Bureau oi bba.:--.

U. S. DEPARTMENT OF COMMERCE

A.

BUILDING

MATERIALS

AND

STRUCTURES

REPORT BMS20

Structural Praperttes^o^X*^)^"''

"Twachtman" Cons^i^,^i^ions for

Walls and Floors Sponsored by

Connecticut Pre-Cast Buildings

Corporation

HERBERT L. WHITTEMORE

AMBROSE U. STANG, anci

DOUGLAS E. PARSONS
The program of research on building materials and structures, carried on by the

National Bureau of Standards, was undertaken with the assistance of the Central Housing Committee, an informal organization of governmental agencies concerned with

housing construction and finance, which is cooperating in the investigations through a subcommittee of principal technical assistants.

CENTRAL HOUSING COMMITTEE

SUBCOMMITTEE ON TECHNICAL EESEAECH

Walter Junge, Federal Housing Admin- Abthur C. Shire, United States Housing

istration. Chairman Authority, Vice Chairman

Sterling R. March, Secretary

Albert G. Bear, George E. Knox,

Veterans' Administration. Yards and Docks (Navy).

Pierre Blouke, Vincent B. Phelan,

Federal Home Loan Bank Board. National Bureau of Standards (ComCarroll W. Chamberlain, merce).

Procurement Division (Treasury). Edv/ard A. Poynton,

Joseph M. DallaValle, Office of Indian AiTau's (Interior).

Public Health Service. George W. Trater,

John Donovan, Forest Service (Agriculture).

Farm Security Administration (Agri- Elsmere J. Walters,

culture). Construction Division (War).

CHAIRMEN OF SECTIONS

Specifications Materials Maintenance

Carroll W. Chamberlain Elsmere J, Walters John H. Schaefer

Mechanical Equipment Methods and Practices

Robert K. Thulman

NATIONAL BUREAU OF STANDARDS

STAFF COMMITTEE ON ADMINISTRATION AND COORDINATION

Hugh L. Dryden, Chairman.

Mechanics and Soimd

Phaon H. Bates, Gustav E. F. Lundell,

Clay and Silicate Products. Chemistry.

HoBART C. Dickinson, Addams S. McAllister,

Heat and Power. Codes and Specifications.

Warren E. Emley, Henry S. Rawdon,

Organic and Fibrous Materials. Metallurgy.

The Forest Products Laboratory of the United States Department of Agriculture is cooperating with both committees on investigations of wood constructions.

[For list of BMS publications and how to purchase, see cover page III]
UNITED STATES DEPARTMENT OF COMMERCE • Harry L. Hopkins, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director BUILDING MATERIALS

and STRUCTURES

REPORT BMS20

Structural Properties of "Twachtman"

Constructions for Walls and Floors

Sponsored by Connecticut Pre-Cast

Buildings Corporation

by HERBERT L. WHITTEMORE, AMBROSE H. STANG,

and DOUGLAS e. parsons

ISSUED AUGUST 17, 1939

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 of reports are to be construed accordingly.

UNITED

FOR SALE

STATES GOVERNMENT PRINTING OFFICE • WASHINGTON

BY THE SUPERINTENDENT OF DOCUMENTS, WASHINGTON, D. C. • PRICE

1939

I O CENTS
Foreword

This report is one of a series issued by the National Bureau of Standards on the

structural properties of constructions intended for low-cost houses and apartments.

Practically all of these constructions were sponsored by groups within the building

industry which advocate and promote the use of such constructions and which have

built and submitted representative specimens, as outlined in report BMS2, Methods of

Determining the Structui'al Properties of Low-Cost House Constructions. The sponsor

is responsible for the representative character of the specimens and for the description

given in each report. The Bureau is responsible for the test data.

This report covers only the load-deformation relations and strength of the structural

elements submitted when subjected to compressive, transverse, concentrated, impact^

and racking loads by standardized methods simulating the loads to which the elements

would be subjected in actual service. It may be feasible later to determine the heat

transmission at ordinary temperatures and the fire resistance of these same constructions

and perhaps other properties.

The National Bureau of Standards does not "approve" a construction, nor does it express an opinion as to the merits of a construction, for the reasons given in reports

BMSl and BMS2. The technical facts on these and other constructions provide the

basic data from wliich architects and engineers can determine whether a construction

meets desired performance requirements.

Lyman J. Briggs, Director.

[n]
Structural Properties of "Twachtinan" Constructions

for Walls and Floors

Sponsored by Connecticut Pre-Cast Buildings Corporation

by HERBERT L. WHITTEMORE, AMBROSE H. STANG, and DOUGLAS E. PARSO NS

CONTENTS

Page

Foreword ii

I. Introduction 1

II. Sponsor and product 2

III. Specimens and tests 2

IV. Wall AR 2

1. Sponsor's statement 2

(a) Materials 2

(b) Description 3

(1) Four-foot wall specimens. 3

(2) Eight-foot wall specimens. 3

(c) Comments 3

2. Compressive load 4

3. Transverse load 5

4. Concentrated load 6

Page IV. Wall ^B—Continued.

5. Impact load 7

6. Racking load 8 V. Floor 8

1. Sponsor's statement 8

(a) Materials 8

(b) Description 8

(c) Comments 10

2. Transverse load 10

3. Concentrated load 10

4. Impact load 10

VI. Additional comments by sponsor 11 VII. Selected references 13

ABSTRACT

For the program on the determination of the structural properties of low-cost house constructions the Connecticut Pre-Cast Buildings Corporation submitted

24 specimens representing "Twachtman" precast hollow

reinforced-concrete constructions for walls and floors. The wall specimens were subjected to compressive,

transverse, concentrated, impact, and racking loads; and the floor specimens to transverse, concentrated,

and impact loads. The transverse, concentrated, and

impact loads were applied to both faces of wall speci- mens. For each of these loads, three like specimens

were tested. The deformation under load and the set

after the load was removed were measured for uniform

increments of load, except for concentrated loads, for which the set only was determined. The results are presented in graphs and in tables.

I. INTRODUCTION

In order to provide technical facts on the per-

|j formance of constructions which might be used

in low-cost houses, to discover promising constructions, and ultimately to determine the

properties necessary for acceptable performance,

the National Bureau of Standards has invited

the building industry to cooperate in a program

of research on building materials and struc- tures for use in low-cost houses and apartments.

The objectives of this program are described in

report BMSl, Research on Building Materials

and Structures for Use in Low-Cost Housing,

and that part of the program relating to structural properties in report BMS2, Methods of

Determining the Structural Properties of LowCost House Constructions.

As a part of the research on structural properties, six masonry wall constructions have been

subjected to a series of standardized laboratory

tests to provide data on the properties of some

constructions for which the behavior in service

is generally known. These data are given in

report BMS5, Structural Properties of Six

Masonry Wall Constructions. Similar tests have been made on wood-frame constructions

by the Forest Products Laboratory of the United

States Department of Agriculture, the results of which will be given in a subsequent report in

this series.

[1]
This report describes the structural properties of constructions sponsored by one of the

manufacturers in the building industry. The

specimens were subjected to compressive,

transverse, concentrated, impact, and racking

loads, simulating loads to which the elements

of a house are subjected. In actual service,

compressive loads on a wall are produced by

the weight of the roof, second floor and secondstory walls if any, furniture and occupants,

wind load on adjoining second-story walls,

and snow and wind loads on the roof. Transverse loads on a wall are produced by the wind,

concentrated and impact loads by furniture or accidental contact with heavy objects, and

racking loads by the action of the wind on

adjoining walls. Transverse loads are applied

to floors by furniture and by the occupants;

concentrated loads by furniture, for example,

the legs of a piano; and impact loads by objects

falling on the floor or by persons jumping on

the floor. The deformation and set under each increment of load were measured because the suitability of a wall or floor construction depends in

part on its resistance to deformation under load

and whether it returns to its original size and

shape when the load is removed.

II. SPONSOR AND PRODUCT

The specimens were submitted by the Connecticut Pre-Cast BuUdings Corporation, Ir- vington, N. Y., and represented a wall and a

floor construction marketed under the trade

name "Twachtman." The specimens were manufactured by the Richmond Ready Mix

Concrete Corporation, Richmond, Va., one

of the companies licensed to manufacture

"Twachtman" constructions. These constructions consisted of precast hollow reinforced- concrete wall and floor panels designed to be

erected on masonry foundations by the use of crane trucks.

III. SPECIMENS AND TESTS

The specimens represented two elements of a house which were assigned the following symbols: wall AR and floor AS. The specimens were assigned designations in accordance with

table 1.

Table 1.

Specimen designations

Element

Wall,. Do-. DoDo..

Do.. Do.

Do..

Do..

Floor. Do..

Do..

Construc- tion symbol

AR

AR

AR

AR

AR

AR

AR

AR

AS

AS

AS

Specimen

designation

CI, C2, CS..

Tl, T2, TS..

Ti, T5, T6. . P1,P2,P3»

PI,,P5,P6».

II, 12, IS U, 15, 16...^ R1,R2,RS..

Tl, TS, TS- P1,P2,P3<^

II, 12, IS

Load

Compressive... Transverse do

Concentrated. do Impact

do Racking

Transverse Concentrated. Impact

Load applied

Upper end.

Inside face. Outside face. Inside face. Outside face. Inside face. Outside face. Near upper end. Upper face. Do. Do.

• These specimens were undamaged portions of the transverse specimens. The specimens were tested in accordance

with BMS2, Methods of Determining the Structural Properties of Low-Cost House Constructions, which also gives the requirements for the

specimens and describes the presentation of the

results of the tests, particularly the loaddeformation graphs.

The tests were begun March 14, 1938, and

completed March 23, 1938. The specimens were tested 28 days after they were built. The sponsor's representative witnessed the

tests. IV. WALL AR

1. Sponsor's Statement

(a) Materials

Cement.—Portland, high-early-strength, Lehigh Portland Cement Co.'s "Hi-Early."

Slag.—Blast-furnace, water-cooled, and

crushed, passed K-in. sieve and retained on No.

100 sieve; weight 50 to 55 lb/ft \ The Pottsco

Corporation's "Pottsco."

Mortar.—One part of cement to 5 parts of slag (passed No. 4 sieve), by weight.

Concrete.—One part of cement and 3.3 parts

of slag, by weight.

Welded wire jabric. —Steel wire, No. 13 gage

(0.0915-in. diam), electrically welded in a 4-by

4-in. mesh, complying with the American Society for Testing Materials Standard A 185-37.

American Steel and Wire Co.

Metal lath. —Flat, expanded metal, formed

from open-hearth sheet steel, coated with paint;

weight 3.4 lb/yd ^. Truscon Steel Corporation.

Reinforcement bars.—Steel, structural, billet,

open-hearth, deformed, round. Specified mechanical properties: tensile strength, 70,000 to

2]
80,000 lb/in.2; yield point, 40,000 lb/in.'; elongation in 8 in., minimum, percent, 1,125,000/tensile strength.

Wire.—Steel, black. No. 18 gage (0.0475-in.

diam).

(6) Description

(1) Four-foot wall specimens.—The 4-ft wall

specimens were 8 ft 0 in. high, 4 ft 6 in. wide,

and 6 in. thick. Each specimen was a hollow

FiGUEE 1.Four-foot wall specimen AR.

A, welded wire fabric; B, metal-lath form; C, vertical reinforcement; D, lateral reinforcement; E, end reinforcement; F, eye.

reinforced-concrete slab having faces 1 in. thick

and four studs integral with the faces. The

specimens were cast in a horizontal position with

the inside face down. Mortar was spread to a depth of }^ in., welded wire fabric. A, shown in

figure 1, placed on the mortar, and before the

mortar had set, concrete was placed over the

fabric to a depth of in., completing the inside

face. A metal-lath form, B, with the reinforcement and hooks fastened in their proper relative

positions by wire, was placed on the fresh concrete. The reinforcement consisted of vertical

reinforcement, C, for each stud, lateral reinforcement, D, for the outside face, and end reinforcement, E, at each end. Eyes, F, were fastened

to the upper ends of the reinforcement for the

two inner studs. Concrete for the studs and

outside face was placed in the form, compacted

by vibrators, and leveled to a depth of in. above the top of the metal lath. The outside

face was finished with mortar, )^ in. deep,

placed on the fresh concrete, screeded, and

troweled smooth.

The price of this construction in Washington,

D. C, as of July 1937, was $0.33/ft2.

Welded wire fabric. —The welded wire fabric,

A, was one sheet 7 ft 10 in. by 4 ft 0 in. Metal-lath form. —The metal-lath form, B,

consisted of four strips 6 ft 0 in. by 2 ft 0 in., and one strip 6 ft 0 in. by 1 ft 0 in. The length

of the strips was at right angles to the length of

the specimen. The strips overlapped about 2

in. and were shaped by dies to the form of the

studs.

Vertical reinforcement.—The vertical reiaforcement, G, consisted of one %-in. diam reinforcement bar, 7 ft 6 in. long, in each stud, at midthickness.

Lateral reinforcement.—The lateral reinforcement, D, consisted of eight M-in. diam reinforcement bars, 4 ft 2 in. long, spaced 1 ft 0 in. on

centers, and % in. below the outside face. End reinforcement.—The reinforcement, E, at each end consisted of two Yt-in. diam reinforcement bars, 4 ft 8 in. long, having 3-in, rightangle bends at each end. The bars were spaced

about 5 in. on centers and about 1 in. from the

ends of the specimen.

Eyes.—There were two lifting eyes, F, at the upper end of each specimen. The eyes were

Vi-m. diam reinforcement bars, 3 ft 0 in. long,

with one end bent to a ring, 3 in. diam. Each

eye was in a recess in the end of the specimen.

(2) Eight-foot wall specimens.—The 8-ft wall

specimens were 8 ft 0 in. high, 8 ft 6 in. wide,

and 6 in. thick. The specimens were similar to the 4-ft specimens. Each specimen had a stud

at each edge and five intermediate studs, spaced

1 ft 4 in. on centers.

(c) Comments

The wall panels are cast in adjustable steel forms which provide a smooth inside face complete with trim. Window frames, door hinges,

registers, and other hardware are placed in the

[3]
forms and cast integrally with the panels. The

panels are made full-story height and usually

the width is the width of the room. When

erected, the panels rest on the floor panels and

are fastened to the floor panels and to adjacent

wall panels. At corners, the edges of the panels

are beveled 2 in. back from the inside face to form the joint. The panels are fastened by means of /2-in. diam reinforcement bars which

project 4 in. from the edges of the panels near

the upper and lower ends. The bars overlap

when the panels are in position and are fastened

by /8-in. cable clamps. The outside of the cor- ner is formed by concrete, cast in a steel form.

Intermediate joints usually occur at partitions,

in which case, the inside faces of adjacent wall

panels are each recessed /s by 3 in. for the

story height, the outside face is recessed 2 by 2

by 4 in. at the top and bottom, and the wall

panels are then placed with a %-in. space between the edges. The edge of the partition

panel, which is similar to the wall panels, fits into the inside recess in the wall panels and is fastened by two ^o-in. bolts which project 4%in.

from the edge of the partition and extend

through the space between the wall panels.

One bolt is near the upper end and one near the

lower end. Each bolt engages a 4- by 4- by ji- in. steel plate set in the outside recesses of the

wall panels and is fastened with a nut. The

joint and recesses are filled with cement mortar

and finished smooth.

Wlien joints occur where there is no partition, the edges of the panels are keyed together

with concrete. A recess, 3}^ by 2 in., is formed

in the edge of each panel. The panels are placed with a %-in. space between the edges,

and the recesses and joint filled with concrete. Paint or other decorative finish may be applied directly to the panels. Lap siding, brick

veneer, and other finishes may be used. Wood

finishes are fastened by hardened steel nails.

2. Compressive Load

Wall specimen AR-Cl under compressive

load is shown in figure 2. The results for wall

specimens AR~C1, C2, and C3 are shown in table 2 and in figures 3 and 4. The shortenings and sets shown in figure 3 for a height of 8 ft were computed from the

values obtained from the compressometer

readings. The gage length of the compressometers was 7 ft 6 in. Specimens Cl and C3 failed by crushing of

the upper ends of the specimens, cracking of

the outside faces transversely (across the specimens) near the upper ends, and cracking verFiGURE 2. —Wall spiciimn AR-Cl under compressive

load.

[4]
tically at the edges near the upper ends.

Specimen C2 failed by crushing of the lower

end.

Table 2.

Structural properties, wall AR

[Weight, 3fi.8 1b/ft2]

Load

Compressive

TransverseDo.

Concentrated

Do.

Impact

Do.

Racking.

Load applied

(Upper end, 2 in.

>. from the in-

[ side face

Average.

flnside face; span,

1 7 ft C in

Average.,

rOutside face

[ span, 7 ft 6 in .

Average

Inside face.

Average

Outside faceAverage

/Inside face; span,

1 7ft6in --

Average

fOutside f \ span, 7 ft I

Average.

ace

;

6 inNear upper end

Average

Spefi men

de.sig- nation

Pt

Pi

P5P6

m

R2

PS

Fail- ure of loaded

face, height

of drop

9.5

10.0 8.5

9.3

Fail- ure of opposite

face, height

of drop

5.0 4.0

3.0

Maxi- mum

height

of drop

9. 5 10.0

10.0

b 10.0

1 10.0

tlO. 0

Maxi- mum

load

^Kips/ft 72.0

79.3 88.7

80.0

lb/ft'172

130

110

137

350

391 380

374

lb

" 1, 000

t 1, 000

b 1, 000

!> 1, 000

b 1, 000

b 1, 000

b 1, 000

b 1, 000

^Kips/ft b5.88

b 5. 88

b 5. 88

b 5.

» A kip is 1,000 lb.

b Specimen did not fail. Test discontinued.

3. Transverse Load

The results are shown in table 2 and in

figure 5 for wall specimens AR-Tl , T2, and

T3, loaded on the inside face, and in figure 6

for wall specimens AR-T4, T5, and T6, loaded on the outside face. The transverse loads were applied with the

specimens in a horizontal position. The initial deflection and set readings shown in figures 5 and 6 were taken under a load of about 48

Ib/ft^ caused by the weight of the specimens

60

Co

30

§ 20

I

p 10

0

7f •

o

f OCT o —

o

of c

Of C fo

JO

• p

y

0.02 OM o.oe

shorf^eninq in-ISfi

Figure 3.Compressive load on wall AR.

Load-shortening (open circles) and load-set (solid circles) results for specimens AR-Cl, C2, and C3. The load was applied 2 in. from the

inside face. The loads are in kips per foot of actual width of specimen.

60'

40

JO

20

to

o

o

0\

AR

' 0.2 0.4. 0.6

laferal deflecfion in. Figure 4.

Compressive load on wall AR.

Load-lateral deflection (open circles) and load-lateral set (solid circles) results for specimens AR-Cl, C2, and C3. The load was applied 2 m.

from the inside face. The loads are in kips per foot of actual width

of specimen. The deflections and sets are for a gage length of 7 ft 6 in., the gage length o( the deflectometers.

[5]
120

5S^

80i

J) 4^

I

J. 20

0

•

1

)

-ort

AR-I 0.02 CM

deflection

O.OB

in. Figure 5. —Transverse load on wall AR, load applied to inside face.

Load-deflection (open circles) and 1." ad-set (solid circles) results for specimens AR-Tl , Tg, and T3 on the span 7 ft 6 in.

000

400

300

^200

t/oo:

1 O »•

• O

f/—

•

0 0.2 0.4.

defleciion

0.6

in. Figure 6. —Transverse load on wall AR, load applied to outside face.

Load-deflection (open circles) and load-set (solid circles) results for speci- mens AR-TJ,, T6, and T6 on the span 7 ft 6 in.

between the supporting rollers and the weight

of the loading apparatus.

Specimens Tl, T2, and T3 failed by rupturing

transversely (across the specimen) at or between

the loading rollers. For specimens T!^ and T6 at loads of 260 and

240 lb/ft'' and deflections of 0.26 and 0.17 in., respectively, the inside face of each specimen

cracked transversely (across the specimen) . At

the maximum loads each of the specimens T4,

T5, and T6 failed by rupturing transversely

(across the specimen) at or between the loading

rollers.

4. Concentrated Load

The results are shown in table 2 and in

figure 7 for wall specimens AR-Pl , P2, and PS,

loaded on the inside face, and in figure 8 for

lOOOl

800

600f

i200f

o

Oft

AR-I

Figure 7.-

0 0.02 0.04- o.oe indenfaHon in. -Concentrated load on wall AR, load applied

to inside face.

Load-indentation results for specimens AR-Pl, Pt, and PS.

wall specimens AR-P4, P5, and P6, loaded on

the outside face. The concentrated loads were applied to the

inside face of specimens PI, P2, and PS between two studs and about IK ft from one end.

The indentations after a load of 1,000 lb had

been applied were less than 0.001 in. for each

[6]
of the specimens and no other effect was

observed.

The concentrated loads were applied to the

outside face of specimens P4, P5, and P6

between two studs and at least 1 K ft from one

end. The indentations after a load of 1,000 lb

1000

13'

I'

o

1

1r•

•

1

1•

1•

AR-4 0

indeniation

0.06

in

Figure 8. -Concentrated load on wall AR, load applied

to outside face.

Load-indentation results for specimens AR-PJt, P5, and P6.

had been applied were 0.003, 0.000, and 0.000

in. for specimens P4, PH, and P6, respectively,

and no other effect was observed.

5. Impact Load

The results are shown in table 2 and in figure

9 for wall specimens AR-Il, 12, and 13, loaded on the inside face, and in figure 10 for wall speci- mensAB-/4,/5, and 16, loaded on the outside face. The impact loads were applied to the center

of the inside face of specimens II, 12, and IS,

the sandbag striking midway between the two

inner studs. At drops of 5, 4, and 3 ft and deflections of 0.20, 0.16, and 0.06 in. for specimens

II, 12, and IS, respectively, the outside face of

each specimen failed by cracking transversely

(across the specimen) at midspan. At drops of

8.5, 8.5, and 7.5 ft for specimens II, 12, and IS,

respectively, the inside face (face struck) of each

/o

6

0

• So —

//

/

11

IT

AR-I 0 2 4

def/eciion

Figure 9.-

in.

-i mpact load on wall AR, load applied to inside face.

Height of drop-deflection (open circles) and height of drop-set (solid

circles) results for specimens AR-U, 12, and IS on the span 7 ft 6 in.

/o

8

% 6

0

T

y

AR-4 0 0.2 OA 0.6

deflection in. Figure 10.

Impact load on wall AR, load applied to outside face. Height of drop-deflection (open circles) and height of drop-set (solid

circles) results for specimens AR-I4, 15, and 16 on the span 7 ft 6 in.

[7]
specimen cracked where the sandbag struck.

At the maximum drops, specimens II and 12

failed by breaking in two at midspan. For

specimen IS at a drop of 8.5 ft the inside face

(face struck) failed by rupturing of the face

where the sandbag struck, and at a drop of 10 ft

Figure 1 1. —Wall .specimen AR It :

the specimen failed by rupturing transversely

(across the specimen) at midspan.

The impact loads were applied to the center

of the outside face of specimens 14-, 15, and 16,

the sandbag striking midway between the two

inner studs. At drops of 5 and 5.5 ft and deflec- tions of 0.09 and 0.08 in. for specimens 15 and

16, respectively, the inside face of each specimen cracked transversely (across the specimen)

near midspan. The sets after a drop of 10 ft were 0.067, 0.046, and 0.032 in. for specimens

14, 15, and 16, respectively, and no other effect was observed.

Wall specimen . shown in figure 1

6. Racking Load

AR BS under racking load is

The results for wall specimens AR-Rl, R2,

and R3 are shown in table 2 and in figure 12. The deformations and sets for a height of 8 ft, shown in figure 12, were computed from the

values obtained from the measuring-device

readings. The gage length of the vertical

measuring device was 6 ft 3 in. The

gage length of the horizontal measuring device was 5 ft 0 in. The error of

observation in measuring the deformations and sets was about 0.01 in.,

causing some of the set readings to be

negative. An error of 0.01 in. in a height of 8 ft is negligible for tests of

this kind.

The sets after a load of 5.88 kips/ft

had been applied were less than 0.01

in. for each of the specimens. For

specimens Rl and R2 no other effect was observed, and for specimen R3

only a slight crack about 1 ft long was

observed near the center of the inside

face. V. FLOOR AS

1. Sponsor's Statement

(a) Materials

The materials for floor AS were the same as for wall AR.

(6) Description

The floor specimens were 12 ft 6

in. long, 4 ft 6 in. wide, and 6 in. thick.

Each specimen was a hollow reinforced-concrete

slab having faces 1 in. thick and four joists in- tegral with the faces. The specimens were cast

in a horizontal position with the lower face

down. Mortar was spread to a depth of }{ in., welded \vire fabric, A, shown in figure 13, placed on the mortar, and before the mortar had set concrete was placed over the fabric to a depth

of in., completing the lower face. A metallath form, B, with the reinforcement and eyes

fastened in their proper relative positions by

wire, was placed on the fresh concrete. The

reinforcement consisted of longitudinal reinforcement, C, for each joist, lateral reinforcement, D, for the upper face, and end reinforcement, E, at each end. Eyes, F, were fastened

to each end of the reinforcement for the two

[8]
inner joists. Concrete for tiie joists and upper

face was placed in the form, compacted by

vibrators, and leveled to a depth of in. above

the top of the metal lath. The upper face was

finished with mortar, ji in. deep, placed on the

fresh concrete, screeded, and troweled smooth.

The price of this construction in Washington,

D. C, as of July 1937, was $0.33 ft^. Welded wire fabric. —The welded wire fabric,

A, was one sheet, 12 ft 4 in. by 4 ft 0 in. Metal-lath farm.—The metal-lath form, B,

consisted of six strips of metal lath 6 ft 0 in. by

2 ft 0 in., and one strip 6 ft 0 in. by 1 ft 0 in. The length of the strips was at right angles to the length of the specimen. The strips over- lapped about 2 in. and were shaped by dies to the form of the joists.

Longitudinal reinfarcement.—The longitudinal

reinforcement, C, consisted of three reinforcement bars in each joist fastened together by

wire. The length of the assembled bars was

12 ft 2 in. for the two outer joists and 12 ft 0 in. for the two inner joists. The lowest bar of

each assembly was a %-in. diam bar with each

end bent upward 2 in., and placed with its center Iji in. above the lower face of the

specimen. A y^-m. diam bar was placed just

above the lowest bar, being bent diagonally

upward starting about 1 ft from each end,

extending about 2 in. along the top, then bent

downward for about 2 in. at the ends. The

top bar was % in. diam with its ends bent

0 0.02 0.04

c/e forma/ion

0.06

in./8ff

Figure 13.

Floor specimen AS.

A, welded wire fabric; B, metal-lath form; C, longitudinal reinforcement; D, lateral reinforcement; E, end reinforcement; F, eye.

Figure 12.

Racking load on wall AR.

Load-deformation (open circles) and load-set (solid circles) results for specimens AR-Rl, R2. and RS. The loads are in kips per foot of actual width of specimen. downward 3% in. and with the center of the bar

5% in. above the lower face of the specimen.

Lateral reinfarcem.ent. —The lateral reinforcement, D, consisted of thirteen %-in. diam reinforcement bars, 4 ft 2 in. long, spaced 1 ft 0 in. on centers, and K-in. below the upper face. End reinfarcement.—The

reinforcement, E, at each

end was one %-in. diam bar,

4 ft 8 in. long, having a 3-in. right-angle bend at each

end. The bars were at midthickness and about 1 in. from the ends.

Eyes.—There were two

lifting eyes, F, at each end of

the specimen. The eyes were

Vi-VQ.. diam reinforcement

bars, 3 ft 0 in. long, with one end bent to a ring 3 in. diam.

The eyes were fastened to the reinforcement for the

two inner joists by vAve. Each eye was in a recess in

the end of the specimen.

[9]
(c) Comments

The floor panels are cast in adjustable steel forms in the same manner as the waU panels.

The length of the panels usually corresponds to the length of the room and the width may be

as great as 8 ft. Sleeves and boxes for piping

and conduit are placed in the form and cast

integrally with the panels.

Table 3.Structural 'properties, floor AS

[Weight. 37.7Ib/ft2]

Load Load applied

Speci- men

desig- nation

Maxi- mum

height

of drop

Maxi- mum

load

Transverse- Upper face; span, 12 ft 0 in...

Average

\Tl in

ft Ib/P

236

211 240

Concentrated-. _

Impact.. .

\TS

229

Upper face \P2

lb » 1, 000

» 1, 000

' 1, 000 Average

[PS

' 1, 000

Upper face; span, 12 ft 0 in...

Average

»10. 0 '10.0

\I3 »10.0

» 10.0

» Specimen did not fail. Test discontinued.

'^^ The panels are placed directly on the foundation walls, which have first been leveled with

cement mortar. After the panels are placed,

the exposed ends and sides are finished flush

with the wall panels with a ?^-in. coat of mortar.

The finish floor may be wood block, tile, or linoleum cemented to the panels; or wood

flooring may be laid on wood sleepers.

2. Transverse Load

Floor specimen AS-T2 under transverse load

is shown in figure 14. The results for floor specimens AS-Tl, T2, and T3

are shown in table 3 and in figure 15. For each of the specimens

the lower face cracked trans- versely across the specimen

at several places between

the loading roUers. The first cracks occurred at loads of

120, 100, and 60 Ib/ft^ and

deflections of 0.45, 0.43, and

0.19 in. for specimens Tl,

T2, and T3, respectively.

At the maximvmi loads each

of the specimens fafled by

rupturing transversely

(across the specimen) at one

or more places between the loading rollers.

3. Concentrated Load

Floor specimen A.S-P1 under concentrated

load is shown in figure 16. The results for floor specimens AS-Pl, P2,

and P3 are shown in table 3 and in figure 17. The concentrated loads were applied to the

upper face of each specimen between two studs

and about midlength. The indentations after a load of 1,000 lb had been applied were 0.001,

0.001, and 0.000 in. for specimens Pi, P2, and

PS, respectively, and no other effect was observed.

4. Impact Load

Floor specimen AS-I3 during the impact test

is shown in figure 18. The results for fioor specimens AS~I1, 12, and 13 are shown in table

3 and in figure 19.

[10]
The impact loads were applied to the upper

face of each specimen, the sandbag striking

midway between the two inner studs. At

240

200

160

-^120

\

<D- — C

/

•

-CD- —

— r

T

T

T

77

AS

0.4 as 1.2

c/eflecfion in

Figure 15. —Transverse load on floor AS.

Load-deflection (open circles) and load-set (solid circles) results for specimens AS-Tl, TB, and T3 on the span 12 ft 0 in.

drops of 5.5 and 8.5 ft and deflections of 0.24

and 0.28 in. for specimens II and 12, respectively, the lower face of each specimen cracked

transversely (across the specimen) near midspan.

The sets after a drop of 10 ft were 0.108, 0.095,

and 0.114 in. for specimens 14, 15, and 16,

respectively, and no other effect was observed.

1000^

oo

i

•

•

•u1•

AS

Figure 16.

Floor specimen AS-PI under concentrated

load.

0

indenfaHon in. Figure 17.

Concentrated load on floor AS.

Load-indentation results for specimens AS-Pl, P2, and PS.

VI. ADDITIONAL COMMENTS BY

SPONSOR

"Twachtman" elements for house construction were developed by the sponsor as a result

of 2 years of research work and unit cost analyses of various materials and methods.

Panels of reinforced concrete were finally

chosen as ofi^ering the most desirable combination of cost, transportation, workability, and

long life. In order to overcome unconventionality of appearance, excessive labor in

erection, and waterproofing of many jomts, it was decided to make the panels as large as the width of the structure permitted, provided

this did not exceed the size which could be

readily transported.

About 35 houses embodying these constructions were completed on March 1, 1939. The

[11]
foundations were concrete footings and either

conventional masonry or precast hollow concrete panels, similar to wall AR.

The panels were delivered to the house site by truck and placed in position by a crane

w

3

Figure 18.Floor specime?i AS-IS during the impact test.

trucK, as shown in figure 20. When delivered,

the panels were completely equipped with

hardware, openings for pipe and conduit, etc., and required only to be assembled and to have

the joints between panels sealed.

The walls and floors were the precast hollow

reinforced-concrete constructions described in

this report and the partitions were similar to the wall panels. The buildings had either

flat or sloping roofs. For flat roofs, roof panels, similar to the floor panels, rested directly on the walls. After

the roof panels were placed, the exposed ends

and sides were finished with a %-in. coat of

cement mortar flush with the outside of the

wall. The panels were covered with a built-up

roofing. A precast-concrete coping, 7}^ b}' 5 in., was placed with a /4-in. overhang,

around the edges of the roof, except on one

side which was left open for drainage. On this

side, metal flashing extended under the roofing

and down into a metal gutter. The ceiling was formed by the lower faces of the roof

panels.

Sloping roofs were either precast-concrete

panels or conventional wood-frame construction. The concrete panels were similar to the

floor panels, except that the lower face was

omitted, and the concrete was a lean mix,

containing 1 part of cement and 8 parts of

slag, by volume. The gable ends and ceilings were concrete panels. The

ceiling panels were similar to the roof panels, ex- cept inverted and made

with the same concrete mix used for floor and

wall panels. The roofs were covered by composition shingles nailed di- rectly to the concrete. For wood-frame roof

construction, a wood

plate was fastened by

/2-in. anchor bolts to the

upper ends of the wall

panels and the rafters

fastened to this plate.

The gable ends were wood studs with wood

sheathing, building paper,

and lap siding. The ceilings were wood joists

and either wallboard or metal lath and plaster.

^ 6

T

T

AS

'0 0.2 OA o.e def/ech'on in. Figure 19.

Impact load on floor AS.

Height of drop-deflection (open circles) and height of drop-set (solid

circles) results for specimens AS-Il, 12, and 13 on the span 12 ft 0 in.

[12]
Figure 20. — Erecting " TwacJitiiKui" wall panel by means of a crane truck. Chimneys were supported by the floors and

were 4-in. brick masonry with clay-tile flue linings.

The description, drawings, and sponsor's comments were prepared by E. J. Schell, G. W. Shaw,

and T. J. Hanley, of the Bureau's Building

Practice and Specifications Section, under the

supervision of V. B. Phelan, from information

furnished by the sponsor and from the specimens.

The structural properties were determined

by the Engineering Mechanics Section, under

the supervision of H. L. Whittemore and A. H.

Stang, with the assistance of the following

members of the professional staff: F. Cardile,

R. C. Carter, H. Dollar, M. Dubin, A. H.

Easton, A. S. Endler, C. D. Johnson, A. J. Sussman, and L. R. Sweetman.

The Masonry Construction Section, under

the supervision of D. E. Parsons, cooperated in making the tests.

VII. SELECTED REFERENCES

Architectural Forum 63, No. 6, 548 (1935); 68, No. 2, 70 (1938). American Architect 149, No. 2649, 36 (1936).

Washington, March 8, 1939.

O

[13]

BUILDING MATERIALS AND STRUCTURES REPORTS

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Superintendent of Documents at the prices indicated:

BMSl Research on Building Materials and Structures for Use in Low-Cost Housing lOji BMS2 Methods of Determining the Structural Properties of Low-Cost House Constructions. 100 BMS3 Suitability of Fiber Insulating Lath as a Plaster Base 10^ BMS4 Accelerated Aging of Fiber Building Boards 10^ BMS5 Structural Properties of Six Masonry Wall Constructions 15fi BMS6 Survey of Roofing Materials in the Southeastern States 150 BMS7 Water Permeability of Masonry Walls 100 BMS8 Methods of Investigation of Surface Treatment for Corrosion Protection of Steel 100 BMS9 Structural Properties of the Insulated Steel Construction Company's "Frameless-Steel" Constructions for Walls, Partitions, Floors, and Roofs 100 BMSlO Structural Properties of One of the "Keystone Beam Steel Floor" Constructions Sponsored by the H. H. Robertson Company 100 BMSll Structural Properties of the Curren Fabrihome Corporation's "Fabrihome" Constructions for Walls and Partitions 100 BMS12 Structural Properties of "Steelox" Constructions for Walls, Partitions, Floors, and Roofs

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