NBSIR 73-168

Fire Endurance Test of a Fiber

Glass Reinforced Polyester Double

Wall Assembly

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington. D. C. 20234

April 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C, 20410

NBSIR 73-168

FIRE ENDURANCE TEST OF A FIBER

GLASS REINFORCED POLYESTER DOUBLE

WALL ASSEMBLY

B. C. Son

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

April 1973

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

Fire Endurance Test of

A Fiber Class Reinforced I'olyester Double Wall Assembly

by

B. C. Son

Building Fires and Safety Section

Center for Building Technology

ABSTRACT

As a part of the evaluation of a housing system proposed under

Operation BREAKTHROUGH a standard fire endurance test was performed on

a double wall assembly comprising a load-bearing interdwelling (party)

wall for single family attached housing. The test method was in

accordance with the requirements of ASTM E 119, and the applied load

was 700 pounds per linear foot (plf) per wall. The test results are

valid only for walls of similar construction loaded at or below the

stress level developed by this loading.

The double wall, representative of an interdwelling (party wall)

separation, was made up of two identical parallel panels from two

adjacent modules separated by a 2-1/4 in. air space. Each wall assembly

contained glass fiber-reinforced polyester (GRP) sheet faces, glued to a

corrugated GRP stiffener core. The GRP core members were painted with

an intumescent type fire retardant paint and the core spaces were filled

with mineral wool insulation.

i
The fire endurance of the first (fire-exposed) wall was 27 min:

25 sec. with the initial mode of failure by structural collapse.

The second (unexposed) wall failed at 42 minutes when a hot

(charred) spot was observed on the unexposed surface.

Key Words: Fire endurance; fire test; glass fiber reinforced plastic;

housing systems; interdwelling wall; Operation BREAKTHROUGH

ii
Contents

Page

Abstract 1

1. Introduction 1

2. Construction 1

3. Instrumentation 3

4. Test Method and Equipment 4

5. Test Results . 5

6. Discussion 7

Table 1 8

Appendix I 10

SI Conversion Units

iii
1
t

1.0 INTRODUCTION

A test was performed at the Fire Test Laboratories of the National

Bureau of Standards, Washington, D.C., to measure the fire endurance of

a load bearing interdwelling double wall assembly. The test method and

fire exposure were in accordance with the requirements of Standard

Methods of Fire Tests of Building Construction and Materials, ASTM

E 119—^, for load bearing walls.

The test was part of an evaluation of a housing system proposed

under the Operation BREAKTHROUGH program sponsored by the Department of

Housing and Urban Development.

The double wall, which is required to be a fire barrier between

adjacent modules, was made of two identical symmetrical parallel walls

separated by a 2-1/4 in. air space.

During the test, a jacking load of 730 plf (700 plf superimposed

live load + 30 plf dead load) was applied to each wall.

2.0 CONSTRUCTION

The double wall assembly consisted of two identical, 16 ft. wide x

8 ft. high walls, parallel to each other and separated by a 2-1/4 in.

air space, as shown in Figure 1. The overall thickness of the double

wall assembly was 9.85 in. Each wall was made up of GRP 0.05 in. thick

— Standard Methods of Fire Tests of Building Construction and

Materials, American Society for Testing and Materials Designation

E 119-71. Available at 1916 Race Street, Philadelphia, Pa. 19103.

1
sheet corrugated stlffener sandwiched between 0.08 In. thick face sheets

made of the same material. The two faces and corrugated core were

bonded together with a polyester adhesive to form a 3.80 In. thick

sandwich panel. To provide thermal insulation and fire resistance,

the vertical voids in the panel were filled with mineral insulation

3 which was handpacked to 8 lbs/ft density and contained 10 percent (by

weight) of sodium silicate and water. These material thicknesses and

properties were supplied by the HSP.*

The GRP sheets used for faces and stiffener were made from random

oriented glass fiber mats impregnated with polyester resins. An

intumescent f ire-retardant paint was applied to the entire corrugated

stiffener, except where bonded to the surface skins. This paint was

a proprietary formulation developed by the Housing System Producer.

Each wall, which was received completely assembled for the test,

was made up of four 8 ft. x 4 ft. panels. The panel joints were closed

by 8-1/2 in. wide strips of GRP sheets with an adhesive to form a

structural panel. The top and bottom edges of the panel were closed

by 2 X 4 (nominal) wood strips as a header and sill. Each wall was

weighed at the plant and was reported to weigh 480 pounds (30 plf )

.

The assembly was built into a 16 ft. x 10 ft. loading frame of

the NBS wall test furnace. Prior to the test, a 2 ft. x 16 ft. filler

was placed at the top of the specimen. The filler piece, which was

*HSP (Housing System Producer)

2
made of nominal 2 x 12 pine wood, was protected on the fire side with

two layers of 5/8 inch type X gypsum board plus vermiculite plaster

sprayed on metal lath. The unexposed side was covered with one layer

of 5/8 inch type X gypsum board. The filler piece was expected to have

sufficient fire endurance and rigidity during the test.

3.0 INSTRUMENTATION

The instrumentation consisted of thermocouples, deflection-measuring

devices and loading equipment. A total of 47 Chromel-Alumel (type K)

thermocouples were used in the double wall assembly as shown in Figure

2. The surface thermocouples on the unexposed surface of the second

wall were placed under 6 x 6 x 0.4 in. felted asbestos pads as

specified in the ASTM E 119. The thermocouples on the unexposed surface of the second wall and surface facing the air space were installed

by NBS personnel with the remaining installed by the Housing System

Producer.

Figure 3 shows the unexposed surface of the specimen, the connections

of the thermocouples and the loading equipment during the test. The

temperatures of the thermocouples were printed out at 2 minute intervals

on a data logger from which they were punched onto cards for processing

and plotting by computer.

3
The lateral deflection indicator consisted of a wire which was

strung horizontally at the center height and 1-3/4 in. from the unexposed

surface of the specimen. The variations of the distance from the wire to

the unexposed surface of the double wall were measured periodically at the

center of each panel by a ruled stick during the test, as in Figure 3.

The vertical movement of each wall during the test was measured by four

dial gages which were placed at the quarter points under the bottom of

each loading frame.

4.0 TEST METHOD AND EQUIPMENT

The test was conducted in accordance with the requirements of ASTM

E 119. The double wall was mounted in a 10 x 16 foot frame of the wall

test furnace at the Fire Research Section, National Bureau of Standards.

Five minutes prior to the start of the test, a jacking load of 730 plf

(700 plf live load + 30 plf dead load) was applied to each panel

independently through four hydraulic jacks at the bottom of the specimen.

The total live load per wall was 11,200 pounds throughout the test. THe

details of the wall furnace with typical double wall assembly in place

are shown in Figure 4.

The temperature inside the furnace was measured by twelve type K

thermocouples which were enclosed in sealed, standard weight, 1/2-in.

diameter black iron pipe and were placed 6 in. away from the exposed

surface of the assembly. The average furnace temperature, which was

constrained to follow the standard ASTM E 119 temperature- time curve by

manual control of the gas flow to the burner, is shown in Figure 5.

4
The pressure measurement within the furnace was made with a probe

connected to a differential pressure transducer with tubing.

The probe consisted of 1/8 in. inside diameter stainless steel tubing

which was attached to the edges of a 1-1/8 in. diameter flat metal disk

having rounded edges and connected to a small hole in the center of the

disk. The disk was so positioned that the hole was normal to the upward

flow of gas. The test was run with the furnace neutral pressure point

located at one-third height of the specimen above the bottom of the

specimen.

The fire endurance of a load bearing wall assembly, according to

E-119 , is the time required to reach the first occurrence of any one

of the criteria of failure, which are as follows:

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.

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

at one point on the unexposed surface above the initial

temperature.

5.0 TEST RESULTS

A log of test observations is given in Table I. The average and

maximum temperature rise of the unexposed surface durine the test are

shown in Figure 6. The average temperature profiles across the assembly

at three different positions are shown in the Figures 7 and 8.

5
Structural failure of the first wall occurred at 27 minutes: 25

seconds, as evidenced by a sudden rapid vertical deflection of the lower

edge of the panel and the inability to maintain the applied hydraulic

load. Immediately prior to the failure of the first wall the measured

vertical deflection of the first wall was 1.06 in.

Figure 6 indicates that the maximum permissible temperature rise

of 181°C on the unexposed surface of the second wall occurred at 54

minutes on the thermocouple located on the south top corner. However,

the failure time was taken to be 42 minutes by evidence of a charred

brown spot on the south top quadrant on the unexposed surface, away

from a measuring thermocouple. According to previous experience, the

surface temperature corresponding to charring similar to that shown in

Figure 3 is greater than 250'*C.

The permissible average temperature rise of 139°C on the unexposed

surface did not occur during the test. The remainder of the thermocouples

on the unexposed surf ace, except the one on the south top corner, did

not exceed 50°C rise during test. After the test, it was noticed that

the insulation in the second wall panel was intact except in the south

upper quadrant area.

The lateral deflections at the mid-height of the second wall panel

during the test and the vertical deflections of the lower edge of the

panels are shown in Figures 9 and 10, respectively. Figure 11 shows

the fire side of the specimen after it was removed from the furnace

at the end of the test.

6
6.0 DISCUSSION

The construction of the specimen, as shown in Figure 1, was

symmetrical so that the same fire endurance would have been achieved

if the opposite side had been fire-exposed.

After the exposed GRP sheet and the mineral wool insulation had

fallen off, the corrugated stiffeners of the first wall were directly

exposed to the furnace fire. It was observed that the intumescent

paint did not expand and did not provide appreciable protection.

The localized thermal failure of the second wall occurred at

42 minutes, while the remaining portion of the wall remained an effective

thermal barrier. This was possibly due to incomplete placement of the

mineral wool insulation during assembly and improved quality control

might insure improved performance.

The applied live load on each wall of the assembly was 700 plf.

The results of this test should be applied only to walls of similar

construction loaded to develop stresses not exceeding those developed

in this structure.

7
TABLE I Log of Test Observations

Observations

Start of test.

The exposed surface ignited. Black powdery smoke

appeared around the furnace.

The inside of the furnace filled with smoke. Even

the burner flames were not visible through the observation window.

The inside of the furnace is beginning to clear a little.

The exposed surface appeared to be disintegrating and

pieces of the skin falling down.

Pieces of mineral wool insulation falling into the furnace.

Visibility inside the furnace is better now.

Large pieces of insulation and burning glass fiber skin

from the middle of the specimen fell into the furnace

(Figure 12).

Increasing quantities of white smoke coming out of the

corners of the specimen.

Irritating smoke coming from the specimen along edges.

Yellowish smoke blowing downward off the south bottom

corner of the specimen on the unexposed surface.

Extensive flaming inside the furnace, probably due to

burning of the unexposed surface of the first wall.

Amount of acrid smoke has increased.

First wall could not sustain the applied load. Load

failure of the first wall.

Irritating smoke is still coming out along the edges of

the specimen. Observers experiencing breathing difficulties and eye irritation.

Approximately 50% of the first wall has fallen into

furnace. Part of exposed face of the second wall is

visible from the furnace side.

8
39:00 The exposed face of the second wall engulfed in flame

and starting to open up. The unexposed face of the

second wall bowing in towards the furnace on the south

two panels.

42:00 There is a charred brown spot on the upper quadrant of

the exposed face of the south panel.

45:00 Insulation in the second wall falling down. Considerable

flaming in the middle of the second wall on the furnace

side, and second wall seems to be bowing in towards

furnace. Specimen seems to be bowing out up near the

top, on the unexposed side.

50:00 30% of the second wall (north end) still protected by

remnants of the first wall, but the rest is completely

engulfed in flames. There is now a large brown spot

appearing at the south end (Figure 3).

53:00 Half of the southern most panel is almost charred black.

55:00 The second wall has touched the deflection wire. Deflection measurements discontinued. Hot spot at center

of south panel has turned almost white while edges are black as the burned zone spreads.

60:00 Wall buckling out of the test frame.* Load off.

END OF TEST

*Specimen did not actually fail structurally. "Buckling" of the second

wall was due to movement of the filler piece at the top.

9
In vicv; of present accppted- practice iu this country in this

technological area, cotimion US units of meaflureipent have been used through

out this paper. In rccognitjon of the position of the United States as

a signator-y to the General Conference on Weights and Measurements which

gave official ctatus to the metric SI system of units in 1960, we assist

readers 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 rr^eter

1 ft = 0.3048 meter

Mass

1 lb = 0.45 kilogram

Stress

2

1 psf = 47.88 nev^ton/meter

2

1 psi = 0.332 newton/meter

1 plf = 13.49 newton/meter

Temperature

Temperature in °F - 9/5 (temperature in °C) + 32**?

10
•.SURFACE T/C

UNDER PAD

DIMENSIONS GIVEN ARE NOMINAL

Figure 1, TJc^qst ruction details.
12
Figure 3. The unexposed surface of the

specimen at the test time of

51 min.

13
SECTION LONGITUDINAL SECTION HALF ELEVATION

0 I f 3 A S lO IS' SCALE

FIGURE 4. DETAILS OF WALL-TESTING FURNACE.

A, FURNACE chamber; B, BURNERS; C , THERMOCOUPLE PROTECTION TUBES; D, PIT FOR DEBRIS',

E, OBSERVATION WINDOWS; F, AIR INLETS; G, FLUE OUTLETS AND DAMPERS; H, FIREBRICK

FURNACE LININGl I, REINFORCED CONCRETE FUR N ACE-SHE L L, K, GAS COCKS; L, CONTROL VALVE,

M, LADDERS AND PLATFORMS TO OBSERVATION WINDOWS) N, MOVABLE FtREPROOFED TEST

frame; 0, LOADING seam; P, HYDRAULIC JACKS; Q.TEST WALL, R, ASBESTOS FELTED PADS

COVERING THERMOCOUPLES ON UNEXPOSED SURFACE OF TEST WALL.

USCOMM-NBS-DC

14
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Figure 5.

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21
22
FORM NBS.114A (1-71) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 73-168

2. Gov't Accession

No,

4. TITLE AND SUBTITLE

Fire Endurance Test of a Fiber Glass Reinforced Polyester

Double Wall Assembly

3. Recipient's Access! m No.

5, Publication Date

6. Perfonning Organization Code

7. AUTHOR! S) Byung Chan Son

8. Performing Organization

NBSIR 73-168

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No. 4600430

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, Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.)

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

a standard fire endurance test was performed on a double wall assembly comprising a load-bearing interdwelling (party) wall for single family attached housing. The test

method was in accordance with the requirements of ASTM E 119, and the applied load

was 700 pounds per linear foot (plf) per wall. The test results are valid only for

walls of similar construction loaded at or below the stress level developed by this

loading.

The double wall, representative of an interdwelling (party wall) separation, was made

up of two identical parallel panels from two adjacent modules separated by a 2-1/4 in.

air space. Each wall assembly contained glass fiber-reinforced polyester (GRP) sheet

faces, glued to a corrugated GRP stiffener core. The GRP core members were painted

with an intumescent type fire retardant paint and the core spaces were filled with

mineral wool insulation.

The fire endurance of the first (fire-exposed) wall was 27 min:25 sec. with the

initial mode of failure by structural collapse.

The second (unexposed) wall failed at 42 minutes when a hot (charred) spot was observed on the unexposed surface.

17. KEY WORDS (Alphabetical order, separated by semicolons) ^^^^ endurance; fire test; glass fiberreinforced plastic; housing systems; interdwelling wall; Operation BREAKTHROUGH

18. AVAILABILITY STATEMENT

fvUlNLIMITED.

1 1 FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

USCOMM-DC 66244.P71