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BUILDING SCIENCE SERIES

Fire Resistance

Of Steel Deck

Floor Assemblies

ID J

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards
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UNITED STATE DEPARTMENT OF COMMERCE • Alexander B. Trowbridge, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Fire Resistance of

Steel Deck Floor Assemblies

H. Shoub and S.H. Ingberg

Building Research Division

Institute for Applied Technology

National Bureau of Standards

Washington, D. C.

Building Science Series 11

Issued December 1967

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 25 cents
Contents

Page

1. Introduction 1

2. Materials and construction of test floors 2

2.1. Floor structure 2

2.2. Floor finish (surface insulation) 2

2.3. Ceiling protection 2

3. Test equipment 6

3.1. Furnace and burnout room 6

3.2. Temperature-measuring equipment 7

3.3. Deflection-measurement equipment 8

4. Test method 8

4.1. Loading 8

4.2. Fire exposure 8

5. Results of tests 9

5.1. Burnout tests 1-6 9

5.2. Fire endurance tests 7-16 17

6. Discussion of results 19

6.1. Burnout tests (Tests 1-6) 19

6.2. Fire endurance tests (Tests 7-16) 20

7. Summary 21

8. References 22

n
Fire Resistance of Steel Deck Floor Assemblies

H. Shoub and S. H. Ingberg

Tests were conducted to determine the resistance to fire of welded steel plate and

beam floor assemblies with various conditions of floor covering on the plates, and ceiling

protections beneath the beams. The trials included fire exposures from the burnout of combustible materials ranging from 10 to 40 lb/ft' on the floor surface as well as standard fire endurance tests in which the ceiling of the structure was exposed to fire. The results of the tests indicated that the use of steel floor structures was practical

from considerations of fire safety. For the test conditions established, fire exposure on

top of the floor did not heat the structural steel supporting members sufficiently to cause load failure or collapse, and did not produce untenable conditions in the room

below. In tests involving fire exposure to the underside of floors, the fire endurance

times, based solely on heat transmission criteria, ranged from 1 hr 24 min to over 4 hr. Temperature levels attained by the structural members and deflection of the floor assemblies are also reported.

Key words: fire endurance, steel plate floors, burnout tests, floor tests, fire severity.

1. Introduction

Steel deck floors supported by protected steel beams and girders have been used in multistory

buildings in the past because, with their relatively light weight compared to some other

j types of fire-resistive floors, the structural load on the girders, columns, and foundation of a

[ building could be reduced, with consequent inj crease in allowable live loads. Further advan1] tages were the ease of framing the steel decks

j into irregularly-shaped panels, and the rigidity

which the floors, when suitably attached to structural members, could impart to the build-

: ing as a whole.

The tests described in this paper were designed to determine the fire endurance performjj ance of such floors under design load. Trials

{; were made with the fire either above or below

ij the floor assembly. The work was performed

between 1931 and 1933 with the cooperation of

the American Institute of Steel Construction.

The apparent promising future for steel deck

floor systems at that time failed to materialize

because of the development of other lightweight steel products such as open-web joists

and light-gage decking.

I' This report is being issued with the purpose

of making generally available the large body of

still pertinent data secured in the tests. In some

of the tests, the floors were subjected to fire

I exposure by means of controlled burnout of

j combustible materials from above the floor. It

[j appears that these are the only laboratory tests

' so conducted. In the tests with the fire conventionally below the floor, the performance of

;j the ceiling structures and floor toppings are of

interest in the design of floor assemblies now in

use.For the purpose of the tests, the steel deck

floors were installed in a specially built furnace,

and subjected to 16 separate trials of fire en- durance, 10 with fire exposure below the floor,

and 6 burnout tests of combustible furnishings

typical of office occupancies placed on the floor. The 10 tests with the flre below the floor were

conducted under requirements for fire tests substantially the same as those of the currently

applicable standard [1]\ In two of the set of

10 tests, however, a hose-stream application was made on the floor assemblies subsequent to the fire exposure. This is not listed as a requirement or an option in the standard now in use. As steel in itself has little resistance to the

effects of exposure to high temperatures, the

floor systems were necessarily protected with

various insulating coverings applied as a ceiling

beneath the beams, and also in most cases on

top of the steel floor deck.

The purpose of the six burnout tests where

the fire was above the floor was to determine if heat from fires in combustibles in several con- centrations representing the furnishings, supplies, and records of office-type occupancies

would be transmitted through the floor to an

extent sufl[icient to weaken the plates, beams,

and other structural members to the point of

failure under the applied load. In four of these

tests, insulating floor-covering materials were

applied to the steel deck surfaces to retard the

passage of heat to the structural members.

^ Figures in brackets indicate the literature references at the end

of this paper.

1
2. Materials and Construction of Test Floors

The floors were constructed of materials of

commercial grade supplied by the manufacturers or purchased in the open market. The workmanship was representative of that normally

obtained in construction. Welding and plastering operations were carried out by skilled

craftsmen in the employ of local contractors. Certain special materials such as linoleum,

mastic floor finishes, and ceiling tiles were in- stalled by representatives of the manufacturers.

Casting and finishing of ordinary concrete on

the floor surfaces were done by regular employees of the National Bureau of Standards.

The floors are described, together with

sketches of the various constructions, in table

1 (Tests 1-6, fires above floors), and table 2

(Tests 7-16, fires below floors) . All of the floors were approximately 131/2 ft wide by 18 ft long

and were built in place in the floor furnace.

2.1. Floor Structure

In every case, the floor structures were in

steel plates 18 ft long attached to the upper

flanges of small section I- or H-beams by either

continuous or intermittent welds along their

longitudinal edges. From the tables it will be

noted that the steel beams varied in size and

spacing. In Tests 1-14, seven beams, either in

4-in, 7.7-lb, or 5-in, 10-lb size, were used on

24-ViG in centers. The floor assembly for Test 11

was also used in Tests 13 and 14. In Tests 15

and 16, four beams were spaced 48-^/in in on centers. Two of these were 5-in, 18.9-lb I-beams

placed near the centerline of the panel, with

side support furnished by two 5-in, 10-lb

I-beams, each about 8 in distant from the re- straining frame of the furnace. The same struc- ture sufficed for the two tests. Steel girders were used in six of the tests. They were 12-in, 31.8-lb I-beams spanning the

width of the floor 5 ft from one end of the fur- nace restraining frame. Thus the girder divided

a test floor into two sections, one having a supported clear span of 13 ft, the other consisting

of a 5-ft span cantilevered from the girder. In one test. No. 10, the floor beams were carried over the top flange of the girder. In the other

tests, shelf angles welded to the girders supported the beams, placing the tops of the beams

and the girder in the same plane.

In floor assemblies designed with restrained

or fixed end supports, the beams were welded

along both sides of the lower flanges where they

rested on supporting angles securely bolted to the furnace frame. Additional welds were made

under the flanges at the edge of the supports.

Other restraining angles, bolted to the furnace, were welded to the top of the plate above the

beam supports. The beams of freely supported

floors were not welded to the shelf angles,

although temporary tack welds were used to secure proper spacing of the parts during

assembly of the floors.

2.2. Floor Finish (Surface Insulation)

Three of the tests (1, 2, 15) were conducted

without a covering of any kind on the steel plates. The floor in Test 3 was covered with '-^lu- in thick battleship linoleum while that in Test 4

had a i/^-in coating of an asphalt emulsion concrete. The floors for the remaining tests had

from 1 to 3 in of concrete, or concrete base and

topping. Concretes had gravel or cinder aggregate, or were gas-expanded. Toppings, where

used, were 1/2 in thick, and principally of

cement and sand mix, although limestone con- crete and mastic were also used. Wherever a concrete flooring was to be applied, except in Test 7, an expanded metal reinforcement

binder was tack welded to the steel plates at

2-ft intervals, and raised from the surface

between welds. Details are given in tables 1 and 2.

2.3. Ceiling Protection

Details of lathing, plastering, and application

of ceiling tile on the underside of the floors are

also given in tables 1 and 2. Metal lath, with or without reinforcing rods, was used in all tests except Nos. 6, 10, 12, and

15, which had 2-in precast gypsum ceiling tile. This was usually supported on 1-in hot rolled

channels with wire ties or clips, but in Test 12

was installed directly on the lower flanges of

the beams.

Plaster was applied to plain diamond mesh

metal lath (3.4 lb/yd-) or to lath reinforced

with stamped ribs or welded wires (3.4 or 4.2 Ib/yd^). The ceiling protection varied in materials and thickness for the several tests. Twocoat sanded gypsum plaster % in thick was

used in Tests 1, 3, 4, 5, 7, while an average

thickness of 1% in (range 1 to l%in) was applied for Test 2. For the ceiling in Test 13,

three different materials were used, portland j cement, hair-fibered gypsum, and wood-fibered

gypsum. Other ceilings had three-coat plaster

built up to thicknesses of 1 to II/2 in. Heavier insulation was provided in the four

tests in which 2-in gypsum ceiling tile was

used. For these, an application of 1/2 of unfibered sanded gypsum plaster was applied to the tile, producing a total thickness of 21/2 Where the girders were protected by 2-in

(Tests 6, 10) or 3-in (Test 11, 13, 14) hollow

gypsum tile installed along the web, approximately 1/^ in of sanded gypsum plaster was

2
3


also applied to the tile. In Test 5, the girder was protected by % in of sanded gypsum plas- ter on metal lath, similar to that provided on

the ceiling.

The floors were conditioned about a month

prior to their test for the purpose of drying

plaster and concrete. In many cases the drying was accelerated by application of heat below the

floor. However, it seems unlikely that the con- ditioning procedures used were adequate to dry

the concrete floors to the moisture content levels typical of thoroughly seasoned concrete.

3. Test Equipment

3.1. Furnace and Burnout Room

The tests were conducted in a furnace and

associated burnout room accommodating a floor structure 13 1/2 ft wide and 18 ft long (see fig.

1). The design was such that either the top or under surfaces of test floors could be subjected

to fire exposure. The furnace consisted of a masonry and concrete structure enclosing the

lower side of a horizontal and independently

suported steel restraining frame made of 30-in,

240-lb H-section girders fastened at the corners through a system of angles and plates and supported by steel columns. The girders of the re- straining frame were mounted with their webs

horizontal and the centerline 4 ft 7 in above

the building floor or 6 ft 10 in above the bottom

of the furnace pit. The inner flanges of the

girders were flush with the interior face of the

furnace walls. Holes were provided in the lower

half of the girder for bolting the shelf angles

supporting a test floor assembly. Steel plates were welded to the girder web and flanges for

additional rigidity. To prevent distortion of the

frame girders during a test, they were cooled

by using the upper portion of the girder outside

LOUVER

(ADJUSTABLE)

'II' BURNOUT ROOM

OBSERVATION PORT ^ RESTRAINING FRAME

FLOOR AREA I3'-6"XI8'

FURNACE

the furnace walls as reservoirs for water. As

shown in figure 1, the space above the furnace was enclosed with brick walls permanently built over the restraining frame so that the top sur- face of test floors could be subjected to fire exposures from the burning of combustible

materials on the floor. Louvers near the top of

the burnout room could be used to regulate the

amount of air admitted and so give some control over the rate of burning.

Figure 2 shows a portion of the furnace re- straining frame during construction and before

erection of the furnace walls. The system of corner fastening and column support can be

seen. The burnout room with a bare steel deck

floor in place is shown in figure 3. In figure 4, the furnace space can be seen, with a steel deckand-beam floor in place, prior to installation of

the protective ceiling assembly beneatli the

floor.

Figure 1.—Sketch of furnace and burnout room, for fire tests of floor assemblies. Figure 2.—Floor test furnace during construction; corner fastening and column supports visible.

6
Figure S.— Upper furnace space; bare steel-deck floor. The furnace was gas fired, with 48 venturitype burners, arranged in two rows on each

side. The burners on each side of the furnace were housed in a plenum chamber supphed with

low pressure air. An auxiliary air supply was

provided in the combustion chamber of the fur- nace through six air inlets in line with each

bottom row of burners. Three 9-in diam flues on each side served to carry off the combustion

gases. Some of the burner, air, and flue openings are visible in figure 4.

Figure i.—Lower furnace, steel deck-and-beam floor in place, prior to installation of protective ceiling.

3.2. Temperature-Measuring Equipment

All temperature measurements, except those

in the furnace space in the room burnout Tests

1-6, were made with chromel-alumel thermocouples.

For Tests 7-16, the temperatures in the fur- nace were determined with 12 thermocouples,

mounted in iron pipes and located 12 in below

the ceiling of the test floor. Where the fire exposure consisted of a burnout of combustibles

above a floor (Tests 1-6), temperatures in the

burnout room were measured by 13 thermocouples, similarly protected in iron pipes and

suspended nine at 3 ft and four at 7 ft above

the floor. In these tests, total immersion thermometers, suspended approximately 1 ft below

the ceiling, were used for temperature measure- ment in the furnace space below the fire room.

It is probable that the ceiling temperatures were not high enough to cause appreciable

radiation error in the readings of these

thermometers.

The temperatures of the bottom flanges of

the beams and girders, and also of the floor

plates (lower side), were measured with thermocouples peened into the steel. Thermocouples were placed near the center of the span of these

structural elements, and also at locations approximately 1 ft from their ends.

The temperatures on the upper or "unexposed" surface of the floors which were subjected to fire exposure on the under side were measured with 12 thermocouples symmetrically

located over the floor area. Their bare junctions were placed in contact with the floor surface,

and were protected by weighted asbestos felt pads 6-in square and 0.4-in thick. No measure- ments were made on the surface of test floors

which were subjected to burnout of combustibles above the floor. Thermocouples, usually three or four, with

bare junctions, were also installed in the air

spaces between the steel floor plates and the

ceiling assembly. They were located at the center of the floor span between the beams.

Iron pipes protecting thermocouples in the

furnace may be seen in figure 5, and in the

burnout space above the floor in figure 6. Figure

7 shows the weighted asbestos pads covering

the bare thermocouple junctions in contact with

the unexposed surface of a floor.

Figure 5.—Lower furnace showing iron pipes for protection of furnace temperature-measuring thermocouples.

7
Figure 6.—Burnout space above the floor; thermocouples

contained in suspended iron pipes; showing arrange- ment of combustible materials.

4. Test

4.1. Loading

For the fire tests, load was applied to each

floor to the extent required to produce an ex- treme fiber stress of approximately 18,000

lb/in- in the beams. Where girders were used,

they were only loaded to a small fraction of

their design load and were considered to be

suitably protected, so that the fire exposures

could be taken as critical tests of only the beam

and steel plate assemblies. As noted later, this was not always true. The average weight of the steel in the ISi^-

X 18-ft floor panels ranged from 14 to 15.2

Ib/ft^ A maximum of 28 lb/ft' was added by

the concrete floor covering. Ceiling assemblies

ranged in weight from 10 to 15 lb/ft- in the tests with the fire above the floor and 10 to 18 Ib/ftfor the remaining tests of the series. For all the

floors, the total dead load due to structural

steel, floor covering and ceiling construction

ranged from 24 to 57 lb/ft-.

Part of the applied load in Tests 1-6 consisted of combustible materials in the form of

office equipment, supplies, and records placed on the floor in amounts varying from 10 to 40

lb/ft-. The furnishings were of the same general nature in all burnout tests, with increased

combustible loadings achieved by the addition

of paper in the required amounts. The re3.3. Deflection-Measurement Equipment

The deflections of the floors were measured

by means of graduated invar tapes attached to the floor components. Readings on the tapes were made by use of a transit mounted on a

stable support external to the floor. For floors

subjected to top fire exposure, the tapes were

fastened to pins welded to the beams or under

sides of the floor plates, and brought down

through the celing plaster. In those tests having

bottom fire exposure, the tapes were attached to pins screwed into the top of the steel plates and

extended up to wires running over pulleys (see

fig. 7) . In all cases, the tapes were held vertical

by weights.

Location of deflection measurements varied

according to the structure of the floor. Readings were taken at the centers of spans, and also at some quarter-points. Where a cantilever con- struction was usedi deflection at the extreme

end of the cantilever span was noted.

Method

mainder of the applied load was supplied by

pig iron placed in rows. In Tests 1 to 4, there were four rows, located 3 ft and 6 ft from each

end support. In Tests 5 and 6, there were three

rows, one at or near each quarter-point of the

13-ft span and one at the center of the cantilever span.

In the tests with the fire exposure below the

floor, the applied loads consisted entirely of pig

iron placed in rows on the floor surface, except

in Test 15, where the weights were uniformly

distributed over the entire floor. The weights

used in all of the tests, except that of Test 15, were raised from the floor surface by means of

iron pipes placed directly on the floor. This

established definite points of loading at the

beginning of the test and permitted air circulation under the weights. In the later tests, upright sections of pipe were installed to form a

small gap at the center of each row, thus preventing arch action of the stacked weights due

to deflection of the floor. The arrangement is illustrated in figure 7.

4.2. Fire Exposure

The tests with the fire exposure above the

floor were conducted as burnout tests, for which

no performance standards or criteria have been

established. The fires in the combustible portion

8
FiGUKE 7.— Top of floor for standard fire test, showing

asbestos pads covering surface thermocouples, deflec- tion measuring tapes, and method of loading with

pig iron.

of the applied loading in these tests were representative of fire hazard severities nominally

equivalent to 1 to 41^ hr in a standard fire- endurance test. The fires were ignited by the use of kerosene-soaked cotton waste placed at several locations in the furnishings assembled

as office occupancies, and allowed to continue

until the fuel was exhausted. The burning rate was controlled, but to an indefinite extent, by

regulating the admission of air through louver

openings in the top of the burnout room.

Tests made with the fire exposure below the

floor were generally in accordance with the re- quirements of the Standard Methods of Fire

Tests of Building Construction and Materials,

ASTM Designation E119. By this procedure,

the underside of a floor structure is exposed to a fire controlled to conform as closely as possible to a time-temperature schedule defined by

the following points

:

1000 °F at 5 min

1300 °F at 10 min

1550 °F at 30 min

1700 °F at 1 hr

1850 °F at 2 hr

2000 °F at 4 hr. The fire endurance of a floor is determined by

the earliest time to one of the following criteria

of failure:

1. Failure to sustain the applied load.

2. Passage of flame or gas through the floor

hot enough to ignite cotton waste.

3. A temperature rise of 250 degrees F,

average, or 325 degrees F, one point, above the

initial temperature of the unexposed surface.

For the fire and hose stream tests (13 and

15), the fire exposure was stopped after 1 hr

and the hose stream was applied through the

furnace door to the heated under surface of the

floor. The water was applied through a 21/2-in

hose with a IMj-iri nozzle at a pressure of 40

lb/in- in Test 13 and 45 lb/in- in Test 15. For

Test 13, the duration of water application was

6 min 5 sec, equal to a 21/2 min application for a 100-ft- ceiling, and for Test 15, the duration

of water application was 12 min 9 sec, equal to a 5-min application for lOO-ft- of ceiling area. Fire exposures under the floors were usually

continued beyond the time to reach a criterion

of failure, in order to develop additional information on the behavior of the steel structure

under fire conditions. Particular note was taken

of the time to reach an average temperature of

1000 °F or a one-point temperature of 1200 °F

in the structural steel members. In addition to recording temperatures and deflections, visual

observations were made of the effects on the

floors during the fire tests.

5. Results of Tests

5.1. Burnout Tests 1-6

I The maximum temperatures and deflections

j recorded in the tests with the fire exposure

above the floor are indicated in table 3. More

complete temperature data for these six tests, in the form of time-temperature curves reI corded in the burnout space and floors are availj able in figures 8-13.

The fires burned with varying intensities and

with considerable flaming that lasted until 3 to

j 6 hr after the start of the test. The highest onepoint lower flange beam temperature, 885 °F,

occurred in Test 3 at approximately 6 hr. The

highest average temperature, 729 °F, occurred

at the centrally located thermocouples on one

of the beams in Test 2. The time was 3 hr 10

min. It should be noted that in Test 2 the floor was bare while in Test 3 it was covered with a

thin sheet of linoleum. The maximum one-point

and highest average temperatures in the plate

also occurred in Test 3 (1170 °F at 5 hr 20 min,

and 891 °F at 6 hr, respectively). The corres- ponding temperatures in Test 2 were almost as high but were reached at 3 hr after the start. In all tests of this group, the full applied load was supported during the entire test period.

The average deflection at the center of the

beams due to initial apphcation of load was

approximately 0.3 in. The greatest deflection

observed in any of the tests was 5.80 in (Test

3). However, the maximum permanent set, (2.62 in), was noted after the cooling period

for Test 2. The concrete floor coverings (Tests 4-6) appeared to maintain a bond to the steel floor plates, although cracked through in many places

to the steel surface.

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TEMPERATURE IN DEGREES CENTIGRADE

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TEMPERATURE IN DEGREES CENTIGRADE
The welded joints withstood distortion of the

structures caused by the fire exposure, except

for breaking of some of the fillet welds at beam

supports and several ruptures in the plate seams. No failure in the welds was such as to prevent the floor sustaining its applied load.

Some cracking and separation of ceiling constructions occurred, principally from failure of

iron wire ties. There were no serious ruptures,

and the ceilings generally remained fairly close to their original positions.

5.2. Fire Endurance Tests 7-16

Data for floors tested under the conventional

method of fire exposure beneath the floor, are given in table 4. The temperatures recorded for the furnace were usually in fair agreement with those of

the standard time-temperature curve. Where

required by the extent of the deviations of the

furnace temperatures from those of the standard, corrections were made in the times to limiting temperature rises on the unexposed

surface of the floors. The fire test exposure

severity, shown in table 4, is defined as the

ratio of the area under the curve of average

furnace temperature to the area under the

standard time-temperature curve, each from the

start of the test to the end or time of failure,

and measured above a base temperature of

' 68 °F.

i The fire endurance of the floors, as deter-

! mined by rise of temperature on the unexposed

' surfaces, ranged from 1 hr 24 min (Test 8) to 4 hr 55 min (Test 10). Times to reach an

I average temperature of 1000 °F in the beams

were as low as 1 hr 42 min, ranging up to 4 hr

46 min. Maximum one-point temperatures of

1200 °F were attained at times comparable to

I those required to reach the 1000 °F average.

In Test 11, the specified average and one-point

maximum temperatures were not reached in

\. the beams, although the fire exposure period

! was 3 hr. In Tests 13 and 15, confined to 1-hr

duration followed by application of a hose

i stream, limiting temperatures on the unexposed

I surface as well were not reached.

Fire exposure periods in the other tests were from approximately 2 to 5 hr. In these periods

; maximum average temperature in the beams

, reached levels ranging from 860 °F after 3 hr

j in Test 11 to 1742 °F at 2 hr 43 min in Test No.

Ij 8. In Tests 10 and 14, girder temperatures in

j! excess of 1000 °F were recorded after 2 hr 36

I min and 4 hr 2 min, respectively.

Excluding Tests 11, 13, and 15, which were

terminated before critical temperatures were

attained in the steel, the maximum deflections

observed in the floor beams ranged from 7.8 in reached 30 min after the end of the 5 hr fire exposure period in Test 14 to approximately

13 or 14 in near the ends of the respective fire exposure periods in Tests 8, 9, 12, and 16. Maximum deflections in the beams and girders

usually occured at the center of span. Permanent set in the beams ranged from 3.2 in in

Test 7 to 13.2 in in Test 16. The ceilings used in the floor assemblies in

which the underside was subjected to fire ex- posure began to disintegrate in the first few

minutes of each test, but with wide variations

in behavior thereafter. The ceiling in Test 11

did not rupture to an extent causing it to fall. Gypsum ceiling tile used in Test 10 remained

intact for about 414 hr, but was almost completely down in the next half hour. In Test 14,

the tile protection fell from the lower flange of

the girder just before the end of the fire ex- posure. The ceiling in Test 16 functioned well

for almost 4 hr, when it began to fall in large

sections. Generally, the ceilings remained fairly

well in place for a considerable time after an

average temperature of 1000 °F was exceeded.

All of the floor coverings in these tests showed considerable cracking and some spalling. However, disintegration occurred only in

the floor of Test 12. The concretes adhered well

to the steel deck after the fire exposure, except

in Test 7 where no expanded metal floor binder was used. In four of the Tests (7, 9, 12, 16),

cotton waste applied to the surface of the floors

became ignited in approximately 2 to 4 hr after

start of the fire exposure. The floor covering

in Test 11 was sufficiently intact to be reused

in the hose stream Test 13, and after rehydrating, in Test 14. The welding retained satisfactory strength

in nearly all cases, with five of the floors exhibiting no weld fractures. Only two failures oc- curred in floor plate seams, in locations where

welds 31/2 in long were used. In Tests 8 and 9, 75 percent of the fillet weld joints of the plates

to the exterior (side) beams indicated failure

although the welding on the five interior beams

of the panel was in satisfactory condition after

the test. The welding failures were in no case

of an extent to impair the ability of the floors to support the applied load throughout their

respective fire exposures.

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6. Discussion of Results

6.1. Burnout Tests (Tests 1-6)

In these tests, which may be considered as burnout exposures, the combustible loading

above the floor provided the only fuel for the

fire. Such loadings have been related to equivalent exposures in standard fire endurance tests

[2] . The fire severities in these tests, when cal- culated as the area of the exposure timetemperature curves, including cooling curves, above a base of 150 °C (302 °F), were lower

than those established on the basis of earlier

burnout tests [3]. A comparison of the observed severities and those determined from

the results of the other burnout tests can be

seen in the following table:

Avg. Weight

Combustibles

Severity by

Ref [2] Observed

Severity

lb/ft 2 floor area hrimin hr:min

10 1:00 0:39 1 15 1:30 1:03 20 2:00 1:21 30 3:00 1:40 40 4.30 3:06

• Average of two tests.

The lower than generally accepted values

observed in these six tests were possibly due to differences in the amount and type of ventilation provided and the location of thermocouples,

as well as the size and construction of the

burnout room. Damage to the steel plates of the floors from

the fire exposure above varied with the amount

of protection over the surface of the plates and

the intensity of the fire. The bare plates in

Tests 1 and 2 were subjected to high expansion

stresses caused by the temperature diff"erential between them and the beams to which they were welded. This caused buckling and fracture

of the welds, more in evidence in Test 1 where

the beams were restrained at the ends than in

Test 2 with a freely supported floor structure. The ^/i6-in battleship linoleum of Test 3 appeared to off'er some protection with consequent

reduction in buckling. With 1/2 in of asphalt

emulsion concrete, only slight distortion of the

plates was noted (Test 4). Floors covered with

2 in of concrete, even under rather severe ex- posure, showed practically no distortion of the

plates and no fracture of plate-to-beam welds.

With concrete covering (Tests 4, 5, 6), the

average of the maximum temperatures in the

steel plates was about 70 deg F lower than in

the first three tests, even though the concretes

showed considerable cracking and the fire exposures were greater.

In cases of standard fire tests where struc- tural loading has been impractical, an average

temperature of 1000 °F has often been applied

as a limit for structural steel members exposed

to fire [1]. At this temperature, the steel is considered to have lost approximately half its strength, so that where the usual safety factor

of two applies, the structural members will be

critically stressed. Although this temperature was not reached in the beams in any of the six

burnout tests, there was considerable deflection

of the beams and some permanent set. It should

be noted that, of the four floors made without

cantilevered beams, the one that was freely

supported (Test 2) had the greatest permanent

set, although the maximum deflection of its beams during the fire exposure was less than

that of any of the other three. The smaller

deflections in Tests 5 and 6 were probably due

to both the reduced length of the main floor spans and to the insulating eff"ect of the thicker

floor covering, which limited the increase in temperature in the beams. In these tests, the

cantilevered beams also showed only small deflections at their ends, probably as a result of

the lower temperatures prevailing at the ex- tremities of the fire space.

The greater deflections noted in the beams of

the fully restrained floors were probably due

to the bowing of the floors resulting from their

expansion under exposure to heat. In Test 2, the

freely supported beams had some space for

movement on the shelf angles of the supporting

frame on which they rested. Thus, in this case, the defection of the floor represented principally the actual deformation of the unrestrained

beams under the applied load, which may be

taken as the explanation of its greater permanent set. In a paper proposing criteria for defining

load failures [4] , formulas are given for limiting total deflection and hourly rate of deflection

based on the length of span and the depth of the

structural component or assembly. For floors with 4-in beams on an 18-ft span, this would

allow a maximum deflection of 13.7 in, and a maximum rate of deflection of 73 in/hr. For

5-in beams over the same span, the values are

11.1 in and 59 in/hr. These limits were not approached in the tests with the fires above the

floor. The greatest deflection, 5.8 in, occurred in

test 3, which also exhibited the greatest rate of

deflection, approximately 1.3 in/hr.

While it is generally accepted that a loaded

floor may deflect up to 1 in for 30 ft of span

without the formation of cracks in the ceiling,

somewhat greater deflections were obtained in

these fire tests before damage to the plaster was visually noted. In Test 3, a deflection of

2 in occurred at the center of the span before

19
cracking in the plaster was observed. With

deflections above 3i/^ in, the wire ties holding

the metal lath were overstressed, and some

were broken.

The rise in air temperature in the space

below the floor never exceeded 30 deg F in any

of the burnout tests. In every case, the maximum temperature was attained at a time con- siderably past the peak of flaming on the sur- face of the floor, and was not such as to make

the space untenable. Thus, these burnout tests support the premise that above-floor fires do not

produce excessive structural damage to the

floor, or untenable heat conditions in the room

below.

6.2. Fire Endurance Tests (Tests 7-16)

In the 10 tests in which the ceiling of the

floor assembly was exposed to a fire beneath the

floor, the structure and composition of the

ceiling largely determine the fire endurance of

the floor. The steel components transmit heat

quickly and will themselves soon reach their

yield point in the event of failure of the protective materials below them. In this condition,

there are several interacting effects. Heat from

the fire causes eventual calcining of the ceiling

plaster. However, enough plaster generally re- mains in place to offer insulation to the beams.

This, of course, cannot be complete, and the

expansion of the beams as they are heated,

especially if restrained, causes their deflection

with consequent deformation and partial or

total failure of the ceiling structure. When this occurs, the beams become exposed to the fire,

and quickly undergo progressive yielding as

their temperatures rise. The relationship between the time to an

average temperature of 1000 °F or to 1200 °F

at one point and that of several phases in the

destruction of the celing protection in these

tests can be seen in the following table

:

Test Time to Cracking Hole in Critical No. of Ceiling Ceiling Temp, in Beams

hr:min hr:min hr:min

7 0:40 2:02 1:51 8 0:38 1:44 1:42 9 0:36 1:45 10 4:30 4:43

11 No destruction of Not

ceiling. reached. 12 1:46 2:10 13 No destruction (1-hr Not

test). reached. 14 1:40 3:25 3:29 15 No destruction (1-hr Not

test). reached. 16 1:10 2:00 2.12

With destruction of the ceiling, transmission

of heat through the floor plates also will follow

rapidly, and if the floor has not already failed

structurally, there will be failure by excessive

rise of temperature on the floor surface. The

time to such failure will be governed, in part,

by the insulating properties of the floor covering

material. Those with poor insulating characteristics will quickly transmit the heat required

to give the limiting unexposed surface temperature rise. Surface finish materials that are good

insulators, however, will slow the temperature

rise on the unexposed surface, but can at the same time cause the steel members of the struc- ture to attain higher temperatures, so that

failure under the applied load may occur. Differences in the effect of floor covering on

the fire endurance of a floor assembly can be

observed by comparison of Tests 8 and 9. Both

of these showed an average temperature of

1000 °F on the plates at almost the same times

(1 hr 48 min and 1 hr 52 min respectively).

Their fire endurance, however, as determined

by rise of temperature on the unexposed sur- face was 1 hr 24 min in Test 8, in which the

floor consisted of I14 in of gravel aggregate

concrete, and 3 hr 20 min in Test 9, where the

floor was II/2 in gas-expanded concrete with a

i/4-in limestone-cement topping. In Test 16, in

which the time to limiting temperature rise on

the steel plates ( 2 hr 5 min) was comparable to that in Tests 8 and 9, the floor covering was in

two sections consisting of 214 in of gasexpanded concrete or a like thickness of cinder

aggregate concrete, both with a 1/2-in cementsand topping. Here, the extra inch of gasexpanded concrete apears to have contributed

significantly in raising the endurance to 4 hr

42 min. Under the same conditions of test, however, the limiting temperature rise was at- tained on the surface of the section made with

cinder aggregate concrete in only 3 hr 43 min.

Unlike the burnout test results, rather large

deflections were observed in the fire-endurance

test series. In Tests 8 and 12, in which 4-in

beams supported the floor, maximum deflections

of 13.0 and 13.6 in, respectively, were observed.

These approached the limit, previously described

in the discussion of the results of Tests 1-6, of

13.7 in deflection for floors consisting of beams

4 in in depth plus l^-in thick floor plates and

spanning a length of 18 ft. The times required

to reach these maximum deflections, however, were in each case more than an hour in excess

of those at which failure by temperature rise on the unexposed surface had occurred. The

maximum rate of deflection for any of the trials was noted in Test 12, where the downward

movement of the floor reached a rate of approximately 18 in/hr between 2 hr 20 min and 2 hr

40 min after start of the test. This is only about

one-fourth the limiting rate proposed in the

floor failure criterion [4]

.

20
Maximum deflection of 14.4 and 14.0 in oc- curred in the floors of Tests 9 and 16, respectively. These had 5-in beams, and under the

conditions of these tests, the proposed limit of

i deflection would be 11.1 in. This amount of de-

' formation was reached in 2 hr 30 min in Test 9,

I and 3 hr 45 min in Test 16. However, the highest rate of deflection in these two tests was

approximately 7 in/hr (Test 16), or less than

one-eighth the limiting rate, so that imposition

of the deflection criteria of failure was not

j warranted in any of these tests. It is reasonable

j to assume that the restraining action of the

steel plates welded to the beams served to limit

j the rate of deflection of the structural members,

j The deflections of the end of the cantilevered

: beams were affected by the type of floor struc-

' ture as well as by the heat of the fire. In Test

10, where the beams were continuous over the

girder, the cantilevered ends showed consider-

|! able upward movement as the center of the long

I span moved downward. At the end of the test,

! however, the cantilevered beams were down

|| approximately 14 in, following the large deflec- tion of the girder. In Tests 11 and 13, in which

the deflections at the center of the main span

beams were small, there was only a small upI ward movement of the cantilevered ends, about

i 1 in maximum. The ends of the cantilevered

beams in Test 14 also moved upward in the

, early phases of the fire exposure, but shortly

j after the completion of the test, exhibited a

downward deflection of approximately 11 in,

about the same as the maximum deflection of

the girder. In these tests, it appeared that the

displacement of the cantilevered beams was

more a function of the movement of the supporting girder than the eff'ect of heat on their

unsupported ends. The comparative deformation, after test, of a girder and cantilever beams

supported on it can be observed in figure 14.

Figure 14.—Deformation of girder and cantilever beams

after 5-hr fire exposure (ceiling and girder covering

removed).

7. Summary

An examination of the results of fire exposure tests of steel plate floors supported on steel beams may be summarized as follows

:

First, steel deck floors are practical for use from a fire safety standpoint. In tests made

with the fires in combustible materials above the

floors, burnout of combustible loading of 10

lb/ft- caused no appreciable damage or impairment of load-carrying capacity of the floor

I structures, even those with no protective coverj ing on the surface. Exposure to fires in greater

! concentrations of combustibles, up to 40 lb/ft-,

' were sustained by floor assemblies having only

moderate surface coverings not exceeding 2 in

of concrete.

I In the tests with the fire exposure conventionally below the floor, all of the floor assemblies had fire endurance periods, as determined

by the permissible rise of temperature on the

unexposed surface, of more than 1 hr, with

several structures over 4 hr. Thus, most building code requirements for fire resistance could

be met by the choice of one of the tested floor

assemblies.

The values of equivalent standard fire exposure derived from the burnout tests of this

series, did not correspond to those usually

assigned to burnout of given weights of combustibles. The usual equivalents are 1 hr standard fire exposure for each 10 lb/ft- of combustibles, up to 30 lb/ft-, plus 11/2 hr for each

additional 10 lb/ft-. In these tests the equivalent

exposures based on the area under the timetemperature curves, were somewhat lower than

those based upon the results of earlier burnout

tests, and this may be due to differences in the

amount and type of ventilation provided and

the location of thermocouples, as well as the

size and construction of the burnout room.

Finally, the fire endurance of steel floors,

where the fire is below the structure, appears to be largely a function of the protection provided

by the ceiling and the insulating properties of

the floor covering material. The fire endurance

is usually stated as the time to reach a limiting

temperature rise on the unexposed surface of

the floor, but the endurance may also be limited

by failure of the structure to sustain the applied

load. A good insulating covering on the floor

may retard the temperature rise on the surface,

but, in so doing may cause higher temperatures

in the structural elements, thus hastening their

deformation and the rate of deflection of the

floor assembly. There are, however, no estab21
lished criteria by which failure by excessive

deflection may be determined. It would appear,

that to insure uniformity in the interpretation

of test results and in the assignment of fire resistance ratings necessary for implementing

the requirements of building codes, a criterion

such as the one proposed [4] and referred to in

tliis paper, should be adopted to define the deflection conditions under which a floor assembly

may be considered to have experienced load

failure. Preferably, this point should be reached

before the structure has fallen completely into

the test furnace.

8. References

[1] standard Methods of Fire Tests of Building Construction and Materials. American Society for Testing and Materials, Designation El 19-61

(1961).

[2] Fire Resistance Classification of Building Structures, NBS Building Materials and Structures Report BMS 92, p. 9 (1942).

[3] S. H. Ingberg, Tests of the severity of building

fires, Quarterly NFPA 22, 43-61 (1928).

[4] J. V. Ryan and A. F. Robertson, Proposed criteria for defining load failure of beams, floors, and

roof constructions during fire tests, J. Research

NBS 63C, No. 2 (Oct.-Dec. 1959).

22

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