NATIONAL BUREAU OF STANDARDS REPORT

5313

STRENGTH AND RIGIDITY OF LAP WELDED SPLICES

IN PRECAST REINFORCED CONCRETE FRAMING MEMBERS

by

L, F, Skoda, A. F. Kirstein, and D, Watstein

Report to

Bureau of Yards and Docks

Department of the Navy

<S>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT MBS REPORT

1001-10-4811 January 10, 1958 5313

STRENGTH AND RIGIDITY OP LAP WELDED SPLICES

IN PRECAST REINFORCED CONCRETE FRAMING MEMBERS

by

L. F. Skoda, A. F. Kirstein, and D. Watstein

To

Bureau of Yards and Docks

Department of the Navy

NATIONAL BUREAU OF ST

Intended for use within the

to additional evaluation and i listing of this Report, either the Office of the Director, Ni however, by the Government

to reproduce additional copk

IMPORTANT NOTICE

progress accounting documents

Approved for public release by the rma*4 published It Is subjected

Director of the National Institute ot 18 , on „ obtalned , n wrltlng from Standards and Technology (NIST) Such permission Is not needed, on October 9, 201 5. pmparad If that agency wishes

<QJBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
' / "k i J i '
STRENGTH AND RIGIDITY OF LAP WELDED SPLICES

IN PRECAST REINFORCED CONCRETE FRAMING MEMBERS

b Y

L. F. Skoda, A. F. Kirstein, and D. Watstein

Four box girders with lap welded splices

were tested to determine the effect of rotation

of eccentrically loaded lap welded reinforcing

bars on the lateral rigidity of the splice and

precast thin-shelled concrete framing members.

Each specimen was made of six precast thinshelled elements that were welded and spliced

together to form a hollow box girder 1- by 2-ft

in cross section and 8 ft 10 in. long. These

girders were used to compare the relative

rigidities of lap welded splices with and without transverse reinforcement. The comparative

results of flexural tests of these girders indicate that there was little difference in the

observed lateral displacements up to stresses

in splices of about 35,000 psi. However, at

higher stresses, the lateral movement of the

end portion of the girders and the concrete

surrounding the splices was significantly greater

in the girders which contained no transverse reinforcement .

1. INTRODUCTION

In the previous tests of precast girders and Tee Heads

with welded splices made at the request of the Bureau of

Yards and Docks, it was observed that the eccentrically

loaded lapped splices caused large displacements of the

concrete which covered the welded splices in the joint.

Four girders described in this report were tested to determine means of reducing the rotation of lap welded splices

of the type used by the Department of the Navy in their precast thin- shelled structural framing members.
' I"
2. DESCRIPTION OF SPECIMENS AND MATERIALS

The type of specimen selected for this test was a combination of the modified center section of "Precast Continuous

Girder," (BuY&D sketch B-3, dated 5-3-53) » and the end blocks

of the "Tee Head," ( BuY&D sketch B-l, dated 1-12-53). This

combination produced a six element specimen with four welded

splices. The cross section of the girder was 1- by 2 ft and

the length was 8 ft 10 in. Each element was essentially

channel shaped In cross section as can be seen in the detail

sketch of the resulting composite box girder shown In figure 1.

Transverse reinforcement was added to the welded splices

in girder No. 1. Two No. 7 bars 10 in. long were selected to

reinforce one of the splices and an equal volume of steel in

the form of a plate J- "by 3/8- by 10 in, long of intermediate

grade steel was used to reinforce the other. The welding was

completed as Indicated in detail views A and B of figure 1,

by a qualified Navy welder. The transverse reinforcement

added to the welded splices of girders Nos. 3 and 4 consisted

of a single No. 2 bar that was tack welded In place simply to

keep it in position during the grouting operation. Detail

view C of figure 1 indicates the location of this bar. Girder

No. 2 did not contain transverse reinforcement.

2.1 Forms

The forms used for casting the box girder elements were

those used in the previous investigations of the Tee-Heads

and continuous girders as reported in NBS Reports Nos. 2597

and [|_286. The center section of the continuous girder form

was shortened to 5 ft 2 in, while no changes were necessary

in the Tee-Head end forms.

Although the forms had been used several times before,

the plywood and Ip- by l|-in, timber construction was sturdy

enough to withstand additional repeated use.

2.2 Concrete

The concrete was made of Type III cement and had proportions of 1 : 2 „ L|_5 ' 2 . 02 , by weight. A water-cement ratio of 0.49

was used to produce a fairly workable mix with a slump of 2 to

3 in. Both aggregates were siliceous materials that were obtained from White Marsh, Maryland, The coarse aggregate was

a well rounded pea gravel with a maximum size of 3/8 in.

2 .
.
Two batches of concrete were required to cast each girder,

and two 6- by 12-in. control cylinders were cast from each

batch. All elements and their corresponding control cylinders

were kept under damp burlap for 24 hr and then transferred to

a curing chamber where they were moist-cured for six days.

The control cylinders were tested on the seventh day, and the

average compressive strengths for girders Nos. 1,2, 3? and 4

were 5460, 4740? 6590, and 6525 psi, respectively. The elements were then air-dried until assembled and tested.

2.3 Reinforcement

The arrangement of longitudinal and web reinforcement is

shown in figure 1. The reinforcement in the lower flanges of

the center sections of each girder consisted of four No. 8

deformed bars. The two inner bars in the flanges of the

channel sections were completely embedded while the outer bars

extended 5 in. beyond the edge of the concrete. Similarly,

the upper flanges of the center sections of each girder were

reinforced with No. 4 bars.

The lower flanges of the end sections were reinforced

with single No. 8 bars that extended beyond the form and

lapped the extended No. 8 bar of the center section. Similarly,

the upper flanges of the end sections were reinforced with No.

4

bars

.

Tensile tests were made of No. 8 reinforcing bars of the

type used throughout this investigation. The average yield

strength of the bars was 42? 300 psi and the modulus of elasticity was 27 x 10° psi.

Three inclined stirrups of No. 4 bars were placed in the

web of each element to resist diagonal tension. A bent No. 4

bar was also- placed in the web of each element near the joint.

The webs and flanges of each element were also reinforced

throughout with 2- by 2-in. welded wire fabric of No. 6 gage.

All the deformed reinforcing bars were of intermediate grade

steel

.

2.4 Girder assembly

After sufficient air drying, the girder elements were

welded together to form the composite end sections and center

section. These units were carefully positioned to form the

girder, and the 4~in » lap welded splices of the reinforcement

in the upper and lower flanges were made as indicated in

figure 1.

3 .
>

.
The cavities that contained the lap welded splices were

filled with concrete of the same mix proportions as was used

in casting the girder elements. The 7-day compressive

strength of this concrete for girders Nos. 1 , 2, 3* and 4

was 6000, 4^75* 6840, and 6840 psi, respectively.

3, TESTING PROCEDURE

3.1 Test setup

The girders were tested over an 8 ft span in a 600,000 lb

capacity hydraulic testing machine. The load was applied applied through a loading beam with a knife edge at one end and

a roller-plate assembly at the other. These load points were

40 In. apart and were placed symmetrically about the centerlines of the girders. Figure 2 is a sketch of a girder in

the testing machine.

The girders were first flexed to a load of 5*000 lb,

after which all load was removed and zero readings were taken

on all gages. A complete set of readings was taken after each

10,000 lb increment of load until failure occurred.

3.2 Instrumentation

One thousandth inch dial gages with a range of one inch

were used for all displacement measurements. Six of these

gages were used to measure the lateral displacement of the

concrete in the vicinity of each lap welded splice. These

gages were supported by ring stands that rested on the platen

of the testing machine. The vertical deflection at the center

of the girder was measured by a dial gage on each side. These

gages were attached to aluminum bars that were supported at

their ends directly over the rocker supports of the girder.

The lo cation of all dial gages is shown in figure 2.

In addition to the dial gages, girders Nos. 3 and 4 had

electrical resistance type strain gages attached to the No. 8

reinforcing bars of the center section which projected into

the splice section. The location of the gages near the splice

and at mid-span can be seen In detail C and Section 1-1 of

figure 1; Readings on these gages were taken at the same time

as the dial gages were being read.

4 -
V
4, RESULTS AND DISCUSSION

The primary cause of failure in the flexural tests of

the girders appeared to be yielding of the tensile reinforcement in the splices* This Is indicated by the views of the

girders after test in figures 3 through 10 and by the loadstrain relationship for girders 3 and 4 shown in figure 11.

The views of all girders tested show wide cracks at the

straight boundary of the grout pocket. These cracks were

sufficiently wide in most of the specimens to reduce the compressive zone of the concrete to a depth which permitted

shear failure to occur as a secondary mode of failure.

Girder No. 1, containing the most transverse reinforcement failed at a load of 174,000 lb while girder No. 2 having

no transverse reinforcement failed at a load of 150,000 lb.

Girders Nos. 3 and 4 containing a small amount of transverse

reinforcement failed at Identical loads of 155,000 lb.

The observed stresses in the longitudinal reinforcing

steel at the centerline of girders Nos. 3 and 4 are shown In

figure 12. Since the stress at the lap welded splice is of

greater magnitude than the stress at the midspan, it is the

limiting factor when considering the yielding of the reinforcement. The stresses observed at the lap welded splices of

girders 3 and 4 are compared with the theoretical stresses in

figure 11.

The lateral displacements of the concrete surrounding

the welded splices and the adjoining elements are shown in

the diagrams of figures 13 through 18, The load-displacement

relationships for all girders are shown in the same manner

for each gage position. The values of displacement shown on

these curves are the total changes in the transverse dimensions of the specimens calculated as the algebraic sums of

the movements measured by gages on opposite sides of the

girders

.

The load-displacement relationships for the girders

were essentially the same up to a load of about 80 kips which

corresponds to a theoretical stress in the steel at the splice

that is approximately 15 percent below the yield strength of

the material. However, as the load was increased, the load

displacement curves for the girders displayed an increasing

disparity. This difference in lateral rigidity is directly

attributed to the effect of the various amounts of transverse

reinforcement in girders Nos. 1, 3> and 4»

5 .

The load deflection diagrams for the girders are shown in

figure 19. Attention is directed to the fact that the greater

rotation of the splices in girder No, 4 had no appreciable

effect on the center deflection.

Comparison of the displacement graphs in figures 13

through 16 shows that for loads exceeding 80,000 lb the lateral

movement of the end sections of the girders and of the concrete

surrounding the splices was significantly greater for the

girder with no transverse reinforcement than for the three girders which contained varying amounts of transverse reinforcement

The theoretical steel stress in the splices at the load of

80,000 lb was approximately 354000 psi. At higher stresses,

the effect of the transverse reinforcement became particularly

pronounced in reducing the lateral movement of the concrete

surrounding the splices. As can be seen :f.n figures 15> and 16,

the maximum observed increases in the transverse dimensions of

the splice pockets were about 0.01 in. for girder No. 1, 0.03

to 0,06 in. for girders Nos. 3 and 4 and about 0.2^ in, for

girder No. 2 which had no transverse reinforcement.

Figure 20 through 23 are crack patterns of the girders.

The encircled numbers at the bottom of the crack pattern diagrams indicate the order in which the cracks appeared. Due to

the fact that the lap welded splices in girder No. 2 rotated,

large longitudinal and transverse cracks were evidenced in the

concrete pocket while no cracking occurred in the end sections

of the girder. Since the transverse reinforcement in girders

Nos. 1, 3? and 4? reduced the rotation of the lap welded splices

a wider dispersion of small cracks appeared along their entire

length.

It is concluded that a small amount of transverse reinforce

ment in the splices is well worth the slight additional cost In

order to guard against excessive rotation of eccentrically

tensioned lap welded splices and the accompanying lateral displacement of the concrete in the splice pockets which are observed at steel stresses in excess of 354000 psi.

USC0m-NBS-DC

6 .

PL. 2

<D

ID

C\J

SECTION I -I

NO. 2 HOOKED

BAR

FIG. I
II
FIG.

2

TEST

SETUP

FIG. 3 VIEW OF FAILURE, GIRDER NO. I SOUTHWEST 8 TOP.

\

’ \

FIG. 4 VIEW OF FAILURE, GIRDER NO. I NORTHWEST a BOTTOM.

FIG. 5 VIEW OF FAILURE, GIRDER NO. 2 SOUTHWEST 8 TOP.

FIG. 6 VIEW OF FAILURE, GIRDER NO. 2 NORTHWEST 8 BOTTOM.

FIG. 7 VIEW OF FAILURE GIRDER NO. 3 NORTHEAST

Q TOP.

FIG. 8 VIEW OF FAILURE, GIRDER NO. 3 SOUTHEAST 6 BOTTOM.

FIG. 9 VIEW OF FAILURE, GIRDER NO. 4 NORTHEAST

a TOP.

I I

I

1

\

"7

1

1

\

v \ M,

\ \ I K ‘j\

y

i x.

1 / X/

1

(

J

FIG. !0 VIEW OF FAILURE GIRDER NO. 4 SOUTHEAST a BOTTOM

MACHINE

LOAD.

KIPS

FIG. II OBSERVED AND THEORETICAL STRESSES AT SPLICES

OF GIRDERS NOS. 3 AND 4.

120

100

80

60

40

20

0

STEEL STRESS, PSI

. 12 OBSERVED STRESSES AT MID-SPAN, GIRDERS

NOS. 3 AND 4.

160

140

120

100

80

60

40

20

0

NO. ! NO. 2

NO. 3

NO. 4

.2 .3 .4 .5

DISPLACEMENT, INCHES

. 13 LATERAL DISPLACEMENT, EAST END SECTION OF

ALL GIRDERS.

160

140

120

100

80

60

40

20

0

GIRDERS

NO. I NO. 2

NO. 3

NO. 4

I

.2 .3 .4 .5

DISPLACEMENT, INCHES

. 14 LATERAL DISPLACEMENT, WEST END SECTION

OF ALL GIRDERS.

160

(40

120

100

80

60

40

20

0

DISPLACEMENT, INCHES

. 15 LATERAL DISPLACEMENT, EAST SPLICE POCKET

IN ALL GIRDERS.

160

140

120

100

80

60

40

20

0

i

GIRDERS

NO. I NO. 2

NO. 3

NO. 4

.05 .10 .15 .20

DISPLACEMENT, INCHES

.25

. 16 LATERAL DISPLACEMENT, WEST SPLICE POCKET

IN ALL GIRDERS.

FIG. 17 LATERAL DISPLACEMENT, EAST END OF CENTER

SECTION OF ALL GIRDERS .

160

140

120

100

80

60

40

20

0

GIRDERS

NO. I NO. 2

NO. 3

NO. 4

JO .15 .20

DISPLACEMENT, INCHES

r IG. 18 LATERAL DISPLACEMENT, WEST END OF CENTER

SECTION OF ALL GIRDERS.

FIG. 19 LOAD VS. CENTER DEFLECTION

LOAD LOAD

LOAD LOAD

TOP

W

<—• LOCAL CRUSHING

LOAD

( LOCAL CRUSHING

LOADFIG. 20 CRACK PATTERNS, GIRDER NO. I

.

LOAD LOAD

LOAD LOAD

TOP

W

W

FIG. 21 CRACK PATTERNS, GIRDER NO. 2.

LOAD LOAD

TOP

w

BOTTOM

FIG. 22 CRACK PATTERNS GIRDER NO. 3.

LOAD LOAD

LOAD LOAD

TOP

w

BOTTOM

FIG. 23 CRACK PATTERNS, GIRDER NO. 4.

U. S. DEPARTMENT OF COMMERCE

Sinrluir Weeks, Secretary

NATIONAL BUREAU OF STANDARDS

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

The scope of activities of the National Bureau of Standards at its headquarters in Washington,

D. C., and its major field laboratories in Boulder, Colorado, is suggested in the following listing of

the divisions and sections engaged in technical work. In general, each section carries out ope*

cialized research, development, and engineering in the field indicated by its title. A brief

description of the activities, and of the resultant reports and publications, appears on the

inside front cover of this report.

WASHINGTON, D. C.

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