NBSIR 73-164

Fire Endurance Test of a Steel

Sandwich Panel Floor Construction

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 73-164

FIRE ENDURANCE TEST OF A STEEL

SANDWICH PANEL FLOOR CONSTRUCTION

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 Steel

Sandwich Panel Floor Construction

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 fire endurance test was performed at the

National Bureau of Standards on a floor, made up of sandwich panels

consisting of a paper honeycomb core with steel and plywood surfaces,

supported on steel joists.

The test method was generally in accordance with the requirements

of ASTM E 119, Fire Tests of Building Construction and Materials, for

loadbearing floor constructions. The applied live load was 40 psf and the

test results are valid only for floors of similar construction loaded at

or below the stress level developed by this loading.

Failure occurred by flame through of the floor assembly in 8 min.

45 sec. , with structural failure (inability to sustain the applied load)

following immediately.

Key Words: Fire endurance; fire test; flame penetration; floor assembly;

housing systems; Operation BREAKTHROUGH; paper honeycomb;

structural panel

i
TABLE OF CONTENTS

Page

ABSTRACT ....... i

1.0 INTRODUCTION 1

2.0 TEST SPECIMEN AND INSTALLATION 1

3.0 TEST METHOD AND INSTRUMENTATION 3

4.0 TEST EVALUATION . . 4

5.0 RESULTS OF TEST . 4

6.0 DISCUSSION OF RESULTS 5

APPENDIX I - SI Conversion Unit 7
1.0 INTRODUCTION

A sandwich panel floor system designed for single family housing

under Operation BREAKTHROUGH was subjected to a test to determine its

fire endurance under the Standard Methods of Fire Tests of Building

Construction and Materials, ASTM E 119^. The test was conducted at

the National Bureau of Standards for the Department of Housing and Urban

Development (sponsor)

The steel joists supporting the panels were unprotected from the

effects of fire, and so were representative of constructions applied

over habitable basements and crawl spaces. For this test, the floor

assembly had a 40 pounds per square foot (psf) applied load and complete

perimeter support for the stringer beams and end joists.

2.0 TEST SPECIMEN AND INSTALLATION

The floor consisted of five panels, each 10 ft 7-1/4 in. long. Three

were 4 ft wide, the other two 2 ft 11-1/2 in. The core of a panel consisted of a 3 in. thick paper honeycomb; the top surface 3/8 in. C-D plugged interior grade (with exterior glue) plywood; the bottom, 26 gage

(0.0179 in.) galvanized and phosphatized steel sheet. This sheet was

bent up on the long sides to cover the bottom 1-1/2 in. of the paper

core, and was shaped to contain a 5/16 in. by 5/16 in. boss which compensated for an approximate 5/16 in. setback of the paper core as shown in

Figure 1. Thus, contact between panels was made at the boss and at the

1/

Standard Methods of Fire Tests of Building Construction and Materials , American Society for Testing and Materials, available at 1916 Race St.,

Philadelphia, Pa. 19103.

1
edges of the plywood top surfacing. Edges at the ends of the floor

were indented. Short edges of the panels were closed by 3-1/8 in. by

1-1/2 in (actual size) pine wood members.

The panels rested on light gage steel C-shape joists and stringer

beams, each 8 in. high, 3 in. wide, and 0.075 in thick. The assembly

and fastenings of the floor framing members are shown in Figure 2.

Butyl sealant strips 3/8 in. wide were placed in the intermediate

joints between the floor panels. Both strips of the same material 7/32

in. wide and an equivalent gun-type butyl sealant (due to insufficient

supply from HSP*) were applied to the end joint and stringer beams.

After assembly, it was noticed that the gaps between the plywood

top sheets of adjacent floor panels did not exceed 1/16 in. Outer edges

of the floor assembly were closed with 3-1/4 x 3-1/4 in. 18 gage (0.0495

in.) steel angles attached to the panels with 1/2 in No. 6 sheet metal

screws on 16 in. centers. Figure 3 shows the angles in place on a corner

of the floor assembly. The floor was finished with carpeting attached

with a commercial natural latex releaseable adhesive. Figure 4 illustrates

the details of the joist and stringers and the perimeter support beams.

The underside (furnace exposed side) of the complete test specimen can

be seen in Figure 5.

Since the size of the test specimen (17 ft 11 in. by 10 ft 7-1/4 in.)

was smaller than the opening (18 ft 0 in. by 13 ft 6 in.) of the NBS floor

test furnace, the test specimen was supported on two wide flange W 21 x

96 steel beams. Closure of the spaces between the floor assembly and the

*HSP : Housing System Producer

2
furnace walls was made with nominal 2 x 10 in. wood members. Fire protection of the steel supporting beams (not of the floor joists) and the

closures wood members was provided by two layers of 5/8 in type X gypsum

board mechanically fastened and protected with sprayed vermiculite plaster

on metal lath. The fire protection on the steel beams and closures was

expected to have sufficient fire endurance and rigidity during the test.

3.0 TEST METHOD AND INSTRUMENTATION

In the test of the floor assembly, the underside of the assembly

was exposed to a fire controlled to give an average temperature in the

furnace conforming as closely as possible to the time-temperature curve

as specified in the ASTM E 119 standard.

The temperature within the furnace was determined by 12 protected

thermocouples which were symmetrically distributed within the chamber

and placed 12 in. away from the exposed surface of the specimen.

Nine Chromel-Alumel (type K) thermocouples, each under a standard

6 in. by 6 in. by 0.4 in. thick felted asbestos pad, were applied to the

exposed surface of the specimen. Five of these were positioned between

joints, four were over joints. Additionally, eleven thermocouples were

placed as follows: six internally in two adjacent panels, two on the

supporting beams, and one each under the carpet, on a joist, and at a

plywood joist. See Figure 6 for locations of thermocouples.

Temperature readings from all the thermocouples (specimen and

furnace were recorded at 1-minute intervals on a data logger, and

later processed and plotted by computer.

3
The movement of the floor during the test was measured at five

points with deflection indicators attached to the top surface at the

center, at a quarterpoint , at the mid-point of the two supporting beams,

and at the mid-point of one edge. The indicators consisted of wires,

with measuring riders passing before a vertical scale. The wires, held

taut by weights, passed over pulleys connected to linear deflection

potentiometers

The live load of 40 psf, distributed approximately uniformly through

24 channels of four overhead hydraulic jacks, was applied 11 minutes before the fire exposure started.

4.0 TEST EVALUATION

The fire endurance of a floor assembly according to ASTM E 119 is

the time required to reach the first occurrence of any of the following

criteria of failure:

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

at one point, above the initial temperature on the exposed

surface

5.0 RESULTS OF TEST

Flame penetration, denoting failure, occurred at a joint between

two panels at 8 min. 45 sec. after start of the test. This was followed

by load failure at 9 min. , as evidenced by the inability to maintain

hydraulic pressure in the loading system. The deflections of the floor,

4
which increased continuously during the test, are shown in Figure 7.

The location where flaming occurred and the pattern of surface deflection

after load removal can be seen in Figure 8.

The average temperature rise indicated by the thermocouples on the

unexposed surface away from the joints was less than 35°C (96°F) and a

maximum temperature rise of over 300°C (572°F) was observed on a joint

during the test, as shown in Figure 9. Temperature histories of other

thermocouples in the structure are given in Figures 10 and 11.

Average furnace temperatures during the test period are shown in

Figure 12. The severity of the fire exposure was sufficiently close to

that prescribed by the ASTM E 119 time-temperature curve as to preclude

the necessity for adjusting the observed times to failure to compensate

for furnace deviation.

Delamination and charring occurred at the top and bottom surfaces

of the paper honeycomb during the test. As early as 1 min. 30 sec. , the

temperature at the bottom of the core was 282°C (540°F) , probably high

enough to initiate pyrolysis (chemical decomposition by the action of

heat) of the adhesive and ignition of the paper.

6.0 DISCUSSION OF RESULTS

The deflection and torsional rotation of the light gage steel joists

were main causes of failure in the test. The joists were then unable

to sustain the applied load and resulted in opening of the joints permitting flame through. Because of their asymmetry, the joists, unless

restrained, will have a mode of failure in torsional bending with the

open side down. An illustration of this phenomenon is indicated in the

after-test photographs of Figures 13 and 14.

5
The early deformation of the joists followed the general behavior

pattern of unprotected steel structural members in the standard fire

2/ test. Many steels lose approximately half their strength-1

- , and with

this the usual design safety factor, at about 538°C (1000°F) which was

the furnace temperature at 5 minutes. Therefore, extended duration

beyond this time cannot justifiably be expected. From Figure 10, it

can be seen that this limiting temperature was attained at the thermocouple at the top of a joist at about the time that failure occurred.

The applied load was 40 psf and the results of this test should

be applied only to floors of similar construction loaded to develop

stresses not exceeding those developed in this assembly.

— Speader, C.E., The Elevated-Temperature Properties of Basic Oxygen

Steel , DS 40, American Society for Testing and Materials, 1916 Race

St., Philadelphia, Pennsylvania 19103, July 1965.
Appendix I

SI Conversion Units

In view of present accepted practice, in this country in this

technological area, common US units of. measurement have been used through

out this paper* In recognition oJ; the position o^: the United States as

a signatory to the General Conference on Weights and Measurements which

gave official status 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 meter

1 ft = 0.3048 meter

Mass

1 lb - 0.45 kilogram

Stress

2. 1 psf = 47.88 newton/meter"'

2 1 psi - 0.332 newton/meter

1 plf = 13.49 newton/meter

Temperature

Temperature In °F = 9/5 (temperature in *C) + 32°F

7
10' - 7 1/4"

THREE MIDDLE PANELS Width /

DETAIL A

10'— 7 1/4"

TWO END PANELS

Figure 1. Details of specimen construction.

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400 _,

TIME (MINUTES)

FIGURE 9

MAXIMUM AND SURFACE TEMPERATURE RISE FOR TEST 480

16
400_

900_

800_

TIME (HINUTES)

Figure 12.

AVERAGE FURNACE TEMPERATURE FOR TEST 480 COMPARED WITH STANDARD E119

19

21

FORM NBS-114A (1-71) u.s. dept. of comm. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA msm y3_164

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Fire Endurance Test of a Steel Sandwich Panel Floor

Construction

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

Byung C. Son

8. Performing Organization

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Taslc/Work 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

Ij. I ype of Report & Period

Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

This is a revision of NBS Report 10404

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

BREAKTHROUGH, a fire endurance test was performed at the National Bureau of

Standards on a floor, made up of sandwich panels consisting of a paper honeycomb

core with steel and plywood surfaces, supported on steel joists.

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

Fire Tests of Building Construction and Materials, for loadbearing floor constructions. The applied live load was 40 psf and the test results are valid only for

floors of similar construction loaded at or below the stress level developed

by this loading.

Failure occurred by flame through of the floor assembly in 8 min. 45 sec. , with

structural failure (inability to sustain the applied load) following immediately.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Fire endurance; fire test; flame penetration; floor assembly; housing systems;

Operation BREAKTHROUGH; paper honeycomb; structural panel

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