instruments 6
Field and Office Work 7
Comparison of Instruments. 7
Results Stresses and Impact 13
Distribution of Stresses. (Stringers) 16
Distribution of Stresses. (Floor Beams) 17
Distribution of Stresses. (Hip Verticals) 17
Distribution of Stresses. (Truss Members) 18
Computed Stresses 18
Strain Gauge Checks 18
Bureau of Public Roads New Photographic Mirror Extensometer. . 18
Possibilities for Future Work 19
Instruments for Future Work 20
Number of Instruments .20
ILLUSTRATIONS AND TABLES
Truss Diagram and Load Plate Figure 1 8
Distribution of Stress in Stringers Figs. 2, 3, 4 9, 10, 11
Laboratory Calibration Figure 5 12
Photographs of Instruments on Bridge Members. .Figs. 6, 7, 8 14, 15
Original Data
Main Span : Stringers Tables 1, 2 21, 22
Floor Beam Table 3 23
Hip Vertical Table 4 24
Diagonal Table 5 25
Intermediate post Table 6 26
Approach Span Stringers Tables 7, 8 27, 28.
Tabulated Impact Percentages Tables 9-11 29, 30
Summary of Impact Percentages Table 12 31
Computed Stresses . .Table 13 31
PREFACE
This bulletin is published \viih llic consent of the
United States Bureau of Public Roads and the Iowa
State Highway Commission, cooperating parties with
the Iowa Engineering Experiment Station, as a prog-
ress report of the~ 1922 impact studies, conducted
on the Skunk River Bridge on the Lincoln Highway
near Ames, Iowa.
Tne data herein given is to be considered, not as
a piece of finished work, but as a mere beginning of
the study. It is published at ihis lime with the pur-
pose of making available for general use the results
of the progress to date and to invite such discussion
as may serve as a guide in conducting future in-
vestigations.
PRELIMINARY IMPACT STUDIES SKUNK RIVER BRIDGE ON
THE LINCOLN HIGHWAY NEAR AMES, IOWA
Introduction. The work was undertaken as a cooperative project
of the United States Bureau of Public Roads, the Iowa State Highway
Commission and the Engineering Experiment Station of Iowa State
College.
The structure selected was the Skunk River bridge on the Lincoln
Highway one mile east of Ames, Iowa, a 150-foot span, 20-foot road-
way, through riveted steel highway bridge with a 6-inch concrete
floor on steel stringers. An elevation of the bridge is shown in Fig. 1.
Although the object was primarily to investigate the effect of im-
pact of trucks and tractors upon the particular structure, two related
problems naturally presented themselves : first, the distribution of
stress throughout various members and portions of members and,
second, the comparison of a number of different instruments and an
endeavor to determine which ones would be the most suitable for
future work..
Organization. The Bureau of Public Roads furnished the services
of J. W. Hewes and Frank Kerekes throughout the season and E. B.
Smith, senior testing engineer, for a few days in September during
which time the new photographic mirror extensometer was used in
checking against the instruments which were used during the working
season.
The Highway Commission was represented by A. H. Fuller, con-
. suiting bridge engineer, who was in general charge and by Herbert
Schmidt and R. J. De La Hunt (each about half time) as observers.
The Commission also furnished the services of E. C. Tripp and other
truck drivers, all of the loads, staging and nearly all of the supplies.
The Experiment Station furnished the services of R. A. Caughey,
who was in direct charge of field and office 'work, and of L. W. Bartow
and W. H. E. Dunham as observers.
Much of the work was necessarily of a pioneer nature and required
patience, as well as ability and good judgment. These qualities were
much in evidence and without them the work would have been of
little value. An appreciation is hereby given all the regular force,
particularly Professor Caughey who has given much time to the
interpreting of the data since the close of the season.
Loads. Two trucks and a caterpillar tractor were used as loads.
Their dimensions and concentrations are shown in Fig. 1. Load A,
consisting of a load of gravel on a 3%-ton Liberty truck, provided a
total load of nearly 15 tons with about 12 tons on the rear axle. Load
B, another 3%-ton Liberty truck was loaded with kegs of nails and
anvils to a total of about 11 tons with a little over 8 tons on the rear
axle. Load C was a 10-ton Holt caterpillar tractor.
In investigating the floor system loads A and C were used separately
and A and B together. For the trusses the loads were A and B to-
gether and a train consisting of C pulling B and A.
The maximum speed of A and B was about 13 miles an hour and
C about 5 miles an hour whether alone or with the train.
Instruments. 1. Four direct reading West extensometers with 20-
inch gage. Loaned by department of civil engineering, Iowa State
College.
2. One Turneaure recording extensometer with gage from 48 to
54-inch. Loaned by Dean F. E. Turneaure of University of Wisconsin.
3. Eight stremmatographs (recording on smoked glass disks) with
20-inch gage. Loaned by Prof. A. X. Talbot of Universityof Illinois.
4. One Bureau of Public Roads photographic mirror extensometer
with 14-inch gage. Brought out and used by E. B. Smith of Bureau
of Public Roads September 18 to 22.
5. One "max" compression instrument of Bureau of Public Roads
with 10-inch rag< i . Brought out and used in laboratory only by E. B.
Smith, Bureau Public Roads, September 18 to 22.
6. Two "max" compression instruments loaned by Prof. C. T.
Morris of Ohio State University; gage about 24-inch. (Used a few
days only at end of season in field and laboratory.)
. 7. One combination instrument arranged by using the stremma-
tograph smoked glass disks on the frame of a West extensometer. 20-
inch gage.
8. One West strain <ra<re 20-inch gage for checking distribution of
stress in stringers, floor beam and hip vertical. Loaned by A. II. Fuller.
9. One Berry strain gage, 20-inch gage used as in 8. Loaned by
department of civil engineering, Iowa State College.
Space will not be taken for extended description of the instruments.
The Turneaure extensometer. which has been used so extensively for
impact in railway bridges is described in transactions of the Am. Soc.
C. E. Vol. XLI (1899) p. 412, and in proceedings of the Am. Ry. Eng.
Assoc., Vol. 12 (1911), Part 3, pp. 1S.V202. The stremmatographs
developed for measuring the stress in railroad rails by the special
committee of this society to report on stresses in railroad track are
described in transactions AIM. Soc. C. K. Vol. LXXXII i IDlS), p. 1224.
The West extensometer consists of two yokes about 20 inches apart
held together by a constant distance bar connected (with the neces>arv
freedom of motion) to the center of each yoke. A forked end of each
yoke is fastened to the bridge member by means of two hardened
screws. The movement, due to the deformation of the member. i>
transmitted to the other ends of the yokes where it is read directly
by means of a Last Word Dial. This instrument was developed in
the instrument shop of the department of civil engineering at Lafayette
College by M. L. West, mechanician, under the direction of the author.
A general idea of all the instruments and manner of attachment
are given in Figs. 5 to 8.
Field and office work. The greater part of the field work was
done during the months of July 'and August, 1922. The office work
necessary to keep the notes worked up was cared for, usually, by
keeping the force inside for a day or two after two or three days
in the field.
Observations were taken for four different conditions of the load :
first, at rest for basic static readings ; second, runs for various speeds
on the clean floor; third, runs for speeds up to the maximum (about
13 miles an hour) over a 1-inch obstruction (usually Ix2-inch cast
iron) ; fourth, runs up to about half speed over a 2-inch obstruction
(usually a timber, 2x4-inch.) All of these runs in each series were
made with the same setting of instruments.
Results. As it has been impossible to work up all of the data
into final form with the available force and impractical to do it in-
side of several months with any force that could be expected, a few
of the most outstanding and significant results have been gathered
together and analyzed in a preliminary way so as to give an early
indication of the trend of the summer's work.
In a preliminary report presented to the three cooperating in-
terests were given individual readings of about 400 of the 2,500 runs
comprising the season's work. These have been condensed to about
200 runs for this bulletin and are given in Tables I to VIII. Averages
are made for the static loads and for speed runs under various condi-
tions. The results show many inconsistancies. These are due to a
number of causes, such as condition of the tires, position of the trucks,
irregularities of the floor surface, the position of obstructions in addi-
tion to errors of observation, vibration and inertia of the instruments,
etc. On the other hand certain characteristics are so persistent that
the interpretation of results becomes a matter of determining the
degree of precision rather than the general indication.
Comparison of instruments. The West extensometers and the
stremmatographs were calibrated in standard testing machines on a
steel bar in tension for relation between actual unit stresses and the
reading of the instruments, and on the vibrating apparatus of the
Bureau of Public Roads for inertia and vibration. The West instru-
ments showed a remarkably satisfactory behavior in each respect
and apparently assures results which have a precision up. to that with
which the needle of the dial can be easily read.
"~ The stremmatograph also gives evidence of being reliable, when
working normally, but to a much lesser degree of precision. The
time required for adjusting the disks in the field and reading them
in the office would apparently produce fewer data with less precision
(particularly for the lower stresses) than the same time devoted to
either the West or the Turneaure extensometers.
No suitable testing machines, or other apparatus were available for
calibrating the Turneaure extensometer in direct tension or for
inertia or vibration. It was calibrated, in connection with all the
-*-Wes+ ^o Amos
YTTTTiv
Eoe+
8 ponpls of ie>'-9"
Spoo
ELEVATION OF TEST
Load *C
Lood B
IMPACT LOADS
Load A'
Fig. 1 Elevation of Skunk River bridge and diagrams of impact loads used, showing
concentrations.
DISTRIBUTION OF STRESSES
IN STRINGERS OF WEST APPROACH SPAN TO I50' X 20'HT. BR.
UNDER TRUCK A-15 TONS AT REST
9-lines of IB" 14 55* Is
8 spacer p-F 2-5/ Appro*. \<2>'-7*
Tola I O bserved Stress
Posi+ion I - ZIZOO*/a
Z l)300
5 19200
A- I91OO
Total Computed Stress
Stringers only AO.ZOO.
Including T-Beom action
of Concrete 35,?>OO
Fig. 2 Stress distribution diagram for stringers of west approach Span. Truck A
at rest.
10
DISTRIBUTION OF STRESSES
IN STRINGERS OF WEST PANEL OF 150' X 2OHTBR.
UNDER IO-TON HOLT CATERPILLAR TRACTOR AT REST
2-l.nes of IO*l53*Cs
7-l.ncso-P I
8 - SpQcee cyP Z'-<o" -2O'-O"
Observed
Position I - Incomplete
Z- -ZS.GOO
3- 26.3OO
4- 29,300
To+al Com puled
Springers olone 38.9OO-
Incluaing T'Boam action
o-F concre-fe 34, TOO
Fig. 3 Stress distribution diagram for stringers of west panel. 10-ton Holt caterpillar
tractor at rest.
11
DISTRIBUTION OF
IN STRINGERS OF WEST PANEL OF l50'x20'HT BR
zo'-o" UNDER TRUCK A-15TON AT REST
- lines of I0" x 15.3* La
7- linos of 10"* -254*13
8 -Spaces of Z'-S"- 2O'-O"
Totol Observed Stress
Position -I- 37500 */a
-Z- 3G500 -
-3- 35300 -
-4- 35100 -
Tofol Cornpuiad Stress
Stringers only 52,100 ,
Including T- Beam ocl"i'on
of concrete 45.4OO.
Fig-. 4 Stress distribution diagram tor stringers of west panel. Truck A at rest.
L ,:
other ones, on the tension flange &. an I-beam in flexure. As all of
the readings were dependent upon the initial tension in the connecting
rod which was not constant, the calibrations have not yet been carried
far enough to insure confidence in the precision of the results. Still
it seems apparent that this instrument has added materially to the
confidence which may be placed on the season's work as a whole. It
has furnished significant data for high impacts resulting from the
blows of the truck wheels in passing over obstructions. This is par-
ticularly helpful where it was impossible to read the dial on the West
instruments as illustrated in Table II for runs 1798 to 1602 on
stringers.
The fact that the dial could not be read indicates a much higher
impact than in the preceeding runs where it could be read. The
Turneaure not only gives the same indication but suggests a value.
It will be noticed that the impact percentages are usually in closer
accord than the unit stresses and, as impact is the factor most needed,
the matter of calibration under static stress loses some of its apparent
importance.
The continuous vibration produced by the caterpillar tractor was
reflected in the erratic behavior of the instruments of which the West
seemed to be the most affected. Calibration has not yet been carried
far enough to secure a satisfactory interpretation except that this
vibration seems more or less distinct from the inertia due to single
blows and of greater effect at times and that many of the suggested
impacts are doubtless too high.
Results Stresses and impact. The average impact percentages from
Tables I to VIII have been tabulated in Tables IX, X and XI after
using some liberty in combining the results of two or more instruments
on the same member. These are recorded first by instruments and
from these values a figure has been suggested as a probable impact
percentage for the member and the loading.
The basis for the interpretation of these impacts will be illustrated
by a few references. In Table I for the second stringer, truck B
was at rest and A moving; while in Table II both were moving.
The apparent inconsistencies between the two sets of runs where the
impact is more for the 1-inch obstruction and less for the 2-inch when
both trucks are moving may be due to the possibility that in the first
instance the maximum effects of both trucks were simultaneous, and
in the second were timed so as to conteract each other. The brackets
in Table IX indicate impacts beyond the practicability of reading the
dial of the West instruments as indicated in Tables I and II, and thus
serve to substantiate the high impacts of the Turneaure. For the
floor beams with both trucks, Table III, there is a marked contrast
between the readings of the West and the stremmatograph for the
clean floor and the 1-inch obstruction and a close check for the 2-inch
obstruction. The results of the West are given greater weight for
the first two conditions because of general dependence for the lower
14
impacts and the fact that the impact indicated by the stremmatograph
for the clean floor is far greater than any other checked result for the
floor without obstruction.
For the hip vertical, Ul LI, (Table IV) the West and the Turneaure
check nicely for the clean floor but only the Turneaure yields readable
results when obstructions are placed. Both instruments however indi-
cate very high impacts for this member, a result which was also ap-
parent in a few observations made in 1921.
In the west approach span there is a remarkable coincidence be-
tween the West and the Turneaure instruments on the second stringer
Fig. 6 Set-up of several instruments on the bottom flanges of stringers. 1. 2, 3, 4.
and 5, stremmatographs. 6, Turneaure extensometer. 7, 8, and 9, West extensometers.
(Table Vll) and large discrepancy between the West and the strem-
.matograph on the first or outside one (Table VIII) especially for the
1-inch obstruction. The general tendency to give the greater weight
to the West is counterbalanced by the fact that it is an unusually high
reading and therefore does not inspire the same degree of confidence
as do the IOAVCI- ours. Therefore an average figure is used.
The "probable percentages" of impact, previously referred to,
have been taken from the pages just under discussion and tabulated
in Table XII after again taking liberty in combining various results
for the same class of members and for the two different obstructions.
15
In admitting that these values hayje been selected by judgment, based
upon observation, rather than by true averages it is pointed out that
some of the original data have been given and that anyone interested
may draw his own conclusions.
The condensed results will be discussed separately for clean floor and
for obstructions. For the clean floor there is no indication of impact
above 15 per cent for the floor system and hip verticals of the main
span. The suggestion of higher impact for the truss members and for
the stringers of the approach span may be due to the cumulative effect
as the load travels a greater distance. The high values for reverse
l (1 ig. 7 Instruments on hip vertical, Ul LI.
South truss, West end. 1, Bureau Public
Roads photographic extensometer. 2, Turn-
eaure extensometer. 3 and 4, West extenso-
meters.
Fig. 8 Instruments on diagonal, L6 U7.
North truss, east end. One Turneaure exten-
someter, two stremmatographs and three West
extensometers.
stresses in web members (see Tables V and VI) are based upon fewer
data than \most of the other results and need further verification.
They are sufficiently persistent, however, to warrant careful investiga-
tion at a future time.
It may be well to call attention to the fact that full speed (about 13
miles an hour) was used for 1-inch obstructions but that it was
thought prudent to keep the speed to about half that amount when
the 2-inch obstruction was used. The impacts were somewhere near
the same for the two cases. There are many indications above 50
per cent and several above 100 per cent.
16
The foregoing discussion has been based upon percentages of im-
pact which are averages of all runs for each condition. As a matter
of interest an average of the two highest stresses has been added in
each instance. When the two averages differ to any great extent the
higher indications are probably from an unusual combination of
conditions which sometimes occur. These should be recognized and
provided for but possibly not by the usual unit stresses.
Too great reliance should not be placed on high individual results
recorded on such members as stringers and hip-verticals which re-
ceive a very direct effect from sudden blows, such as used in these
experiments. Difficulties due to inertia effects in the instruments and
in securing reliable readings under such conditions, make the problem
a very difficult one and the values here recorded should be considered
in the light of these facts. The use of the mirror extensometer of the
Hureau of Public Roads in future experiments promises to throw
much light on this particular phase of the problem.
It seems evident that the percentage of impact on a highway bridge
is likely to be small when the floor is clean and the tire in good condi-
tion but that a considerable impact is apt to 'occur with defective
solid tires, chains, blocks of wood, small pieces of rock and other
obstructions which may be encountered.
More study and mature judgment are necessary in determining the
impact which should be provided for within the usual unit Stresses
and also for the higher unit stresses which may he allowed for the
high impacts which are likely to occur under certain conditions but
at long intervals.
Results Distribution of stresses. (Stringers). Figs. _>. :', and 4 show
the distribution of observed static stress due to loads A and T among
the stringers of the main span and due to load A on the stringers
of the approach span. As a means of comparison of the total stresses
for the various positions of the leads among themselves ami with
computed stresses, the sums of observed stresses are given, for each
position, and compared with the total stresses which would be in-
dicated by the usual methods of computation. To the computed unit
stresses under the usual assumption that the steel stringers carry all
of the load as simple beams have been added the computed unit
stresses under an imperfect T-beam action. These computations were
ingeneously made, by Prof. R. A. ('anglicy, after the neutral axis had
been located by strain gage readings under the assumption that tin-
compression in the concrete floor plus the compression in the steel
stringers would equal the tension in the stringers. Sufficient data have
not been secured to determine to what extent the differences be-
tween observed and computed stresses may be due to partial con-
tinuity of the stringers.
An analysis of the results show, for the stringers of the main span,
that when the live load is placed at the center of the roadway the
greatest stress in one stringer equals about one-eighth of the total com-
17
puted stress and about one-sixth &f the total observed stress ; and that
when the load is placed near one side that the stringer nearest the out-
side one is stressed about one-fifth of the total stresses as indicated by
computations and about one-fourth of those shown by the measure-
ments.
The outside stringers are channels of somewhat more than half
the strength and stiffness of the intermediate I-beams. The observa-
tions bring out the inadequacy of these outside stringers to give the
necessary support to the second stringer and suggests that, in order
to keep the stresses and the deflection of the outside two stringers
within the range of the intermediate ones, more material perhaps,
rather than less, should be placed in the outside ones.
It might be well to state that the stresses given for stringer distri-
bution were not taken altogether from the runs which have been in-
cluded in this report but also from some special ones which were made
for the purpose.
No stress distribution readings were taken on the stringers when
two trucks were on the panel. The stresses due to two trucks, parallel,
may be anticipated by adding the stresses in each stringer due to one
load separately on each side of the roadway. Additions have been
made for the two different loads on the main span and for the one
load on the approach span. In each case these figures approach, bur
do not exceed, for the five center stringers, 25 per cent of the observed
stress due to the entire load. Under truck A the second stringer (the
one next to the outside channel) of the main span would evidently
carry between 25 per cent and 30 per cent of one entire truck, but
as suggested above, this is a situation which could be relieved in de-
sign. On the approach span where the outside stringer is the same
size as the others the maximum load on the second stringer, with two
loads on the span, appears to be just about one-fourth of one load.
In addition to the distribution of load among the different stringers
there is a distribution between the flanges of each stringer which
may be uniform or quite irregular depending upon the position of the
wheel (which was not always known within a few inches) and other
causes. The apparent results are influenced by instrumental varia-
tions as well as the actual distribution.
Results Distribution of stresses. (Floor beams.) The distribution
in the two bottom flanges of the one floor beam investigated seemed
good for static loads, and also for dynamic stresses except as indicated
by stremmatograph No. 4 in runs 1868-93 and stremmatograph No. 12
in runs 1868-77, Table III. It does not seem justifiable to charge the
floor beam with unequal distribution because during the same runs
the West instruments, generally more dependable, indicated a high
degree of uniformity.
Results Distribution of stresses. (Hip verticals.) All the infor-
mation is in agreement to the effect that the inside portions of the
hangers are considerably more stressed than the outside and also that
18
the impact in hangers is uniformly high. In the hangers of this
structure, however, no unit stresses were found high enough to cause
concern. It is perhaps well that the usual practice prevails of using
excess material in order that these members may have the same
general dimensions as the intermediate posts.
Results Distribution of stresses. (Truss members.) The tendency
in the hangers for greater stress in the inside of the members is also
apparent in all of the intermediate posts and the diagonals. It is less
however in the diagonals than in the hangers and still less in the
intermediate posts.
Results Computed stresses. In Table XIII are given, for com-
parison, the computed stresses and unit stresses in the members and
for the loads on which readings were taken.
Results Strain gage checks. No systematic checks were attempted
by use of the strain gage though a number of static readings were
taken on the second stringer in the west panel, the floor beam at LI
and the hip vertical, ri-Ll, on west end of north truss. Xo thorough
comparison has yet been made of the results with those from the
extensonieters ; and the strain rare notes are not incorporated in this
preliminary bulletin. They an- available, however, for any further
study which may be made. Sufficient consideration has been given
to them to make it apparent that they check, in a general way, the
magnitude and the distribution of the static stivssrs obtained by the
other instruments. These results have been of particular service al-
ready in locating the neutral axis of the stringers.
Bureau of Public Roads new photographic mirror extensometer. The
season's work was planned with the expectation that the new photo-
graphic mirror extensometer designed and built by the IJim-aii of
Public Roads would be available. However it did not arrive on the
ground until the active field work was closed. E. B. Smith, senior
testing engineer for the Bureau, who had a large part in the develop-
ment of the instrument, kindly consented to bring it for comparison
with the instruments used during the season and reached Ames on
September 18. It was used in comparison with all of the other in-
struments on the bridge and for laboratory calibrations September
18, 19 and 21.
One of the most interesting parts of the laboratory work was a com-
parison, on the flanges of a 12-inch 31.5-pound I-beam in flexure, of
the new instrument with the Turneaure, two Wests, a stremmatograph,
two Morris "max" compression instruments and a ''max" instrument
brought out by Mr. Smith. These are shown in Fig. 5. Fig. 7 shows
the photographic instrument, the Turneaure and two West's on the
west hip vertical of the south truss of the Skunk River bridge. The
readings show a close comparison of the photographic and West in-
struments on the northwest flange and of the Turneaure and a West
on the northeast flange but a decided difference in impact between
19
the two flanges when obstructions were used. It seem* ^robable that
the obstructions were so placed that the blows of the truck wheels
were applied slightly to the east of the center of the floor beam (the
far side) and that the effect of thesje blows was greater on that side
of the hanger. These conclusions are based upon five runs over a 1-
inch block and five over a 2x4-inch plank, which are reasonably con-
sistent. Four runs on clean floor indicate, rather consistently, an
impact just below 20 per cent, while, for the obstructions less than
75 per cent is indicated for the northwest flange and over 100 per cent
for the northeast one.
Possibilities for future work. It is no less evident now than when
the season's work was started (and perhaps no more so) that the
problem would not be completed in 1922, in fact,, that it would be just
nicely begun. Assuming that the problem should be followed up in
a truly scientific manner and laws or even empirical formula deduced
the work would naturally include :
A. Investigations for:
1. Other span lengths.
2. Other types of structures.
3. Other floor surfaces.
4. Other loads with various tires.
B. Certain studies to be made upon this and other structures
such as :
1. The effect of speed.
2. The effect of tractor treads.
The effect of the condition of solid tires.
The effect of sudden starting and stopping.
5. Stress distribution to be checked against computed second-
ary stresses.
6. The relation between the intensity of a blow such as may
be struck by a truck wheel and the resulting stresses in
a structure. This may make it possible to take advantage
of any work, such as that recently done by the United
States Bureau of Public Roads, which gives a quantitative
measure of the impact of a vehicle. (The present work
shows that high stresses, and perhaps the highest ones in
stringers, floor beams, and hip verticals result from a
single blow of a rapidly moving truck passing over an
obstacle.)
7. The relation between impact and the roughness of floor
pavement. (Profiles showing roughness of floor of Skunk
River bridge were taken by the Engineering Experiment
Station force after the close of the season's work. No de-
tailed examination has yet been made of the profiles but
it has been noted that the roughness was more pronounced
over the first floor beam on the profile 1 foot from south
20
curb than at 2 feet. It seems possible therefore that that
is one reason why greater impact was observed in the runs
where the outside wheels were 1 foot from the curb than
when the distance was 2 feet.)
Instruments for future work. Every instrument used during the
season has contributed to the value of the work. It has been pointed
out, however that there was considerable variation in the consistency
of results and in the time consumed in taking and in working them up.
The season's work has brought out the desirability of two distinct
types direct reading and self recording. A recording instrument has
naturally the greatest value as it gives a graphic picture of stress varia-
tions during the passage of a load. Direct readings are almost in-
dispensable in giving, instant indications of the intensity of stresses,
thus, making it possible to "feel the way" and avoid conditions of
overs! ress and to serve as a check upon the graphic record. The possi-
bilities of the personal factor in making occasional faulty set-ups, of
instruments getting otit of adjustment, of neglect to make the proper
imlentification of any particular reading and other causes are so
great that occasional if not constant, checks should be made by differ-
ent instruments.
For a recording instrument the photographic mirror extensometer
of the Bureau of Public Roads appears to be the most satisfactory
and it seems desirable that they be constructed in sufficient quantity
so that a number of them may be available for the coming season.
For direct readings, the West has given the most consistent results
for static loads and low impacts. Recent trials indicate that by
choking the dials high impacts as well may be accurately observe* 1.
No one instrument combines the factors of approximate immediate
results, positive identification, quick computations and permanent
record as the Turneaure. It seems that the gage length is too long
and the force necessary to put the instrument in action is too great
to give results as high in precision as the ones just mentioned. Yet,
it is an instrument which should be welcomed upon any impact in-
vestigation.
The Morris "max" instrument while slower in action and less pre-
cise in results would be of special value when large impacts were
under observation and the other instruments were not yielding con-
sistent results.
The stremmatograph, while perhaps the most cumbersome in use,
and the less precise for small stresses, might be even the best available
for certain high stresses under severe impact conditions. The combi-
nations of the stremmatograph and the West, as mentioned on page
13 might well be considered in this connection.
Strain gage readings for distribution of stress under static loads will
always add a finish to any extended series of stress measurements.
Number of instruments. It would be very nice, in work of this
nature, to have at least eight instruments on each of the thirty odd
21
members of each truss and at, v least two on each of the eighty-one
stringers and floor beams with a few defectometers and other special
instruments thrown in for good measure. Then assuming them all
to work perfectly all the time, with a few applications of each of a
few different loads, a very interesting and rather complete story would
be told of the elastic behavior of the structure.
This is manifestly impossible. Four instruments, one for each of
the four flanges of the ordinary member seems to be the minimum
number which would be at all efficient; and with four the efficiency
would be low. It would seem desirable that no party be sent out
with less than eight of which four or more be of a recording type.
TABLE I. STRINGER 2 FEET NORTH OF SOUTH CURB
(10 in. 25 Ib. I-beam)
Load Truck A, headed west, moving-, south wheel 1 ft. from south curb.
Truck B, headed east, at rest, north wheel 2 ft. from north curb.
Instruments All on center line of stringer span.
Gage of Instruments West 20 in. Turneaure 48 in.
Run
Speed
Obstruction
North Flange
South Flange
Turneaure
West No. 1
West No. 2
Stress
% Imp.
Stress
% Imp.
Stress
% Imp.
1580
1582
1584
1586
Average
static
11,300
10,700
10,800
11,000
9,300
9,300
9,300
9,300
9,300
9,600
9,300
9,400
9,600
11,000
9,500
1579
1581
1580
1585
1587
Average
Av. two
12.8
10.7
10.7
9.1
9.8
10.6
highest
None <
[
12,300
12,500
11,600
12,800
12,500
12,300
12,700
12
15
9,300
9,800
9,700
3
5
10,200
9,900
10,200
9,900
6
7
9,600
9,800
10, 100
10,200
11,600
14,500
13,100
1590
1501
1592
1593
Average
Av. two
11.7
16,0
10.7
12.8
} I"x2"
1 south
f wheel
Truck A [
15,300
15,300
14,700
14,700
36
39
13,100
33
38
45
12.8
highest
15,000
15,300
13,100
13,100
13,800
1598
1599
1600
1601
1602
Average
Av. two
9.1
9.8
10.7
11.7
9.1
2"x4*
south
wheel
Truck A
19,500
21,500
23,600
23,100
22,000
100
112
Impossible
to read de
finitely
10.0
highest
21,900
23,400
22
TABLE II. STRINGER 2 FEET NORTH OF SOUTH CURB
(10 in. 25 Ib. I-beam)
Load Truck A, south wheel 1 ft. from south curb.
Truck B, north wheel 2 ft. from north curb.
Both trucks headed west, moving parallel
Gage of Instruments West 20 in. Turneaure 48 in.
Instruments Center line of span.
Run
Speed
Obstruction
Noith Flange
South Flange
Turneaure
West No. 1
West No. 2
Stress
% Imp.
Stress
% Imp.
BfMI
% Imp.
1620
1621
1622
1623
Average
static
11,200
10,800
11,200
10,600
11.700
11,100
10,300
10,100
10.400
10,400
10.400
10,300
1,900
9,900
9,900
9,600
IH.IMIII
9.900
1624
1630
1632
1633
1635
Average
Av. two
9.1
10.7
12.8
10.7
12.8
None I
13,200
11,600
11.900
13,800
12,300
11
16
11,800
11,300
10,500
11,700
10
14
10.200
9,900
10,400
3
4
11.2
highest
'12,400
u.ooo
11.300
.11.800
10,200
10.300
1645
1646
1647
1648
1649
1650
1651
1652
Average
Av. two
14.2
10.7
12.8
12.8
11.7
9.8
9.8
14.2
I*x2'
north
wheel
Truck A
19,000
16,000
11,900
18,900
18,100
17.100
17.800
17.200
17,000
18,700
53
67
Impossible
to lead de
finitely
12.0
highest
1653
1654
1655
1656
Average
Av. two
6.4
6.1
9.8
9.8
8.0
highest
2*x4"
south
wheel
Truck A
16.400
16,900
21,600
16,800
60
72
14,800
14.800
43
43
11,600
12,700
11,700
22
24
17,900
19,200
14.800
14,800
12,000
12,200
23
TABLE III. FLOOR BEAM AT LI
(24 in. 80 Ib. I-beam)
Load Trucks A and B headed west parallel.
Truck A, south wheel 2 ft. from south curb.
Truck B, north wheel 2 ft. from north curb.
Instruments All 1.5 ft. south of center line.
Gage of Instruments All 20 in.
Run
Speed
Obstruc-
tion
East Flange
West Flange
West No. 1
Strem. No. 4
West No. 2
Strem. No. 12
Stress
% Imp.
Stress
% Imp.
Stress
% Imp.
Stress
% Imp.
1864
1865
1866
1867
Average
static
6,500
6,500
6,700
6,500
6,500
7,400
6,700
6,800
6,700
6,200
6,400
6,400
6,600
6,900
6,400
(6,600)
1868
1869
1870
1871
.1872
1873
1874
1875
1876
1877
Average
Av. two
9.8
10.6
12.8
9.8
12.8
11.6
9.8
12.8
C.8
None
7,300
7.400
7,500
7,200
7,200
7,100
7.200
7,000
7,400
7,200
10
14
8,300
11,600
11,600
9,500
10,000
11,600
11,600
11,200
10,800
55
67
7,300
7,500
7,300
7.100
7,000
7,300
7,100
7.400
7,400
13
17
7,500
7,000
12.500
10,000
8,300
36
72
11.1
highest
7,200
7,500
10,700
11,600
7,300
7,500
9,000
11,300
1886
1887
1888
1889
1890
1891
1892
1893
Aveiage
Av. two
10.6
12.8
12.8
9.8
8.5
10.6
9.8
12.8
North
wheel
( Truck ,
( A
over
1"
9,400
9,900
8,700
7,000
9,000
8,700
8,700
33
46
13,700
13,300
10,800
10,800
11,600
13,300
14,500
14,100
85
106
8,800
9,100
8,700
8,700
7,300
8,800
8,000
8,000
31
40
8,300
9,100
8,300
10,000
10,400
7,500
35
55
10.9
highest
8,800
9,700
12,800
14,300
8,400
9,000
8,900
10,200
18S9
1900
1901
1902
1903
Average
Av. two
7.9
7.1
7.5
7.1
7.5
7.4
highest
North
wheel
Truck
A
over
2"x4"
8,600
9,000
8,600
7,100
7,000
23
33
10,000
8,300
8,100
7,100
22
33
9.100
8,700
8,800
7,700
7,300
30
40
10,000
8,700
7,900
9,100
35
45
8,100
8,800
8,400
9,200
8,300
9,000
8,900
9,600
1904
1905
1906
1907
1908
Average
Av. two
7.5
6.4
5.8
6.7
6.4
] Both
wheels
of A -
over
2"x4"
8,700
8,600
8,600
8,400
9,100
32
35
8,300
8,500
10,000
8,500
10,000
9,100
10,000
32
45
9,000
9,400
9,100
9,400
10,200
47
53
10,600
8,300
11,500
9,300
52
68
6.5
highest
8.700
8.900
9,400
9,800
10,000
11,100
TABLE IV. HIP VERTICAL Ul LI SOUTH TRUSS WEST END
(2 channels 8 in. x 11.5 Ib.)
Load Truck A, headed west, south wheel 2 ft. from south curb.
Truck B, headed west, north wheel 2 ft. from north curb.
Instruments Turneaure lower point 7.50 ft. above LI.
West No. 3 lower point 8.75 ft. above LI.
West No. 4 lower point 8.75 ft. above LI.
Gage of Instruments West 20 in. Turneaure 53 in.
Run
Speed
Obstruction
N. W. Flange
S. \V. Flcnge
Turneaure
West No. 4
West No. 3
Stress
% Imp.
Stress
% Imp.
Stress
% Imp.
1864
1865
1866
1867
Average
static
4,500
4,400
4.500
4.400
4,400
4,400
4,500
Mm
2,800
2,500
2,000
2,300
4,500
4.400
2.600
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
Average
Av. two
8.5
9.8
10.6
12.8
9.8
12.8 ,
11.6
9.8
12.8
9.8
None
5,200
4,900
5,400
5.100
,000
,600
,800
,600
,000
.700
10
19
4,400
4.900
4.500
4,900
l.MMI
5,200
1,800
4.800
5,100
4,600
9
18
2,900
2,900
2,800
2,800
2,900
2,600
8
11
10.8
highest
4,900
5,300
4,800
5,200
2,800
2,000
1878
1879
1880
1881
Iss2
1883
ISM
1885
Average
iAv. two
12.8
9.8
9.8
11.6
11.6
9.8
10.6
9.8
I"x2*
south
wheel
Truck A
8.400
:.">,,
B,00
9,900
7.700
6,700
7,600
8,600
85
110
Impossible
to read de
finitely
10.7
highest
8,200
9.400
1894
1895
1896
1897
1898
Average
11.6
11.6
9.8
9.1
11.6
10.7
2*x4*
south
wheel
Truck A
11,600
9,200
6,500
7,800
12.400
114
Impossible
to read de
finitely
9,500
25
TABLE V. DIAGONAL L5 U6 NORTH TRUSS EAST END
(2 angles 2V 2 x 3 x 5-16 in.)
Load C, B, A train 2 ft. south of north curb headed west.
Instruments "West No. 2 and No. 3 lower point 12.5 ft. above L5.
West No. 4 15.5 ft. above L5.
Turneaure 11.5 ft. above L5.
Gage of Instruments West 20 in. Turneaure 48 in.
NOTE: All figures not preceded by a minus ( ) sign are plus (tension).
Run
Speed
Obstruc-
tion
North Angle
South Angle
West No. 3
West No. 4
West No. 2
Turneaure
Stress
% Imp.
Stress
% Imp.
Stress
% Imp.
Stress
% Imp.
2198
2199
2200
2201
Average
tension
,tatic
4,400
4,900
4,900
4,500
4,600
4,800
4,600
4,500
4,800
5,400
5,400
5,400
5,200
5,200
5,200
5,300
4,700
4,600
5,300
5,200
2210
2211
2212
2213
2214
2215
Average
comp.
static
2,300
2,300
2,300
2,300
2,200
2,300
2,300
2,300
2,300
2,300
2,300
2,300
2,200
2,200
1,800
"1,900
2,000
2,000
2,000
1,000
1,000
1,000
-2,300
2,300
1,000
2202
2203
2204
2205
2206
2207
2207
2208
2208
2209
2209
Average
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
None
5,200
5,500
5,500
6,400
4,800
4,100
4,800
3,500
4,900
2,800
5,500
11
6,500
7,000
6,100
6,400
6,200
4,200
6,100
4,200
6,100
3,900
6,100
37
5,800
5,700
5,800
5,800
6,100
2,900
5,800
2,500
5,500
2,900
5,800
10
6,500
6,700
6,600
6,800
7,000
6,200
6,400
27
tension
5,200
6,300
5,800
6,600
2217
2218
2219
2220
2221
Average
5.0
5.0
5.0
5.0
5.0
tension
All
wheels
over
2"x4"
atL5
6,000
6,000
6,200
5,500
6,100
28
6,500
4,100
7,000
3,800
7,100
4,200
6,500
3,600
6,200
4,100
46
2,600
6,100
-2,900
6,200
2,600
5,800
7,300
19
6,600
7,800
6,800
7,400
7,200
38
27
6,000
6,700
6,300
7,200
2222
2223
2224
2225
2226
2227
Average
5.0
5.0
5.0
3.0
3.0
4.0
tension
All
wheels
over
2" x 4"
atL6
[
-^,600
4,400
4,900
6,200
5,100
5,100
5,800
5,100
5,500
5,100
5,800
5,700
5,800
5,500
4,800
5,100
4,400
20
2,900
5,800
2,900
5, SCO
2,600
5,800
10
1,700
6.200
2,600
6,800
2.000
6,700
1,600
6.500
1,600
6,500
1,100
6,300
5,500
5,800
6,600
TABLE vi. POST UG LG NORTH TRUSS EAST END
(2 channels 8 in. 11.5 Ib.)
Load Train C, B, A, headed west 2 ft. from north curb.
Instruments West, lower point 9 ft. above L6.
Turneaure, lower point 8 ft. above L6.
Gage of Instruments West 20 in. Turneaure 48 in.
NOTE: All figures not preceded by a minus ( ) sign are plus (tension).
N. E. Flange
S. E. Flange
S. W. Flange
N. W. Flange
Run
Speed
Obstruc-
West No. 1
West No. 2
Turneaure
West No. 3
West No. 4
Stress
% Imp.
Stress
%Imp
Stress
%Imp
Stress j%Imp
Stress
%Imp
2166
2,600
2,300
2,800
2,300
1,700
2168
2,800
2,800
2.900
1.900
1,600
2169
2,600
2,800
2,700
1,900
1,900
2175
2,300
-2,800
2,700
1,900
2,000
2176
1,900
2,300
2,700
1,600
1,700
2177
2,600
-8,600
2,800
1,900
1,700
2178
2,000
2,500
2,700
1,700
1,600
Av.
comp.
sta.
2.300
2,600
2.800
1,900
1.800
2179
1,500
2,200
2.400
1,000
2,200
2180
2,200
2.700
1,200
2.300
2181
400
2,200
2.600
1,200
2,200
2182
600
2.200
2,800
1,200
2,300
Av.
tens.
sta.
800
2.200
2,600
1.200
2,200
2170
5.0
7.500
3,400
3,600
3,300
3,800
8,106
2,800
2,300
2171
5.0
2,900
7.300
3,400
2.900
4,300
3,300
8,600
2,300
2172
5.0
2,300
8.7W
3.400
3.000
4,100
3,200
1,600
1,606
2,000
2173
5.0
2,800
1,300
3.000
2,600
5,100
None
:; :,no
None
:;.:im
1,606
2.200
6,400
2174
5.0
3,000
9,400
3,100
2,900
6.500
3, no
MINI
1,100
i'.:>( MI
2183
5.0
1,000
5,800
3,300
1,500
4,400
2.800
2,900
1,600
2184
5.0
900
7.300
3,600
_'.:,( m
4,100
L'.IKMI
2.600
2,000
2185
5.0
1,000
5.100
4,300
2,800
4,100
2.800
2.900
1.900
Av.
comp.
-3,100
35
3.400
30
-3.000
7
2,100
10
2,400
33
2186
5.0
1,000
7,300
3.700
2.200
4,500
2.800
2.900
-'. i
-2,200
2,600
2187
5.0
900
7.300
3,300
2,900
4,400
All
-3,000
2.900
2,600
-2.600
2188
5.0
wheels
no
7.300
3,100
3,000
4,200
over
3,000
2,900
3,100
-_' HIM.
2,800
2189
5.0
2*x4'
900
8,080
3,300
3.900
4,600
2,900
2,900
3,000
J.
2,800
2190
5.0
700
.V.sim
3,800
3.600
4,200
2,600
2,900
2,900
2,000
-2,000
Av.
omp.
( )
4,300
87
2,900
11
3,000
7
-2.200
16
-2.600
45
2191
5.0
8,000
6,800
5,800
7,200
2,800
2.200
2,200
2192
5.0
7,300
3.800
1,500
6,500
2,800
2,900
2,900
2.000
-2,200
2193
5.0
All
5,800
4,500
4,200
6,500
wheels
2.600
2.900
2,200
2194
5.0
over
7,300
4,800
4,800
5,800
2*x4*
-2,200
2195
5.0
atL6
8,000
6,800
6,500
7,300
2,800
2,000
-2.200
2196
5.0
6,500
3,900
4,100
6,100
-2,000
2197
5.0
7,700
5,200
4,600
7,400
2,800
-2,200
-2.200
Av.
omp.
(-)
2.700
18
2,800
8
-2,900
4
-2,100 10
-2.200
23
TACLE VII. WEST APPROACH SPAN. STRINGER 2 FT. NORTH OF
SOUTH CURB.
(15 in. 80 Ib. I-beam)
Load Truck A headed west 1 ft. from south curb.
Instruments All on center line of span.
Gage of Instruments West 20 in. Turneaure 48 in.
North Flange
South Flange
Run
Speed
Obstruction
Turneaure
West No. 4
West No. 3
Stress | % Imp.
Stress
% Imp.
Stress
% Imp.
2011
5,200
5,300
5,100
2012
5,200
5,500
5,100
2013
5,100
5,500
5,100
Average
static
5,200
5,400
5,100
2014
11.9
6.200
6,700
7,300
2015
11.9
6,200
6,700
6,400
2016
10.8
6,200
6,500
6,100
2017
11.9
6,300
6,700
6,400
2018
11.9
6,000
6,700
5,900
2019
12.5
None
6,000
6,700
5,900
2020
11.4
6,500
7,000
6,500
2021
10.8
6,500
6,700
6,400
2022
11.9
6,300
7,000
5,900
2023
10.8
6,200
6,700
5,800
2024
10.4
6,500
6,700
6,200
2025
11.9
6,600
6,500
5,900
Average
11.4
6,300
21
6,700
24
6,200
22
Av. two
highest
6,600
27
7,000
30
6,900
.35
2026
13.3
7,000
6,800
8,400
2027
10.8
8,000
7,200
8,700
2028
10.4
7,100
8,000
6,400
2029
10.4
6,800
7,200
7,400
2030
11.4
7,100
7,700
7,700
2031
11.4
I*x2"
7,800
8,000
8,700
2032
10.8
south
7,000
7,800
8,000
2033
10.4
wheel
7,200
7,800
7,800
2034
10.4
Truck A
7,100
7,500
8,400
2035
10.4
7,000
8,000
8,100
2036
11.9
7,400
8,000
6,500
2037
11.4
7,100
7,800
8,600
2038
11.9
7,500
8,300
8,000
2039
10.4
7,100
6,700
7,000
Average
11.0
7.200
39
7,600
41
7,300
43
Av. two
highest
7,900
52
8,200
53
8,700
70
2052
5.6
8,000
8,300
8,400
2053
5.6
7,500
8,500
7,700
2054
6.3
2x4"
7,300
8,200
7,500
2055
5.7
south
7,500
7,500
7.500
2056
6.5
wheel <
7,100
7.500
7,000
2057
6.3
Truck A
7,500
8,000
7,500
2058
6.3
7,800
8,700
8,400
2059
7.2
7,200
8,300
7,500
2060
6.8
7,500
8,700
7,700
Average
6.2
7,500
44
8,200
52
7,700
51
Av. two
liighest
7,900
52
8,700
61
8,400
65
TABLE VIII. WEST APPROACH SPAN. STRINGER UNDER SOUTH CURB
(15 in. 80 Ib. I-beam)
Load Truck A, 1 ft. north of south curb headed west.
Instruments Center line of span.
Gage of Instruments All 20 in.
Run
Speed
Obstruction
North Flange
West No. 2
Strem. No. 12
Stress
%Imp.
Stress
% Imp.
2011
3,300
3,300
3,300
2,800
2,800
2.800
2012
2013
Average static
3,300
2.800
2014
11.9
11.9
10.8
11.9
11.9
12.5
13.0
10.8
11.9
10.8
10.4
11.9
None
4.000
4.200
4,100
3,900
4.100
4,100
4,500
4,400
4,500
4,200
1,600
4,500
30
39
3,500
3,100
3,200
3,200
1,000
3,200
3,300
3,400
18
M
2015
2016
2017
2018
2019 . . .
2020
2021
2022
2023
2024
2025
Avenft
11.6
4.300
4.600
3,300
3,500
Averagp two highest .
2026
13.2
10.8
10.4
10.4
11.3
11.3
10.8
10.4
11.0
south
wheels
over
I*x4*
at Mid-
span
5,500
5.9QQ
6,400
6,400
5,800
7,400
6,700
6,800
6,400
7,100
94
115
3,200
4.200
3,700
32
2027
2028
2029
2030
2031
2032
2033
Average
Average two highest
2052...
5.6
5.6
.3
.7
.5
.3
.3
.2
.8
6.2
South
wheels
over
2'x4'
at Mid-
span
4,500
5,400
5.500
5.BOQ
5,700
6,100
5,600
5,500
6,200
70
7?
4,500
Cl
2053
2054
2055
2056
2057
2058 '
2059
2060
Average
5.600
5.900
4,500
Average two highest
20
TABLE IX. PER CENT OF IMPACT IN STRINGERS
South Outside Stringer- 0.5 Ft. North of South Curb
Runs
Speed
Obstr.
Trucks A and B
Truck A
Tractor C
West
Turn.
Prob.
West
Turn.
Strem.
Prob.
West
Turn.
Strem.
Prob.
1707-13
1717-24
1725-8
1787-94
1797-1822
13.4
13.4
6.9
9
106
152
33
160
130
10
100
140
1 in.
2 in.
72
170
112
?
?
Second Stringer 2 Ft. North of South Curb
40-166
8.9
17
13
15
96-172
8.7
1 in.
38
28
30
1579-87
10 6
5
12
10
1590-3
12.8
lin.
35
26
35
1598-1602
10.1
2 in.
( )
100
75
1624-35
11.2
7
11
10
1645-52
12.0
lin.
( )
53
50
1653-6
8.0
2 in.
( )
60
50
1707-13
13 5
4
4
4
1717-24
13.3
lin.
46
40
1725-8
6 9
2 in.
( )
38
40
1787-1801
5.0
200
18
*'
TABLE X. PER CENT OF IMPACT IN DIAGONALS AND VERTICAL POSTS
Diagonals
Number
Runs
Speed
Obstr.
Trucks A and B
Train C, B, and A
West 1 Turn.
West
Turn.
Prob.
U2L3
853-5
860-2
874-5...
691-5
698-700
712-15
708-11
2154-7
2158-65
2202-9
2217-21
2222-7
6.4
6.8
6.9
7.1
8.9
4.7
6.8
5.0
5.0
5.0
5.0
5.0
23
73
90
22
31
65
68
19
82
150
U3L4
2 in.
2 in.
Tin."
2 in.
2 in.
U6L7
L5U6
7
15
20
30
15
3
12
27
38
27
5
15
20
30
2 in.
2 in. L5
2 in. L6
Vertical Posts
U2.L2
917
7.5
20
918-23
6.3
2 in.
50
932-5
6.1
2 in.
70
U6L6
2170-85
5
30
7
95
2186-60
5
2 in. L5
40
7
30
2191-7
5.0
2 in. L6
15
4
U5L5
2234-8
*
5 01
42
20
30
2239-43
5
2 in. L4
110
30
60
2244-8
5.0
2 in. L5
65
10
30
TABLE XI. PER CENT OF IMPACT MISCELLANEOUS
Hip Verticals LI II
Runs
Speed
Obetr.
Trucks A and B
Truck A
TraotorC
West
Turn.
Strem.
Prob.
West
Turn.
Stn-in.
Prob.
West
Turn.
Strem.
Prob.
1831-41
1868-77
1878-85
1894-8
4.8
10.8
10.7
10.7
170
80
105
100
9
170
180
10
85
114
10
100
125
1 in.
2 in.
Floor Beam AT LI
1853-63
4 7
70
70
1868-77
11 1
12
45
15
1886-93
10 9
1 in.
32
60
35
1809-1003
7 4
2 in
27
29
:w
1904-8
6 5
2 in
40
42
40
West Approach Span South Outside Strintfer
2014-25
11 6
30
18
25
2026-33
>05 9 -GO
11.0
6 2
1 in.
2 in
94
70
32
61
60
65
U , Approach Span-Strinik* 2 Ft. North of South Curb
2014-25
11 4
23
21
20
2026-39
11
1 in.
42
39
40
2052-60
6 2
2 in
52
44
50
31
TABLE XII. SUMMARY OP IMPACT PERCENTAGES CONDENSED FROM
TABLES IX, X AND XI.
Approach Span
Load
A
A-B
C-B-A
C
Condition of floor members
Clean
Obstr.
Clean
Obstr.
Clean
Obstr.
Clean
Stringers . .
25
50
Main Span
Stringers
15
50
15
50
100
Floor beam
15
35
70
Hip vertical
10
100
100
Int. posts
30
-60
Diagonals
20
75
20
30
TABLE XIII. COMPUTED STRESSES AND UNIT STRESSES.
STATIC LIVE LOADS.
Note. Loads C-B-A are considered in series as- a train. Loads A and B are
considered parallel. No sign denotes tension. Minus sign denotes compression.
Member
Gross area
Stresses due to loads
Unit stresses
A
A&B
C. B,A
A
A&B
C,B, A
U1L1...
U2L2
U2 L2 Rev
6.72
6.72
6.72
6.72
6.72
25.08
6.84
3.86
3.86
2.88
2.88
2.88
am
19,250
7.370
10.6
-7.8
11.4
12,500
11,370
9.400
11,560
8,660
8,660
23,450
8,980
12,900
9.5
13.9
'"14,500
11,000
13,100
14,600
51,600
27,300
23,400
9,800
21,300
12,300
12,300
2,700
1,100
1,570
1,160
1,700
1,830
2,930
3,260
4,020
3,000
3,000
3,500
1,340
1,920
1,410
2,070
2,230
3,600
4,000
4.880
3,660
3,660
9,350
"'2,' 060
1,640
1,950
2,170
2,080
4,000
6,060
3,400
7,400
4,280
4,280
U3L3
U3 L3 Rev
loUl
U1 L2
15,250
13,840
11,500
14,050
10,540
10,540
1,627.000
U2L3
U2 L3 Rev
U3L4
U3 L4 Rev
L3U4
Floor beam 24in. 80lb. I-be
Stringers See Figs. 2, 3 and 4.
GENERAL LIBRARY
UNIVERSITY OF CALIFORNIA BERKELEY
RETURN TO DESK FROM WHICH BORROWED
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date to which renewed.
Renewed books are subject to immediate recall.
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REC'D LD
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NTERLIBRARY LOAN
OCT221979
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UNIVERSITY OF CALIFORNIA LIBRARY
