NBSIR 73-135

Fire Endurance Tests of Steel

Sandwich Panel Exterior Wall and

Roof/Ceiling Constructions

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington. D. C. 20410

December 1972

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington. D. C, 20410

NBSIR 73-135

FIRE ENDURANCE TESTS OF STEEL

SANDWICH PANEL EXTERIOR WALL AND

ROOF/CEILING CONSTRUCTIONS

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington. D. C. 20410

December 1972

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington. D. C. 20410

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent. Secretary

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director
•1
Fire Endurance Tests of

Steel Sandwich Panel Exterior

Wall and Roof /Ceiling Constructions

by

B. C. Son

Building Fires and Safety Section

Center for Building Technology

ABSTRACT

As part of the evaluation of a housing system proposed under

Operation BREAKTHROUGH, fire endurance tests were performed at the

National Bureau of Standards on an exterior wall assembly and a roof/

ceiling assembly. Both constructions were assemblies of sandwich panels

composed of paper honeycomb core with sheet steel facings.

The test method was in accordance with the requirements of ASTM

E 119, Standard Methods of Fire Tests of Building Construction and

Materials,, for loadbearing structures. The applied live load was 237 pounds

per linear foot (plf) for the wall assembly and 28.6 pounds per square

foot (psf) on a 13 ft 5 in. span for the roof /ceiling assembly. The

results of these tests are valid only for walls and roof /ceilings of

such constructions described in this report and loaded at or below the

stress levels developed by these loadings.

The fire endurance of the wall assembly was 7 minutes 50 seconds

;

and of the roof /ceiling, 9 minutes 09 seconds. In both cases, the

failure was due to maximum temperature rise of 181° C (325°F) above the

initial temperature on the unexposed surface.

Key Words: Exterior wall; fire endurance; fire test; housing systems;

Operation BREAKTHROUGH; paper honeycomb; roof /ceiling

assembly; structural sandwich panel

1
TABLE OF CONTENTS

Page

ABSTRACT i

1.0 INTRODUCTION 1

2.0 DESCRIPTION OF TEST STRUCTURES 1

2.1 General 1 2.2 Wall Assembly 2 2.3 Roof/Ceiling Assembly 3

3.0 TEST METHOD AND EQUIPMENT 4

4.0 TEST EVALUATION

.....

6

5.0 RESULTS OF TESTS 6

5.1 Wall Assembly Results 7 5.2 Roof/Ceiling Assembly Results , 8

6.0 DISCUSSION OF RESULTS ..... 9

Table I 10

Log of Wall Test Observations

Table II 11

Log of Floor/Ceiling Wall Test Observations

Appendix I 12

SI Conversion Units

ii
1 . 0 INTRODUCTION

A loadbearing sandwich panel exterior wall assembly and a similarly

constructed roof/ceiling assembly bpth designed for single family housing were submitted for fire endurance testing at the National Bureau of

Standards. The work was sponsored by the Department of Housing and

Urban Development under its Operation BREAKTHROUGH program. The test

methods were generally in accordance with the requirements of the Standard

Methods of Fire Tests of Building Construction Materials, ASTM E 119—^.

The test structures consisted of steel-faced panels with paper

honeycomb cores with wood tongue-and- groove edging. The constructions

were innovative to the extent that the available results from existing

fire tests could not be made applicable. Although the heat transmission

characteristics of thin steel sheet has been long established, the

performance of paper core sandwich panel, especially when partially filled

with insulating material, required investigation.

2.0 DESCRIPTION OF TEST STRUCTURES

2.1 General

Both the exterior wall assembly and the roof /ceiling assembly were

made of 4 ft wide panels consisting of a 3 in. thick paper honeycomb core

partially filled with a solid polyurethane foam, and 26 gage (0.0179 in.)

sheet steel facings.

— Standard Methods of Fire Tests of Building Construction and Materials , American Society for Testing and Materials Designation E 119-71,

available at 1916 Race St., Philadelphia, Pa. 19103

1
The paper honeycomb core weighing 99 lbs. per ream (3000 sq ft of

sheet stock) had 3/4- in. hexagonal cells. The weight includes an impregnating phenolic resin representing 11 percent of the finished weight of

the material. A rigid and friable sheet of polyurethane foam weighing

3

1.5 lb/ft was pressed into the honeycomb core. An epoxy adhesive bonded

the honeycomb core to the steel facing sheets. The steel sheets were

galvanized, phosphatized and finished on exterior surfaces with a baked

on silicon paint.

The long sides of each panel were closed with tongue-and-groove wood

edge pieces and the short sides with nominal 2 x 4 in. wood edge pieces,

which were attached to the steel sheets with 14 gage (0.08 in.) 5/8-in.

leg staples at 12 in. centers for the wall assembly and at 15 in. centers

for the roof /ceiling assembly. The wood members were hemlock-fir. No.

2/

2 structural grade (West Coast Rules)— .

2 . 2 Wall Assembly

The 16 ft wide 8 ft high wall assembly consisted of four 4 ft wide

by 8 ft high panels. The wall test specimen and construction details

are illustrated in Figures 1-a and 1-b. The panel joints consisted of

the tongue-and-groove wood edge pieces which were milled from nominal

2 by 4 in. stock. The solid polyurethane filling in the honeycomb core

was 1-1/2 in. thick. Joint sealants were formed of butyl sealant 1/4 x

1/4 in. tape on the unexposed side, and vinyl 1/16 x 3/8 in. tape on the

fire exposed surface (Figure 1-b)

.

TJ West Coast Rules, available from Western Wood Products Association,

1500 Yeon Building, Portland, Oregon 97204

2
Galvanized steel angles, 2-1/2 in. by 2-1/2 in., 11 gage (0.1196 in.)

were attached to the panels at the bottom of the exposed side and the

top of the unexposed side with 1/4 by 2-1/2 in. lag screws. The top

edge of the exposed side was trimmed with galvanized sheet metal angles,

1-1/8 by 1-3/8 in., 26 gage (0.0179 in.), attached with No. 6 sheet metal

screws on 24 in. centers. Grooves in the wood top and bottom edges of

the unexposed side were filled with 1/4 in. butyl sealant tape (Figure

1-a) .

2 . 3 Roof /Ceiling Assembly

The 17 ft wide 13 ft 5 in. long roof/ceiling assembly consisted of

four 4 ft wide 13 ft 5 in. long panels and one 1 ft 10 in. wide 13 ft

5 in. long panel. Although similar in construction, the roof /ceiling

assembly differed from that of the wall principally in the size of the

wood edge closures, the thickness of the polyurethane foam, and the

closing of the joints between panels. The floor/ceiling specimen and

construction details are shown in Figures 2-a and 2-b.

As can be seen in the illustrations, the vertical long edge closures

were 5-1/4 in. overall height, forming a double tongue-and-groove joint.

The design calls for the exterior steel facing sheet to be bent up at

the wood blocks. A sheet metal cap over the joint and overlapping the

vertically up turned edges of the steel sheet formed a weather seal,

which was augmented with butyl and vinyl tapes. In this assembly, the

polyurethane foam in the honeycomb core was 2-1/4 in. thick.

The photograph in Figure 3 show a typical joint on the underside

(fire exposed side) of the completed floor/ceiling test specimen.
3.0 TEST METHOD AND EQUIPMENT

The tests of both the wall and the roof /ceiling assemblies were made

generally in accordance with the requirements of ASTM E 119, which provides that one side of a wall or the underside of a roof structure be

exposed to a fire controlled to conform as closely as possible to a

time- temperature curve specified in ASTM E 119.

The specimens were installed in furnaces suitable for testing each

type of assembly. Temperatures in both the wall testing and roof

testing furnaces were determined from the readings of 12 thermocouples

in each, mounted in iron pipes and symmetrically distributed in the

furnace chamber.

A total of 12 thermocouples was applied to the unexposed surface

of the wall, four on ioints and eight at locations away from the joints

between the panels, at the center of the core and under each of the two

facing sheets (disposition indicated in Figure 1-a)

.

For the roof /ceiling assembly, 18 thermocouples were used, two on

joints and 10 away from the joints on the unexposed surface, and six

within two of the panels at three different levels. (See Figure 2-a.)

All thermocouples on the unexposed surface of the test specimens

were covered with 5 in. by 6 in. by 0.4 in. thick felted asbestos pads.

Temperature readings indicated by thermocouples in the furnace, on the

unexposed surface, and inside the panels were recorded at one minute

intervals by a data logger and were later processed and plotted by

computer.

A lateral deflection reference wire was stretched horizontally

4 1/4 in. from the unexposed surface of the wall at the specimen center

4

I
height. The distance from the wire to the unexposed surface of the

specimen was measured at the mid-point of each of the four panels periodically during the test with a ruled gage.

Deflections of the roof/ceiling assembly were measured at four

points along the longitudinal center line: at the center, both quarter

points, and at the joint nearest the center. Wires with measuring riders

fixed to pass before a vertical scale were attached at the reference

points and also passed over pulleys connected to linear deflection

potentiometers

.

A calculated load of 237 plf was applied to the wall specimen through

four hydraulic jacks 5 min. before the test started. The loading represented the weight of the roof (30 plf) and the roof live load (207 plf)

Figure 4 shows the unexposed surface of the wall, the thermocouple connections and the loading equipment with the test frame in place as a

wall of the panel testing furnace.

Seven minutes prior to the test a load of 31.6 psf (28.6 psf live

load + 3 psf dead load) was applied approximately uniformly through 36

channels (2 ft x 5 in. x 1/4 in. thick) of the loading rig on the roof/

ceiling assembly. The unexposed surface of the roof /ceiling assembly

with the loading rig in place may be seen in Figure 5. The 28.6 psf

load produces the same bending moment over a 13 ft 5 in. span as a 40

psf load over a 12 ft span. The loading rig, which supplied 15 psf of

the required load, was placed on the specimen a day prior to the test.

5
4.0 TEST EVALUATION

The fire endurance according to ASTM E 119 of an assembly of either

type is determined by the time required to reach the first occurrence of

the following failure criteria:

1. Inability to sustain the applied load.

2. Passage of flame or gas through the structure to the unexposed

surface hot enough to ignite cotton waste applied at the point

of passage.

3. A temperature rise of 139°C (250°F) average, or 181°C (325°F)

i';;. .i, at one point, above the initial temperature on the unexposed

: ^ surface.

5.0 RESULTS OF TESTS

A log of test observations is given in Table 1 for the wall test

and Table 2 for the roof /ceiling test.

The plotted results of the tests indicated as the average and onepoint maximum temperature rises of all the thermocouples on the tinexposed surfaces of the assemblies are shown in Figure 6 for the wall

assembly and in Figure 7 for the roof /ceiling assembly. The average

temperature profile across the wall and roof /ceiling assemblies are

shown in Figures 8 and 9, respectively. Movement of the four panel wall

assembly from the vertical plane is indicated in Figure 10. Figure 11

shows the deflections of the four measured points on the roof /ceiling.

The severity of the fire exposure in the wall assembly test was

slightly below that prescribed by the standard time-temperature curve

(Figure 12). According to the standard correction formula in ASTM E 119,

based on the comparison of the areas under the actual time-temperature

6
curve and the standard curve, the fire endurance time was corrected.

Similarly, a correction was made in the time to failure observed in the

roof/ceiling test to compensate for the somewhat higher than standard

furnace severity that occurred in that test (Figure 13)

.

5 . 1 Wall Assembly Results

The fire endurance time for the wall was 8 mint 25 sec observed,

corrected to 7 min:50 sec, with failure by maximum temperature rise of

181°C (325°I) on the unexposed surface. Initial inability to sustain load

was observed at 23 min. Flame through occurred at 26 min on a joint

between an end panel of the wall and the adjacent panel.

Deflection of the unexposed surface of the wall from its initial

vertical plane varied from 1 1/4 in. toward the furnace to 2 1/2 in.

away from the furnace chamber.

During the test, smoke appeared in the furnace almost at the beginning of the test, and by 2 min. it was seeping through to the unexposed

side of the wall (Figure 14) . Buckling of the exposed wall surface was

observed at 2 1/2 min. At 5 min the smoke was of sufficient volume and

density to largely obscure the surface (Figure 15) . Flaming occurred on

the exposed joints at 3 1/2 min, with extensive flaming by 8 min (Figure

16).

Figure 17 is a photograph showing the fire side of the panel after

it was removed from the furnace just before extinguishment of the fire.

Surfaces were buckled and most of the wood members, paper honeycomb, and

polyurethane foam were consumed.

7
5.2 Roof /Celling Assembly Results

For the roof /celling assembly, the fire endurance time was 9 mln:09

sec with failure by maximum temperature rise on the unexposed surface

(rise of 325°F or 181°C). This was corrected from 8 mln:30 sec observed

because of excessive furnace temperatures. Deflections showed a steady

increase until the occurrence of a sudden failure to withstand the

applied load at 17 mln at the joint nearest the center of the specimen

(Figures 18 and 19) . .

Light flaming was observed on the exposed roof /celling surface as

early as 1 mln. after the start of the test. The exposed sheet steel

facings began buckling soon thereafter, and by 2 mln. there was considerable generation of smoke.

The photographs in Figures 18 and 19 show the unexposed surface of

the assembly after the loading rig was removed and the exposed surface

at the failed joint, respectively, at the end of the test.

Although most of the wood members and polyurethane foam was' consumed during the test and the paper honeycomb was charred and delamlnated

from the bottom facing, it was not necessary to apply any extinguishment

agent after the test. All of the exposed joints had opened up and the

failed joint showed the maximum opening of 4-1/4 inch (figure 19) compared with 11/16 inch (Figure 13) before the test.

When the specimen was being demantled 15 hours after the end of the

test, some flaming occurred at the east end of the second joint from

the north end to a height of several feet (Figure 20)

.

8
6.0 DISCUSSION OF RESULTS

Although the wall assembly and the roof /ceiling structure carried

their expected service loads, failure in both cases occurred by the

attainment of the limiting average temperature rise on the unexposed

surface

.

The load applied to the wall was 237 plf and the results of this

test are applicable to such a structure loaded to develop a stress in

the structural members not exceeding that developed in the structure

tested. Similarly, the results of the roof/ceiling assembly are

applicable to such a structure loaded to develop a bending moment in

the structural members not exceeding the equivalent of 40 psf over

a 12 ft span.

9
Table I - Log of Wall Test Observations

Observations

Start of test.

Smoke appearing on top of the unexposed side of the

panel. (Figure lA.) Cracking sound from back of the

specimen.

Exposed surface buckling.

Flames observed on the joints of the exposed surface.

Much black smoke filling the furnace.

Much gray dense smoke appearing on the unexposed

side through joints and at the hole at the bottom of

the second panel from the north end where the internal

thermocouples came out . (Figure 15)

.

Smoke seemed to clear up

.

All joints on the exposed surface flaming severely.

(Figure 16 is a photograph taken through observations

window .

)

The color of the unexposed surface appearing to change

from light buff to brown. An average temperature rise

139°C above its initial temperature on the unexposed

surface was observed.

Cotton waste, applied on the joint opening of the un- exposed surface, was not ignited.

Load failure.

Gas off. (END OF TEST)

.

Flame through on the third joint from the north end.

10
Table II - Log of Roof/Ceillng Test Observations

Time Observations

Min:Sec

0:00 Start of test.

0:30 Severe cracking sound from underside of the specimen.

1:00 Light flaming on the exposed surface.

1:30 Sheet metal on exposed surface buckling.

2:00 Much smoke observed all around furnace.

3:00 Dense gray smoke puffing out through the hole where

the internal thermocouple leads ran out.

8:00 Smoke seemed to clear up. About 4 inch deflection

observed at center of the panel.

17:00 Load failure near center of second joint from the

north end.

Gas off.

(END OF TEST)

NOTE

Fifteen hours after the end of the test, the specimen, when it was dismantled, burst into flame at the east end of the second joint from

the north end. The height of flame was approximately 3 ft. (See

Figure 20.)

r

11
SI Conversion Units

In view of present accepted practice in this country in this

technological area, coininon US units of measurement have been used

throughout this papei . In recognition of the position of the United

States as a signatory to the General Conference on Weights and Measurements which gave official st.atus to the metric SI system of units in

1960, V7e assist readings interested in making use of the coherent system

of SI units by giving conversion factors applicable to US units used

in this paper.

Length

1 in = 0.0254 meter

1 ft = 0. 3048 meter

Mass . •

.

1 pound = 0.A5 kilograms

Force

1 kip = A4A8 newton

Stress

1 psf = 47.88 newton/meters^

Temperature

Temperature in "F = 9/5 (Tnnporature in °C) + 32°F

12
13

60C

a

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o

o

E

u

0)

oo

H
4'-0-7/l6"

3'- 9 -7/16" PftN 1-1/2" r

l-5/8"±

•FIN. SIDE

TYPICAL

3'- 9-7/16" FIN. SIDE

'-STAPLES Q 15 CTRS

TYR AT ALL LEGS

3' -I I- 1/2" PAN

OUTSIDE

INSIDE

TYPICAL HORIZONTAL ROOF PANEL SECTION

1/4 X 1/4 BUTYL TAPE FIELD APPLIED

ROOF CAP - 26 GA.

l3'-5" LONG -GALV. TAN COLOR

GALV * 4-D NAILS

AV6. 1/16" CLR.

26 GA

^

26 GA.

1 i /

1-1/2"

99(11) 3/4 HONEYCOMB

2 1/4- in POLYURETHA^k SLAB

^

2 1/4"

13-2 CORE LGTH.

13'- 5" OVERALL LGTH.

4 -0

1/16 X 3/8 VINYL TAPE

p , „ FIELD APPLIED ^-

SECTION X-X

TYP SEC. AT PANEL ENDS

TYPICAL ROOF JOINT

'igurc 2-b Construction details of Roof/Ceiling panel.

16

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18

900

O flVERRGE TEnP

.

A MflXIMUM TEflP.

800_

TIME (MINUTE)

Figure f>

.

MAXIMUM AND AVERAGE SURFACE TEMPERATURE Roof/Ceiling Assembly

20
600^

O RVERRGE TEMP

A MflXIMUM TEMP

500_

400-

o

UJo

liJ

Q£ 300

»-a

OliJ 200-

100_

TIME (MINUTES)

Figure 7.

FAXIKUN AND AVERAGE SURFACE TEMPERATURE _^RISE- Wall Assembly
900_

800

700_

600_

^ 500_

o

oc

cr nUJ

400.

300.

200_

100_

0

® T/CS Locat i on a ^ T/CS Location b r T/CS Location c .J

T/CS on the unexposed surface

See figure 1-a

0

T I

T

12 16

TIME (MINUTE)

Figure 8

TEMPERATURF CRADIENT ACROSS THE WALL PANEL ^ (TEST

22
900^

800-

700-

600_

o

a

lij o

500-

I—

(Xoc

O-n

UJ

400_

300-

200_

100

O T/CS Location Row b n A T/CS Location Row m ?- See figure 2-a

+ T/CS Location Row t y'

X T/CS on the unexposed surface

1 !7

TIME (MINUTES)

16

Figure Q

.

TEMPERATURE GRADIENT ACROSS THE FLOOR/CEILING ASSEMBLY (TEST 490)

23

NIBONVlSia

25

900

800_

0 5 i Vz fe to

TIME (MINUTES)

Figure 13.

AVERAGE FURNACE TEMPERATURE FOR ROOF/CEILING TEST COMPARED WITH STANDARD E119

time-tf;-mpf,ratttt!f curve.
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28
29
Figure 16. All joints on the exposed

surface of the wall panel burning.

Test time of 8 min. (Inside furnace)
(-4 0)

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0) 13

S-l <U •H >OE HD 01 00 j-i

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Figure 19. The exposed surface at the

failed joint (second joint from the

north) of roof/ceiling assembly at the

end of the test.
I

I
I FORM NBS-lUA tI-71) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 73-135

Z. Gov t Accession No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Fire Endurance Tests of Steel Sandwich Panel

Exterior Wall and Roof/Ceiling Constructions

5. Publication Date

6. Perfonntng Or^oizacion Code

7. AUTHOR(S)

Byung Chan Son

8. Performing Organization

NBSIR 73-135

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Worlc Unit No. 4600450

11. Contract/Grant No.

IAA-H-16-70

12. Sponsoring Organization Name and Address

Department of Housing and Urban Development

Washington, D.C. 20410

13. Type of Report & Period

Covered

Final

14, c>f)onsonng Agency Code

15. SUPPLEMENTARY NOTES

This is a revision of NBS Report 10406.

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

As part of the evaluation of a housing system proposed under Operation BREAKTHROUGH,

fire endurance tests were performed at the National Bureau of Standards on an exterior wall assembly and a roof /ceiling assembly. Both constructions were

assemblies of sandwich panels composed of a paper honeycomb core with sheet steel

facings.

The test method was in accordance with the requirements of ASTM E 119, Standard

Methods of Fire Tests of Building Construction and Materials, for loadbearing

structures. The applied live load was 237 pounds per linear foot (plf) for the wall

assembly and 28.6 pounds per square foot (psf) on a 13 ft 5 in. span for the

roof /ceiling assembly. The results of these tests are valid only for walls and

roof /ceilings of such constructions described in this report and loaded at or below the stress levels developed by these loadings.

The fire endurance of the wall assembly was 7 minutes 50 seconds; and the roof/

ceiling, 9 minutes 09 seconds. In both cases, the failure was due to a maximum

teii?)erature rise of 181°C (325°F) above the initial temperature on the unexposed

surface.

17. KEY WORDS (Alphabetical order, separated by semicolons) Exterior wall; fire endurance; fire test

housing systems; Operation BREAKTHROUGH; paper honeycomb; roof /ceiling assembly;

structural sandwich panel.

18. AVAILABILITY STATEMENT

IZD UNLIMITED.

J FOR OFFICIAL DISTRIBUTION. DO NOT R|;I.I;ASH

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

22. Pt

USCOMM-DC 66244-P7I