NBSIR 73-187

The Effect of Impact Loadings on the

Performance of Wood Joist Subflooring

Systems

H. S. Lew

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1973

Final Report

Prepared for Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C. 20410

NBSIR 73-187

THE EFFECT OF IMPACT LOADINGS ON THE

PERFORMANCE OF WOOD JOIST SU8FL00RING

SYSTEMS

H. S. Lew

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

May 1973

Final Report

Prepared for Office of Research and Technology , Department 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, Director

Impact Tests on Wood Joist Subflooring Systems

by

H. S. Lew

Structures Section

Structures, Materials and Life Safety Division

Center for Building Technology, IAT

National Bureau of Standards

ABSTRACT

This report presents the results of an experimental

study of wood- joist subflooring systems subjected to impact

load, Six different types of subflooring systems were tested

following the test method described in the ASTM Standard

Methods (ASTM Designation E-72). The magnitude of impact

load was varied by dropping a 60-lb bag from different heights.

A concentrated static load of 400 lb was applied to

the subfloor after it was exposed to impact load. It is

suggested that the deflection under this concentrated load

be used as a measure of the impact resistance of the subfloor.

Key Words: Concentrated load; deflection; floor; hardboard;

housing; impact energy; Operation BREAKTHROUGH;

plywood; subfloors; underlayment ; wood; wood joists.

i
CONTENTS

ABSTRACT

SI CONVERSION UNITS

GLOSSARY

1. INTRODUCTION 1

1 . 1 Background i

1 . 2 Scope i

1.3 Test Program i

1.4 Concentrated Load and Loaded Area 3

2. DESCRIPTION OF TESTS 5

2.1 Test Specimens 5

2.2 Test Setup 7

2.3 Test Procedure 8

2.4 Single Versus Successive- Impact Tests 10

3. TEST RESULTS AND DISCUSSIONS 12

3.1 Deflection From Concentrated Static Load 12

Prior to Impact Loading

3.2 Impact Load versus Floor Deflection From 13

Concentrated Static Load

4. CONCLUSIONS 16

5. ACKNOWLEDGEMENTS 18

6. TABLES AND FIGURES 19

7. APPENDIX 39

8. REFERENCES 42

i

iii

i v

ii
SI CONVERSION UNITS

In recognition of the position of the United States

as a signatory to the General Conference of Weights and

Measures, which gave official status to the metric SI system

of units, the author assists readers 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 metre (exactly)

1 ft = 0.3048 metre (exactly)

Area

.2 -4 2

1 in = 6.5416 x 10 metre (exactly)

Mass

1 lb (lbm) = 0.4536 kilogram

Energy

1 ft-lb (ft-lb force) = 1.356 joule

iii
GLOSSARY

Hardboard: A dense panelboard manufactured primarily

of wood fibers with the natural lignin

in the wood reactivated to serve as a

binder for the wood fibers.

Subfloor: The structural material or surface which

supports floor loads and the finish flooring.

If the subfloor material possesses sufficient

density, smoothness, stiffness, dimensional,

stablity, and adequate bonding properties,

finish flooring may be applied directly

on it without the use of underlayment

.

Underlayment : A mastic or panelboard 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 finish flooring.
1. INTRODUCTION

1 . 1 Background

Performance criteria need both descriptive and quantified limits to adequately define their intent. It became

apparent, in the course of the development of the Guide

Criteria [1]-^ for the Operation BREAKTHROUGH program, that

no reliable test data for conventional wood floors of dwelling

construction are available to establish quantified limits

relative to impact resistance. For this reason, the experimental

program presented in this report was undertaken.

1 . 2 Scope

Because wood joist floor construction is widely used

and has shown a generally acceptable level of performance,

it was decided that the impact strength of wood-joist floors

would provide an appropriate datum for comparison. The tests

reported herein were carried out on wood-joist floors with

several combinations of plywood subflooring.

1 . 3 Test Program

From the user's point of view, one feature of the

serviceability of the floor is considered to be impaired

when the local deformation of the floor is excessive

— The number in the bracket refers to the reference listed in

Reference

.

1
under static loads. When an impact load causes damage to

the floor, application of a static load on that part of the

floor can produce a larger deflection than that produced by

the same load on the undamaged floor at the same location.

If this deflection under the static load is greater than

a tolerable limit, the performance of this floor can become

objectionable to the user. The serviceability of the floor

would then be impaired.

The incidents which produce impact load in dwellings may

range from accidental dropping of household items and furniture

to a person falling from a ladder. The magnitudes of these impact

loads on the floor have not been documented. Therefore,

the resistance of floor systems to specific levels of impact

loads associated with specific causes cannot be determined

at present. On the other hand, deflection of the floor under

a given static concentrated load can be determined experimentally

relative to the stiffness reduction of the floor that might be

caused by the application of impact load. Thus, for a limiting

deflection under a given static concentrated load, the

corresponding impact energy could be obtained for a specific

floor system. Conversely, after being subjected to this

maximum level of impact energy, the floor should not deflect

more than a set limit under the same concentrated static

load

.

2
A series of tests were made to establish a relationship

between the impact load and the deflection at the impacted

area under a concentrated static load. In each test, an

impact load was applied to the specimen and subsequently

the static deflection was measured under a concentrated

load of predetermined magnitude applied to that area. The

magnitude of the concentrated load and the size of the loaded

area will be discussed in section 1.4.

The impact was delivered to the specimen by dropping

a 60-lb bag from a given height. For simplicity, the energy

delivered to the specimen is measured by the product of the

weight of the bag and the height of drop. Thus, the energy

is expressed in terms of the potential energy rather than

the kinetic energy delivered to the specimen. In this test

program, the magnitude of impact energy is expressed in "ftlb. M

1 . 4 Concentrated Load and Loaded Area

When concentration of load is considered for design,

both the load and the loaded area should be taken into account.

A study by Boyd [2] shows that typical concentrated loads found

in houses are as follows:

3
1. A person carrying a heavy load 350-400 lb

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

3. An upright piano (per caster) 200 lb

4. A player-piano (per caster). 280 lb

5. A hand- truck carrying an upright

piano (per wheel). 250-350 lb

6. A hand-truck carrying a player-piano

(per wheel). . . 350-450 lb

Since the frequency of occurrence of a large load produced

by such items as a player-piano is low, Boyd concluded that

it would be inappropriate to design for such an extreme load.

He suggested that it would not be unreasonable to consider

a short-term load of 400 lb for a duration of a few seconds

over an area of 1.5 in . The magnitude of such a load appears

reasonable to consider as a design load. However, the bearing

pressure produced by this loading condition is substantially

less than a maximum bearing pressure that could be expected

from stiletto heels. It has been observed that due to a small contact area, stiletto heels can produce a bearing

pressure as high as 1,400 psi.

A test program that deals with evaluation of the performance of floors under concentrated load must consider

both high magnitude loads and corresponding pressures that

reflect what the floor would experience in practice.. For

4
this test program, it was decided to use a concentrated

load of 400 lb applied over a 5/8-in dia. disc. This results

in about 1,300 psi of bearing pressure which is close to

the upper range of bearing pressures that could occur in

practice

2. DESCRIPTION OF TESTS

2 . 1 Test Specimens

Four different groups of plywood subflooring were tested.

Two groups consisted of a single sheet of plywood and two

groups of a sheet of plywood overlayed with a sheet of

underlayment (see glossary). To examine the effect of discontinuous edges of subflooring on the impact strength, the

specimens with underlayment had both spliced sheets as well

as full continuous sheets of plywood. Figure 1 illustrates

the layout of the test specimens and table 1 gives a description

of the specimens and the number of tests for each group.

All materials were typical of those presently used

in conventional wood-frame house construction and were purchased

from building material suppliers in the Washington, D. C.

area. The plywood used for the specimens had five piles and

met the Federal Product Standard PS 1-66 for soft plywood [3].

Designations used to describe grades of the plywood used

in this test program are given in the appendix. The hardboard

underlayment satisfied the Federal Spec:. f ication LLL-B-810a [4],

5
All specimens were constructed in accordance with the

provisions in FIIA "Minimum Property Standards" (FHA-MPS) Sections

817.3 and 815.4 [5]. As shown in table 1, groups 1, 2,

3a and 4a specimens were constructed using full-size (4 ft x

2 /

8 ft) sheets nailed on a frame made of 2 x 8— wood members.

For group 3b and 4b specimens, a full-size sheet of plywood

was first split into two halves of 2 ft x 8 ft and then nailed

on the frame. A full-size (4 ft x 8 ft) sheet of underlayment

was nailed on top of the plywood for all group 3 and 4 specimens.

As specified in FHA-MPS, 8d common nails were used

for nailing the plywood. Six-inch spacing was used for interior

and 10-in spacing for exterior joists. The underlayments

were nailed directly on the plywood using 4d annular- threaded

nails spaced 6 inches on center in each perpendicular direction.

For all test specimens, 2x8 joists were spaced at

16 inches on center, thus providing 6 equally spaced test

panels (see fig. 1). The joists were end-nailed to the 2

x 8 edge members. The plywood sheet was oriented with the

grain of the outer ply perpendicular to the axis of the joists.

The letter designations A, B, C, and D shown in figure

1 indicate the test panels of each specimen on which the

test load was applied. In all cases, tests were made on panels

— 2 x 8 is designation in nominal dimensions of wood joist

whose actual cross - sect ional dimensions are 1-1/2 in by

7-1/2 in.

6
A and B first. If the test on these two panels produced

damage to either the plywood sub flooring or the underl aymen t

,

the specimen was discarded. On the other hand, if no damage

to the specimen was observed, additional tests were made

on panels C and D.

2 . 2 Test Setup

The test setup was essentially the same as the one described in ASTM E-72 [6] and is shown in figure 2. However,

the test panel assembly was placed directly on the floor

of the laboratory instead of placing it on steel roller supports

as described in the ASTM test. This support condition minimized

flexing action of the joist, thus providing a rigid support

condition for impact loading. This also created a more severe

test than if the joists were allowed to respond in flexure

and hence, corresponded to a more critical situation in actual

floors. The material and size of the 60-lb sandbag shown

in figure 3 conformed to the specifications of ASTM E-72.

The bag was dropped from a release -mechanism as shown.

The setup for the concentrated load test is shown in

figure 4. The test load was applied by a single-acting

hydraulic ram of 20,000-lb capacity. The load applied

at a rate of one lb/sec and was monitored by a load cell

of 500-lb capacity. All deformations under the concentrated

load were measured using a rig shown in figure 5. The rig

7
consisted of a 16- in long reference beam that spanned between

two adjacent joists and a dial gage graduated to read 0.001

inch

.

2 . 3 Test Procedure

Each group of the specimens described in table 1 was

tested following two different test procedures. Part of

the specimens of each group were tested under impact load

only and the remaining specimens were subjected to both impact

load and the static load of 400 lb. The significance of

the static load test was described in section 1.3. The number

of tests conducted under each test procedure for each group

of specimens is given in table 2.

For the specimens that were subjected only to impact

load, residual deflection was measured at the center of the

impacted area. The magnitude of impact, as defined by the

product of the weight of the bag and the height of drop,

was increased in increments of either 60 ft-lb or 120 ft1b until breaking and/or splintering of the plywood subfloor

was noted at the underside. For group 1 specimens, the

test started from 60 ft-lb load and for other groups the

test started from 120 ft-lb load. After the bag was removed

from the specimen, residual deflections were measured on

the top with respect to the top surface of test specimen

as shown in figure 3.

8
Impact was repeated on a panel as long as distress was

not observed anywhere in that panel. It should be pointed

out that this procedure assumes that, as long as no breakings

or splinterings are observed, the previous impact loads would

not have damaged the test panel for the subsequent test,

provided that the magnitude of the loads in the preceding

tests were less than the subsequent test. This assumption

is reasonable as it will be shown subsequently that no statistically significant difference was observed in residual deflections

between those from successive impact load tests on the same

test panel and those from single impact load tests where

each increment of impact load was applied on a new test panel.

For those specimens which were subject to impact and

the 400-lb static load, the following procedure was used.

Prior to any load application, a reference deflection, designated as dl, was taken with the device shown in figure 5. Next,

a concentrated load of 400 lb was applied. After maintaining

the load for one minute, a deflection reading, designated

as d2, was taken while the load being applied on the top

surface. After unloading and waiting for five minutes the

top surface deflection, designated as d3 , was again measured.

The concentrated load was again applied, and maintained

for one minute, and then the deflection, designated as d4

,

was measured under the load. The purpose of applying two

cycles of loading \^as to minimize the indentation produced

9
by the concentrated load. The deflection at the beginning

of the second load cycle, d3, was used as a datum for all

subsequent deflection measurements. Following the two static

loading cycles, an impact load was applied on the same area

which had received two cycles of static loading.

Deflections were measured before and after the impact,

designated as d5 and d6, respectively, with the device shown

in figure 3. The static load of 400 lb was again applied.

As before, deflection measurements were taken before loading,

while the load was being applied on the test panel and after

unloading. They are designated as d7, d8 and d9, respectively.

Subsequent impact loading was applied in increments of either

60 or 120 ft-lb. The deflection measurements d5 and d6 were

taken with each application of impact load. Immediately

following each application of impact load, the concentrated

load of 400 lb was applied, and the deflection measurements

d7 , d8 and d9 were taken. This sequence was repeated until

damage to the test panel was noted.

2 . 4 Single versus Success ive - Impact Tests

Under the previously described scheme of testing,

it was considered desirable to show that successive impact

loading would not cause substantial cumulative damage to

the subflooring. In order to verify this, two series of

tests were performed on group 2 specimens. In one series

10
of tests impact load was applied successively on the same

panel until it broke. In another series of tests each impact

load was applied on a separate panel. The magnitude of impact

load was increased and the residual deflections were measured

after impact load in both series.

The residual deflection measurements of the two series

of tests are compared at 360 ft-lb, 420 ft-lb, and 480 ft-lb

levels in table 3. The measurements of single - impact tests

are listed under column A and the measurements of successiveimpact tests under column B.

A two-sided statistical t-test was made to determine

whether or not the averages of residual deflections of the

two schemes differed significantly. . Although the distribution

of measured values is not necessarily normal, the t-test

procedure, as described in reference 7, can still be used to

give approximate result. It is assumed that the variances

of the residual deflection measurements of the two schemes are

not known and are not equal. The statistical quantities

computed at a five-percent significance level corresponding to

the 360 ft-lb, 420 ft-lb, and 480 ft-lb levels are given in

table 4.

In comparing the means from each of the two testing

schemes, a hypothesis is set up such that it is possible to

discredit it from the facts. The hypothesis, in this case,

is that the two sample means may be regarded as means of

samples from the same population. The hypothesis is examined

by testing whether the difference between the two means,

11
XA

- X

}i

, is significant. The computed statistics are compared

with the absolute difference between the two means in the

last row of table 4. It is seen here that, in all three

levels of impact energy, the computed statistic, u, is greater

than the actual difference between the mean from the singleimpact tests and the mean from the s uccess ive - impact tests.

The conclusion is that the hypothesis could be true, i.e., the

two schemes of testing do not differ significantly.

3. TEST RESULTS AND DISCUSSIONS

3 . 1 Deflection From Concentrated Static Load Prior to Impact

Loading

As described previously in section 2.3, two cycles of

a static concentrated load of 400 lb were applied to the

test panel prior to impact loading. Static deflections from

the second cycle of loading, d4 , are given in table 5. It

is seen that deflection measurements are reasonably consistent

even though there were noted a number of defects such as knotholes and bore holes in the plywoods used in the specimens.

The ranges of the deflection for each group are depicted

in figure 6. They varied from 0.017 in for group 2 specimens

to 0.060 in for group 1 specimens. A large range of variation

of data for the group 1 specimens is reasonable because

of the use of A-D grade plywood.

12
Average values of deflections show that a single layer

subflooring of 5/8-in C-C plywood (group 2) deflected about

30 percent less than the subfloors which had 1/2-in C-D plywood

with either 1/4-in A-A plywood or 1/4-in hardboard underlayment

(groups 3a and 4a, respectively). It is also apparent that

the specimens which had discontinuous plywood subflooring

(groups 3b and 4b) showed approximately 1.5 times average

deflections of the specimens which had continuous subflooring

(groups 3a and 4a). These results suggest that discontinuous

edges in plywood subflooring may lead to excessive deflections.

3. 2 Impact Load Versus Floor Deflection from Concentrated

Static Load

Figures 7 through 12 show a plot of static deflections

against impact energy for each group of specimens. The

deflections plotted were measured under a concentrated load

of 400 lb which was applied after each impact load. In the

figures the ordinate is the potential energy of the bag and

the abscissa is the deflection d8 for each level of impact

energy as described in section 2.3. It should be noted

that the deflection d4 was used at zero impact energy. Thus,

the offset from the origin of each -Figure indicates the

amount of static deflection produced by the second cycle

of the 400-lb load applied on a 5/8-in disc prior to impact

loading

13
In each figure, the mean of the test points at each impact

energy level is shown as an open circle. The means for

each group of specimens are given in table 6. Because there

were an inadequate number of test panels of the group 1 and

3a specimens that sustained 600 ft-lb impact, the mean of

these groups at this level was not determined. Most specimens

of these groups were damage at this level of impact to such

an extent that the deflection measurements were not possible.

For ease of comparison, the average deflections given

in table 6 are plotted in figure 13. The initial position

of each curve indicates relative stiffness of the subflooring

from the concentrated load of 400 lb applied prior to impact

loading. Except for groups 1 and 3b specimens, the static

deflection from the 400-lb concentrated load increased

linearly with increasing impact energy up to about 360 ftlb. Above this level the group 2 specimens began to show

increasing deformation and the remaining three groups of

specimens remained linear up to 600 ft-lb. It is interesting

to note that there is little difference in the deflection

resistance of two different kinds of underlayment used in

this study; namely, 1/4-in A-A plywood or 1/4-in hardboard

in combination with 1/2-in C-D plywood. However, for subflooring

which had a discontinuous edge under the impact area, the

1/4-in hardboard underlayment showed greater deflection resistance

than the 1/4-in A-A plywood underlayment.

14
A limiting level of impact energy could be obtained

from figure 13 for a specific floor system provided that

an acceptable deflection limit under the 400-lb concentrated

load is established. At present, no such limit is found

in the design specifications and standards used in the U.S.

Based on results of tests conducted on 1/2-inch plywood

subfloors with wood joists spaced at 16 inches o.c., the

Canadian National Building Code - CAS 0152 [8] has a requirement

for a maximum deflection limit for plywood subfloors. The

deflection limit is 1/180 of the span under a static concentrated

load of 175 lb. An extrapolated value of the deflection

of 1/2-inch plywood subfloor supported at 16 inches o.c.

under a 400-lb concentrated load is about 0.2 inch. If this

value is taken as a maximum allowable deflection, figure 13

gives a limiting impact energy for group 1, group 4a, group

3a and group 2 specimens of about 60, 300, 360 and 520 ftlb , respectively. Thus, if an expected maximum impact energy

in dwelling is known, from a figure such as this, a practical

choice of subflooring can be made for a limiting deflection.

15
4. CONCLUSIONS

4 . 1 Conclusions

An investigation was conducted to determine the effect

of impact load on the static deflection resistance of plywood

subfloors nailed to wood joists. The following conclusions

are based on the results of this investigation:

1. The plywood subfloors tested showed that deflection

resistance under a concentrated load of 400 lb

decreased gradually as impact energy increased.

Except for group 1 and group 3b specimens , the

increase in the deflection under the concentrated

load with increase in the impact energy remained

linear up to an impact energy level of 360 ft-lb.

For group 3a, 4a and 4b specimens, the linearity

extended up to 600 ft-lb. Croups 3a and 4a specimens

showed about the same rate of increase in

deflection

.

2. It was shown that a limiting impact energy for the

floor could be obtained from a relationship between

impact energy and static deflection under a concentrated load applied to the impacted area. However,

an acceptable limit of the static deflection under

the concentrated load needs to be established prior

to obtaining such a limiting value of impact energy

from the relationship.

16
Static deflections from a static concentrated load

of 400 lb applied after impact loading indicate that

increasing the thickness of plywood subflooring is

more effective in increasing the deflection resistance

of the subfloor than adding a layer of underlayment

over the subfloor for about the same total thickness

of subflooring. It was shown that the average

deflection of a single layer 5/8-inch C-C plywood

subfloor was about 30 percent less than that of the

subfloor comprised of 1/2-inch C-D plywood with

1/4-inch A-A plywood or 1/4-inch hardboard underlayment.

It was shown that for the specimens which had a layer of underlayment over the subflooring, the

subflooring with discontinuous edge of plywood

deflected approximately 1.5 times the subflooring

with continuous sheet of plywood.

17
5. ACKNOWLEDGEMENTS

The tests reported herein were performed by Mr. James

Seiler, engineering technician of the Structures Laboratory

and Mr. Bruce Bean, a graduate student at University of New

Hampshire, who was a student summer worker in 1971. Mr. Bean

also analyzed the test data. The author wishes to thank them

for their contributions to this investigation.

Constructive criticisms of Dr. Robert Crist, Assistant

Chief of Structures Section and careful review of the report

by Dr. Norman F. Somes, Chief of the Structures Section are

gratefully acknowledged.

18
TABLES AND FIGURES

19
TABLE 1. Description of Test Specimens

Group Component of Specimens No. of Tests

1 1/2 in. A-D INT, Group 1* 56

2 d/o in. unaer laymenr

Plugged

A A

3

a 1/2 in. C-D Plugged INT with

1/4 in. A-A Underlayment

25

V 1/2 in. C-D Plugged INT with

1/4 in. A-A Underlayment

28

4

a 1/2 in. C-D Plugged INT with

1/4 in. Hardboard Underlayment

36

b

+ 1/2 in. C-D Plugged INT Split

with 1/4 in. Hardboard Underlayment .

28

*For designations of plywood, refer to Appendix.

+These specimens had splitted sheets of plywood panel thus

providing discontinuous edge at the center of test panel.

20
TABLE 2 Distribution of Tests

Group

Impact Test

Only

Impact § StaticLoad Test

Total No.

of Tests

1 46 10 56

2 36 8 44

3a 18 7 25

3b 22 6 28

4a 30 6 36

4b 24 4 28

21
TABLE 3 Single and Successive Drop Test Data

for Group 2 Specimens

Residual Deflection (in )

No. of

Tests

360 ft -lb* 420 ft -lb* 480 ±t -lb*

A B A B A B

1 0.003 0.008 0.011 0.004 0.012 0.014

2 0.004 0.008 0.013 0.007 0.022 0.016

3 0.005 0.010 0.018 0.009 0.026 0.018

4 0.005 0.020 0.018 0.027 0.022

5 0.005 0.036 0.024 0.024

6 0.011 0.040 0.054 0.031

7

8

0.011

0.012

0.034

0.055

9 0.016

10 0.019

11 0.029

A = Single Drop Test on different test panel

B = Successive Drop Test on the same test panel

* = 60 lb bag x height of Drop

Note: Data have been rearranged for convenience of comparison in

increasing order of residual deflection.

22
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2.3
TABLE 5 Initial Static Deflection Under 400 lb

No. of

Test

Static Deflection (in)

Group 1 Group 2 Group 3a Group 3b Group 4a Group 4b

1 0.162 0.089 0.154 0.248 0.151 0.210

2 0.167 0.110 0.158 0.251 0.150 0.217

3 0.170 0.100 0.153 0.242 0.151 0.201

4 0.191 0.102 0.158 0.234 0.164 0.205

5 0.222 0.102 0.157 0.205 0.149

6 0.193 0.099 0.154 0.200 0.129

7 0.192 0.109 0.139

8 0.168 0.117

9 0.199 0.114

10 0.200 0.108

Avg. 0.186 0.104 0.153 0.230 0.149 0.208

V 24
TABLE 6 Mean Deflections Under 4 00 -lb Static Load

Impact Energy

(ft -lb)

Static Deflection (in.)

Group 1 Group 2 Group 3a Group 3b Group 4a Group 4b

0 0.186 0.104 0.153 0.230 0.149 0.208

60 0.193

120 0.212 0.111 0.161 0.254 0.161 0.227

180 0.240

240 0.304 0.117 0.174 0.294 0.186 0.262

300 0.331

360 0.363 0.132 0.198 0.363 0.210 0.244

480 0.442 U.170 0.222 0.416 0.228 0.318

600 0.245 0.251 0.247 0.347

25
6 atl6"=8'-0"

SPECIMENS ONLY

1/2 -in A-D INT (GROUP I)

5/8-in UNDERLAYMENT C-C(6ROUP2)

l/2-in C-D PLUGGED (GROUP 3 84)

l/4-in PLYWOOD A-A UNDERLAYMENT ( GROUP 3a 5 3b ) l/4-in HARDBOARD UNDERLAYMENT (GROUP 4a 6 4b)

Jp

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FIGURE 1 Test Specimen

26
. .... .< . ..- ..

FIGURE 2 Impact Test Setup

27
BAG RELEASE

MECHANISM

60-ib. BAG

DEVICE USED TO

MEASURE DEFLECTIONS

i

FIGURE 3 60-ib Sandbag,

Bag Release Mechanism and

Device Used to Measure Deflections

28
RGURE 4 Concentrated Load Test Setup

29
FIGURE 5 Rig Used for Deflection Measurements in Static Tests

30
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FLOOR SYSTEMS (GROUP)

FIGURE 6 Range of Static Deflection Measured Prior to Impact Loading

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38
APPENDIX

For reference, the following tables and grade descriptions

for veneers are reproduced from NBS Voluntary Product Standard

PS 1-66 "Softwood Plywood, Construction and Industrial" and

from a publication of the American Plywood Association.

Interior Type Grades

Panel Grade Designations Face Minimum Veneer Quality Back Inner Plys Surface

N-N N N C Sanded 2 sides

N-A' N A C Sanded 2 sides N-B' N B C Sanded 2 sides N-D' N D D Sanded 2 sides A-A A A D Sanded 2 sides A-B A B D Sanded 2 sides A-D A D D Sanded 2 sides B-B B B D Sanded 2 sides B-D B D 0 Sanded 2 sides Sanded or touch-sanded Underpayment C (Plugged) D C

3 & D as specified Unsanded or touch- C-D (Plugged) C (Plugged) D D sanded as specified STRUCTURAL See Paragraph 3.4.4 Unsanded grade' STANDARD C D D Unsanded grade J STANDARD WITH

E.XTERIOR GLUE

(See para. 3.4.5) C D D Unsanded grade4

(1) Natural finish items imended primarily for cabinet work. Ava<'able (3) Veneer immediately adjacent to face shall be C or better, generally only in 3/4" thickness ana only from certain mills.

(4) Panels shall not be sanded, touch-sanded, or th,c*ness s.zed by

(2) Natural finish item, intended primarily for panelirg and wainscot- any mechanical means,

ing. Available generally only in 1/4" thickness and only from

certain mills.

Exterior Type Grades 1

T— - -r -

Panel Grade Designations Face' Minimum Veneer Quality Back 5 Inner Plys Surface

Marine See paragraDh 3.4.1 Special Exterior See paragraph 3.4.6 A-A A A C Sanded 2 sides A-B A B C Sanded 2 sides A-C A C c Sanded 2 sides B-B (Concrete Form) See paragraph 3.4.3 B-B B B c Sanded 2 sides B-C B C c Sanded 2 sides C-C (Plugged) C (Plugged) C c Sanded or touch- sanded as specified c-c C C c Unsanded grade 3 A-A High Density Overlay A A C (Plugged)

B-B High Density Overlay B B C (Plugged)

B-B High Density Concrete B 8 C (Plugged) Form Overlay (See para. 3.4.3) B-B Medium Density Overlay B B C or C (Plugged)

as specified Special Overlays C C C

(1) Available also in STRUCTURAL I classification as provided in plywood is overlaid on two sides unless otherwise specified When

paragraph 3.4 4. only one side is surfaced, the exposed back shall be C or bv er.

(2) For overlaid plywood, the grade c'esirnation for face and oack (3) Panels shall not be sanded, touch-sanded or thickness sized by

refers to the veneer directly underlying the surface. All overlaid any mecranical means.

39
Classification of Species

Group 1 Group 2 Group 3 Group 4 Group 5 D I ILI

1

Cedar, Port Orford Douglas Fir 2 Maple, Black All,, I") ,, _l Alder, Red Aspen ill, Dd Ibdll 1

T 1 IUW Meranti Cedar Bigtooth rUpidl, Odlodlll SW6Gt Fir Mengkulang Alaska Quaking

Douglas Fir 1 California Red Pine Pine Birch, Paper

Larch, Western Grand Pond Jack Cedar

h/l^ai-ilo Ivldpic, QOUgdl i mar Noble Red Lodgepole 1 ncense

Pine, Caribbean Pacific Silver Western white Ponderosa Western Red

Pine, Southern White Spruce, Sitka Spruce Fir, Subalpine

Loblolly Hemlock, Western Sweet Gum Redwood Hemlock, Eastern Longleaf Lauan Tamarack Spruce Pine

Shortleaf Red Black Sugar

Slash Tangile Red Eastern White

Tanoak White

Almon

White *Poplar, Western

Spruce, Engelmann

Bagtikan

* Black Cottonwood

40
Veneer grades used in plywood

Veneer Grade Limiting Characteristics N

Intended for Natural Finish

Presents smooth surface. Veneer shall be all hcartwood or aM sapwood free from

knots, knotholes, open splits, pitch pockets, other open

defects, and stain, but may contain pitch streaks averaging not more than 3/8" wide blending with color

of wood.

!f joined, not more than two pieces «n 48" width: not more than three pieces m wider panels. Joints parallel

to panel edges and well-matched ' for color and grain. Repairs shall be nestly made, well-matched for color and gram, and limited to a total of six in number in any 4' x 8' sheet.

• Maximum of three "router" patches not exceeding

3/4" x 3-1/2" admitted. No overlapping.

• Shims admitted not exceeding 12" in length but may

occur only at ends of panel. (Examples of permissible combinations: 3 router patches and 3 shims, 2 router patches and 4 shims, 1 router patch and 5 shims, or

6 shims).

Suitable synthetic fillers may be used to fill 1 j 32" wide

checks, splits up to 1/16" x 2", and chipped areas or other openings not exceeding 1/8" x 1/4".

A

Presents smooth surface Admits-Pitch streaks blending with color of wood and

averaging not more than in width. -Sapwocd. — Oiscolorations. Veneer shall be free from knots, knothoies. splits, pitch pockets and other open defects If of more than one

piece, veneer shall be well joined. Repairs shall be neatly made, parallel to grain, and limited to 18 in number in any 4' x 8' sheet, excluding

shims; proportionate limits on other sizes.

Patches of "boat," "router," and "sled" type only, not exceeding 2-1/4" in width, and may be die-cut if edges

are cut clean and sharp. Radius of ends of boat patches

shall not exceed 1/8".

• Multiple patching limited to 2 patches, neither of which may exceed 7" in length if either is wider

than 1". Shims admitted except over or around patches or as multiple repairs. Suitable synthetic fillers may be used to fill 1/32" wide

checks, splits up to 1/16" x 2", and chipped areas or other openings not exceeding 1/8" x 1/4".

Presents solid surface. Admits-Knots up to 1" across the gram if both sound and tight. —Pitch streaks averaging not more than 1" in width. —Oiscolorations. —Slightly rough but noi torn gram, minor sanding and patching defects, including sander skips not exceeding 5°o of panel area. Veneer shall be free from open detects except for splits not wider than 1 32". vertical holes up tc "1 16" in diameter if not exceeding an average ot one per square

foot in number, and horizontal or surface tunnels up to 1/16" in width and 1" m length not exceeding 12 in number in a 4' x 8' sheet (proportionately on other sizes) Repairs shall be neatly made and may consist of patches, plugs, synthetic plugs and shims.

• Patches may be "boat," "router," and "sied" type not exceeding 3 in widtn indivioualiy wnen used m multiple repairs or 4" in width when used as single repairs.

• Plugs may be "circular, " "dcg-bcne." and "leaf- shaped." not exceeding 3" in width when used in multiple repairs or 4" .n width when used as single repairs

• Synthetic plugs shall present a solid, level, hard sur- face not exceeding above dimensions.

Suitable synthetic fillers may be used to fill small splits or openings up to 1/16" x 2", and chipped areas or other openings not exceeding 1/8" x 1/4".

Admits-Tight knots up to IVz" across the grain. —Knotholes not larger than \" across the grain. Also an occasional kncthole not more than 1- measured acrcss the grain, occurring in any

section 12" along the gram in which the aggre- gate width of all knots and knotholes occurring

wholly wtthm the section does not exceed 6" in a 48" width, and proportionately for other widths. —Splits Vz" by one-half panel length; 3 a " by any

panel length if tapering to a point; i .;" maximum

where located within 1 of parallel panel edge. —Worm or borer holes up to s 3" x V.'z"- —Open pitch pockets not wider than 1".

Repairs shall be neatly made and may consist of patches,

plugs, and synthetic plugs. Patches ("boat." including die-cut) not exceeding 3" in width individually when used in multiple repairs or 4" m width when used as single repairs. Plugs may be

circular, "dog-bone" and leaf-shaped. Synthetic plugs

shall present a solid, level, hard surface not exceeding above dimensions.

C Admits— Knotholes, worm or borer holes, and other open —Ruptured and torn grain, defects up to : 4 " x Vz". -Pitch pockets if solid and tight. -Sound tight knots up to V.'z" across the gram. -Plugs, patches and shims, (plugged) -Splits up to V wide.

D veneer used only in Interior type plywood and may

contain plugs, patches, shims, worm cr borer holes. Backs: Admits tight knots no: larger than 2 1 '>" measured across

the gram and knotholes up tc 2 ." in maximum dimension. An occasional tight knot larger thin 2' ;" but not

larger than 3 measured across the gram or knothole

larger than 2 1 " but not larger than 3 maximum dimension, occurring in any section 12" along the grain in which the aggregate width of all knots and knotnoles

occurring wholly wilhm the section does not exceed 10'

in a 48" width and proportionately for other widths. Inner Plys Permits tight knots Knotholes limited as for backs — In sanded panels, knotholes not larger Ihan 2 1 '?" maximum dimension m veneer thicker than 1/8".

—Knotholes not exceeding 3';" maximum dimension ir. center ply of 5-ply STANDARD and C-D

Plugged grades.

All Plys: Pitch pockets not exceeding ZVzM measured across the

grain. Splits up to 1" except in backs only not more than one

exceeding /': not exceeding i 4 " maximum width where

located within 1" of parallel panel edge; splits must

taper to a point. White pocket in inner plys and backs, not exceeding

three of the following characteristics in any combination

tn any area 24" wide by 12" long.

(a) 6" width heavy white pocket.

(b) 12" width light white pocket.

(c) One knot or knothole or repair U/j" to 2VV\ ° r two

knots or knotholes or repairs 1" to IV!:

- *.

41
REFERENCES

1. National Bureau of Standards, U.S. Department of Commerce, "Guide

Criteria for the Evaluation of Operation BREAKTHROUGH Housing

Systems ."

Vol. 1. Multifamily High Rise - Accession No. PB- 212055

Vol. 2. Multifamily Low Rise - Accession No. PB 212056

Vol. 3. Single Family Attached - Accession No. PB 212057

Vol. 4. Single Family Detached - Accession No. PB-212058

National Technical Information Service, U.S. Department of

Commerce, Springfield, Va. 22151.

2. Boyd J. D., "Minimum Strength and Stiffness Necessary for Wooden

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

Technology, Melbourne, Australia, 1964.

3. U. S. Department of Commerce, "Product Standards PS 1-66- -Softwood

Plywood, Construction and Industrial," Washington, D. C. , November

1966.

4. General Service Administration, "Federal Specification, LLL-B-810a -

Building Board, (Hardboard) Hard Pressed, Vegetable Fiber,"

Washington, 1). C, July 1965.

5. Federal flousing Administration, "Minimum Property Standards for

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

subsequently amended.

42
6. ASTM Designation 1-7 2-68 , "Standard Methods of Conducting

Strength Tests of Panels for Building Construction,"

American Society for Testing Materials, Philadelphia

Pennsylvania, 1971.

7. Natrella, M. G. , "Experimental Statistics," National

Bureau of Standards Handbook 91, Washington, D. C.

,

August 1963.

8. "Performance of Construction Plywood," CSA Standard

0159, Ottawa, Canada, 1964.

43

FORM NBS-114A (1-71) U.S. dept. of comm. 1. PUBLICATION OR REPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

The Effect of Impact Loadings on the Performance of

Wood Joist Subflooring Systems

5. Publication Date

6. Performing Organization Code

7. AUTHOR(S)

H. S. Lew

8. Performing Organization

NBSIR 73-187

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/ Work Unit No. 4600461

11. Contract/Grant No. IM-H-16-70

12. Sponsoring Organization Name and Address Office of Research and Technology

Department of Housing and Urban Development

Washington, D. C. 20410

\i. 1 ype or Keport <x Period Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) This report presents the results of an experimental study of wood-joist subflooring

systems subjected to impact load. Six different types of subflooring systems were

tested following the test method described in the ASTM Standard Methods (ASTM

Designation E-72). The magnitude of impact load was varied by dropping a 60-lb

bag from different heights.

A concentrated static load of 400 lb was applied to the subfloor after it was exposed to impact load. It is suggested that the deflection under this concentrated

load be used as a measure of the impact resistance of the subfloor.

7. key words (Alphabetical order, separated by semicolons) Concentrated loads ; deflection; floor

hardboard; housing; impact energy; Operation BREAKTHROUGH; plywood; subfloors;

underlayment ; wood; wood joists.

18. AVAILABILITY STATEMENT 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

1^1 UNLIMITED.

UNCL ASSIFIED

1 1 FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

20. SECURITY CLASS

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USCOMM-DC 66244-P7I