AlllDO TTEbT?

NATL INST OF STANDARDS & TECH R.I.C.

A1 11 00992697

/NBS building science series ^ „

TA435 .U58 V53;1974 C.I NBS-PUB-C 1974

CO NBS BUILDING SCIENCE SERIES

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards!
The Building Science Series

The Building Science Series disseminates technical information developed at the National Bureau of Standards on

building materials, components, systems, and whole . structures. The Series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems. These publications, similar in style and content to the NBS Building Materials and Structures Reports (1938-59),

are directed toward the manufacturing, design, construction, and research segments of the building industry, standards organizations, and officials responsible for building codes. The material for this Series originates principally in the Center for Building Technology of the NBS Institute

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please contact the Scientific and Professional Liaison Section, Center for Building Technology, Institute for Applied Technology, National Bureau of Standards, Washington, D.C. 20234.

[See mailing list announcement on last pageli
ai/ojial Bureau of

JUL 1 6 1974

T^ M^^ Study of the Local Resistance

Kio is of Conventional Plywood Subflooring

to Concentrated Load

a .a

Felix Y. Yokel

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Prepared for the

Office of Research and Technology

Office of Housing and Urban Development

Washington, D.C. 20410

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, D/rec/or

Issued May 1974
Library of Congress Catalog Number: 74-600075

National Bureau of Standards Building Science Series 53

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 53, 43 pages (May 1974) CODEN: BSSNBV

Supersedes NBSIR 73-116 (PB 220-432/9)

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974 For sale by the Superintendent of Documents, U.S. Government Printing OflSce, Washington, D.C. 20402 (Order by SD Catalog No. C13.29:2/53). Price 85 cents.
TABLE OF CONTENTS

Page

SI Conversion Units

1. Introduction 1 1.1 Purpose of Study 1 1.2 Background Information 1

2. Scope of Testing Program 4

3. Test Specimens 6 3.1 Materials 6 3.2 Description of Specimens 6

4. Testing Procedure 10

5. Test Results 12

6. Interpretation of Test Results 21

6.1 Compliance with the Criterion 21

6.2 Failure Modes 28

6.3 Effect of Test Location on Load Capacity and Stiffness 32

6.4 Relative Stiffness of Floor Systems 34

7. Conclusions 34

8. Acknowledgement 34

9. References 36

iii
SI Conversion Units

In view o£ the present accepted practice in this country for building

technology, common US units of measurement have been used throughout this paper.

In recognition of the position of the United States as a signatory to the

General Conference on Weights and Measures, which gave official status to the

metric SI system of units in 1960, assistance is given to the reader interested

in making use of the coherent system of SI units by giving conversion factors

applicable to US units used in this paper.

Length

1 in = 0.0254 meter (exactly)

Force

1 lb (Ibf) - 4.448 Newton (N)

Pressure

1 psi - 6895 N/m^

Temperature

5/9 (Temperature °F - 32) = Temperature °C

iv
Study of the Local Resistance of Conventional Plywood

Subflooring to Concentrated Load*

F. Y. Yokel

Representative specimens, simulating the performance of five conventional

plywood floor systems, were tested under concentrated load in order to com- pare their performance with that stipulated by performance criteria developed

on the basis of anticipated occupancy loads.

In 24 out of 26 tests the performance of the specimens exceeded that

required by the criteria. Data on failure loads, load-deflection characteristics and failure modes are presented and discussed.

Key Words : Evaluation criteria; floors; hardboard; load capacity;

performance criteria; plywood; plywood subflooring; subflooring; underlayment

;

wood-frame construction.

1. Introduction

1 . 1 Purpose of Study

This study was conducted as part of an effort to develop and improve

evaluation criteria for industrialized housing. The criteria were used to

guide the development and evaluation of prototype housing for the Department

of Housing and Urban Development's Operation Breakthrough.

The subject of this study are requirements for the resistance of floors

to concentrated loads. The objective of the study is to determine the level

of performance of conventional floor systems and compare their performance

with that required in the evaluation criteria for Operation Breakthrough [1]—

which were based on anticipated occupancy loads.

1 . 2 Background Information

1.2.1 The need for Evaluate the Structural Performance of Floors Under

Concentrated Load

Present U.S. building codes and design standards for residential con- struction provide for floor capacity under distributed load. One of the few

U.S. recommendations related to concentrated loads acting on floors is con- tained in a performance standard by HUFA [2] which is advisory and not enforcable. The standard recommends deflection limitations under a 250-lb concentrated load, and an "extended-load capacity" of 450 lb with a residual deflection

not to exceed 25 percent of the maximum deflection. The concentrated loads

are to be applied over a 1-inch diameter area.

Research Sponsored by the Office of Research and Technology, Department

of Housing and Urban Development , Washington, D. C. 20410

Figures in brackets indicate literature references at the end of this paper.

1
The lack of enforceable provisions for concentrated-load capacity is

not attributable to a lack of need for such provisions. It is merely brought

about by the fact that codes are based on conventional building systems,

which by and large tend to perform in a manner acceptable to the user under

conditions of normal use. On the other hand it is envisioned that some innovative systems may comply with Code provisions for distributed loads,

but exhibit unsatisfactory performance under other types of occupancy load.

It is therefore necessary to evaluate these innovative systems under various

types of loading generated by occupancy, including critical concentrated

loads

.

1.2.2 Occupancy-Generated Concentrated Loads acting on Floors

Concentrated loads on floors may be caused by heavy furniture or by

human activity. Two critical conditions are identified:

1. A concentrated load of critical magnitude that may cause damage to the

entire floor, or more likely to a section of the floor, by exerting

excessive bending moments and/or excessive shear.

2. A load that is concentrated over a very small area, thereby causing

failure by excessive compressive stress and/or excessive punching shear.

Typical heavy concentrated loads have been studied by Boyd [3] and are summarized below:

1. A person carrying a heavy load 350-450 lb

2. A crowded sofa (per front caster) 300-350 lb

3. An upright piano (1 caster) 200 lb

4. A grand piano (1 caster) 280 lb

5. Transportation of an upright piano (per wheel) 250-350 lb

6. Transportation of a grand piano (per wheel) 350-450 lb

Boyd concluded that since the use of grand pianos is relatively rare,

the following design-loads should be used:

(a) 400 lb for several seconds

(b) 350 lb for 1/2 hour

(c) 200 lb indefinitely.

In extreme cases some casters may spread these loads over an area as small

2 as 0.5 in . Critical loading caused by load concentration over a small bearing area

is also caused by stiletto heels. Even though these heels may no longer be

fashionable, their future use cannot be ruled out. A study of typical

stiletto-heel pressures [4] indicates a range of compressive stresses from

550 psi to 1390 psi , and one extreme value of 2,260 psi. Values of punching

shear computed from these data range from 80 lb/in to 117 lb/in. The case

that produced the 2260-psi compressive stress produced a punching shear of

156 lb/in.

2
1.2.3 Discussion of Evaluation Criteria for Concentrated Load on Floors

The following criterion has been adopted as a guide for Operation

Breakthrough [1] : "The structural floor should resist a 400-lb load, applied on a circular

area of 5/8-in diameter and sustained for one hour, without causing a re- sidual indentation of the structural surface in excess of 1/16-in, measured

1 hour after removal of the load, and a 280 lb long-term sustained load,

applied on a circular area of 5/8-in diameter.

If the wearing surface is of non-durable material, or if there is a possibility that this surface may be removed during the useful life of

the structure, the floor should satisfy (this) criterion with the wearing

surface removed."

This criterion is intended to test the structural floor and not the

wearing surface. However, permanent -type wearing surfaces which are left

in place throughout the service-life of the building may have a beneficial

effect on the load capacity of structural floors which could be relied upon.

The criterion requires reasonable deflection recovery under a 400-lb

concentrated load sustained for one hour, and a 280-lb long-term sustained

load capacity. The term "sustained-load" capacity is not defined in the

criterion. In this investigation it is assumed that the intent of the

criterion is that a 280-lb load applied over a 5/8-in diameter area continuously during the service life of the structure should not cause serious

distress.

The 400-lb requirement would be in many cases associated with the

capacity to support a higher short-term load; however, the relationship

between the short-term capacity, the one-hour capacity, and the long-term

capacity would depend on the material of the structural floor. As an example, this relationship is considered for the case of wood.

The following approximate capacities can be calculated using the information in Reference [5] and assuming that capacities are interpreted in

terms of maximum residual deflection and that the residual deflections are related to flexural strength:

30-second capacity 485 lb

1-hour capacity 400 lb

1-year capacity 290 lb

On the other hand, for another material, instantaneous and long-term capacities may differ very little from the one-hour capacity.

The compressive stress caused by the 400-lb load required in the

criterion is 1300 psi and the punching shear is 203 lb/in. If we compare

the concentrated load, the compressive stress and the punching shear with

the data in section 1.2.2, it is evident that the criterion represents

reasonable minimum requirements with no substantial margin with respect to

extreme occupancy loads. However, it should be noted that some of the ex3
treme loads, caused by the moving of heavy furniture, could be modified

or avoided by simple precautions.

The loading requirements in the criterion differ from existing techniques, such as the ASTM E72 test [6] and the ASTM D 2394 test [7]. Both of

these tests methods use a 1-in diameter disc to transmit the load, while

the criterion requires a 5/8-in diameter loading area. The E72 test is intended to measure the structural capacity of the

system, and the D 2394 tests measure the strength of the finished flooring.

These tests, with proper choice of load levels, could adequately evaluate

most floor systems. A problem, however, arises with floor systems that

consist of a thin structural skin supported by stiffening elements. In

this case the system may perform satisfactorily under the D 2394 test, while

under different support conditions the structural skin may fail by punching

shear. On the other hand, in order to generate adequate stress under a 1-in

diameter disc, the concentrated load would have to be increased to over

1000 lb, and in order to generate adequate punching shear the load would have

the to be increased to at least 500 lb. These heavier concentrated loads

would be higher than the extreme concentrated loads that actually act on the

floor in service.

2. Scope of Testing Program

21 Seven different types of plywood subflooring— were tested. Most of

the subflooring specimens were supported by wood joists of 2 x 4-in nominal

size, spaced 16 in on center. In a small number of specimens joist spacings

of 24 in, 20 in, 10 in and 6 in were used in order to investigate failure

modes. The small 4-in joist depth was selected, since in all cases the

joists were fully supported, and joist - deflection and hence, joist size, was not a variable considered in this investigation. Test loads were con- centrated loads which were increased until failure occurred. For part of

the specimens loads were applied in several cycles of unloading and reloading.

Deflections were measured near the point of load application. The test loads were applied over circular areas of 1 in, 5/8 in, and in a limited number of

tests, 1/2 in diameter. Table 2.1 shows the test variables and the scope of

the testing program.

—The structural material or surface which supports floor loads and the

finish flooring. If the subfloor material is sufficiently dense, smooth

stiff, dimensionally stable and possesses adequate bonding properties,

finish flooring may be applied directly without the use of underlayment

.

4
TABLE 2.1. Test Program

Joist Spacing (in) 16 24 20 10 6

Diameter of

Loaded area (in

J

1 5/8 1/2 1 5/8 1 5/8 1 5/8 1 5/8 TOTAL

A 12 18 6 6 6 6 6 6 6 72

1

B 18 12 6 11 6 53

Sysl C 5 6 2 13

•S D 14 7 21

o

n

E 14 7 21

Subfl< F

G

6

7

6

7

Total No . of Tests 193

SUBFLOORING SYSTEMS:

A: 15/32 -in-thick underlyament grade Southern Pine interior-type, 5 -ply

plywood.

B: 1/2 -in-thick standard grade Southern Pine interior-type with exterior glue,

5 -ply plywood.

C: 1/2 -in-thick standard grade Douglas Fir interior -type, 3 -ply plywood.

a/

D: 1/2 -in-thick standard grade Douglas Fir interior-type, 3-ply — plywood.

E: 1/2-in-thick plywood as in D under 1/4-in-thick plywood underla>'ment

.

F: 1/2-in-thick plywood as in C under 7/32 -in-thick hardboard underlayment

.

G: 1/2-in-thick plywood as in C under 1/4-in-thick plywood underlayment.

a/ The core of this plywood was laminated giving the interior ply double thickness.

5
3. Test Specimens

3. 1 Materials

All materials were purchased from local suppliers and were typical of

those presently used in building construction. Plywoods met the requirements

of Product Standard PSI-66 [8] for softwood plywood. Dimensions and physical

properties of the different plywoods used are shown in table 3.1.

3 / Hardboard underlayment— complied with Federal Standard LLB-810a, Type

VI [9] . Dimensions and physical properties of the hardboard used are shown

in table 3.2.

Wood joists were Construction Grade—^ Douglas Fir. Moisture content

was 9.7 percent—^ and specific gravity was 0.41.—^

3. 2 Description of Specimens

Except as noted below, the standard specimens were constructed in

accordance with the provisions in "FHA Minimum Property Standards" [15]

,

Sections 817.3 and 817.4.

Standard Specimens were constructed in small widths compared to the

size of plywood sheets actually used in construction. This conservatively

simulated conditions representing the least strength and stiffness that the

floors may be expected to develop in service.

3.2.1 Standard Specimens without Underlayment

Figure 3.1 shows a typical specimen. The 2x4 joists were 16 in

long and were spaced 16 -'in on center. Plywood sheets, nominally 1/2 in

thick, 14 in wide, and 48 in long, were nailed to the top and bottom faces

of the joists. The plywood sheets were oriented with the grain of the outer

plies perpendicular to the axis of the joists. The joists were 2 in longer

than the width of the plywood sheet to give the specimens stability under

concentrated loads applied at the long edge of the plywood. The plywood

sheets were nailed to the joists with 8d common nails. Three nails, spaced

6 in on center, were used for the two outside joists. The inside joists were nailed with two nails, spaced 10 in on center.

—Hardboard is a dense panelboard manufactured of wood fibers with the natural lignin in the wood reactivated to serve as a binder for the wood fibers.

Underlayment is a material installed over the subfloor to provide a suitable base for the finish flooring when the subfloor does not possess the

necessary properties for direct application of the flooring.

4/-'In accordance with WCLIB Rules No. 15 [10]

-^Determined in accordance with ASTM D2016 [13]

-"^Determined in accordance with ASTM D2395 [14]

6
TABLE 3.1

Physical Properties of Plywoods—'

Designation Thickness

in

.

No. of pliesSpecies Grade Identif ication

Index Type

d/ MoistureContent

%

Speclflc^^

Gravl ty

a — 15/32 5 Southern

Pine Underlayment Plugged and Touch Sanded InteriorExterior with

Glue

7.1 0.60

1/2 5 Southern

Pine

Standard 32/16 Interior

Exterior with

Glue

7.3 0.54

1/2 3 Douglas

Fir C-D 32/16 InteriorExterior with

Glue

6.3 0.53

1/2 3^/ Douglas

Fir Standard 32/16 InteriorExterior withGlue

9.5 0.47

Under layment y 1/4 3 Douglas

Fir A-A Interior 8.0 0.48

a/ Properties are defined in conformance with Product Standard PSl-66.

b^/ Properties identified in DFPA Grade-Trademark except for species, moisture content and specific gravity.

£_/ Properties identified in TECO Gradestamps, except for species, moisture content and specific gravity.

d_/ Properties determined in accordance with ASTM designation D-805 [ 11] .

e/ The core of this plywood was laminated, giving the interior ply double thickness.

TABLE 3.2

Physical Properties of the Hardboard a/

Modulus of Water Thickness Specific Average Thickness Rupture Absorption Swelling Gravity Moisture Content

0.215 in 4,500 psi 13.73% 7.08% 0.998 5%

a/ Tested by manufacturer in accordance with Commercial Standard CS 251-63 [12] .

7
I ,_:„;; : ... . \ 7.

FIGURE 3.2 STANDARD SPECIMEN WITH UNDERLAYMENT

8
Standard specimens, as described in this section, were made for three

different floor systems:

7 / System A, using plywood a—' System B, using plywood b

System C, using plywood c

S. 2 . 2 Standard Specimens with Underlayment

Figure 3.2 shows a typical standard specimen with underlayment. The two

48-in long 2x4 joists were spaced 16-in on center. Four 12-in long by 16-in

wide sections of nominally 1/2 -in th? ck plywood were nailed to the top and

bottom faces of the joists. Each 12 x 16-in plywood section was nailed on each side by three 8d common nails, spaced 5—in on center. This spacing

was less than the 6-in spacing required in "FHA Minimum Property Standards."

The reduced nail spacing was chosen in an attempt to compensate for the fact

that this specimen was only 16 inches wide, while in an actual building an

8 ft sheet would be used, and FHA Minimum Property Standards require, continiuty at least at one of the two joist supports ("over two or more spans").

The 1/2 -in plywood sheets were oriented with the grain of the outer ply perpendicular to the axes of the joists. A continuous sheet of underlayment,

16 in wide by 48 in long, was nailed to the outer face of the 1/2 in plywood

sheets. This underlayment consisted of either 7/32-in thick hardboard or 1/4-in thick plywood. The 1/4-in thick plywood underlayment was oriented

with the grain of the outer plies parallel to the joists. The underlayment

was nailed to the 1/2 -in plywood sheets by 4d annular- thread nails spaced

6-in on center.

Standard specimens with underlayment were made for four different

floor systems:

System D, using plywood d with 7/32-in hardboard underlayment;

System E, using plywood c with 1/4-in plywood underlayment;

System F, using plywood c with 7/32-in hardboard underlayment:

System G, using plywood c with 1/4-in plywood underlayment.

3.2.3 Specimens With Other Than 16 in Joist Spacing

Several Specimens were made with other than 16 in joist spacing. These

specimens were all without underlayment and were similar to the specimens

described in Section 3.2.1 with the exception of the joist spacing.

—For description of plywood refer to Section 3.1 and table 3.1.

9
3.2.4 Deviations from the provisions of "FHA Minimum Property Standards " The test was performed on small specimens and a conservative simulation

of the worst conditions was desired. Some aspects of the simulation may have

adversely affected performance. Deviations from the provisions of MPS and

their possible effects are listed below:

1. Subflooring System A used 15/32-in thick plywood, while MPS requires

a minimum thickness of 1/2 in. The reduced thickness would cause a reduction in strength and stiffness.

2. The specimen in figure 3.1 is 14 in wide. In an actural floor 4-ft

wide plywood sheet would be used. Any free edge of such a sheet

would have to be blocked, and either blocking or Tongue-and-grove

joints would have to be used where two sheets meet. Thus an actual

floor may be somewhat stiffer than the test specimen.

3. In addition to the lack of continuity noted in Section 3.2.2, 12-in

wide plywood subflooring strips were used in the specimens with

underlayment shown in figure 3.2. Stiffness and possibly strength

may have been reduced by engaging 12-in wide plywood strips, rather

than the 4-ft wide sheets normally used in construction.

4. Testing Procedure

The specimens were fabricated and stored in the laboratory at approximately 73°F and 50 percent relative humidity. All the tests were performed

in the same laboratory.

The load was transmitted from the head of a 60,000-lb capacity testing

machine. The test setup is shown in figure 4.1. The specimen rested on the platten of the testing machine. Load was applied to the specimens through

the end of a 6.5-in long steel rod. The end of this rod was sharp edged and

machined to the required diameter. The steel rod was connected to a load

cell which was inserted between the upper end of the rod and the head of the

testing machine.

Deflection—^ was measured by a displacement transducer (LVDT) . The

transducer was connected to a base, made of a 2 x 4 wood member, 18-in long,

that rested on three adjustable bolts. These bolts were so spaced that the

base could be supported on the centerline of two joists on 16 in centers.

Deflections were measured to the face of a bracket which was connected to

the upper end of the load cell, thus measuring the downward movement of the

— The term "indentation" used in the criterion was interpreted as a deflection of localized nature which was measured relative to two points on the

surface of the floor, spaced 16 in apart and which in some cases included

a well defined indentation of the floor surface, as well as a localized deflection between two adjacent supporting joists. In the case of the standard

specimens, the measured deflections at the critical locations were referenced

to two points at the floor surface located above the centerlines of two adjacent supporting joists.

10
11
loading device relative to points, spaced 16 in apart and located at the

surface of the specimen. The distance between the centerline of the displacement transducer and the centerline of the loading rod was 4 in.

Deflections thus measured also included shortening of the loading rod

and the load cell. To determine the magnitude of this effect the shortening

of' the rod and the load cell was measured for loads up to 1000 lb. It was determined that the effect of this shortening on test results was of second

order magnitude and corrections for this effect were therefore unnecessary.

Data were recorded electronically by transmitting the output from the

displacement transducer and the load cell to an X-Y recorder. The X-Y re- corder plotted loads on the Y axis to a scale of 100 lb per 1 in, and deflections on the X axis to a scale of 0.1 in per 1 in. This produced a graphical

record of the data which had adequate resolution.

The load was applied at a rate of 1/2 lb/sec. Most specimens were

loaded continuously to failure, but several specimens were 'iubjected to

cycles of unloading and reloading. After each load increment of 100 lb

these specimens were completely unloaded and reloaded to a load 100 lb

greater than the previous load or to failure, whichever came first. This

procedure left a record of instantaneous deflection recovery for each

specimen. On two specimens, a 400-lb load was maintained for one hour and

the specimens were then unloaded and deflection recovery was measured after

one hour. In some tests failure occured at loads higher than 1000 lb. In

these cases the load cell which had a 1000-lb capacity was removed prior to

the completion of the test and loads were measured by the testing machine.

For these tests, only failure loads as defined in Section 5 were recorded

since the deflections at failure were not measured.

5. Test Results

The test data which consist of a plotted load-deflection curve for

each specimen tested are summarized in table 5.1. The first column in the

table identifies the floor system, in accordance with the list of floor

systems in table 2.1. The diameter of the loaded area is shown in the second

column, the joists spacing in the third column, and the location of the test

load in the fourth column. Test-load locations are identified as shown in

figure 5.1. The other three columns identify failure load, load causing initial structural damage, and deflection at failure load, respectively.

The method by which these values were determined is illustrated in

figure 5.2 which shows a typical load-deflection curve. In general, specimens

could be loaded to a certain level without any sign of distress. First

signs of distress, which were usually associated with some cracking sound, can be identified on the load-deflection curves as a drop in the applied

12
TABLE 5.1. Test Results

Floor Diameter Spacing Location Failure Load Causing Deflection

System or or or Load Initial Structural at Failure

Loaded Area Joists Test Damage Load

in in lb lb in

540 480 0 52

700 670 0 54

1 620 570 0 39 400 400 0 30

565 530 Average

2 450 450 0 34 600 460 0 38

525 455 Average

310 310 0 67

3 210 210 0 51

440 440 0 68

490 460 0 84 A 5/8 16 363 355 Average

15/ 32-in„

4 300 300 0 61

5 ply 300 300 0 36 plywood 300 300 Averaee

1000 b/ 980 0 12 a/

1000 b/ 950 0 14 a/

5 1000 b/ 920 0 13 a/

1000 b/ c/ 0 08 a/

1000 b/ c/ 0 07 a/

1000 b/ £/ 0 .08 a/

1 670 460 1 .20

430 280 0 89

820 590 1 .32 5/8 24 640 343 Average

1044 1044 1 .22

2 740 300 1 .14 600 600 0 .75 795 648 Average

£./ Deflection readings were taken at 1000 lb.

b/ The test was discontinued at the load level indicated.

c/ No information is available.

13
Floor Diameter Spacing Location Failure Load Causing Deflection

System of of of Load Initial Structural at Failure

Loaded Area Joists Ti-k f f- i es L Damage Load

in in -L D 1 D in

1 540 460 0.63

610 610 0.64

/ Ju n QQ U . oo

A 9 7 510 Average

540 540 0.50

2 740 450 0.80

fii n n fii D jU 503 Average

1 990 890 0.39

71/ xun nU . AiHX

ovju /weragc

3/0 =; /ft -LU ±uuu xuuu 1 nnn nu . ->77/ 1138 1138 0.30 a/

2 960 940 0.27

1XUmJ.Un nu 71 a /

. J X a/

1 n9 7 xuu / /werdgc

1 1082 1082 0.25 a/

T '^7 9 X177 9 J / Z nu 1ft o / . xo a/

fku 19 97 xzz/ 1 997 rtveragfc lilT£^r- ^ CT £

QQA QQA nu 9ft . zo

2 1290 c/ 0.22 a/

1122 c/ 0.22 a/

117 9 c/ nu 90 o /

. zz a/

1 1 /i A'\7fi 1" p * ix V c J. d

1 n/. n A A n u. Do a/

1X 9nft zuo 1xuuu nnn nu A A a /

. HO a/

1XhAft9 oZ 1xuuu nnn nu /iQ a / . a/

1 o / yj A7n n "^fi XUDJ 1 df\^ u . J o a / 970 860 0.54 ~

795 700 0.43

n A9

1 fi XUUJ 801 Average

X1 X1 JR9z ±vJWU nu Aft a / • H-o a

/

2 590 590 0.31 ~

800 710 0.62

590 590 0.32

783 723 Average

14
Floor

System

Diameter

of

Loaded Area

in

Spacing

of

Joists

in

Location

of

Test

Failure

Load

lb

Load Causing

Initial Structural

Damage

lb

Deflection

at Failure

Load

in

1 845

860

530

845

860

370

0.64

0.74

0.51

20 745 558 Average

2 8501242

1264

660

1000

560

0.66

0.87 a/

0.84 a/

A 1 1119 /4U i^^T IT ^ 0

1 1788

1706

c/

c/

c/

c/

10 1747 Average

2 16621182

1726

1268

c/

c/

c/

c/

c/

c/

c/

1460 Average

1 1750

1740

c/

c/

c/

c/

6 1745 Average

2 1546

1564

1508

1584

c/

c/

c/

c/

c/

c/

c/

c/

1551 Average

1 895

860

825

600

895

660

810

600

0.51

0.61

0.61

0.40

795 741 Average

B l/2-in«

5 ply

plywood

5/8 16 2 730

790

700

790

0.43

0.51

760 745 Average

3

290

480

425

590

290

470

360

590

0.43

0.68

0.68

0.79

446 428 Average

15
Floor

System

Diameter

of

Loaded Area

in

Spacing Location Failure Load Causing Def lection

of of Load Initial Structural at Failure

Joists Test Damage Load

in lb in

4 440 440 0 57 634 634 0 68

16 537 537 Ave ra^

840 840 0 .14 1000 b/ 0 .12 a/

950 950 0 13

5 1000 b/ 0 .14 a/

1000 b/ f,C // 0 .11 a/

1000 hi C/ 0 11 a/

890 780 \ . 29

945 790 1 .29 730 640 1 .20

910 910 1 .25

1 652 360 1 .06 640 600 1 .08 600 600 0 . 94 920 500 1 .27 24 748 640 Average

680 660 0 .81

2 670 670 1 .07 795 795 0 .97 770 770 0 .92 729 724 Avera^

785 785 0 79

1 634 "634 0 .59 800 630 0 .90 20 740 683 Averaj

990 890 0 .78

2 810 660 0.71

810 810 0.61

870 787 Ave raj

940 690 0 39

650 650 0 .24

1 830 550 0 .31 1126 570 0 44 a/

900 900 0 25 10 889 672 Average

5/8

16
Floor

System

Diameter

of

Loaded Area

in

Spacing

of

Joists

in

Location

of

Test

Failure

Load

lb

Load Causing

Initial Structural

Damage

lb

Deflection

at Failure

Load

in

B 5/8

10 2

660

960

660

840

800

990

620

820

660

830

800

670

0.36

0.38

0.23

0.31

0.27

0.35

818 / -* J rive L c

6 1 830

1012

680

1012

0.20

0.28 a/

921 846Average

2

790

810

938

975

790

810

938

830

0.17

0.18

0.32

0.29

878 842Average

C 1/2-in.

3-ply

plywood

5/8 16

1 580 540 0.31

2 770 770 0.37

3 250

380

250

380

0.31

0.62

315 315Average

5 1000 hi

1000 hi

520

470

0.12 a/

j 0.13 a/

^95 Average

1/2 16 5 1000 hi

1000 hi

280

700

0.21 a/

0.19 a/

490Average

1 16 1 710

710

620

630

0.59

0.37

710 625 Average

3 420

660

350

460

0.76

0.85

540 405 Average

4 400 350 0.45

17
Floor Diameter Spacing Location Failure Load Causing Deflection

System of of of Load Initial Structural at Failure

Joists Damage Load

in in. ID 1 u in

1 11 / OU D / u 675 620 0.53

695 660 0.57

680 480 0.71

5/8 16 708 583 Average

2u 568 330 c/

J_UUU D/ c/ nu 1 R 3 / . J.O a

/

1xyUU nnn vT/ D/ c_/ nu . 1xoR ^/a

/

1025 910 0.74 a/

1006 730 0. 70

~"

1002 1000 0. 71 D 1 16 lu 1008 1008 0.70

1064 1064 0.71

l/2-in„

^ OD QAO 0U • AOoU 3-ply

plywood oUU J / u J. . J ^ 2u 640 440 1.31

700 570 1.50

D OU 1 '^O

1000 b/ c/ 0.09 a/

1000 b/ c/ 0.09 a/

3u 1000 b/ c/ 0.11 1/

1000 b/ c/ 0.11 a/

410 360 0.51

lu 542 542 0.53

540 540 0 ^9 E 5/8 16 497 481 Average

1/2-in. 2u 400 390 0.73

3-ply 450 420 0. 96

425 405 Average

plywood

+ 1/4-ino 3u 670 670 0. 22 plywood

880 810 0.18

775 740 Average

18
Floor Diameter Spacing Location Failure Load Causing Deflection

Sj'stems of of of Load Initial Structural at Failure

Loaded Area Joist Test Damage Load

in in lb lb in

1002 1002 0.65

1104 1000 0.63 a/

890 890 0.63

lu 830

670

700

830

500

550

0.58

0.50

0.70

E 1 16 866 795Av6r3g6

820 630 1.31

380 380 0.63

2u 670

545

530

240

1.48

1.50

604 445Average

3u 1000 b/

1000 b/

1000 hi

1000 hi — c/

c/

c / c/

0.16 a/

0.16 a/

0.21 a/

0.21 a/

F 5/8 16 lu 950 950 0. 55 1/2-in. + 7/32-ino 890 860 0.58

920 905 Average

3-ply hardboard

plywood 2u 420

310

420

290

0.66

0.39

-+ l/4-in„ 365 355 Average

plywood

3u 1000 hi

1000 b/

c/

c/

0.12 a/

0.12 a/

720 670 0.43

lu 860

770

680

690

0.56

0.56

783 680 Average

G 5/8 16 2u 350 300 0.55

1/2-in. 370 370 0.53

3-ply

plywood + 1/4-ino

360 335 Average

3u 1000 hi c/ 0.20

plywood 1000 hi c/ 0.19

19
2u

3u

jC3_:

(a) SPECIMEN WITHOUT UNDERLAYMENT (b) SPECIMEN WITH UNDERLAYMENT

FIGURE 5.1 LOCATION OF TEST POINTS

800r

FAILURE

600-

400- <

o

200

0.2 0.3 0.4 DEFLECTION, in FIGURE 5.2 INTERPRETATION OF TEST RESULTS

20
load which is not associated with a change in deflection. Such a drop in

load is associated with a residual deflection which is roughly proportional

to the magnitude of the drop in load. The load level at which this first

distress occurred is identified in column 6 of table 5.1, and is shown in

figure 5.2. If loading was subsequently continued, most specimens were able

to support additional load increments without an appreciable change in the

slope of the load-deflection curve, until an additional drop in load occurred

at a higher load level.

The failure load in column 5 of table 5.1 identifies the lowest load

level at which a load drop of 30 lb or more occurred. This point does not

always represent the highest load that the specimen can support. The definition of failure load is based on the observation that a load drop of 30 lb was associated with irrecoverable deflections approaching l/16in. It is

reasonable to assume that after such a drop in load most specimens would not

meet the deflection-recovery requirements in the criterion which specifies

a residual deflection of less than 1/16 in, and that a clearly identifiable

residual deflection would remain on all specimens after removal of the load.

The information presented in Table 5.1 is summarized in Table 5.2, where

the average loads causing failure and initial distress are tabulated for

specimens with 16-in joist spacing. Other information that can be derived

from the test data, together with plots of typical load-deflection curves, is

presented in Section 6 where test results are interpreted.

6. Interpretation of Test Results

6 . 1 Compliance with the Criterion Adopted for Operation Breakthrough

6.1.1 Concentrated-load capacity

Figure 6.1 is a plot showing the range of load capacities and average

load capacities for specimens with 16-in joist spacing. The test data are for test locations 1 and lu in figure 5.1 since these locations are considered

critical. Actually tests at locations 3, 4, and 2u yielded lower results,

however, in accordance with FHA Minimum Property Standards, free edges of

plywood sheets should be either blocked or tongue and groove joints should

be provided. Compliance with the criterion at test locations 3, 4 and 2u is

therefore not required.

The shaded rectangles in figure 6.1 show the range of the failure loads

and the unshaded rectangles show the range of loads that caused initial

distress. The solid and hollow circles-^ show the average loads at failure _

—'In some cases the test results do not cover a significant range, or only

one single test was performed. In these cases only the solid and hollow

circles are shown.

21
TABLE 5.2

Summary of Average Test Results for Specimens with 16-in Joist Spacing

5/8-in Diameter Area Lf J. aillK^ 1 flL cd

Tloor Location Average Average Load Average Average Load

Systems of Failure Causing Initial Failure Causing Initial

Test Load Structural Damage Load Structural Damage

lb lb lb lb

A 1 565 530 1003 801

2 525 455 783 723

3 363 355

4 300 300

5 1000+ 975+

B 1 795 745

2 760 745

3 446 428

4 537 537

5 1000+ 903+

C 1 580 540 710 625

2 770 , 770

3 315 315 540 405

4 400 350

5 lOOOf 495

D lu 708 583 1015 945

2u 568 330 700 520

3u 1000+ lOOCHE lu 497 481 866 795

2u 425 405 604 445

3u 775 740 1000+

F lu 920 905

2u 365 355

3u 1000+

G lu 783 680 . 2u : 360 335

3u 1000+

22
c

1400

RANGE OF FAILURE LOADS

RANGE OF LOADS CAUSING

INITIAL DISTRESS

AVERAGE FAILURE LOAD

AVERAGE LOAD CAUSING

INITIAL DISTRESS

1200

<

o

_l

Q

UJ

a:

UJo

z

o

1000

800

600-

i-O

400

200

5/8

B

5/8

n:

5/8 5/8 5/8 5/8 5/8

CRITERION

IN SEC. 1.2.3.

FLOOR

SYSTEM

DIA. OF LOADED

AREA, in

FLOOR SYSTEM AND DIAMETER OF LOADED AREA

23
and initial distress respectively. Test results are plotted for loaded areas

of 5/8 in, as well as 1 in diameter. The heavy horizontal line shows the

load level required by the criterion.

The following conclusions can be derived from figure 6.1:

1. ) All specimens tested failed at load levels equal to, or higher

than that required by the criterion.

2. ) Except for floor system E, all specimens tested showed first signs

of distress at load levels equal to or higher than that required

by the criterion. For system E, two out of the three specimens

tested showed first signs of distress at load levels higher than

that required by the criterion, and the third specimen showed first

signs of distress at a load of 390 lb.

3. ) In all cases, specimens tested by the 1-in diameter disc had significantly greater load capacity than specimens tested with the

5/8-in diameter disc.

The overall conclusion is, that except for one specimen in system E,

all specimens satisfied the criterion and most specimens exceeded the capacity required in the criterion by a substantial margin. It should be noted

that this conclusion is based on a test setup which uses specimens of 14 in

and 12 in width, respectively. This is a conservative simulation of the

least strength that a floor may be expected to develop. In an actual building, where floors are continuous over much larger areas, load capacities may

be higher.

6.1.2 Deflection Recovery

Figure 6.2 shows the load-deflection curve for a test in which floor

system C was loaded in accordance with the requirement of the criterion.

Deflections are plotted along the abscissa, and loads along the ordinate.

Note that the instantaneous deflection under the 400- lb load was approximately 0.178 in. When the load was sustained for an hour, this deflection

increased to 0.190 in and when the load was removed there was an instantaneous

deflection recovery to a residual deflection of 0.02 in. One hour after un- loading, the remaining residual deflection was 0.01 in. Thus residual deflection measured for this specimen was substantially smaller than the maximum

1/16-in (0.0625 in) residual deflection stipulated by the criterion.

Figures 6.3 through 6.7 show deflection-recovery characteristics for

floor systems A,B,C,F, and G, respectively. In all cases the residual deflection, measured immediately after removal of the 400-lb load, was substantially less than 1/16 in. This is taken as an indication that all these

floor systems have deflection-recovery characteristics which would satisfy

the criterion. Floor systems D and E were not tested under cycles of un- loading and reloading. The observation that load-deflection curves for the

24
I HOUR SUSTAINED LOAD

* See Figure 5.1

DEFLECTION, in

FIGURE 6.2 COMPLIANCE OF FLOOR SYSTEM C WITH BREAKTHROUGH

CRITERION

600h

0.1 0.2 0.3 0.4 0.5 0.6 DEFLECTION, in FIGURE 6.3 DEFLECTION RECOVERY CHARACTERISTICS OF FLOOR

SYSTEM A

25
DEFLECTION.In

FIGURE 6.4 DEFLECTION RECOVERY CHARACTERISTICS OF FLOOR

SYSTEM B

DEFLECTION.in FIGURE 6.5 DEFLECTION RECOVERY CHARACTERISTICS OF FLOOR

SYSTEM C

26
800-

DEFLECTION, in FIGURE 6. 6 DEFLECTION RECOVERY CHARACTERISTICS OF FLOOR SYSTEM F

800r

DEFLECTION, in FIGURE 6.7 DEFLECTION RECOVERY CHARACTERISTICS OF FLOOR SYSTEM G

•27
tested specimens of floor systems D and E tended to be linear below the

400-lb load is taken as an indication that these systems have deflectionrecovery characteristics similar to those of systems A,B,C,F, and G.

6.3.1 Sustained-Load Capacity

No long-term tests were conducted to determine the sustained-load

capacity of the specimens. Some indication of the magnitude of that capacity can be derived using the data presented in reference [5], In accordance

with these data, a 1-hr capacity of 400 lb would correspond to a 1-year

capacity of 290 lb and to a 30-year capacity of 265 lb.

If we define the 30-year capacity as the required sustained load capacity, a one-hour capacity of 422 lb would satisfy the 280-lb requirement

in the criterion. Of the 26 specimens tested at load locations 1, 2 and lu,

24 exceeded this capacity. Thus it can be concluded that the floor systems

tested generally satisfy the requirement for sustained-load capcity.

6 . 2 Failure Modes

Figures 6.8 and 6.9 illustrate two typical modes of failure. Figure

6.8 shows a typical failure of a specimen of floor system A loaded over a 1-in diameter area and gives the appearance of a flexural tensile crack.

Figure 6,9 shows the failure mode of a specimen of floor system B, loaded

over a 5/8-in diameter area, which is typical for most specimens under this

loading except for specimens that were loaded over the joist support at

locations 5 and 3u. This mode of failure has the appearance of a combination

of a local shear failure (punching shear) in the upper four plies together

with a flexural tensile failure in the lowest ply.

When test results are interpreted, some conclusions could be drawn from

a theoretical consideration of the effects of the variation of the loaded

area, the joist spacing, and the location of the applied load. The following

theoretical considerations apply to loads acting at locations 1, 2 and lu:

1. ) Flexural stress would vary with joist spacing, however the diameter

of the loaded area would have relatively little effect. Flexural

failure would probably occur under the loaded area.

2. ) Local (punching) shear would vary with the diameter of the loaded area and would not vary with joist spacing. Failure by local shear

would occur close to the perimeter of the loaded area.

3. ) Vertical compression would vary with the diameter of the loaded

area and would be independent of the location of the loaded area

and of joist spacingIndentations caused by vertical compression were determined in the testing program by applying concentrated loads over the joists at locations 5 and

3u. On this basis it was determined that vertical compression would not be

critical for the 1-in and the 5/8-in diameter loading discs. The 1/2-in

28
FIGURE 6.8 TYPICAL FAILURE OF FLOOR SYSTEM A LOADED

OVER A 1-in DIAMETER AREA
diameter disc was ruled out on the basis of tests performed at location 5 on floor system C where it caused a residual deflection in excess of 1/16 in

under a 400-lb load. Data for these tests are shown in table 5.1.

Some conclusions about the failure mode can be drawn by considering the

effect of joist spacing and of the diameter of the loaded area. It has

already been noted in section 6 . 1 . 1 that load capacity increased with an increase in the diameter of the loaded area. This effect, and the effect

of joist spacing are illustrated in figures 6.10 and 6.11.

Figure 6.10 shows the effect of joist spacing on failure loads and

load levels at which initial damage occurred in system A. Note that there

was considerable variation in strength between individual specimens. The

a/erage values therefore only represent approximate trends since the number

of samples used was small.

For the 1-in diameter test load there was no difference in strength

between the 6-in and the 10-in joist spacing. At these spacings failure

probably occurred by punching shear. For larger joist spacing the failure

load decreased with increased spacing. This decrease, together with the

characteristics of the typical failures which is shown in figure 6.8, leads

to the conclusion that these specimens probably failed by flexural compression and tension.

For the 5/8-in diameter test load the failure load tends to decrease

with increased joist spacing between the 6-in and the 16-in spacing. For

spacings larger than 16 in the failure load increased. This inconsistency

may be attributable to the strength variability (this sample was too small

to be statistically significant). The dashed curve, which shows loads causing

initial damage, shows a consistent decrease of load with increased joist

spacing. Since for flexural failure the failure load would be independent

of disc-size and for local shear the load would be independent of joist

spacing, it is concluded from figure 6.10 that for the 5/8-in loading diameter failure probably was caused by a complex combination of flexural

stresses and local shear.

Figure 6.11 shows the relationship between load capacity and joist

spacing for floor system B, loaded over a 5/8-in diameter area. In this case capacity only slightly decreased with joist spacing. The dominant failure mode for these specimens was probably local shear. Tests on specimens

with other than 16-in joist spacing were only performed on floor systems A

and B.

30
1800

1600

1400

1200

1000

800

600

400

200-

FAILURE LOAD, |-in DISC

FAILURE LOAD, 5/8-in DISC

FIGURE 6.10 RELATIONSHIP BETWEEN JOIST

SPACING AND STRENGTH

10 20

JOIST SPACING, in

FIGURE 6.11 RELATIONSHIP BETWEEN JOIST

SPACING .\ND STRENGTH

1000

800

600 <

I-y 400

200

FAIUURE LOAD, 5/8-in DISC

10 In

r I INITIAL DAMAGE, 5/8-in DISC

16 In 20 In 24 in

FLOOR SYSTEM B TEST LOCATION I

10 20

JOIST SWCING, in

31
6 . 3 Effect of the Test Location on Load Capacity and Stiffness

6.3.1 Floor Systems IVithout Underlayment

Floor systems A, B and C were tested at 5 different locations. Locations 1 and 2 were between joists and 6 in from the free edge of the plywood

sheet. These locations differed only in the fixity of the plywood sheet at

the joist support. At location 1 the edge of the plywood was nailed to one joist support and the plywood was continuous over the other joist support.

At location 2 the plywood was continuous over both joist supports. It was reasoned that location 1 should be weaker than location 2 since there was

less fixity at the joist that supported the edge of the plywood sheet. However, comparison of the average test results in table 5.2 indicates that

the strength at location 2 was similar to that of location 1 in systems A and

B. Only system C had greater strength at location 2. Locations 3 and 4 were

at the edge of the plywood sheet between joists and represented points of

least strength. This can be seen from the data in table 5.2. Location 5 was over the joist support, and as expected, supported much higher loads.

A comparison of load-deflection characteristics for various loading

points is shown for system A in figure 6.12. As expected, location 5 is

the stiffest. There is little difference in stiffness between locations 2 and 1, and locations 3 and 4 also have comparable stiffness. This is con- sistent with the observation that there was no significant difference in

strength between locations 1 and 2, as well as between locations 3 and 4.

Location 1 is considered to correspond to the most critical condition

in an installed floor since, in a properly constructed floor, the free edge

at locations 3 and 4 should be supported by blocking.

6.3.2 Floor Systems With Underlayment

Floor systems 0, E, F and H were tested at three locations. Location

lu is halfway between joists and at a point where two free edges of the plywood sheet are covered by underlayment. Location 2u is at a free, unsupported

edge midway between joists, and location 3u is over a joist. The test results

at these locations are shown in table 5.2. As expected, location 3u is the

strongest and location 2u the weakest.

The load -deflection characteristics for these loading points are compared

in figure 6.13 for floor system E. Location lu is considered to represent a simulation of the most critical

condition that should be considered, since in accordance with "FHA Minimum

Property Standards" the free edge at location 2u should be blocked.

32
DEFLECTION.in FIGURE 6.12 RELATIONSHIP BETWEEN THE LOAD-DEFLECTION

CHARACTERTISICS AND THE POSITION OF THE

CONCENTRATED LOAD FOR FLOOR SYSTEM A

DEFLECTION.in FIGURE 6.13 RELATIONSHIP BETWEEN THE LOAD-DEFLECTION

CHARACTERISTOCS ADN THE POSITION OF THE

CONCENTRATED LOAD FOR FLOOR SYSTE^I E

33
6 . 4 Relative Stiffness of the Floor Systems

The load-deflection curves of the floor systems without underlayment

,

loaded at location 1, are compared in figure 6.14. The ratio between applied

load and measured deflection at location 1 can be taken as a measure of

stiffness. System A was the least stiff. This system also had the least

strength. It has been noted in Section 3.2.4, that system A does not meet

the requirements set by "FHA Minimum Property Standards" since the thickness

of the plywood was reduced by 1/32 of an inch by the sanding of one surface.

The load- deflection curves of floor systems with underlayment, loaded

at location lu, are compared in figure 6.15. Again, the least stiff system

(E) developed the least strength.

7. Conclusions

1. ) Out of 26 tests performed on the specimens at the weakest location

likely to be encountered in a built floor, 24 exceed the one-hour

load capacity stipulated in the Operation Breakthrough criterion

for concentrated - load capacity, which is based on anticipated

occupancy loads, by a substantial margin, one test exactly satisfied

the criterion, and one test did not comply with the criterion.

2. ) For those tests that exceeded the one-hour load capacity requirement,

residual deflections were generally smaller than the 1/16-in maxi- mum stipulated in the criterion.

3. ) On the basis of the data presented in reference [5], it can be con- cluded that in 24 out of 26 tests conducted the specimens probably

met the performance level under sustained load stipulated in the

criterion

.

4. ) The observed mode of failure under the 5/8-in diameter loaded area was punching shear or a complex combination of flexure and punching

shear. Vertical compressive stresses developed under the concentrated load were not critical.

5. ) Load capacity under a 1-in diameter loaded area exceeded the capacity under a 5/8-in diameter loaded area by a substantial margin.

Under a 1/2-in diameter loaded area vertical compressive stresses

caused by a 400-lb concentrated load exceeded the compressive

strength of the material.

8 . Acknowledgement

The contribution of the following persons is acknowledged. Frank A.

Rankine, James F. N. Seiler and Lymus Payton from the staff of the Center for

Building Technology and James Warfield, formerly on the Staff of the Building

Research Division of the National Bureau of Standards.

34
DEFLECTION, in FIGURE 6,14 RELATIVE STIFFNESS OF FLOOR SYSTEMS WITHOUT

UNDERLAYMENT

DEFLECTION.in FIGURE 6.15 RELATIVE STIFFNESS OF FLOOR SYSTEMS WITH

UNDERLAYMENT

35
9. References

[I] The Buildinj; Research Division Team, Cluide Criteria for the Evaluation

of Operation Breakthrough Housin?! Systems, dated December 1970 (NTIS

Accession Numbers PB-212n55 , 212056', 212058).

[2] Housing and Home Finance Agency, Performance Standards, Structural

and Insulation Requirements for Houses, Washington, D.C., June 1947.

[3] Boyd, J. D., Minimum Strength and Stiffness Necessary for V/ooden Floors

in Houses, Paper No. 34, CSIRO, Division of Forest Product Technology

Melbourne, Australia, 1964.

[4] Thorburn, H. T., Flooring Damage by Heels, ?!aterials Research Standards,

ASTM, Vol. 2, No. 9, Philadelphia, Pa., September 1962.

[5] Wood, Lyman W. , Relation of Strength of Wood to Duration of Load,

Forest Products Laboratory, Madison IVisconsin, December 1951.

[6] ASTM Designation E72-68, Conducting Strength Tests of Panels for Building Construction, American Society for Testing Materials, Philadelphia,

Pa., 1968.

[7] ASTM Designation D 2394-69, Tests for Simulated Service Testing of Wood

and Wood-Base Finish Flooring, American Society for Testing Materials,

Philadelphia, Pa., 1969.

[8] National Bureau of Standards, Voluntary Product Standard PS 1-66,

Softwood Plywood, Construction and Industrial, U.S. Covernment Printing

Office, Washington, D.C., July 1970.

[9] General Service Administration, Federal Specification, LLL-B-810 a. Building Board (Hardboard) Hard Pressed, Vegetable Fiber, Washington,

D.C. , July 7 , 1965.

[10] West Coast Lumber Inspection Bureau (WCLIB) , Rules No. 15, Grading and

Dressing Rules, Portland, Oregon, January 1, 1969.

[II] ASTM Designation D 805-63, Veneer, Plywood and other Glued Veneer Construction Testing, American Society for Testing Materila, Philadelphia,

Pa., 1963.

[12] U.S. Department of Commerce, Commerical Standard, CS 251-63, Washington,

D.C. , April , 1967.

[13] ASTM Designation D 2016-65, Tests for Moisture Content of Wood,

American Society for Testing Materials, Philadelphia, Pa., 1965.

[14] ASTM Designation D2395-65 T, Tests for Specific Gravity of Wood and

Wood-Base Materials, American Society for Testing *!aterials,

Philadelphia, Pa., 1965.

[15] Federal Housing Administration, Minimum Property Standard for One

and Two Living Units, Washington, D.C, November 1966, as subsequently

amended

.

36
>iaS-l 14A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. I'lMU l( ATION OK !<! \ NO. NBS BSS-532. Oov 't Act c- s s I on No.

3. I<( I i)iu-n['s Accession No.

4. rn i.i-; and suH i ri i.i. Study of the Local Resistance of Conventional Plywood

Subflooring to Concentrated Load

5. l^ublication Date Mav 1974

6. Performing Organization Gode

7. AU rHOR(S)

Felix Y. Yokel

8. Perft)rrning Organ. Rcpcjrt No.

9. pi-;kformin(; organization name ano addrhss

national bureau of standards

department of commerce

washington, d.c. 20234

10. IVoject/Task/Vt'ork Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Namf and C omplete Address (Street, City, State, ZIP)

Office of Research & Technology

Department of Housing & Urban Development

Washington, D.C. 20410

13. Type of Report & Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLIiMENTARY NOTES

Library of Congress Catalog Card Number: 74-600075

16. ABSTRACT' (A 200-word or less (actual summary ol most significarjt information. If document includes a significant

bibliography or literature survey, mention it here.) Representative specimens, simulating the performance of five conventional

plywood floor systems, were tested under concentrated load in order to compare

their performance with that stipulated by performance criteria developed on the

basis of anticipated occupancy loads.

In 24 out of 26 tests the performance of the specimens exceeded that

required by the criteria. Data on failure loads, load-deflection characteristics

and failure modes are presented and discussed.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Evaluation criteria; floors; hardboard; load capacity, performance criteria;

plywood subflooring; subflooring; underlajnnent; wood-frame construction.

18. AVAILABILITY Unlimited

For Official Distribution. Do Not Release to NTIS

Order From Sup. of Doc, U.S. Government I^LntUig Difice Washington, D.C. 20402. SD Cat. No. ClJ,'^y/ ^ •->J

1

^ Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

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Published in two sections, available separately:

• Physics and Chemistry (Section A)

Papers of interest primarily to scientists working in these fields. This section covers a broad range of

physical and chemical research, with major emphasis on standards of physical measurement, fundamental

constants, and properties of matter. Issued six times a year. Annual subscription: Domestic, $17.00; Foreign, $21.25.

• Mathematical Sciences (Section B)

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design,

numerical analysis, theoretical physics and chemistry,

logical design and programming of computers and

computer systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic, $9.00; Foreign,

$11.25.

DIMENSIONS, NBS

The best single source of information concerning the Bureau's measurement, research, developmental, co- operative, and publication activities, this monthly

publication is designed for the layman and also for the industry-oriented individual whose daily work

involves intimate contact with science and technology —for engineers, chemists, physicists, research managers, product-development managers, and company

executives. Annual subscription: Domestic, $6.50; Foreign, $8.25.

NONPERIODICALS Applied Mathematics Series. Mathematical tables, manuals, and studies. Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) de- veloped in cooperation with interested industries, professional organizations, and regulatory bodies. Special Publications. Proceedings of NBS conferences, bibliographies, annual reports, wall charts, pamphlets, etc. Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities. National Standard Reference Data Series.

NSRDS provides quantitative data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality, and methods for testing various industrial products. ^These standards are developed co- operatively with interested Government and industry groups and provide the basis for common understanding of product characteristics for both buyers and

sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other-agency and

NBS-sponsored work) of limited or transitory interest. Federal Information Processing Standards

Publications. This series is the official publication within the Federal Government for information on

standards adopted and promulgated under the Public Law 89-306, and Bureau of the Budget Circular A-86

entitled, Standardization of Data Elements and Codes

in Data Systems.

Consumer Information Series. Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's tech- nological marketplace.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey bibliographies are issued periodically by the Bureau

Cryogenic Data Center Current Awareness Service (Publications and Reports of Interest in Cryogenics).

A literature survey issued weekly. Annual subscription: Domestic, $20.00; foreign, $25.00.

Liquefied Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00. Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription : $20.00. Send subscription orders and remittances for the preceding bibliographic services to the U.S. Department

of Commerce, National Technical Information Service, Springfield, Va. 22151. Electromagnetic Metrology Current Awareness Service (Abstracts of Selected Articles on Measurement

Techniques and Standards of Electromagnetic Quantities from D-C to Millimeter-Wave Frequencies). Issued monthly. Annual subscription: $100.00 (Special rates for multi-subscriptions). Send subscription order and

remittance to the Electromagnetic Metrology Information Center, Electromagnetics Division, National Bureau

of Standards, Boulder, Colo. 80302.

'

Order NBS publications (except Bibliographic Subscription Services)

from: Superintendent of Documents, Government Printing Office, Washington, D.C. 20402.
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