This report has been prepared

for informatiGn and record

purposes and is not to be referenced

in any publication.

NATIONAL BUREAU OF STANDARDS REPORT

h-920

FIRE TESTS OF PRECAST THIN-SHELL CONCRETE ROOF PANELS

by

J. V. Ryan

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 STANDARDS REPORT

NBS PROJECT NBS REPORT

1001-10-^811 November 5, 1956 4920

FIRE TESTS OF PRECAST THIN-SHELL CONCRETE ROOF PANELS

by

Jo Vo Ryan

to

Bureau of Yards and Docks

Department of the Navy

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication

unless permissii 25|D.C, Such

cally prepared

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

or in part, is prohibited

r Standards, Washington

I report has been specifiir report for its own use.

FIR^. TESTS OF PRECAST THI I--SIPCLL CO:.'CRETE ROOF PATT^LS

Fourteen fire tests were made on precast tliinsliell concrete roof panels. The panels' crosssections v/ere channel shape. Some had intermediate

transverse rihs; others did not. The panels for the

first two tests were reinforced conventionally , the

remainder had prestressed reinforcement. The last

four panels 'had insulating underfaces. The observed

fire endurances ranged from 6 min to 31 min.

1. Introduction

The desirability of conservation of materials, reduction

of wei,ght, speed of erection, and other factors has lead to

the investigation of new design techniques or nev/ combinations

of , existing techniques in building construction. One such

combination is, represented by precast thin-shell prestressed

concrete construction.

. Precasting removes the fabrication of concrete building

elements from the field to the factory and makes possible

greater control of materials, mix proportions, curing

conditions, and other factors tending to improve quality.

The use of precision casting forms is essential to permit rapi

erection of close fitting elements on the building site.

Thin-shell design makes use of efficient cross-sections

thereby providing the necessary strength, or other characteristics, with the minimum amount of materials. This in turn

leads to reduced v/eight for the building.

Prestressing involves putting a high tensile stress on

the primary reinforcement and maintaining it by one of

several methods, thereby producing compressive stresses in

the concrete. The applied load on the structure in service

must overcome, these compressive stresses before tensile

cranks can develop in the concrete.

A research program on the fire resistavice of roof panels

of this type was carried out under the sponsors'',ip of the

Bureau of Yards and Docks, U. S. '"^avy. Department of DefenseFourteen fire tests were carried out in the lational Bureau
-2 -

of Standards' large floor furnace. All the roof panels were

precast thin shell concrete. Those for the first two tests

were reinforced conventionally; the remainder were prestressed.

The last four panels had insulating underfaces. The panels

were tested without load or under one of various applied loads.

2, Materials and Specimens

In order to reduce the possibility of batch-to-batch

variations, the concretes for the specimens were prepared

and poured by the laboratory staff rather than by an outside

contractor. The gravel aggregate was graded to size and the

mix components weighed carefully. Therefore, the quality of

the concrete and workmanship may have not been representative

of that obtained ordinarily. Also, one of the insulating

underfaces, a lightweight concrete, was a recent laboratory

development not yet used extensively in the field.

2.1 Materials

Wire fabric, a 2 by 2 in. square mesh of 12 ga galvanized

wires (SW ga), was used in all the panels. The longitudinal

reinforcement was of 3/^ in. deformed steel bars for conventional and of 1/2 inch diameter smooth bars with threaded ends

for prestressed construction. The transverse bars were 1/4 in.

deformed in the conventional panels and 1/2 in. (No. 8) deformed for the prestressed panels. One inch hexagonal 13/16 in.

long nuts tapped 1/2 - 20, 1 1/4- in, diameter washers, and

2 1/2 by 2 1/2 by 5/8 in, bearing plates were used with the

prestressed bars.

The coarse aggregate was White Marsh gravel, a siliceous

aggregate. All the gravel had passed through a 3/^ in. mesh

sieve. The cement factor was seven bags per cu yd for all

panels

Glass fiber mats 1/2 in, thick were used as underface

material on two panels. A perlite aggregate foamed concrete

was used similarly on two other panels.

2.2 Specimens

The individual panels were in the form of long

channels. For the conventionally reinforced construction,

they were 17 ft 10 in, long, 4 ft 2 1/2 in. wide, 1 1/4 in,

thick shell, with an 8 in. deep flange along each size plus

6 in, deep transverse flanges at each end and equally deep

transverse ribs at center and quarter points, thereby dividing

the panel into four thin-shelled bays. The reinforcement
-3-

consisted of a single No. 6 deformed steel bar located 3A in,

from the bottom of each longitudinal flange; two No. 2 d'-^formed

steel bars in each transverse rib or flange; and 2- by 2-in.

mesh No. 12 ga welded wire fabric at the center of the 1 1/4

in. thick top shell. The wire fabric was turned down into

each longitudinal flange. The panels were cast in a mold

prepared for the purpose and the flanges, ribs, and shell were

all cast at the same time. The concrete was mixed on^ part high

early strength Portland cement, 2 1/2 parts clean bank sand,

two parts clean White Marsh gravel. The concrete was vibrated

in the mold to eliminate voids. The details of the panels,

including locations of reinforcing bars, are given in figure 1.

The prestressed panels were 17 ft 7 3/8 in. long, 4 ft

2 1/2 in. wide, 1 in. thick shell, with a 6 in. deep flange

along each side and 5 1/2 in. deep flanges across each end.

For some of the panels transverse ribs 4 in. deep were located

at the center and 4 ft 5 1/2 in. each side of center,

reinforcement consisted of a single 1/2 in. diameter prestressed bar in each longitudinal flange; single No. 4

deformed bars in each transverse rib or flange; and 2- by

2-in, mesh No. 12 ga welded wire fabric at the center of the

1 in. thick shell and turned down into the longitudinal and

transverse flanges. The No. 4 bars were turned into the

longitudinal flanges for a length of 8 in. The panels were

cast in a mold prepared for the purpose. Before the

concrete was poured, the mesh, deformed bars, and ducts

for the prestressed bars were placed in the mold, the latter

so that the center of the bars would be 3 in. from the bottom

of each flange at each end and 2 in. at the center. The

concrete was mixed in the same ratios as for the conventiopially

reinforced panels. The flanges, ribs, and shell were cast at

the same time. The concrete was vibrated in the mold to

eliminate voids. The same procedure and mold, with’ appropriate

modifications of the latter, were used for the panels without

intermediate transverse ribs and for the panels with' insulating

underface. The insulating material was placed in the mold

to provide a 1/2 in, thick layer below the 1 in. thick shell but

none on the flanges. The concrete was then poured onto theinsulation. The details of the prestressed panels are shown

'in figure 2.

Each specimen was covered with burlap in the mold, and the

burlap wet down periodically for several days. The prastressing

bars were placed in the ducts after the sides of the molds had

been stripped. The bearing plates, washers, and nuts were

put on the ends of the rods and the nuts tightened sufficiently

that the panel could be lifted and stored. Later in che aging

period the bars were stressed by a jack and the nuts tightened

against the plates and washers, holding th'e stress.
3. Test Method

3ol Aging and Conditioning

The panels were aged for various periods of time in a

large work room that was heated and ventilated according to the

season and weather

Three of the specimens were further conditioned by heating

the furnace chamber to temperatures of about 125 to 150°F

during the 10 days prior to test. The specific period of

aging for each test specimen, as well as other information,

is given in table 1.

3*2 Fire Test Procedures

For the two tests of conventionally reinforced construction,

and the first test of prestressed construction, three of the

panels were placed in the floor furnace as shown in figure 1.

Thereafter only one panel was placed in the furnace, centered

between the sides, and the remainder of the furnace opening

closed with previously exposed panels or filler slabs. The

panels were in close contact along their edges and the joints

filled with grout. In the case of a single panel and filler

slabs, a space of a few inches width was left between to permit I deflection of the specimen. This space was filled with

mineral wool or glass fiber insulation.

The conditions of loading varied. Some specimens were

loaded by the dead weight of the hydraulic loading equipment;

others by concrete cylinders as weights; and still others

were not loaded. Table 1 gives the load applied and the number

of panels in each test specimen.

The furnace fires were controlled to provide temperatures

as near as possible to those defined in ASTM E-119j which

include; 1000° F at 5 min, 1300° F at 10 min, 1550°F at 30

min, 1700°F at 1 hr, and l850°F at 2 hr. The performances of

the specimens were determined by the following end point

criteria: 1) rise of the average temperature on the unexposed | surface to 250 deg F above its initial value, 2) rise of

the maximum temperature on the unexposed surface to 325 deg F

above its initial value, 3) failure to sustain the applied

load, 4-) development of cracks or openings large enough to

permit the passage of flames or gases hot enough to ignite

cotton waste.
he Results

The thin-shell or weh sections of one of the conventionally

reinforced panels and of two of the prestressed panels spalled

explosively. The spalling involved the entire thicknesses

of the webSo Otherwise, the results of the various tests were

such that they could be separated into two representative groups

within each of which the results of the individual tests were

similar. The ten tests of panels without insulating underfaces

make up one group, the four tests of panels with such underfaces make up the other,

^-,1 Non-insulated Panels

Cracks developed in the unexposed surfaces of all the

panels. The pattern included cracks parallel to the edges,

ends, and transverse ribs* Cracks also developed in the

unexposed vertical surfaces of the longitudinal flanges and of

the end transverse flanges. The unexposed surface cracks became

as wide as 1/8 in, during tests of 1 hr or more duration. Very

few cracks were observed in the exposed surfaces during the

tests but were observed after cooling.

In three tests, one of a conventionally reinforced panel

and two of prestressed panels, the thin-shell webs spalled

through explosively. Prior to the spalling, which occurred

at 10 min in two tests and 6 min in the other, there were a

few fine cracks. Figures 3 and show views of two of the

spalled panels.

The deflections of the longitudinal flanges were upwards,

initially, reaching individual maxima of 0,7 to about 8 in.

An example is shown in figure 5» Except in the very short

tests, the deflections decreased from these maxim.a and, with

one additional exception, became downward with respect to the

initial' position of panel* The additional exception was one

test (384) in which the thermal expansion of one of the prestressed bars was sufficient to jam against the furnace frame

and hold the panel in an arched position. The downward

deflections of the other panels reached values of 8 in, to 2 ft.

In many Instances these deflections represented the limit of

slack in chains attached at mid-span to prevent complete collaps

The thin-shell webs of the panels with intermediate transverse

ribs, and the ribs, sagged with respect to the longitudinal

flanges. The deformations of the webs of the panels without

transverse ribs were less consistant. In some cases they were

upwards, in others downwards, and in still others upwards along

part of the panels length and downwards along other parts at

the sam.e time. In general, the deformations of the webs

became downward as the tests progressed.
-6 -

The limiting temperature rises on the unexposed surfaces

were reached in from 6 to 1^ min; the test durations were

from 7 min to 2 hr 3 min. Table 2 gives a summary of the

observed results for the individual tests.

h,2 Insulated Panels

The cracks that developed in the unexposed surfaces of

the four panels with insulating underfaces were less

prominent and less extensive than those in the other panels.

Cracks up to 6 in. in length were spaced every few inches

across each end. These cracks extended down the end faces.

In two panels single cracks developed in one longitudinal

flange and in one panel a few short disconnected cracks

parallel to the longitudinal flange developed in the unexposed surface.

The glass fiber insulation on the exposed surfaces of

two of the panels fused and dropped off in pieces. By the

end of an hour of exposure, most of the insulation appeared

destroyed as shown in figure 6, The perlite-foam concrete

underface did not show any signs of damage other than

craze cracks. None of the exposed structural concrete of

the panels spalled or sluffed off.

The deflections of the four panels were in the downward direction throughout and reached values of from 11

to 20 in. by the ends of the tests. The thin shell webs

sagged with respect to the longitudinal flanges. The

deflections of the panels and sag of the webs were so

large that some of the concrete cylinders used as applied

load on two panels were toppled over, as shown in figure 7*

The limiting temperature rises on the unexposed surfaces were reached in from 28 to 31 min. Corrections for

fire exposure in accordance with the procedure given in

ASTM E-119 reduces the time range to 29 to 31 niin for the

corrected fire endurance limits. Other data from the

individual tests are given in table 2,

4.3 Load Failures

Although the fire endurances of the non-insulated panels

were limited to not over l4 min and of the insulated panels

to not over 31 min, all by temperature rise on the unexposed

surface or passage of flames through openings resulting

from spalling, most of the tests were continued in order

to obtain as much information as possible. Five of the

panels, as indicated in table 2, were considered to have

failed under load. The times at which this occurred ranged
-7-

from 1 hr to 1 hr 53 min« Of the five, two collapsed. In

addition, three other panels had deflected to such an extent

that they were supported by chains installed in several of

the later tests to prevent collapse. The conditions of these

three panels were such as to indicate that load failure was

imminent.

5. Summary and Discussion

The cause of the violent spalling of the thin shell

webs of three panels is not obvious. Possible causes include

stresses set up by the very steep thermal gradient across

the web, and superheating of trapped moisture with the

resultant development of high pressure steam.

The high moisture content of freshly poured concrete

decreases with age as the excess water moves to the surfaces

and evaporates. This process continues until the concrete’s

moisture content reaches equilibrium with the surrounding

air. The process is slow but may be accelerated by raising

the temperature of the concrete. However, the temperature

cannot be raised above the boiling point of water without

the danger of damaging the concrete. A comparison of the

various specimens that spalled with those that did not spall,

in terms of age~at~test and heating to not above 150°F, is

given in table 3® The data indicate that each of three

specimens aged up to four months and not heated spalled

whereas two specimens aged four months each and heated did

not spall, and those aged 7 1/2 months or more did not spall,

whether or not they were heated. Although it was not practice

to make moisture content determinations of the specimens

before test, it is reasonable to believe that the specimens

that spalled had greater moisture contents than the specimens

that had been heated or aged for a longer time. However,

the strong possibility that the spalled specimens had

comparatively high moisture contents does not prove that the

latter caused the former. Had moisture content been the

cause, spalling should have occurred in the transverse

ribs and longitudinal flanges. These, members were not

spalled in any instance. Therefore, it appears that moisture

content was not the sole cause of the spalling, but may have

been a contributing factor.

The thermal gradient through a homogeneous material

is not linear, ordinarily, when the temperature to which

the hot surface is exposed is changing. The data from these

tests, and published data from other standard fire tests of

concrete slabs, show that the thermal gradient is steepest

near the hot surface and lessens with increased depth from

that surface during the first half hour of exposure. Comparison of the data from these tests with the published data
-8

-

at the end of 30 min indicates that the average gradient

across the 1 in» thick weh was not nearly as steep as that

across the first 1 in. of thicker specimens. The expansion

of the hot surface layer produces tensile stresses in deeper

concrete. Even though the above comparison of gradients

indicates that these stresses should be greater at 1/2- and

1-in. depths in thick specimens than at the center and back

face of 1 in. thick webs, the former have the support of

the additional depth to resist the formation of tension

cracks and spalling. In addition, the presence of the wire

mesh in the center of the thin webs might be expected to

produce a slight discontinuity, similar to that between

successive layers of laminated materials, at a depth where

a steep thermal gradient would produce shear stresses parallel

to the plane of the mesh. Therefore, it appears that the

thermal gradient would be more likely to lead to spalling

of the webs than of thicker sections such as the flanges

and transverse ribs.

The foregoing discussion indicates that 1) high moisture

content should be less likely to produce spalling in specimens

having had long aging and heating than in those having had

shorter aging and no heat, 2) moisture content should be

more likely to produce spalling of the surface from thick

sections than from thin sections having been aged under

similar conditions, 3) that the stresses resulting from steep

thermal gradient should be more likely to produce spalling

of thin sections than of thick sections. Points 1 and 3 are

in agreement with the observed results whereas point 2

disagrees. This tends to support the thermal gradient as

the cause. However, further examination of the data weakens

this support. The average temperatures of the furnace fires,

the wire mesh at the centers of the thin webs, and on the

unexposed surfaces of the three specimens that spalled

were very nearly equal to the overall averages for all the

non-insulated specimens and were slightly lower than those

for two specimens, of the same age, that did not spall.

These two specimens had been heated during aging. The

thermal gradients, as indicated by graphs of temperature

versus depth from the exposed face, were of the same order

of magnitude for the several specimens.

From the above considerations it can be seen that there

is some support and some contradiction for both thermal

gradient and high moisture content as the cause of the

spalling. In the absence of clear indications for one, it

may be assumed that each was a contributing cause to an

effect, spalling, that neither could produce alone.
-9-

The results of the several tests in the program

indicate that thin shell concrete slabs of the type and size

investigated will provide about 10 min fire endurance as

determined by the methods given by ASTM E-119. However,

the addition of 1/2 in. of either glass fiber or perlite

concrete insulation to the underface of the thin-shell

sections will lead to fire resistances of about 30 min*

Well aged specimens can be expected to continue as

effective barriers to the passage of flames for about

1 hr but panels may spall through if exposed to fire

within the first four to seven months after casting unless

heated to reduce moisture content®
Table

1«

Details

of

Specimens

and

Test

Conditions

Td

cd CM CM CM CM o -P -P -P -P

hi ft ft P-l ft CM CM CM CM CM \ -P -P -P -P P

Td H H 12 12 ft ft ft ft ft

0 1—1

—1

—1 H \ \ \ \ •H 12 H 12 p P

rH nonono 0 no 0 rH 1—10 1—10 1—10 1—1 P » • • P • P P P P

P ItnUMts OUn OOO CO oJ- oj- o ph

t—1 1—1

1—1 S 1—1 S CM CM S rH S H S 1—

-PCM P fcuO * ft Si Si o o o o O O O O O

a 0 -H OnOCO ON OJ- H NO CM o p\ CO CM t>- 1—

hunctn cm O -P NO NO NO IfN nonoj- NO

CO H

-P -P P P P to 0 0 0 0 >5 0

H POO O^HP-PPOOOOO o

txO-P. O Td Td Td TJ P o Td Td Id td Ti Td p d 0

•H !3 :so n

P 1—

O 1—1 1—1 •H o P a

•tH o o

rd ana

P 1—1 o o o o o

o tJ CM 1 CM a a a p a

o p \CM \ o

"H 1—1 1( CM CM CM CM a CM U H o\ o\ o o\ o\ <4 no no a H a H S S iH S rHOO rH

I o I ro H noJ- ^ l^^ CO O\00 CO O- no 0

cd •H

Td w

0 rQ

a -H

fH ^

0

-P

Si

0dooo oooooo o

nononoo'TiTci'ci Td'dTd'Ti'ri'rJ Td

I—

M

si •Ho

p

0

Ch

si •H0

01

1—1 p Td p 0

o to

•iH to P O 0

P Td p

0 p

> to P 0

o p o ft

o o o o oooooo o

TJ Tl Tl Tl 'll Tl

Ch 0

O H

0

* si O cd

0-, nononOH H H H I—I I—I rH I—I i—I

I—I i—

0

-P

Cd Q

nOJ- J- UMcaItn

\WONsOCO Itn OvOoO H H OJ WO rH C\J C\J \ O no rH H I—I rH no

^0^D\D\0^0

\0 lp\'Lr\l{Mr\lP\

. C\] J- lTN\D ON

00 I—I I—1 I—I I—I I—

no no no no no no

vO

lT\ \o

CM \no

-P » in o

0

EH

ICNONvO [N-CO CTsCM no no no no no no no

noJ- 1>-00 CT\ \OnOnOnO\DnO no nononononono no
Test

Times

at

which

end

points

reached

DuraTime

at

which

Fire

Load

Fire

Footnotes

No-.

Temperature

rise

Load

Flame

tion

main

reinfo

Exposure

lifted

Endur,

2^0°

F

32

5"° F

FailPassage

reached

temp^

Severity

Corrected

0

0 rO

03 0 o ^ -H ^ H

p

P

cti

6

h 1) -pP P

1

r—

1

P

0

> 0 0 P -H1 #s t3 -H 0 ft 0 p

0 m ft ft 0 a t3 p

rH 0 ct3 P P •H 01 rP

.—1 1—1 rH 0 -H 0 a

03 ft .—1 cti 0 a! 0 0

P-W 0 P ;P ft rai P P

0 0 000 W T-3 cd 0

o3 rP 0 0

0 0 M) vO 0-00 ON 1 1 0 0 OnH (JN H H 0 0 0 0 0 1 1 I—

1

rH rnCM roCM

0 000600 6 6 60006

OO

O

CM a

iH

fe

0S > O o3

0

P

P

a

>

o3

0 0 0

CM ON J" NO

IfN un UN

1 .. 1 1 1 1 ^ 1 • 1 1 1 •• 1 1

1 1 0 0 0

0 ONHOO^ J-nD on 0- (V\J- UnUnO

-0 0 0 » f> 0 > 0 0 rn CM UN 0-00 H CM H CM UNO onoo

ON 0 H 0^ 0 0^ (ON (ON 0 ONO (ON (ON

I—i I

1—1 I—i

1—

1

00 ro 1—

1

on J" NO

00 I—1 UN 0 Un

«• • • 1 1 •• 1 1 • • • • •• 1 1 1 1 0 H I—

1

0 - H 0

0 0

'O' iTN vo on ON 00 NO ONC^ 0 '• CM-

• • 1 1 0 UN UN 0 IfN CM

•• •• 1 1 1

t—

1

I—

1

I—

1

0 0 0 I 0 1—

1

-h1(NJ CM OOOOO-OO CM rH J—

1

(ON unoo o-on 0 0 rH 0 CM 0 0 0 on CM CM UNrH 0

I—1 CM 0 0 1—1 1—1 1—

1

1—

1

I—1 1—1 1—1 0 1—1 1—

1

p P P

D ITN OnO

H rH H 0

1 1ft t* 1 1 1 1 1 t 1 1 1 DO 0 0

r 0

rP rP 0

rn 00 J- (ON 0

UN CM 0 0 p CM CMO 0

1 •• 1 1 .• 1 1 1 •• •• 1 1 ••

I—1

1

1 1—It—1 1—

1

0 CM nD 00 CJNrH CM NO CM ONCM rH CM

I

rH 0“t f 1 0 0 rH 1—

1

r—1 rH 00 (p(p 0n 6 0 0 006 c) 6 06660

0 oco 0-00 (ON 1—

1

0 HOO rHOO

1—

1

.

1 0 000 f“H 1—

!

H on CM on CM 6 6 6 006 c:) 6 6 6 0 6 6

iTN OnO IN-OO on cm on UnnO O-OO (ON CM J- J-nO NO NO nOnDnDnOnO

00 Ip on no no 00 00 on on (p on (p on on
Table 3o Ages of Panels and Behavior as to Spalling

Condition Spall

,

ase

No spall,

ase

Conventional , no heat, 1/2 loaded 3 1/2 mo 10 1/2 mo

Prestressed, no heat, loaded. 8 mo

Prestressed, no heat, 1/2 loaded 3-3 1/2 mo 9 mo

Prestressed, no heat, no load 4 mo 8 mo

Prestressed

,

heated, loaded - 7 1/2 mo

Prestressed, heated, 1/2 loaded - 4 1/2 mo

Prestressed

,

heated, no load - 4 mo

Insulated, prestressed, no heat. 1/2 load 3 1/2 mo*

Insulated, prestressed, no load. no heat 7 1/2-8 1/2 mo

*Includes consideration of results from two tests
FIG. I

CONSTRUCTION

DETAILS

OF

PRECAST

ROOF

PANELS
t OF PRESTRESSJNG STEEL (PARABOLIC CURVE! t OF PRESTRESSING STEEL TO BE 2" UP FROM BOTTOM OF RIB AT ^ OF PANEL

SIDE ELEVATION

PLAN

SECTION 1-1

i * 1 , ‘

^ :

^HCJ lZ :• ^ INSULATING UNDERFACE

ON THIN SHELL ONLY

SECTION 2-2 SECTION 2-2

ALT I SECTION 2-2

ALT 2

FIG. 2 CONSTRUCTION DETAILS OF PRECAST- PRESTRESSED ROOF PANELS

NOTES

CEMENT FACTOR MAXIMUM SIZE AGGREGATE7 BA6S/CU YOr

e

INTERMEDIATE GRADE REINFORCING 24,000 PSI ^IRE MESH 30,000 PSI
m

< ' V

Fig. 3. Exposed surface of center panel, test 3^+6, showing spalled area of panel with transverse

ribs

.

Fig. 4. Exposed surface of center panel, test 3^7,

showing spalled area of panel without

intermediate transverse ribs.

:k..

Fig. 5. Arched condition of panel, test 364, tested

v/ithout applied load.

• V

^ * "!• '

Fig. 6. Exposed surface of specimen having had glass

fiber underface, showing remains of same and cracks in concrete.
v*|t
(1) o *H a' +j a' w s

0 iH cl CD CD <i-i <D -H

1-f Q) CX'O

Ch TJ CO

0> P

T3 fH to C

(U -H -Ci

r-t £ C C'

0) -P -H\0 -H C fn CO rP

cO 3 £! >> >>

01 tin O ,0 o

CO

Cl

CP

tuO

2400

0o‘3dniVid3dlAI31

Figo 8« Representative time -temperature curves of

non-insulated panels* 325, spalled panel;

3^8, about same age as 325 , heated, rio spall;

362, heat, longer aging, no spall.

TIME.

HRS.
2400

0o‘3dniVH3dlM3l

Fig. 9» Representative time -temperature curves of

panels with insulating underfaces. 366,

lightweight concrete insulation; 368, glass

fiber insulation.

TIME.

HRS.
THE NATIONAL BUREAU OF STANDARDS

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