Natioral Bureau of Standards

Library, N. W. BIdg.

AUG 1 9 1952

Fire Tests of Steel Columns Protected With

Siliceous Aggregate Concrete

United States Department of Commerce

National Bureau of Standards

Building Materials and Structures Report 124
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UNITED STATES DEPARTMENT OF COMMERCE . Charles Sawyer, Secreiary

NATIONAL BUREAU OF STANDARDS • E. U. Condon, Dirtclor

Fire Tests of Steel Columns Protected With

Siliceous Aggregate Concrete

Nolan D. Mitchell

Building Materials and Structures Report 124

Issued May 25, 1951

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 four

steel building columns protected by concrete made with certain highly siliceous

aggregates. The results of the column tests were further confirmed by tests on concrete walls made with the same aggregates. Such materials are available

in wideh" distributed areas, and are common constituents of much of the

commercialh" available concretes. 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

requu'ements, and as a measure of the extent of compliance of building practice

with existing codes.

E. U. Condon, Director.
CONTENTS

Page Foreword ni

I. Introduction - 1 II. Materials 2

1. Steel columns 2

2. Concrete 2

III. Construction of columns 4

1. Placement of concrete 4

2. Workmanship 4

3. Seasoning of concrete 4

IV. Equipment and method of testing 5

1. Equipment 5

2. Method of testing 5

(a) Bearing of columns 5

(b) Restraint of columns 5

(c) Loads on columns 5

(d) Measurement of deformations 5

(e) Test specification t 5 V. Results of tests 6

1. Columns 1 and 2—Potomac River gravel aggregate concrete protections. _ 6

2. Columns 3 and 4—Milky and clear quartz aggregate concrete protections. 6 VI. Summary and discussion 6

IV
Fire Tests of Steel Columns Protected

With Siliceous Aggregate Concrete

Nolan D. Mitchell

Results of fire-endurance tests of four 6-in. steel H -columns protected with concrete made with highly siliceous aggregates are presented.' The concrete was of 2-in. thickness around the column shaft and filled the reentrant spaces. The aggregates investigated were

river gravel and crushed quartz.

The columns were subjected to load throughout the tests. The loads on three columns

of magnitude as computed by a standard formula for allowable load were constant. One

column sustained a double load throughout the earlier part of the test. The fire-endurance limits ranged from 2 hr 50 min for a column with crushed quartz

aggregate concrete to 3 hr 34 min for one with gravel aggregate concrete. The results were

consistent for columns protected with gravel aggregate concrete, and within reasonable limits

for columns covered with quartz aggregate concrete. The results of the column tests with respect to lack of spalling of the concrete were

confirmed by tests on concrete wall slabs made with the same or like aggregates.

I. Introduction

Fix'e-endurance tests were conducted at the

National Bureau of Standards on four 6-in. 20-lb

H -columns having protective coverings of siliceous

aggregate concrete. The aggregate for the concrete on two columns was Potomac River sand

and gravel, on the third crushed milky quartz,

and on the fourth clear crushed quartz. These

aggregates are widespread both in distribution and

use and are available in the vicinity of Washington,

D. C.

The information developed by these tests supplements that derived from the tests of columns

with concrete coverings included in the series of

tests conducted jointly by the Associated Factory

Mutual Fhe Insurance Companies, the National

Board of Fire Underwriters, and the National

Bureau of Standards, at Underwriters' Laboratories, Chicago, in 1917-18.^ Related through use

of siliceous aggregates are the fire tests of concrete columns conducted at the former Pittsburgh test- ing station of the National Bureau of Standards.^

In the early tests, it was observed that column

protections of concrete made with highly siliceous

gravel aggregates cracked and spalled so as to expose the steel shaft or reinforcing of the column

before its temperature had reached the critical range for failure xmder load. Further, siliceous

aggregate concrete monolithic floors and walls

showed varying and contradictory behavior in

fire tests. To illustrate, a 6-in. -thick concrete

1 The term "siliceous" as used herein conforms to the usage in building codes in which it is construed to embrace the minerals composed wholly or largely of quartz, chert, flint, etc.

- Fire tests of building columns, Underwriters' Laboratories, 1920; also published as B. S. Tech. Pap. T184 (1921).

3 Fire resistance of concrete columns by W. A. Hull and S. H. Ingberg, B. S. Tech. Pap. T272 (1925).

floor slab made with Potomac River gravel concrete began spalling within 35 min after the start of the fire-endurance test. At 1 hr 45 min the

fire had penetrated through a large hole formed

in the spalled area. However, another floor specimen and three wall specimens made of concrete

having aggregate from the same source showed no

tendency to spall. The best surmise possible

from the meager data was that the spalling could

be due to the disruptive effect caused by superheating of water entrapped in the dense concrete. The tests of columns at the National Bureau of

Standards were for the purpose of again investigating the reaction of siliceous aggregate concretes to fire exposure, especially under the conditions of high stress peculiar to column encase- ments. To supplement the tests on the columns

encased with siliceous aggregate concrete, results are given for four walls constructed of similar concretes. Three of these were made with

Potomac River gravel and one with the crushed

quartz that served as both the fine and coarse aggregates for the coverings of two of the fom*

columns.

The columns, which were alike in size, were

tested under an allowable load computed from a formula recommended by the American Institute

of Steel Construction. However, as no tendency

of the concrete to spall was evident in the first test, the second of the columns with gravel

aggregate concrete protection was subjected to twice the load of the other columns until a specified

temperature of the steel was attained to determine

whether excessive strain would induce spalling

of the encasement, after which the load was re931035—51 1
duced to that of the formula and maintamed until

failure had occurred.

The failure of silica gravel concrete protection

observed early in the test at the Underwriters'

Laboratories was not duplicated in the present

tests. The fire-endurance limits for the columns

of this series ranged from 2 hr 50 min to 3 hr 34

min.

It should be noted that, although both groups of

tests used concrete made with siliceous aggregates,

there was dissimilarity in composition of the

aggregates of the two groups. The aggregates

of the concrete that failed earliest in the tests at the Underwriters' Laboratories contained 98

percent of chert, whereas the aggregate for the

concrete used for the present tests consisted

of either a mixture containing principally quartz,

sandstone, and quartzite, with only a minor

quantity of chert or a relatively pure crushed

quartz. Also, despite the general assumption of

poor performance of siliceous aggregate concretes, columns protected with this material

have shown a reasonable resistance to fire. This

is indicated by tests made at the Underwriters'

Laboratories where an 8 in. column protected with

2 in. of sandstone concrete showed a fire-endurance

limit exceeding 4 hr, even though considerable

cracking and spalling of the concrete had occurred

early in the test.

II. Materials

1. Steel Columns

The column shafts were fabricated from 6-in. 20-lb stanchion sections 5.97 in.^ in area. The

heads of the columns were restrained for 32 to 33

in. by K-in. plates of two types, leaving an effective

column length of 124 in. End fittings were so applied as to allow the milled ends of the column

shafts to rest directly on the 1%-in.-thick planed

steel bearing plates. The column fitting assemblies were made with hot rivets. The least radius of gyration of the columns was 1.5 in. and

the l/r ratio was 82.67. Figure 1 shows a column

in place after a fire test. The details of the

column shafts are shown in figure 2.

2. Concrete

The concrete for encasing the first two columns

of the tests was made of 1 part of portland cement,

2% parts of Potomac River concrete sand, and

3K parts of Potomac River gravel. Equal parts

of two sizes of screened gravel were mixed to produce the coarse aggregate. The densities of

the sand and screened gravel were determined,

and the batches were proportioned by weight of

materials. A typical batch consisted of 94 lb (1 bag) of cement, 300 lb of damp sand, 197 lb of fine

gravel, 181 lb of coarse gravel and 6% gal water. The sieve and petrographic analyses of the

aggregates used in the concretes are shown in

table 1.

Table 1. Sieve and petrographic analyses of concrete aggregates

Sieve designation

Sieve analysis of concrete aggregates—percentage retained

Poto- mac

River

gravel

Poto- mac

River sand

Clear crushed

quartz

Milky

crushed

quartz

Clear crushed

quartz sand

Milky

crushed

quartz sand

f'i in.. . . 0.0

a 50.0

50.0

0.0

.0

.0

.0

.0

.0

0.0

.0 4.9

19.5

13.7

13.2

22. 5 18.8 7.4

0.0

1.7 40.3

63.7 3.4

0.2

. 1 .2

.4

0.0

1.2 42.6

53.5

2.1 0.1

. 1

. 1 .3

0.0

.0

.0

.0.2

5. 7

42. 1 38.5

13.6

0.0

.0

.0

. 1

. 1

2. 2 61.7 29.6

6.4

% in No. 4 No. 8 No. 16 No. 30 No. 50 No. 100 Pan_..

Minerals Petrographic analyses of concrete aggregates: Mineral

content—percent

Vein quartz

Quartzite Sandstone

2138

23

12

90 100 100 100 100

Chert Mica - 4 other, C

b 6

Figure 1. A test column in furnace after fire exposure.

» Potomac River grarel screened to size.

b One or more of the following: chlorite, magnetite, schist, gneiss. In the tests, the third and fourth columns were

covered with concrete made with fine and coarse aggregates of relatively high purity; that for one was of milky quartz, the other of a clear variety.

Photomicrographs of these materials, figure 3,
H" HOLES

FOR I' BOLTS

tI'holes forTbolts

6"X4"xi ANGLES

6 H 20 STANCHION

i RIVETS

{I HOLES FOR I' BOLTS

-2i

TESTS I AND 2

MILL

II'holes for i" bolts

I iDIA. slotted hole

TESTS 3 AND 4

Figure 2. Details of columns.

show small inclusions. Because of the unusual

grading of the coarse quartz aggregate, a workable

mix was found to have the proportions approximately 1 part of cement, 3 parts of sand, and 2 parts of coarse aggregate. The batches were

proportioned by weight and consisted of 94 lb

(1 bag) of cement, 293 lb of quartz sand, and 195

lb of crushed quartz.

Each batch was mixed for not less than lyi

min dry and 2 min wet. Three test cylinders were cast from each of four batches of Potomac

River aggregate concrete and three each from

the single full batches of the milky and of|the

clear-quartz aggregate concretes. The water_^was

controlled to give slumps of concrete in the range

of 6 to 8 in. The average compressive strength of the cylinders of Potomac River gravel aggregate concrete was 2,580 Ib/inl The average batch strengths

ranged from 2,240 to 2,800 Ib/inl The initial tangent modulus of elasticity of six cylinders was 2.97X10'' lb/in I The modulus determined

from stress-strain relations at a working load of

1,600 lb/in.2 was 2.03X10'' Ib/inl

For the concrete made with milk}^ quartz

aggregate, the average compressive strength of three cylinders was 1,930 lb/in l The initial

3
Figure 3. Photomicrographs of crushed quarts aggregates showing inclusions or voids (X96): A, milky; B, clear.

tangent elastic modulus as determined on one

cylinder was 2.8X10'^ Ib/in^. The three cylinders made with clear quartz aggregate concrete had an average compressive strength of 2,600

Ib/in^. The modulus of elasticity for one of these

cylinders determined from the initial tangent was 2.6X10^ Ib/in^

In all of the tests, a No. 8 SWG wire (0.16 in.

in diameter) wound spirally around the column

on an 8-in. pitch provided anchorage for the concrete covering. The wire spiral had 1-in. clearance at the midwidths of the column flanges,

leaving a distance of 1 in. from the wire to the

outside surface of the concrete. Thus the wire was covered with 1 in. of concrete at the midwidth

of each of the four sides of the column.

III. Construction of Columns

1. Placement of Concrete

Plywood forms were spaced 2 in. on all sides

from the vertically placed column shafts. Concrete poured into the tops of the forms was compacted around the columns by vibrating the sides

of the forms with an air hammer. The few small

voids, visible after the forms were removed, were

filled with a cement and sand mortar.

A 4- by 8-ft. by 4-in. -thick wall slab was poured

from the same batches of the clear and of the

milky quartz aggregate concretes that were used

for the column coverings. The slab was divided

into quarters with the sections of like aggregate

concrete diagonally opposite each other.

2. Workmanship

The steel columns were of good commercial

quality of fabrication. The concrete was of ordinary good worlonanship with a mixing time ex- ceeding that of the prescribed minimum, and was

well placed with the exception that the form

around the enlarged portion of the top of one column was tlirough inadvertence laterally dis- placed about 1 in. As this imperfection occurred

in the upper restrained portion of the column,

well above the section under test, it was thought

incapable of adversely affecting the results.

3. Seasoning of Concrete

The forms were stripped from the columns

encased with Potomac River gravel concrete on

the fifth day after pouring. The columns were

kept moist for 8 days. Beginning the ninth day

after removal of forms, the weights of the colimins were checked until such time as drying was essentially complete. In 30 days, concrete that weighed

approximately 2,900 lb had lost 37 lb, after which its weight remained constant. The colimin protections of crushed quartz aggregate concrete were allowed to remain in the forms

15 days, after which the concrete was kept moist

5 days. The concrete was further seasoned under

atmospheric conditions for 2}i months prior to test. 4
IV. Equipment and Method of Testing

1. Equipment

The tests were made in gas-fired furnaces

equipped witli hydraulic jacks for applying load.

The furnace, loading equipment, and the column

under test are shown in figure 4. The furnace,

I while not originally designed for columns, was

j modified by an increase in height to accommodate

i a colmnn having an effective length of 124 in. The jack piston was raised by an electrically

driven oil piunp equipped for automatic control

of pressures. The movable floor of the furnace

rested on a spherical bearing block raised and

lowered by the hydraulic jack.

Temperatures at 12 locations in the furnace were measured with chromel-alumel thermocouples

protected by ii'on tubes. The temperatures at 16

or more points on each column were also measured

with similar thermocouples made of No. 18 AWG

wires. The thermocouple junctions were formed

by inserting carefully cleaned ends of the respective wires into 1.1-mm diameter paired holes

spaced at % in. drilled into the column shaft. Steel was swaged around the holes to secure metalto-metal contact with the wires. The thermocouples were disposed at each of four levels of the

column shafts as indicated by the positions B, N,

M, and T in figure 4.

2. Method of Testing

(a) Bearing of Columns

Steel bearing plates were bolted at either end

of a test column. The plate at the bottom was

20 in. sq and 1% in. thick. The top plate, 25 by

27 by 1% in. was fixed to the column with, fourteen

%-in. bolts 2^2 in. long, and in turn was bolted to the overhead bearing of the loading frame of the

furnace in such a position as to center the bottom

plate over the loading jack. The furnace floor was then raised to Avithin % in. of the bottom plate

and the space between fiUed with portland cement

grout. As the floor rested on a well-lubricated

ball-and-socket joint coincident with the vertical center line of the column shaft, the column was

considered to have a spherical end bearing at its lower extremity.

(b) Restraint of Columns

The plates attached to the head of a colmnn

were designed to give effective restraint against

bending of the upper 33 in., thus offering substantially full continuity from the top of the fire- exposed test portion of the column shaft to the

overhead bearing.

(c) Loads on Columns

The load imposed during the test on three of

the columns was computed fi'om a formula for

allowable load recommended by the American

Institute of Steel Construction

F=(^17,000-0.485 A

in which P=8 1,700 lb, total load on a column,

equivalent to a stress of 13,700 Ib/in.^ on the cross- sectional area A of the column (5.97 in.^); Z=124

in., the efl'ective length of the column; r=1.50 in., the least radius of gyration of the steel column.

The load was applied before starting the test

fire and was maintained until rapid yielding of the

column occurred, the load being removed when

the yield of a column from its maximum expansion amounted to approximately 0.6 in., or threefourths of the amount of its expansion.

The second of the columns protected with

Potomac River gravel aggregate concrete was

loaded to 163,000 lb before the test, and this load was maintained until the average of the temperatures at 16 points in the steel reached 445° C

(833° F), the maximum at any of the 16 points

being 490° C (914° F). These "temperatures were

attained in 1 hr 51 min after the start of the

test, at which time the load was reduced to that of

the other tests.

(d) Measurement of 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 a column. Measurements made during previous

tests indicated that the thermal expansion of the

vertical framework 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 the lateral deflections of a column were made during or after a test.

(e) Test Specification

The tests were conducted in accordance with

the American Society for Testing Materials

Standard Methods of Fire Tests of Buildmg Construction and Materials, El 19-41 (ASA No.

2.1-1942) as applicable to loaded columns. The

loading schedule for one column, as previously

described, deviated from that of the specification.

The limit of fire endurance was selected as the

time from the start required to attain a yield of

about 0.6 in. from the point of maximum expansion of a column.

5
V. Results of Tests

1. Columns 1 and 2—Potomac River Gravel

Aggregate Concrete Protections

The results of fire tests of columns protected

with concrete made with Potomac River gravel

aggregate are shown in figures 5 and 6. Figure 5 shows the temperatures within the

furnace and the standard furnace reference curve. Also shown are the maximum observed temperatures at any thermocouple, the temperatures at the level having the highest average most consistently, and the minimum level temperatures in a column. The average of temperatures for the

several levels are arithmetical. They were not

weighted in proportion to the areas involved as were those reported in previous tests.* It was

considered that the greater temperature effects on

the column strength at the edges of the flanges, as compared to the effects at the midpoint of the

flange or web, compensated for the smaller cross- sectional area contributory to each thermocouple

near the edges.

The failure of both columns involved deformation throughout the fire-exposed lengths. The

lateral deformation of column 1 was somewhat

greater than that of column 2 and was centered

somewhat lower in the shaft. Although the lateral deflections were unequal, the total shortening of both columns, as determined by measurements

before and after the tests, was the same, 0.4 in. The expansion of the columns with increases in

the average temperatures of the steel shafts are shown in figure 6. Column 2 was subjected to double the load applied to column 1 until the

average temperature in the shaft reached 445° C

(883° F), after which the load was reduced to that

of column 1. Yielding of the steel under constant load with

increasing temperature began in column 1 after

the average temperature of the steel shaft had

exceeded 570° C (1,058° F) and in column 2 after it had exceeded 610° C (1,130° F). Endpoint temperatures for column 1 were 730° C

(1,346° F) as the average of all thermocouples and

775° C (1,427° F) maximum at one location; for column 2, 725° C (1,337° F) was the average endpoint temperature and 760° C (1,400° F), the

maximum at one location. The fire-endurance

limit for column 1 was 3 hr 34 min and for column

2, 3 hr 32 min.

The condition of the gravel aggregate concrete column protections after the fire test are shown

in figures 1 and 7. Figure 8 shows the two columns

after removal of the concrete encasement.

The Potomac River gravel concrete of three

monolithic walls did not spall or develop serious

cracks throughout the fire- and load-test periods.

Two reinforced concrete walls 4 and 6 in. thick were exposed for 1 hr 27 min and 4 hr, respectively.

Figure 9 shows the fire-exposed face of an 8-in.

* Fire tests of building columns, Underwriters' Laboratories 1920; also published as B. S. Tech. Pap. T184 (1921).

unreinforced wall after 5}^ hr test. These walls

suffered only minor cracking and in no case was

there evidence of spalling.

2. Columns 3 and 4—Milky and Clear Quartz

Aggregate Concrete Protections

Figures 10 and 11 show the results of fire tests on steel columns protected with crushed quartz

aggregate concrete. Temperatures within the

furnace and the standard reference curve are shown in figure 10, as well as the observed temperature at any thermocouple in a column, the

temperature at the level having the highest average

most consistently, and the minimum average

temperature at one level. As was true for the

first two columns, the averages are arithmetical

and not weighted.

Both columns suffered lateral deformations in their fire-exposed portions. The concrete with

milky quartz aggregate of column 3 showed only

minor cracking at the end of the test, as is seen in figure 12. Failure to cease application of the load

at the end of the test when the contraction had

reached the predetermined value of % in. caused

severe bending of the shaft of column 4. The

clear quartz aggregate concrete showed little cracking and no evidence of spalling prior to the excessive deformation.

The expansion of the columns with increase in average temperature of the shafts is shown in figure

1 1 . Yielding under constant load and increasing

temperature began in column 3 at an average

temperature of the steel of 525° C (977° F) and

in column 4 at 535° C (995° F). End-point temperatures for column 3 at the fire-endurance limit

of 3 hr 10 min were 625° C (1,157° F) as the aver- age of all thermocouples and 730° C (1,346° F)

maximum at any one thermocouple. For column

4, the average end-point temperature was 620° C

(1,148° F) and the single point maximum was 755°

C (1,391° F). The fire-endurance limit was 2 hr

50 min. A correction of 4 min may be added to the

fire-endurance time of column 3 because of the

excess of the furnace exposure over the standard.

The quartz aggregate concrete of a 4- by 8-ft wall slab 4 in. thick showed only a fine crack in the line of a pouring joint after a fire exposure of

V/i hr. The slab was poured in quarters from the same milky and clear quartz concrete batches

used for columns 3 and 4, the sections with like aggregate being diagonally opposite. Figure 13

shows the fire-exposed face of the wall after removal from the furnace.

VI. Summary and Discussion

The steel columns of these tests were of a type

commonly used as structural members. The

concrete protections were made with sUiceous

aggregates of widespread occurrence. The concrete used on columns 1 and 2, made with a gravel

6
FLOOR LEVEL

6-1 BEAMS 24" 80"

-N-- -

J'

3 H BEAMS 9 90.5" MACHINED

2-3''X2'-rxi^8 TOP BEARING PLATE

FLANGE COVER PLATES

r-8Vr-8"Xll'g'

, BEARING PLATE

GRILLAGE OF CONCRETE S

7-1 BEAMS 12" 55*

500 TON

HYDRAULIC JACKI I SPHERICAL

BEARING BLOCK

25" RADIUS

60 X45 REINFORCED CONCRETE FOUNDATION

2-3/2 TENSILE RODS

2-H COLUMNS

8" 34.5*

Figure 4. Furnace and loading equipment with typical column in place.
- TEMPERATURE IN DEGREES FAHRENHEIT _I00 200 300 400 500 600 700 600 900 1000 1100 1200 1300 1400

300 400 500 TEMPERATURE IN DEGREES CENTIGRADE Figure 6. Expansion curves for columns with Potomac River gravel concrete—Tests 1 and 2.
Figure 7. Condition of gravel aggregate concrete column

protection after Sji-hr fire exposure.

Figure 8. Condition of colutnns after tests 1 and 2—

Concrete removed.

aggregate, was of conventional mix. The concrete witli crushed quartz aggregate, however,

had a disproportionate amount of sand, necessitated b}" the difficulty of working and the unusual

fineness, sharpness, and gradation of the crushed

sand and stone. The columns were subjected to the loads computed hy a formula for allowable loads recom- mended by the American Institute of Steel Construction. One column with Potomac River

gravel aggregate concrete was subjected to a load

twice that of the other columns until an average

column temperature of 445° C (833° F) was at- tained, after which the load was reduced to that

under which the other columns were tested. The

delay in yield of this column can possibly be

attributed to set caused by the greater load imposed on the column during the early part of the

test. However, the double load did not reach

the compressive yield strength of structural steel at the attained temperature of 445° C.^ The fire-endurance limits of columns with Potomac River aggregate concrete was somewhat

greater than that of columns made with crushed

quartz aggregate. The comparative times were

3 hr 34 min and 3 hi' 32 min with the gravel

aggregate concrete, and 3 hr 10 min and 2 hr 50

min with the quartz. The maximum measm'ed

expansions of the coliunns ranged from 0.59 to 0.76 in. The end-point temperatures as averages

of the thermocouple readings at four levels for columns 1 through 4, respectively, were 730° C

(1,346° F), 725° C (1,337° F), 625° C (1,157° F),

and 620° C (1,148° F). The corresponding singlepoint maximums were 775° C (1,427° F), 760° C

(1,400° F), 730° C (1,346° F), and 755° C (1,391°

F).

The fire resistance of structural-steel columns

with solid concrete protections and all reentrant

spaces filled with concrete, can be estimated from

the formula « R=c (^D-0.4

where

J?=the fire resistance of the column

Z)=the dimension of the outside column sec- tion

d= the dimension of the inside section or core c=a constant depending on the composition

of the concrete. Substituting the fire-endurance limits which are the results of the present tests, and the colrunn

dimensions, coefficient c becomes 5.5 for columns

with Potomac River gravel aggregate concrete,

4.9 for milkj^ quartz aggregate, and 4.4 for clear quartz aggregate.

The fire resistance of columns with 8-, 10-, and

12-in. steel shafts protected b}^ 2-in. coverings of

concrete, as determined from the formula, are shown in table 2. The results obtained from the tests reported

herein indicate that the conclusions reached in the

fire tests of siliceous aggregate concrete for column

protection as reported in National Bm"eau of

Standards Technologic Papers 184 (1920) and 272

(1925) need to be reexamined. In the present

tests there was no spaUing of concrete such as had

been reported in the previous tests and the cracking was not sufficient to expose the shaft before the

critical-temperatm-e range of the steel was attained.

5 p. D. Sale, Compression tests of structural steel at elevated temperature,

J. Research NBS 13, 713 (1934) RP741.

6 Fire-resistance classifications of building constructions, NBS Building

Materials and Structures Report BMS92, p. 70 (1942).

9
Figure 9. Fire-ex-posed face of an 8-in. unreinfarced wall of Potomac River gravel concrete after SYt-hr test.

a

2 100O O

2 900

Ulu

(0 ^u

LJ

OC 700 o

U

a

600 z

LJ

a.D

< 400

Lia

E 300

LJ

200

TEST NO. 3 TEST NO. 4 r

.J

UWNflCE AVG r rURNACE AVG

1 1 /I 1

./ r — REFEfiENCe CURVE t

3

-REFERENCE CURVE

/ Y

T

/

r.r

i

A AT ANY TMERMOCOUPLE^^^^ MAXIMUM AT ANT THEHMOCOUPLE i-

^

AVERAGE AT LEVEL B

1 AVERAGE AT LEVEL

GEAIANTLEVEL-MIN -

f

AVERAC ATANrUEVEL-Mm-v y

*

i AVER A

< /

—

</

/ /

/V 1

/

y

/

/ >Y

zzoo 2100

2000

1700

1600

1500 1400

1300

1200

1100

1000 900

600

700

600

500

TIME IN HOURS Figure 10. Furnace and column temperatures for columns with crushed quartz concrete—Tests 3 and 4-
11
Table 2. Derived fire-resistance ratings of steel shaft H -columns with 2 inches of concrete protection

blze of X* ire- Concrete aggregate column resistance shaft rating

in. HT

( ^

. - } in

1 10 oy2

I 12 (S'A

1 8 4 Milky quartz _ 1 s

56

1 &

ZV2 Clear quartz,. _ _ iVi

I 12 6M

The resistance of a concrete to high temperatures

is probably influenced by its density. The spalling

caused by the explosion resulting from superheated

water in a dense concrete was previously mentioned

in connection with the failure of a floor slab made

with siliceous aggregate concrete. Further evidence of this effect can be seen in figine 12, which

shows failure of the concrete top of the furnace

after the first fire-endurance test to which the concrete was subjected. The failm-e occurred with ex- plosive force 34 min after a 3-hr 10-min fire ex- posure, at which time the furnace still retained

considerable heat. Examination of the debris

showed the concrete, made with carefully graded

firebrick aggregate, to be extremely compact.

The structure of the spalled material can be seen

in the photograph of the sample in figure 14. The aggregates used in both series of tests, while

siliceous in character, differed in mineralogical

composition. Those composed largely of chert

Figure 14. 'Sam-pie of firebrick aggregate concrete spalled from top of furnace.

gave the poorest results in the tests at Underwriters' Laboratories. It is possible that an impurity or vaporizing water in the chert caused a disruptive force upon the application of heat. The

characteristically rapid volume change of the

siliceous minerals at critically high temperatures

had no apparent effect upon the concrete used in the present tests. The results of the tests indicate that concrete made with siliceous aggregates, as herein described,

provides an acceptable material for the protection

of structural steel against fire. The consistency of the results allowed definite conclusions as to the

reliability of the protections for the demonstrated

fire-endurance limits. Washington, September 12, 1950.

12 U. S. GOVERNMENT PRINTING OFFICE: 1951
BUILDING MATERIALS AND STRUCTURES REPORTS

[Continued from cover page ii] BMS32 Structural Properties of Two Brick-Concrete-Block Wall Constructions and a Concrete-Block Wall Construction Sponsored by the National Concrete Masonry

Association 15^ BMS33 Plastic Calking Materials 15^ BMS34 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 1 15^ 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 * BMS38 Structural Properties of Two "Dunstone" Wall Constructions Sponsored by the W. E. Dunn Manufacturing Co lOjS 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 15(i 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 15jS BMS43 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 2 15^ BMS44 Surface Treatment of Steel Prior to Painting 10^ BMS45 Air Infiltration Through Windows 15^ BMS46 Structural Properties of "Scot-Bilt" Prefabricated Sheet-Steel Constructions 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

Sponsoi'ed by the Homasote Co 15ji 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(i 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 10^ BMS54 Effect of Soot on the Rating of an Oil-Fired Heating Boiler 100 BMS55 Effects of Wetting and Drying on the Permeability of Masonry WoJls 10^ BMS56 A Survey of Humidities in Residences 10^ BMS57 Roofing in the United States—Results of a Questionnaire * BMS58 Strength of Soft-Soldercd Joints in Copper Tubing lOjS BMS59 Properties of Adhesives for Floor Coverings 15^ BMS60 Strength, Absorption, and Resistance to Laboratory Freezing and Thawing of Building

Bricks Produced in the United States 30(4 BMS61 Structural Properties of Two Nonreinforeed Monolithic Concrete Wall Constructions.- 10^ BMS62 Structural Properties of a Precast Joist Concrete Floor Construction Sponsored by

the Portland Cement Association 15^ BMS63 Moisture Condensation in Building Walls 15^ BMS64 Solar Heating of Various Surfaces 10^ BMS65 Methods of Estimating Loads in Plumbing Systems 15^ 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 15j5 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 200 BMS71 Fire Tests of Wood- and Metal-Framed Partitions 200 BMS72 Structural Properties of "Precision-Built, Jr." Prefabricated Wood-Frame Wall Construction Sponsored by the Homasote Co 100 BMS73 Indentation Characteristics of Floor Coverings 100 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 200 BMS75 Survey of Roofing Materials in the North Central States 150 BMS76 Effect of Outdoor Exposure on the Water Permeability of Masonry Walls 150 BMS77 Properties and Performance of Fiber Tile Boards 100 BMS78 Structural, Heat-Transfer, and Water-Permeability Properties of Five Earth-Wall

Constructions 250 BMS79 Water-Distributing Systems for Buildings 200 BMS80 Performance Test of Floor Coverings for Use in Low-Cost Housing: Part 4.- 150 BMS81 Field Inspectors' Check List for Building Constructions (cloth cover, 5 x TYt inches) 300

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

[Continued from cover page ni]

BMS82 Water Permeability of Walls Built of Masonry Units 25i

BMS83 Strength of Sleeve Joints in Copper Tubing Made With Various Lead-Base Solders 15p

BMS84 Survey of Roofing Materials in the South Central States 15^ BMS85 Dimensional Changes of Floor Coverings With Changes in Relative Humidity and

Temperature 10)5 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 Comnoittee on Research,

Design, and Construction 20(5 Recommended Building Code Requirements for New Dwelling Construction With

Special Reference to War Housing * Structural Properties of "Precision-Built, Jr." (Second Construction) Prefabricated

Wood-Frame Wall Construction Sponsored by the Homasote Co 15^

Structural Properties of "PHC" Prefabricated Wood-Frame Constructions for Walls,

Floors, and Roofs Sponsored by the PHC Housing Corporation 15j5 A Glossary of Housing Terms 15^

Fire-Resistance Classifications of Building Constructions 30^

Accumulation of Moisture in Walls of Frame Construction During Winter Exposure. _ 10^ Water Permeability and Weathering Resistance of Stucco-Faced, Gunite-Faced, and

"Knap Concrete-Unit" WaUs 150 Tests of Cement-Water Paints and Other Waterproofings for Unit-Masonry Walls 250

Properties of a Porous Concrete of Cement and Uniform-Sized Gravel 100 Experimental Dry-Wall Construction With Fiber Insulating Board 100

Physical Properties of Terrazzo Aggregates 150

Structural and Heat-Transfer Properties of "Multiple Box-Girder Plywood Panels" for Walls, Floors, and Roofs 150

Relative Slipperiness of Floor and Deck Surfaces 100 Strength and Resistance to Corrosion of Ties for Cavity Walls 100

Painting Steel 100 Measurements of Heat Losses From Slab Floors 150

Structural Properties of Prefabricated Plywood Lightweight Constructions for Walls,

Partitions, Floors, and Roofs Sponsored by the Douglas Fir Plywood Association. _ 300

Paint Manual with particular reference to Federal Specifications $1. 25

Laboratory Observations of Condensation in Wall Specimens 160

Building Code Requirements for New Dwelling Construction * Temperature Distribution in a Test Bungalow With Various Heating Devices 160 Strength of Houses: Application of Engineering Principles to Structural Design $1. 50

Paints for Exterior Masonjy Walls 150 Performance of a Coal-Fired Boiler Converted to Oil 150

Properties of Some Lightweight-Aggregate Concretes With and Without an Air- entraining Admixture 100

Fire Resistance of Structural Clay Tile Partitions 150 Temperature in a Test Bungalow With Some Radiant and Jacketed Space Heaters 250

A Study of a Baseboard Convector Heating System in a Test Bungalow 150 Preparation and Revision of Building Codes 150

Fire Resistance of Walls of Lightweight Aggregate Concrete Masonry Units 200

Stack Venting of Plimibing Fixtures . 150 Wet Venting of Plumbing Fixtures 200

Fire Resistance of Walls of Gravel-Aggregate Concrete Masonry Units 150

Investigation of Failures of White-Coat Plasters 250

Physical Properties of Some Samples of Asbestos-Cement Siding . **

Fire Tests of Wood-Framed Walls and Partitions With Asbestos-Cement Facings 150

Fire Tests of Steel Columns Protected With Siliceous Aggregate Concrete 150

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