Bureau of Standards

SEP 2 1 1938
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UNITED STATES DEPARTMENT OF COMMERCE • Daniel C. Roper, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director

BUILDING MATERIALS

and STRUCTURES

REPORT BMS2

Methods of Determining the

Structural Properties of Low-Cost

House Constructions

by HERBERT L. WHITTEMORE and AMBROSE H. STANG

ISSUED AUGUST 10, 1938

The National Bureau of Standards is a fact-finding organization;

it does not "approve" any particular material or method of construction. The technical findings in this series ol reports are to be construed accordingly.

UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON • I938

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, WASHINGTON, D. C. • PRICE 10 CENTS
Foreword

The present report describes the methods now in use in the laboratories of the National Bureau of Standards for measuring the strength,

stiffness, and resistance to abuse of constructions intended for walls,

partitions, floors, and roofs of low-cost houses and apartment buildings.

These tests represent an attempt to develop a standard procedure for

evaluating the structural properties of house constructions.

Tests of new constructions according to tliis uniform procedure as to

size of specimen and test methods, along with similar tests on conventional constructions, are expected to form a more reasonable basis for judging the value of new constructions than any method now available.

Ultimately, such performance tests may find their way into building

codes to replace present requirements, which specify details of sizes of

members for use in conventional types of construction.

Adequate performance requirements of Nation-wide acceptance would

facilitate the rapid development of new, better, and, it is hoped, cheaper

methods of construction.

Lyman J. Briggs, Director.
Methods ot Determining the Structural Properties of

Low-Cost House Constructions

by HERBERT L. WHITTEMORE and AMBROSE H. STANG

CONTENTS

Page Foreword ii

I. Introduction 2 n. Cooperation with industry .... 3

1. Approval 3

III. Cooperation with the United

States Forest Service 4 IV. Definitions 4

1. House 4

2. Element 4

3. Construction 4

(a) Wood construction . . 4

4. Sponsor 4

V. Specimens 4

1. General 4

(a) Size 4

(b) Length or height ... 5

(c) Width 5

2. Age 6

3. Sponsor's obligations .... 6

(a) Description 6

(b) Caution 6

(c) Specimens 6 VI. Method of testing walls 7

1. Compressive load 7

(a) Specimen 7

(1) Height 7

(2) Width 7

(b) Loading 7

(c) Apparatus 7

(d) Results 8

2. Transverse load 8

(a) Specimen 8

(1) Height 8

(b) Loading 8

(c) Apparatus 9

(d) Results 9

(e) Masonry constructions. 10

3. Concentrated load 10

(a) Specimen 10

(b) Loading 10

(c) Apparatus 11

(d) Results 11

Page VI. Method of testing walls—^Contd.

4. Impact load 11 (a) Specimen 11

(b) Loading 11

(1) Sandbag. ... 11

(2) Height of drop . 1

1

(c) Apparatus 12

(d) Results 13

(e) Masonry constructions. 13

5. Racking load 14

(a) Specimen 14

(b) Loading 14

(c) Apparatus 14

(d) Results 14

VII. Method of testing partitions, nonload-bearing 15

1. Impact load 15

(a) Specimen 15

(b) Procedure 15

2. Concentrated load 15

(a) Specimen 15

(b) Procedure 15 VIII. Method of testing floors 15

1. Transverse load 15

(a) Specimen 15

(b) Procedure 16

2. Concentrated load 16

(a) Specimen 16

(b) Procedure 16

3. Impact load 16

(a) Specimen 16

(b) Procedure 16 IX. Method of testing roofs 16

1. Transverse load 16

(a) Specimen 16

(b) Procedure 17

2. Concentrated load 17

(a) Specimen 17

(b) Procedure 17 X. Presentation of results 17

[1]
ABSTRACT

This paper describes methods used by the National Bureau of Standards to determine the structural properties of elements of a low-cost house: that is, struc- tural properties of wall specimens under compressive,

transverse, concentrated, impact, and racking loads; of partition specimens under impact and concentrated

loads; of floor specimens under transverse, concentrated, and impact loads; and of roof specimens under

transverse and concentrated loads. A graphic method

of presenting the results of the tests is also described.

It is believed that the tests of house constructions by

the methods described in this paper wiU give information on the structural properties which wiU greatly

assist in the selection of a low-cost construction for given conditions.

I. INTRODUCTION

In the past, few tests have been made and

therefore few data are available on the strength,

stiffness, and other structural properties of

houses, even for the conventional brick or frame

houses which have been so widely used in this

country. Progress since the time of the early

settlers has been made largely by "cut and try."

Constructions not proving satisfactory under

service conditions were discarded, but constructions which were unnecessarily strong or ex- pensive were replaced only very gradually by more economical constructions.

To insure more rapid progress in determining

the structural properties of houses it is desirable to use research methods which have proved

to be efficient and economical in the solution of

other industrial problems. Houses might be

observed imder service conditions to obtain

data for determining the minimum requirements for a house wliich has proved to be

satisfactory. However, more definite information could be obtained by applying known loads

to the house and measuring their effect. If loads were applied to houses of different constructions and if the effect of service on houses

of the same constructions was also recorded over a period of years, minimum requirements

could be established for the structural properties which would insure satisfactory houses

for a particular climate (temperatures, rain,

snow, wind) and which would comply with

reasonable requirements for health, safety, etc. Subjecting complete houses to known loads is very expensive and requires much time; therefore, this method of carrying out investigations

of houses is not likely to be used to any great

extent. Such tests have the further disadvantage that only the strength of the weakest ele- ments of a particular house could be measured.

As an illustration, to determine the strength of

the second-story floor in a house, loads coiild be

applied to the floor. If the walls crushed before

the maximum load for the floor was applied it would be necessary to test another house having

stronger waUs.

For these reasons it seems more practicable

to apply loads to specimens which accurately

reproduce a structural portion of a finished

house. ^ These portions of a house have been

designated as "elements"; for example, floor,

wall, roof, etc. For the program described in

this paper, the elements have been restricted to the most important structural portions of a house. For each element the methods of loading were prescribed which simulated the loads

to which the element would be subjected under

service conditions. It is believed that the re- sults of these measurements on the structural

elements of a house will be more useful to architects and engineers than the results of tests on

specimens of the materials from which the house was fabricated, or the results of tests of the in- dividual structural members of a house. In all probability, the results will approximate closely

those which would be obtained by testing a complete, full-sized house. Provided a sufficient

number of constructions are included, some of

which have been widely used for many years, and others which may never have been used for a house subjected to service conditions, it should be possible, by comparing the results, to determine approximately whether or not a new

construction will be satisfactory as regards

structural properties. Carrying out this program will be much less expensive than budding

houses of these new constructions and awaiting

the test of actual service over a period of years. Although it may be impracticable to determine all of the structural properties of each

element of a house, it is believed that the more

important properties may be determined by

tests described in this report.

Under this program, walls and load-bearing

partitions are being subjected to compressive,

1 Any residential structure.

[2]
transverse, concentrated, impact, and racking

loads, in the laboratory. In actual service,

house walls are subjected to vertical compi-essive loads by the dead weight of the walls,

floor, and roof above, and by the live loads

above (wind, and the weight of snow on the

roof, furniture, or persons on the floor, etc.)- Horizontal transverse (bending) loads, caused

by wind, act upon the outside faces of such

walls, and sometimes upon their inside faces on the leeward side. Walls may also be subjected to concentrated

loads (large forces over a small area, such as a

ladder placed against either face). Impact

loads may be applied accidentally to a wall, for example, by a coal truck backing against the

outside, or by a person or bookcase falling

against the inside face of the wall. Concentrated and impact loads come under the head

of abuse, and, to a considerable extent, are unavoidable under service conditions. Racking

(shearing) loads are applied to a wall by intersecting walls against which a wind is blowing.

Load-bearing partitions are subjected to the same loads except transverse loads caused by

wind. However, transverse loads are applied

to load-bearing partitions in the laboratory be- cause if the outside face is weatherproofed but no other change in the construction is made,

they may be used for the outside wall of a house.

Nonload-bearing partitions are not designed

to withstand compression, transverse or racking loads, and under service conditions, such

loads on a nonload-bearing partition are negligible, and therefore may be ignored. On the

other hand, impact and concentrated loads,

through accidents, are sometimes applied to nonload-bearing partitions. Therefore, partitions are subjected to impact and concentrated

loads.

Floors are subjected to transverse, concentrated, and impact loads. Transverse (bending) loads are applied to a floor by the weight of

furniture and persons. Concentrated loads are applied by pianos, bookcases, etc. Impact

loads are applied by objects and persons falling on the floor, as a person jumping or falling from

a stepladder.

Roofs are subjected to transverse and concentrated loads. Transverse (bending) loads are applied by wind, and the weight of snow, or by

workmen. Concentrated loads are applied by

the weight of material and tools during the construction or repair of the roof.

II. COOPERATION WITH INDUSTRY

In order to cooperate with industry to the

fullest extent, specimens for one or more structural elements of a house are solicited for inclusion in this program. Any number of constructions may be submitted. It is believed that in

this way the invaluable experience of individuals,

organizations, architects, engineers, and others

may be coordinated so as to be of the greatest

value to those concerned with the design and

construction of houses, particularly low-cost

houses. Many organizations have had considerable experience with different constructions

under service conditions in various parts of the

country, and over comparatively long periods

of time. They are, therefore, in an excellent

position to recommend constructions which

they believe are satisfactory for low-cost

houses.

Specimens accepted for inclusion in this pro- gram will be tested without expense to the

sponsor. The sponsor or his representative and

any others he may designate are invited to wit- ness the tests and make suggestions. A report

giving results of the tests on his construction

will first be submitted to the sponsor for his criticism and comments. These will be given

careful consideration in the preparation of the

final report, which will then be published by the

National Bureau of Standards and made available to the public.

The sponsors are earnestly requested to submit constructions wliicli in their opinion are the

least expensive, and in this way, assist in providing houses for those lower-income families

which heretofore have not been adequately

housed.

1. Approval

The reports on this program will be available

to all organizations concerned with housing.

The responsibility for selecting suitable constructions, issuing building permits, approving

a construction, granting mortgage loans, fixing

insurance rates, etc., rests with these organizations.

[3]
The National Bureau of Standards neither

approves nor disapproves any construction.

It makes available to the public the results of

the tests and inspections made by members of

its staff. This Bureau has no requirements for any house or portion of a house. At the present

time, it is impracticable to comply with re- quests for the determination of structural properties of any portion of a house except the ele- ments described hereafter. This Bureau does

not test building units or members, such as

brick, concrete block, open bar joists, etc., for the public if such tests can be made hi the materials testing laboratories of commercial or- ganizations and technical schools. A Directory

of Commercial Testing and College Research

Laboratories has been published by the Bureau

as Miscellaneous Publication Ml25. Copies of

this directory may be obtained from the Superintendent of Documents, Government Printing

Office, Washington, D. C, for 15 cents.

III. COOPERATION WITH THE UNITED

STATES FOREST SERVICE

Because of the long experience of the Forest

Products Laboratory of the United States Department of Agriculture in the study and development of wood constructions, and the requirement in the appropriation act that this program

shall not duplicate any work now performed by

that Laboratory, the National Bureau of Standards requested the assistance of the Forest

Service in this program for the determination

of the structural properties of low-cost house

constructions. The Forest Service very kindly

offered its cooperation in tests of wood constructions, that is, constructions havmg wood

structural members.

The Forest Products Laboratory at Madison,

Wis., has unequaled facihties for determining the

species and commercial grade of wood, moisture

content, etc., essential to insure adequate

results in wood constructions, and has a per- sonnel experienced in the study of the structural

properties of wood. This Laboratory has constructed and tested specimens of conventional

wood construction by essentially the same procedure as described in tins report. The

Laboratory has agreed to the inclusion of the

results of its tests in the present series of reports.

It has been jointly decided that it wiU be most

convenient to test other wood constructions at the National Bureau of Standards with the

active cooperation of personnel representing the

Forest Products Laboratory.

IV. DEFINITIONS

1. House

Any residential structure.

2. Element

A portion of the completed house ready for occupancy, having one primary function,

for example, a floor or wall.

3. Construction

The materials, dimensions, and method of fabricating an element of a house. Elements

are of different constructions if there is a significant difference m the materials, dim^ensions,

and methods of fabrication. Exam.ple : A floor having rolled steel I-beams covered by a reinforced concrete slab is one construction, and a

floor having the same I-beams and spacing

covered by a wood floor is a different construction.

(a) Wood Construction

A construction having wood structural members.

4. Sponsor

A sponsor of a house construction is an

individual or an organization which submits

specimens for inclusion in this program for the

determination of their structural properties.

V. SPECIMENS

1. General

(a) Size

The specimens should be as large as practicable to minimize the effect of variations in the

material and workmanship, and thereby obtain

[4]
results representative of the construction in an

actual house. Obviously, the size of the speci- mens is limited to the size which can be tested

in the larger testing machines available in a well-equipped laboratory, and which can be

subjected to loads in accordance with good

testing procedure, and for which the deformation can be measured with sufficient accuracy.

(6) Length or height

A length or height of specimen for each ele- ment was chosen which is about the length or height of that element in a small house.

(c) Width

The width was chosen which, for most constructions, would include several of the principal load-carrying members to insure, insofar

as possible, that the specimen under load would

behave like a portion of a house under service

Figure 1. —Typical wall specimen.

A, three wood studs (2 by 4 inches); B, wood blocks to support the edges

of the faces, optional with sponsor; C, inside face (lath and plaster) ; and

D, outside face (wood sheathing, paper, and lap siding)

FiGTJKE 2.—Typical wall specimen.

A, two woDd studs (2 by 4 inches); B, two wood "half" studs (1 by 4

inches); C, inside face (lath and plaster); and D, outside face (wood

sheathing, paper, and lap siding).

conditions. With the exception of that for the

racking load, a nominal width of 4 feet was

chosen for wall specimens.

The actual width of specimens shall be a whole number multipHed by the spacing of the

principal load-carrying members. In no case

shall the actual width exceed 6 feet, as this is the greatest width which can be tested under

transverse loads in equipment available m the

Engineering Mechanics Section of the National

Bureau of Standards.

If the structural properties of a particular

construction are to be compared with another

construction, there should not be a great differ- ence in the actual widths of the specimens.

For example, under the impact loading a satis- factory comparison cannot be made if for one

construction the specimens had an actual

width of 2 feet and for another 12 feet. For

walls sunilar to conventional wood construction

having studs spaced 16 inches, the actual width

of the specimen shall be 4 feet and have three

[5]
studs. At the option of the sponsor this specimen may either have three "full-sized" studs

as shown in figure 1, or two "full-sized" studs

and two "half-thickness" studs, as shown in figure 2. If the sponsor prefers three "full- sized" studs (fig. 1) he may tie the edges of the

faces together at intervals of about 1 foot by

blocks, as shown by dotted lines in figure 1. These blocks should prevent damage to the

specimen when being shipped or handled and

may remain in place when the specimen is tested, because their effect on the structural

properties of the specimen will not be appreciable. The nominal width of 4 feet was also chosen for specimens of partitions, floors, and

roofs.

2. Age

Constructions, such as concrete and masonry

(brick, structural clay tile, cement block) for which the structural properties depend upon the

age of the specimen, will be tested 28 days after fabrication to obtain comparable results on

different constructions. Constructions having

plastered or stuccoed faces will be tested 28

days after fabrication.

3. Sponsor's Obligation

fa) Description

If a construction is to be considered for the

determination of structural properties, the

sponsor shall: First : Select one or more of the four elements

of a house for which he wishes to submit specimens, that is, wall, partition, floor, and roof. Second: For these elements choose one or more low-cost constructions.

Third : Submit dimensioned drawings of spec- imens and a complete description of the construction for each element. The description

should give all available information which will identify the materials or units in the construction, such as name of manufacturer, trade

name, commercial grade, manufacturing process, purchase specification, approximate chemical composition, tensile strength, etc. The

information and drawings furnished by the

sponsor will be used to determine whether the

construction will be included in this program.

Table 1.

Price of low-cost house constructions Maximum

price Element per square

foot Wall and load-bearing partitions; including

weatherproofing on outside face of the wall and

the finish on inside face of the wall and on

both faces of the partition $0. 60

Partition, nonload-bearing; including finish on

both faces . 35

Floor; including finish floor on upper face and

ceiling (if any) on lower face .75

Roof; including weatherproofing on upper face and ceiling (if any) on lower face . 60

Fourth: State the price as of July 1937 of each element per square foot complete, as used

in a house, delivered in Washington, D. C. To

be included in this program, the price of the

specimens shall not exceed the values given in

table 1, and preferably should be much lower.

These prices apply to low-cost houses, in- cluding apartments in congested areas of large

cities and free-standing small houses in suburban or rural districts. Sponsors are earnestly

requested to submit the lowest-priced constructions which they believe would be satisfactory

for a low-cost house.

Q)) Caution

1. Do not fabricate specimens before the

National Bureau of Standards has agreed to include your construction in this program.

2. Because storage space at the laboratory is limited, do not deliver specimens until advised

by the Bureau.

3. For specimens wliich are to be tested 28

days after fabrication, obtain an assignment of

dates for testing to prevent a conflict with other

specimens.

(c) Specimens

The specimens of each construction shall comply with the following requirements:

Wall.—Fifteen specimens, height 8 feet,

nominal width 4 feet (480 ft^) ; three specimens,

height 8 feet, nominal width 8 feet (192 ft^). Total area 672 feetl

Partition.—Three specimens, height 8 feet,

nominal width 4 feet (96 ft-). Floor.—Six specimens, length 12 feet 6 inches,

nominal width 4 feet (300 ft^). Rooj.—Three specimens, length 14 feet 6

inches, nominal width 4 feet (174 ft^).

[6]
VI. METHOD OF TESTING WALLS

1. Compressive Load

(a) Sj^ecimen

Tests are made on three duplicate specimens,

each having a height of 8 feet and a nominal

width of 4 feet.

(1) Height.—A height of 8 feet from floor to

celling has been widely recognized as satis- factory for a low-cost house. Therefore, a

.height of 8 feet was selected for the wall speci- mens for compressive load. This is about the

least height that can be used in a low-cost house.

The actual height of a wall in a complete house

may be somewhat greater than 8 feet, depending upon the connections between wall and

floor, roof, etc. For a wall, as for any column,

the higher the wall, the less the compressive

strength. Most walls for low-cost houses are

short, sturdy columns; therefore, the strength

is about the same for any height used in a house.

For some constructions, particularly thin walls,

the strength may be much less if the height is greater than 8 feet; it may be necessary to determine the relation between the height and

strength of these constructions by making additional tests. It appears probable, however,

that the strength of a wall, having a height

greater than 8 feet, can be estimated by the

usual engineering methods with sufficient ac- curacy for practical purposes.

(2) Width.—The nominal width of these

specimens is 4 feet.

{h) Loading

The specimen is tested, as shown in figure 3, as a column having a flat end at the bottom.

Compressive loads are applied to a steel plate

covering the upper end of the specimen. The

load is applied uniformly along a line parallel to the inside face, and one-third the thickness

of the specimen from the inside face.

(c) Apparatus

To measure the shortening of the specimen

four compressometers. A, are attached to the

faces of the specimen, B, one near each corner

of the specimen, as shown in figure 4. For each

Figure 3.Compressive load on specimen.

compressometer a bracket, C, is attached to the specimen near the upper end. The bracket

supports a metal rod, D. A bracket, E,

attached to the specimen near its lower end

supports a dial micrometer, F, with the spindle

up. The conical end of the rod, D, seats in a

hole in the end of the spindle and the rod and

spindle are held in contact by stretched rubber

bands, G. The dial is graduated to 0.001 inch

and the readings are recorded to 0. 1 of a division.

To measure the lateral deflection, two deflect- ometers, H, are attached, one to each edge of

the specimen. Each deflectometer consists of a small wire, /, attached at its upper end to a

clamp, J, near the upper end of the specimen.

The lower end, K, connected to stretched

rubber bands, L, is attached to a clamp, M,

near the lower end of tlie specimen. A mirror,

N, having a paper scale, 0, one-half the width

of the mirror is attached horizontally to the

edge of the specimen at midheight. The scale

is graduated to 0.1 inch and the readings when

TOseO-—38 2 [7]
Figure 4.

Apparatus for compressive load on specimen.

A, compressometer; B, specimen; C, upper bracket; B, rod; E, lower

bracket; F, dial micrometer; G, rubber bands; H, deflectometer; /, wire; J, upper clamp; K, lower end of wire; L, rubber bands ; M, lower clamp; N, mirror; and O, scale.

the image of the wire coincides with the wire

are recorded to 0.1 division.

(d) Results

For each compressometer, the shortening

under each load is the difference between the

reading of the compressometer and the initial reading. The shortening of the specimen in

8 feet is the average of the shortenings .for each of the four compressometers multiplied

by the ratio: 8 feet divided by the compressometer gage length. Using a similar method,

the shortening sets are obtained. The lateral deflection and the lateral set for each deflectometer is the difference between the reading of the deflectometer and the initial reading. The

lateral deflection and lateral set for the specimen

is the average of the lateral deflection and

lateral set of the two deflectometers. The

maximum load for each specimen is recorded.

2. Transverse Load

(a) Specimen

Tests are made on six duplicate specimens

each having a height of 8 feet and a nominal

width of 4 feet. (1) Height.—As it appeared desirable to avoid

unnecessary differences in the heights of the

wall specimens, 8 feet was selected for the

height of the wall specimen for transverse load.

Necessarily, the span is slightly less than 8 feet.

(b) Loading

Because there is no satisfactory method of

applying loads uniformly over the face of a

transverse specimen, particularly if the loads

are applied in increments, the deflection re- corded, then the load released, and the set recorded, "two-point" loading was chosen for

the transverse load tests on walls, floors, and

roofs. The two equal loads are applied, each

at one-quarter of the span from the supports,

toward the middle of the span. The bending

moment then is constant for the portions of the

specimen between the two loads, a longitudinal

distance of one-half the span. This bending

moment is equal to the bending moment which

would exist at midspan if the total load were

uniformly distributed over the face of the specimen between the supports.

The vertical shear is constant for the two

portions of the specimen between each load

and the adjacent support. This shear is equal

to the shear which would exist at the supports

if the total load were uniformly distributed over the face of the specimen between the

supports.

Under "two-point" loading, much larger portions of the specimen are subjected to the maximum bending moment and to the maximum

shear, than if the same total load were uniformly distributed over the face of the specimen between the supports. The deflection at midspan, however, is not equal to the defiec-

[8]
tion if the load were uniformly distributed.

The deflection under uniformly distributed load can be estimated with sufficient accuracy for practical purposes by the usual engineering

methods, or the deflection can be measured

under a uniformly distributed load.

The strength is of much greater importance

than the deflection for house construction, and

"two-point" loading is more satisfactory for determining the strength from the results on

these specimens than uniformly distributed

loading.

The specimen is tested as shown in figure 5, as a simple beam on a span, S, of 7 feet 6

inches. The two supports for specimen, A,

figure 6, are steel rollers, B, to prevent longitudinal constraint. There is a steel plate, C,

between each supporting roller and the speci- men. Two equal loads are applied uniformly

across the specimen, one at each quarter point

of the span, through two rollers, D, to prevent

longitudinal constraint. There is a steel plate,

E, between each loading roller and the specimen.

For wall specimens tested horizontally, as shown in figure 6, the load on the specimen

includes weight of specimen between the

supports.

For three of the specimens the transverse loads are applied to the outside face and for three of the specimens to the inside face.

Figure 5.

Transverse load on specimen.

l''lc;uitE ().

^[pijurutiis for traitsi'cr.sr luiul on tij/vciinen, tested horizontally. A, specimen; B, supporting roller; C, plate; D, loading roller; E, plate; F, frame; G, ball; //, blocks; and /, dial micrometer.

(c) Apparatus

To measure the deflection of the specimen,

a frame, F, is placed on the upper face of the

specimen, as shown in figure 6. To prevent

stresses deforming the frame as the specimen

deforms under load, this frame rests on three

hardened steel balls, G, each supported by a

steel block, H, on the face of the specimen.

Two of the balls are in a line vertically above

one support and the third ball vertically above the other support.

One foot of the frame is free to rotate about a point, one to move

along a line, and one to move in a plane; the frame therefore is Idnematically nonredundant or

stress-free. Two dial micrometers, /, one

near each longitudinal edge of the

specimen, are attached to the

frame, F, at midspan. The spindles rest on the upper face of the

specimen. The micrometers are graduated to 0.001 inch and the

readings are recorded to the nearest division.

(f/) Results

For each micrometer, the deflec- tion under a given load is the

[9]
Figure 7.

Apparatus for transverse load on specimen

tested vertically. A, specimen; B, channel; C, roller; D, supporting roller; E, frame; F, loading roller; O, screw jack; H. ring dynamometer; and /, deflectometer.

difference between the reading of the micrometer and the initial reading. The deflection of

the specimen, for the span of 7 feet 6 inches, is the

average of the deflections for each of the two

micrometers. By using a similar method, the

sets under the initial load are obtained. The

maximum load for each specimen is recorded.

(e) Masonry Constructions

For wall constructions, such as masomy, to which transverse loads cannot be applied satis- factorily with the specimen in a horizontal

position, the loads are applied with the specimen

in a vertical position, as shown in figure 7, thus simulating service conditions.

The specimen. A, on a steel channel, B, rests on cylindrical rollers, C, to prevent constraint.

The axes of the rollers are parallel to the faces

of the specimen. The two supporting rollers,

D, are in contact with the vertical surface of the

frame, E, and each roller rests on sponge rubber

about ji inch thick to prevent longitudinal constraint. Each of the two loading rollers, F,

also rests on sponge rubber. The loads are applied horizontally by a screw jack, G, and

measured by a ring dynamometer, H, between

the jack and the specimen. The error in the

load indicated by the dynamometer does not

exceed 1 percent. Two taut-wire mirror-scale

deflectometers, /, are attached to the specimen, one to each vertical edge. These deflectometers

are similar to those used to measure the lateral deflection of walls under compressive loads and

described in section VI-l-(c).

3. Concentrated Load

(a) Specimen

Tests are made on each transverse specimen

after the transverse load tests, the load being

applied to the same face of the specimen.

(6) Loading

Either the entire specimen or a portion of the

specimen. A, figure 8, is placed on a horizontal

support. A steel disk, B, having a diameter of

1 inch and the lower edge rounded to a radius of

0.05 inch is placed on the upper face of the

specimen at what is judged to be the weakest

Figure 8. - Concentrated load on specimen.

A, specimen; B, disk; C, screw: D, wrench; E, spring dynamometer;

F, ring dynamometer; and G, depth gage.

[10]
place. A load is applied vertically downward

to the upper surface of the disk by the screw, C,

which can be rotated by the ratchet wrench, D.

To measure the load, either the spring dynamometer, E, or the ring dynamometer, F, is placed between the disk, B, and the lower end of

the screw, C. The error in the load, indicated

by either of these dynamometers, does not ex- ceed 1 percent. The capacity of the spring

dynamometer, E, is 500 pounds and the principal elements are a helical steel spring and a dial micrometer. The shortening of the spring under compressive loads is indicated on the dial of

the micrometer. The capacity of the ring dynamometer, F, is 20,000 pounds and the principal elements are a heat-treated steel ring and a

dial micrometer. The shortening of the vertical

diameter of the ring under compressive loads is indicated on the dial of the micrometer.

(c) Apparatus

To measure the depth of the indentation the

depth gage, G, figure 8, is used. This gage consists of a light tubular frame, having two legs at one end and one leg at the other. A dial micrometer is attached to the frame at midlength. The micrometer is graduated to 0.001

inch and the readings are recorded to the nearest division. Readings are taken by placing

the depth gage on the specimen with the spindle

of the micrometer at the center of the indentation and recording the reading of the micrometer.

{(1) Results

The depth of the indentation (set) after a given load has been applied and the disk re- moved is the difference between the depth for that load and the initial reading of the micrometer before a load has been applied to the speci- men. The maximum load is recorded, provided

this load does not exceed 1,000 poimds.

4. Impact Load

(a) Specimen

Tests are made on six duplicate specimens

each having a height of 8 feet and a nominal

width of 4 feet.

(b) Loading

The specimen is tested as shown in figure 9 as a simple beam on a span of 7 feet 6 inches.

The two supports for the specimen, A, figure 10, are steel rollers, B, to prevent longitudinal constraint. An impact load is applied to the middle of the upper face of the specimen by dropping a sandbag, C.

(1) Sandbag.—The wall of the bag is Indiantanned lace leather, type B, Federal Specification KK-L-201, purchased from I. B. Wilhams

& Sons, Dover, N. H. It is 28 inches high by

29 inches wide. The vertical edges were sewed

together flesh side out. The wall then was

turned hair side out and one end sewed to a

disk, D, having a diameter of 9 inches. The

disk was either harness or belting leather having

a thickness of inch. All seams were stitched

with linen shoe thread and there were two rows

of stitching.

To hoist the bag a strap inch thick, % inch

wide, and 24 inches long having a buckle at one

end and holes near the other end is passed

through two diametrically opposite holes in the

wall 1/2 inches from the upper end and budded.

There are two reinforcements sewed to the wall on the inside, one at each hole. The reinforcements are made of the same leather as the wall

and are 3 by 3 inches.

Building sand was placed in a cloth bag, tisd

with a cord, and placed inside the leather bag.

The sandbag weighs 60 pounds and the

weight is adjusted to this value before each

series of impact tests. After a few tests the

diameter of the bottom of the bag was 10 inches.

Before testing a specimen, the bag is rolled on

the floor to loosen the sand and obtain insofar

as possible constant conditions. When making

a test (flg. 10), the bag is hoisted by the over- head crane and released by pulling the trip cord,

E, when the bag is at the desired height.

(2) Height of drop.—For the first drop, the

height of the bag is measured from the upper

face of the specimen and for subsequent drops

from a taut cord in contact with the face vertically above the supports. The height of the

bag is indicated by a series of light (duralumin)

tubes, F, the lengths of which are multiples of

6 inches.

For three of the specimens, the impact loads

[11]
Figure 9.

Impact load on specimen.

are applied to the outside face and for thi'ee of

the specimens to the inside face.

(c) Apparatus

To measure the instantaneous deflection of

the specimen, the deflectometer shown in figure 11 is used. The deflectometer consists of a metal tube, A, having a base, B, at the lower end

and a friction clamp, C, at the upper end. A

light metal rod, D, movable in the tube is held

in contact with the middle of the lower face of

the specimen by the clamp. The rod, D, is graduated to 0.1 inch and readings relative to the fiduciary mark, E, on tube, A, are estimated

to 0.1 division. When the specimen deflects under the impact load this rod is held in its lowest position. The deflectometer is placed on the concrete floor under the specimen as shown at A in figure 12. To measure the set, the set gage, B, figure 12,

is placed on the upper face of the specimen.

This gage consists of a light (duralumin) tubular frame having two legs at one end and one

leg at the other. The distance between the

legs is equal to the span.

A dial micrometer is at- tached to the frame at midlength. The micrometer is graduated to 0.001

inch and the readings are recorded to the nearest

division.

Readings are taken as shown in figure 12 by placing the set gage on the

specimen with the legs

vertically above the supports and the spindle of

the micrometer in contact

with the middle of the

specimen and the reading

of the micrometer. If the

set exceeds the range of the

micrometer, gage blocks,

C, are placed between the

specimen and the spindle

of the micrometer.

For some specimens, the

upper face is broken by the impact of the sandbag while the lower face remains vmbroken;

therefore, the set measured to the upper face

is greater than the deflection measured to the

lower face.

Figure 10.

Impact load on specimen, tested horizontally. A, specimen; B, supporting roller; C, sandbag; D, bottom disk; E, trip cord; and F, height-measuring tube.

[12]
((/) Results

For each height of drop the

deflection is the difference between the reading of the deflec- tometer and the initial reading.

Similarly, the set is the differ- ence between the reading of the

set gage and the initial reading.

The maximum height of drop is recorded, provided this height

of drop does not exceed 10 feet.

(e) Masonry Constructions

For wall constructions, such

as masonry, to which impact

loads cannot be applied satis- factorily with the specimen in a horizontal position, the loads are applied with the specimen in a vertical position, as shown in figure 13, thus simulating service

-Apparuliis jOr iiii pud Imid on. s pcciinr ii , It^^lcil lior LZiinlull ij

.

A, deflectometer; B, set gape; and C, gage block.

conditions. The specimen, A, on a steel channel, B, rests on cylindrical rollers, C, to prevent

Figure 11.

Deflectometer for measuring instantaneous

deflection of specimen under impact loads. A, tube; B, base; C, friction clamp; D, rod; and E, fiduciary, mark.

Figure 13.

Impact load on specimen, tested vertically.

^.specimen; B, channel; C, roller; D, supporting roller; E, frame; F, sandbag; and G, height-measuring tube.

13]
constraint. The axes of the roUers are parallel to the faces of the specimens. The two supporting rollers, I), are in contact with the vertical surface of the frame, E, and each roller rests on sponge rubber about Yo inch thick to prevent longitudinal constraint. The impact

load is applied by the sandbag, F, weighing 60

pounds, described in section VI-4-(b). The

bag is supported as a pendulum and from its initial position against the middle of the face of

the specimen is raised to the desired height, as determined by the measuring tube, G, and then

released. The deflection under the impact load

and the set are measured, using the instruments

described in section VI-4-(c), for the impact

tests on specimens in the horizontal position.

5. Racking Load

(a) Specimen

Tests are made on three duplicate specimens,

each having a height of 8 feet, and a nominal

width of 8 feet. A nominal width of 8 feet, twice the width of

the wall specimens for the other tests, was

chosen because the less the width, the greater

the vertical forces on the upper and lower ends

required to prevent rotation of the specimen

under a racking load.

{h) Loading

The specimen is tested as shown in figure 14,

supported on its lower end with a block at the

right to prevent horizontal movement when the

racking load is applied. There are two tie rods

at the left, one on each side of the specimen to prevent an upward movement of the left edge

of the specimen. There are two steel plates

separated by rollers between the upper end of

the specimen and the plate on the tie rods to prevent horizontal constraint. The racking load

is applied near the upper end to the left edge of

the specimen, causing shearing stresses. The racldng loads are applied horizontally

to the specimen A, figure 15, by a hydraulic

jack, B, having a capacity of 50 kips. (A kip

is 1,000 pounds.) To measure the load, the ring

dynamometer, C, having a capacity of 50 kips

is placed between the jack and the specimen.

The error in the load indicated by the dynamometer does not exceed 1 percent. Horizontal

movement of the specimen longitudinally under

the racking loads is prevented by the stop, A,

shown in figure 16. The stop is bolted to the

base of the racking frame. There are plates

between the end of the specimen and the stop.

(c) Apparatus

To measure the horizontal deformation of the

specimen parallel to the faces and the set, a

taut-wire mirror-scale measuring device is used

for the racking load similar to the deflec- tometers used to measure the lateral deflection

of the wall specimens imder compressive load.

The deflectometers are described in section

VI-l-(c).

Two mirror scales. A, are attached horizontally to one face of the specimen, as shown in

figure 17, one near the upper end and the other near the lower. A vertical wire, B, is attached to the frame, C, and tension in the

wire is maintained by rubber bands. The

frame, C, resting on the floor is moved to position the wire near the mirror-scales. Both

mirror scales are read simultaneously before the

specimen is loaded, then under a racking load,

and again after the load has been released.

The tie rods shown in figure 14, and at D,

figure 15, are provided to prevent vertical move- ment of the edge of the specimen to which the

racking load is applied. However, there is a

rotation of the specimen because the tie rods

stretch elastically under load. A taut-wire

mirror-scale device having the wire horizontal

is used to measure this rotation which is subtracted from horizontal movement indicated

by the mirror scales and the vertical wire to obtain the horizontal deformation and the set of the specimen.

id) Results

For each mirror scale the movement under

each racking load is the difference between the

reading of the mirror scale and the initial reading. For the vertical wire the horizontal

movement of the specimen is the difference

between the movements for the two mirror

scales multiplied by the ratio : 8 feet divided by

the vertical distance between the mirror scales. Using a similar method and the readings for

the horizontal wire, the vertical movement of

[14]
the specimen is obtained and subtracted from

the horizontal movement to obtain the actual

horizontal deformation and the set of the

specimen in a vertical distance of 8 feet for a

given racking load.

The maximum racldng load is recorded, pro- vided this load does not exceed 50 kips.

VII. METHOD OF TESTING PARTITIONS,

NONLOAD-BEARING

1. Impact Load

(a) Specimen

Tests are made on three dupHcate specimens,

each having a height of 8 feet and a nominal width of 4 feet. Because most partitions are symmetrical about a plane midway between the faces, the results for impact loads applied

to one face of a specimen should

be identical with those obtained

by applying impact loads to the other face.

(b) Procedure

The test procedure is identical

with that for impact load on

walls described in section VI-4,

except that only three specimens

are tested.

2. Concentrated Load

(a) Specimen

Tests are made on each of

the impact specimens after the

impact tests, the load being

applied to the same face of the

specimen.

(6) Procedure

The test procedure is identical

with that for concentrated load on walls described in section

VI-3.

VIII. METHOD OF TESTING FLOORS

L Transverse Load

(a) Specimen

Tests are made on three duplicate specimens,

each having a length of 12 feet 6 inches and a nominal width of 4 feet. In a small house the length of a floor between

supports and parallel to the joists is about 12

feet. A span of 12 feet was chosen for floor specimens because for shorter spans in the

floor of a house the construction usually is identical with that for spans of 12 feet. For

floor constructions included in this program,

the strength for spans greater than 12 feet can

Figure 14.Racking load on specimen.

[15]
Figure 15.

Hacking load equipment.

A, specimen; B, hydraulic jack; C, ring dynamometer; and D, tie rod.

on walls described in section j VI-3, except that the loads are | applied only to the upper (finish

floor) face of the specimen.

3. Impact Load

(a) Specimen

Tests are made on three dupli- cate specimens, each having a

length of 12 feet 6 inches and a , nominal width of 4 feet.

(b) Procedure

The test procedure is identical

with that for impact load on walls

described in section VI-4, except

that the span is 12 feet and the

impact loads are applied only to the upper (finish floor) face of

the specimen.

be estimated with sufficient accuracy for practical purposes by the usual engineering methods.

The specimens are 6 inches longer than the

span so that each end extends 3 inches beyond

the support.

(b) Procedure

The test procedure is identical with that for transverse load on walls described in section

VI-2, except that the span is 12

feet and the loads are applied

only to the upper (finish floor)

face of the specimen. No speci- mens are tested in the vertical

position.

2. Concentrated Load

(a) Specimen

Tests are made on each of

the transverse specimens after the

transverse tests.

(6) Procedure

The test procedure is identical

with that for concentrated load

IX. METHOD OF TESTING KOOFS

1. Transverse Load

(a) Specimen

Tests are made on three duplicate specimens,

each having a length of 14 feet 6 inches and a nominal width of 4 feet. In a small house if the supports for the roof

are vertically above those for the floor and the

Figure 16.

End of racking frame.

A, stop.

[16]
horizontal distance between tlie supports is 12 feet (floor span)

the roof span is also 12 feet if the

roof is fiat. If the roof slopes at an angle of 30° with the horizontal, the distance between roof

supports measured along the roof

is about 14 feet. For a low-cost

house it is unlikely that the slope

of the roof will exceed 30° (3 in 5)

because the cost of the roof in- creases more rapidly than the in- crease in the angle of the slope. A

roof span of 14 feet was, therefore, chosen for the roof specimen

because for shorter spans in the

roof of a house the construction

usually is identical with that for spans of 14 feet. For roof constructions included in this program, the strength for spans

greater than 14 feet can be esti- mated with sufficient accuracy for practical

purposes by the usual engineering methods. The

specimens are 6 inches longer than the span

so that each end extends 3 inches beyond the

support.

(6) Procedure

The test procedure is identical with that for transverse load on walls described in section

VI-2 except that the span is 14 feet and the

loads are applied only to the upper (weatherproofed) face of the specimen.

2. Concentrated Load

(a) Specimen

Tests are made on each of the transverse specimens after the transverse tests.

(6) Procedure

The test procedure is identical with that for concentrated load on walls described in section

VI-3, except that the loads are applied only to

the upper (weatherproofed) face of the specimen.

X. PRESENTATION OF RESULTS

The results of the tests are shown graphically.

A. tjjpical graph for transverse loading of a

17.

Apparatus for racking load on specimen.

A, mirror scale; B, wire; and C, frame.

wall, floor, or roof, is shown in figure 18. Results for the other tests are presented in a similar way. For all tests the loads are plotted as ordinates and the deformations as abscissas.

For all specimens the load is applied in increments so chosen that a sufficient number of

readings is obtained to determine definitely

the load-deformation curve. The initial reading of the load and the reading of the deformation is recorded either with no load on the

specimen or under a small initial load as at a, figure 18. The load is increased to the first increment, b, and the deformation recorded.

The load is then decreased to the initial load, a, and the set (sometimes designated "permanent

set") recorded. This set is plotted at c, the

ordinate being the load which, when released,

caused this set. The load is then increased to two increments, d, and the set when it is released to the initial load, a, plotted at e. This sequence of readings and points on the

graph is then followed for three increments,

four increments, etc. of load. There are three

duplicate specimens for each test and the results

for each specimen are shown on the same

graph. Although the particular specimen for each point on the graph is not designated, they were recorded on the laboratory data sheets. The points for deformation under load are

[17]
I'

I

I

—

c

—•- —o~ C • •

•

—"-^

T

3

0 0.1 OA 0.6

deflecfion in. Figure 18.—Typical graph showing results. Open circles—deformations under load; solid circles—sets after loads removed; continuous line—load-deformation curve; and broken line—

load-set curve.

shown by open circles and those for set by solid

circles. The three values for either the deformation or the set are averaged and tliis average

value plotted in pencil on the graph. A smooth

curve is drawn among the average points to show the average behavior of the construction.

The load-deformation curves are continuous

lines and the load-set curves are dashed lines. If readings are obtained under greater loads

for some specimens than for others, all the

values are plotted, but the curves are only

drawn to the average values for which there

are three values. When for each specimen

the behavior of the specimen under load indi- cates that the specimen might fail suddenly

and damage the deformation-measuring apparatus, this apparatus is removed from the

specimen and the load increased continuously

imtil the maximum load which can be applied

to the specimen is determined. The maximum

loads are not plotted on the graph but are given

in the report. This method of testing by

applying the loads in increments and measuring

the deformation, then the set under the initial load, simulates, to some extent, repeated loading imder service conditions. Therefore, results by such a method of loading may be more

useful than those obtained by increasing the

load continuously. They may show whether

different portions of a construction act as a

unit under load, whether the fastenings or bonds have adequate strength, or whether

they rupture imder repeated loads. For any

engineering structure, including low-cost houses,

it is necessary not only that the strength be

adequate, but also that the deformation under

load shall not appreciably decrease the useful- ness of the structure. If the working load and

the allowable deformation for an element for a house are Icnown, constructions complying

with these requirements may be selected by

inspection of the graphs, provided the construction was included in this program.

A structure is elastic if, after a load has been

applied and then removed, the set is inappreciable. If the set is small for an element of a house it may be assumed that the construction

has neither been damaged nor appreciably deformed by the load. The set, therefore, is another property which may be used when comparing different constructions and may be useful when selecting a construction for a particular purpose.

Obviously, the differences between the points

and the curve are a measure of the variations

in the properties of the construction.

The variations in the properties of a construction as used commercially for houses, in all probability, are greater than the variations for the three specimens tested in this program be- cause these specimens were all fabricated at the same time by the same workmen and from the same lot of material.

Building codes and specifications for house

construction might logically give definite maximum values for either the deformation or the

set, or for both, when the available information

is adequate for determining these values. It is believed that the graphs and the maximum

loads for the constructions included in this program for the determination of the structural

properties of house constructions will give in- formation which has not heretofore been

available. This information should be of value

to the construction industry and the public.

Washington, May 5, 1938.

18

O
The program of research on building materials and structures imdertaken by the

National Bureau of Standards is planned with the assistance of the following advisory

committee designated by the Subcommittee on Design and Construction of the Central

Housing Committee:

TECHNICAL RESEARCH GROUP

Harold D. Hynds, Chairman

Walter Junge, Federal Housing Administration, Vice Chairman

Pierre Blouke,

Home Owners' Loan Corporation.

C. W. Chamberlain,

Procurement Division.

Charles E. Matette,

United States Housing Authority.

Vincent B. Phelan,

National Bureau of Standards.

A. C. Shire,

United States Housing Authority.

George W. Trayer,

United States Forest Service.

Elsmere J. Walters,

Quartermaster Corps, War Department.

Sterling R. March,

Secretary.

The program is administered and coordinated by the following staff committee of the Bureau:

Hugh L. Dryden, Chairman

P. H. Bates W. E. Emley A. S. McAllister

H. C. Dickinson G. E. F. Lundell H. S. Rawdon

The Forest Products Laboratory of the United States Department of Agriculture

is cooperating with the National Bureau of Standards in studies of wood constructions.

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