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00 NBS BUILDING SCIENCE SERIES

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.U58

Imp

on the P

of

^jl i« .J. g floorin
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UL 1 6 1974

lo The Effect of Impact Loadings on the

Performance of Wood Joist Subflooring Systems

H. S. Lew

Center for Building Technoiogy

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Prepared for the

Office of Policy Development and Research 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

Issued May 1974
Library of Congress Cataloging in Publication Data

LeWjHai Sang,

The effect of impact loadings on the performance of

wood joist sub flooring systems.

(National Bureau of Standards Building Science

Series, 52)

"Sponsored by the Office of Policy Development and

Research, Department of Housing and Urban Development."

Includes bibliographical references.

Supt. of Docs. No.: C 13.29/2:52.

1. Wood floors —Testing. I. Title. II. Series:

United States. National Bureau of Standards. Building

Science Series, 52.

TAU35.U58 no. 52 [TA666] 690'. 08s [62^'.l8ii] 7^-7013

National Bureau of Standards Building Science Series 52

Nat. Bur. Stand. (U.S.), Bldo;. Sci. Ser. 52, 35 pages (May 1974)

CODEN: BSSNBV

Supersedes NBSIR 73-187 (PB 221-188)

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

le by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.29/2:52). Price 70 cents.
Table of Contents

Pape

SI Conversion Units iv

Glossary iv

1. Introduction 1

1.1 Background 1 1.2 Scope 1 1.3 Test Program 1 1.4 Concentrated Load and Loaded Area 2

2. Description of Tests 3 2.1 Test Specimens 3 2.2 Test Setup h 2.3 Test Procedure ^ 2.4 Single Versus Successive-Impact Tests 5

3. Test Results and Discussions 6

3.1 Deflection from Concentrated Static Load Prior to Impact

Loading 6 3.2 Impact Load versus Floor Deflection from Concentrated

Static Load 6

4. Conclusions 7

5. Acknowledgements

.

8

6. Tables and Figures 9

7. Appendix 26

8. References 28

iii
SI Conversion Units

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

General Conference of V/eights and Measures, which gave official status to the

metric SI system of units, the author assists readers interested in m.aking use

of the coherent system of SI units by giving conversion factors applicable to

US units used in this paper.

Length

1 in = 0.025'^ metre (exactly)

1 ft = 0.3048 metre (exactly)

Area

1 in^ = 6.5416 X

10"'^ metre^ (exactly)

Mass

1 lb (Ibm) - 0.4536 kilogram

Energy

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

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 posses sufficient density, smoothness, stiffness, dimensional stability,

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.

Iv
The Effect of Impact Loadings on the Performance

of Wood Joist Sub flooring: Systems

H. S. Lew

This report presents the results of an experimental study

of wood-Joist subfloorlng systems subjected to impact load. Six

different types of subfloorlng systems were tested follov;lng the

test method described in the ASTM Standard Methods (AST?4 Designation E-72), The magnitude of impact load v/as varied by dropping

a 60-lb bag from different heights.

A concentrated static load of ^00 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.

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 subfloorlng.

1 . 3 Test Program

Prom 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 under static loads . When an im.pact 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.

Figures in brackets Indicate the literature references on nage 28.

1
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 sam.e concentrated static load.

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 v;as 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 v;as 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 "ft-lb."

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 follov;s

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-^50 lb

Since the frequency of occurrence of a large load produced by such

items as a player-piano is lov;, 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.

2
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 v/ould experience In practice.

For this test program, It was decided to use a concentrated load of '400 lb applied over a 5/8-in dla. disc. This results In about 1,300 psl of

bearing pressure which is close to the upper range of bearing pressures

that could occur In practice.

2,0 Description of Tests

2 . 1 Test Specimens

Four different groups of plywood subfloorlng were tested. Two groups

consisted of a single sheet of plywood and tvjo groups of a sheet of plywood

overlayed with a sheet of underlayment (see glossary). To examine the

effect of discontinuous edges of subfloorlng on the Imnact strength, the

specimens with underlayment had both spliced sheets as well as full con- tinuous 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 VJashington, 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 plyv/ood used In this test

program are given In the appendix. The hardboard underlayment satisfied

the Federal Specification LLL-B-8lOa [^i].

All specimens were constructed In accordance with the provisions in

FHA "Minimum Property Standards" (FHA-MPS) Sections 817.3 and 815. 'I [5].

As shown in table 1, groups 1, 2, 3a and 'la specimens were constructed using

full-size ft x 8 ft) sheets nailed on a frame made of 2 x 8— wood mem.bers.

For group 3b and 'lb 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 'I 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 'Id 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 2x8 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 A and B first. If the test on these two

— 2 X 8 is designation in nominal dimensions of wood Joist whose actual cross- sectional dimensions are 1-1/2 in by 7-1/2 in.

3
panels produced damage to either the plywood subfloorinp; or the underlayment

,

the specimen was discarded. On the other hand. If no damape 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 ASTri E-72. The bag

was dropped from a release-mechanism as shov/n.

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 consisted of a l6-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 ^100 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 ft-lb 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 vjere measured on the top with respect

to the top surface of test specimen as shown in figure 3. 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 ImDact and the i|00-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 , was measured

under the load. The purpose of applying two cycles of loading was to minimize

the indentation produced 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 follov;lng each application of Impact load,

the concentrated load of ^00 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

.

^ Single versus Successive-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 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, i^20 ft-lb, and ^180 ft-lb levels in table 3. The

measurements of single-impact tests are listed under column A and the measurements of successive-impact 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.

It is necessarily assumed that the variances of the residual deflection

measurements of the two schemes are not known and are not equal; and hence,

the means are not equal. The t-test procedure is described in reference

7. The statistical quantities computed at a five-percent significance level

corresponding to the 360 ft-lb, ^120 ft-lb, and i^QO ft-lb levels are given

in table ^.

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, X". - X , is significant.

5
The computed statistics are compared with the absolute difference between

the two means in the last row of table ^. It is seen here that, in all

three levels of impact enerp;y, the computed statistic, u, is greater than

the actual difference between the mean from the single- impact tests and

the mean from the successive-impact tests. The conclusion is that the hypothe-.

sis is 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, tv;o cycles of a static concentra-rted load of ^00 lb vfere 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 AD grade plywood.

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/^-in hardboard underlayment (groups 3a and ^a, respectively). It is also

apparent that the specimens which had discontinuous plywood subflooring

(groups 3b and ^b ) 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 ^JOO 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 d'^ 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 ^100-

Ib load applied on a 5/8-in disc prior to impact loading.

In each figure, the mean of the test points at each imnact energy level

is shown as an open circle. The means for each group of specimens are given

in table 6. Because there were an Inadeauate 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 HOO lb applied

6
prior to impact loading. Except for groups 1 and 3b specimens, the static

deflection from the ^00-lb concentrated load increased linearly with increasing

impact energy up to about 36O ft-lb. Above this level the group 2 specimens

began to show increasing deformation and the remaining three groups of specimens

remained linear up to 6OO 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/^-in A-A plywood or 1/H-ln hardboard

in combination with 1/2-in C-D plywood. However, for sub flooring which

had a discontinuous edge under the impact area, the 1/^-in hardboard underlayment showed greater deflection resistance than the 1/4-in A-A plywood underlayment .

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 plyv;ood

subfloors. The deflection limit is I/I80 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 ^00-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, 36O and 520 ft-lb, respectively.

Thus, if an expected maximum Impact energy in dv;elling is known, from a figure

such as this, a practical choice of subfloorlng can be made for a limiting

deflection

.

M. Conclusions

4.1 Conclusions

An investigation was conducted to determine the effect of Impact load

on the static deflection resistance of plyx-jood 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 remiained

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

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

extended up to 6OO ft-lb. Groups 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 con- centrated 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.

7
3. Static deflections from a static concentrated load

of ilOO 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 i/2-inch C-D plywood with

1/^-inch A-A plywood or l/'l-inch hardboard underlayment.

H. 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.

5. Acknowledgements

The tests reported herein were performed by Mr. James Seller, 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 v/ishes 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.

8
6. Tables and Figures
TABLE 1. Description of Test Specimens

Group Component of Specimens No. of Tests

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

2 5/8 in. Underlayment C-C

Plugged

44

3

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

1/4 in. A-A Underlayment

25

1/2 in. C-D Plugged INT with

1/4 in. A-A Underlayment

28

4

1/2 in. C-D Plugged INT with

1/4 in. Hardboard Underlayment

36

1/2 in. C-D Plugged INT Split

with 1/4 in. Hardboard Under1 ayment

.

28

*For designations of plywood, refer to Appendix.

^Tlaese specimens had splitted sheets of plywood panel thus

providing discontinuous edge at the center of test panel.

TABLE 2 Distribution of Tests

Group

Impact Test

Only

Impact 5 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

10
TABLE 3 Single and Successive Drop Test Data

for Group 2 Specimens

Residual Deflection (in )

No. o£

Tests

360 ft -lb* -lb* i-D 480 ±t -lb* J-U 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.

11
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TABLE 5 Initial Static Deflection Under 400 lb

No. o£

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 U 222 0 lOZ 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

lU 0 200 0 108

Avg. 0 186 0 104 0 153 0.230 0.149 0.208

TABLE 6 Mean Deflections Under 400-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 0.170 0.222 0.416 0.228 0.318

600 0.245 0.251 0.247 0.347

13
z

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SPLIT FOR GROUP 3ba4b

SPECIMENS ONLY

2x8

l/2-in A-D INT (GROUP I) 5/8-in UNDERLAYMENT C-C(GR0UP2)

l/2-in C-D PLUGGED (GROUP 3 8 4)

1/4- in PLYWOOD A-A UNDERLAYMENT ( GROUP 3a S 3b ) l/4-in HARDBOARD UNDERLAYMENT (GROUP 4a & 4b)

1 II 'I

1 1

1

! 1 1

1

11 1

1 n i 1

1

II 1

FIGURE 1 Test Specimen

in
FIGURE 2 Impact Test Setup

15
BAG RELEASE

MECHANISM

60-lb. BAG

DEVICE USED TO

MEASURE DEFLECTIONS

FIGURE 3 60-lb Sandbag.

Bag Release Mechanism and

Device Used to Measure Deflections

16
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25
7. Appendix

For reference, the followinp; 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 Minimum Veneer Quality Gr3d6 Ossignstions Face Back Inner Plys

N-N' N N c Sanded 2 sides N-A' N A c Sanded 2 sides N-B' N B c Ssndcd 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 D Sanded 2 sides Sanded or touch-sanded Underlayment C (Plugged) u as specified Unsanded or touch- C-D (Plugged) C (Plugged) D 0 sanded as specified STRUCTURAL See Paragraph 3.4.4 Unsanded grade' STANDARD C D D Unsanded grade' STANDARD WITH

EXTERIOR GLUE

(See para. 3,4.5) C D D Unsanded grade'

(1) Nntural finish items inienried priman'v for cabinet work. Available (3) Veneer immediately adjacent to face shall be C or better, generally only in 3/4" thickness ana only from ceri3in mills.

(4) Panels shall nc! be sanded, touch-sanded, or thickness sized by

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

ing. Available genera :iy only m 1/4 ' thickness and only from

certain mills.

Exterior Jype Grades'

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

Marine See Daragraoh 3.4.1 Special Exterior See paragraph 3.4.S 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 Sand(.d 2 sides B-C B C c Sanded 2 sides C-C (Plugged) C (Plugged) C c Sanded or touch- sanded as specified CO C C c Unsanded grade' A-A High DSYisity Overlay A A C (Plugged)

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

B-B High Density Concrete B B C (Plugged) Form Overlay iSee para. 3.4.3) B-B Medium Density Overlay B 6 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. oniy one side is surfaced, the exposed back shall be C or better.

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

refers to the veneer directly underlying the sur'sce, AH overlaid any mccranical means.

Classification of Species

Group 1 Group 2 Group 3 Group 4 Group 5

Birch Cedar, Port Orford Maple, Black Alder, Red Aspen Fir, Balsam

Yellow Douglas Fir 2 Meranti Cedar Bigtooth Poplar, Balsam

Sweet Fir Mengkulang Alaska Quaking

Douglas Fir 1 California Red Pine Pine Birch, Paper

Larch, Western Grand Pond Jack Cedar

Maple, Sugar Noble Red Lodgepole Incense

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 White *Poplar, Western Almon Spruce, Engelmann

Bagtikan * Black Cottonwood

26
Veneer grades used in plywood

Veneer Grade Limiting Characteristics

N

Intended for Natural Finish

Presents smooth surface. Veneer shall be all heartwood or all 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.

If joined, not more than two pieces in 48" width; not more than three pieces in wider panels. Joints parallel to panel edges and well-matched for color and grain. Repairs shall be neatly made, well-matched for color and grain, 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 1/32" 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 Ve" in width. -Sapwood.

-Discolorations. Veneer shall be free from knots, knotholes, 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 tillers 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".

B

Presents solid surface. Admits-Knots up to 1" across the grain if both sound

and tight. -Pitch streaks averaging not more than 1" in width. — Discolorations. -Slightly rough but not torn grain, minor sanding and patching defects, including sander skips not exceeding 5% of panel area. Veneer shall be free from open defects except for splits not wider than 1'32", vertical holes up to 1/16" in diameter if not exceeding an average of one per square

foot in number, and horizontal or surface tunnels up to 1/16" in width and 1' in 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 "sled" type not exceeding 3" in width individually when used in multiple repairs or 4" in width when used as single repairs.

• Plugs may be "circular," "dog-taone." and "leaf- shaped," not exceeding 3" in width when used in multiple repairs or 4" in 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 11'2" across the grain. -Knotholes not larger than 1" across the grain. Also an occasional knothole not more than IK'-/' measured across the grain, occurring in any

section 12" along the grain in which the aggre- gate width of all knots and knotholes occurring wholly within the section does not exceed 6" in a 48" width, and proportionately for other widths. —Splits 1/2" by one-half panel length; Va" by any

panel length if tapering to a point; ' 4" maximum

where located within 1" of parallel panel edge. -Worm or borer holes up to s.g" x IV2". -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"

in 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 'V x 1/2". -Pitch pockets if solid and tight. -Sound tight knots up to V/2" across the grain. -Plugs, patches and shims, (plugged) -Splits up to I'e" wide.

D

D veneer used only in Interior type plywood and may

contain plugs, patches, shims, worm or borer holes. Backs: Admits tight knots not larger than 2'''2" measured across

the grain and knotholes up to 2'/2" in maximum dimension. An occasional tight knot larger than 21/2" but not

larger than 3" measured across the grain or knothole

larger than 2V2" but not larger than 3" maximum dimension, occurring in any section 12" along the grain in which the aggregate width of all knots and knotholes

occurring wholly within 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 than 2V2" maximum dimension in veneer thicker than 1/8".

-Knotholes not exceeding 31/2" maximum dimension in center ply of 5-ply STANDARD and C-D

Plugged grades.

All Plys: Pitch pockets not exceeding 21/-" measured across the

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

exceeding -'2"; not exceeding ' 4" maximum width where

located within 1" of parallel panel edge; splits must

taper [0 a point. White pocket in inner plys and backs, not exceeding

three of the following characteristics in any combination

in 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 IV2" to 21/2", or two

knots or knotholes or repairs 1" to 11/2".

27
8. References

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

for the Evaluation of Operation BREAKTHROUGH Housing Systems".

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

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

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

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

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

in Houses," Paper No. 3^ CSIRO, Division of Forest Product Technology,

Melbourne, Australia, 196^.

3. U. S. Department of Com.merce, "Product Standards PS 1-66 —Softwood Plywood, Construction and Industrial," Washington, D. C, November 1966.

H. General Service Administration, "Federal Specification, LLL-B-8lOa - Building Board, (Hardboard) Hard Pressed, Vegetable Fiber," V/ashington,

D. C. , July 1965.

5. Federal Housing Administration, "Minimum Property Standards for One and

Two Living Units,: VJashlngton , D. C, November I966, as subsequently

amended.

6. ASTM Designation E72-68, "Standard P^ethods 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 I963.

8. "Performance of Construction Plywood," CSA Standard 0159, Ottawa, Canada,

196i|.

28
NBS-n4A IREV. 7-7J)

U .S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. iniHI.lC A I ION OK KI'I'OK r NO. KBS BSS-52

2. CiDv 't Acccs.s ion No.

3, Kec ipic-nt \s Act cs.sicjn No,

4. TITl.I'; AND SUin iTI.l':

The Effect of Impact Loadings on the Performance of Wood

Joist Subflooring Systems

5. Publication D.itc May 1974

6. Performing Organization ( ode

7. AUTIIOR(S-) H. S. Lew8. Performing Organ. Report No.

9. I'HKFORMINC; ORGANIZATION NAMH AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit .-!;.. 4600461

11. Contrai l /C'lrant No. IAA-H-16-70

12. Sponsoring Org.in izat ion Name and ( omplctc Address (Street, City, State, ZIP)

Office of Policy Development and Research

Department of Housing and Urban Development

Washington, D. C. 20410

10. I ypf of Kcport & Period CoveredFinal

14. sponsoring Agency Code

15. SUPPI.HMENTARY NOTHS Library of Congress Catalog Card Number: 74-7013

Supersedes NBSIR 73-187 (PB 221-188).

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

bibliography or 1 iterature 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.

17. KEY WORDS fsjx to twelve entries; alphabetical order: capitalize only the first letter of the first key word unless a proper name; separated by semic olons

)

Concentrated load; deflection; floor; hardboard; housing; impact energy;

Operation BREAKTHROUGH; plywood; subfloors; underlayment ; wood; wood joists.

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