NATIONAL BUREAU OF STANDARDS REPORT

2597

TEST OP PRECAST GIRDER WITH WELDED SPLICES

(TEE -HEAD NO. 1)

by

L. P. Skoda and D. Watstein

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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NATIONAL BUREAU OF SJAMBARBS REPORT

Nil PROJECT NBS REPORT

1001-10-4701; June 23, 1953 25>97

TEST OF PRECAST GIRDER WITH WELDED SPLICES

( TEE -HEAD N0 o 1)

The publication, n

unless permission I

25. D. C. Such 1 prepared tf that

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

In part, Is prohibited

landards, Washington

has been specifically

>ort for Its own use,

CONTENTS

Page

1. Introduction 1

2. Description of Test Specimen 1

2.1 General Description of Specimens 1

2.2 Forms 1

2.3 Concrete 2

2 .ip Reinforcement 2

2.5 Assembly of Specimens 3

3. Testing Procedure and Results 3

3.1 Test Set-Up 3

3o2 Instrumentation l\.

3.3 Test Results J4

.

TEST OF PRECAST GIRDER WITH WELDED SPLICES

(TEE-HEAD NO. 1)

1. INTRODUCTION

The test of the precast girder was 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 the

test of the specimen which was designated as Tee-Head No. 1

by the Bureau of Yards and Docks.

2. DESCRIPTION OF TEST SPECIMEN

2.1 General Description of Specimens

The precast Tee-Head was constructed in accordance with

the Bureau of Yards and Docks plans and specifications, (see

sketch B-l, January 12, 1953, attached) . The Tee-Head consisted essentially 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 channel.

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. The girder ends which 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 Forms

In order to keep the cost of casting the specimens to a minimum, only one set of forms was made and the two halves of

the Tee-Head were cast on two different days; the first half

of the Tee-Head was cast on March 16 and the second half on

March 26.

The forms were fabricated of wood and so constructed

that the sides were easily removed. A base of Iq-in. by 4--i n * 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
2 . 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 forms with reinforcing steel in place are shown

in figures 3 and 4*

2.3 Concrete

The proportions of the concrete mix were 1 : 2 . Ip8 : 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 were mixed

for each pour and the slump varied from 2 1/2 in. to 4 l/2 in.

Six standard 6 in. by 12 in. control cylinders were cast to

represent each half of a specimen and the average compressive

strength realized at the time of the test of the Tee-Head was

7270 psi. Stress-strain curves were determined for each set

of concrete cylinders and are shown in figure 5. All concrete

specimens were cured for two days under damp burlap; they were

then transferred to a curing chamjber until it was necessary to

remove them for fabrication Into a Tee-Head.

2.i| Reinforcement

The channels composing the Tee-Head were reinforced with

bars of intermediate grade and with welded wire fabric. Two

No. 9 deformed reinforcing bars were located along the upper

leg of each channel and a No. 4 deformed bar was located along

the bottom leg of the channel. Both top and bottom reinforcing

bars projected four inches beyond each end of the specimen.

The purpose of extending the bars was to form a welded joint

with the beam end sections. The webs of the channels were reinforced with 2 in. 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 and lower leg of the channel.

The beam 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 .
3.

2,5 Assembly of Specimens

The two halves of the Tee-Head, 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 2- by, 3/8-in.

steel plates to the adjoining 2- by 3- by 3/8-in. plates which

were embedded into each half of the specimen. The embedded

plates were anchored by being welded to a No. 4 reinforcing

bar placed in the leg and web of the specimen. Similar welding plates were also cast into the beam ends at four points

on the stiffening ribs.

After the channels and beam end sections were assembled,

the welded splices were made by placing all three parts of

the Tee-Head so as to form welded lapped joints of the reinforcing bars projecting from the Tee-Head and the two beam

ends as shown in the close-up in figure 2. The outer No. 9

reinforcing bars of the Tee-Head were welded to the No. 7

bar of the beam end at the top of the specimen. In the same

manner, the No. 4 bar of the Tee-Head was welded to the No.

bar in the beam end at the bottom of the specimen. In all

cases the length of the welded lap joint was 3 inches. After

the welding was completed, the gaps between the Tee-Head and

the beam ends were filled with a 1:3 mortar.

3. TESTING PROCEDURE AND RESULTS

3.1 Test Set-Up

The Tee-Head was tested to failure in a 600,000 lb

capacity 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 lli-ft 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" Ny 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 6. At the reaction

points 7 feet on either side of the vertical centerline, the

Tee-Head was supported by rollers. The top of the Tee-Head

was covered with a II4.- by 18 - by 1-in. steel plate and a

10- by 12- by 4~in « steel bearing block was interposed between the first plate and the crosshead of the testing

machine. The load was applied through a 3-in. diameter steel

roller which was sandwiched between two steel plates. Neat

plaster of Paris was used to assure intimate contact between

all steel parts of the assembly.
4 .

3.2 Instrumentation

Deflection of the Tee-Head was measured at the center of

the specimen by a taut-wire 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 the 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. A pair of dial gages

were mounted over the east and west ends of the test specimen

directly over the support in order to detect any settlement of

the supporting members in reference to the platen of the testing machine

.

3.3 Test Results

The stress-strain curves obtained for the concrete and

the mortar used in grouting the girder splices are shown in

figure 5. The concrete in the first half of the Tee-Head was

32 days old at the time of test, and the second half of the

specimen was 22 days old. The compressive strengths of the

cylinders representing the two halves of the specimen were

7100 and 7250 psi, while their tangent moduli were 4 ,700,000

and 5,400,000 psi, respectively. The mortar grout was 8 days

old at the time of test and its compressive strength and

tangent modulus were 5700 psi and 3,800,000 psi, respectively.

The properties of the reinforcement used in the Tee-Head

are given in the Table on Properties of Materials. All the

bars were deformed reinforcing bars of intermediate grade,

while the welded wire fabric used as web reinforcement was

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

The Tee-Head was tested in an inverted position as a simple beam having a 14 ft span with a concentrated load

applied at the center. The load was applied in increments of

5000 lb up to a load of 10,000 lb and in increments of 10,000 lb

until a maximum load of 130,000 lb was reached.

Shrinkage cracks were observed at the start of the test

in planes where the mortar in the girder splices was bonded
to the concrete. The first visible tensile crack in the concrete appeared at a load of 28,5>00 lb. In all, a total of 57

cracks appeared throughout the test. These cracks were all

carefully marked and numbered and the crack pattern is shown

in figure 7. The load-deflection curve shown in figure 3 represents the averaged results obtained with both the tautwire device and the micrometer dial gages. There was good

agreement between the data obtained by the two different

methods

The load-deflection relationship observed in the test

of Tee-Head as a simply supported beam was in accord with

similar results usually obtained with conventionally reinforced concrete beams. The relatively steep initial portion

of the curve corresponds to the load-deflection relationship

observed prior to cracking which started at about 30,000 lb.

As the number of cracks increased, the beam began to deflect

more rapidly. The maximum value of deflection at the center

of the Tee-Head was 0.362 in. at 120,000 lb, at which load

the last ddf lection reading was made.

The width of several cracks was measured with a Brinnell

microscope at loads of 60,000 and 90,000 lb. The width of

cracks varied from 0.05 to 0.10 mm at the 60,000 lb load, and

from 0.09 to 0.6 mm at the 90,000 lb load.

The Tee-Head failed at a load of 130,000 lb. The east

end of the Tee-Head appeared to fail in diagonal tension,

with the major crack running up and toward the applied load

from the center of the girder splice. However, a closer examination of the splice revealed that the lap weld in one half of

the east girder splice failed in tension, causing shear failure

in the web as a secondary failure. A close-up of the girder

splice which failed is shown in the views of the northeast and

southeast corners of the specimen, figures 9 and 10.
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v
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by 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

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Information on the Bureau’s publications can be found in NBS Circular 460, Publications of

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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 Bureau of Standards, Washington 25, D. C.