NATIONAL BUREAU OF STANDARDS REPORT

3353

TEST OF PRECAST PANEL FRAME NO. 1

fey

Leopold F. Skoda and D. Watstein

Report to

Bureau of Yards and Docks

Department of the Navy

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

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NIBS REPORT

1001-10-4811 June 10, 1944 3353

TEST OF PRECAST PANEL FRAME NO. 1

by

Leopold F, Skoda and D. Watstein

Report to

Bureau of Yards and Docks

Departmenln^f^the Navy <NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, reprin

unless permission Is obi

25, D, C. Such permls

cal ly prepared If that

. . „ ... . 1 ,1 Dart, is prohibited Approved tor public r release by the , lards, Washington Director of the National .Institute of , has been specifi . Standards and Technology (NIST) rt for its own use, on October 9,2015.

TEST OP PRECAST PANEL FRAME NO, 1

by

Leopold F. Skoda and D„ Watstein

Abstract

The stiffness and strength of a precast panel frame

were determined under a load uniformly distributed

over the roof area, The frame consisted of two wall

panels and two roof panels assembled with welded and

bolted connections „ The span of the frame was 30 ftj

the wall panels were 9 ft 8 in, high and 4 ft wide

and the roof panels were l£ ft 5 in„ by 4 ft forming

a pitched roof with a rise of 1.8? in, per foot.

The frame was loaded with concrete sand, A uniformly

distributed load of 40 psf was applied in four increments and was maintained on the franle for a period of

4l days. An additional load of 40 psf was applied

then, and the total load of 80 psf was left on the

structure for a period of 4 days. The load was then

removed and the structure dismantled.

Measurements during this test included determination

of rotation at. the crown and the two knee joints, deflection at the center and measurements of the width

of cracks at the three joints.

1, INTRODUCTION

The test of a precast panel frame was made at the request

of the Bureau of Yards and Docks for the purpose of evaluating

such a structure under severe uniformly distributed loads to

determine any existing points of weakness in the proposed design.

The following report represents observations and data obtained during construction, erection, testing and dismantling

of precast panel frame No, 1

2 o CONSTRUCTION OP PANELS

2 0 1 General Description of Specimen

Precast panel frame No. 1 consisted of two wall panels

and two roof panels constructed of precast, thin- shell reinforced concrete, in accordance with the Bureau of Yards and

Docks plans and specifications titled, **Precast Panel Frame,**

Sketch A, dated September 8, 1953° (Pig° 1)°

The wall panels were 9 ft 8-in, high and 4 ft wide with

a 3 ft by 4 tt- 1-in, window opening located 3 ft from the

floor level. Tapered stiffening beams were located at the

outer edges and varied in depth from 1 ft 2 in, at the top

to 6 in, at the bottom of the panel, with the Inner surface

being held plumb. Transverse stiffening ribs were located

at top and bottom of the panel and also above and below the

window opening. The panel above the window had a 2-in, web

thickness and the lower panel had a 1-in, web thickness.

The roof panels were 15 ft 5"In, long and 4 ft wide with

tapered longitudinal stiffening beams at the outer edges which

varied In depth from 1 ft 2 in, at the wall-roof joint to 8

in, at the crown. Transverse stiffening ribs were located at

either end of the roof sections. The web thickness of the

roof panels was 1 in, throughout. The roof panels were designed to produce a pitched roof spanning 15 ft each, with a rise of 1,866 In, per foot.

The sections were joined together with welded and bolted

connections. The end and crown connections will be described

more fully in succeeding paragraphs,

2 , 2 P orms

Due to the fact that the proposed structure was bilaterally symmetrical, it was only necessary to construct forms

for one wall panel and one roof panel. The forms were constructed at the National Bureau of Standards carpenter shop.

The materials used for all cast surfaces were 3/4 in, plywood.

The forms were so constructed as to be easily disassembled and

reused. They were rigidly braced with structural timber in

order to eliminate warping and swelling. Further precautions

were taken to assure duplication of the original specimens on

subsequent castings by coating all surfaces with a special

phenol formaldehyde resin varnish. Prior to casting, all interior surfaces were coated with a mixture of oil and asbestine powder to facilitate stripping. In spite of all these

precautions some displacement of concrete was observed which

indicated that any mass production of specimens would require

metal or concrete forms to produce the desired accuracy and

duplication of specimens

,

2,3 Concrete

The proportions of the concrete mix were Is 2, 48 s 2, 02 by

weight. High-ear ly-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. Six batches of concrete were mixed for

each casting operation and the slump varied from 4 i/2 in, to

6 in. Two standard 6 In, by 12 In, control cylinders were cast

for each batch and an average compressive strength of 7200 psi

for the first casting* and 6370 psi for the second casting was

realized at time of test. 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; the wall panels were then transferred to a curing chamber

where they were cured at 72° F and 100 percent relative humidity until it was necessary to remove them for assembly. The

roof panels were too large to be put into the curing chamber

so the damp burlap curing was continued for a period of 10 days,

2,4 Reinforcement

The wall panels were reinforced with No, 4 and 7 reinforcing bars and 2-' by 2-in, by 12 gage welded wire fabric.

Two No, 4 reinforcing bars were located in a plane bisecting

the web longitudinally at a distance of 1 1/4 In, from the

outer edges. Two No, 4 bent bars were used to reinforce the

concrete adjacent to the window openings and were placed so as to tie in the vertical legs with the transverse sill extending

Into the sill to a depth of 8 in. Two No, 4 bent bars were

placed in the upper sill and extended 8 in. Into both vertical

legs. One No, 4 bent bar was placed in the lower sill and extended 8 in, into each vertical leg, A single No, 7 bar was

placed in each edge beam along the outer edge and was bent so

as to form anchorage for the weld connector plate, A 2 1/2-

by 1/2- by 6-in, plate was welded to the end of the No, 7 bar

and was so arranged as to be half exposed and match a similar

plate extending from the roof panel.

The roof panels were reinforced with No, 4 and. No, 6 reinforcing bars and 2- by 2-in, by 12 gage welded wire fabric,

A single No, 4 "bar was located at the bottom of each longitudinal edge beam and was bent at each, end to extend upwards

toward the web, A single No, 6 bar was placed near the top

of each longitudinal edge beam with a 2 l/2- by l/2- by 6-In,

steel plate welded to It at the wall end of the panel, A 4 -t

3 o
'
piece of No, 4 bar was placed near the bottom of the transverse

rib at the crown, It is emphasized that this bar was not anchored at the ends and the effect of the absence of anchorage

is discussed under Test Results

„

The 2- by 2-in„ by 12 gage welded wire fabric was placed

in a single layer throughout the web and all reinforcing members

of both the wall and roof sections

„

At each end of the roof panel 1-in. pipe sleeves were cast

Into the transverse ribs 3 ft on center. They were placed so

as to allow 3/4”in ° bolts to be used to hold the panels together. Matching sleeves were also cast into the upper web of

the wall panel to permit bolted connections to be made.

3. ASSEMBLY OP PANELS

3 »1 Footings

It was decided that the footings included on the proposed

drawing of "Precast Panel Frame’1 were Inadequate for this test

due to the fact that It would have been necessary to cast a floor section to tie the footings together. Footings were

then designed to resist the maximum possible thrust Imparted to

them by any extreme loading of the panel frame.

The footings consisted of heavily reinforced concrete

blocks 10- by 26- by 60 in. with a 2= by 10-in. cavity centered along their length. Four No. 9 reinforcing bars anchored

at each end served to tie the footings together. Control cylin

ders representing the footings were cast and an average compressive strength of ?200 psi was realized at time of test.

3.2 Wall and Roof Erection

In order to aid erection, a timber structure was designed

to support the wall and roof panels while the bolted and welded

connections were made. It consisted of a center pier of upright 4" by 4“in ° timbers cross-braced with 2 by 4

5

3

° Planking

extended from the center pier beyond the footings at a level

with the top of the window openings to provide anchorage for

the walls during the erection of the roof panels. Braces extended from the footings to the center pier to counteract any

lateral movement.

The wall panels were then set In place with the aid of an

electric lift truck and securely wedged and braced against the

extended planking. The walls were purposely set out of plumb

to allow more room for the roof panels to be placed.

Because of the limited space in the laboratory the roof

panels had to be hoisted in place with the use of the electric lift truck and an overhead crane. The roof panels were

placed with the crown end resting on the center pier and the

wall end suspended from the overhead crane. The 3/4-“in ° bolts were inserted and tightened to make the wall roof connection. After the two roof panels had been placed and

secured to the wall panels the bolts at the crown were inserted and tightened pulling the roof panels together and

thereby plumbing the attached side walls.

3o3 Welding and Grouting

After all bolted connections were securely tightened^

the welded connections were made at each corner of the roofwall joint. All welding was done by a qualified Navy welder.

A welding plate 1 l/2- by l/2- by I4

. in. was centered over

the exposed connector plates so that welding could be accomplished on all four sides of the plates.

During the welding operation cracks appeared in the concrete adjacent to the embedded connector plates. The cracks

appeared on both wall and roof panels parallel to the vertical end of the reinforcing bars which served to anchor the

connector plates. The cracks averaged from 2 to I4. in. in

length and appeared at all four welded connections. Due to

the heat applied to the connector plates a slight amount of

buckling occurred causing the connector plates to be displaced and break bond from the concrete. It was thought at

first that the cracks would close on cooling of the plates

but the distortion was permanent and no such closing was observed . As soon as the welded connections had cooled sufficiently , the bolts were grouted in with a cement-water paste

mixed to a cake batter consistency. This was accomplished

with a caulking gun that had been adapted to fit the imbedded

l=in„ pipe sleeves. Each bolt was grouted individually byremoving the nut and washer , applying the grout s and replacing and tightening the assembly. Control cylinders of the

grouting mixture had a compressive strength of 5810 psi at

the time of test.

This procedure appeared to be satisfactory until the

specimen was taken apart after the test. On close observation, It was evident that some of the grout had penetrated

the pipe sleeves at the joint between the wall and roof

thereby causing a slight separation of the wall from the

roof. This separation was noticed during the test but

was thought to have been caused solely by the fact tha 1

. a 5 *

cast surface was adjoining a troweled surface „ These facts

clearly indicate that some revision is necessary in the grouting procedure or in the bolt-sleeve assembly in order to allow more bearing area between the wall and roof sections

„

After the bolt grouting was completed* the footing

pockets* in which the wall sections were resting was filled

with a lt3 mortar mix, A compressive test of 6= by 12~in,

control cylinders showed a strength of 6230 psi at time of

test

,

Ip, TESTING PROCEDURE AND RESULTS

Ip o 1 Test Set-Up

It was decided to use measured amounts of damp sand as

the medium for applying the specified uniformly distributed

load. Plywood forms 12= in, high were made to extend about

the perimeter of the roof sections In order to hold the sand

in place. The forms had flexible couplings every two feet to

compensate for bending In the roof panels. The amount of sand

to be applied was determined by a calculation of the projeeted roof area. Sand was then weighed in 100 lb quantities

and placed in heavy duty paper bags ready to be applied,

ip, 2 Instrumentation

Measurements of deflections* rotations and crack widths

was accomplished with 0,001 in. Federal dial gages. Footing

movements were measured with 0,001 in, Ames dial gages, A

single gage was used to measure the deflection of the roof

panels and was placed as near the center of the structure as

possible. Rotations were measured at ail four corner joints

and at the center joint. Rotation of the side walls were

measured with respect to the footings and also with respect

to the floor. Crack widths were measured at the end joints

and center joints. Side sway of the entire structure was

measured at the center of the structure with respect to bhe

floor. Details of the position of the gages can be seen in

figures 2, 3 S and ip,

ip , 3 Rate of Loading and Unloading,

At the inception* this test was to have been a s‘hor~

term test to destruction, but due to the steady increase In

deflection after application of the first two increments of

load it was decided to apply a load equal to two '’design

loads” and allow enough time to elapse so that the specimen

would reach a state of equilibrium before any further loads

were applied,

‘ 6 ,

Loads were applied in 10 lb/sq ft increments by distributing six 100 lb bags of sand over each roof panel, The

sand was placed one bag at a time on each end and spread over

one sixth of the area of each roof panel „ The bags were distributed alternately on each panel until the required amount

of sand had been applied.

One design load of 20 lb/sq ft was applied during the

course of the first day and readings were taken before and

after each increment of load. The following day another design load of 20 lb/sq ft was added making a total of IpO

lb/sq ft. As before 3 readings were taken before and after application of additional load.

Readings were taken and recorded every day for a period

of 2lq. days at which time the structure appeared to have

reached equilibrium. On the twenty fifth day two additional

design loads were applied making a total load of 80 lb/sq ft s or four times the design load. No planes of weakness were

noticed at this time and the structure was allowed to remain

so loaded for an additional five days until it again reached

equilibrium.

The structure was then unloaded in a manner similar to

the manner in which it had been loaded. Readings were taken

to determine immediate recovery and a period of seven days

elapsed until maximum recovery was realized. The structure

was then carefully disassembled and stored for future testing,

I4. 0 I+ Test Results

The stress-strain curves obtained for the concrete used

in Precast Panel Frame No. 1 are shown in figure 5= The original casting schedule was such as to produce a wall panel

and roof panel for each of two castings % however s the roof

panel of the second pour was damaged during removal from the

form and necessitated casting on additional roof panel. The

concrete in the first wall and roof section was 62 days old

at the beginning of the test and a compressive strength of

7210 psi was realized from the 6= by 12-in. control cylinders.

Wall panel No. 2 was l\.Q days old and roof panel No. 3 was 31

days old at the beginning of the test and produced compressive

strengths of 6530 psi and 6870 , respectively., ^he tangent

modulus of the average of all sections was Ij. j 650 5 000 psi.

Compressive tests were made of control cylinders of the

1 s 3 mortar mix that was used to anchor the wall sections in

the footings and a strength of 6230 psi was realized at 25

days. The compressive strength of the neat cement paste used

to grout in the bolts was 58l0 psi at 27 days.

7 °

The first visible cracks occurred at the inside intersection of the wall with the footing at a load of 30 psf both

at the north and south ends „ No further cracking was observed

until a load of IqO psf was applied at which time cracking was

observed at the intersection of the transverse ribs and longitudinal legs of the roof panels at the crown. Cracks occurred

at each of the four intersections and were the most prominent

to appear throughout the test. These cracks are clearly visible in figure lip 0 It is recalled that the reinforcing bars in the transverse

ribs terminated at the midplanes of the longitudinal edge

beams. Had the reinforcement in the transverse ribs been extended into the edge beams, the width of the cracks at the

corners would have been considerably less, and the opening at

the bottom of the crown joint would have been less pronounced.

Also observed at the ipO psf load was longitudinal cracking on the under-side of the roof panels located approximately

at the third points and extending the length of the panels.

Transverse cracks were also observed in the roof panels about

2 ft from the wall. The cracks in the roof panel are visible

in figure 12,

Prominent cracking also occurred at the bolted connections

of the wall and roof sections, A typical crack of this kind can

be seen in figure 12, When these cracks appeared, it was believed that they were caused by high bearing stresses in the

immediate vicinity of the bolted connections. This hypothesis

was confirmed by examination of the bearing surfaces of the

roof and wall panels upon dismantling the structure. It was

found that some of the cement grout which had been forced between the bolts and pipe sleeves had come between the wall and

roof panels causing a slight separation and therefore a stress

concentration. This result dictates either a change in the

application of the bolt grout or abandonment of the procedure

altogether to insure more bearing area between the wall and

roof panels. It appears that greater precautions will have to

be taken during the casting of sections to insure proper fit

and consequently greater bearing area between all sections.

The greatest movement was observed, at the crown, A

single l/lOOO in, dial gage was placed at the center of the

specimen at the crown as seen in figure ]q , The maximum defle . tion occurred just prior to the removal of the total load of

80 psf and amounted to 2,88 Inches, Upon removal of load the

observed recovery was 1,15 inches.

The spread of the entire structure reached a maximum au

the same time and the average spread of both ends was Jp6 in,

accompanied by a recovery of ,20 in.

Figure 7 shows the deflection of the center joint and

the spread at ends plotted against the applied load c The

displacements plotted are the values observed immediately

after application of each load increment and do not include

the increases resulting from the loads being sustained over

long periods of time. It is noted that the structure was

subjected to a load of IpO psf for a period of Ip 1_ days, after

which the load was increased to 80 psf. Figure 7 shows that

the structure was apparently stiffened by the sustained load

test, as can be seen from the steeper slope of the loaddeflection curve for the increments of load added subsequent

to the sustained load test.

Measurements were made of rotation at the end joints,,

center joint and also of the side walls with respect to the

footings . Figures 3 and 4 show the instrumentation used for

the measurement of the rotation at the end joints and center

joint, respectively „ Figures 8 and 9 give the results of

these measurements plotting rotation in radians against time 0 Rotation at the center and end joints reached a maximum four

days after the application on the 80 psf increment of load.

The maximum observed rotation at the center joint was

O 0325 radians with a recovery of .0120 radians observed after

removal of live load. The average of north and south end rotations was .0080 radians with a recovery of .0053 radians.

The observed rotation at the footings reached a maximum

just prior to removal of the live load and was .00011? radians

with a resulting recovery of .000047 radians.

The calculated instantaneous rotations as shown In

figure 10 verify the conclusions stated with regard to the

Instantaneous deflections shown In figure ?»

Changes in the width of crack between the wall and roof

sections and also at the crown were measured with 1/1000 In.

dial gages as seen In figures 3 and 4= The gages were placed

in such a way as to measure the maximum opening. Figure 11

Is a graphic picture of the results of these measurements.

The maximum crack opening at the crown occurred at the maximum load of 80 psf and was .25 in, just prior to removal of

load. The maximum crack opening between the wall and roof

panels was .075 in. Recovery was observed for six days af’er

the removal of the live load and amounted to .098 in. for the

crack at the crown and .030 in. for the cracks between the

wall and roof panels.

As can be seen in figures 6, 8, 9 , and 11, the displacements and rotations observed in the structure were affected

markedly by the duration of the test as well as by the magnitude of the applied load. A time Increment of 4l days elapsed

9 .

between the application of the i_|_0 psf load and the application of the 80 psf load, The continued increase in deflections and rotations under the second increment of l^O psf

indicates that considerably larger movements in the structure would have been observed had the maximum load of 80 psf

been allowed to remain on the structure for a longer period

of time

„

10 .



FIG. 1IT

4-0

44

12 note: eon STEEL /// PANELS

SEE DETAIL "A"

TYP

/

CAL SECT!ON THRU

RD"F Y : ICE '//ALL PA HELL

MO. 4 BENT 3

"

CACHEMO

—y~

"T I

I- 0

. Ps .

"h

*

Or) £

1 _I_

'EOT! ON A -A

SEAL s: Z"= / - o"

4 - o

I 5

Zk Is

fSYM ABOUT £

3ECT/ON 5-5

scalz: 2~*r-c n

1

—

— \f

- f * BOLT

r 4

1

J.

0

, i

PRECACT PANEL

frame

DA'S 9-8-53 SKETCH A

Pig

o 2

-

Precast

panel

frame

(before

test)

: A

f

lr/

' r

jl

Center

joint

(before

test)

6000

CO

Q_

_ 4000

CO

c

o

LU

cr\—

CO

2000

FIG. 5

STRESS-STRAIN CURVES OF PRECAST PANEL FRAME NO. I

COMPRESSIVE TESTS OF 6" X 12" CONCRETE CONTROL CYLINDERS

STRAIN, MICRO IN. /IN.

DEFLECTION,

INCHES

DEFLECTION,

INCHES

FIG. 6

FIG. 7

DISPLACEMENTS VS. APPLIED LOAD

.6 .8

INCHES

350

300

250

200

150

100

500

55

350

300

250

200

150

100

50

0

FIG. 8

ROTATION AT JOINTS VS. TIME

TIME, DAYS

ROTATION,

RADIANS

1.50

55

ROTATION,

RADIANS

1.50

FIG. 9

ROTATION AT FOOTINGS VS. TIME

i

pc

/cr>

PT

P

RATIONS GIVEN

CD IMMEDI

-OF EACH

NOT INTING

OVER

i f

1 0 10 20 30 40 50

I ' 

. I V

ROTATION AT JOINTS VS. APPLIED LOAD

20

0

P^

V/' /S/ /

/

/

/

/

/ /

1 1

i

i / /

/

/

/

/

/

/

0 10 20 30 40 50 60 0

/

/

/

/

/

/

/

/

/

/ note: the values of rotations given

7 HERE ARE THOSE OBSERVED IMMEDI -

/ ATELY AFTER APPLICATION OF EACH

INCREMENT OF LOAD AND DO NOT INCLUDE THE INCREASES RESULTING

FROM LOADS BEING SUSTAINED OVER

LONG PERIODS.

/

100 150 0 10

/

/

/

/

/

/

/

/

/

/

20 30

ROTATION, RADIANS x 10

-4

CRACK

WIDTH,

INCHES

.30

.25

.20

.15

.10

.05

55

FIG. II

WIDTH OF CRACKS VS. TIME



13 - Crack pattern, north wall panel

(load = 80 psf)

Cracking at center joint (load = 80 psf)

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

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