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Fire Endurance of Open-Web Steel-Joist

Floors With Concrete Slabs and Gypsum Ceilings

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United States Department of Commerce

National Bureau of Standards

i Building Materials and Structures Report 141
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[List continued on cover page m]
UNITED STATES DEPARTMENT OF COMMERCE • Sinclair Weeks, Secretary NATIONAL BUREAU OF STANDARDS • A, V. Astin Dinner

Fire Endurance of Open-Web Steel-Joist

Floors With Concrete Slabs and Gypsum Ceilings

James V. Ryan and Edward W. Bender

Building Materials and Structures Report 141

Issued August 23, 1954

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C. Price 20 cents
National Bureau of Standards JUN 2 1965

130,244

TA 4 1

Contents

' Page

1. Introduction and scope 1 2. Materials 2

2.1. Steel joists and accessories 2

2.2. Materials for floor slabs 2

2.3. Gypsum lath 2

2.4. Lathing accessories 2

2.5. Wire reinforcing 3

2.6. Plaster and aggregate 3

3. Construction 3

3.1. Placement of joists 3

3.2. Floor slabs 6

3.3. Furring and lathing 6

3.4. Reinforcing for lath and plaster 6

3.5. Plastering 7

3.6. Aging ^ 8

4. Test method and equipment 8

4.1. End-point criteria 9

5. Test results j. 9

5.1. Group 1. Exploratory tests ‘ 9

5.2. Group 2 10

5.3. Group 3 : 10

5.4. Group 4 11

5.5. Group 5__ 11

5.6. Group 6 11

5.7. Group 7 12

6. Discussion 14

6.1. Deviation from standard test methods 14

6.2. Nature of failures 14

6.3. Effectiveness of reinforcing or extra support _• 16

6.4. Plasters 16

6.5. Balance of designs 16

7 . Conclusions _ 17

8. References 17

ii
Fire Endurance of Open-Web Steel-Joist

Floors With Concrete Slabs and

Gypsum Ceilings

James V. Ryan and Edward W. Bender

The results presented were obtained in a program of 18 fire tests on open-web steeljoist floors, 16 of which were protected by ceilings of gypsum-perlite plaster on gypsurn

lath “furred” directly to the joists. Variables included plaster thickness, plaster mixe-. spacing of furring channels, system of lath clips, reinforcing in the ceilings, and type of

floor slab. An acoustical plaster finish was applied to one ceiling. The range of fire endurances obtained, from 1 hour to 4 hours 26 minutes, was sufficient, to cover the requirements for

floors in many building codes. The importance of the ceiling’s protective function was

demonstrated in two tests without ceilings, in each of which failure occurred at 7 minutes.

1. Introduction and Scope

The anticipated occupancy for which a building

is designed predetermines the necessary strength

of the whole structure and its various components,

which fact frequently limits the designer’s choice

as to the type of construction to be used. This

is especially true of the roof and floors upon which

the “live load” rests directly. Floors and roofs

of reinforced concrete slabs on open-web steel

joists may be designed to provide load-bearing

capacities within a wide range, including those

adequate for houses, apartment buildings, stores,

and office buildings. The Steel Joist Institute’s

tables of safe allowable loads [l] 1 list total loads

ranging from 28 to 530 lb/ft2 of floor area for the

various combinations of size, spacing, and clear span of open-web steel joists. This type of construction is widely used for roofs and floors in

buildings of the types mentioned above.

Standard laboratory fire tests as well as actual

fires in structures have shown that unprotected

steel has a very low’ fire resistance in that it loses

its strength at temperatures that are reached

quickly in such fires. Therefore, the loadbearing

capacity of a combination of a thin concrete slab on open-web steel joists wroulcl be “short lived” in

a fire and its fire endurance correspondingly short.

However, the joists may be protected with some

type of ceiling and the fire resistance increased

thereby. Such protection is provided by a ceiling

of lightweight gypsum plaster on gypsum lath. The “calcined” gypsum used to prepare gypsurn plaster, or gypsum concrete, is identified by

the chemical formula CaS04 -|H2 0. When mixed

with water, the powdery calcined gypsum takes

up water into chemical combination and sets into

a hard, strong substance, hydrated gypsum,

1 Numbers in brackets indicate literature references at the end of this

report.

changing from CaS04 -JH2 0 to CaS04 -2H2 0. Tim

latter form is that present in gypsum plaster-,

gypsum-fiber concretes, and the cores of laths,

wallboards, and formboards. The calcine. j gypsum (CaS04 -JH2 0) is 6.2 percent water by v eight

and hydrated gypsum (CaS04 -2H20) is 20.9 per- cent water. Thus every 100 lb of calcined gypsum has about 3 qt of water in chemical combination, which increases to 12 qt as the gypsum

“sets,” or hydrates. When the gypsum plaster

and lath are subjected to high temperature-, the

gypsum calcines, or loses its combined water, at temperatures near the boiling point of the latter. Although gypsum calcines at temperatures that are low compared to those in a fire, test or otherwise, the high thermal capacity and heat <0 vaporization of water make the process slow.

This change is accompanied by decrease in strength, shrinkage, cracks, and eventual breakage

of plaster and lath. As the cracking of the lath and plaster progresses, the areas into which the

ceiling is subdivided by the cracks become -' and smaller until some of them are not supported

by any component of the system by which

whole ceiling has been supported. As the-c

supported areas of lath and plaster tall, the ''.sn- are exposed to the flames and soon lose their strength, resulting in load failure. I p to a limit,

the lire endurance may be extended b\ increasing

the amount of plaster applied, which lengthens

the time required for the gypsum to calc no However, after calcination, the gypsum sor\ - is a good shield to protect the joists trom

energy and from direct contact with the

Therefore, means of keeping the lath and plaster

in place following calcination will contribute to greater fire resistance.

In order to determine the elleets ot addei p

as thickness and ot dillerent means ot ivm

retaining the lath and plaster. 2 explore. ey\ s -
and 16 standard fire-endurance tests were per- formed in the furnaces of the National Bureau of

Standards. Two of the latter tests (324 and 329) were made on joists and slab without any ceiling.

In the other tests, ceilings of gypsum-perlite plaster on %-in. perforated gypsum lath were applied

by 1 of 3 supporting systems. The plaster thick- nesses ranged from }{ in. to IK in. In 6 tests (311,

312, 313, 316, 318, and 326) an extra number of

clips or 1 of 2 forms of supplementary reinforcing were employed. In test 326, an acoustical plaster was applied as the final coat, following gypsumperlite plaster base coats.

2. Materials

Some of the materials were delivered from the

manufacturer directly, some were purchased from

distributors of building materials, and some were

provided by local contractors. They were considered representative of the materials available on the market in the local area and in many other

metropolitan areas, except for the plasters used,

which set faster than those generally available on

the East Coast. The details of the particular

materials used in each test, and of the variation of

materials from test to test, are given in table 4.

2.1.

Steel Joists and Accessories

The'steel joists were an open-web type, designated SJ103 under the system adopted by the

Steel Joist Institute. The top chord consisted of

two if- by 1 /4 - by %-in. angles; the bottom chord

of two %6-in. rods; and the web of a combination

of a single in. rod near each end and a

7/6 -in. rod

in the center. The web was of a zigzag form and was welded between the angles at the top and the

%6-in. rods at the bottom. Bearing plates of

%6-in. steel were welded to each end. The joists were 10 in. deep and 13 ft 4 in. long for the large

floors and 9 ft long for the small floors. They

were finished by the manufacturer with a bitumi- nous coating applied hot after the joist assembly was completed.

The bottom chords had been bent up near each

end, and the 10-in. depth did not extend to the

furnace wall. Therefore, formed %- or %6-in. rods were provided to hang on each end of each joist

and continue the line of the lower chords for the

attachment of the ceiling. Lengths of %-in. coldrolled channel, factory cut to the proper length,

with a flat piece at each end to be bent around the

joist chord were provided as bridging for the

joists.

2.2.

Materials for Floor Slabs

The bases for the portland-cement concrete

floors were expanded metal laths with /(-in. V-ribs

and b-iri. inverted V-ribs between the %-in. ribs. Two varieties were used; one, nominally 4.0

lb/yd2

, came in sheets 96 by 24 in.; and the other,

nominally 3.4 lb/yd2

, came in sheets 96 by 27 in. A check" on one order of the latter showed an

actual weight of 3.29 lb/yd2

. The formboard

base for the gypsum-cement slabs was a %-in.

J, paper-faced gypsum board, which came in sheets ! 90 by 32 in. and weighed 2.2 lb/ft2

. Except for tests 261 and 266, the portlandcement concretes were mixed 1 part by weight of ! Portland cement, 2 parts of washed Potomac River i (siliceous) sand, and 4 parts of pea gravel (silice- ous). For tests 261 and 266 the mix was 1:2:3| by

weight. The concretes were machine-mixed on

the job for tests 257 and 260, and delivered truckmixed for the remainder.

The gypsum concrete was a mill mix of the

gypsum plaster and aggregate, requiring only the

addition of water. A chemical analysis indicated

the major constituents were CaSO^pRO, §2.4

percent, and wood fiber (wood chips), 6.2 percent.

A sample mixed 3 parts to 2 parts of water, by

weight, in the laboratory and cast in 2-in. test cubes had a compressive strength of 720 lb/in. 2 after aging about 7 weeks.

Reinforcing in each concrete slab was provided

by 1 of 3 types of welded wire fabric. Two types 1 consisted of a 6-in. square mesh, one of 10 gage

wires and the other of 8-gage wires, and the third j type consisted of 14-gage wires spaced 8 in. and

12-gage wires spaced 4 in. at right angles to the

former.

Accessories used in assembling the floor-slab forms included bulb-T rails in floor-length pieces

for test 296, T-rails in 2- to 3-in. lengths for test

'

297, and galvanized 18-gage tie wire for the re- i. maining tests. This wire was also used in all the ( ceiling assemblies.

i

i

2.3.

Gypsum Lath

The laths used in these tests were %-in. perfoj rated gypsum lath in pieces 48 by 16 in. Each

piece contained 48 perforations, each %-in. diam- j; eter, one for each 16 in. 2 The products of four ( manufacturers were used as representative of the ; materials available on the market. Ordinarily, ( sufficient lath was available to provide samples | for the strength tests that were made on the 12- by ( 16-in. specimens. Table 1 gives the results ob- f tained in these tests. It should be noted that the , strengths of most of the samples tested parallel to the fiber were less than the minimum required by

the test specification (ASTM C26-52).

2.4.

Lathing Accessories

Furring for the placement of the gypsum lath was provided by %-in. steel channels. The

channel came in 20-ft lengths and was cut on the

job to the required size. The type of channels,

either “hot-rolled” or “cold-rolled”, used in each

test specimen was determined by the system of

clips to be used and is given in table 4. Several different types of formed wire and sheetmetal clips were used in connection with the placement and support of the gypsum lath. These j clips are shown in figure 3.

2
Table 1. Results of tests on gypsum laths a

Specimens 16 by 12 in. mounted on parallel 12-in.-lcng bearings, 14 in. apart and load applied from above through third 12-in.-long bearing parallel to and midway between first two. Samples tested to breaking with bearings

parallel to paper fiber and other samples with bearings perpendicular to fiber. Bearings rounded to Ji-in. radius.

Breaking loads

Lot Measured

thickness

Parallel to

fiber Perpendicular

to fiber

Average Mini- mum

Average Mini- mum

in. ib lb lb lb

1 0. 353 26.6 84.4

9 .368 19.4 17.4 55. 0 51.0

3 23.3 21.6 75.2 72 0

4 19.6 18.0 70.5 67.0

5 .359 24.0 22.2 77.5 75.4

6 .362 19.8 18.0 71.4 68.4

7 .360 22.4 22.0 78.0 74.8

8 .380 37.0 35.0 73.7 71.0

9 .357 23.8 22.4 80.6 79.8

10ASTM require- .376 ( J

) (‘) 54.8 52.4

merits « .375 ± .031 27 — 60 —

| « Tests under the provisions of ASTM C26-50 and -52 and C37-50.

* Xot enough extra lath for all tests.

2.5. Wire Reinforcing

Additional support for the gypsum lath and

j reinforcing for the plaster were provided in two

'test specimens (311 and 312) by the use of 1-in.

i hexagonal-mesh galvanized 20-gage wire fabric,

approximately 3 ft wide. For three test specimens

j (313, 318, and 326) lengths of galvanized 14-gage

: wire were used to provide support supplementary

i to that of the clips.

2.6. Plaster and Aggregate

The regular plasters used were extra-fibered

; gypsum plasters of well-known manufacturers and

I are commonly available in most parts of the

I country. The chemical compositions and physical

| properties were determined in accordance with

I the methods prescribed by Federal Specification

! SS-P-402 and met the requirements set forth

i therein. They also met the requirements set

| forth in ASTM Designation C28-50, except that

i Table 2. Results of chemical and physical tests of plasters a

Chemical analysis

CaS04 .l/2H2 0 (by ammonium acetate)—%—

CaS0,.l/2H2 0 (byS03 ) %.. CaS 04. 1/ 2 H2 0 (by loss at 230° C) %_

CaS 04. 1/2H2 0 (average) %--

Maximum Minimum

93.7

92.7

93.6

» 93. 6

74.1 73.9

75.0

<>74.4

Physical tests

Consistency _ _ __ _ ‘48

11 245

1,540

‘18 m160 770

Time of set - .. .hr.. Tensile strength __ lb/in.2 _. Compressive strength lb/in.J _

“ Only maximum and minimum values for determinations of 10 samples.

b Maximum and minimum of averages of the three methods of determination.

• Consistency giving time of set on following line.

Table 3. Sieve an/ilyses of perlite aggregates

Sieve

Proportion of material passing

Sample 1 Sample 2 Sample 3 j

6 Percent Percent Percent

8 100 99.9

99

98 6

10 96 12...

14 87 84

16 7860

45

20 58

30 37 45

40

50 21 24 23

70

100 12 12 12 200 4.9 7.3 7.9

the mill-mixed plaster for test 266 had a longer

time of set than the maximum allowed for -'tch plasters. The results obtained from the prescribed

tests are given in table 2. The plasters used for tests 257, 260, 261, and 266 were mixed with the

aggregate at the manufacturer’s plant.

The aggregate used for the regular plasters was

expanded perlite, weighing 8 to 8 % lb fth The

sieve analyses of three shipments of perlite are given in table 3. The acoustical plaster used in the specimen for

test 326 was a proprietary mix that required only

the addition of water. The particular acoustical

plaster had been chosen as having shown the

highest thermal conductivity in a group of comparison tests on samples of about 4 ft 2 exposed

surface. The plaster appeared to be a mixture of gypsum and a lightweight aggregate in granules

slightly larger than those of sand. However, its application characteristics were different from

those of sanded or lightweight aggregate gypsum

plasters. 3. Construction

The constructions of the test specimens were

similar to those obtainable in regular building

practice. The major part of the construction

work was done by regular employees of various

contractors, with general supervision by Nal ional

Bureau of Standards personnel who have bed

considerable experience in the preparation of test specimens. The differences between the doors

tested in the large furnace and those tested in the

small furnace were made necessary by the si.- >s and designs of the furnaces and the provisions

for mounting the test floors. The\ were not variations in the basic type of construction being

tested. The variables in the construction of the

individual test specimens are given in table 4. Typical constructions are shown in figures t and 2.

3.1. Placement of Joists

In the large furnace, nine of the 13-ft 4-in. joists were placed to span the short dimension of the furnace. They w ere spaced 24 in. on centers,

which put each end joist approximately 7 in from

the furnace brickwork. The end ot the joists
4
Table 4. Summary of construction elements and fire endurance limits AD specimens with No. SJ103 open-web steel joists; 18 in. on centers in tests 257 and 2C0, 24 in. on centers in all others. Plaster base was K-in perforate 1 sum lath in each ceiling. Floor-slab dimensions were 9 ft by 4 ft 4 in. for tests 257 and 260; 18 ft by 13 ft 6 in. for all others.

Tests

Floor

Base Reinforcing Slab

Joist exten- sion

size

Exploratory tests: 257

260

Standard tests: 261 266 287

295

296- 297_

316-

317- 319-

313,

31S_

326-

311-

312_

324- 329-

4-lb rib lath- do

4-lb rib Iath__ do

3.4-lb rib lath. do

*4-in. gypsum board. do

3.4-lb rib lath. do

do.__

.do.

-do_

-do.

-do_

.do.

_do_ _do_

m. 6X6

6X6

6X6

6X6 6X6

6X6

8X4

8X4

6X6

6X6 6X6

6X6 6X6

6X6

6X6

6X6

6X6

6X6

Gage 10X10 10X10

10X10

10X10

10X10

10X10

14X12

14X12 8X8

8X8

8X8 8X8

8X8

8X8

8X8

8X8 8X8

8X8

1:2:4 gravel concrete, 2 in. over joists. 1:2:3*do

*£ gravel concrete, 2 in. over joists. do

1:2:4 gravel concrete, 2 in. over joists do

Mill-mix gypsum concrete, 1*4 in. over base. do

1:2:4 gravel concrete, 2 in. over joists.. do

do

_do.

-do_

-do_

_do.

.do.

.do_. -do.

in. Ms

Ms

MsMsn

?4*4MsMs

MsA

Ms

H

H

None

Ceiling

Age at

test*

Fire en- durance

limit * Furring

Clip types « Reinforcing

Plaster

Type Spacing Mix (by volume) Thickness

in. on

Exploratory Tests: center in. Days hr min

257 _ f4-in. cold-rolled 16 C, E. . None. 1 *4:2*4 (mill) A 47 X 10 * 260 __do . 16 _ __do- _ do do. % 49 i 56 *

Standard tests: 261 16 C, E-. None.. 1*4:2*4 (mill)... A 30 1 24

266 do_ 16 _ do _ _ ___do_ _ _ __ do_ A 28 0 55 • 287_ _ do. 16 D, E, F, G do_ . __ . 1*43*4 A 36 1 00/

295 16 ____ do. 1*4:2; 1*4:3 1 42 1 42

296_ 12 do._ ___do ______ do 1*4 42 1 48 297 12 1*5 43 1 43 »

316_ 12 A, B, G Extra A clips.. do_ A 35 3 00/

317 16 _ do _ None 1 *4:2*4 A 38 1 04 319 . 12 do. A 33 1 15

313 12 D, E, F, G-. Diagonal wires.. 1*5:2; *4:3 A 34 3 15

318 16 __ . do__ __ do._ 1*43*4 H 3S 2 46

326 12 C, E, F, G _ __do. __ (*) 1*3 31

*> 44

311 12 D, E, F, G._ Hexagonal mesh 1*4:2; 1*4;3. 1 28 4 26 312 16 1 *4:2*4 *5 34 3 28

324 None None . None 42 0 07

329 34 0 07

<* Clip types shown in figure 3.

6 Age of final base coat of plaster except when no ceiling, then age of concrete slab. . ‘ The fire endurance limit was obtained by applying a correction formula, given in ASTM E119, to the time at which the lu st end point « as table 5).

s Size less than minimum specified in Standard Test Methods (E119), hence does not represent standard fire endurance.

• Not loaded, estimated time at which specimen would have failed under load.

f No end point reached; load removed at this time and test discontinued to prevent damage to joists and slab and to permit iciise ot sann in \

» Power failure caused brief interruption of test; 3 min added to observed time.

* Base coat *4 in. of 1 *4:2*4 gypsum-perlite plaster, acoustical finish of A in. of proprietary mill-mix plaster.

rested on the furnace shelf angles but were not

attached thereto in any manner. A formed rod

extension of the bottom chord was hooked to each

end of each joist and a single row of X-bridging was placed transversely to the joists at centerspan.

The end joists were anchored to the furnace wall

in line with the bridging. In the small furnace,

three of the 9-ft-long joists were placed to span

the long dimension of the furnace and v et c spaced

18 in. on centers. Channel X-bridging at center- span and formed rod extensions were attached . the same manner as in the larger constructions
3.2. Floor Slabs

The expanded-metal rib lath was laid on the

joists with the long dimension perpendicular

thereto. The ends of successive sheets were over- lapped from 4 in. to 1 ft, and the edges of adjoining sheets were overlapped from 3 to 9 in. The

lath was tied to the top chords of the joists, with

tie wire at each rib. The lapped joints between

laths were secured with single-strand wire ties. Small holes were cut in the lath at the necessary

locations over the joists to allow the passage of

the leads from the thermocouples attached to the

joists.

Above the metal lath, a welded wire fabric of

8- or 10-gage wires in a 6-in. square mesh was

placed and the portland-cement concrete was

poured and screeded to a depth of 2 in. above the

joists.

In preparation for the gypsum floor slab of test 296, six bulb-T rails were fillet-welded to the joists, one at each end and the other four spaced 32% in. They were perpendicular to the joists and ex- tended the full length of the floor. The 32-in.

wide sheets of gypsum formboard were laid on

the flanges of the rails and the top chords of the

joists. The rectangular-mesh reinforcing was

forced down between the rails to lie very close to the upper surface of the formboard, with the 12- gage wires, 4 in. on centers, parallel to the rails and the 14-gage wires, 8 in. on centers, transverse

to the rails and parallel to the joists. The gypsum

concrete was mixed with water to the desired consistency and poured to a depth of 1% in. over the

formboard.

For the other test specimen with gypsum concrete slab, test 297, the formboard was placed on

the joists without the bulb-T rails. Short lengths

of regular steel T-sections were welded to the top

chords and transversely thereto in an inverted

position, and the vertical leg of the T was put

through the formboard. The same rectangularmesh wire fabric as in the other gypsum-concrete

slab was laid down, also with the 14-gage wires

parallel to the joists. Gypsum concrete was

poured to a depth of 1% in. over the formboard.

Between the joists, the metal lath sagged under

the concrete as much as 3 in., but the gypsum

formboard did not sag noticeably under the gypsum concrete. The floor slabs and steel joists were not damaged excessively in tests 261, 287,

316, and 319 and were reused in tests 266, 295,

317, and 324, respectively.

3.3.

Furring and Lathing

The initial step in the construction of each

ceiling was the attachment of the furring channels.

They were applied transversely below the bottom

chords of the joists and extensions and secured

thereto with double-strand wire ties. They were

spaced at either 12 or 16 in. on centers. The use

of either “hot-rolled” or “cold-rolled” steel furring

channels was determined by the type of lath clips

to be used in the particular test specimen (see

table 4). The gypsum lath was placed with the long

dimension at right angles to the furring channels J and was attached thereto by clips of one of the

types illustrated in figure 3. Two of the types,

! C and D, provided continuous support across the

width of the lath, hooking over the furring channel at one edge and joining with the adjacent

clip at the other edge. A third type of clip, B,

provided support only at the lath edges but was

used with type A, which punctured the lath to hook over the furring at intermediate points.

This combination was used in tests 316, 317, and

319 only. Still other clips (E, F, G) were used at the ends and edges of each piece of lath to keep it in alinement with the adjoining ones. These

latter clips, some or all types of which were used

in each ceiling, did not transmit any support from

the furring channels to the lath. The lath was

cut, where necessary, to carry the ceiling to the

n

Figure 3. Various clips used in applying ceiling laths for

the test specimens .

furnace wall and to make the ends fall between

furring channels. Ordinarily, the cut pieces were

long enough that they obtained support from at

least two furring channels, whereas the full 48-in. I length pieces were supported under 3 or 4 channels,

depending on the spacing of the latter.

3.4.

Reinforcing for Lath and Plaster

In five test specimens (311, 312, 313, 318, 326),

following the lathing, 1 of 2 wire products was

included in the construction to provide additional

support and reinforcing to the lath and plaster. 1 For tests 311 and 312, 1-in. liexagonal-mesh wire

fabric—“chicken wire”—was stretched below the

gypsum lath. It was tied to the lath clips during

placement, but the main support was provided by

double-strand wires tied between the edges of the

lath to the furring channels. These wires were

tied to each channel at each junction between

laths. For tests 313 and 318, galvanized 14-gage

wire was secured below the lath on the diagonal.

6
The wire passed under the lines of dips at the lath

edges—the locations of clip connections—and

hooked to the clips or was tied to them. In one

half of the ceiling area, continuous lengths of

wire extended from wall to wall and were tied to the clips with lathers’ tie wire; in the other half,

short lengths, approximately 2 ft long, were used

and looped around the lower portions of the clips.

The spacing of the diagonal wires was determined

by the spacing of the lines-of-clips (furring channels); 12- and 16-in. spacrngs of the latter resulting. respectively, in 10- and 11.3-in. spacings of

the wires.

Figure 4 shows the diagonal wire support in

place below the lath during the construction of

test floor 313.

type clips, shown in figure, 3, one clip of type A 1 ,i - placed through the center of the 16-in. width of the lath along each furring channel, as in test..-. : ] 7 and 319. However, in test 316 two A dips wca- used along each channel for each lath, one at each

third point of the width.

3.5. Plastering

Wood strips of the proper size were tied to the

gypsum lath to provide the temporary grounds for the plaster. They were removed after they had

served their purpose, and the space left was filled with plaster. The depth of grounds, and thick- ness of plaster, was measured from the lower face

of the gypsum lath. In each construction except

Figure 4. Lathed ceiling with diagonal wire reinforcing.

For test 326, 14-gage diagonal wires were also

| placed below the gypsum lath, but in a slightly

I different manner than described above. In one

half of the ceiling, the short lengths bent around

| the clip junctions were used as described in the

preceding paragraph. In the other half, 4-ft

1 lengths were placed between the lath and supporti ing clips. They were neither bent around nor tied

i to any other component of the ceiling. The ends

| of successive lengths overlapped about 8 in. In the five tests above, special reinforcings

j different from the other materials in the constructions were used. In test 316 additional support was provided to the ceiling by use of extra amounts

of materials ordinarily a part of the construction.

In usual building practice involving the A- and lithe acoustical plastered ceiling (test 326), tic grounds were set to %6-in. less than the intended

total plaster thickness so that the base eoat or coats could be brought even with the grounds and

the thickness completed with a fiVin. white finish coat. The base-coat plasters were applied by either

the double-back process (tests 257. 260. 261. 200.

287, 312, 317, 318, 319), in which the full thickness

of plaster is built up without waiting for part to

set, or by the scratch- and brown-coat process

(tests 295, 296, 297, 311, 313, 316. 320' . in which

the initial, or scratch, coat is applied, scratched to provide a better bond with the plaster to follow and allowed to set before the second, or brown,

coat is applied to complete the base-coat thick300167—54 2
ness. The base-coat plasters were mixed in the

ratio of 1 % ft3 (equal to 100 lb) of gypsum plaster

to 2/( ft3 of expanded perlite for all double-back

applications and in the ratio of 1 ^ : 2 (or 100 lb:

ft3

) for the scratch coats and 1^:3 (or 100 lb : 3 ft3

) for the brown coats. The plasters for all the

white finish coats were mixed 3 parts of lime

putty to 1 part of gaging plaster, also by volume.

3.6. Aging

Following the completion of the constructions,

the test specimens were allowed to age for various

periods before being subjected to test. These

periods ranged from 28 to 49 days, as measured

from the day on which the last of the base-coat

plaster was applied to the day of the test, except

for those test specimens (324 and 329) without

ceilings, in which case aging was measured from

the day the concrete was poured.

4. Test Method and Equipment

The tests of the larger floors were conducted inj accordance with the provisions of the Standardi

Methods of Fire Tests of Building Construction

and Materials of the American Standards Associa-j

tion and the American Society for Testing Materials (current ASTM Designation El 19-53), but,

with certain exceptions. In most instances the)

tests were continued as long as practicable rather

than being stopped as soon as the first end-point

criterion was reached; therefore, the reloading test)

could not be made properly. The hose-stream'

test was also omitted. The reasons for and sig-i nificance of these exceptions are discussed in sec-! tion 6.1. The tests were conducted in furnaces at the I National Bureau of Standards designed for the fire! tests of floors and roofs. Tests 257 and 260 were: made in a small furnace, which would take a floor ';

8
9 ft by 4 ft 4 in., and the other tests were made in a large furnace, which took a floor 18 ft by 13 ft 6 in. The latter is shown in figure 5. Each

furnace was in the form of a box open at the top,

with gas burners along the sides. The test floor

| closed the open top, and the underside of the

specimen was exposed to the furnace flames.

Six thermocouples were placed in the small fur- nace and 12 in the large to measure the temperature in the furnace chamber. They were en-

' cased in porcelain insulators and iron pipes closed

at one end and placed so the thermocouple junctions were about 1 ft below the ceiling surface.

The furnace flies for all tests were controlled to approximate closely the temperatures specified in

i the above mentioned standard test methods, which

include: 1,000° F at 5 min, 1,300° F at 10 min,

' 1,550° F at 30 min, 1.700° F at 1 hr, 1,850° F at

2 hr, 2,000° F at 4 hr, and 2,300° F at 8 hr or over. The fire-exposure severity, defined as the ratio of

the area under the curve of average furnace temperatures to the area under the standard timetemperature curve, is required to be between 90

and 110 percent for tests of 1-hr duration or less, between 92.5 and 107.5 percent for tests over 1 hr ' but not over 2 hr, and between 95 and 105 percent

for tests over 2 -hr duration.

The junctions of chromel-alumel thermocouples

were placed on the upper surface of the floors. They were distributed over the surface in a symmetric pattern, with their junctions and short

lengths of the thermocouple wires coiled under

felted asbestos pads 6 in. square and 0.4 in. thick.

A total of 6 such surface thermocouples were used

on the small floors and 10 or 12 on the large floors. The junctions of chromel-alumel thermocouples

were placed on the joists at three levels; on the

: joist webs, the upper chords, and the lower chords.

The individual thermocouple junctions on the top

| chords were approximately above those on the

webs and bottom chords. Their locations on the

; various joists were such as to make a symmetrical

| distribution throughout the structure. They were

| attached to the joists by peening each wire into a

j separate drilled hole in the steel with a short dis-

| tance between holes in each pair, so that the juncI tion was completed through the steel. This was

| done to provide a more accurate determination of

; the temperature of the steel and to prevent false indications from thermocouples that might become

detached from the joists. The thermocouple wires were encased in asbestos sleeving and brought up

! vertically above the anticipated level of the upper

I surface of the floor. The loads applied to the large floors were eom1 puted on the basis of 145 to 150 lb/ft2 of floor

j surface, the design load for No. SJ103 joists spaced

24 in. on center and having a 13-ft clear span.

The loads for the small floors were computed on

the basis of 3,900 lb per joist, uniformly dis- tributed. These loads included the dead weight

of the test specimen, the weight of the loading

mechanism, and the applied load. The latter was

provided by hydraulic jacks above the larger floors

and distributed by the device illustrated m 3. . 5, and by a similar device for the smaller floor- The deflections were measured at regular inln

throughout the tests by a system of wire- atfaefied

to the floor and passed over pulleys to a -' ;ie . where riders on the wires indicated the change from

the initial level of the floor.

4.1. End-Point Criteria

The previously mentioned standard test met bod

specify that the performance of the specimen shall be determined as the time at which any of the

following end-point criteria shall be reached or observed

() The floor shall no longer sustain the <|e- im

load. () Cracks or openings shall develop, allow ing

the passage of flames or gas hot enough to ignite

cotton waste.

(c) The average temperature, as measured at five or more points on the unexposed surface, shall

rise 250 deg F above its initial temperature.

(d

)

The temperature as measured by one of the

unexposecl surface thermocouples shall rise by

325 deg F above its initial temperature.

Although not required by the ASTM Standard

Test Methods, additional data were obtained

relative to the following criteria, which have be- come common practice, apply to tests of ceilings, or were considered of known interest

(e) The times at which the main steel structural

members attained average temperatures of 925 : F

and 1,000° F at one level, or

(J) The time at which a main steel-structural

member attained a temperature of 1,200° F at any

one point.

The behavior of these steel-joist floors made the

determination of a time at which they no longer

sustained the load a difficult process. In the earlier

tests, in which this end point was determined by

a visual estimate of how rapidly the deflections were changing or of how the oil pressure fluctuated

in the loading system, a survey of the data indi- cated deflections of about 3 in. at the time of load

failure. Therefore, in the interests of consistency,

criterion (a) was taken arbitrarily to be indicated

by a 3-in. maximum deflection in the later tests.

5. Test Results

The results are presented as summaries of the

test logs, including condition after test, and repre- sentative views of test specimens and graphs of the temperatures and deflections observed

well as tabulations of the various end points and

critical information, tables 4 and 5 The tests have been grouped in these summaries accord eg

to certain variables, mainly size and plasn e- in forcing.

5.1. Group 1. Exploratory Tests

This group was established on si e and tncltn s the two specimens of smaller size than the tu 9
Table 5. Observed times of failures and other significant test data

Test Load failure

Unexposed surface temperature increase

250° F

(average)

325° F

hr min hr min hr min

257 1 10 1 11 260 1 56

261-.. 1 25

266.... Not loaded .. . . 287 *> 1 00

295 1 43

296 1 48

297 1 40

311 6 40 4 25 4 46 312 6 26 3 27 3 46

313 4 12 3 14 3 19 316 b 3 00 __ 317 1 06-.- 318 2 46

319 1 16-_-

324 ... 0 07 326 ... 2 54 2 44

329. _. 0 07

Joist temperatures •

925° F

(average)

hr min

45

50

4138

11

04

5730

0 04

2 58

0 05

1,000° F

(average)

hr min

10

5124

1 46 T 41

6 19

18

5840

04

05

1,200° F

hr min

08

5324

55

40

49

3939

15

0 55 2 13

1 04

0 06

2 26

0 08

Fire- exposure

severity

Percent

99.9

103.3 98.4

101.0 97.7

99.4

100.0

101.3 100.2

100.4

100.6

101.4 97.1 100.7 99.7

92.2

99.8

86.4

Unexposed surface-tem- perature increase at

load-failure time

Average

° F

245

12686

76

10670

54 457

500

362

18783

196 112

2140

Maxi- mum

o F

293

140 10686

14286

68

488

562

490

245

137

225

144

419

0

« These data do not represent end points specified in ASTM E119-53 but

1 Test stopped before load failure, or any end point, to save joists and slab mum required by the ASTM Standard Test Methods. They were tests 257 and 260.

Test 257. One-half in. of mill-mixed plaster on %-in.

lath. At 4 min, fine cracks outlined lath; 10 min, largest cracks under joists; 26 min, main cracks in. or more wide,

plaster along one edge of cracks offset below that along

other edge; 40 min, offset as much as 1 in., plaster surface warped; 42J4 min, approximately 3 ft2 of lath and plaster

fell; 55 min, more ceiling fell; 1 hr 10 min, deflections of

floor increasing rapidly, concrete floor slab cracking, load removed; 1 hr 15 min gas to furnace fires turned off. After the test, most of the lath and plaster had fallen, the slab was cracked, and the chords of two of the three

joists were found to have been distorted.

Test 260. Three-quarter in. of mill-mixed plaster on

%-in. lath. At 4 min, first fine cracks; 15 min, more

cracks up to in. wide and full length along centerline; 40 min, }4-in. offset along one crack; 1 hr 20 min, plaster

warped, offset 1% in.; 1 hr 35 min, lath and plaster offset 4 in.; 1 hr 39}4 min, first plaster fell; 1 hr 50 min, most of

ceiling fell; deflections increasing rapidly, load off at 1 hr 56 min; gas off at same time. After the test, nearly all the ceiling had fallen, the bottom

chords of the joists were bowed, and the top chords buckled.

5.2. Group 2

This group included four large-size concrete slab

floor tests in which no extra reinforcing was in- corporated into the ceiling.

Test 261. Five-eighth in. of mill-mixed plaster on %-in.

lath. At 2 min, first small crack with a small local bulge in plaster; 6 min, bulged white-coat- plaster flaked off spot

3 in. in diameter, cracks outlined lath; 19 min, crack in concrete slab; 34 min, large cracks and slight sag of ceiling at center; 1 hr, longitudinal centerline crack widest, some

sag and offset; 1 hr 17 min, pronounced offset along cracks;

1 hr 22 min, half of ceiling fell; 1 hr 25 min, more of ceiling- down, load off; 1 hr 27 min, gas off. After test, the slab was intact but the joists had sagged

somewhat, some of the top chords had buckled slightly, and

the ceiling was nearly all down.

Test 266. Mill-mixed plaster, l/i in. on %-in. lath. At

6 min, first cracks outlined lath; 15 min, slight sag along

a crack; 27 min, smoke into furnace chamber from crack; 37 min, general sagging over ceiling plus local variations

s known to be of interest to various building-codo groups and to others. use in following test.

if along cracks; 50 min, crack at center % in. wide; 52 min,

first portion of ceiling fell, additional portions fell until, at

1 hr 1 min about three-fourths of entire ceiling down; i gas off 1 hr 1 min. The floor slab and joists having been used in a previous

test, no load was applied, and the deflections were small. Nearly all the ceiling was down by the end of the test. Test 287. Plaster of % in. on %-in. lath. At 10 min

first cracks; 18 min, more cracks, with some sagging along

them; 28 min, lath pattern beginning to show in cracks, some smoke in furnace; 34 min, flames into furnace from

ceiling cracks; 49 min, offset of % in. along full-length [' crack Y$ in. wide; 1 hr, several cracks % in- wide, load ; removed to prevent damage to slab and joists; 1 hr 4 min,

first fall of ceiling, about 4 ft2

; 1 hr 7 min, gas off, more of ceiling down.

After test, less than one-quarter of the ceiling had fallen, and both the slab and joists were undamaged. However, |: overnight most of the ceiling fell as it cooled. Test 295. Ceiling of 1 in. of plaster on %-in. lath, same

slab and joists as in test 287. At 2 min, white-coat plaster

peeling from over half ceiling; 18 min, spot about 6-in.- diameter sagging; 27 min, half of above spot fell, another

sagging 1 in.; 34 min, cracks along lines of lath joints over [j most of ceiling; 48 min, slight sag along crack; 1 hr 3 min,

several cracks in. wide, others less; 1 hr 26 min, offset of J4 in. along crack; 1 hr 36 min, sag of 2 in. at lath cor-

' ner; 1 hr 36}j min, about 5 ft2 of ceiling fell; 1 hr 43 min,

load removed, floor continued to deflect under deadweight,

about one third of ceiling down; 1 hr 49 min, nearly all ceiling down, joists buckling; 1 hr 53 min, gas off. Most of the joists were buckled or bent, and only a few ; small pieces of plaster or lath remained after the test.

5.3. Group 3

This group consisted of the two gypsum concrete-slab floors. The ceilings were job-mixed

gypsum-perlite plasters on perforated %-in. gypsum lath. No extra reinforcing was incorporated

in the ceiling.

Test 296. Plaster in. thick on %-in. lath. At 22

min, first crack; by 1 hr, only 5 cracks, each 2 to 8 ft long but not over 6 in. wide; 1 hr 10 min, very slight

general sag of ceiling; 1 hr 35 min, flames into furnace ' from ceiling crack; 1 hr 46 min, offset of / in. at. crack

10
across lath joint; 1 hr 47% min, about 35 ft2 of ceiling fell, exposing joists; 1 hr 48 min, more of ceiling sagging badly,

load off, floor continued to deflect under dead load; 1 hr

53 min, gas off, most of ceiling down.

After the test, most of the plaster and lath had fallen, but the clips that held the lath to the furring channels were in place. Several of the joists were buckled slightly. Test 297. Plaster 1% in. thick on %-in. lath. At 9 min, first crack; by 23 min, several cracks, which outlined some of the lath; 51 min, power failure for 4 to 5 min stopped operation of air blower and other equipment,

such as loading pump, clocks, potentiometers; 1 hr 10

| min. maximum crack width % in., slight sag along some

cracks; 1 hr 28 min, sag of % in. along % in. wide crack;

1 hr 31 min. flames into furnace from same crack; 1 hr

34 min. about 12 ft2 of ceiling fell; 1 hr 40% min, more

ceiling down, load off: 1 hr 45 min, gas off. The times after 51 min do not include the period of power failure, during which the clocks were stopped and

the furnace fires were greatly reduced by lack of air presI sure. At the end of the test, nearly all the ceiling was

down, but the lath clips were still !in place. The joists were bent somewhat, as were the cross-bridging members.

5.4. Group 4

This group consisted of the three tests of floors

in the ceilings of which the laths were secured to

' the furring by one type of clip, which provided

support at the edges only, and by other related

; clips through the laths across their width (types A

and B, fig. 3).

Test 316. Plaster % in. on %-in. lath, extra clips. At

I 8 min, white-coat plaster flaking off in pieces about 2-in. diameter: 31 min, crack about half length of ceiling; 1 hr

12 min, maximum crack width % in.; 1 hr 21 min, slight sag near center: 2 hr, sag of 3 in. along centerline crack,

• offset of at least % in. on one side: 2 hr 42 min, offset of

1 3 in. or more; 2 hr 52 min, some cracks 1 in. vide, others

! offset 4 to 5 in.; 3 hr, test stopped, gas and load off. The test was stopped before an end point was reached

| in order that the joists and slab might not be damaged and

h could be used for another test. At the end of the test, no

| significant amount of the ceiling had fallen but some

, pieces were sagging about 1 ft and left openings. Upon

cooling, a few square feet of the ceiling fell; but the remainder did not.

Test 317. Same joists and slab as in test 316. Plaster

1 % in. on %-in. lath. At 13 min, several cracks in two

straight lines, apparently across lath ends; 19 min, cracks

outlined all laths, also two full-length cracks; 43 min,

i maximum crack width % in., slight offset; 46 min, distinct

! wave in ceiling surface; 48 min, ceiling fell from area of

j one lath, much larger area very irregular; 1 hr 2 min,

I about half of ceiling down, 1 hr 6 min, load off; 1 hr 7

j min, gas off. During cooling the remainder of the ceiling fell. Several

] of the joists were buckled slightly. Test 319. Plaster of % in. on %-in. lath. At 8 min,

! first crack with local peeling of white coat; 17 min, 3

I full-length cracks; 24 min, 6 full-length cracks, some

I % in. wide; 39 min, cracks outlined all laths and divided

I some, slight sag and %-in. offset; 55 min, offset of 1 to 2

' in. ; 59% min, section of ceiling about 5 ft2 fell ; 1 hr 4 min, more ceiling down; 1 hr 16 min, load and gas off. The joists were bent slightly, but the slab was not

cracked. About one-quarter of the ceiling fell during the

test and as much again during cooling. The remainder was

j badly cracked. 5.5. Group 5 This group was composed of the tests in which

diagonal wire was used as additional reinforcement below the lath, in addition to the wire clips.

Test 313. Diagonal wires 10 in. apart, plaster % in. bn %-in. lath. At 13 min, first cracks along each side;

17 min, thin black smoke into furnace from some crar

30 min, cracks over most of ceiling without -harp outlining of lath, y4

- in. sag; 50 min, sag % to % in. at -e oral places; 1 hr, cracks along lat h joints had become prorr ire about % in. wide, offset of % to % iri

; 1 hr 30 min, general sag over ceiling, local variations nearly all disappeared

1 hr 50 min, offset 1% in., cracks % in. wide near center of

ceiling; 2 hr 21 min, two small strips of plaster harming

down 4 to 5 in. where previously offset; 2 hr 46 rein, plaster fell from 1-ft 2 area; 3 hr 20 min, small piece- of plaster hanging or offset at additional locations; 4 hr 7 min, sag of ceiling at least 12 in., overall cracks; 4 hr 24 min, gas and load off. After the test, very little plaster and lath had fallen, but both fell from over half the ceiling during the folio it ig 2 days. Instead of having been buckled, the joists were

bent in smooth arcs. Test 318. Diagonal wires 11.3 in. apart, pla- : er % i r,

on %-in. lath. At 8 min, first crack; 15 min, smoke from

single crack; 19 min, cracks partially outlined laths: 24

min, slight sagging along two cracks; 31 min, offset of % in., some peeling of white coat; 35 min, entire ceiling surface had wavy appearance; 50 min, wavy appearance

lessening except for 3-in. sag along two cracks; 1 hr 15 min, corner of lath and plaster sagging 1% in.; 1 hr 35

min, maximum crack width 1% in., local sag as much as 4

in.; 2 hr 6 min, many cracks % to 2 in. wide, corners of lath and plaster hanging down 3 to 8 in., leaving openings

about 6 and 10 in. square; 2 hr 27 min, about 2% ft2 of

ceiling fell; 2 hr 47 min, load off; 2 hr 53 min, gas off. Less than one-quarter of the ceiling fell during the test and subsequent cooling. Most of the joists were bent, a few buckled slightly, and the floor slab showed no appreciable cracking.

Test 326. Diagonal wires 10 in. apart, regular base- coat plaster % in. thick, plus- % in. of acoustical plaster on %-in. lath. At 2 min, plaster surface blackened; by 25 min the blackening was burped off, and a 3-in. -diameter

hole % in. deep had appeared in plaster; 33 min, a second

hole about same size but % iri.. deep popped open; 43 min,

first observable crack; 47 m®, acoustical plaster down

from 1%-ft-diameter area, exposing base coat; 1 hr 1 min,

plaster of depth to expose diagonal reinforcing v ire down

from 4- to 5-ft 2 area, scaling of acoustical plaster from

other areas; 1 hr 23 min, more plaster down, ceiling had a ragged appearance, some laths exposed in offsets; 1 hr 57 min, general sag of ceiling; 2 hr 38 min, deflections in- creasing rapidly, pieces of plaster hanging 1 to 2 ft below

ceiling on wires; 2 hr 46 min, large area of ceiling fell: 2 hr 54% min, load off, crack across center of slab; 3 hr 4 min, gas off. A single area of about one third of the ceiling and s >n other small areas had fallen. Nearly all the acoustical

plaster was down, mostly as small granules. The joists were bent and buckled. The floor slab was craeke 1 across the middle, one end having sagged excessively.

5.6.

Group 6

This group consisted of the two tests of doors

with 1-in. hexagonal-mesh galvanized 20-gage

wire fabric secured below the lath before plastering.

Test 311. Plaster 1 in. on %-in. lath. At 15 min.

first crack; 19 min, small blister in white coat popped: 41 min, thin smoke from crack, maximum crack width

in.; 1 hr 29 min, slight sag at junction of cracks in center

of ceiling, cracks nearly full length and full width:

min, flames into furnace front center: l hr 42 min. odset

of % in. at center, cracks not over %g in. wide: 4 hr, no

noticeable change in cracks, sag, or offset since abot: to 2 hr; 4 hr 50 min, sag at center about % in.; 5 hr 10 min,

local sag at center 1% in., widest crack '•> to 1 in. 0 whole ceiling had settled slowly into a curve whose dop:

at the center was about 1 ft . local offset of 2 in., local sag about same; 6 hr 25 min, oily burlap bag that had Ivon on top of floor ignited, some cracks l in. wide, ot Iters otlse: up to 6 in.; 6 hr 34 min, opening 6 to S in. w ide due t sag
and offset through which some lath had fallen but no

plaster; 6 hr 40 min, load off; 6 hr 43 min, gas off. At the end of the test no plaster had fallen, but it was

thoroughly cracked. The joists were bent but not buckled. No appreciable amount of plaster fell after the test. Test 312. Plaster in. on %-in. lath. At 13 min,

first crack; 27 min, short cracks outlined laths over part of

ceiling; 1 hr, maximum crack width Yie in., length 3 ft,

1 hr 45 min, several parallel transverse bulges or sags of small depth, probably between lines of support for wire mesh; 2 hr 43 min, small edge cracks in floor slab, little change in ceiling; 3 hr, maximum crack width % in., length

6 ft; 4 hr, ceiling had developed 1 to 2 in. general sag; 5 hr, general sag of ceiling had developed into curve of

9-in. depth at center; 5 hr 20 min, local sag of 14 in. over

area 3 ft in diameter; 6 hr 15 min, ceiling fell from 4-ft2 area near center; 6 hr 27 min, load off; 6 hr 34 min, gas

off, more ceiling down.

A total of about 24 ft2 of the ceiling fell by the end of the test. The remainder stayed up through cooling and

several days after. The joists were bent in smooth curves but were not buckled.

5.7. Group 7

This group was made up of the tests of two

floors without ceilings. One was the same slab

and joists from a previous test. This floor had

withstood loading to twice the live load before

the retest. The other test floor consisted of all new materials.

Test 324- Same slab and joists as in test 319. By 4 j min the channel bridging was a dull red and the deflec- tions were as much as }£ in.; 7 min, the maximum deflec- tion reached 3 in. and all were increasing rapidly, load off; 1 8 min, the joists were bright red and the gas turned off. The joists recovered about one fourth of the total deflection after the cooling and removal of load. Test 329. All new materials, no ceiling. Some difficulty was encountered with the burners in the first 4 min, during which time some smoke came out above the slab, and

the deflections became about 1 in.; at 7 min 15 sec the maximum deflection reached 3 in. and the load was re- moved; by about 13 min, when the gas was turned off, the joists and bridging gave off a bright glow.

The joists upon cooling recovered about in. of the more than 3-in. deflection. There was a thin diagonal crack across each corner of the slab. Because of the

trouble with the burners, the fire-exposure severity was

quite low (86.4%) and outside the limits set by the test

specification. However, the behavior and endurance were

essentially the same as those of the reused floor and joists in test 324. Figures 6, 7, 8, 9, 10, and 11 show the after-test conditions of some representative specimens and ; representative graphs of the temperatures observed in the tests.

12
I] Figuhe 7. Condition of ceiling after test 818 of specimen with diagonal wire reinforcing. One or two smoothly bent joists may be seen through the opening in the ceiling.

13
TEST NO. 296

-1300

-1200

1

1

I

-II00

1

FMAX.s,

s 71 -1000 1

Tc jfWE —

r-"

1

I FMI n/ V -900 J

; / NJN AX. -800 K

LU /,/

(T -700 ^<

(ZLU -600 Q_

1

// ! 1 / 1

1 / > LU •j

1 / /

' V/ \

,IA\ / \ I -500 H

-- 1 rj B 1

i r

1 -400 1

n

1 t

IN TYPICAL FLOOR CROSS SECTION -300 1

(i I -200 1

1 -7

MA

- -100 A

S -0

)

TIME, HRS. Figure 9. Time-temperature curves from tests 295 and 296, unreinforced ceilings.

Sketch indicates thermocouple locations. Curves labeled as follows: Standard exposure curve of E 119, Reference curve; furnace temperatures, average, maximum, - and minimum, F, Fm»x, Fm i„, respectively; average of bottom chords of joists, Jb; maximum on joists, J„„; unexposed surface, average and maximum, S and Sm ax.

6. Discussion

6.1. Deviation from Standard Test Methods

Ordinarily, fire-endurance tests at the National

Bureau of Standards have been continued until as many as possible of the end points defined by the

applicable test criteria (those for floor tests are given in 4.1) were reached, so that all possible

information could be obtained from each test. This practice is at variance with the standard

test methods, under which tests are ended as soon

as the first end point is reached and immediately

followed by the hose-stream test. Although the

fire endurances of the floors were determined by

the initial end point in each test, so that these

results were equivalent to those under strict compliance with the standard test methods, the total

fire exposures were usually much greater by the

end of the fire exposure period. Consequently,

the conditions of the test specimens were not

equivalent at the times the hose-stream tests and

the double-reloading tests would have been made.

For this reason, these portions of the standard

test methods for floors were omitted. The observations of the temperatures of the various components and the conditions of the floors and ceil- ings indicated that alternate specimens would have

withstood hose-stream and reloading tests where

required.

14

6.2. Nature of Failures

Table 5 shows that the determining end points

in the tests were usually either load failure in j comparatively short tests or temperature rise on

' the unexposed surface in the longer tests. This

may be related to the behavior of the ceiling and

the joists. _

i In the tests of floors with ceilings in which the

lath-clip systems were not supplemented by other i reinforcing, progress from the end of the calcina- | tion period to load failure was rapid, with little I difference noted for ceilings of the thicker plaster

coats. Once the gypsum calcined, the lath and

plaster cracked extensively and soon lost the

strength necessary to support themselves. Por-j

tions of the ceilings fell, exposing the joists above

directly to the hot flames and gases. These ex- posures resulted in high steel temperatures, loss of strength, and load failures. In contrast to the previously mentioned tests involving rapid load failure, the tests in which means were taken to prevent the breakup and

fall of the ceiling indicated a slow rate of heat

transfer through the ceilings and floors until the

temperatures on top of the latter had been raised

by the limiting 250 deg F average, or 325 deg F

at one point. The means utilized to prevent the

fall of the ceiling consisted of extra, more closely 1 spaced supports for the lath so that much more
Figure 10. Time-temperature curves from tests 813 and 816, the former having a ceiling with diagonal wires and the latter one with extra clips.

LlJ cr3

crUJ

0.2Ld

TIME. HRS. Figure 11. Time-temperature curves from test 311 having a ceiling with 1-in. hexagonal-mesh tr: re-tab :e

15

.1
breakup would be necessary before any pieces of

lath and plaster were small enough to be unsupported. As long as the ceiling was kept in place,

it continued to protect the joists and floor slab, even after the gypsum calcined. The joists were

heated slowly and uniformly, yielding gradually

into smooth curves rather than sharp buckles.

In some cases, the joists were acting as suspension

members by the ends of the tests. 6.3.

Effectiveness of Reinforcing or Extra

Support

The various means of providing extra support

for the ceiling were: closer spacing of furring

channels and clips, use of additional intermediate

clips, wires laid in or tied in on the diagonal,

and 1-in. hexagonal-mesh wire fabric (“chicken

wire”). The effectiveness of these added rein- forcements, as well as the regular supporting

clips, is due not only to the fact that they pass

under the lath but to the direct support given to the whole ceiling because they become at least partly embedded in the plaster. The change in spacing of the furring channels, and therefore

of the supporting clips, from 16 to 12 in. gave

an increase of 11 min from a test of 1 hr 4 min

on a comparatively thin (% in. total) ceiling.

This increase amounted to about 17 percent, or

one-sixth. The addition of diagonal wires to an

equally thin ceiling on furring at 16-in. centers gave triple the resistance obtained without rein- forcing. The use of hexagonal-mesh wire fabric

in a %-in. ceiling gave almost four times the re- sistance obtained without. The results of tests on moderate (1 in. total) ceilings, one with diagonal

wire and one with extra intermediate clips, were

essentially equal. The combination of the closer

(12-in.) furring and either extra intermediate

clips or diagonal wires gave about- 2% to 3 times

the resistance of a moderate ceiling on the wider

(16-in.) furring with no reinforcement. With a

l/g-in. ceiling, the use of closer furring and hexagonal-mesh wire fabric increased the fire resistance

to about 2/2 times that of an equally thick ceiling

without reinforcing. This increase in time was

2 hr 44 min. The greatest increases, both in time and percentage wise, were obtained with the

hexagonal-mesh wire fabric. The use of the

various reinforcements was especially valuable to thick and comparatively heavy ceilings. The

results of test 326 did not indicate a significant

difference between the effectiveness of the short- diagonal wires with each end bent around the

clip junctions and that of the 4-ft. lengths neither

bent not tied.

6.4.

Plasters

The various plasters and mixes employed in the

tests seem to have been of about equal value. The

mill-mixed and job-mixed plasters gave approximately the same results when in equal thicknesses.

However, not enough tests were made with the

mill-mixed plasters to draw definite conclusions.

A research program consisting of tests in different ; thicknesses, including representative floor, wall, or column constructions, would be necessary to 1 evaluate the relative merits of mill-mixed and

job-mixed plasters.

The plasters of y2 -in. and %-in. thickness on , unreinforced ceilings, were mixed 1

1/2 parts of gypsum to 2 )'2 parts of aggregate, by volume (100

lb of gypsum to 2 % ft3 of perlite), and those of

1-in. or greater thickness were in two coats, the

first, or scratch, mixed 1)4:2 (100 lb:2 ft3) and the

second, or brown, 1)4:3 (100 lb : 3 ft3 ). As the

different mix ratios were not used in equal thick- f nesses, no comparison was attempted. In the

scratch and brown-coat- work, the two coats were

of approximately equal thicknesses. As mentioned in the preceding section, the thicker

plasters were most effective when given additional

support.

Comparison of the results of test 326 with those

of test 318 indicated that the acoustical plaster as applied to the former contributed nothing to the j fire resistance of the test specimen. During construction of this specimen numerous drop-outs

occurred on application of the acoustical plaster,

which at- the time were blamed on improper drying ; of the base coat. Later experience with the same

type of acoustical plaster has, however, indicated

that the difficulties were caused by segregation of the components during shipment- and that the

additional % in. of acoustical plaster should have ^ considerably increased the fire resistance of the

specimen.

6.5.

Balance of Designs

It is of importance to economical construction

that- no more materials be used than necessary to achieve the desired results, with appropriate margins or factors of safety. Therefore, the design

and construction should be such that the materials

are employed in the most efficient manner. The

design must be “balanced” with all considerations

in mind, including fire resistance. Much information on the fire resistances of various building;

components has been obtained and published.

Some of these publications are listed in section 8. In the majority of the tests, load failure occurred

and the high temperatures were reached in the

joists, but the limiting temperature rise on the

unexposed surface was not reached (see table 5), indicating that the floor slab still had considerable

insulating value some time after the joists had

failed. It was considered necessary to stop mosti

of these tests before the limiting temperature rise was reached in order to prevent the collapse of the

test specimens. However, in three tests, the

limiting temperature rise on the unexposed surface was reached from 1 to 3 hr before load failure, in- dicating that the protection for the joists was much greater than needed. In each case the

designs may- be said to be unbalanced in that some

part of the assembly had an unused reserve of fire

16
resistance compared with the other parts. As

(this represented costly materials that were not

contributing to the fire resistance, it is of interest

do the architect and the builder to use a balanced

design. It is important to realize that it is not a simple problem of adding or substracting the correct amount of material but, frequently, the diffi- culty of keeping the materials in place as long as they have any fire resistive value. This is shown

by comparison of tests 295 and 311, in which the same types and amounts of lath and plaster were

used—

in. of lath plus 1 in. of plaster. In the

‘former, this ceiling protected the joists for only

1 hr 43 min, whereas in the latter the same ceiling,

kept in place and nearly intact on more closely

spaced furring by wire-fabric reinforcing, projected the joists against load failure for 6 hr 40

min, although the fire endurance was limited to 4 hr 26 min by temperature rise on the unexposed

isurfaee. Subsequently, in test 312 only }2 in. of plaster was applied to the lath and wire fabric,

but the joists were still protected for over 6 hr. ,The fire endurance of this assembly was limited

to 3 hi’ 28 min by temperature rise. Thus %-in. thickness of plaster on %-in. lath, which was the

thinnest ceiling in the test series (tests 257, 266,

i312, 317, 318, 319), gave the second longest fire >endurance when sufficiently reinforced.

7. Conclusions

On the basis of the tests reported in this paper,

iand comparison with those in other BMS reports

j[2, 3], several conclusions may be drawn.

1.

Open-web steel-joist floors with ceilings of

perforated g3"psum lath and gypsum-perlite plaster

will provide fire resistances up to 1% hr and those

;With adequate reinforcement to more than 4 hr,

covering the range of requirements in man y building codes.

2. Even relatively thin coats of plaster arid bub

as normally applied without reinforcing lose strength to the point they can no longer support

their own weight while still of considerable fire protection value.

3. The use of some form of reinforcing to reduce the span of lath and plaster between supports and thereby keep the ceiling in place and

functioning as protection to the joists and slab is essential for fire resistances of 2 hr, or longer.

The authors acknowledge the contribution of

N. D. Mitchell under whose direction the work

reported herein was initiated.

8. References

[1] Open web steel joist construction, a design manual,

AIA File No. 13G, Catalog ST-52, Steel Joist Insti- tute, Washington, D. C. (Nov. 1952).

[2] Fire resistance classifications of building constructions,

NBS BMS92, U. S. Government Printing Office, Washington 25, D. C., 35 cents.

[3] N. D. Mitchell and J. V. Ryan, Fire tests of steel columns encased in gypsum lath and plaster, NBS

BMS135, U. S. Government Printing Office, Washington 25, D. C., 15 cents.

[4] National Building Code, National Board of Fire Underwriters, New York, N. Y.

[5] Manual of fire loss prevention of the Federal Fire Council, U. S. Government Printing Office, Washington 25, D. C. (in revision).

[6] NFPA handbook of fire protection, National Fire Protection Association, Boston, Mass.

[7] Fire tests on structural elements, National Building

Studies Research Paper No. 12, Her Majesty's

Stationery Office, London, England.

Washington, March 25, 1954.

i

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ii

!

U. S. GOVERNMENT PRINHS

BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page n]

BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete- Block Wall Construction Sponsored by the National Concrete Masonry Association. '' BMS33 Plastic Calking Materials * BMS34 Performance Test of Floor Coverings for Use in Low-Co3t Housing: Partly- . 15c BMS35 Stability of Sheathing Papers as Determined by Accelerated Aging _ * BMS36 Structural Properties of Wood-Frame Wall, Partition, Floor, and Roof Constructions

With “Red Stripe” Lath Sponsored by The Weston Paper and Manufacturing Co.. 10

BMS37 Structural Properties of “Palisade Homes” Constructions for Walls, Partitions, and

Floors, Sponsored by Palisade Homes . * BMS3S Structural Properties of Two “Dunstone” Wall Constructions Sponsored by the W. K. Dunn Manufacturing Co lot BMS39 Structural Properties of a Wall Construction of “Pfeifer Units” Sponsored by the Wisconsin Units Co 10^ BMS40 Structural Properties of a Wall Construction of “Knap Concrete Wall Units” Sponsored

by Knap America, Inc BMS41 Effect of Heating and Cooling on the Permeability of Masonry Walls BMS42 Structural Properties of Wood-Frame Wall and Partition Construction with “Celotex”

Insulating Boards Sponsored by The Celotex Corporation

BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 BMS44 Surface Treatment of Steel Prior to Painting

BMS45 Air Infiltration Through Windows 20£ BMS46 Structural Properties of “Scott-Bilt” Prefabricated Sheet-Steel Construction for Walls,

Floors, and Roofs Sponsored by The Globe-Wernicke Co * BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions, and Floors Sponsored by American Houses, Inc 20^ BMS48 Structural Properties of “Precision-Built” Frame Wall and Partition Constructions

Sponsored by the Homasote Co * BMS49 . Metallic Roofing for Low-Cost House Construction 25<i BMS50 Stability Of Fiber Building Boards as Determined by Accelerated Aging * BMS51 Structural Properties of “‘Tilecrete Type A” Floor Construction Sponsored by the

Tilecrete Co * BMS52 Effect of Ceiling Insulation Upon Summer Comfort _ 15c BMS53_ Structural Properties of a Masonry Wall Construction of “Munlock Dry Wall Brick”

Sponsored by the Munlock Engineering Co lOe BMS54 Effect oUSoot on the Rating of an Oil-Fired Heating Boiler 10e BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls * BMS56 A Survey of Humidities in Residences...: 10^ -BMS57 Roofing in the United States—Results of a Questionnaire * BMS58 Strength of Soft-Soldered Joints in Copper Tubing lot BMS59 Properties of Adhesives for Floor Coverings * BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 30C BMS61 Structural Properties of Two Nonreinforced Monolithic Concrete Wall Constructions .. BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by the Portland Cement Association.. lot BMS63 Moisture Condensation in Building Walls.... „ 15t BMS64 Solar Heating of Various Surfaces 10c BMS65 Methods of Estimating Loads in Plumbing Systems 20c BMS66 Plumbing Manual ...^ 40t BMS67 Structural Properties of “Mu-Steel” Prefabricated Sheet-Steel Constructions for Walls,

Partitions, Floors, and Roofs, Sponsored by Herman A. Mugler 20c BMS68 Performance Test for Floor Coverings for Use In Low-Cost Housing: Part 3 25t BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated Aging 10c BMS70 Asphalt-Prepared Roll Roofings and Shingles 20c BMS71 Fire Tests of Wood- and Metal-Framed Partitions 30c BMS72 Structural Properties of “Precision-Built, Jr.” Prefabricated Wood-Frame Wall Con-

. ^ struction Sponsored by the Homasote Co * BMS73 Indentation Characteristics of Floor Coverings 10C BMS74 Structural and Heat-Transfer Properties of “U. S. S. Panelbilt” Prefabricated SheetSteel Constructions for Walls, Partitions, and Roofs Sponsored by the Tennessee

Coal, Iron & Railroad Co. 20c BMS75 Survey of Roofing Materials in the North Central States 15c BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls. BMS77 Properties and Performance of Fiber Tile Boards * BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

t Constructions 35c BMS79 Water-Distributing Systems for Buildings 20c BMS80 Performance Test of Floor. Coverings for Use in Low-Cost Housing: Part 4 25c BMS81 Field Inspectors’ Check List for Building Constructions (cloth cover, 5x7# inches)... 35c

'Out of print. [List continued on cover page iv]
BUILDING MATERIALS AND STRUCTURES REPORTS ^

[Continued from cover page nr] BMS82 Water Permeability of Walls Built of Masonry Units 250 BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 15<6 BMS84 Survey of Roofing Materials in the South Central States * BMS85 Dimensional Changes of Floor Coverings With Changes in Relative Humidity and

Temperature . * BMS86 Structural, Heat-Transfer, and Water-Permeability Properties of “Speedbrik” Wall

Construction Sponsored by the General Shale Products Corporation. _. 150 BMS87 A Method for Developing Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research,

Design, and Construction . i 4. 200 BMS88 Recommended Building Code Requirements for New Dwelling Construction With

Special Reference to War Housing 1 * BMS89 Structural Properties of “Precision-Built, Jr.” (Second Construction) Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co : 1 50 BMS90 Structural Properties of “PHC” Prefabricated Wood-Frame Construction for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation. 150 BMS91 A Glossary of Housing Terms ... * BMS92 Fire- Resistance Classifications of Building Constructions 350 BMS93 Accumulation of Moisture in Walls of Frame Construction During Winter Exposure.. * BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

“Knap Concrete-Unit” Walls _V . „ * BMS95 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls.... 250 BMS96 Properties of a Porous Concrete of Cement-and Uniform-Sized Gravel 100 BMS97 Experimental Dry-Wall Construction With Fiber Insulating Board. y_ * BMS98 Physical Properties of Terrazzo Aggregates r „ .- '.. * BMS99 Structural and Heat-Transfer Properties of “Multiple Box-Girder Plywood Panels” for Walls, Floors, and Roofs. ^ j.__ : * BMS100 Relative Slipperiness of Floor and Deck Surfaces r * BMS101 Strength and Resistance to Corrosion of Ties for Cavity Walls * BMS102 Painting Steel 150 BMS103 Measurements of Heat Losses From Slab Floors * BMS104 Structural Properties of Prefabricated Plywood Lightweight Construction for Walls,

Partitions, Flo'ors, and Roofs Sponsored by the Douglas Fir Plywood Association. * BMS105 Paint Manual with particular reference to Federal Specifications $1. 50 BMS106 Laboratory Observations of Condensation in Wall Specimens.. 100 BMS107 Building Code Requirements for New Dwelling Construction (y-. * BMS108 Temperature Distribution in a Test Bungalow With Various Heating Devices 150 BMS109 Strength of Houses: Applicantion of Engineering Principles to Structural Design $1. 75 BMS110 Paints for Exterior Masonry Walls : . 200 BMS111 Performance of a Coal-Fired Boiler Converted to Oil _ ... 150 BMS112 Properties of Some Lightweight-Aggregate Concretes With and Without an Air- Entraining Admixture • * BMS113 Fire Resistance of Structural Clay Tile Partitions ... 150 BMS114 Temperature in a Test Bungalow With Some Radiant and Jacketed Space Heaters... 250 BMS115 A Study of a Baseboard Convector Heating System in a Test Bungalow... 200 BMS116 Preparation and Revision of Building Codes : 200 BMS117 Fire Resistance of Walls of Lightweight Aggregate Concrete Masonry Units 250 BMS118 Stack Venting of Plumbing Fixtures. ... 250 BMS119 Wet Venting of Plumbing Fixtures 25? BMS120 Fire Resistance of Walls of Gravel-Aggregate Concrete Masonry Units... 150 BMS121 Investigation of Failures of White-Coat Plasters 300 BMS122 Physical Properties of Some Samples of Asbestos-Cement Siding 200 BMS123 Fire Tests of Wood-Framed Walls and Partitions With Asbestos- Cement Facings 150 BMS124 Fire Tests of Steel Columns Protected With Siliceous Aggregate Concrete 150 BMS125 Stone Exposure Test Wall .... 300 BMS126 The Self-Siphonage of Fixture Traps ... 200 BMS127 Effect of Aging on the Soundness of Regularly Hydrated Dolomitic Lime Putties.-.-. 150 BMS128 Atmosphere Exposure Tests of Nailed Sheet Metal Building Materials 200 BMS129 Fire Endurance of Shutters for Moving-Stairway Openings 100 BMS130 Methods and Equipment for Testing Printed-Enamel Felt-Base Floor Covering 150 BMS131 Fire Tests of Gunite Slabs and Partitions I .... 150 BMS132 Capacities of Plumbing Stacks in Buildings. ... , 250 BMS133 Live Loads on Floor in Buildings , . 250 BMS134 Fire Resistance of Concrete Floors ... ... 150 BMS135 Fire Tests of Steel Columns Encased With Gypsum Lath and Plaster . _TT 150 BMS136 Properties of Cavity Walls —.-. 150' BMS137 Influence of the Wash From Bronze on the Weathering of Marble. ... 150 BMS138 Effect of Edge Insulation Upon Temperature and Condensation on Concrete-Slab

Floors 200 BMS139 Studies of Stone-Setting Mortars 200 BMS140 Selected Bibliography on Building Construction and Maintenance ... ... 300 BMS141 Fire Endurance of Open-Web Steel-Joist Floors With Concrete Slabs and Gypsum

Ceilings ^ 200

Out of print.