Fire Tests of Steel Columns

Encased With Gypsum Lath and Plaster

United States Department of Commerce

National Bureau of Standards

Building Materials and Structures Report 135
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UNITED STATES DEPARTMENT OF COMMERCE • Sinclair Weeks, Secreta, NATIONAL BUREAU OF STANDARDS • A. V. Astin, Diriclor

Fire Tests of Steel Columns

Encased With Gypsum Lath and Plaster

Nolan D. Mitchell and James V. Ryan

Building Materials and Structures Report 135

Issued April 3, 1953

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.

Price 15 cents
Foreword

This report, one of a series issued by the National Bureau of Standards on building materials and structures, presents the results of fire tests of steel building columns protected by gypsum lath and gypsum plaster, the latter in- corporating three different aggregates. Such materials are generally available

and are in common use in standard building practice.

The fire-endurance limits of protected columns described in this report may

serve as a guide for the selection of constructions to meet building-code requirements and as a measure of the extent of compliance of building practice with

existing codes.

A. V. AsTiN, Director.

Contents

Pago

Foreword ii 1. Introduction 1 2. Materials 1 2.1. Steel columns 1 2.2. Laths 1 2.3. Lathing accessories 2

2.4. Plaster 2

2.5. Aggregates 2

3. Construction details 3 3.L Thermocouple mounting 3

3.2. Column end protection 3

3.3. Assembly of plaster bases 3

3.4. Plastering 4

3.5. Aging 4

4. Test method and equipment 4

4.1. Specifications and end-point criteria 4

4.2. Column-testing furnace 7

4.3. Temperatures 8

4.4. Deformations 8

5. Results of tests 8

6. Discussion.. 12

6.1. Variations among test specimens 12

6.2. Plaster bases 12

6.3. Plasters 13

6.4. Plaster aggregates 13

6.5. Plaster thicknesses 13

6.6. Plaster reinforcement 13

6.7. Size of column 14

6.8. Workmanship 14

6.9. Effectiveness of combined and free water. . 14

7. References 14
Fire [Tests of Steel Columns Encased With Gypsum Lath

and Plaster

Nolan D. Mitchell and James V. Ryan

The results presented are those derived from fire-endurance tests of 1(5 steel cohuuns

encased with gypsum lath and gypsum plasters. The laths were wired into place ; those on eight columns were of the %-in. thick perforated type in a single layer, those on seven

of the other eight columns were of two layers of the Vj-in. thicli plain type, and on the other a single layer. Six of the latter eight also had a layer of wire fabric to reinforce the plaster. Expanded perlite was used as the plaster aggregate for 13 columns, sand for two, and vermiculite for one. The thickness of the plasters ranged from % in. to 2 in. and those of the encasements from "vs in. to 2% in. The fire-resistance values indicated by the tests varied with the composition, rein- forcement, and thickness of the protective coverings, and to some degree with the size of the column. The fire-endurance limits, as determined from the tests, ranged from 1 hr

23 min for a 10-in. steel H-section column protected with %-in. perforated lath and % in. of sanded gypsum plaster to 4 hr 42 min for one protected with two layers of %-in. lath, and a

1%-in. thickness of perlite-gypsum plaster reinforced with wire fabric.

1. Introduction

Tlie fire resistance of columns is considered of

l^rime importance in buildings. Building regulations usually require fire-resistive columns,

whether they support roof or floors. Columns are

also frequently used in conjunction with partitions or walls in the subdivision of large buildings into fire areas. The number of these areas

is determined by the required fire resistance which,

in turn, is governed by the type of construction

and the amount of combustible material involved

in the occupancy of the building. The fire-re- sistance ratings of columns or other building members are based upon the results of standard fire tests on representative constructions.

Inasmuch as gypsum laths and lightweight

jl plasters are extensively used as protective cover1 ings for steel structures, a series of fire tests of

; columns so protected was undertaken as a part of

I the program of i^esearch on building materials and

structures at the National Bureau of Standards.

Sixteen steel H-section columns encased with vari- ous combinations of gypsmn laths and plasters

comprised this series. Two of the 16 columns

were subjected to fire tests while under load.

2. Materials

The materials used in the test columns were of

j commercial quality typical of those normally used

i in building construction.

2.1. Steel Columns

I The steel columns were fabricated to the designs

I I shown in figure 1. Those to be subjected to test

'i without load are shown as A, and those for test under load as designs B and C. They were fabri-

; cated under contract by a local plant and the

workmanship was of good quality.

2.2. Laths

The thicknesses and breaking loads for the three

brands of long lengtli i/^-in. laths and five brands

of 16- by 48- by perforated gypsum laths

received, as well as the ASTM specification re- quirements for these characteristics, are given in

table 1. Two or more brands of laths were used as the i:)laster bases on each of 13 of the columns, for

the other three colimms, 273, 294, and 314, a separate brand was apiDliecl on each.

Table 1. Characteristics of gypsum laths

Lot 2

Thickness Load on bearing edge '

Nominal Measured

Across fiber Parallel to fiber

Average Mini- mum

Average Mini- mum

in. in. lb lb lb lb A, Yi 0. 532 162 161 47 47 A2 .495 162 148 57 52 As .500 155 154 43 42 Bi .484 148 142 43 42 B2 Yi .475 142 129 40 37 C Yi .507 122 117 42 39 D, y% .360 78 75 22 22

r)2 .380 74 71 37 35 Ds %

%

69 64 21 E, .359 78 75 24 22 Es y% .362 71 68 20 18 Es y% 71 61 19 IS

Fi % .357 81 80 24 22 F2 % 80 25 24 G Yi .390 85 82 3 22 21 H Yi .376 66 62 (*)

S5 Y2 . 500 ±0. 031 100 ICO 40 40

S5 . 375 ±0. 031 60 60 27 27

' The samples were tested under the methods specified in ASTM Designation: C37-50, except that in some cases the supply of lath was insuiBcient

to provide the five specimens required.

2 Lots A, B, and C were '4-in. unperforated laths, all others were of the %-

in. perforated type. All lots having the same letter designation were from the same manufactuier.

3 The results of strength tests of two of the five specimens of lot G, as tested

parallel to the fiber, were discarded because they differed by more than 15 percent from the average, as required by the test method.

i There weie no specimens of the sample from lot H available for the test

for strength with load applied parallel to the fiber.

5 Specification requirements of ASTM Designation: C37-50.
LIFTING EYE

LZl

I I

A. WELDED CONSTRUCTION

FOR NON-LOADED TESTS

B. WELDED CONSTRUCTION

FOR LOADED TEST

^MILL k-6

C. RIVETED CONSTRUCTION

FOR LOADED TEST

Figure 1. Details of steel test columns.

2.3. Lathing Accessories

The lathing accessories used included: woven

wire fabric, tie wire, expanded metal angles

(cornerite), corner beads, and staples.

The plaster encasements of six columns had 1-in. hexagonal mesh, 20-gage (0.036-in. diameter),

galvanized Avire fabric weighing 0.6 Ib/yd^ as reinforcement. The galvanized tie wire used by

the lathers Avas standard 18-gage, 0.04:2-in. diameter. The expanded metal angles were a commercial

product known as cornerite, fabricated from 6 in. wide strips of 2.5-lb/yd^ expanded metal lath

bent 90 degrees along the centerline. The corner beads were a solid nose type made from 26-gage

galvanized steel with 21^ -in. wide expanded metal

flanges. They weighed 190 lb/1,000 lin ft.

2.4. Plaster

Several lots of each of two brands of fibered

gypsum plaster were used. Each lot complied

with the requirements of Federal Specification

SS-P-402 for fibered neat gypsum plaster. The

physical and chemical properties of these two

f)lasters, as determined by the methods prescribed

in the specification and compressive strengths of

2-in. cubes prepared in the laboratory, are given

in table 2. 2.5. Aggregates

The three types of aggregates used, sand, perlite, and vermiculite as shoveled into a 1-ft^ measure, weighed, respectively, 100, 8.6, and 7.3 lb/ft^. Typical sieve analyses of the three are given in

table 3.

2
' "HERMOCOUPLE NUMBERS AND LOCATIONS FOR THERMOCOUPLE NUMBERS AND LOCATIONS FOR

reST COLUMNS NOT SUBJECTED TO LOAD TEST COLUMN NO. 279. WELDED TEST COLUMN

N0.280 HAD SAME THERMOCOUPLE ARRANGEMENT

Figure 2. Locations of theri>iocoitples on columns.

3. Construction Details

3.1. Thermocouple Mounting

Thermocouples were mounted on the flanges and

i webs of the steel columns at each of four levels,

I four at each level on those tested Avithout load, and

|i seven at each level on those tested under load, as shown in figure 2. The thermocouple wires were

laid along the column web, thence through a 1-in. pipe at the top to the instrument indicating temperatures.

3.2. Column End Protection

The columns for test without load were provided

I with steel plates to restrain the protective cover- ings of the column shafts from longitudinal ex- pansions greater than that of the steel column, as required by the standard method of test. These

plates were, in turn, protected from the furnace

fires by 5-in. thicknesses of pumice concrete. The

ends of the columns subjected to load were not sub1 jected to intense heat and therefore did not re-

' quire such protection.

3.3. Assembly of Plaster Bases

The %-in. laths, cut to width from 16- by 48-in.

pieces, were bound to the column shafts by four

ties of doubled wires to each 4 ft of column length,

as shown in figures 3 and 4. The %-in. laths, cut

to width and length from 24- by 120-in. pieces, were applied to seven of the column shafts in two

I' HA ui ' uiinnii.s in various sialics of iuihiiuj anil apijlication of corner bead.

Figure 4. Culiihin hip .sliniriin/ pcfforaicil lath, tics, cor- ner bead iritli metal lath extensions, and conteritc at junction betn-cen latit and cap.

3
Table 2. Characteristics of gypsum plasters

Chemical analysis

Lot

1 2 3 4 5 6 7 8 9 10 11 12

CaSO^'J^ II2O (computed from loss at 220° C) 83.1 80.1 83.8 87.2 84.2 93.0 93.6 94.7 88.2 94.7 94.9 91.7 CaSOf42H20 (from ammonium

acetate insoluble) 86.8 89. 8 83.9 83. 2 81.8 92.7 93. 7 94. 3 92.8 93. 3 94.6 89.3 CaSO< HH2O (computed from SO 3) % 85. 7 88. 6 84. 5 79.8 92. 4 93.

93. 3 93. 6 89.6 CaS04-}4 H2O (average) %-_ 85. 2 86.

83.8 85.0 81.9 92.7 93.6 94.5 91.3 93.8 94.4 90.2

Physical tests

Consistency for time of set.ml/100 g. _ 17 16 18?'3 mi 16;i 16 195^ 18 19 18 18 Time of set.._ hr _ 8 12 >8, <16 >9, <10 23 19 5 >8, <lbH 7 >9, <16 m >9, <16

Consistency for strength -.ml/100 g— 18?^ 18 22 211,^ 18 18 22 201/2 2m 2014 20^4 Tensile strength ' __lb/in.2.. 200 230 2 175 185 220 230 215 230 250 255 2 260 220 Compressive strength. __ ...lb/in.2_. 1,080 1, 320 980 1, 070 1,170 1,310 1, 340 1,410 1, 320 1, 450 1,600 1,210

' Average of 6, except as noted. 2 Average of 5.

Table 3. Sieve analyses of aggregates

Sieve desig- nation

Sieve analyses—percentage passing

Sand Perlite Vermiculite

4

6

812

14

202830

50 100 200

100 ""99"

100 98

09

93 ........

72 37

21

12

5 3

7

3

thicknesses, and to one in one thickness, and bound

with doubled wires spaced about 23 in. on centers. The Avire-fabric reinforcement for the plaster was wrapped horizontally outside of the gypsum

lath as applied to five of the columns and outside

the scratch coat of plaster as applied on a sixth

column, test 277. The longitudinal edges of the

fabric were fastened together with Avire ties. Details of the assembly of plaster bases and plaster are shown in figure 5. All the columns were provided with corner beads set as grounds to give the required thickness

of plaster. With one exception, the corner beads were fastened directly to the gypsum lath or to

strips of expanded metal lath if the flanges of

the corner bead were not Avide enough to fasten

to the lath. At least %-in. clearance was provided at each end of the corner beads to allow for

expansion. In addition to staples or nails fastening the corner beads or extension strips to the

gypsum lath, wire ties threaded through the

flanges of the corner beads and surrounding the

column secured the four corner beads at seven

levels on each assembly. See details in figure 4. In attempting to prevent the development of

openings between the protective coverings and

the caps of the columns, such as had occurred

during previous tests due to shrinkage of the gyp- sum during calcination, 3- by 2-in. angles of expanded metal lath were stapled to the gypsum

lath and attached by nails through the outstanding

leg to caps of columns 294, 302, and 308.

3.4. Plastering

The basic plaster of 1 in. or less thickness was

applied in a single rendering by the double-back

method. That of greater thickness was applied as

t wo distinct renderings with sufficient time between

for the first or scratch coat to set thoroughly, before the second or brown coat was applied. A

white-coat finish about YiQ-in. thick was applied

to each column to bring the surfaces even with the corner beads.

The proportions of the plaster mixes, the number of coats applied, the total thicknesses and the

strengths of 2-in. cubes made from the various

batches of the plasters as they were ready for

application to the individual columns are given in

table 4. 3.5. Aging

To condition the specimens for test, the plastered columns were allowed to stand for periods

of 26 to 67 days in a large, well-ventilated room

heated from 70° to 85° F. Each specimen was

weighed periodically until the rate of loss of

weight resulting from the drying of the plaster

became less than 1 lb a day. The 2-in. cubes pre- pared during the application of the plaster were

conditioned by placing them at the bases of the

columns and were tested on the same day as the

column.

4. Test Method and Equipment

4.1. Specifications and End-Point Criteria

The tests were conducted in accordance with

the Standard Methods of Fire Tests of Building

Construction and Materials of the American Society for Testing Materials, ASTM Designation

Eri9-47.

4
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CORNER BEAD STAPLED AND TIED TO LATH

TEST NO. 273

SANDED GYPSUM PLASTER DOUBLED

BACK ON PERFORATED GYPSUM LATH TIED TO COLUMN WITH DOUBLED 18 GA. WIRE I5"0.C.

CORNER BEAD STAPLED AND TIED TO LATH

I 2 TEST NO. 274

J

SANDED GYPSUM PLASTER DOUBLED

BACK ON PERFORATED GYPSUM LATH TIED TO COLUMN WITH DOUBLED 18 GA. WIRE I5"0.C.

CORNER BEAD STAPLED AND TIED TO LATH

TEST NO 275

22CUFT PERLITE TO I BAG GYPSUM DOUBLED BACK ON PERFORATED GYPSUM LATH

TIED TO COLUMN WITH DOUBLED 18 GA. WIRE I5"0.C.

CORNER BEAD STAPLED AND TIED TO LATH

10 49

LA- TEST NO 276

2:VCU FT PERLITE TO 1 BAG GYPSUM DOU"

BLEo'bACK ON 2 LAYERS OFGYPSUM LATH TIED TO COLUMN WITH DOUBLED 18 GA. WIRE 23"0,C. AND WRAPPED WITH l" HEX MESH 20GA.GALV. WIRE FABRIC.

CORNER BEAD TIED TO WIRE FABRIC

10 W^49 •

V LA- TEST NO 277

2 ^CU. FT PERLITE TO I BAG GYPSUM FOR

SCRATCH AND BROWN COATS ON GYPSUM LATH

TIED TO COLUMN WITH DOUBLED 18 GA. WIRE 23" D C. WRAPPED WITH I" HEX MESH 20GA.GALV. WIRE FABRIC OVER SCRATCH COAT

CORNER BEAD TIED TO

, LATH WIRE TIES

I0W^49 FOR TESTS

2 78,280 AND 294 6H20 FOR TEST 279

TESTS NO.278,279,280,294

2 CU. FT PERLITE TO I BAG GYPSUM FOR SCRATCH AND 3CU.FT PERLITE TO I BAG GYPSUM

FOR BROWN COAT ON 2 LAYERS OF GYPSUM LATH

TIED TO COLUMN WITH DOUBLED 18GA.WIRE23"

O.C. AND WRAPPED WITH l"HEX MESH 20 GA. GALV WIRE FABRIC. TEST 294 USED VERMICULITE.

Figure 5. Cross sections of protective coverings for test columns.
CORNER BEAD STAPLED AND TIED TO LATH

CORNER BEAD STAPLED AND TIED TO LATH

TESTS NO. 288,292,302

2 CU.FT PERLITE TO I BAG GYPSUM FOR SCRATCH AND 3CU. FT PERLITE TO I BAG GYPSUM

FOR BROWN COAT ON PERFORATED GYPSUM LATH

TIED TC| COLUMN WITH DOUBLED 18 GA. WIRE I5"0.C.

TESTS NO 289,293

2 CU.FT PERLITE TO I BAG GYPSUM FOR SCRATCH AND 3CU,FT PERLITE TO I BAG GYPSUM

FOR BROWN COAT ON 2 LAYERS OF GYPSUM LATH

TIED TO COLUMN WITH DOUBLED 18 GA.WIRE 23"O.C.

CORNER BEAD LAPPED l OVER

AND WIRED TO 3"X B'-O" STRIPS OF METAL

LATH STAPLED TO GYPSUM LATH CORNER BEAD CUT,FOLDED AND STAPLED TO LATH AT 6" INTERVALS

10 W^49'

V~TEST NO. 308

2 CU.FT PERLITE TO I BAG GYPSUM FOR SCRATCH AND 3 CU.FT TO I BAG GYPSUM FOR BROWN COATS ON PERFORATED GYPSUM LATH

TIED TO COLUMN WITH DOUBLED 18 GA.WIRE I5"0.C.

TEST NO. 314

2 CU, FT PERLITE TO I BAG GYPSUM FOR SCRATCH AND 3 CU.FT TO I BAG GYPSUM FOR BROWN COATS ON PERFORATED GYPSUM LATH TIEDTO COLUMN WITH DOUBLED I8GA.WIRE I5"0.C

Figure 5. Cross sections of protective coverings for test coluiuns—Coutiuued

These methods require that the cohimiis be ex- posed on all sides to furnace tires controlled to have average temperatures of approximately

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; 2,300° F at 8 hr or over. Fourteen of the columns were tested without

load, in which the conditions of acceptance re- quire that the average temperature of the steel at any one of the four levels shall not exceed 1,000°

F (538° C), and that at any one measured point

shall not exceed 1,200° F (649° C), during the

period for which classification is desired. The

fire-exposed length of the column is specified to be at least 8 ft. The other two columns were

tested under load, a method which requires that

the exposed length be not less than 9 ft and that

the column sustain the applied load during the

fire-endurance test for a period equal to that for

which classification is desired.

4.2. Column-Testing Furnace

The tests were made in a gas-fired furnace which

Avas equipped with a hydraulic jack for applying

loads, as shown in figure 6. The hydraulic pres- sure Avas controlled by a motor-driven rotary

pump and a spring-loaded pressure-regulating

valve, thus raising or lowering the movable fur- nace floor, which rested on a spherical bearingblock on top of the jack. Tlie fluid pressures used

weie determined by the loads required to be

imposed on the columns.

To accommodate the 10-ft 4-in. effective length

of the loaded column, a brick chamber was built

above the furnace roof slab. A framework of

steel beams provided a fixed bearing for the upper

end of the column. Tlie bases of the columns and

the furnace floor were covered with loose perlite.

7
6-1 BEAMS 24" 80"

InnrnL MACHINED BEAMS 9" 90-5**

1

1 •;

TOP SEARING PLATE

FLANGE COVER PLATES

r-8Vr-B"Xl?g BEARING PLATE

- SPHERICAL

BEARING BLOCK

25" RADIUS

60'X45" REINFORCED CONCRETE FOUNDATION

FiGXJEE 7. Ill i)rc>:r)itatiL'c nonloadcd coliiiiiii in furnace

before test.

Figure 6. Column-test furnace. A column representative of those tested without

load is shown as installed in the furnace for test in figure 7. 4.3. Temperatures

TAA'elve thermocouples were located in the fur- nace—four suspended from the ceiling and two

protruding from each of the four walls. The

thermocouples were pi'ovided with porcelain in- sulators and enclosed in iron tubes with the junctions about 24 in. from the test column. The pyrometer arrangements were completed by connecting

the thei^mocouples to an indicating potentiometer.

The furnace temperatures were recorded at 5-min

intervals during the first 2 hr of the tests and

at 10-min intervals thei-eafter. The temperatures at selected locations in the

column shafts were determined at regular intervals throughout the test by means of thermocouples, previously described, and a potentiometer.

4.4. Deformations

Movement of the piston of the hydraulic jack as observed on a dial indicator was taken as a measure

of the longitudinal deformation of the column

under load. Measurements made during previous tests indicated that the thermal expansion of

the vertical frameAvork was closely compensated

by the expansion of the unexposed section of the

column and the thermal deflections of the over- head beams supporting the upper bearing plate.

No measurements of lateral deflections of the col- umns were made during or after test.

5. Results of Tests

Table 4 summarizes the characteristics of the

test specimens and results of the tests. A general pattern of behavior was observed in

all the tests. A network of fine craze cracks

covering the plaster surface and thin cracks parallel to and about 1 or 2 in. away from the corner beads developed early in the tests. The latter extended over the full exposed length of the protective covering and by midtest had grown to widths ranging from % to I/2 in., with evidence of

curling of the whitecoat finish along the edges of

the plaster. Usually, too, by midtest shrinkage oi

the column covering caused it to begin separating

from the column cap, thus creating an opening all around the column. In comparison with the other

cracks, these oi^enings widened more rapidly

during the rest of the test and are considered to have contributed to hastening the failure of the

coverings protecting the steel. The widths of

these openings at the times the column-shaft temI^eratures reached the allowable limits were esti8
Figure 8. Representative column ivithout comerite at

top, after test.

' mated to range from i/o to 2 in., not excepting those

columns liaving cornerite and plaster intended to

• cover the opening. See figures 8 and 9. Because

of the narrowness of these openings and their position on the column, they were probably a minor

factor in the failure of the columns tested under

load. Shrinkage of the type mentioned above is characteristic of gypsum exposed to fire [1, 2,

3, 4].^ Graphs of the furnace and column temperatures observed in a representative selection of

. tests are given in figures 10, 11, 12, and 13.

! In no test did any significant amount of plaster

covering fall before the limit of temperature had

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

Fiouia: '). Ri iirvs( II III I i re ro/iiiiiii irilli curiirrHc at top, after test. Other than the cornerite, the construction of the column was

the same as that of the column shown in figure S. Fire ex- postures were of the same length. been reached, notwithstanding tlie large cracks

parallel to the corner and the bulging of the plaster and plaster bases, as shown in figure 11. In

three instances, however, soon after the permis.-ible

temperature limit of the steel had been reached,

the coverings fell, exposing a large part of the

steel column shaft to the fire, as shown in fiuure 15

[2,4].

In test 280, because of undue heating of oil in the hj'-draulic systein, difficulty was encountered in

maintaining the load. Consequently, the load was

reduced to about half value when the average

temperature of the steel was 212° F (100^ C),

9
llj X

<enLU

CL

TIME, HOURS

FiGUBE 10. Temperatures observed in colanui tests 273 and 274. Columns with sanded gypsum plaster.

2400 2300

2200

2100 2000

1900

1800

1700

1600

1500 1400

1300 1200

1100 1000 900

800

700 600

500 400

,300 200

1000

TEST NO, 278

I iEFE ,ECJRV E /

V

z

X

o

o

OMIN

- X f o

o r 1 /

i

MAX BY ANY THERMOCOUPLE^"^MIN BY ANY THERMOCOUPLE

^AVG AT LEVELT

Ul3

LU

CL

2 3 4 5 6 TIME , HOURS

Figure 31. T< iiiiierdtiires ohscrved in colinini test 278.

Perllte gypsum plaster and wire fabric reinforcing.

10

Figure 14. Loaded, 10-in. column in furnace after test. The bulging in the plaster near the bottom was observed in a few

of the uonloaded columns.

resulting in the behavior shown in figure 16. The

full load was reapplied at 4 hr 27 min when

buckling of the column covering indicated the approach of the fire-endurance limit, at which time

the temperatures of the steel averaged slightly over 716° F (380° C). Failure under load oc- curred soon thereafter, at which time the highest

temperature at any thermocouple was 1,058° F

(570° C).

6. Discussion

6.1. Variations Among Test Specimens

The variations included among the test specimens, which should be considered with respect to

12

Figure 15. One of three columns from ivhich lath and > plaster fell after reaching limiting conditions. t

their influence on the test results, are those in i such items as plaster bases, gypsum-cement plas- , ters, plaster aggregates, plaster thicknesses, plas- 1 ter reinforcement, size of columns, and workman- , ship. Evaluation of the effects of certain of these

items can be made by comparing the results

obtained from specimens differing in one major

resjDect, whereas others can be evaluated only

indirectly [5].

6.2. Plaster Bases

Only gypsum laths were used as plaster bases on the columns for the series of tests covered in

this report. Those on eight columns were single

thicknesses of %-in. perforated laths. Those on ;
TEMPERATURE °F

200 400 600 800 1000 — -t — i- —It -t- —rt- M"-p-jt

-Ai-\

/

'- 4-l- A -

1 V — t-- V- —1/ -I / V -f-[l

I -L 280 s 4- /> 4

/

279 ± I

1 4-

L- /

1

-t --t I i i

/ —»

-A f

r I

0 100 200 300 400 500

TEMPERATURES

1 FiGtTEE 16. DeforiHatio7is of loaded columns with in- crease of temperature.

I The sudden jump in the curve from, test 280 resulted when mei chanical difficulties made it necessary to reduce tlie load to about

half value. The load was restored to full intensity after the temperature of the steel had risen to 716° F at the hottest section.

t seven columns were double thicknesses of the

i/^-in. plain lath, and that on the other column was a single thickness. Two thicknesses of i/^-in. thick lath were used on the column for test 276

and a single thickness on that for test 277. These

columns had protections of the same total thickness, 2 in. The first had a fire-endurance limit of

|i 3 hr 50 min, whereas the limit in test 277 was

X'eached at 3 hr 39 min. This difference is in

agreement with previous findings that the gypsum

board, on the basis of a given thickness, affords

slightly greater resistance to heat penetration

than an equal thickness of perlite plaster. From

' the derived data, no comparison can be made on

I the relative effectiveness of %-in. perforated lath

I and the i/2-in. plain lath.

I 6.3. Plasters

I The plaster was composed of gypsum-cement

plasters, produced by two manufacturers, mixed

with selected plaster aggregates. Distinct differ- ences in the hemihydrate content of the plasters

, produced by these manufacturers did not usually

enter into the results, inasmuch as the two plasters were mixed together, bringing the hemihydrate

content to about 90 percent in all specimens except

that of test 314, in which only plaster from lot 11

(table 2), having a hemihydrate content of 94

l^ercent, was used. It is probable that a part of

the 1-hr increase in the protection afforded by

the covering of test 314 over that of 308 resulted

from the differences in the plasters used. The

random manner of cracking of the protective coverings, as influenced by the plasters, may also

have played a part in the differences observed

among the results.

6.4. Plaster Aggregates

The three aggregates differed slightly in effec- tiveness as components of fire protective coverings. On the basis of the I'esults obtained from

tests 273 and 274 in comparison with tests 288,

292, and 302, it was found by plotting the thick- ness of covering versus time to failure on log log

paper that the plaster made with perlite aggregate and applied on %-in. gypsum lath gave protection of the steel one-fourth longer for a given

thickness than did the plaster made Avith sand

aggregate [4]. However, an exception must be

noted for the results from test 308, in which the

effectiveness of the perlite gypsum mixture approximated that of the sanded plaster, tests 273

and 274, if compared on the basis of a common

thickness.

The slight difference in the results obtained

Avith plaster having vermiculite aggregate (test

294) and those obtained with perlite (tests 278

and 280) can possibly be attributed to the quality

of workmanship of the column encasement for

test 294 rather than to the plaster aggregate. This

is discussed later under "workmanship."

6.5. Plaster Thicknesses

The tests were not well adapted to making determinations of the relative effectiveness of the

coverings with relation to total thicknesses. The

difference in the thickness of the sanded gypsum

plaster plus lath (tests 273 and 274) was only

% in. The coverings appeared to slump as the

result of shrinkage due to calcination of the gyp- sum and to expose the steel before they had served

to their full capacity as protections. It is probable that the opening of the relatively large cracks

at the top of the protective coverings brought

about a more rapid rise in the temperature of the

column than would otherwise have been observed.

This effect was more noticeable in the tests of

columns without wire-fabric reinforcement in the

coverings.

6.6. Plaster Reinforcement

The effectiveness of reinforcement for the plaster can be seen by comparing the average of the

results obtained in tests 289 and 293 with the aver13
age of results obtained in tests 278 and 280. 'By

extrapolating graphically on the basis of the etfec- tiveness of the reinforced plaster, an increase of

54 niin, or 24 pei cent, in time to failure was found

from the nse of wire-netting remiforcement in 2i/^- in. thick coverinj^'s. Properly designed reinforcement increases tlie reliability and efficacy of gyp- sum protective coverings hj insuring that they

remain in place [2, 4]

If the results of test 302 or 288 are compared

with those obtained in test 276, by extrapolating

from the 1%-in. thickness of 302 to 2 in., the thick- ness of the covering for test 276, it is found that

the increased protection attributable to the reinforcement is 67 min, or 40 percent.

All the reinforcement used in the tests Avas wrapped around the column. In view of the difference in resistance to compression in the trans- verse and longitudinal directions of the wire fabric, it is probable that better results could have

been obtained with the fabric a])plied as continu- ous strips from top to bottom of the column, thus

providing less opportunity for the sag of the plaster to open wide cracks at the top cap, such as are

illustrated in figures 8 and 9.

6.7, Size of Column

The only opportunity to study the effect of size of column is by comparison of the results obtained

in tests of columns under load, namely, 279 and

280. It has been found in fire tests of columns

with monolithic protections, that the smaller the

roliunn the less resistant a given thickness of cov- ering [2]. In this instance, the 6H20 column with

21/^ -in. thickness of covering failed 18 min, or 10

percent, sooner than did the 10WF49 column of

the same length having the same thickness of

protective covering.

6.8. Workmanship

The quality of workmanship found in the plastering of the column for test 294 was somewhat

inferior to that in the plastering of the similar

column, test 278. At least one of the corner beads

of the former had little plaster between the ex- panded metal flanges, and the earlier failure of

this column by 26 min, or 9 percent, in time might

be attributable, in large measure, to this apparent

defect. Continuous strips of expanded metal lath were attached to the wings of the corner beads for

column 308 to extend their Avidth to allow for a

2-in. thickness of plaster. Because of the double

thickness of these wings, it is suspected that the

expansion of the metal produced wider than usual

cracks through the plaster and in consequence the

covering afforded less protection than should have

been expected. The other test constructions had

the spaces between the flanges of the corner beads

Avell filled.

6.9. Effectiveness of Combined and FreeWater

A characteristic of hydrated gypsum plaster is the relatively large amount of chemically combined Avater in the crystallized gypsum. This

water can be driven off by heating the plaster.

The dehydration process begins at temperatures

about that of boiling Avater. The effectiveness of

the process of driving off Avater in retarding the

heating of the columns under test can be seen in

figures 10, 11, 12, and 13, wherein it is observed

that the temperature of the steel column shafts

i-emained at or near steam temperatures, ranging

from about 10 min for the column Avith %-in.

thick gypsum protective covering to 100 min for some of the columns having 2i/2-in. thickness of

covering. The heat-retarding effect up to this

])oint A^aried approximately as the square of the

thicknesses of the protectiA^e coverings. The pro-

])ortion of the amount of this effect that resulted

from chemically combined water to the amount

resulting from free Avater remaining in the i^laster and the lath was not determined by the tests. This

dehydration characteristic is found in few other

building materials to such a large degree as in gy])sum.

7. References

[1] W. A. Hull, A comparison of the heat-insulating propei'ties of some of the materials used in fire-resistive constructions, NBS Tech. Pap. 130 (1919).

[2] S. H. Ingberg, H. K. Griffin, W. C. Robinson, R. E. Wilson, Fire tests of building columns, NBS Tech.

Pap. 184 (1921).

[3] W. A. Hull and S. PI. Ingberg, Fire resistance of concrete columns, NBS Tech. Pap. 272 (1925).

1 4] Nolan D. Mitchell, Fire tests of columns protected

with ijyjisum, ES .J. Research 10, 737 (1933) KP.56.3, [5] Fire-resistance classifications of building constructions, NBS Building Materials and Structures Report 92 (1942).

[6] Nolan D. Mitchell, Fire tests of steel columns protected with siliceous aggregate concrete, NBS Building Materials and Structures Report 124 (1951).

Washington, October 13, 1952.

14 U. S. GOVERNMENT PRINTING OFFICE: 19S3
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS36 Structural Properties of Wood-Frame Wall, ParititioDj^Floor, and Roof Constructions With ''Red Stripe" Lath Sponsored by The Weston Paper and Manufacturing Co 10^ BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co 10^ BMS39 Structural Properties of a Wall Construction of "Pfeifer Units" Sponsored by the Wisconsin Units Co . . ^. lOjS BMS44 Surface Treatment of Steel Prior to Painting- OP*

BMS45 Air Infiltration Through Windows.. 15^ BMS47 Structural Properties of Prefabricated Wood-Frame Constructions for Walls, Partitions, and Floors Sponsored by American Houses, Inc 20fi BMS48 Structural Properties of "Precision-Built" Frame Wall and Partition Constructions

Sponsored by the Homasote Co 15^ BMS49 Metallic Roofing for Low-Cost House Construction 20^ BMS50 Stability of Fiber Building Boards as Determined by Accelerated Aging 10^ BMS51 Structural Properties of "Tilecrete Type A" Floor Construction Sponsored by the

Tilecrete Co 10$5 BMS52 Effect of Ceiling Insulation Upon Summer Comfort 15^ BMS53 Structural Properties of a Masonry Wall Construction of "Munlock Dry Wall Brick"

Sponsored by the Munlock Engineering Co ^ lOfi BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler lOfi BMS55 Effects of Wetting and Drying on the Permeability of Masonry Walls OP*

BMS58 Strength of Soft-Soldered Joints in Copper Tubing 10^ BMS60 Strength, Absorption', and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 30^ BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by

the Portland Cement Association.-.. 15(i BMS63 Moisture Condensation in Building Walls 15^ BMS65 Methods of Estimating Loads in Plumbing Systems 15(S BMS66 Plumbing Manual 35^ BMS67 Structural Properties of "Mu-Steel" Prefabricated Sheet-Steel Constructions for Walls,

Partitions, Floors, and Roofs, Sponsored by Herman A. Mugler 15^ BMS68 Performance Test for Floor Coverings for Use in Low-Cost Housing: Part 3 20^ BMS69 Stability of Fiber Sheathing Boards as Determined by Accelerated^Aging 10^ BMS70 Asphalt-Prepared Roll Roofings and Shingles 20i

BMS71 Fire Tests of Wood- and Metal-Framed Partitions. OP*

BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co . 10^ BMS73 Indentation Characteristics of Floor Coverings 10^ 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 20ji BMS75 Survey of Roofing Materials in the North Central States 15^ BMS77 Properties and Performance of Fiber Tile Boards _._ 10^ BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

Construction , 25jS BMS79 Water-Distributing Systems for Buildings i 20^ BMS80 Performance Test of Floor Coverings for Use in Low-cost Housing: Part 4 15<i BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5 x 7 inches) 30f5 BMS82 Water Permeability of Walls Built of Masonry Units. 25^

BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 15^ BMS84 Survey of Roofing Materials in the South Central States 15^ BMS86 Structural, Heat-Transfer, and Water-Permeabilit-7 Properties of "Speedbrik" Wall

Construction Sponsored by the General Shale Proclucts Corporation 15j5 BMS87 A Method for Developing Specifications for Building Construction—Report of Subcommittee on Specifications of the Central Housing Committee on Research, Design,

and Construction 20^ BMS89 Structural Properties of "Precision-Built, Jr." (Second Construction) Prefabricated

Wood-Frame Wall Construction Sponsored by the Homasote Co 15ft BMS90 Structural Properties of "PHC" Prefabricated Wood-Frame Construction for Walls, Floors and Roofs Sponsored by the PHC Housing Corporation. 15f5 BMS92 Fire-Resistance Classification of Building Constructions SOji •Out of print. [List continued on cover page iv]
BUILDING MATERIALS AND_ STRUCTURES REPORTS

[Contmued from cover page ui]

BMS94 Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" WaUs... - . — 15* 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 10^ BMS99 Structural and Heat-Transfer Properties of "Mutiple Box-Girder Plywood Panels" for Walls, Floors, and Roofs . . 15ji BMSlOO Relative Slipperiness of Floor and Deck Surfaces 10^ BMSlOl Strength and Resistance to Corrosion of Ties for Cavity Walls 10^ BMS102 Painting Steel - 10^5 BMS103 Measurements of Heat Losses From Slab Floors 15* BMS105 Paint Manual With Particular Reference to Federal Specifications $1. 25

BMS106 Laboratory Observations of Condensation in Wall Specimens. 10^ BSM108 Temperature Distribution in a Test Bungalow With Various Heating Devices 15^> BMSlOO Strength of Houses: Application of Engineering Principles to Structural Design . $1. 50 BSMllO Paints for Exterior Masonry Walls 15* BMSIU Performance of a Coal-Fired Boiler Converted to Oil - 15yt BMS112 Properties of Some Lightweight-Aggregate Concretes With and Without an Air- entraining Admixture lOfi BMS113 Fire Resistance of Structural Clay Tile Partitions: : 15^ BMS114 Temperature in a Test Bungalow With Some Radiant and Jacketed Space Heaters , 25fi BMS116 A Study of a Baseboard Convector Heating System in a Test Bungalow 20f4 BMS116 Preparation and Revision of Building Codes :__ . 15^ BMS117 Fire Resistance of Walls of Lightweight Aggregate Concrete Masonry Units 20^ BMS118 Stack Venting of Plumbing Fixtures . 150 BMS1 1 9 Wet Venting of Plumbing Fixtures . . - 200 BMS120 Fire Resistance of Walls of Gravel-Aggregate Concrete Masonry Units 150 BMS121 Investigation of Failures of White-Coat Plasters . 250 BMS122 Physical Properties of Some Samples of Asbestos-Cement Siding . 150 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 Atmospheric 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 - 150 BMS132 Capacities of Plumbing Stacks in Buildings 200 BMSI33 Live Loads on Floors in Buildings.. 200

BMS1 34 Fire Resistance of Concrete Floors -. 150 BMS135 Fire Tests of Steel Columns Encased With Gypsum Lath and Plaster 150