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NATIONAL BUREAU OF STANDARDS REPORT

5375

FIRE TEST OF STEEL DECK FLOOR SYSTEM AND BEAM

by

J* V 0 Ryan
THE NATIONAL BUREAU OF STANDARDS

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BUREAU OF STANDARDS REPORT

NBS PROJECT

1002-30-^-820

NBS REPORT

July 8, 1957 5375

FIRE TEST OF STEEL DECK FLOOR SYSTEM AND BEAM

by

J* V* Ryan

for

Department of the Air Force

(AFCIE-ES)

IMPORTANT NOTICE

NATIONAL BUREAU OF ST At intended for use within the Gi

to additional evaluation and re\ listing of this Report, either in the Office of the Director, Nati however, by the Government a to reproduce additional copies

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

egress accounting documents

ially published it is subjected

production, or open-literature m is obtained in writing from

uch permission is not needed,

repared if that agency wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FIRE TEST OF STEEL DECK FLOOR SYSTEM AND BEAM

ABSTRACT

A fire endurance test was conducted with a

floor specimen consisting of cellular and fluted

steel deck units supported by a steel beam# The

beam was encased in metal lath and gypsumvermiculite plaster* The deck units had concrete

fill above and vermiculite acoustical plastic below#

The results indicated a fire resistance of 3 hr

hi min for the particular specimen tested#

1# Introduction

Formed steel deck units, with concrete fill above,

have found increased use in buildings# The units act

as structural support during construction and as form

upon which to cast a concrete slab, or fill, without

the need for the inclusion of reinforcement such as bars

or wire mesh in the slab. Some of the units are corrugated,

or fluted, in a cross-section nearly rectangular rather

than curved, and others are cellular, formed by facing one

side of a fluted unit with a flat plate or with another

fluted unit# The cellular units are suggested to provide

enclosed raceways for utility services such as electricity

and telephone# This utilization permits the direct application of suitable finish materials directly to the under

surface of the floor system without exposed utility service-,

conduits and raceways# This produces a thin floor-ceiling

system, leading to reduction of building height without

reduction of head room#

Because such construction is of interest to the public

and the government, a specimen of this type was subjected

to fire test, the second of a series of related tests#

The specimen consisted of a combination of cellular and

fluted units, with concrete fill above and vermiculite
acoustical plastic on the bottom surface of the units. The

specimen included a steel beam encased in gypsum-vermiculite plaster on metal lath.

2, Materials and Specimen

A steel beam, 10 in. deep (10WF21) and 17 ft 9 in.

long was secured to li in. thick steel plates by conventional angle connectors. The plates were bolted to the

furnace frame, a 1*+ in. steel H-section, so that the centerline of the 10WF21 beam lay along the centerline of the

18 ft by 13 ft 6 in. furnace opening. A gap was left

between each plate and the furnace frame to permit thermal

expansion of the beam and some tilting of the plates as

the beam deflected. The two gaps totalled 3/^ in. This

arrangement permitted consideration of the beam as only

partially restrained at the ends. This was intended to be

representative of the conditions existing in buildings

having such beams.

Formed steel deck units of two types were used. The

units of the first type were fluted. The flutes were spaced

6 in. on centers, were 1-g- in. deep, 2 3/8 in. wide at

the top and 2 1/8 in. wide at the bottom. Both edges of

each unit were formed in such a manner that an interlocking

joint between adjoining units was provided. Each unit

was 2 ft wide by 6 ft 9 in. long, and was made of 1^ gage

steel. The units of the second type were cellular, consisting of two sheets of steel. The upper sheet was of

18 gage steel formed to the same shape as the fluted

unit just described except that the edges were not formed

for the interlocking joint. The lower sheet was 16 gage

steel and, except for the formed edges, was flat. The

two sheets were spot welded together to make a unit 2 ft

wide and 6 ft 8 in, long.

The steel deck units were placed to span from the

steel beam to the bearing angles bolted to the inside of the

furnace frame along the two long sides of the furnace

opening. The arrangement was symmetrical with both the

transverse and longitudinal centerlines of the furnace

opening. Starting at one end, the order of units was:

one fluted, one cellular, two fluted, one cellular

(centered on transverse centerline of furnace opening),
-3"

two fluted, one cellular, and one fluted* The ends of the

cellular units butted together over the beam; those of

the fluted units were crimped slightly and overlapped

approximately 2 in. The cellular units were welded to the

beam and bearing angles at 12 in. on centers. The fluted

units that were on the bottom of the overlap joint were

welded to the beam at 12 in. on centers before the

overlapping units were placed. The overlapping units were

welded to the beam on 12 in* centers but staggered 6 in.

(one flute) from the welds of the lower units. After the

units had been welded, the interlocking joints were

pinched together at 2 ft on centers.

Holes were punched through the units and 9 gage wire

hangers dropped through. The hangers were 6 in. from each

end of the beam and then 18 in., on centers. They were

about i to ^ in. out from each edge of the top flange of

the beam. They were bent to turn under, and in contact with

the bottom flange of the beam. Pairs of wires, one from

each side of the beam, were laid together for about

in. directly below the beam and wire tied.

Transit-mixed concrete, proportioned 1 part cement,

2 parts Potomac River sand, and U parts Potomac River

gravel (both aggregates of a siliceous composition) was

poured on the steel deck and screeded to a depth of 2-g- in. above the tops of the fluted and cellular units. No

reinforcing bars or mesh were included in this concrete

fill* The concrete supplier stated that the gravel had

passed through 3A- in. sieve.

Sheets of flat diamond mesh 3*^ lb/yd^ expanded metal

lath were bent to form long channel- shaped pieces of such

size that they boxed the beam and fit against the wire

hangers. The lath was tied to the hangers by 18 gage

lathers' tie wire. Corner beads, consisting of a formed

sheet metal nose and woven wire legs, were tied to the

metal lath along the two bottom edges of the beam protection.

The corner beads were positioned to provide grounds for

not less than 1-g- in. of plaster, as measured from the face

of the metal lath, on the soffit and up both sides of the

beam.

Gypsum-vermiculite plaster was applied to the metal

lath in two coats. The first or scratch coat was prepared

in two batches; the first proportioned 1^ bag (nominal
-4-

99*25 lb/bag) unfibered gypsum cement to ft3 of vermiculite plaster aggregate; the second bag to 1 ft’, The

second, or brown coat* was proportioned 1 bag of unfibered

gypsum cement to 3 ft’ of vermiculite plaster aggregate

for each of three batches • Each batch included 4 oz of

accelerator. The water averaged 10.2 gal (85 lb) per bag

of cement for the scratch coat and 13.4 gal (111 lb) per

bag for the brown coat. Each batch of plaster was mixed

in a commercial plaster mixing machine. The scratch coat

was applied by trowel to fill the corner beads and to

provide about half the total thickness. Strips of plaster

were built up to full thickness at the center and about

1 ft from each end. The surfaces of those on the sides

were checked for plumb. After about 4-g- hours had passed,

the brown coat was applied by spraying from a commercially

available machine designed for this use. The surface was

screeded.

The average density of the vermiculite aggregate

used was 7*4 lb/ft^; of the freshly mixed plaster was

77 lb/ft^ for two samples of the scratch coat and

67 lb/ft’ for three samples of the brown coat. The

average density of the brown coat plaster as discharged

from the spray nozzle was 7 8 lb/ft^,

Vermiculite acoustical plastic was applied to the

underside of the steel deck® The plastic was prepared by

mixing a dry loose material with water. The dry

material was a proprietary product. Its composition was

not identified, either by analysis or by manufacturer's

statement. The first two base applications were made with

the "regular" material; the last two with material that

contained white pigment. It came in bags which contained

an average of 22.4 lb each for the base coats and 24,7 lb

for the white pigmented coats. The contents of each bag

were mixed with 10,5 gal (88 lb) of water for the initial

application, 9*8 gal (82 lb) for the second, and 10,7 gal

(89 lb) for the third. The plastic was prepared and applied

utilizing the same mixer and spray machine as for the

plaster

The deck units had been clean when received. After

the application of plaster to the beam, all spattering

s

were wiped from the units before the plastic was applied.

The first application was started the day after the

plastering of the beam had been completed; the second
5

”

6 days after the first; the third 8 days after the second;

and the final 24- days after the third „ No grounds were

used as a guide to thickness but frequent checks were made

with depth gage or wire probes* The average wet densities

of the freshly mixed plastic and of the plastic as^delivered

from the spray nozzle, respectively, were 4-9 lb/ft^ and

58 lb/ft^ for the first application; 4-7 lb/ft3 and 58 lb/ft^

for the second; and 50 lb/ft3 and 58 lb/ft3 for the third.

Shrinkage of the acoustical plastic, as each application dried, produced numerous cracks over the surface.

In most instances the subsequent applications covered the

existing cracks satisfactorily. Between the third and

final applications, cracks in and parallel to the flutes

were patched by trowelling considerable added material

into the flutes. This was followed by application of the

final thin texture coat. The combination of spraying and

trowelling resulted in a surface with flutes of curved

or V-shape rather than nearly rectangular cross-section.

The day before and the day of the fire test, a series

of measurements were made of the thickness of acoustical

plastic by probing with fine wires* Measurements were

made of the thickness beneath the flat plates of the

cellular units and beneath the flutes and between the

flutes of the other units* The maximum, minimum, and

average under the cellular units were 1 11/16 in,,

1 l/lo in,, and about 1 7/16 in, respectively; under the

flutes 1 3/4- in., 1 in., and about 1 3/8 in, respectively;

and between the flutes 2 9/16 in,, 1 1/16 in,, and about

1 5/8 in. , respectively* The overall average of these

measurements was about 1 7/16 in* (1,4-6 in, actually).

3. Test Method

The specimen was subjected to fire endurance test

in general compliance with the methods defined in the

Standard Methods for Fire Tests of Building Construction

and Materials, ASTM E-119*

3*1 Furnace

The furnace was in the shape of a large, fire-brick

lined box with the specimen filling the otherwise open top.
- 6-

The furnace was equipped with steel frame to support

and restrain the specimen, gas-air burners, thermocouples,

loading apparatus, means for measuring deflections, and

windows through which the exposed surface could be

observed during the test*

3*2 Ag ing

The specimen was allowed to age 21 days from the day

of the last patching of cracks and application of texture

coat. The period of aging was determined by weighing a

representative sample of the construction until the weight

was essentially constant for four consecutive days and

gained slightly on the fifth day*

3*3 Loading

The dead load, or weight, of the specimen was M+.4-

lb/ft2 of floor area. The live or applied load computed

to produce a deflection of 1/360 span of the weaker floor

unit was 87*5 ib/ft * The design load for the 10WF21

beam on 17 ft 9 in* span was 16.2 kips® The combined

dead and live loads on the floor were such that the

portion carried by the beam was 14-.6 kips. Therefore,

about 1*6 kips extra load on the beam was provided by

weights on the floor directly above the beam*

3.4- Temperatures

Temperatures were measured by means of chromelalumel thermocouples connected to self-balancing potentiometers calibrated to read directly in degrees C. Thermocouples were placed in the furnace chamber, on the beam,

the steel deck units, and the unexposed surface. Those

in the furnace chamber were in porcelain insulators and

encased in wrought iron pipes* The pipes were placed

so that the thermocouple junctions were 12 in. below the

specimen* The other thermocouples were in glass fiber

sleeving® Their locations are indicated in figure 1.

The furnace fires were controlled to produce temperatures

as near as feasible to those of the Standard Time-Temperature
- 7

“

Curve defined in ASTM E-119? which include:

1000° F at 5 min, 1300°F at 10 min,

1550°F at 30 min, 1700° F at 1 hr,

2000° F at 4 hr and 2300° F at 8 hr.

3 .5 End-Point Criteria

The Standard Test Method required that: 1) the specimen

continued to sustain the applied load, 2) flames, or gases

hot enough to ignite cotton waste, not have passed through

the specimen, 3) transmission of heat shall not have been

such that the average temperature of the unexposed

surface increased 250 degrees F nor the temperature at

any one point have increased 325 degrees F above their

initial values® The fire endurance was defined as the time

at which the first of these conditions was attained, with

a correction to the time for variation, if any, of the

furnace temperatures from those defined.

Results

The fire test was conducted May 28 , 1957® The observations of physical behavior, temperatures, and deflections

are reported together although each was made independently.

At 12 min there was a vertical crack at the center of the

West face of the beam protection. At 36 min there was a

similar crack in the East face® At V7 min there was a

small piece of piaster protruding from the East edge of

the beam soffit at center span® Around 1 hr 22 min to

1 hr 25 min several mild thumps were heard _ probably the

muffled sounds of breaking of welds between beam and deck

units. At 2 hr 1 min a few more thumps were heard. There

were no cracks in the concrete and only three fine cracks

in the plaster around the beam. There were a few small

black spots in the acoustical plastic. The net deflection

at the center of the beam was 0.6 in®, the maximum beam

temperature was 524-°F, and the maximum temperature on the

unexposed surface was 175 degrees F above the initial

value. By 3 hr, the two vertical cracks in the beam protection were about 1/8 in. wide but there were no other noticeable changes in the appearance of the specimen. The net

deflection at the center of the beam was 1.6 in., the

maximum beam temperature 8l5°F, and the maximum rise on
- 8-

the unexposed surface 220 degrees F. At 3 hr 4l min the

limiting average temperature rise of 250 degrees F was

reached on the unexposed surface. The maximum rise of 325

degrees F at one point was reached at 4 hrs. By 4 hr

35 min, the vertical crack in the center of the East face

of the beam plaster was about 1/4 in. wide, that on the

West about 1/8 in® wide® The net deflection at the center

of the beam was 3°0 in® and the maximum temperature on the

beam was 1024° F» By the end of the test at 6 hr 4- min,

the deflection of the beam had exceeded 5*6 in., the

cracks in the beam cover were 1/4 to 1/2 in. wide, and

there were very fine cracks across the corners of the

concrete fill.

After the test, and cooling, the only significant cracks

in the beam cover were those across the soffit and up each

side at the center of the beam. The plaster was a light

brown color, somewhat darker than before the fire exposure.

Measurements were made of the thickness of the fire exposed

plaster, from the face of the metal lath. The soffit

varied from 1 3/8 to 1 7/8 in. and averaged 1 1/2 in.; the

West side varied from 1 9/16 to 2 in. and averaged 1 3/4 in.;

the East side varied from 1 1/2 to 2 5/16 in. and averaged

1 13/16 in. One section of the East side was 1 5/8 in.

thick at the bottom and 2 5/16 in. about 2 in. from the top.

The beam had a permanent deflection of 5 in. at its centero

The acoustical plastic was covered with craze cracks and

fissures, some 1/2 to 1 in. wide and deep. The original

surface was a slightly darker brown than the beam.

However, the base application material that showed in the

cracks and fissures was a very dark brown and fairly shiny.

The concrete fill had hairline cracks across the four

corners plus two 1/16 in. wide East-to-West cracks, one

about 5 ft from the North end and the other the same

distance from the South end. The former was about 10 ft

long, the latter about 3 ft long. The concrete was still

in close contact with the steel deck units and the joints

between units were closed.

The fire endurance of the specimen was limited by 250

degree F temperature rise on the unexposed surface at

3 hr 4l min. The furnace fire control was such that no

correction was applicable to the failure time. The fire

exposure severity, as determined by the ratio of the area
-9-

under the curve of average furnace temperatures to the area

under the Standard Time -Temperature Curve, was 100 A

percent. The beam continued to support the applied load

for 6 hours although temperatures were reached at about

5 hrs which would have been considered indicative of failure

in a test of a steel beam without applied load.

do‘3anivH3diAi3i

Figure b. Undersurface of specimen the day after fire

exposure.

U. S. DEPARTMENT OF COMMERCE

Swicluir Works, Secretary

NATIONAL BUREAU OF STANDARDS

A, V, Astin, Director THE NATIONAL BUREAU OF STANDARDS

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