NATIONAL BUREAU OF STANDARDS REPORT

2926

TESTS OP PRECAST GIRDERS WITH WELDED SPLICES

(Tee-Heads Nos, 2 and 3)

by

Leopold P« Skoda and D, Watstein

Report to

Bureau of Yards and Docks

Department of the Navy

<NBp>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
U. S. DEPARTMENT OF COMMERCE

Sinclair Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

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# Office of Basic Instrumentation • Office of Weights and Measures.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

November 12^ 1953 2926

TESTS OP PRECAST GIRDERS WITH WELDED SPLICES

(Tee-Heads NoSo 2 and 3)

by

Leopold P„ Skoda and Do Watstein

To

Bureau of Yards and Docks

Department of the Navy

<NBS>

y. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, re)

unleispermlsilon Is 25,D.C. Such pen

cally prepared If th

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 201 5.

n part, Is prohibited

indardt, Washington

)ort has been speclflport for Its own use.

Contents

page

1. Introduction 1

2„ Description of Test Specimens 2

2.1 General Description of Specimens

2.2 Forms

2.3 Concrete

2 , 14. Reinforcement

2,5 Assembly of Specimens

3 . Testing Procedure and Results

3ol Test Set-Up

3.2 Instrumentation

3.3 Test Results

CVJ

C\J

OJ

00

-d-IACm

TESTS OF PRECAST GIRDERS WITH WELDED SPLICES

(Tee-Heads Nos. 2 and 3)

by

Leopold P. Skoda and D. Watstein

Abstract

Two precast girders with welded splices

were tested as simply supported beams to

determine the resistance of the splices

to shear. The girders consisted of thin

web channels assembled by welding to produce members of a hollow section. The

addition of six Inclined bars on each

side of the welded splices in Tee-Head

No. 3 resulted in a marked increase in

the shear resistance of the specimen as

compared with Tee-Head No. 2 which contained no inclined stirrups.

1. INTRODUCTION

The tests of the precast girders were made at the request of the Bureau of Yards and Docks for the purpose of

evaluating the resistance to shear of the welded splices and

the thin web of the hollow girder.

The following report presents the data obtained in test

of specimens which were designated as Tee-Head No, 2 and Te

Head No. 3 by the Bureau of Yards and Docks

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2,12. DESCRIPTION OP TEST SPECIMENS

General Description of Specimens

The precast Tee-Heads were constructed in accordance

with the Bureau of Yards and Docks plans and specifications,

(Precast Tee-=Heads Sketch B=I, dated January 12, 1953? for

Tee-Head No. 2, and Precast Tee-Head Revised Joint Assembly,

Sketch B-2, dated May 5, 1953j for Tee-Head No. 3) • The TeeHead consisted essentially of an assembly of two reinforced

concrete channels with straight haunches. The two channels,

12 ft 6 in. long and 3 ft 6 in. deep at the mid section, were

Joined together with welded plate splices along the top and

bottom legs of the channels. Each channel was stiffened

with four ribs, one near each end and one 9 in. each side

of the centerline of the specimen. The overall thickness

of the assembled specimen was 12 in. and the web thickness

was 2 l/2 in. for each channel throughout. Girder ends were

constructed to match the ends of the Tee-Head simulating a

girder suspended between two adjoining Tee-Heads as shown in

figures 1 and 2.

2.2

F orms

In order to keep the cost of casting the specimens to

a minimum, only one set of forms was made and one half of a Tee-Head was cast at a time, Tee-Head No. 2 was cast on

May 20 and June 2. Tee-Head No. 3 was cast on June l8 and

Jione 25 . The forms were fabricated of wood and so constructed

that the sides were easily removed. A base of h\.~ by li-in,

timbers was topped by sheets of l/2-in. plywood. Plywood

panels were then bolted to the base to form the inside of

the vertical stiffening ribs, the legs of the channels and

the inside of the web. The end channel sections were cast

in an additional set of two forms. Three coats of spar varnish were applied to all surfaces within the form and prior

to casting a mixture of oil and asbestine powder was applied

to facilitate stripping. The form's with reinforcing steel

in place are shown in figures 3 through 6.

2,3

Concrete

The proportions of the concrete mix were 1 j2 &[|.8 ^2 . 02

by weight. High-early-strength cement was used in order to

expedite the curing of the specimens. The aggregates were

White Marsh, Maryland sand and pea gravel, maximum size of

the coarse aggregate being 3/8 in. Three batches of concrete

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were mixed for each casting operation and the slump varied

from 2 in. to 3 l/2 in. Six standard 6 - by 12-in. control

cylinders were cast to represent each half of a specimen and

the average compressive strength realized at the time of

test was 7900 psl for Tee-Head No. 2 and 8200 psi for TeeHead No. 3o Stress- strain curves were determined for each

set of concrete cylinders and are shown in figures 7 and 8 , All concrete specimens were cured for two days under damp

burlap j they were then transferred to a curing chamber where

they were cured at 72° P and 100 percent relative humidity,

until it was necessary to remove them for fabrication into

Tee-Heads

.

2,[|. Reinforcement

The channels composing the Tee-Heads were reinforced

with intermediate grade reinforcing bars and with welded

wire fabric. Two No. 9 deformed reinforcing bars were located along the upper leg of each channel and a No, I4

. deformed bar was located along the bottom leg of the channel.

The extreme top and bottom reinforcing bars projected l4.-in.

beyond each end of the specimen. The purpose of extending

the bars was to form a welded joint with the girder end

sections. The webs of the channels were reinforced with

2“ by 2-in, welded wire fabric of No. 6 gage. The fabric

extended throughout the web and was bent at a 90 ° angle to

extend into the upper end lower leg of the channel.

The girder end sections were similarly reinforced with

a single No, 7 deformed reinforcing bar in the upper and

lower legs and were so placed as to permit being welded to

the bars projecting from the Tee-Head, Wire fabric of the

size used in the Tee-Head was also placed in the same manner

in the beam ends.

Each channel of Tee-Heads No. 2 and No. 3 was reinforced at the joint with a single hooked No, I4

. deformed reinforcing bar to resist shear, as shown in the attached

sketch. In addition to that, Tee-Head No. 3 was also reinforced against diagonal tension in the web on each side of

the joint with thr^ee inclined No. L|. bars located as shown

in the sketch.

The girder ends were reinforced the same way as their

accompanying Tee-Heads.

(For details of reinforcing refer to enclosed sketch)

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2«5o Assembly of Specimens

The two halves of the respective Tee-Heads were joined

together at six points « Three of these points were located

on the upper leg and the remaining three on the lower leg of

the channels. These connections were made by welding 1- by

3“ by 3/8“in, steel splice plates to the abutting 2- by 3~ by

3/8“ln, plates embedded into each half of the specimen. The

embedded plates were anchored by being welded to a No, 5 reinforcing bar placed in the leg and web of the specimen.

Similar welding plates were also cast into the girder ends

at four points on the stiffening ribs.

After the channels and girder end sections were assembled,

all three parts of the Tee-Head were aligned so as to form

welded lap joints of the reinforcing bars projecting from the

Tee-Head and the two girder ends as shown in the close-up in

figure 2, The protruding No, 9 reinforcing bars of the TeeHead were welded to the No, 7 bar of the girder end at the

top of the specimen; in the same manner, the No, 4 bar of

the Tee-Head was welded to the No. 7 bar in the girder end

at the bottom of the specimens. In all cases the length of

the welded lap joint was 3 inches ± l/8 in. After the welding was completed, the gaps between the Tee-Head and the

girder ends were filled with concrete of the same proportions

as had been used in casting the specimens. At the time of

test the compressive strength of this concrete was 8270 psi

for Tee-Head No, 2 at 34 days and 6770 psi for Tee-Head No,

3

at l5 days. Stress- strain curves for 6- by 12-in, cylinders

of the concrete are shown in figures 7 and 8, respectively.

3, TESTING PROCEDURE AND RESULTS

3.1 Test Set-Up

Both Tee-Heads were tested in a similar manner to failure in a 600,000 lb capacity hydraulic testing machine. It

was necessary to support the test specimen on a 20 ft length

of I-beam since the length of the platen of the testing

machine was only 12 ft, whereas a 13 ft 6-ln. span was specified in the test of the Tee-Head, The supporting I-beam was

30-in, deep and was supported at points 12 ft apart by

4 “ by 4" by 12-in. steel blocks. The Tee-Head was then

placed in an inverted position on top of the supporting I-beam

as shown in figure 9. At the reaction points 6 ft 9 In. on

either side of the centerline, the Tee-Head was supported by

rollers. The top of the Tee-Head was capped with a l4“ by

l8- by 1-ln, steel plate and a 10- by 12- by 4"in.„ steel

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bearing block was interposed between the capping plate and

the crosshead of the testing machine. The load was applied

through a 3-in., diameter steel roller which was sandwiched

between the two plates. Neat plaster of paris was used to

assure intimate contact between all steel parts of the

assembly.

3.2 Instrumentation

Deflection of the Tee-Heads was measured at the center

of the specimen by a taut-wire mirror-scale device and also

with micrometer dial gages. The taut-wire device consisted

of .011 in. diameter wire stretched taut with weights suspended over anchor pins located directly above the reaction

points, A scale calibrated in hundredths of an inch was

cemented to a specimen along its centerline and readings were

taken at the point on the scale intersected by the wire. The

micrometer dial gages having one- thousandth inch divisions

were placed at the centerline and bore against brass angles

cemented to the sides of the specimen. The dial gages were

mounted on tripods which rested on the platen of the testing

machine. Another pair of dial gages mounted over the oast

and west ends of the test specimen directly over the supports

measured the movement of the supports with reference to the

platen of the testing machine.

In addition to these measurements, the angular rotation

of the girder ends about the reaction points was measured

during the testing of Tee-Head No, 3<. This was accomplished

with a horizontal clinometer with a gage length of 20 in.

Direct and reverse readings were taken at increments of

25,000 lbs.

3o3 Test Results

The stress-strain curves obtained for the concrete and

the grout used in the girder splices for Tee-Head No. 2 are

shown in figure 7« The concrete in the first half of this

Tee-Head was 6 l days old at the time of test and the second

half of the specimen was days old. The compressive

strengths of the cylinders representing the two halves of

the specimen were 8l 65 and 768O psi, while their tangent

moduli were 4 j 600,000 and 4.j 700,000 psl, respectively. The

concrete grout was 3k- days old at the time of test and its

compressive strength and tangent modulus were 8370 psi and

LI- 55OO 5 OOO psi, respectively

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The stress-strain curves obtained for the concrete and

the grout used in the girder splices for Tee-Head No» 3 SiVe

shown in figure 8„ The compressive strength of the first

and second halves of this specimen at age ^0 and I4.3 days were

8370 and 8030 psi respectively, and the corresponding tangent

moduli were 5^000,000 and I4., 900,000 psi. The l5 day old grout

attained a strength of 6,770 psi and its tangent modulus was

I4., 500, 000 pslo In both Tee-Heads, 1 percent calcium chloride

was added to the concrete grout to accelerate the strength.

The properties of the reinforcement used in both TeeHeads are given in the table on Properties of Materials for

each Tee-Head, All the bars were deformed reinforcing bars

of Intermediate grade and the welded wire fabric used as web

reinforcement was 2- by 2-in. wire mesh of No. 6 gage.

Both Tee-Heads were tested in an inverted position as

simple beams having a 13 ft 6-ln. span with a concentrated

load applied at the center. The load was applied in increments of 5? 000 lb up to a load of 10,000 lb and then in

Increments of 10,000 lb until a maximum load was reached.

The maximum load for Tee-Head No, 2 was li|0,000 lb and for

Tee-Head No. 3, l8l,000 lb.

The first visible cracks observed during the test of

Tee-Head No. 2 occurred at 26,000 lb and the total number of

observed cracks was 88, Initial cracking of Tee-Head No-. 3

was observed at 2^,000 lb and the total number of cracks was

70 o In both cases the observed cracks were carefully marked

and numbered and the crack patterns are shown in figures 10

and 11. Load-deflection curves are shown in figures 12 and

13 for the two specimens and represent the averaged results

of data obtained by the taut-wire and dial gage methods.

There was good agreement between the data obtained by the

two different methods.

The load-deflection relationship observed in the tests

of the Tee-Heads as simply supported beams was in accord

with similar results usually obtained with conventionally

reinforced concrete beams. The relatively steep initial

position of the curve corresponds to the load-deflection relationship observed prior to cracking which started at about

25,000 lb. As the number of cracks increased, the beams

began to deflect more rapidly. The maximum value of deflection at the center of Tee-Head No. 2 was .392 in. at 114.0,000

lb, (maximum load), and the maximum deflection at the center

of Tee-Head No, 3 was .370 in. at l80,000 lb (last set of

readings prior to failure)

.

6 .

SR-=4. strain gages were applied to the No, 9 bars In each

Tee-Head at a point as near the centerline of the specimen as

possible. Strain readings were taken at each increment of

load and the data was reduced and plotted as observed stress

versus the bending moment at the centerline. There was good

agreement among the values of stress observed in individual

bars in both Tee-Heads as well as between the average values

of stress in both specimens. The maximum values of stress

recorded during the test were 32,2 ksl and 4O0O ksi in TeeHeads Nos, 2 and 3s respectively. These values of stress were

observed at loads of 140,000 lb and 170,000 lb in the two

specimens

,

SR -.4 strain gages were also applied to the hooked and

bent bars in the joint assemblies of their respective TeeHeads, Readings were taken but no uniformity was observed in

either case. Figure I6 is a plot of the data obtained for

Tee-Head No, 2 and shows machine load versus stress, A similar graph for Tee-Head No, 3 was eliminated from this report

as it did not show anything significantly different and it was

felt that the graph herein presented was representative of

the erratic action of both Tee-Heads,

( After the tests of the first two Tee-Heads had been completed, a request was made for a determination of rotation of

the ends of the specimen. Accordingly, rotation was measured

on Tee-Head No, 3 with a horizontal comparator and a graphic

representation of the results appears in figures 17 and I8,

Figure I7 shows the angular rotation of each end versus machine

load. The similarity of these curves shows that the specimen

was stressed equally at the ends. The last reading taken was

at 140,000 lb and each end shows a rotation of ,006l radians.

Figure I8 is a graph of the average end rotation versus the

deflection as measured at the centerline of the specimen.

This relationship is fairly linear. At the maximum measured

rotation of ,006l radians, the deflection of the specimen at

the centerline was ,2475 in,

Tee-Head No, 2 failed at a load of l40,000 lb. Failure

occurred at the east end by diagonal tension accompanied by

spalling of the concrete on the inside of the joints. Spalling was caused by the outward bending of the eccentrically

stressed lap welded connections. Breaks were observed in the

horizontal and vertical wires of the welded wire fabric.

Diagonal tension cracks in the concrete tended to extend into

the compression zone merging into a plane of cleavage along

the top of the specimen. The north welded joint failed in

bending and a crack was observed extending into the smaller

bar. Photographs showing the north and south sides of the

east end failure are labeled figures 19 and 20,

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Tee-Head No, 3 failed at a load of l8l,000 lb. Failure

occurred at the west end of the specimen as a crack formed

in the weld of the eccentrically stressed welded splice. This

was accompanied by diagonal tension failure in the web. The

principal tension crack was just inside the region reinforced

with the inclined bent bars. Tensile failure of the welded

wire fabric occurred in horizontal and vertical directions and

can be seen in the photographs labeled figure 21 and 22,

The addition of inclined stirrups on each side of the

welded splices in Tee-Head Wo, 3 resulted in a marked Increase

in the shear resistance of the specimen. It is noted that the

shear strength of Tee-Head Wo, 3 was sufficient to produce a

stress in the longitudinal reinforcement (Wo. 9 bars of intermediate grade steel) in excess of ij-OgOGO psi, whereas the

maximum recorded stress in the longitudinal reinforcement of

Tee-Head Wo. 2 was about 32,000 psi.
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THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The fuiictions of the National Biu'eau of Standards are set forth in the Act

of Congress, March 3, 1901, as amended hy Congress in Public Law 619, 1950.

These include the development and maintenance of the national standards of

measurement and the provision of means and methods for making measurements

consistent with these standards; the determination of physical constants and

properties of materials; the development of methods and instruments for testing

materials, devices, and structures; advisory services to Government Agencies on

scientific and technical problems; invention and development of devices to serve

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codes, and specifications. The work includes basic and apphed research, development, engineering, instrumentation, testing, evaluation, calibration services

and various consultation and information services. A major portion of the

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Information on the Bureau’s publications can be foimd in NBS Circular 460,

Publications of the National Bmreau of Standards ($1.00). Information on cali- bration services and fees can be found in NBS Circular 483, Testing by the National

Bureau of Standards (25 cents). Both are available from the Government Printing Office. Inquiries regarding the Bureau’s reports and publications should be

addressed to the Office of Scientific Publications, National Bin*eau of Standards,

Washington 25, D. C.
NBS