NBSIR 73-173

Fire Endurance Tests of Double

Module Walls of Gypsum Board

and Steel Studs

B. C. Son, H. Shoub

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
1
NBSIR 73-173

FIRE ENDURANCE TESTS OF DOUBLE

MODULE WALLS OF GYPSUM BOARD

AND STEEL STUDS

B. C. Son. H. Shoub

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

April 1973

Final Report

This document has been prepared for the use of the Department of Housing and Urban Development.

Responsibility for its further use rests with

that agency. NBS requests that if release to the public is contemplated, such action be taken

only after consultation with the Office of Public

Affairs at the National Bureau of Standards.

^^^^^^ Q

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director
1
FIKK ENDUIUNCF. TESTS OF DOUBLE MODULE

WALLS OF GYPSUM BOARD AND STl'EL STUDS

by

H. Shoub

B. C. Son

ABSTRACT

Standard fire endurance fire tests were conducted on two 8 foot high by

16 foot long assemblies, each consisting of double modular partition

walls. In these tests, the applied loads represented the weight of

modules supported by the walls, and other applicable design live loads.

The partitions were of gypsum board on metal studs and simulated the

juxtaposition of walls of two adjoining housing modules. As each of

the parallel module walls was an independent load bearing member both

were required to meet a specified fire endurance under the applied load

in tests conducted in accordance with the requirements of ASTM E 119-71,

Fire Tests of Building Construction and Materials.

The load applied was 1078 pounds per linear foot (plf) per wall and the

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

or below the stress level developed by this loading.

The fire exposed wall of the first test specimen (with 3 inch "C" type)

studs) failed structurally at 42 minutes and the outer wall failed

structurally at 1 hour 13 minutes. In the second test specimen, with

i
tubular studs for increased strength, the fire exposed wall failed

structurally at 1 hour 7 minutes and the outer wall failed at 1 hour

37 minutes by passage of hot gas.

Key Words: Fire endurance; Fire tests; Housing systems; Modular

construction; Operation BREAKTHROUGH; Steel framing

ii
TABLE OF CONTENTS

Page

ABSTRACT i

1.0 INTRODUCTION 1

2.0 DESCRIPTION OF TEST SPECIMENS 2

3.0 TEST METHOD AND INSTRUMENTATION . 3

4.0 RESULTS 6

5.0 DISCUSSION OF RESULTS 10

6.0 CONCLUSIONS 12

LIST OF FIGURES 13

APPENDIX I 14

iii

1.0 Introduction

The fire resistive characteristics of two separation walls proposed

for low rise raultifamily residential occupancy were determined in tests

conducted by the Fire Research Section of the National Bureau of Standards.

The tests were sponsored by the Department of Housing and Urban Development as part of the program of evaluating housing systems under Operation

BREAKTHROUGH

.

The walls were constructed of gypsum boards on metal studs, with several

innovative features that necessitated full scale fire test validation.

First, they represented walls that would be formed by the juxtaposition

of two factory built housing modules. As such they were of identical

construction from the facing surfaces outward. By their position they

were part of the first story units in a three-story structure, and thus

had to support the units above with their respective design live loads.

The structural members also were of a type not extensively used, and for

which little fire performance data were available.

The tests were conducted in accordance with the requirements of ASIM

Standard E 119-71, Fire Tests of Building Construction and Materials.—''

— Standard Methcas of Fire Tests of Building Construct -oa ana Materials , American Society for Testing and Materials Designation E 119-71,

available at 1916 Race Street, Philadelphia, Pa. 19103.
2.0 Description of Test Specimens

The wall specimens for the two tests were similar in construction, with

several modifications made to the second test specimen as a means of

enhancing its fire performance to a level commensurate with the requirements for the structure of its occupancy type.

Construction details for both walls are shown in Figure 1. The wall

for Test 1 was constructed of cold-rolled steel "C" type studs (3 inches

by 1 3/4 inch, with 1/2 inch lip, 18 ga, 24 inch o.c), welded at top

and bottom to steel channels, 3 1/8 inches by 1 1/8 inch, 1/16 inch

thick. The inner or facing surfaces of the dual wall, separated by a

1/2-inch cavity, were of 1/2-inch gypsum board, the outer surfaces (or

room side) 5/8-inch. All the gypsum board was type "X" (special fire

rated) .

•

• •

'

The tapered joints between boards were filled with joint compound and

taped with a paper strip. Fastening of the 4 foot wide gypsum boards

to the studs and channels was by 1-inch long S-12 bugle head screws

spaced at 12 inches in the field of the boards and 8 inches on their

perimeter. The boards were cut short about 1/2 inch at top and bottom

to prevent edge restraint during the test.

Batts of friction fit low binder content glass fiber insulation 2 1/2

inches thick were placed between the studs of each wall.

2
Tlie spacin}?, of the two studs at one end of the specimen was reduced by

1 inch, making the overall length of the wall 15 feet 11 inches, to

insure easy fit in the 16-foot opening of the test frame. Representing

actual conditions of use, the height of the test wall was 8 feet.

The wall assembly for the second test was similar in size and construction

to that for the first, but with the following notable exceptions:

1. The "C" studs were replaced by tubular members having

dimensions 3 inches by 2 inches with a wall thickness

of 0.065 inches.

2. Insulation was by 3 1/2-inch glass fiber batts compressed

to 3 inches to fit between studs.

3. As shown in Figure 1, the 5/8-inch gypsum board outer

sheets were supported on angles set on the edge of the

channels, which, in practice, would allow fitting of

floor and ceiling assemblies. The spaces along the

channels were filled by separate gypsum board strips.

3.0 Test Method and Instrumentation

The frame in which a wall test specimen was mounted formed one side of a

wall test furnace which was controlled to give an average temperature

within the furnace chamber in accordance with the time-temperature

schedule prescribed in the ASTM E 119 standard.

Twelve thermocouples, protected in iron tubes, were symmetrically distributed for temperature measurement within the furnace.
The first occurrence of the following criteria of failure determines

the fire endurance of a wall assembly in accordance with the ASTM E 119

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

held against the surface.

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

(181°C) at one point, above the initial temperature

on the unexposed surface.

Since, in the assembly under test, each wall of the double wall was

intended to serve as an independent loadbearing member, the ability to

sustain the applied load was required for each of the wall elements.

Failure criteria based on heat penetration, however, were applied only

to the unexposed surface of the double wall assembly.

To determine temperature rises on the unexposed surface and at points

on the interior of the structure, 68 Chromel-Alumel (Type K) thermocouples were distributed about the test specimen. Twelve were placed

on the unexposed surface under 6- by 6- by 0.4-inch felted asbestos

pads as required in the E 119 standard. Of these, four were on the

surface over the studs, one was over the center joint, and seven were

at midpoints between studs. A wall, mounted in the furnace frame and

with surface thermocouples applied, is shown in Figure 2.

4
The remaining 56 thermocouples were placed within the wall structure,

in all cases against gypsum board faces, either at or between the studs.

The locations of the specimen thermocouples are indicated schematically

in Figure 3. The temperature readings from all of the thermocouples

were recorded at two minute intervals on the data logger for computer

processing.

The 8-foot height of the test specimens, while representing the conditions

of actual use, was less than the 9-foot minimum dimension for test

structures specified in ASTM E 119. The walls, however, did exceed the

minimum area required of the standard.

As the 8-foot high specimens did not fill the 10-foot high opening of

the test frame, the bottom of the frame over the loading jacks was

closed with separate fillers, made in 8-foot lengths, for each of the

two sections of a double wall. A load of 1078 pounds per linear foot

(1028 plf live, 50 plf dead weight of wall) was applied to each of the

wall sections. This load was calculated from design live loading for

residential occupancy.

The filler panels in the frame had structural strength and fire resistance

which would not be impaired by fire exposure for the expected duration

of the test. All structural steel in the wall that could in any way be

subject to direct fire exposure was also adequately protected. The test

specimen was sealed into the test frame with noncombust ible insulation;

gaps between the frame and furnace were also sealed.

5
Lateral deflections of the unexposed surface of the wall were determined

by its position relative to a horizontal wire stretched across the test

frame at the midheight of the wall specimen.

During the test, the neutral point in the furnace, that is the height

at which the pressure in the furnace was equal to that outside, was

maintained at the one-third height of the specimen (2 feet 8 inches

above the bottom) . This provided a positive furnace pressure above the

neutral point increasing linearly with height. Under positive furnace

pressures representing conditions usually occurring in actual fires,

combustion gases may be forced through fissures or openings in the

specimen.

Hose stream tests, described in Section 8 of E 119 were not conducted

on the specimens after the fire exposure. According to the standard,

these are not required for structures exhibiting fire endurance of less

than 1 hour. , ;i

4.0 Results

Wall No. 1, "C" Type Studs

A fire endurance of 42 minutes was established for the fire-exposed

wall of the assembly with "C" type studs by failure to sustain the

applied load. The unexposed wall failed similarly at 1 hour 13 minutes.

Flame penetration to the unexposed surface occurred at 1 hour 15 minutes.

6
The furnace temperatures throughout the test were in close conformance

with the standard time-temperature curve and no correction was necessary

to the times to failure (Figure 4)

.

As can be seen in Figure 5, temperature rise at the thermocouple locations

on the unexposed surface did not approach the limiting rises established

as criteria of failure in the ASTM E 119 standard. There was little

temperature variation over the surface as indicated by the close correspondence of the maximum one point and average temperature curves.

The temperature gradient across the wall assembly can be seen in

Figure 6 (maxima) and Figure 7 (average)

.

Horizontal deflection measurements made on the unexposed surface indicated

a very small back and forth movement in the early stage of the test.

A significant movement of about 1/4 inch toward the fire was noted at

28 minutes at the center and at two quarterpoints . At 1 hour 6 minutes,

before failure of the outer unexposed wall, deflections of 1 inch at the

center and 1/2 inch and 7/8 inch at the sides were measured. At the

conclusion of the test the 3-inch deflection at one quarterpoint greatly

exceeded the 1 1/4 inch measured at the other quarterpoint and was

greater than the 2 3/4 inches at the center. All movement subsequent

to the early waviness was toward the fire.

Observations of the wall during the test indicated that the joint compound on l\\c exposed surface flamed after a few minutes exposure and by

2\ minuLi's llioro was opening at some o\' the joints. Some cracks

7
appearc'c] in <i fire exposed board aL 2 1 minutes, and In all boards on

the fire side by 34 minutes, with visible buckling. By 41 minutes,

just prior to failure, there was considerable falling away of the fire

exposed board, exposing the studs in the inner wall (fire-exposed).

At 58 minutes the boards of the inner wall had fallen away sufficiently

to allow full exposure of the inner face of the outer wall. Just prior

to failure of the outer wall, there was considerable opening of board

joints with consequent rapid buckling of the studs.

Wall No. 2, Tubular Studs

In the fire endurance test of the second wall assembly failure (Inability

to sustain the applied load) occurred at 1 hour 7 minutes for the fire

exposed wall and at 1 hour 43 minutes for the unexposed member. Failure

by passage of hot gas through the whole assembly occurred at 1 hour 37

minutes when cotton waste held against a joint between boards on the

unexposed surface was ignited. The furnace temperatures, while slightly

higher than the prescribed standard, were so close to those of the

standard curve that no correction was required for the indicated fire

endurance times (furnace and standard curve in Figure 8)

.

As could be expected from the results of the tests on the first wall,

temperature rises on the unexposed surface remained considerably below

the limits established as failure points in the fire test standard

(Figure 9) . Here again there was little variation in temperatures

over the surface, with maximum temperatures only slightly greater than

averages. Temperature gradients across the wall assembly were also

8
similar to those for the first test specimen, but with indication of

somewhat slower heat penetration which could be attributed to the

greater thickness of insulation in the second test specimen (Figures

10 and 11).

Deflection measurements were made up to 1 hour 40 minutes of test time.

Movements of the walls were mostly minor up to the last stages of the

test. The 1/2-inch deflection towards the fire that occurred at one

quarterpoint at about 10 minutes was probably the result of initial

unevenness of the wall. Deflections, all toward the fire, at 1 hour

35 minutes were 7/8 inch at the center, 1 1/2 inch at one quarterpoint

and 1 3/4 inch at the other (the point initially bowed out). Three

minutes before load failure on the unexposed wall, the deflections

were 1 5/8 inch at the center and 2 1/4 and 2 3/4 inches at the two

quarterpoints

.

Visual observations indicated flaming occurred at the joints on the

fire-exposed surface at 3 minutes. Cracks in the boards appeared at

23 minutes and by 34 minutes had opened to about 3/8 inch. At 48 minutes

an end panel began to disintegrate, exposing the fiber glass insulation.

By 1 hour the studs of the exposed wall were bowing toward the fire

leading to load failure at 1 hour 7 minutes. By 1 hour 20 minutes

enough of the wall next to the fire had fallen away to expose a considerable portion of the second wall. After this there was progressive

opening of the joints of the second wall, on the side toward the fire

9
and then on the unexposed side, causing the 1 hour 37 minute failure

by passage of hot gas.

5.0 Discussion of Results

The distributed load on the wall studs of modules designed as the first

story of a three-story structure was calculated from the weight of the

two modules above, a design live load of 40 psf, a ceiling and a roof

plus a design snow load of 30 psf. This gave a design load of 2244

pounds per stud. The load was reduced to 2055 pounds per stud to

compensate for the lack in the test structure of the restraint ordinarily

imposed on wall studs by their contiguous floor and ceiling assemblies.

End fixity, in actual practice, effectively reduces stud column length.

The actual load applied in the tests, 1918 pounds per stud (1078

pounds per linear foot of wall) represented a further small reduction

of the load on each stud, about 11 percent less than calculated.

An examination of the walls after the tests indicated that the "C" type

studs of the first test specimen twisted in failure, probably because

of their asymmetry, while the tubular studs of the second test specimen

exhibited simple buckling, which left the welds intact (Figures 12 and

13, respectively). The studs were changed to the tubular shape for the

second test specimen to provide higher strength without increase in wall

thickness. An alternate method of obtaining a higher fire endurance

level with the "C" type studs would be by the use of additional layers

of gypsum board.

10
Deflection of the walls occurred by bowing toward the fire, the apparent

consequences of the earlier heating of the fire side of the studs , allowing the initiation of and continued greater yielding on the side , as

compared to the side away from the fire.

Heat penetration of the studs probably occurred initially through the

joints between the gypsum board coverings. Cracks in the gypsum accelerated to heat transmission process and bowing of the steel led to the

formation of ever wider cracks and eventual collapse of the boards. An

indication of the action of the gypsum boards can be seen in the wall

temperature charts wherein the temperature rise plateau at about 100°C

is attributable to cooling provided by the evaporation of the combined

water in the gypsum. From the same data the air space between the two

walls did not appear to provide much thermal resistance.

Observations in other tests have indicated that in double wall assemblies,

as here tested, the fire endurance time of the total assembly is about

1.75 times the time of failure of the wall directly exposed to the fire.

This v/as almost exactly true for the first test specimen (42 minutes and 1

hour 13 minutes). In the second test, however, the relationship did

not hold, the unexposed wall failing by passage of hot gases at 1 hour

37 minutes, significantly earlier than the expected time (67 minutes x

1.75 = 117 minutes).

11
6.0 Conclusions

From the results of these tests, It can be seen that a single layer of

5/8-inch Type "X" gypsum board will not provide protection to "C" type

steel studs from failure under load for a one hour fire endurance period

Besides the applied load, critical factors include the size and shape of

the studs and the quality of the gypsum board joints. In these tests a

particular source of weakness appeared to be the joints between the

gypsum boards where the filling compound was either quickly destroyed

or loosened, allowing rapid heat transmission to the studs. This

suggests that a better practice would be the use of a two layer construe

tion, with application of the boards staggered to eliminate direct heat

access to the steel through joints.

The load applied to the wall in these tests was 1078 plf per wall and

the results of these tests may be made applicable only to structures

and loads in which the stresses developed in the members do not exceed

those tested.

12
List of Figures

Figure 1 Construction of Wall Specimens

Figure 2 Wall with Surface Thermocouples, Near Start of Test, 1st Test

Figure 3 Thermocouple Locations in Test Structure

Figure 4 Average Furnace Temperature for Wall No. 1 Compared with

Standard E 119

Figure 5 Maximum and Average Temperature Rise on the Unexposed

Surface Wall No . 1

Figure 6 Maximum Temperature Gradient Across the Assembly Wall No. 1

Figure 7 Average Temperature Gradient Across the Assembly Wall No, 1

Figure 8 Average Furnace Temperature for 2nd Test Compared with Standard

E 119-71 Curve

Figure 9 Maximum and Average Temperature Rise on the Unexposed Surface

2nd Wall

Figure 10 Maximum Temperature Gradient Across the Assembly Over Steel

Studs - 2nd Wall

Figure 11 Average Temperature Gradient Across the Assembly Over Steel

Studs - 2nd Wall

Figure 12 First Test Specimera, Exposed Side Near End of Tests, Studs

Twisted

Figure 13 Second Test Specimen, After Test, Showing Buckling of

Unexposed Wall

13
Appendix I

" j

SI Conversion Units • ^

In view of present accepted practic. in this country in this

technological area, coiranon US units of measurement- have been used throughout this paper. In recognition of the position of the United States as

a signatory to the General Conference on Weights and Measurements which

t gave official status to the metric SI system of units -in 1960, we assist

readers interested in maMng 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 Kilograms

Stress

1 psf - 47.88 newton/meter^

1 psi - 0.332 newton/meter^

1 plf = 13.49 newtcn/meter

Temperature

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

14

o g;- o

cn

M-(M CO 0 <D to CD r-l 0)

"5 o

•H o 0 OB

r-(

U

t-f

m to CO W 3 H C/5

CM

(1>

16
South North

6'

2'

f f

qDAi

1

1

1

1

1

1

1

1

1

itl A?

1

1

1

1

1

1

1

1 BIO [tlA3

1

1

1

rpo rriA4

1

1

1

1

1

1

B30

AC2

B40

C3A

C4A

8

-0"

»s

r

I5'-II"

VIEW TOWARDS UNEXPOSED SURFACE

A = AT STEEL STUDS

B = ON GYP. BOARD NOT AT STUDS

Cl= ON BOARDS AT STUD

C2,C3,C4=0N BOARDS NOT AT STUDS

FIRE SIDE

2 2 ^ ( »

1 »4 1

r.4

^5 '

^ .

•5

^

\ ^7

LOCATION A LOCATION B LOCATION C

UNEXPOSED SIDE

Figure 3 - Thermocouple Locations in Test Assembly

500.

400_

CD 300.

Ui

in

»—cru ZOO.

a.

szUI

100^

O AVE . 3UR . TEMP

A nnx. 3UR. TEMP

One Point Maximum Rise Failure

Average Temperature Rise Failure

10 "5o "40 TIMEtWINUTE)

Figure 5 - Maximum and Average Temperature Rise on the Unexposed Surface Wall No. 1 19

1100_

1000_

900_

800.

700 _

" 600_

CDa

5 500 _

t—OS

UJ

a.S 400_

300_

Z00_

100_

1 ©

3 t SEE THERMOCOUPLE

5 J LOCATION DWG.

6 7 X FIG. 3

10 '40 To

TIME(niNUTE)

Figure 7 - Average Temperature Gradient Across Wall Assembly No. 1 21
1 100

m flVEf?RGC FUFNRCE: TEflFERflTURE"

- STRNORRD El 19

TItlEl MINUTE)

Figure 8 - Average Furnace Temperature for Test No. 2 Compared with Standa
300^

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ui

a:

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a.

100_

0 riRX. SURFflCC TChP

A HVC. SURFflCf TEtiP

-bmax. temp, rise failure

-a AV. TEMP. RISE FAILURE

rinciniNUTE)

Figure 9 - Maximum and Average Temperature Rise on the Unexposed Surface 2nd Wall

23

1 IQO

1® See Thermocouple

2 * Location DWG.

TiriECniNUTE)

Figure 11 - Average Temperature Gradient Across the Assembly Over Steel Studs of Wall Nn. 2.

25



FORM NBS-114A (1-71) U.S. DEPT. OF COMM. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA mdctd ti t i > SHEgT NBSIR 73-173

3. Recipient s Accession No.

111 Lb AI\U oU tJ 1 1 1 Lr, Fire Endurance Tests of Double Module Walls of Gypsum

Board and Steel Studs

5, Publication Date

6. Performing Organization Code

7. AUTHOR(S)

Byung Chan Son and Harry Shoub

8. Performing Organization

NBSIR 73-173

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 4600447

11. Contract/Grant No. IAA-H-16-70

12. Sponsoring Organization Name and Address Office of Research and Technology

Department of Housing and Urban Development

Washington, D.C. 20410

13. Type of Report & Period

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.) Standard fire endurance fire tests were conducted on two 8 foot high by 16 foot long

assemblies, each consisting of double modular partition walls. In these tests, the

applied loads represented the weight of modules supported by the walls, and other

applicable design live loads. The partitions were of gypsum board on metal studs

and simulated the juxtaposition of walls of two adjoining housing modules. As each

of the parallel module walls was an independent load bearing member both were required

to meet a specified fire endurance under the applied load in tests conducted in

accordance with the requirements of ASTM E119-71, Fire Tests of Building Construction

and Materials

.

The load applied was 1078 pounds per linear foot (plf) per wall and the test results

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

developed by this loading.

The fire exposed wall of the first test specimen (with 3 inch "C" type studs) failed

structurally at 42 minutes and the outer wall failed structurally at 1 hour

13 minutes. In the second test specimen, with tubular studs for increased strength,

the fire exposed wall failed structurally at 1 hour 7 minutes and the outer wall

failed at 1 hour 37 minutes by passage of hot gas.

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

Fire endurance; fire tests; housing systems; modular construction; Operation

BREAKTHROUGH; steel framing

18. AVAILABILITY STATEMENT

I I UNLIMITED.

I ! FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

21. NO. OF PAGES

27

22. Pr

UNCLASSIFIED

USCOMM-DC 66244.P7I


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