C.2

NBS BUILDING SCIENCE SERIES 122

A Study of Lumber Used

for Bracing Trenches

in the United States ° ;>^ "

U.S. DEPARTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS ''^i^.^'''
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act ot Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities^ — Radiation Research — Thermodynamics and

Molecular Science — Analytical Chemistry — Materials Science. THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering- — Mechanical

Engineering and Process Technology- — Building Technology — Fire Research —

Consumer Product Technology — Field Methods.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. ^Some divisions within the center are located at Boulder, CO 80303.
MATtONAl. BUnSA-t.' OF OTAWOAKOS

NBS BUILDING SCIENCE SERIES 122

MAY 2 7 1980

A Study of Lumber Used -rficfzc

for Bracing Trenches ,ar?

in the United States

Lawrence I. Knab and Felix Y. Yokel

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

and

William L. Galligan and B. Alan Bendtsen

Forest Products Laboratory

P. O. Box 5130

Madison, Wisconsin 53705

and

John F. Senft

Department of Forestry and Natural Resources

Purdue University

West Lafayette, Indiana 47907

Report to: Occupational Safety and Health Administration Department of Labor Washington, D.C. 20210

*Z CO Q* /

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued March 1980
Library of Congress Catalog Card Number: 80-600015

National Bureau of Standards Building Science Series 122

Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 122, 221 pages (Mar. 1980)

CODEN: BSSNBV

Supersedes NBSIR 79-1946

Foi' sale by the Superintendent of Documents, U.S. Government Printing Office Wasliington, D.C. 20402 - Price $6.

Stock Number 003-003-02164-4
CONTENTS

Page

Conversion Factors for (SI) Metric Units vii

ABSTRACT viii

EXECUTIVE SUMMARY (Includes Findings, Conclusions, and

Recommendations) ix

1. BACKGROUND AND PURPOSE 1

2. APPROACH AND SCOPE 3

3. FIELD INVESTIGATION 5

3 . 1 Purpose -. 5

3.2 Approach and Scope 5

3.3 Profile of Trenching Lumber Properties and Uses ... 7 3.4 Geographic Areas, Investigation Team,

Sampling Plan 7 3.5 Description of Data Entries 8

3.6 Lumber Sampled 10

3.7 Summary - General Observations at Supply Yards .... 10

3.7.1 Wane 10

3.7.2 Species 10

3.7.3 Storage, Moisture Content, and Fungal

Deterioration 11

3.7.4 Reused Lumber 12

3.7.5 Lumber Quality 12

3.8 Summary of Field Data Analysis 13

3.8.1 Lumber Grade Disregarding Wane,

Damage and Decay 13

3.8.2 Regrading 14

3.8.3 Reduction of Cross-Sectional Area and

Moment of Inertia 14

3.8.4 Decay 15

3.8.5 Trimming 15

3.8.6 Damage 16

3.8.7 Species 16

3.8.8 Slope of Grain 16

3.8.9 Moisture Content 16

iii
Page

4. RECOMMENDATIONS FOR ALLOWABLE DESIGN STRESSES 17

4.1 Introduction 17

4.2 Hardwood Allowable Properties 18

4.3 Softwood Allowable Properties 18

5. USE RECOMMENDATIONS 19

5.1 Introduction 19

5.2 Duration of Load 20

5.3 Damage 20

5.4 Wane 20

5.5 Bark 21

5.6 Decay 21

5.7 Insect Attack 22

5.8 Inspectability 22

5.9 Exposure 22

5.10 Storage 23

REFERENCES 25

GLOSSARY 27

APPENDIX A - Sampling Procedures and Description of Data

Entries and Coding A-1

APPENDIX B - General Observations and Descriptions

of Yards Visited B-1

APPENDIX C - Analysis of Field Investigation Data C-1

APPENDIX D - Trenching Lumber: Stress Derivation and

Use Recommendations D-1

COVER: In (ii2Atcu.n aAiicu> the. UyuXe^d StatQJ>, ZimboJt -a> iU>^d

(LxtQ,vii>l\)2Xy to bfiadz tAe-vickdi, agcu.yii,t aotlapi^.

iv
LIST OF TABLES

Page

1. Trenching Lumber Sampled 30

2. Summary of Findings for the Strength Ratio Grades (G)

for full length Wales and Sheeting 31

2a. Strength Ratio (SR) Values in Terms of Grade 31

3. Summary of Frequency and Economic Impact of Wane

on full length Wales 32

4. Allowable Unit Stresses for Hardwood Wale and Strut

Trenching Lumber 33

5. Grouping of Some Domestic Woods According to Heartwood

Decay , . 34

LIST OF FIGURES

1. Components of a Shoring System 35

2. Wane in 12 x 12's 36

3. Lumber Storage 37

4. Sheeting Lumber 37

5. Lumber Storage 38

6. A Clean Lumber Yard 38

7. Reused Wale Material 39

8. Reused Sheeting Material 40

9. Lumber Defects 41

10. Slope of Grain 42

11. Lumber Defects 43

12. Lumber Defects 44

13. Lumber Defects 44

14. Reusable Timber 45

V
Page

15. Relative Frequency of Strength Ratio Grade 46

16. Wane Example 45

17. Climate Index Map 47

18. Poor Storage Problems 48

19. Examples of Decay in Trenching Lumber 49

20. Insect Infested Trenching Timber 50

ACKNOWLEDGEMENTS

The authors are indebted to all those persons in the Center for Building

Technology who contributed in the preparation of this report. In

particular, Mr. Stephen Webber is thanked for his editorial review and

assistance in preparing the final manuscript. Appreciation is also

extended to Ms. Charity Starr for her efforts in preparing the typed

manuscript

.

vi
CONVERSION FACTORS FOR (SI) METRIC UNITS

In view of the presently accepted practice in this country in this

technological area, common U.S. units of measurement have been used

throughout this paper. In recognition of the position of the U.S.A.

as a signatory to the General Conference on Weights and Measures, which

gave official status to the metric SI system of units in 1960, we assist

readers interested in making use of the coherent system of SI units by

giving conversion factors applicable to U.S. units used in this paper.

Length

1 in = 0.0254 meter* (m)

1 ft = 0.3048 meter* (m)

Area

1 in^ = 0.000645 square meter (m^)

1 ft^ = 0.0929 square meter (m^)

Volume

1 in^ = 0.0000164 cubic meter (m"^)

1 ft^ = 0.0283 cubic meter (m^)

Mass

1 lb = 0.454 kilogram (kg)

Mass/Volume (Density)

1 Ib/ft^ = 16.02 kilogram/meter^ (kg/m^)

Temperature

degree Celsius (°C) = 5/9 (°F - 32)

Pressure

1 psi = 6895 pascal (Pa)

*Exactly

vii
ABSTRACT

In certain areas of the United States, lumber is used extensively to

brace trenches against collapse. The life and safety of the workers

in these trenches therefore depends on the structural adequacy of the

lumber bracing used. This report presents a study of the properties

and characteristics of trenching lumber which are critical to its

structural performance. Using these properties and characteristics,

allowable stresses and use recommendations are proposed.

The National Bureau of Standards (NBS) conducted a field study of

trenching lumbej: and found that either ungraded eastern species, primarily

hardwood, or graded Douglas-fir is used. For graded Douglas-fir, allowable

design stresses and other properties are established by existing standards.

The eastern species, however, are ungraded and no accepted guidelines are used to assign allowable design stresses and other properties. The

results of the field study indicate that 80 percent of the eastern species

trenching lumber, when graded by existing softwood grading rules (Southern

Pine Inspection Bureau Grading Rules, 1977 edition) is No. 2 grade or higher; 60 percent is No. 1 grade or higher. These percentages do not

reflect the effects of wane (deficiency in cross-sectional area) and

decay, which are additional problems. NBS therefore recommends tha-t, for

hardwood wales and struts, allowable stresses and other properties be

based on a No. 2 minimum grade with appropriate provisions to control wane and decay.

Use recommendations were developed, which consider duration of load,

mechanical damage to lumber, presence of bark, decay, insect attack,

inspectability , exposure, and storage for various aspects of trenching

lumber applications. These recommendations reflect a severe trenching

environment, possible reuse of structural members, and the need for

structural integrity to protect life and property.

Key Words: Construction lumber; construction safety; excavation; hardwood;

lumber grading; shoring; softwood; timber engineering; trench

bracing; trenching.
EXECUTIVE SUMMARY

I. SUMMARY OF CONCLUSIONS

In certain areas of the United States, lumber is used extensively to

brace trenches against collapse. The life and safety of the men working

in these trenches, therefore, depends on the adequacy of the lumber

bracing. The National Bureau of Standards (NBS) conducted a field study

of trenching lumber and found that either ungraded eastern species,

primarily hardwood, or graded Douglas-fir is used. Allowable design

stresses and other properties are readily available for Douglas-fir, but are non-existent for most of the eastern species. The NBS field study

indicated that, based on softwood lumber grading rules (Southern Pine

Inspection Bureau Grading Rules, 1977 edition) 80 percent of the eastern

species trenching lumber is No. 2 grade or higher; 60 percent is No. 1 grade or higher. These percentages do not reflect the effects of wane (deficiency in cross-sectional area) and decay, which are additional

problems. NBS therefore recommends that, for hardwood wales and struts,

allowable stresses and other properties be based on a No . 2 minimum

grade. It is also possible to base allowable stresses, etc., on a No. 1 minimum grade, depending on the level of quality control desired. In

either case, quality control is necessary and can be implemented in two

steps

.

Step 1: A specification, as part of OSHA regulations, stipulating minimum

quality, such as limits on wane, decay, defects, and exclusion of weak

species. The specification would be based on a traditional strength

ratio concept and be consistent with the stress level chosen.

Step 2 : Introduction of a voluntary grading system by industry, which

would ensure the Step 1 specification for trenching lumber.

II. BACKGROUND, PURPOSE, AND SCOPE OF STUDY

Prior to this study, criteria and guidelines on the use, quality, and

performance of lumber bracing systems, particularly for hardwood, were virtually non-existent. Moreover, particularly for hardwood, very little was known about the actual size, species, grade, supply patterns, storage,

moisture content, reuse patterns, defects, and structural strength of

trenching lumber.

The purpose of this study was to investigate the properties and characteristics of trenching lumber which are critical to its structural performance. On the basis of this investigation, allowable stresses, minimum

quality or grade requirements, and use recommendations are proposed.

This study was performed in three steps:

(1) the identification of a profile of needed properties and

critical structural uses of trenching lumber.

ix
(2) the determination of profiles of trenching lumber characteristics

at selected trenching lumber distribution sites in Washington,

D.C.; Houston, Texas; and southern California. Critical strength

characteristics of trenching lumber were determined.

(3) the development of recommendations concerning allowable stresses,

minimum quality or grade requirements, and conditions of use

for trenching lumber, based on steps (1) and (2) above.

This study was performed as a cooperative effort of NBS and the Forest

Products Laboratory (FPL). FPL served in a consulting and advisory

capacity for steps (1) and (2) and was primarily responsible for step (3).

III. FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS

A brief summary of the findings, conclusions, and recommendations of each

of the 3 steps follows.

Step (1) - A National Profile of Trenching Lumber Properties and Uses

Based on discussions with supply yards, contractors, and code authorities,

the following conclusions were drawn prior to conducting the field

investigation:

o most of the hardwood and softwood lumber used is rough sawn and

green.

o the hardwood is ungraded (mill run) and consists of a variety of

species, with a high frequency of oak.

o much of the hardwood wales and struts used are left in place (not

reused); most of the hardwood sheeting is left in place. (Sketches

of wales, struts, and sheeting are shown in fig. 1, ch. 3.).

o some softwood is used in Los Angeles, San Francisco, New York

City, and Chicago.

o the softwood used on the West Coast is primarily stress graded

Douglas-fir; Southern Pine and Douglas-fir are sometimes used

in New York City and Chicago.

o for solid sheeting (fig. 1), where there is essentially no space

between the sheeting, wales cause the most difficulty for con- tractors from a structural standpoint, struts next, and sheeting

the least difficulty.

Step (2) - Field Investigation with Case Studies

The major findings of the field investigation, based on case studies

for eastern species, primarily hardwood, in Washington, D.C., and Houston,

Texas, and for Douglas-fir in southern California, are as follows:

X
Lumber grade disregarding wane, damage, and decay : The most important

grade analysis disregarded the effects of wane, damage, and decay to

emphasize the basic strength characteristics of the lumber. The resulting

grades were termed the strength ratio (G) grades (see section 3.8.1).

This concept, used for analysis purposes only, provided a basis for

evaluating the effects of: (a) regrading by grading partial lengths or upgrading by hypothetical trimming, and (b) downgrading due to wane,

damage, or decay effects.

Table 2 shows the major findings for the G grades. As shown in the table,

80 percent or more of the eastern species trenching lumber was No. 2 grade

or higher; 60 percent or more of the pieces sampled were No. 1 grade or higher. The percentages of full length wales of eastern species (primarily hardwood) having strength characteristics of No. 2 grade or higher

(col. 2, table 2) and No. 1 or higher (col. 3) were about 20 percentage

points lower than for Douglas-fir. This is to be expected since stress

grades for larger size material are generally limited to No. 1 or No. 2 in Douglas-fir. However, the percentages of eastern species sheeting

of No. 2 or higher and No. 1 or higher were about 10 percentage points

higher than for the Douglas-fir sheeting. The average strength ratio, SR,

(col. 4 - defined in table 2a) and coefficients of variation for SR agree

well for eastern species and Douglas-fir wales and sheeting.

Regrading : Wales were regraded by grading partial lengths —either 1/2 or

the middle 1/3 of a full length wale. Partial length grading was used to assess the increased structural potential for wales, since loads may be

non-uniform; may cause the maximum moment to occur in the center third;

and may occur with load sharing.

Depending on major geographical area, the percentage of wales that was

found to contain higher grade portions upon regrading ranged from about

15 to 45 percent if the partial length was 1/2 the full length and 12 to

30 percent if the partial length was the middle 1/3 of the full length.

The degree of upgrading for both 1/2 and middle 1/3 length cases ranged

from about 10 to 20 SR units. Using a No. 2 grade as a base (SR = 45),

10 SR units would represent an increase to a No. 1 grade (SR = 55); 20 SR

units an increase to Industrial 65 or Select Structural grade (SR = 65).

Wane: The frequency of wane on wales was assessed by determining if the

member was downgraded, relative to its G grade, due to wane. The potential

economic impact of a wane limitation was measured by the frequency of downgrade from No. 2 or higher to lower than No. 2. The frequency of downgrade

due to wane and the potential economic impact of a wane limitation were shown to be significant for eastern species wales. For Douglas-fir, wane

was controlled by grading rulesDecay: About 7 percent of the eastern species full length wales were downgraded to a non-stress grade status from their G grade due to decay.

No downgrade due to decay was observed for 37 new Douglas-fir full

length wales.

xi
Trimming : The purpose of the trim analysis was to provide preliminary

economic information on the potential upgrading due to trimming. The

following trimming analysis is based on the choice of No. 2 as a minimum acceptable grade. Of the full length eastern species wales, approximately 125 (50 percent) were less than No. 2 in quality for strength ratio,

wane, or decay. Of the 46 wales that could be upgraded by trimming and

which were less than No. 2, 38 (83 percent) could be trimmed to a grade

of No. 2 or higher.

Considering all grades, only 4 (11%) of the 37 new Douglas-fir full

length wales could be upgraded by trimming; all of these were No. 2 or higher before trimming.

Damage: Very little mechanical damage, caused by handling or use, was observed. Only 1 percent of the eastern species full length wales were downgraded relative to their G grade. No eastern species sheeting was

downgraded. For new and used Douglas-fir members, only 1 percent of the

full length wales and struts and 3 percent of the sheeting were downgraded.

Species: At least 50 percent of the eastern species full length wales

and sheeting were either red or white oak. The softwood in southern

California was Douglas-fir.

Slope of grain : Only about 5 percent of all full length wales, struts,

and sheeting had a general slope of grain of 1 in 10 or steeper. Thus,

few pieces of No. 1 or 2 level were limited by slope of grain in the grading

process.

Moisture content : Almost all the eastern species lumber sampled was green.

The moisture content of the Douglas-fir varied from green to 10 percent.

Step (3) - Allowable Properties

Hardwood allowable properties : Formally approved allowable lumber stresses

do not exist for most hardwood species. Applicable ASTM standards (D2555,

D245) were followed in conformance with procedures recognized under the

American Lumber Standard PS 20-70 to develop example allowable stresses

(Table 4).

The allowable stresses in table 4 reflect the limiting defects of No. 2 grade as specified by the National Grading Rule and as listed in the

Southern Pine Inspection Bureau Grading Rules, 1977 edition. FPL has

suggested these rules as a basis for grading agencies to use in developing

grades and properties for trenching lumber. A minimum grade of No. 2 was

chosen based on the field investigation results which indicated that for

the eastern species, 80 percent of the wales and 85 percent of the sheeting were No. 2 or higher when wane, damage, and decay were disregarded. It

appears that eastern species lumber of grade No. 2 and higher is being

used frequently and apparently performing satisfactorily. Example stresses

in table 4 were based on several possible species groupings of potential

economic feasibility.

xii
Separate properties were developed for the white oak species group because

of its relatively high occurrence as observed in the field investigation

and its superior decay resistance. Properties for the mixed oak species

group were developed to reflect the relatively high occurrence of mixed

oak as compared to other species. The field investigation indicated

that at least 50 percent of the eastern species sampled were mixed oak.

Groups I and II (table 4) demonstrate properties for hardwoods in which

the majority of the eastern species encountered are included and only a few of the weaker species are excluded.

Tentative specif ictions for wane for eastern species wales and struts

are the wane requirements for a No. 2 grade, as given in the Southern

Pine Inspection Bureau Grading Rules, 1977 edition. In retrospect, additional studies in the field are needed to evaluate the effect of the

recommended wane requirements on mill yield.

Softwood allowable properties : A minimum grade of No. 2 is recommended

for softwood wales and struts. The corresponding allowable stresses for

species and grade combinations can be derived using traditional ASTM

procedures.

Use Recommendations : FPL developed use recommendations covering duration

of load, damage, bark, decay, insect attack, inspectability , exposure,

and storage for various aspects of trenching lumber applications. The

development reflects the severe trenching environment, possible reuse

of structural members, and the need for structural integrity related to

safety of both life and property for finite periods of time.

xiii
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xiv
1. BACKGROUND AND PURPOSE

In certain areas of the United States, lumber is used extensively to

brace trenches against collapse. The life and safety of men working

in these trenches, therefore, depends on the adequacy of the lumber

bracing to prevent collapse. Criteria and guidelines on the use, quality, and performance of hardwood lumber bracing systems are virtually

non-existent. Moreover, particularly for the hardwoods, very little is

known about: the actual size, species, grade, supply patterns, storage

conditions, moisture content, reuse patterns, defects, and structural

strength of the trenching lumber currently used.

One purpose of this study was to investigate the properties and

characteristics of trenching lumber which are critical to its structural performance. On the basis of this investigation, allowable

1
stresses, minimum quality or grade requirements, and use recommendations

are proposed.

Lumber is used in a variety of ways to brace trenches. In addition to

economic considerations, two primary reasons for using lumber are:

o Code requires that the bracing be left in place

(lumber is economical).

o Bracing needs special fabrication at the job site

(lumber easily fabricated).

Trenching lumber consists primarily of three member types: wales, which

act as beams; struts, which act as compression members; and sheeting,

which act as beams and line the outside of the trench. Wales and struts

form a structural framework over which the sheeting is placed; the sheeting transmits the soil pressures to the structural framework. Figure 1 shows two typical lumber bracing systems used for trenches.

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to ttvu 6tady, no acdzptdd design caJX^aaji

dXAJitdd {^on. hoAdwood txzncklng lumboji.

2
2. APPROACH AND SCOPE

This project was performed in three steps as follows:

(1) the identification of a profile of needed properties and

critical structural uses of trenching lumber.

(2) a field investigation to profile the visual grade

characteristics of trenching lumber.

(3) the development of recommended allowable stresses, minimum

quality or grade requirements, and use recommendations for

trenching lumber.

Step (1) required the identification and investigation of:

o critical lumber properties, such as size, species, and

moisture content.

3
o critical lumber characteristics, such as whether the lumber

is used as a wale, strut, or sheeting member, and the con- figuration and spacing of the members of the bracing system.

Step (2) required the visual assessment of the lumber characteristics

in the field for case studies in Washington, D.C., Houston, Texas, and

southern California. Visual assessment included:

o assignment of grade, based on existing visual grading rules

for softwood lumber,

o the measurement of size and moisture content, and the

identification of species, and

o the documentation of defects including knots, missing

cross section, decay, damage, and slope of grain.

Step (3) involved the development of:

o guidelines to be used by grading agencies to develop grading

rules for trenching lumber,

o allowable stresses and minimum quality or grade requirements

for hardwood trenching lumber,

o use recommendations considering load duration, damage,

bark, wane, exposure, storage, reuse, damage, and decay.

This study was performed as a cooperative effort between the National

Bureau of Standards (NBS) and the Forest Products Laboratory (FPL).

FPL served in a consulting and advisory capacity for steps (1) and (2)

and was primarily responsible for step (3).

Chapter 3 of this report treats the details of steps (1) and (2). Step

(3) is discussed in chapters 4 and 5. Chapter 4 presents guidelines

for developing allowable stresses and minimum quality or grade requirements; chapter 5 presents the use recommendations. Appendix A contains

detailed descriptions of the sampling procedures, and data entries and

coding used, as well as the coded data. Details of the grading methods

used and of the data collection for wane and slope of grain are included

in Appendix A. Appendix B describes the general observations and

descriptions of the supply yards investigated. Appendix C presents the

detailed analysis of the data collected in the field investigation.

Appendix D, written by FPL, presents a practical guide to the interpretation of ASTM standards which are applicable to the derivation of

allowable stresses for hardwood. Appendix D also provides a commentary

on use recommendations that relate to the severe trenching environment.

The commentary provides the basis for assuring structural integrity in

trenching when both new and used lumber are utilized. Chapters 4 and 5 represent a summary of the information in Appendix D.

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4
3. FIELD INVESTIGATION

3.1 PURPOSE

The purpose of the field investigation was to non-destructively profile

those properties and characteristics of trenching lumber which are most

critical to its structural performance in bracing trenches.

3.2 APPROACH AND SCOPE

In order to develop an appropriate plan for the field investigation, the

properties and conditions of use of lumber most critical to its strucstructural performance were identified; the details are summarized later

in this chapter. Properties identified included size, species, moisture

content, and defects such as knots, slope of grain, decay, damage, and

missing cross section. Conditions of use characteristics included:

o intended use (wale, strut, or sheeting - fig. 1).

5
o configuration and spacing of the bracing system.

o type of soil and soil pressure exerted on the bracing

system.

o the length of time the lumber bracing member is subjected

to load.

o typical failure modes for lumber members.

Based on the critical properties and conditions of use, a plan to

investigate trenching lumber in the field was formulated. Visual

grading procedures, based on the Southern Pine Inspection Bureau (SPIB)

grading rules [1]*, were used to assess the equivalent softwood lumber

grade, thus estimating the strength of trenching lumber. Measurement

of cross-sectional dimensions was performed and data on moisture content

defects, including wane, knots, and slope of grain were collected.

Information on species, reuse, damage, decay, storage conditions and

duration, method of sawing (rough sawn or dressed) and supply patterns

was also documented. In the field investigation, case studies were con- ducted in three geographic areas. Washington, D.C. and Houston, Texas were chosen to assess primarily hardwood and southern California was chosen to study softwood.

A field investigation team sampled about 500 full length pieces of

lumber in the three areas. In addition, about 250 partial lengths of

these full length members were assessed. The sampling and measurement

procedures as well as a description of the lumber sampled and the data

collected in the field investigation are summarized in this chapter;

the details are given in Appendix A. The field data for the full and

partial length pieces were coded and computerized; the coded data and

a description of the coding is given in Appendix A. Appendix A also

contains a discussion of the data collected for wane and slope of grain.

General observations and descriptions of the lumber supply yards investigated are summarized in this chapter and the details are given in

Appendix B.

Appendix C presents the details of the analysis of the field data taken

for the 750 pieces sampled. This chapter contains a summary of the

results and findings of the analysis.

It should be noted that about seven percent of the full length wales

sampled in Washington, D.C. and Houston, Texas were ungraded southern

yellow pine. Thus, in this report the wales, struts, and sheeting

sampled in D.C. and Houston are referred to as "eastern species" rather

than hardwood.

*Numbers in brackets refer to references at end of Chapter 5.

6
3.3 PROFILE OF TRENCHING LUMBER PROPERTIES AND USES

Based on discussions with supply yard personnel, contractors, and

code authorities, the following conclusions were drawn prior to

conducting the field investigation:

o most of the hardwood and softwood lumber used is rough sawn

and green.

o the hardwoods are ungraded (mill run) and consist of a variety

of species, with a high frequency of oak.

o the hardwoods are primarily sawn and marketed locally through

small mills. In contrast to the softwood industry, the production of hardwood trenching lumber is not well organized.

o much of the hardwood wales and struts (fig. 1) used are left

in place (not reused); most of the hardwood sheeting (fig. 1)

is left in place.

o some softwood is used in Los Angeles, San Francisco,

New York City, and Chicago.

o the softwood used on the west coast is stress graded Douglasfir; Southern pine and Douglas-fir are sometimes used in New

York City and Chicago.

o in many areas in the United States materials other than lumber

are used for bracing trenches.

o for solid sheeting (fig. 1), where there is essentially no space between the sheeting, wales cause the most difficulty

for contractors from a structural standpoint, struts next,

and sheeting the least difficulty.

o for spot bracing (fig. 1), where there is considerable spacing

between the sheeting, the strut is more critical than the

sheeting from a structural standpoint (wales are not often

used in spot bracing).

3.4 GEOGRAPHIC AREAS, INVESTIGATION TEAM, SAMPLING PLAN

Based on the use profile gathered, NBS, FPL, and the field team

together planned the geographic locations, specific sites to visit, the

formulation of the data to be collected and the questions the investigation would address, etc. Three geographic areas were chosen for sampling. Due to financial restrictions, only limited case studies could

be performed in the three areas. The Washington, D.C. area was chosen

in an attempt to represent New York City and Washington, D.C.

both areas do, to a certain degree, draw on similar hardwood sources. Houston, Texas was chosen in an attempt to represent the Houston-New

7
Orleans area. Moreover, both D.C. and Houston use relatively large

quantities of hardwood trenching lumber. For softwood, southern

California was chosen as a typical example of the use of Douglas-fir.

With the exception of visiting one trenching job site in D.C, lumber

was sampled in distribution yards in each of the three geographic areas,

so that a thorough study of individual members could be made.

The field team consisted of a wood technologist, who was responsible

for coordinating and conducting the field effort, and a professional

licensed softwood lumber grader, who was responsible for grading. One

week was spent in each of the three geographic areas.

Guidelines for selecting lumber to be sampled included the following:

o wales and struts were given a higher priority than

sheeting.

o where possible, two sizes (cross-sectional dimensions) of

wales and struts were sampled at each yard visited. These

sizes were chosen to reflect typical trenching lumber sizes

used in each geographic area (see table 1).

o preference was given to 20 ft. long stock for wales and

struts. This permitted both full and partial length grading.

The purpose of partial length grading was to determine a more

accurate profile of strength, since the load can occur at

several locations on a wale. Appendix A provides further

details of the sampling plan.

3.5 DESCRIPTION OF DATA ENTRIES

Appendix A contains a detailed description of the data collected

for each piece sampled; the coded data and a description of the coding

are also given.

The following is a summary of the more significant data entries,

o actual width and thickness measured at each end

o species

o use—wale, strut, sheeting

o moisture content

o wane (missing cross-section)

o damage

o decay

8
o warp

o slope of grain

o defects, including knots, holes, checks, splits, and shakes

o storage conditions

In addition to these data entries, one or more grades, based on the

Southern Pine Inspection Bureau grading rules, were assigned to each

piece sampled. The most important grade assigned, which was used for

analysis purposes only, was the strength ratio grade, called G, in

which the effects of wane, damage, and decay were disregarded. (One

exception to this was that limited rot in or around the periphery of

a knot, knothole, or wormhole, see Appendix A, was included in the

G grade.) The G grade provided a basis for evaluating: (a) regrading

by grading partial lengths or upgrading by hypothetical trimming of

defective material and (b) downgrading due to wane, damage, or decay

effects. Where applicable, a grade called GW was assigned which took wane into account, disregarding damage and decay. Similarly, where

applicable, a grade called GDA was assigned, which took damage into

account, while disregarding wane and decay; a grade called GDE was assigned where applicable, which took decay into account, while

disregarding wane and damage.

The middle one-third of each wale was assigned a grade called GM3 . This

was done to see if the middle one-third of the length could be regraded

relative to the G grade for the full length. The intent of assigning

the GM3 grade was to reflect that, in many instances, wales will have

their maximum bending stress imposed within the middle one-third of the

wale rather than at some point nearer the ends of the wale.

Further, for selected wales, one or two 10 foot partial lengths were assigned their own G grade, called GIO. If a wale was 20 feet long,

each 10 foot half was assigned a GIO grade. For wales greater than

10 feet but less than 20 feet, a 10 foot piece measured from one end was assigned a GIO grade. The purpose of the GIO grade was to see

if the 10 foot partial length grade could be improved relative to the

G grade for the full length. The intent of assigning the GIO grade

was to reflect that, in many instances, the wales would be supported

at about 10 foot intervals.

A trimmed grade, called GT, was assigned to any full length piece that

could be upgraded by hypothetically trimming one or both ends. Trimming

(of one or both ends) was limited to 20 percent of the length.

Wales were graded as beams and stringers while struts were considered as compression members and graded as posts and timbers. As table 1 shows,

many pieces were graded first as wales and then as struts. With only

limited exceptions, the wale and strut grades were the same.

9
3.6 LUMBER SAMPLED

Table 1 lists the location, member size, use, and sample size of the

lumber sampled.

3.7 SUMMARY—GENERAL OBSERVATIONS AT SUPPLY YARDS

Appendix B presents the details of the general observations of the supply

yards investigated. The following is a summary of the findings of those

observations

3.7.1 Wane

Wane, which is missing wood on the cross-section, was observed to be a major problem for the eastern species sampled. Wane was very widespread

among the pieces sampled and extremely variable as to the location and

extent along the length of a piece. (For further detail see the section

entitled WANE in Appendix A.)

For example, a vast majority of the larger 12 x 12 and 10 x 10 stock

seen in Washington, D.C. had extensive wane. Many pieces had wane on

all four edges and in numerous cases, as shown in figure 2, at least

the small end of a piece of 12 x 12 was completely encircled by bark.

Thus, wane poses very serious problems in developing allowable design

stresses and corresponding grades for these pieces.

One approach would be to require that the large sizes with wane be manufactured to a smaller size. For example, a 12 x 12 could usually be cut

to a 10 x 10 size to eliminate all, or at least most of the wane that was present. It is, of course, possible to limit the amount of wane

in any hardwood grading system for trenching lumber, as is done now in

the softwood lumber grades; however, this undoubtedly would waste material and reduce the availability of 12 x 12 material in the Washington,

D.C. area.

3.7.2 Species

Hardwood species are presently used interchangeably in trenching for

convenience and simplicity. Efficiency in trenching practices, particularly for wales and struts, could be improved if the weaker species

were excluded. In the Houston area, yellow poplar was said to be

excluded in at least one yard. Yellow poplar also was reported not to

be a "preferred" species in the Washington, D.C. area.

However, a problem with excluding certain species is the accompanying

need for accurate species identification. Identification of many species

would have to be made either in the forest or possibly at the mill before

the log is sawn. If the identification is delayed until the member is

delivered to the yard, it is highly doubtful that anyone there could

accurately distinguish among the many species.

10
There are some species that are considerably stronger than others. The

average "green" modulus of rupture for clear material of hardwoods com- monly used in trenching ranges from about 6,000 to 12,000 psi [2]. Certain hickories and oaks have bending strengths approaching 12,000 psi

but other oaks have modulus of rupture values as low as 7,000 psi. Other

high strength species include honey locust, about 10,000 psi, and white

ash, about 9,600 psi. Intermediate strength species include cherry, of

which there were several pieces found in the Washington area at 8,000

psi, beech at 8,600 psi, and elm at 8,000 psi. Lower strength species

would include hackberry, 6,500 psi, red and black gum, 7,000 psi, magnolia

7,400 psi, birch (this was probably gray or river birch) at 6,400 psi,

and sassasfras and poplar, both 6,000 psi. Maples, which are essentially

impossible to segregate in lumber form, have bending strength values

ranging from from 5,800 psi for silver maple to 9,400 psi for sugar

maple.

3.7.3 Storage, Moisture Content, and Fungal Deterioration

Drying of trenching wales and struts, due to their large size, is highly

impractical. Also, its one-time use (reuse does not occur that often)

implies that there is no need to dry this material. However, in areas

like Houston, Texas, and Washington, D.C., deterioration due to fungal

and insect attack during the warm summer months can be a significant

problem (fig. 3). In one sample location, surface mold growth was widespread (fig. 4), indicating conditions favorable for decay. In the

Washington, D.C. area, there was staining of the wood surface and a darkening of the wood which frequently made species identification

difficult. It would be possible to reduce the amount of deterioration

due to stain and decay fungi by stickering all of the material.

(Stickering is a special stacking arrangement which encourages air movement between the pieces.) However, this may not be practical if lumber

is tiered for forklift operations. There is undoubtedly a great need

for yard orderliness and cleanliness which in some yards seemed to be

sacrificed for convenience.

It was observed that in all yards trenching lumber is stored out-ofdoors and uncovered (fig. 5). The lumber is sometimes kept up off the

ground, being placed on stickers. The lumber is subdivided into smaller

stacks by 4 X 4 material; this is done not so much to allow the material

to dry but rather to facilitate its movement by a forklift truck. All

the material is purchased in a green moisture condition. No attempt is

made to enhance the drying rate of the material. Generally, it was con- tended that the material does not stay in the yard long enough to dry

appreciably or to rot. Although desirable, covered storage may be

impractical since in many yards it was observed that higher quality and

higher grade material used for purposes other than trenching, is also

stored in the open. This was particularly evident in southern California

where some very high quality, long length Douglas-fir was stored in the

open. However, in southern California most of the yards (fig. 6) have

asphalted surfaces and the climate is much more conducive to drying

than in Houston or Washington, D.C.

11
3.7.4 Reused Lumber

A problem was observed with reused Douglas-fir lumber because continued

drying led to checking and splitting which resulted in significant sea- soning degrade (fig. 7). This was extensive, but not so damaging as to

prevent reuse (fig. 8). Regrading is possible, but may not always be

economical

3.7.5 Lumber Quality

Several contractors and site inspectors were consulted about problems

with trenching lumber. Uniformly they believe there is no problem with

trenching lumber, either in quality of the material or how the lumber is

used. Accidents are apparently due to poor judgment (mistakes) in

installing trenching lumber or in neglecting to install it at all. A

possible exception to this observation was the use of board road* for

sheeting in Texas; this was uniformly agreed to be a poor practice.

It was commonly expressed in Texas, and implied in southern California,

that each trenching job is relatively unique and that construction

standards and lumber grades would be impossible or very difficult to

impose fairly or satisfactorily from the construction and engineering

point of view. Yet in California, yards purchase the required grade.

In contrast to hardwoods, existing softwood grades are used by an industry which is traditionally used to talking in terms of structural

grades.

All yard managers interviewed, stated or implied that business was quite

good and there was no need for improved quality of material. There were,

however, several comments regarding a need for stricter adherence to size

standards, particularly in Texas. A common opinion among yard managers

was that saw mills cut trenching lumber from lower quality logs which do

not produce good furniture lumber yield. Some of these mills have

trouble maintaining tolerances and appeared financially marginal in their

operation

Imposing strict standards of production on these mills may cause them

to go out of business or to divert lumber from the trenching market to some other market, such as the growing pallet industry.

In southern California there is a small problem with white speck in

Douglas-fir. This is a form of decay which often appears on the surface

of pieces and which does not tend to spread once the piece is dried

below fiber saturation point. Job inspectors and contractors may react

against white speck. However, it was observed in a large percentage of

the pieces graded on the west coast. White speck is controlled in softwood grading rules.

* See discussion in Appendix B of board road (a ground surfacing lumber)

in Houston, Texas.

12
Although much of the trenching lumber observed was well manufactured

(with the exception of wane), the overall quality of the logs from which

this material is manufactured is not high, most particularly in hardwoods. The material is stored in a green condition and is subject to

deterioration in the yard. It is also subject to abuse and deterioration at the trenching site. As a consequence, both hardwood and softwood lumber may have become structurally impaired by the time it is put

into use, or reuse, in a trenching operation.

One purpose of this study was to observe the type and extent of defects

which may be anticipated in lumber used for trenching. Defects may be

put into two broad categories: defects which naturally occur in wood

and defects which are the result of use. The first category would include excessive knots, checks, splits, slope of grain, wane, and limited

decay (figs. 2, 4, 9, 11, 12, 16). Figures 7 and 10 show examples of

checks and slope of grain which are not excessive. The second category

would include various types of damage including forklift splitouts

(fig. 13) and punctures; splits and breaks due to installation or reuse

(fig. 14); brooming on the ends due to driving during installation

(fig. 14), insect damage (fig. 20) and decay, (fig. 19) among others.

3.8 SUMMARY OF FIELD DATA ANALYSIS

The major results of the field investigation, of the eastern species,

(primarily hardwood) in Washington, D.C., and Houston, Texas, and

Douglas-fir in southern California, are given as follows. Appendix C presents the details of the analysis.

3.8.1 Lumber Grade Disregarding Wane, Damage, and Decay

The most important grade analysis was based on the strength-reducing

characteristics (such as knots, slope of grain etc.) of the lumber

disregarding wane, damage, and decay. This is called the strength ratio

grade (G). The G grade provided a basis for evaluating: (a) regrading

by partial length grading or upgrading by hypothetical trimming; and

(b) downgrading due to wane, damage, or decay effects.

Table 2 shows the major findings for the G grades. As shown in the

table, 80 percent or more of the eastern species trenching lumber was

No. 2 grade or higher; 60 percent or more of the pieces was No. 1 grade

or higher. The percentage of eastern species full length wales having

strength characteristics of No. 2 grade or higher (col. 2, table 2) or No. 1 or higher (col. 3) are about 20 percentage points lower than

for Douglas-fir. This is to be expected since stress-grades for larger

size material are generally limited to No. 1 or No. 2 in Douglas-fir.

However, the percentage of eastern species sheeting having grades of

either No. 2 or higher or No . 1 or higher are about 10 percentage points

higher than for the Douglas-fir sheeting. The average strength ratios,

SR, (col. 4 —defined in table 2a) and coefficients of variation for SR

agree well for eastern species and Douglas-fir wales and for sheeting.

13
Figure 15 shows the relative frequency of eastern species wales graded

over their full length in the various G grades.

As previously discussed, the wale and strut grades were the same for

those pieces which were graded as both wales and struts (table 1). Thus,

for the most part, the G grade results for wales in table 2 should apply

as well to struts.

3.8.2 Regrading

Wales were hypothetically regraded by assigning a G grade to a partial

length—either 1/2 or the middle 1/3 of a full length wale. This was done to assess the increased structural potential for wales, since loads

may be non-uniform, may cause the maximum moment to occur in the center

third, and may occur with load sharing.

Depending on major geographical area, the percentage of wales that was

found to contain higher grade portions upon regrading ranged from about

15 to 45 percent if the partial length was 1/2 the full length and 12

to 30 percent if the partial length was the middle 1/3 of the full length

(see Appendix C, table C4). The degree of upgrading for both 1/2 and

middle 1/3 length cases ranged from about 10 to 20 SR units. Using" a No. 2 grade as a base, (SR = 45) 10 SR units would represent an increase

to a No. 1 grade (SR = 55); 20 SR units would represent an increase to an Industrial 65 or Select Structural grade (SR = 65).

3.8.3 Reduction of Cross-Sectional Area and Moment of Inertia

Three methods were used to assess the effects of missing cross-section

on the reduction in cross-sectional area and bending moment of inertia.

The first method used average end dimensions (width and thickness). The

second method was based on using data on the extent of wane occurring

at the worst affected corner (e.g., wane on 1/2 the width and 1/3 the

thickness) and assumed that the wane was triangular in shape. The third

method was based on the amount of downgrading due to wane. The first

and second methods were quantitative, while the third was not.

For the first and second methods, the ratio (A) of the actual cross- sectional area to the nominal ("as sold" - see "Member Size" in table 1)

cross-sectional area was calculated. Similarly, the ratio (l) of the

actual to nominal bending moment of inertia was also calculated.

Due to the assumptions used, the results for the first and second methods

needed to be interpreted in a relative, rather than absolute, sense (see

discussion in Appendix C). Further, of the first two methods, only the

end dimensions method could be applied to both eastern species and

Douglas-fir members.

The results based on the end dimensions method^s showed the following

trends. The average area and inertia ratios (A and l) were similar for

eastern species and Douglas-fir wales; the coefficients of variation for

14
the A and I ratios for eastern species wales, however, were over three

times larger than for Douglas-fir wales. For both spot bracing and solid

shee_ting (j^olid sheeting based on end thickness only, see Appendix C),

the A and I ratios for the eastern species exceeded those for Douglas-fir

_there was one except ion-that of board road sheeting, which had very low

A and I ratios. For spot bracing, the coefficients of variation of the

A and I ratios for eastern species members were larger than for Douglasfir members. Tables C5 and C6 in Appendix C show average and coefficient

of variation values for A and I.

The results of the third method show that the frequency and economic

impact of downgrading due to wane are significant for eastern species

full length wales. The frequency of wane on full length wales was assessed by determining whether the wale was downgraded from its G grade

due to wane. Table 3 shows the high frequency of downgraded wales for

the eastern species.

The potential economic impact of a wane limitation was measured by the

frequency of downgrade due to wane from No. 2 or higher to lower than

No. 2. The frequency, shown in table 3, is the ratio of the number of

wales downgraded (col. 4) to the total number sampled (col. 1). As

shown, there would be a high percentage of eastern species wales which

could not be used if No. 2 wane restrictions were required. For Douglasfir, wane was controlled by the grading rules.

3.8.4 Decay

About 7 percent of the eastern species full length wales were downgraded

relative to their G grade due to decay. Because decay is not acceptable

in significant quantity in high structural grades, the wales downgraded

were generally either No. 3 or None. No downgrade due to decay was observed for 37 new full length Douglas-fir wales.

3.8.5 Tr imming

The purpose of the trim analysis was to provide preliminary economic

information on the potential upgrading due to trimming. The following

trimming analysis is based on the choice of No. 2 as a minimum acceptable

grade. Of the full length eastern species wales, approximately 125 (50

percent) were less than No. 2 in quality for strength ratio, wane, or decay. Of the 46 wales that could be upgraded by trimming and which

were less than No. 2, 38 (83 percent) could be trimmed to a grade of

No. 2 or higher.

Considering all grades, only 4 (11%) of the 37 new Douglas-fir full

length wales could be upgraded by trimming; all of these were No. 2 or higher before trimming.

15
3.8.6 Damage

Very little mechanical damage, caused by handling or use, was observed.

Only 1 percent of the eastern species full length wales were downgraded

relative to their G grade. No eastern species sheeting was downgraded.

For new and used Douglas-fir members, only 1 percent of the full length

wales and struts and 3 percent of the sheeting were downgraded.

3.8.7 Species

At least 50 percent of the eastern species wales, struts, and sheeting

sampled were either red or white oak. The softwood lumber sampled in

southern California was Douglas-fir.

3.8.8 Slope of Grain

Only about 5 percent of all full length wales, struts, and sheeting

had a general slope of grain of 1 in 10 or steeper. Thus, few pieces

of No. 1 or 2 level were limited by slope of grain in the grading

process

3.8.9 Moisture Content

Almost all the eastern species lumber sampled were green. The moisture

content of the Douglas-fir varied from green to 10 percent.

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16
4. RECOMMENDATIONS FOR ALLOWABLE DESIGN STRESSES

4.1 INTRODUCTION

Lumber often is the key structural member in trench bracing, having to

withstand soil pressure during excavation and subsequent construction.

Thus, safe and efficient trenching requires a knowledge of lumber properties. Apparently a high percentage of trenching lumber comes from

hardwoods, which traditionally are not stress graded.

This chapter presents recommendations for allowable stresses. Chapter 5 presents use recommendations with particular reference to trenching lumber

and trenching applications. In combination, the derivation of allowable

properties and use recommendations provide the basis for assigning use- oriented properties to trenching lumber. Appendix D provides detail on

17
both the derivation of the allowable stresses and the commentary on the use recommendations.

4.2 HARDWOOD ALLOWABLE PROPERTIES

Applicable ASTM standards (D 2555, ref. [3], D 245, [4]) were followed

in conformance with procedures recognized under the American Lumber

Standard PS 20-70, [5] to develop allowable properties. The allowable

properties, developed for wales and struts, are shown in table 4.

The allowable stresses in table 4 are for a No. 2 grade. A description

of this grade, including the maximum allowable defects permitted, is

given in the Southern Pine Inspection Bureau Grading Rules, 1977 edition.

Allowable properties for No. 2 are presented because the field investigation results indicated that for eastern species, 80 percent of the wales

and 85 percent of the sheeting were No. 2 or higher when wane, damage,

and decay were disregarded (table 2). Thus, eastern species lumber of

grade No. 2 and higher is used frequently and apparently performing

satisfactorily

Separate properties were developed for the white oak species group

(table 4) because of its relatively high occurrence in the field

investigation and its superior decay resistance. Properties for the

mixed oak species group were developed to reflect the relatively high

occurrence of mixed oak as compared to other species. Field investigation results indicated that at least 50 percent of the eastern species

sampled were mixed oak. The remaining mixed hardwood groups I and II

represent the majority of the hardwoods encountered, excluding a few

weaker species.

Tentative specifications for wane for eastern species wales and struts

are the wane requirements for a No. 2 grade, as given in the Southern

Pine Inspection Bureau Grading Rules, 1977 edition. In retrospect,

additional studies in the field are needed to evaluate the effect of

the recommended wane requirements on mill yield.

4.3 SOFTWOOD ALLOWABLE PROPERTIES

A minimum grade of No. 2 is recommended for softwood wales and struts.

The corresponding allowable stresses for species and grade combinations

can be derived by the appropriate rules-writing agencies following

standard ASTM procedures.

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18
5. USE RECOMMENDATIONS

5.1 INTRODUCTION

Trenching lumber often is large in cross section, green, and marketed

locally. Trenching is a somewhat unique application for structural

lumber since, in most cases, the lumber is in contact with the soil

and is subject to an environment more severe than that for which most

wood products are specified. The following recommendations reflect

the unique circumstances of trenching and are assumed to apply to

lumber after the visual grading standards have been considered.

This chapter also discusses damage, decay, and insect attack that can

be anticipated in structural trenching lumber and includes suggestions

for categorizing damage where reuse is of interest. Particular emphasis

is placed on decay and insect damage, with recommendations on effective

19
service life under trenching conditions. The recommendations are specific to trenching and should not be adopted for other uses without

careful review.

Structural properties of lumber are predicated upon controlled use in

which no degradation of properties occurs. The following sections conside

various aspects of trenching lumber applications assuming severe environment, some reuse of structural members, and the need for structural integrity related to safety of both life and property, for finite periods of

time. Additional detail and specific discussion of recommendations are found in appendix D.

5.2 DURATION OF LOAD

For new lumber, increases in allowable stresses for short-term loading

conditions are specified in the National Design Specification (NDS) [6];

otherwise normal loading is assumed for all use not exceeding 10 years.

For used lumber, the uncertainty of actual loadings in trenching applications and the difficulty in accurately accumulating load duration

history suggest a conservative approach; thus, it is recommended that

normal loading stresses be used in all reuse applications not exceeding

10 years.

5.3 DAMAGE

All lumber is graded under the assumption that strength-affecting

characteristics may be present in a piece provided they do not reduce

the grade level assigned. Thus, some mechanical damage may be tolerated

without a grade change. However, if the damage has the equivalent effect

of a grade reduction, the piece must be regraded. Thus, it is recommended

that used lumber with visible evidence of mechanical damage be regraded

before reuse. Regrading should be according to ASTM D 245 guidelines

based on loss of cross-section, except where damage may be hidden. More

detail for interpretation is given in appendix D.

If a member is judged to have potentially severe structural damage, it

should be: (a) designated for resawing to remove damaged portions and

then regraded, (b) designated for nonstructural use, or (c) discarded.

Figure 14 shows examples of damage where the timbers could be resawed

and be reused as structural members.

5.4 WANE

Successful use of essentially full-round timbers in much trenching lumber,

particularly wales and struts, suggests that wane may not be critical

unless a flat surface is required for fastening other materials. It is

desirable that wane restrictions for trenching lumber be related to

demonstrable need for cross-sectional area as defined by the strength

ratio for the grade or by design requirements. Pieces not meeting wane restrictions may be treated as a smaller size. Figure 16 shows an example

of a timber that probably would not meet the wane restriction.

20
5 . 5 BARK

Traditionally, a substantial amount of trenching lumber is used with the

bark remaining on the piece. This practice is not recommended as the

bark will prevent the sapwood underneath from drying out, thus encouraging decay and maintaining a haven for insect attack. Further, removal

of bark is essential for adequate grading of the members,

5.6 DECAY

Dry wood does not decay. In fact, if kept below approximately 20 percent

moisture content, wood will last indefinitely. On the other hand, if

wood is kept continuously submerged in water (probably comparable to

underground, below water table exposure) even for long periods of time,

it is not decayed significantly by the common decay fungi regardless of

the wood species or the presence of sapwood.

The heartwood of some common native species has varying degrees of natural

decay resistance. Untreated sapwood of all species has low resistance

to decay and usually has a short service life under conditions conducive

to decay.

Precise ratings of decay resistance of heartwood of different species

are not possible because of differences within species and the variety

of service conditions to which wood is exposed. However, broad groupings

of many of the native species based on service records, laboratory tests,

and general experience are helpful in choosing heartwood for use under

conditions favorable to decay. Table 5 shows such groupings.

In a few species, such as spruces and the true firs (not Douglas-fir),

heartwood and sapwood are so similar in color that they cannot be easily

distinguished. Marketable sizes of some species, such as southern pine

and baldcypress, are largely second growth and contain a high percentage

of sapwood.

Sapwood and the heartwood of nonresistant species should only be utilized

for service where the potential for decay is low or moderate or where

the exposure time is limited. Alternatively, nonresistant material can

be treated with preservatives for severe exposure conditions.

Even very decay-resistant species may require preservative treatments

for important structural uses. A general overview of preservation is

available in the Wood Handbook [2]

Decay is prohibited in members for all structural uses if identifiable

by visual inspection. An exception may be pieces in which decay occurs

in a knot but does not extend into the wood. Identification of decay

is discussed in appendix D. Borderline cases should be judged to contain decay and, along with pieces containing decay, should be designated

for nonstructural use or should be discarded.

21
Surface mold and stain is an indication that conditions are extremely

favorable for strength-reducing decay to take place, although the extent

of the decay is difficult to assess [2] . The presence of the mold also

suggests that the storage procedure is inadequate to prevent decay even

at the surface.

5.7 INSECT ATTACK

Grading rules for stress-rated lumber do not permit lumber containing

insect attack to be rated for critical structural use. Insect damage

can occur in seasoned or unseasoned lumber. In trenching operations,

the concern includes attack during storage where established large

colonies of insects are in existence.

No method is known for estimating from appearance the amount of reduction

of strength from insect damage. If damage is evident, critical members

should be removed from service and the piece resawn and regraded or placed in a noncritical use. Additional discussion of insect attack is

found in Appendix D and the Wood Handbook [2].

5 . 8 INSPECTABILITY

Members that are encased with mud or dirt or otherwise rendered nongradable because growth characteristics and other defects are not visible

should be downgraded to nonstructural use or discarded. Alternatively,

they may be hosed clean with water or surfaced clean (planed) if feasible

and then graded.

5.9 EXPOSURE

Trenching lumber will often be exposed to decay organisms and insects

in the use environment. This use exposure determines the useful life

of the trenching material if, during the storage period, it is protected

from moisture and provided with adequate ventilation. If, on the other

hand, the trenching material is close piled and not shielded from rain

or splash during storage, this storage period then becomes part of the

effective life of the trenching material from the perspective of decay

and insect exposure. In essence, close piling, and lack of moisture and

insect control during storage reduce the effective potential life of

the trenching lumber at the trenching site.

Decay in structural members depends upon mean temperatures, moisture

content, and time. Using recorded weather conditions, Scheffer and

Verrall [7] developed climate indexes, fig. 17, which define decay potential for general areas in the United States. Based upon FPL staff judgments, the following exposure periods for different various climate

indexes are recommended:

22
Climate index Maximum exposure

(months)

>65 9

35-65 12

<35 24

Climate data can be used to develop a more specific local index.

These recommendations are for nonresistant to moderately resistant

species. If the anticipated exposure period exceeds the periods listed,

resistant or very resistant species (table 5) or pressure treatment with

preservatives is recommended. Because heavy timbers dry very slowly

(partially dried timber can support decay activity), exposure periods

must include allowance for storage during processing, at holding yards,

and onsite unless rapid drying is assured. When trenching completion

is delayed, a plan must be developed for onsite inspection to assure

that structural integrity is maintained.

The exposure periods recommended above should be considered as rule-ofthumb. Additional interpretation may be appropriate for specific onsite

conditions, season of the year, and the geographical location within

a broad hazard zone.

Protection from insect attack depends upon inspection procedures, good

housekeeping, and onsite treatment. Attack generally is not rapid, but

regular inspection for insect attack is recommended in critical regions

where exposure will be over 6 months on the job site. In reuse, any

evidence of attack should be regarded as damage and requires inspection

before use in critical applications.

5. 10 STORAGE

As a general rule, trenching lumber with moisture content above the fiber

saturation point should be stickered to permit adequate ventilation and

discourage surface decay and insect degradation. Stickering such as that used for railroad ties may be a practical option.

The importance of proper lumber storage cannot be overemphasized. Rapid

deterioration of wood strength can be traced to incipient fungus infections originating during poor storage. Figure 18 shows examples of poor

storage practices which encourage decay and insect infestations. Examples

of decay and insect infestations which can result are shown in Figures 19

and 20. Trenching lumber should be protected against wetting from the

ground and, as noted, should be stickered to promote drying, particularly

after wetting from rain. In permanent or long-term storage, lumber should

be placed under a roof for protection or provided with other protection

from rain; lumber at these sites should be above the ground, preferably

on foundations of concrete, asphalt, or treated wood. These recommendations apply particularly when reuse is anticipated.

23

REFERENCES

Southern Pine Inspection Bureau Grading Rules, Pensacola, Florida,

1977 edition.

Wood handbook, U.S. Forest Products Laboratory, USDA, Agric. Handb.

No. 72, rev. (1974).

Standard methods for establishing clear wood strength values,

D 2555-76, American Society for Testing and Materials, (1977).

Standard methods for establishing structural grades and related

allowable properties for visually graded lumber, D 245-74,

American Society for Testing and Materials, (1977).

American softwood lumber standard, voluntary product standard

PS 20-70, National Bureau of Standards (1970).

National design specification for stress-grade lumber and its

fastenings, National Forest Products Association, Washington, D.C.

(1977 edition).

Scheffer, T. C, and Verrall, A. F., Principles for protecting

wood buildings from decay, USDA For. Serv. Res. Pap. FPL 190,

Forest Product Lab., Madison, WI (1973).

25

GLOSSARY

Allowable Properties - Properties, such as strength and elastic modulus,

recommended for designing with lumber. Allowable properties are identified with grade descriptions.

Board Road - Mis-cut, odd-size sheeting lumber used for ground surfacing.

Check - A lengthwise separation of the wood that usually extends across

the rings of annual growth and commonly results from stresses set

up in wood during seasoning.

Damage - Mechanical damage to lumber such as gouges, splits, or punctures.

Decay - The decomposition of wood substance by fungi.

Dressed Lumber - Machine planed or surfaced on one or more sides.

Eastern Species - In this report, refers to species encountered in

Washington, D.C. and Houston, Texas; over 90 percent of the

pieces sampled were hardwood.

Exposure - Time duration that trenching lumber is exposed to decay

organisms, insects, and damage in the use environment, including

storage.

Fiber Saturation Point - The stage in the drying or wetting of wood at

which the cell walls are saturated and the cell cavities are free

from water. It applies to an individual cell or group of cells,

not to whole boards. It is usually taken as approximately 30

percent moisture content, based on oven dry weight.

Grade - The designation of the quality of a manufactured piece of wood

or of logs.

Green - Freshly sawed or undried wood. In this report, if moisture content was greater than or equal to 30 percent, lumber was considered

green.

Hardwood - The botanical group of trees that has broad leaves in contrast

to the conifers or softwoods. The term has no reference to actual

hardness of the wood.

Heartwood - The wood extending from the pith to the sapwood, the cells of

which no longer participate in the life processes of the tree.

Heartwood may contain phenolic compounds, gums, resins, and other

materials that usually make it darker and more decay resistant than

sapwood

Knot - That portion of a branch or limb which has been surrounded by

subsequent growth of the stem.

27
Moment of Inertia - Measure of the contribution of shape and orientation

to the strength and stiffness of a member.

Rot - see decay.

Rough Sawn - Not dressed (not a smooth finish).

SPIB - Southern Pine Inspection Bureau.

Sapwood - The wood of pale color near the outside of the log. Sapwood

is more susceptible to decay than heartwood.

Shake - A separation along the grain, the greater part of which occurs between the rings of annual growth. Usually considered to have

occurred in the standing tree or during felling.

Sheeting - Members which line the sides of a trench and contain the

soil

Slope of Grain - The angle formed by the fiber direction (grain or orientation of the wood cell) with the longitudinal (long) axis

of the member; usually stated as a ratio of rise to run (e.g.,

1:20 or 1 in 20)

Split - A separation of the wood parallel to the fiber direction due to

the tearing apart of the wood cells.

Spot Bracing (skeleton bracing or spaced sheeting) - Spaced (non-adjacent

vertical sheeting members bearing against the sides of a trench - see fig. 1.

Solid Sheeting - Sheeting in which the members are placed continuously

with no spacing between them - see fig. 1.

Softwood - The botanical group of trees that in most cases have needlelike or scalelike leaves. The term has no reference to the actual

hardness of the wood.

Stickering - Special stacking arrangement using strips or boards to

separate the layers of lumber in a pile and to improve air circulation; thus drying is improved and moist conditions which can cause decay are reduced.

Strength Ratio (SR) - Hypothetical ratio of the strength of a member to

the st rength it would have if no weakening defects (e.g., knots) were present.

Strength Ratio Grade (G) - An assigned grade used for analysis purposes

only within this report which disregarded the effects of wane,

damage, and decay.

28
Strut - Compression bracing member which spans across the trench.

Trench - A short term excavation in which the bottom length exceeds the

bottom width, the bottom width is less than 15 feet and the depth

is less than 20 feet.

Trimming - Cross cutting a member to remove the low grade, decayed, or damaged material at one or both ends; the remaining material

generally will be improved or upgraded in quality.

Ungraded - No grade is assigned to lumber.

Use Recommendations - Refers to recommendations relating to duration of

load, damage, bark, decay, insect attack, inspectability , exposure,

and storage for trenching lumber.

Wale - Longitudinal bracing member which is used in bending and which

transmits the load from the sheeting to the struts - see fig. 1.

Wane - Missing cross-sectional area caused by bark or lack of wood from

any cause on edges or corners of a piece of lumber.

White Speck - Small pockets of decay in Western softwood caused by the

fungus Fomes pini .

29
Table 1. Trenching lumber sampled

Full-length grading

Regraded in

10 ft. lengths

bamp le

INUniDc i Me tropolitanArea Member Size

a Member

b Number

or

r 1 C c S Member

Tic useo

^1. ..^ w « —

Wumber

or Pieces

1 wasn«j u • K/

8 X 8 X 20 w 1

1 A

W , D JZ19

9 wasn • , u»Kj m 12 X 12 X 20 W1 A L7 C W , O

9 Q Zo

OJ was n • J u «

6 X 6 X 10 w , o

9 1 AH wasn •

) u* u3 X 12 X 12-16 on 9 7

i; wasn • y u* u

8 X 8 X 10 W , o

D wasn • , LI • ^ • 12 X 12 X 24 W

Qo W , O

1 9 1 z

7 wasn*

12 X 12 X 10 Un Q , O 1

1 4y 0 was n • , u • u

8 X 8 X 12 W , O

1 q i J

Q tiouston, lA 8 X 8 X 12-21 W , o9 1 Z 1

i

1 nu nousLon, iA 4 X 6 X 10 W 1 9 1

1 1 1

nouscon, iA 4 X 6 X 16 W Zf9 A 12 Houston, TX 2 X 8 X 10 SH 10

13 Houston, TX 8 X 8 X 16-23 W 17 W,S 29

14 Houston, TX 4 X 6 X 12 W 31

15 Houston, TX 3 X 12 X 12 SH 24

16 Houston, TX 8 X 8 X 18-20 W 15 W,S 15 17 Houston, TX 4 X 6 X 9-14 u 28

18 Houston, TX 2 X 8 X 10 SH 30

19 Southern Calif. 4 X 12 X 7-10 SH 30

20 Southern Calif. 8 X 8 X 20 Vi 16 W,S 32

21 Southern Calif. 6 X 6 X 20 W 21 W,S 42

22 Southern Calif. 3 X 12 X 16 SH 35

23 Southern Calif. 4 X 10-12 X 6-18 SH 20

24 Southern Calif. 8 X 8 X 5-8 S 11

8 X 8 X 12-14 W,S 14

25 Southern Calif. 3 X 12 X 12 SH 30

26 Southern Calif. 8 X 8 X 9-12 S 8

^ W = Wale; S = Strut; SH = Sheeting. Where W and S appear in the same entry

(W,S), members were graded both as struts and as wales.

^ Figures here varied somewhat from those used in the analyses (see tables

2 and 3 and app. C) due to missing data for a small number of pieces.

^ Where possible, long wales were regraded in one or two 10 ft. lengths.

A trenching jobsite rather than a supply yard.

30
Table 2. Summary of Findings for the Strength Ratio Grades^ (G)

for Full Length Wales and Sheeting

Sample Percent of Pieces Percent of Pieces Average Strength Coefficient of Size With a No. 2 Grade With a No. 1 Grade Ratio, Sr'', Based Variation of

N or Higher or Higher on No. 2 or Higher Strength Ratio Grades

(1) (2) (3) (4) (5)

Eastern Wales'^ 241 80 62 57 192 Species

Sheeting'* 83 85 60 56 16Z

Douglas- Wales^ 37 100 86 58 19Z

fir New

Sheeting^ 65 74 52 55 163!

^ Graded visually for strength but ignoring presence of wane, damage, and decay.

The strength ratio, SR, is defined in ASTM as the hypothetical ratio of the strength of a member to the strength it would have if no weakening defects were present. For example, a member with an SR of 45 would be expected to have at least 45 percent of the strength of an equally sized member which is free

of any defects. The grades and corresponding SR values are given below in Table 2a. Note that only

grades of No. 2 and higher could be assigned SR values for large trenching members; thus average SR values are based only on grades of No. 2 and higher. Grades shown were based on SPIB Grading Rules,

1977 edition.

^ Sizes were 4 x 6, 6 x 6, 8 x 8, and 12 x 12.

^ Thicknesses were 2 and 3 inches.

^ Sizes were 6x6 and 8x8.

^ Thicknesses were 3 and 4 inches.

Table 2a. Strength ratio (SR) values in terms of grade

Minimum Strength Ratio Grade

86 Industrial 86

72 Industrial 72 65 Industrial 65 65 Select Structural

55 No. 1 45 No. 2 Not assigned No. 3 Not assigned None

The strength ratios that correspond to each stress grade are specified under the ALS for lumber 2 to 4 inches thick only. For purposes of simplicity in this trenching study, the ALS strength ratios

for dimension lumber were adapted to timber sizes. The practical consequence of this decision is to make the field survey SR data conservative since No. 1 SR and No. 2 SR for timbers under SPIB actually

are somewhat higher than for lumber 2 to 4 inches thick.

31
Table 3. Summary of frequency and economic impact of wane on full length wales

Economic Impact - Frequency (f„) and

Frequency (f ) of Number(N^) of Wales

Wales Downgraded Downgraded Due to Due to Wane Wane From a No. 2 or Higher to a Grade

Lower Than No. 2 (1) (2) (3) (4)

f(%) f^(%) N„

e w

Eastern

Species

Washington, D.C. 106 53 37 39

Houston 142 25 18 25

Wash ., D.C. and

Houston Combined 248 37 26 64

Douglasfir, NewSouthern

California 37 3

^ N = sample size,

f = (N„/N) X 100.

32
Table A. Allowable Unit Stresses for Hardwood Wale and Strut

b Trenching Lumber

Hardwood group"^ Fj. F^ F^ ¥^ E

2 to 4

White oak*^ Mixed oak^

Mixed hardwoods

Mixed hardwoods II^

in. thick, 2 to 14 in. wide

875 575 550 105 355 800,000

850 550 500 80 355 800,000

725 475 375 65 165 800,000

600 400 350 50 115 800,000

5 in. and thicker

5 to 20 in wide

White oak'^ 975 650 525 120 355 800,000

Mixed oak^ 925 625 475 90 355 800,000

Mixed hardwoods if 800 550 350 75 165 800,000

Mixed hardwoods Il8 675 450 325 60 115 800,000

^ Allowable unit stresses in psi are symbolized by the notation ¥^ for bending, F^. for tension, F^, for compression parallel, F^ for shear,

F^j_ for compression perpendicular, and E for modulus of elasticity.

Ref. Southern Pine Inspection Bureau Grading Rules, 1977 edition,

for general grade description as follows:

Grade Paragraph Size

No. 2 313 2 to 4 in. thick, 2 to 4 in. wide

No. 2 343 2 to 4 in. thick, 5 to 14 in. wide

No. 2 SR 406 5 in. and thicker, 5 to 20 in. wide

Assumes 10-yr. load duration basis. For new (first use) lumber, adjustments for load duration may be made: for 1-yr. duration multiply by 1.1; for 1 wk. , multiply by 1.25; for 2 days, multiply by 1.30. Load duration

adjustments for used trenching lumber are not recommended. For hardwood

trenching lumber, requirements are waived for manufacture, compression

wood, firm knots, skips, stain, and warp. Holes limited as knots; wane limited as given for No. 2 grade in SPIB, 1977 edition.

^ Hardwood species defined per ASTM D 1165.

*^ White oak: The following white oaks —bur, chestnut, live, overcup,

post, swamp chestnut, swamp white, white.

® Mixed oak: Red oak (black, cherry bark, laurel, northern red, pin,

scarlet, southern red, water, willow); white oak (footnote d).

f Mixed hardwoods I: Ash (black, blue, green, Oregon); beech; birch

(sweet, yellow); cherry; elm (American, rock, slippery); hackberry;

hickory (mockernut, pignut, shagbark, shellbark); locust (black,

honeylocust) ; magnolia (cucumber, southern, sweetbay) ; maple (bigleaf,

black, red, silver, sugar); mixed oak (footnote e) ; pecan (bitternut

hickory, nutmeg hickory, pecan, water hickory); red alder; sassafrass;

sugarberry; sweetgum; sycamore; tanoak; tupelo (black, water); yellow

poplar. Excludes all cottonwood, all aspen, basswood, and balsam

poplar.

8 Mixed hardwoods II: All hardwoods in Mixed hardwoods I (footnote f) plus black and eastern cottonwood; quaking and bigtooth aspen; basswood. Excludes balsam poplar.

33
Table 5 . Grouping of some domestic woods according to heartwood decay

(taken from [2])

Resistant or Moderate ly Slightly or vprv resistant res is t ant nonres is t ant

Baldcypress Baldcypress Alder

(old growth)^ (vounp prowth) ^ Ashes

Cfl ta 1 na Douglas~fir Aspens

Cedars Honeylocust Basswood

Cherry, black. Larch, western Beech

CVi p c f mi t Oak swamn Birches J-/ -t- ^ ^ 1. 1 ^ o che W L 1 sO tnii U> LI. KJk t^ BuckevG

Junipers Pine, eastern Butternut

Locust, black^ white^ Cot tonwood

Elms

Mulberry, red^ Southern pinet Hackberry

Oak: LongleafHemlocks

Bur Slash^ Hickories

Chestnut Tamarack Magnolia

GambeMaples

Oregon white Oak (red and black

Post s pec ie s

White Pines (other than

Osage orange^ longleaf, slash

Redwood and eastern

Sassafras wh i t e

Pnnl J3 T

Q

Spruces

Yew, Pacific^ ttj w y.^ \^ ^ v^kLi Tfiip firs

(western and

eastern)

Willows

Yellow-poplar

The southern and eastern pines and baldcypress are now largely second

growth with a large proportion of sapwood. Consequently, substantial

quantities of heartwood lumber of these species are not available.

These woods have exceptionally high decay resistance.

34
35
Figure 2. Wane in 12 x 12's.

36

Figure 5. Lumber storage.

Figure 6. A clean, asphalt-surfaced, and well organized yard.

38

40

Figure 10. Slope of Grain—The appearance of slope of grain, evidenced by

drying checks, in this Douglas-fir 12 x 12 may be deceptive.

The actual slope of grain over any relatively long length was approximately 1 in 20, which qualifies the piece for higher

stress grades.

42
Figure 11. Lumber defects. Close-piled 8 x 8's showing wane,

end checks and rot.

I 43
Figure 12. Lumber defects. Rot around a knot.

Figure 13. Lumber defects. Forklift damage.

44
Figure 14. Timbers that appear to have potential for resawing and

structural reuse. Resawing could remove the apparent

bending failures near the end (top) or the brooming

failures (bottom).

45
>

o

z

\kl D

o

tuK

u.h

Z

tuo

kU

Q.

40 1-

30 -

20 -

10

T i

*e GRADE

Figure 15.

3 2 1 65 72 86

*KEY:

SYMBOL GRADE

n NONE

3 NO. 3

2 NO. 2

1 NO. 1 65 INDUSTRIAL 65 OR

SELECT. STRUCTUAL

72 INDUSTRIAL 72

86 INDUSTRIAL 86

Relative frequency of strength ratio grade (G) of eastern species

full length wales in Wash., D.C. and Houston, Texas. Note that

the grades of No. 3 and None are not strength grades for wales.

Figure 16. An example of wane in trenching timber that may need to be

treated as a structural defect or downgraded to a smaller size.

46
>^ c C CO 0) s CO o o cu CO

)-l 4-1 XI 4-1

u M-l *« ' 01 U u CO J3 XI 0) o 01

4-1 CO 4-1 14-1 4.1 CO > CO CO CO 0) 0) <u B o 3 )-l u ^ •H 4J

0) CO 00 XI 1—1

01 T3 CO o

4-> x; 4-1 CO

J-l

X CO 0) •r-l 4J

0) XI

D 0)

x o -o c CO 0) u C •H X) •H CO 4-1 c

XI

Q CO 1-1 <u 0) >> CO 0)

CO 4-1 (0 01 4-1 O CO o 1—1 CO CO a. B CO 0) V-i B X •H iJ a 0) CO

CD 1—(CO CO XI • 1-1

a T3 )-i 0) o c

^3 o 4-J s CO o CO ,—4 •4-1 CO 60 o 1—1 a U 3 C CO (U 1-1 CO O o 4-1 rH 1-H CO

l-l

C J3 o 01 >^ o T) •r4 CO u CO

<^-> 01 CO 4-1 4-1 CO

u

CO ^ •r-l CO 0) t—1

to 3 0) >> X)

CO x> X) CO • 1-1 CO

•1-1 c u

4-1 <u CO 4-1 XI

O o a o CO oj o

4-1 > l-l S CO 0) O u CO in 1—1

a. 0) 4-1 <U CO X3

CO CO CO

M CO >, l-l ai CO c 4J

CO X) 01 4-1 CO •l-l o c a, CO 4J x: d

0) 3 B

B CO CO •o o (U • l-l CU 4J 1—1 4-1 CO >~,

14-1 00 o CO 1—1 --^ o 0) X3 00 01 01 > !-i 4-1 •H 1—1 4J

CO o CO CO hJ CO 1—1 XI X) 0) X >-l 0) CO c 4-1 01 01

B > CO 4J 13 T3 O

cu

a 4-1 0)

C

O

u

•H CO 3 •r-l

B y-i

<uu3

60

•l-l

1+7
Figure 18. Examples of how poor storage leads to problems.

Top: solid stacking of green timbers prevents drying and

promotes decay infestation. Bottom: poor housekeeping

and piling practices in a holding yard.

48
Figure 19. Examples of decay in trenching lumber. Top: decay

probably occurred because of close piling.

Bottom: decay has occurred in large green timbers

before they seasoned.

49
•GO

ri 4J

CO • 4J CO CO r-" >-• (U o• I-i c 4J

•i-i COo

j-i o o 1—1 0)

CO <u c 1—1 • 1-1 o

M)C 0) •H N C •H

•i-l CO CO CO C Cu o B o (U

CO

0)

C

B • I-I u

4-1 o

J3

aoa 4-1 i-i O O CO c (U 1—

>-l •H H CM o3

50
APPENDIX A - SAMPLING PROCEDURES AND DESCRIPTION OF DATA ENTRIES AND

CODING

This appendix contains descriptions of the sampling procedures, data

entries and coding used. Detailed descriptions of the grading methods,

and data collection for wane and slope of grain are given. Chapter 3 presents a summary of this appendix.

SAMPLING PROCEDURES

A similar sampling procedure was followed at each geographical area

visited. The visits to each area were of one week duration. The first

day was spent locating each yard to be visited, contacting the yard personnel, obtaining general usage and inventory information, and choosing

what stock was to be sampled. If time permitted, data was taken on the

first sample at the first yard. (In Washington, D.C. only one supply

yard was visited.) The next three days were spent obtaining data. The

last day of the week was usually spent in concluding sampling, interviewing yard personnel, and/or visiting trenching sites in the area.

Within a yard, trenching lumber samples were chosen using the following

rationale

1. Where possible, at least two sizes of wales and/or struts were chosen for study, a relatively large size and a relatively

small size. The actual sizes chosen depended on the number

of pieces of each size in stock at the time of the visit and

the general usage factor for the sizes in stock. For example,

in the Washington area, 12 x 12' s and 8 x 8's are the most

commonly used sizes. Consequently, these two sizes were emphasized in the sampling. In the Houston area 8 x 8's and 4 x 6's were chosen predominantly because they were the more common

sizes in that area.

2. Where time permitted, a sample of sheeting material was chosen

from each yard. Sheeting, however, had secondary importance

in the project. As with wales and struts, a commonly-used

size of sheeting was chosen for study.

3. If time permitted, large wale stock was given third priority.

That is, in some yards a relatively large stock of a particular

size and length was sampled which did not necessarily coincide

with the size chosen in 1 above. Stock for which only a small

number of pieces was available was avoided.

A-1
4. Where possible, preference was given to 20-foot stock for wales

or struts to permit two ten-foot lengths for regrading (see

table 1). In 20-foot 12 x 12 pieces, for example, the piece

was graded as a full-length 12 x 12 wale, as two 10-foot wales,

and as two 10-foot struts. A 20-foot 12 x 12 could conceivably

be used as an unsupported beam or as a beam supported on 10-

foot intervals or cut into 10-foot pieces and used as struts.

This procedure derived a maximum amount of information from

each member.

5. An attempt was made to sample trenching lumber while keeping

yard disruption at a minimum. Yard operators were most cooperative and helpful. Competent yard personnel and equipment

were made available in all cases and a spirit of mutual cooperation was maintained. However, it was not possible to sample

stock as desired due to yard lay-out and activity. Occasionally, too much movement of large, strapped bundles of lumber

was required. Other stock was unavailable because it was being banded for sale or cut to length.

Once a sample size and length had been chosen, several (usually 10-20)

pieces were transported by forklift to an out-of-the-way area in the

yard where they could be studied. The forklift was used to place the

pieces of large stock in a row; individual pieces were turned or moved

by use of a cant hook.

EXPLANATION OF DATA ENTRIES AND CODES

Figure Al shows the sheet used to record data for the field study. The

data was coded for two reasons: (1) it was not practical to publish the raw data sheets (about 750), and (2) the coding was needed to perform

the computer analysis. Information on lumber sampled is summarized in

table 1.

The following is a description of the data sheet entries and the coding

used. (Entries deserving additional detail, including grading methods,

wane, and slope of grain, are treated later in this appendix.) The

coding was done by using 48 separate data entry groups. Each group was then assigned a numerical code which covered the data entries for that

group. In the information which follows, the group code number (column

number in table Al) and group title are given first; then a description

of the group is given; and the numerical code for the entries of that

group is given last. A code of "0" or "-1" was used when no information

was recorded.

A-2
Group Number

and Title

Description of Group

- Remarks

Numerical Code

Code Location

1. Lumber Yard Lumber was evaluated

at 7 supply yards and

1 job site.

Wash. , D.C.

Wash. , D.C.

( jobsite)

Houston, TX

Houston, TX

Houston, TX

Southern CA

Southern CA

Southern CA

2. Sample Number There were 26 samples

taken at the 7 supply

yards and 1 job site.

With one exception

(No. 23) each sample

contained only one size

(width, thickness) of

lumber

.

Codes used were the

sample numbers given

in table 1

3. Specimen Number There was an assigned

specimen number for

each full length piece

evaluated

.

4. Length Classification Each piece was graded

as full length or one

or two 10 ft. sections

of the full length

piece

.

1 = Graded full

length

2 = Graded for the

first 10 ft.

section

3 = Graded for the

second 10 ft.

section

5. Member Use Each piece was evaluated

according to its intended

use of wale (beams and

stringers, bending) strut

(post and timber, column)

or sheeting (beam-plank

and joist, bending). A

code of 1 was used for

full length pieces or 10

ft. partial length pieces

of 16 to 24 ft. full length

pieces; the full length

pieces were first graded

1 = Wale or strut

2 = Strut alone

3 = Sheeting

A-3
Group Number

and Title

Description of Group

- Remarks

Numerical Code

Member Use

(Cont. )

6. Species

as wales and then, in

certain cases, as struts

(see table 1); the 10 ft.

partial length pieces were

first graded as wales and

then as struts. In almost

every case, the wale and

strut grades were the same

(only 3 exceptions were

noted). Also see details

of grading methods, given

later in this appendix.

The species of each specimen

was determined through hand

lens examination of a smoothed cross-sectional

area. Accuracy was checked

by sending small pieces from

numerous specimens to the

Forest Products Laboratory

for verification. Field

identification seemed to be

relatively accurate; errors

were generally restricted

to mis-naming species within

a genus (red oak vs. white

oak for example).

1 = red oak (Quercus sp.

2 = white oak (Quercus

sp. ) 3 = Black gum, tupelo

(Nyssa sylvatica)

4 = Sweet gum, red gum

(Liquidambar

styracif lua)

5 = White ash (Fraxinus

sp. ) 6 = Yellow poplar

(Liriodendron

tulipifera)

7 = Southern yellow

pine (Pinus sp. ) 8 = Sycamore (Platanus

occidentalis

9 = Hickory (Carya sp. ) 10 = Elm (Ulmus sp.

11 = American elm

(Ulmus Americana)

12 = Slippery elm

(Ulmus rubra)

13 = Cherry (Prunus

serotina)

14 = Sassafras

(Sassafras

albidum)

15 = River birch

(Betula nigra)

16 = Beech (Fagus

grandifolia)

17 = Birch (Betula sp.

A-4
Group Number

an Title

Description of Group

- Remarks Numerical Code

6. Species (Cont.) 18 = Pecan (Carya

il linoens is

)

19 = Hackberry (Celtis

occidentalis)

20 = Maple (Acer sp.)

21 = Magnolia

(Magnolia grandiflora)

22 = Sugarberry (Celtis

laevigata)

23 = Honey locust

(Gleditsia

triacanthos

)

24 = Douglas-Fir

(Pseudotsuga

menzies 11 )

7. Sold as Species name or grade

by which lumber sold.

1 =

2 =

Mill Run

(applies

eastern

i.e., no segregat

eastern

No. 1 or

( appl ied

Douglasor Mixed

to all

species - species

ion for

species)

better

to some

fir)

8. Nominal Thickness Thickness for which

wood sold as (given

in "Member Size" in

table 1).

Nominal thickness

coded in inches

9. Nominal Width Width for which

wood sold as (given

in "Member Size"

table 1).

Nominal width

coded in inches

10. Length Actual length measured

to nearest 1/8 in.

Actual length coded

in feet (rounded to

nearest hundredth of

ft.)

A5
Group Number

and Title

Description of Group

- Remarks Numerical Code

11. Width at End 1 Actual width at end 1 measured to nearest

1/16 in.

Actual width coded

in inches (rounded

to nearest thousandth

of an in.

12. Width^ at End 2

13. Thickness^ at

End 1

Actual width at end 2 measured to nearest

1/16 in.

Actual thickness at

end 1 measured to

nearest 1/16 in.

Code same as for 11,

Actual thickness coded

in inches (rounded to

nearest thousandth of

an in.)

14, Thickness^ at

End 2 Actual thickness at

end 2 measured to

nearest 1/16 in.

Code same as for 13,

15. Moisture Content - First Reading

Moisture content at one quarter point taken

by an electric moisture

meter.

99 = green (greater

than or equal to

30% was assumed

green) . If moisture content less

than 30%, actual

content coded in

percent and rounded

to nearest 1 percent .

16. Moisture content

Second Reading

Moisture content at the

other quarter point taken

by an electric moisture

meter

Code same as for 15.

^ When wane at the end was present, measurements for width and thickness

were taken at a location containing no wane, but as close to the end

of the member as possible. Width and thickness measurements did not

include bark.

^ With only rare exceptions the eastern species were all green. For

eastern species, moisture contents on the very outer surfaces were often dry (12-20%), but the wood was usually above fiber saturation

point within one-half inch or less of the surface.

A-6
Croup Number

and Title

Description of Group

- Remarks Numerical Code

17. Wane on Face

18. Wane on Length

19. Wane on Thickness'

Wane was recorded for the 1 = <l/4

worst face. Face refers 2 = 1/4

to width. For example, 3 = 1/3

1/4 means wane was on 1/4 4

= 1/2

of the width. 5 = 3/4

6 = Full

7 = 2/3

Wane was recorded for Code same as for 17

length.

Wane was recorded for Code same as for 17

thicknes s

,

20. Rings per Inch For purposes of this

study, "density" was implied by measurement

of the number of growth

rings per inch measured

along a line from the

pith outward, and the

average percent summerwood within a growth

ring. The purpose of

density measurements

was to be able to assign

"dense" grades as per

SPIB grade rules later,

if needed. Density was measured for the Douglasfir and Southern Yellow

Pine members only; no density data were taken

for hardwoods. Ring

count was taken on one

end of a member only, but

consistently at one end

of a stack for all members within a sample.

The rings/in. and percent

summerwood information

was estimated by the

grader. Rings/in. was

Rings per inch rounded

to nearest ring were

coded.

^ See section describing wane at the end of this appendix.

A7
Group Number

and Title

Description of Group

-Remarks Numerical Code

20. Rings per Inch

(Cont. )

measured by a scale when

the wood had only a few

rings per inch (3-6);

it was estimated when the

number of rings per inch

was large (12-20+).

21. Percent Summerwood Average percent summerwood recorded (see

remarks for 20)

Percent summerwood,

rounded to nearest

whole percent, coded.

22. Bow Recorded per SPIB grade

book

1 = Very light

2 = Light

3 = Medium

4 = Heavy

23. Crook Recorded per SPIB grade

book

Code same as for 22

24. Cup Recorded per SPIB grade

book.

Code same as for 22,

25. Twist Recorded per SPIB grade

book

Code same as for 22,

26. Critical Knot Type

27. Knot Length

(larger dimension)

of Critical Knot

in 26.

Type of knot in critical

section, usually recorded

only for grades of No. 2 and lower. A cluster was defined as more than two

knots. The two-knot

code was used when two

knots were judged important; the knots were not

necessarily adjoining.

Higher grades often con- tained numerous, widely

scattered knots in sizes

permitted in the grade.

A "critical" knot was often difficult to pick.

With the two-knot code,

measurements for the

largest of the two knots,

(as determined by the

product of the knot length

times the width) were coded

123

4

5

Edge

Center

Spike

Cluster

Two Knots

Actual dimension

coded in inches

(dec imal )

A-8
Group Number

and Title

Description of Group

-Remarks Numerical Code

27 . Knot Length

(larger dimension)

of Critical Knot

in 26 (Cont. )

.

28. Knot Width of

Critical Knot

in 26.

29. Slope of Grain - Face 1

30. Slope of Grain - Face 2

except when the critical

knot was identified (e.g.,

spike or rot around knot)^

then the critical knot

dimensions were coded, even though the critical

knot may have been the

smaller of the two. For

cluster knots, the dimensions of the cluster were

coded, and included all

knots in the cluster.

Knot size was recorded

only for the lower grade

pieces (No. 2 and No. 3).

Determining the knot sizes

posed some problems. Knots

should be measured counting

only growth rings within

the branch cross-section

forming the knot. However,

not all knots are cut perpendicular to the branch

axis and, hence, the wood

on the periphery of a knot

tends to blend into the

wood of the tree surrounding the knot. This is particularly true of live knots

Actual dimension

coded in inches

(decimal)

.

99 when X > 20;

otherwise, when

X < 20 actual

value of X was coded (e.g., a 1:12 slope of

grain was coded

as 12 and a 1:20

value coded as 99).

Code same as for 29.

1:X.

A9

and in rough-sawn wood.

(See description under

27.)

Recorded as a rise to run ratio in the form 1:X.

For additional detail see slope of grain description

later in this chapter.

Recorded as a rise to run ratio in the form of
Group Number

and Title

Description of Group

- Remarks Numerical Code

31. Type of Checks

32. Size of Checks

1 = End or Pith

2 = Surface or Seasoning

3 = End and Surface

1 = Light

2 = Medium

3 = Large or Heavy

or Long

4 = Checks present

but neither type nor size given

33. Size of Splits Pitch pockets included, 1 = Very short

shakes excluded (see 2 = Short

34, 35). 3 = Medium

4 = Long, Very Long, or Full Length

5 = Split present

but size not

recorded

34. Size of Shake

35. Type of Shake

1 = Very Short

2 = Short

3 = Medium

4 = Long

5 = Very Long

6 = Full Length

1 = Ring

2 = Heart or Pith

3 = Through

4 = Shake present

but type not

recorded

5 = Burl

36. Grade Disregarding

Wane, Damage, and

Decay

Called G grade.

SPIB grade recorded

for almost all pieces

evaluated (i.e.

length classifications

of 1, 2, and 3 - group

No. 4). This grade

includes limited decay

around the periphery

of knots, knotholes,

wormholes, and holes

(see group No. 37 -

1 = Industrial 86

2 = Industrial 72

3 = Industrial 65

4 = Select Structural

5 = No. 1 Strength

Ratio

6 = No. 2 Strength

Ratio

7 = No. 3

8 = None or Economy

A-10
Group Number

and Title

Description of Group

- Remarks Numerical Code

36. Grade Disregarding

Wane, Damage, and

Decay (Cont. )

.

37. Critical Defect for

Grade in 36. (Not

always recorded.)

code numbers 4, 6, 22,

27, 28). When limited

decay was included, it was not recorded under

the Decay Grade (group

40) or Decay Type

(group 41 and 42). This

grade (G) does include,

for No. 3 joist and plank

grade, unsound wood in

spots or streaks limited

to 1/3 the cross-section

at any point along the

length. For additional

detail, see the description of grading methods

later in this appendix.

1 Knot Cone knot

or no information

given about number of knots)

2 = Knot cluster or clusters (fig. A2)

3 Knot hole or knot holes

4 Knot with limited

decay (fig. 12,

fig. A3)

5 Wormhole or wormholes

6 Wormhole(s) with

limited rot

7 Bark pocket

(fig. A4)

8 Shake (fig. A5)

9 Split (fig. A5)

10 Checks (fig. 7)

11 Hole or Holes

12 Slope of Grain

(fig. 9)

13 Bow

14 Crook

15 Cup

16 Twist

18 Two knots

19 Burl

A-11
Group Number

and Title

Description of Group

- Remarks Numerical Code

37. Critical Defect

Grade in 36.

(Not always

recorded) (Cont.)

38. Additional Critical

Defect for Grade in

36 (when recorded).

20 = Too thin

(Scant thickness

fig. A6)

Compression

Failure

Knothole with

limited decay

Size too small

( scantness)

(fig. A6)

Too narrow

(scant width - fig. A6)

Knots with

termites

Pitch Pocket

Hole with limited

decay (fig. A7)

28 = White speck

(fig. A8)

21 =

22 =

23 =

24 =

25 =

26 =

27 =

Code same as for 37

39. Grade for wane disregarding damage or decay (when recorded)Called GW. For

members which were graded as struts

only (see samples 24

amd 26 in table 1), the

amount of wane was recorded but a wane grade was omitted.

Code same as for 36,

40. Grade for decay

disregarding wane

or damage

41. Decay type for

grade in 40.

Called GDE. Limited

decay around knots,

knotholes, wormholes,

and holes was included

in group 36 but not in

groups 40, 41, and 42.

Decay type may be given

even though there was no decay grade given (i.e.,

the decay present did

not cause a grade reduction) .

Code same as for 36.

1 = Surface (fig. 4)

2 - Pith (fig. 11)

3 = Streak

4 = Decay at knot

(fig. 12)

A-12
Group Number

and Title

Description of Group

-Remarks- Numerical Code

41. Decay type for

grade in 40.

(Cont.

)

42. Additional Decay

Type for Grade

in 40.

43. Grade for Damage, Called GDA

Disregarding Wane

or Decay

44. Type of Damage for Damage type may be

Grade in 43. present even though

no damage grade was given (i.e. , the

damage present did

not cause a grade

reduct ion)

.

TlL^C^-ciy O r* 3 X7 d3 t"LT.ir^ VJkJ TTTl L lllLLKJ r\ ^*^ L1 O rue tS-C L 7 wnLue opecK v. rig, ao /

8 DU T* \7 T~ O t" L y 1. W L. Q

y S spwood

1 n White speck , same sls H o 7

1

1

JJcCciy pLcocllL

hilt" t* T7 n f"

Rot at hole

ffiac A7 AQ")

1

4

J. *-r L ype S V J- -Lg . H- ^ 1 J raLCil Vi-J-g» H-y 16 Riiff Rot

\ I -Lg . i J- /

J.1 7/ iLQge

18 = End (fig. 9)

19 Heart (fig. 11,

tig. Ao;

20 Soft Rot

21 Rot at bark pocket

(fig. A4)

Code same as for 41.

Code same as for 36.

1 = Gouge (fig. AlO)

2 = Puncture (fig. All)

3 = Saw cut, (fig. A12) saw mark, saw kerf

4 = Brooming

(fig. 14)

5 = Tear Out (fig. All)

6 = Split Out

A- 13
Group Number

and Title

Description of Group

-Remarks Numerical Code

44. Type of Damage

(Cont.

45. Grade on Middle 1/3

Length, Disregarding

Wane, Damage, and

Decay

46. Length of Trim

Called GM3. All wales

(full and 10' - group 4,

code 1, 2, and 3) were attempted to be regraded

on their middle 1/3

length relative to their

G grade (group 36).

Amount of end trimming

required to increase

grade. If trimming was required at both ends,

the total trim length

for both ends was coded.

Up to 20 percent of the

length of a piece was assumed trimmable.

7 = Dog mark (a "dog"

refers to the

steel device which

holds the log in

position on a saw carriage during

the sawing operation)

8 = Caused by fork

lift or lift

truck ( fig. 13)

9 = Shattered End

(fig. 14,

fig. A13)

Code same as for 36.

Actual length of trim

was coded in feet and

rounded to nearest

whole foot.

47. Trimmed Grade

48. Trimmed Grade

Statement

Called GT. Grade

resulting from trimming

Statement recorded con- cerning trimmed grade

in 47.

Code same as for 36.

1 = Grade "with wane"

2 = Grade "without

wane"

3 = Nothing said about

grade

4 = Grade "for" everything except wane

(e.g., knot, shake,

etc.

A-14
Group Number

and Title

Description of Group

- Remarks Numerical Code

48. Trimmed Grade

Statement (Cont.)

56

Grade "for wane

Grade "with wane

and some other

defect (e.g.

,

knot)

.

II

II

7 Grade "without

wane" and for some defect

(e.g. , knot) other

than wane

.

COMPUTER CODING

The 48 groups and their corresponding numerical codes were used to code

the data for each of the 726 pieces investigated (467 eastern species

and 259 Douglas-fir). Two computer cards were required to record all 48

group entries for each piece. The coded data for groups 1-23 were recorded on the first card, denoted as "a"; the remaining coded data for

groups 24-48 were entered on the second card, called "b". The 28 pages

of Table Al present the coded data in the following format. Group numbers

appear at the top line of each page. Coding on the first or "a" card

(for group 1-23) for the 467 eastern species pieces is shown on the first

nine pages and is denoted by H-al through H-a9 at the upper right hand

corner. The next nine pages, labeled H-bl through H-b9 , show the coded

data for groups 24-48 for the 467 eastern species pieces. Similarly the

next five pages, labeled S-al through S-a5, present the coding for the

259 Douglas-fir pieces for groups 1-23. The final five pages, marked

S-bl through S-b5 , show the Douglas-fir coding for groups 24-48. In

order to identify each piece, the coding for groups 1-5 was repeated on

the second (b) card.

GRADING METHODS

The lumber grader had, until recently (1977), been a grading supervisor

for the West Coast Lumber Inspection Bureau (WCLIB). He had many years

of softwood lumber grading experience. The grade rules used in this study

were, however, those of the Southern Pine Inspection Bureau (SPIB); this was because there were more structural grades available for assignment,

particularly in the large timber sizes. In general this did not pose

any problems for the grader. Frequent reference was made to the grade

rule book during the grading operation. The grader made an attempt to

assign each piece to a recognized grade so that lumber strength characteristics of the trenching lumber sampled would be assessed as accurately

as possible.

The grader also interpreted the defects in any particular piece in relation to their effect upon member strength. For example, a knot covering

A-15
a rather large area on one face and not appearing on the opposite face

(or being very small on the opposite face) was considered for its wood

displacement rather than its absolute surface area. This was in keeping

with normal grading practice. In other cases, a piece was graded lower

than its knot size would perhaps indicate; this was due to the presence

of other nearby defects or to an accumulation of strength-reducing

characteristics. Again, the piece was placed into a grade according

to recognized grading practice.

In order to study the effect of wane, damage and decay on grade, the

following considerations were emphasized by the grader:

a) A strength ratio grade, called G, was assigned to each specimen

without regard to wane, damage and decay. However, a description of these defects when present was recorded. One exception

to this was in the case of rot in or around the periphery of a knot, knothole, or wormhole. Refer to paragraph 413.5 in the

SPIB grade rules. Although ASTM standards pertaining to lumber

grading make no allowance for decay. Number 2 grade in the

SPIB rules permits decay "in knots only." In Number 3 Joist

and Plank grade (assigned in this study to pieces which graded

lower than Number 2 SR but were within the limits of Number 3 J and P grade) the grading rules permit "unsound wood in spots

or streaks limited to 1/3 the cross section at any point along

the length." There was no SPIB stress grade for wales and

struts less than No. 2. Thus for wales and struts, any grade

assignment less than No. 2, was approximated by the field team

for illustration only.

b) Where applicable, a grade was assigned taking wane into

account, without regard to damage or decay. One exception

was that for members which were graded as struts only (see

samples 24 and 26, table 1), the amount of wane was recorded

but a wane grade was omitted.

c) Where applicable, a grade was assigned taking damage into

account, without regard to wane or decay.

d) Where applicable, a grade was assigned taking decay into

account, without regard to damage or wane.

e) Where applicable, a G grade was assigned to the middle 1/3

length if it was of higher grade than the G grade for the

entire specimen.

All pieces were assigned a full length G grade as prescribed

in SPIB rules which require full length grading. However, for

all wales the middle 1/3 was given special consideration. If

it was a higher G grade than that assigned to the full-length

piece, the G grade of the middle 1/3 was recorded. That

information was recorded because the maximum bending stress

A-16
in wales is commonly within the middle 1/3 of the member. Thus,

if a limiting defect fell outside the middle 1/3 (graded full

length or as a 10' piece of a longer member —see f, next paragraph), the middle 1/3 was assigned a higher G grade than that

assigned to the entire specimen. Wane, damage and decay were ignored in the middle 1/3 of the length for this purpose. For

struts, the loading mode is compression and middle 1/3 grading

does not apply.

In addition, selected members were assigned a G grade (GIO)

in 10' intervals both as a wale and as a strut. This was done

for wales to reflect that wales are sometimes loaded as continuous beams (10' support intervals assumed) and to reflect the

grade potential of the wales if resawed to shorter lengths.

The 10' interval was also chosen to represent strut length, even though the actual strut length used in trenching is often

less than 10'. Thus a member was given as many as five grade

assignments: a full length wale, two 10' wales, and two 10'

struts. With only limited exceptions, the 10' pieces had the same GIO grade as a wale or as a strut. (This statement also

applies to members which were 10 feet full length and graded

as wales and struts - see table 1.) As given in the EXPLANA- TION OF DATA ENTRIES AND CODES , these 10' wales and struts were coded as "wale or strut" for a member use (code of 1,

group 5) and as a 10' piece of a longer member for length

classification (code of 2 or 3, group 4).

Where a critical defect occurred close to an end, members were upgraded by hypothetical end-trimming to estimate the effect

of elimination or reduction of the defect. This hypothetical

end-trimming could occur on one or both ends and was limited

to 20 percent of the member length. The amount of end-trimming

and the resulting increase in grade were recorded. Quite often

end-trimming removed extensive wane, although the extent of wane removed was not documented.

The structural grades used, with pertinent descriptive comments,

ranked from highest to lowest grade, were as follows:

1. Industrial 86 ( IND 86 ) paragraph 441 in SPIB grade rules

book. B & B finish on face requirements omitted; no density measurement requirements applied. Permissible

slope of grain is 1 in 18. No rot permitted.

2. Industrial 72 ( IND 72 ) paragraph 442 in SPIB grade rules

book. C finish on face requirements omitted; no density

measurement or rings per inch requirements applied.

Permissible slope of grain is 1 in 14. No rot permitted.

A-17
3. Industrial 65 ( IND 65 ) paragraph 443 in SPIB grade rules

book. D finish on face requirements omitted; no density

measurement or rings per inch requirements applied.

Permissible slope of grain is 1 in 12. No rot permitted.

This grade is very similar to the grade of Select

Structural in joist and plank sizes. In some instances

the distinction between the two grades was made, disregarding size classification. Select Structural rules

are found in paragraph 341 in the SPIB grade rules book.

Select Structural has a strength ratio of 65%, as does

IND 65. However, there are some small differences in

permissible defects between the two grades. Rot is not

permitted in either grade.

4. No. 1 SR Timbers ( No. 1 ) paragraph 405 in SPIB grade

rules book. Decay permitted in knots only. Permissible

slope of grain is 1 in 11. (Here "SR" means stress rated.)

5. No. 2 SR Timbers ( No. 2 ) paragraph 406 in SPIB grade

rules book. Decay permitted in knots only. Permissible

slope of grain is 1 in 8.

6. No . 3 paragraph 344 in SPIB grade rules book. This is a joist and plank grade and does not actually apply to large

members (that is, members greater than 4 inches thick).

However, the knot sizes and other defects applicable to

the wide face of this joist and plank grade were applied

to larger members in this study in an attempt to delineate

defects (primarily knots) for a grade lower than Number 2 SR. (in other words, if the poorest face on a wale did

not meet Number 2 SR requirements, the face was graded

as a two-inch thick joist.) It should be understood

that this was for estimation only; no corresponding SPIB

grade existed. Limited unsound wood is permitted in

this grade.

7. None . This grade designates any piece below No. 3.

Pieces assigned this grade most often did not meet wane restrictions of higher grades.

For lower grades of lumber (Number 3 and None, and occasionally for

Number 2) a plot of the knots (or at least of the "critical" knot) was

made as part of the data sheet* set for a member. Many pieces had a large number of knots on several faces. To aid in grading, a knot plot

was made for several locations along the length of a member. In many

instances, the visually chosen weakest spot occurred where two to several

knots or other defects were close together, often on adjoining faces.

The largest, single knot was not necessarily the critical defect.

* Knot plots are not included in this report.

A-18
There is no "Post and Timber" designation in the SPIB grading rules;

consequently, for consideration of columns versus bending members the

Post and Timber grades of the WCLIB grade rules (paragraph 131) were applied by the grader. These considerations primarily involved knot

size restrictions. There were about 3 pieces for which the strut grade

differed from that assigned to the wales.

Sheeting was graded under joist and plank grading rules. Sheeting thicknesses were nominal 2", 3" or 4". It is noted that both SPIB and WCLIB

grade rules permit limited unsound wood only in 2" thicknesses in the

No. 2 grade. Unsound wood is also permitted in the No. 3 grade for

all thicknesses.

The Douglas-fir sampled in southern California had been graded according

to WCLIB or Western Wood Products Association (WWPA) rules, which are quite similar for the data collected in this study. The grade most

usually purchased would have been Number 1 and higher. Beam and Stringer

grade. There are several small differences, including slope of grain

and knot requirements, between the SPIB (used in this study) and WCLIB

grading rules.

WANE

Since wane was a serious problem for eastern species wales and struts,

a description of the type of wane encountered, the procedure for recording wane data, and the interpretation of the data is given in the following paragraphs. Wane was not always recorded for sheeting.

A piece's worse wide* face (with respect to wane) was turned up for

grading purposes and the recording of wane data. The piece was graded

for wane on the worse corner of the two exposed (on the wide face turned

up). The procedure for recording the wane data follows. If bark was continuous across the wide surface of the piece anywhere along its length,

it was recorded as FULL wane. The length of wane was not recorded but

could range from a few inches to full length (grading rules interpret

wane in the same manner). The same criteria for FULL wane was applied

to the thickness dimension. For all practical purposes, however, FULL

wane rarely, if ever, extended more than 1/4 of the length of a piece.

Wane was recorded as a fraction of the face width, i.e.: 1/2 face, 1/3

face, etc. (or thickness). A recording of, say, 1/2 face could represent

two situations: wane was limited to one side of a member and extended

approximately half of the distance toward the other side (fig. A14-a)

,

or, wane existed on both exposed edges and, combined, covered 1/2 the

face (fig. A14-b)

.

* For a non-square member, the "face" (when used in this wane discussion)

refers to the worse wide dimension, the "thickness" refers to the worse

narrow dimension. For a square member the face and thickness were arbitrarily assigned.

A-19
Again, wane could extend from one or two inches to the entire length of

the member. Note that these wane designations cover an extremely wide

range of "missing wood." Nothing is said about the depth of the wane;

i.e., how deep into the piece one must go to reach sound wood. The

implication of this situation on member cross- section may be illustrated

with two extremes shown in fig. A14-C and d; in each, the wane would

have been listed as FULL face and 1/2 thickness.

Note that the same rating could apply to even more severe wane if wane

also had appeared on one or both of the bottom edges as was quite often

the case.

The same fractional system was used to record the length of wane. If wane was discontinuous, the fraction recorded represented a summation

of the separate wanes. No distinction was made between continuous and

discontinuous wane.

Wane was generally estimated by eye; although it was measured by tape

in questionable cases.

It is evident, therefore, that some ambiguity existed in the methods for

recording wane. It is noted, however, that in all cases a considerable

amount of wood was exposed on any given member. For example, a piece

recorded as FULL face (or thickness) rarely, if ever, had bark over the

full face for more than 25 percent of the length of the piece. Figure

A14-e and f show the extremes in wane represented by the same FULL

length-FULL face rating. Thus, wane listed as FULL thickness would add

obvious complications in interpreting the data. However, even though a large majority of pieces graded in the larger sizes, particularly in

the Washington, D.C. area, had extensive wane, nearly all of the pieces

could be classed as serviceable. Pieces rated FULL length-FULL face for wane frequently had 80 percent or more of the cross-section intact as solid wood. From the point of view of mechanics, however, the wood which

was missing was very detrimental to the moment of inertia of the member.

SLOPE OF GRAIN

The slope of grain was assigned by the grader. Grain angle was easily

observed by surface check orientation for a vast majority of the pieces

sampled; at times a scribe was used to follow the grain. Slope of grain

was recorded as a rise-to-run ratio (1:14, etc.). Ratios less than 1:20 were recorded as straight grained. Slope of grain is commonly measured

over a distance of two to several feet ignoring local grain deviations

around knots, for example. If slope of grain was evident on adjacent

faces, the worse slope of grain was recorded. It appeared that in quite

a few pieces localized, steep grain deviations could be the limiting

defect rather than general slope of grain or other defects. Refer to

fig. 9.

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A-48
Trenching Lumber. Page of Date:

Y^"^*^- Spec. No.: Use Class

Species: Actual Sold as: Nom. Dim. x L: W: . T: . MC at quarter points:

Assigned (stamped) grade:

ALS stress grade assigned by grader:

Trimmed ALS stress grade by grader:

Max. wane: Face Length Thickness

(circle) il/h 1/4 l/3 l/2 a/4 l/4 l/3 ill <l/4 l/4 l/3 l/2

3/4 FULL 3/4 FULL 3/4 FULL

Density (soft wood only): Rings/in. 7= summerwood

Damage: Type Est. grade reduction

Description

Warp: Bow Crook Cup Twist

(Very It, Lt, Med, Hvy)

Knot type in critical section: Edge Ctr Spike Cluster

Knot Size: Length , Width

Slope of Grain (degrees): Face 1 (critical spot) Face 2 Decay: Type Est. grade reduction

Extent

Checks: Type Size: Light , Medium

Splits: Very short Short Medium Long

Storage Conditions:

Open Stickered Ground contact

Sheltered Non-stick. Elevated

Figure Al. Sheet used to record data for the field study.

A-49
1

! Figure A2. Lumber defect - knot cluster.

Figure A3. Lumber defect —limited decay at a knot.

A-50
Figure A4 . Lumber defects. Decay, rot at bark pocket.

Figure A5 . Lumber defects. Sewer planks used as sheeting.

Boards are severely end checked; many have included

pith and extensive shake and splits.

A-51
A-52
Figure A8. Lumber defect - white speck in Douglas-fir

Figure A9 . Lumber defect - rot at a hole.

A-53
A-54
Figure A12. Use defects in trenching lumber. Saw cut, 2 inches deep in 12 x 12.
BARK

Figure A14. Wane Configurations

A-56

i
APPENDIX B - GENERAL OBSERVATIONS AND DESCRIPTIONS OF YARDS VISITED

This appendix presents the general observations and descriptions of

the supply yards investigated. Chapter 3 presents a summary of this

appendix. A discussion follows of the yards visited.

WASHINGTON, D.C.

Only one yard was visited in the Washington, D.C. area. The yard

carried a large amount of trenching lumber. Most material was purchased from five counties in southern or eastern Maryland. Stock was bought on a Mill Run basis; that is, "as it comes," ungraded, of any

species, and green. According to hardwood grade rules this includes 3B

and BTR^ grades, with 25 percent sound wood and unlimited wane permitted.

Generally, lower grade logs are merely slabbed on the saw to produce a square cant^ and delivered by truck to the lumber yard where the cants were piled by size and length. The stock was generally stored on wood

foundations to keep it off the ground and to allow room for a forklift

to get under it. Stock was separated every several courses by 4 x 4°s

for the same purpose.

There were relatively few pieces for which knots had to be mapped. By

far the most prevalent defect was wane. There was no material which

was reused at this yard.

An estimated species breakdown was: 50 percent red and white oak, 35

percent gum, 15 percent poplar, hickory, sycamore, maple, beech, birch,

cherry and pecan. The yard foreman commented that yellow poplar was not

used for trenching purposes if possible. However, poplar was not

segregated in the piles observed; according to the company personel, it was just not sought as a species by the company.

Table Bl presents some general information for the Washington, D.C.

yard.

A trenching site was visited in the Washington, D.C. area. Although the

the excavation itself was not seen, several large cribs made of 12 x 12' s, 24 feet long, were observed (fig. Bl). The 12 x 12 members were measured

and graded; however, the members obviously could not be moved by hand to

observe all four faces in all cases. The grade was assigned based upon

only what could be seen without dismantling or moving the large cribs.

^ 3B and BTR grades include the low grade of 3B and of all higher

(Better) grades.

^ A cant is a piece which has been sawn on all four faces; wane may

be present.

B-1
An interesting insect attack was observed on these cribs. Numerous holes

holes had been drilled into the wood by an insect (fig. 20, ch. 5). The

holes were about 3/16 of an inch in diameter and disappeared into the

wood. One implication of this is that green hardwoods may be assumed to

be quite susceptible to insect infestation during yard storage and even

on the job site.

HOUSTON, TEXAS

The trenching lumber in Houston was green, mill run, mixed species

hardwoods. The Houston stock is purchased green, and, because of the

very high relative humidity, much of the material had surface stain and

mold. Outdoor storage in the Houston area appears to lead to very rapid

deterioration. It was claimed that much of the stock is kept only 2-3

weeks before sale and, thus, mold is no problem. However, at this time

the stockpile was said to be high for winter or bad weather demands.

Popular sizes in the Houston area are 8x8,4x4, and 4x6 for wales

and struts, and 2-inch thick lumber for sheeting.

Contrary to the situation found in the Washington, D.C. area, wane was only a minor problem; off-size was claimed to be a major problem. Wane,

however, still resulted in many pieces being graded "None" by SPIB rules.

There were several discussions with mill managers and trenching contractors regarding sheeting material called "board road" and "sewer lumber".

Sewer lumber is two-inch material which is satisfactory for use as sheeting. Board road is usually mis-cut, odd-size material which is intended

to provide roadway support for heavy oil drilling equipment. It has a one-use lifetime and can be of very poor quality. It appeared to consist

primarily of the last board or two cut from a log, usually very

close to the pith. However, it is frequently reported that board road

is used as sheeting because it is sold cheaply. (On the other hand, an inspector for the city of Houston pointed out that the cost of trenching

lumber is small relative to the overall cost of a job. Hence, no one

pays much attention to the cost or quality of sheeting lumber in contract

bids.) Wane is permissible in board road. Although it is purchased and

sold as nominal 3x8 material, it comes in various dimensions, ranging

from 1-1/4 to 2-1/2 inches thick and 6-1/2 to 7-1/2 inches wide. Most

board road was claimed to be about 1-1/2 inches thick and about 6 inches

wide. The range, mean, and standard deviation for thickness measurements

for a stack of 65 board road members sampled at a yard in Houston were:

Range: 1.25" to 2.50 II

Me an: 1.66 II

Standard Deviation: 0.275 II

B-2
Sewer lumber, on the other hand, is said to be 2 x 8 material with relatively uniform thickness and variable width (nominal 2 x 8 is actually

2" X 6", nominal 2 x 6 is actually 2" x 5", according to yard personnel).

Sewer lumber is satisfactory for trenching; board road is not, but is

used because the "price is right" according to lumber yard and contractor

personnel. The National Hardwood Lumber Associat""' r>n grade rules contain

rules for "sheet piling, sewer sheathing, and hardwood hearts". There

are no products resembling board road, however.

Of interest is that the general foreman at a Houston yard seemed quite

familiar with various species. However, what he was sure was an oak

was actually white ash. The conclusion is that, once a log is cut into

lumber, it is doubtful if accurate species segregation is feasible or even possible by yard personnel. It was also observed at the Washington,

D.C. yard that the yard manager was the only one to exhibit an ability

to identify red and white oak by the bark characteristics. (It is rather

doubtful if bark can be used as a consistently accurate characteristic.)

Two trenching sites were visited in Houston (figs. B2 , B3). Neither

site utilized very large members. It was the opinion of a trenching

contractor and of an inspector that each trenching job is so totally

unique that it would be impossible to write standards or grades for

trenching lumber use.

Table B2 summarizes the general information for the three Houston yards

visited

.

SOUTHERN CALIFORNIA

Based on the grader and the few grade stamps that were readable, all

trenching material sampled in southern California was Douglas-fir.

However, species were not checked on a piece-by-piece basis. All material is purchased green. If it is stored very long, moderate to severe splitting or surface and end checking occur. Downgrading is occassionally

the result.

Wales and struts are usually 6x6 and 8x8 stock. Sheeting stock is

3 x 8 to 3 x 12 and 4 x 10 to 4 x 12. Other sizes are stocked in the

yards for use in home-building and general construction, but not as trenching material. One yard uses 3 x 8 to 3 x 12 ECONOMY grade; in

service it is cut into 6 to 7 foot lengths (rib sets) for use as "lagging" (horizontal members inserted between the flanges of I-beams

and often left behind when the trench is filled).

In Los Angeles all jobs have specifications for trenching lumber

(usually No. 1 and higher grades). Thus, most dealers buy No. 1 and

higher grades for the job.

The three yards in southern California were clean a>.id two of them had

asphalted surfaces (Fig 6). Yard personnel were usually knowledgeable

about lumber grades and grading practice.

B-3
Wales are specified as to either grade or allowable stress value by the

contractor according to local ordinances (city specifications). They

are usually No. 1 or No. 2 (often purchased by one yard as No. 2 and

higher grade). Grades are checked at the site by city inspectors.

Grades lower than No. 2 are used for blocking.

The manager of one yard indicated that it is difficult to regulate

lumber used in trenching because each job is "different"; the same opinion was heard in Houston.

White speck, a form of white pocket rot, is common in Douglas-fir

trenching lumber; it is caused by the fungus "Fomes pini" and is a problem in trenching because the inspectors react adversely to it.

One yard manager stated that he generally purchased only one or two grades of lumber for use as wales - No. 2 and BETTER (BTR) or

No. 1 and BTR; these were as specified by the contractor or city

of Los Angeles specifications. The same grades were purchased in

3 X 12 size for use as sheeting. Economy grade 3 x 12 's are cut into

shorts, which are relatively defect-free pieces two to five feet long

that are used as blocking or in pallet manufacture.

In one yard, a small colony of termites was discovered in a piled stack of sheeting. The material was relatively green,

been stored up off the asphalted surface. A portion of two

been attacked, and the infestation appeared to be about six

inches and about 1/4 inch deep.

One set of 3 x 12 sheeting examined was, like nearly all the other

Douglas-fir sampled, not grade-stamped. It had been purchased as No. 1 and BTR; however, most pieces had a grader's mark of one or zero on them,

indicating that the piece had been graded and marked, but not gradestamped. Some pieces had a one on one side and a zero on the other,

indicating that regrading of some sort had taken place. The source of

the lumber was unknown. The grader for this study indicated that most

of the material was Number 1 in quality.

At one yard, the trenching lumber, which was purchased new as No. 1 and

BTR, green Douglas-fir, was reused many times. The lumber was typically

used numerous times on one job site and then stored until needed elsewhere. Material was discarded at the job site if it was deemed unfit for

further use, usually as the result of a lengthwise split. Used 4 x 12

sheeting stock was observed and only about a foot or less on the end had

been visibly damaged during driving and subsequent withdrawal (fig. 8).

Some 4 x 12 sheeting had reportedly been used at least 26 times. This

material was never regraded. However, regrading could be readily accomplished because dirt appeared to be only a relatively minor hindrance.

The reused material was drier than when originally graded and had a tendency to check and split quite a bit. This downgraded roughly 25 percent

of the pieces (fig. 7).

closebut had

pieces had

square

B-4
Discussions with the Construction Division of the Los Angeles County

Flood Control District were informative. Trenching lumber is closely

specified by the state codes and OSHA specifications. For "rib sets"

3x8 Utility and Construction grades are often used. In one tunnel

site 3 X 10 sheeting was used both horizontally (lagging) and vertically

(sheeting). The tunnel was 45 feet beneath the road surface. Although

no grade stamps were observed, the sheeting appeared to be of good quality

(few knots, but one piece with extensive white speck was observed). Some

sheeting failures were observed, but these were isolated instances. Both

3" and 4" thick material were being used. Refer to figs. B4 and B5

.

Table B3 shows the general information for the three yards visited in

southern California.

B-5
Table Bl . General Information for the Yard in the Washington D.C. Area

General Yard Descriptions:

Species in stock:* Red Oak, White Oak, Gum, Beech, Poplar, So. Pine,

Sycamore, Hickory, Elm, Birch (water or river), Cherry

Source of lumber: 1-5 Local mills usually, occasionally from as many

as 10 mills - southern or eastern Maryland

Species and grades normally purchased:

Mill run hardwoods

Some So. Pine sheeting & bigger sizes.

Sizes normally in stock:

6x6 8x8 12 X 12 2, 3, 4 in. thick by 6 to 12 in. wide

6x8 10 X 10

Storage Conditions: Open, stickered, elevated

Estimated no. of reuses: None

Comments: Large yard, very cooperative

Turn over time - 30 days for some, more for others, usually 6 to 24 mo. No Reused material

This is "normal" stock period

Mill Differences - Most cut for grade; some veneer high grading

and use lower material for trenching;

some mills cut to better tolerances

* Observed by survey personnel.

B-6
Table B2. General Information for Yards in Houston, Texas

General Yard Descriptions: Two yards clean and well organized,

one yard not clean or neat.

Species in stock:*

Red & White Oak, one yard manager reported 70-85% Red and White Oak.

Elm, Hackberry, Hickory, Pecan, Gum (Tupelo), Red Gum, White Ash, Beech

(rarely) Sycamore (rarely), Magnolia (rarely), no Poplar, Cypress

(rarely), Pine, and Douglas-fir (12 x 12 x long)

Source of lumber: Local mills — East Texas, Louisiana, Mississippi

Species and grades normally purchased:

Mill run, green, mixed species, hardwoods, (one yard manager reported

50% Oak; two yards reported no Poplar; one yard reported no Birch; one yard reported So. Pine 4x, 6x and 8x in shorter lengths.)

Sizes normally in stock:

2x4 2x6 2x10 4x4 6x6 8x8 10x10 12x12

3x12 2x8 2x12 4x6 6x8 8x10

Storage Conditions: Open; stickered and non-stick ered; ground contact

and elevated conditions

Time in storage before use: 2-9 weeks

Estimated no. of reuses: None

Comments: Amount of lumber sold for trenching varies widely from year

to year, depending on large construction jobs in Houston area.

Major problem is with local mills — they won't separate species

Material is left on site at trenches

Ninety percent of lumber is left in place

Contractor reuses 4x and large squares; none is returned to the

yard, however.

Board road contractors reuse the material (it is rented)

"Big problem — get size standards for 2", 3", and 4" materiall"

"2 X 6's should be outlawed for trenching"

* Obseirved by survey personnel, unless noted otherwise.

B-7
Table B3. General Information for Three Yards in Southern California

General Yard Descriptions: Neat, clean, and orderly (two yards on asphalt

surfaces)

Species in stock: Douglas-fir

Source of lumber: California and Oregon

Species and grades normally purchased:

(One yard reported that all lumber bought is green)

No. 1 and BTR

No. 2 and BTR

Sizes normally in stock:

8x8 6x6. 4x12- sheeting

10 X 10 6x8 3 X 12 - sheeting

12 X 12 3 X 8 - sheeting

Storage Conditions: Open, stickered, and elevated.

Time in storage before use: 1 week to 6 months

Comments: One yard sometimes buys No. 1 or Select Structural, etc.,

as job specifies rather than buying several grades together.

B-8
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B-9
Figure B2. Trenching site in Houston, Texas.

B-IU
^lgu^e bJ. irenchmg site in Houston, Texas showing the way in which

the trench is braced directly following the back-hoe

excavation. On the ground beside the trench may be seen sections of sheeting waiting for placement.

B-U
Figure B4. Lagging in place in a 45-foot deep tunneling operation

in California.

B-12
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B-13
I
APPENDIX C - ANALYSIS OF FIELD INVESTIGATION DATA

This appendix presents the details of the analysis of the data collected

in the field investigation. A summary of the results, findings, and

conclusions of the analysis is given in chapter 3.

STRENGTH RATIO GRADE (G)

The most important grade taken was a strength ratio grade called G, in

which the effects of wane, damage, and decay were disregarded. The G

grade provided a basis for evaluating the effects of:

a) regrading, by partial length grading, or upgrading by

hypothetical trimming, and

b) downgrading, by taking into account wane, damage, or decay.

Figure CI shows bar charts of the relative frequency of the G grade for

full length eastern species wales (D.C. and Houston-primarily hardwood).

A wale graded over its full length is hereafter called a "full" wale

whereas a 10' length of a full length wale is called a "10'" wale.

Figure CI shows both individual and combinations of lumber size and location. Figure C2 shows similar information for eastern species sheeting;

figures C3 and C4 present bar charts for Douglas-fir wales and sheeting,

respectively. On each bar chart in the four figures, the location,

size (width and thickness), and sample size (N) are given.

In order to estimate and compare the average grade and grade variability

associated with each bar chart, the strength ratio (SR) was used. The

strength ratio is defined in ASTM as the hypothetical ratio of the strength

of a member to the strength it would have if no weakening defects (e.g.,

knots) were present. For example, a member with an SR value of 45 percent

would be expected to have at least 45 percent of the strength of the same piece if it were free of defects. Table 2a shows the SR values for grades

of No. 2 and higher. The following information is also shown for each

bar chart:

° percentage, P, of the sample of size N which had G grades

of No. 2 or higher

° the average value, SR, and coefficient of variation,

CVgj^, of the SR values

Note that SR and CVg^^ are based only on grades of No. 2 and higher,

since SR values could not be assigned to grades lower than No. 2 for

wales and struts. Also, the SR is not the actual value for each piece

but the SR for the grade assigned to that piece. That is, the SR based

on the grade represents a lower limit for the SR for each piece. Thus,

C-1
the SR values presented in this report are lower than the actual SR

values. Because pieces which were less than No. 2 were excluded from

the calculation of CVgj^ and since the actual SR values greater than 86

were not included, the CVg^^ values given in this report are less than

the actual CVg^^ values. Further, it should be noted that the larger

sizes of No. 1 and 2 in the SPIB grade rules have SR values greater

than 45 and 55; yet in this study these ratios were assigned to cor- responding grades of timbers and joists and planks. This was done to

permit combining all sizes in one grading characterization.

Table CI summarizes the range of values of SR, CVgj^, and P (col. 1-3

and 7-9) for the bar charts shown in figures CI to C4 . The range is

the minimum and maximum values which occurred when analyzing the lumber sizes separately. That is, the minimum is the smallest value for

all sizes; similarly, the maximum is the largest value. Table Cl also

shows SR, CVgj^, and P values (col. 4-6 and 10-12) for various combinations of the bar charts taken collectively; these combined values

represent either a geographic area or new versus used lumber.

As seen in table Cl, the range of the SR values (column 1) did not vary

much for both eastern species (D.C. and Houston) and new Douglas-fir

wales, ranging from 55-60; the range of the SR values of 52-53 for used

Douglas-fir wales was even less. The combined (as previously defined)

CVgg^ value (col. 5) of 19 was the same for all eastern species wales

as it was for the new Douglas-fir wales. In contrast, the combined CVg^^

value for all used Douglas-fir wales was only 10.

The combined values of SR (col. 10) for sheeting did not vary significantly, and with the exception of used Douglas-fir, agree closely with

the corresponding wale values. Comparing combined values of CVg^ for

sheeting (col. 11) shows that used Douglas-fir sheeting is lowest at

13 percent (this agrees with the trend for wales: 10 percent in

col. 5).

The use of the strength ratio to estimate and compare the grade average

and variability has the limitation that the No. 3 grades could not be

assigned strength ratio values for wales and struts. The strength ratio,

however, appears reasonable to use since the percent of the wales for

which a strength ratio could be assigned (P) was relatively high. As

table Cl (col. 3) shows, P ranged from 71 to 100 percent for all wale

cases considered, with the combined values of P ranging from 77 to 100

percent (col. 6). It should be noted that for new Douglas-fir wales,

P was 100 percent. Hence, if SR values could be assigned to No. 3 and

None grades, the eastern species SR values for wales would be lowered

while the Douglas-fir SR values for the new wales would remain the same.

Except for several cases, then, the SR values had a rather narrow range,

with values from about 55 to 60 for both wales and sheeting and for both

eastern species and Douglas-fir. The 55-60 range for SR represents a

C-2
grade range between No. 1 (SR = 55) and Industrial 65 or Select Structural (SR = 65). The range of CVgj^ values for all wales and sheeting

cases, however, was relatively larger, ranging from 7 to 24 percent.

Wales were graded as beams and stringers while struts were considered

as compression members and graded as posts and timbers. As table 1 shows, many pieces were graded first as wales and then as struts.

With only limited exceptions, the wale and strut grades were the same. Thus, for the most part, the G grade results for wales in table CI

should apply as well to struts.

ANALYSIS OF REGRADING

Two methods, A and B, were used to assess the quality variability of

wales. Both methods involved comparing partial length to full length

grading.

In method A, each wale was initially assigned a full length G grade.

If a wale was 20' long (Type I) each 10' half was also assigned a G

grade (GIO). If the GIO grade for either 10' piece exceeded the G

grade for the 20' length, the higher GIO grade was recorded. For wales

greater than 10' but less than 20' (Type II), a 10' piece measured

from one end was assigned a G grade (GIO). If the GIO grade exceeded

the G grade for the full length wale, it was again recorded.

The 10' length was chosen on the assumption that the basic structural

module for wales used with solid sheeting is often 10' —that is, the

wale would be supported by struts at 10' intervals.

Method A-Type I addresses the question: What is the grade improvement,

if any, of a 10' piece of a wale relative to the grade based on a full length wale? In other words, what is the more correct strength

distribution, considering the possibility of load sharing and the probability that the maximum load may not occur on the weaker 10' section.

Table C2, based on 66 full length wales, shows the GIO grade versus the

full length grade based on method A, Types I and II, for wales in D.C.

and Houston combined.

The partial length used in the method B was the middle 1/3 of each wale.

The method was applied to both full and 10' wales, as well as wales

whose actual total length was 10' (which would also be termed "full").

If the G grade on the middle 1/3 (GM3) exceeded the G grade on the

total wale length, then the GM3 grade was recorded. Middle-1/3 grading

was chosen to reflect that the maximum bending stress might often occur

in the middle 1/3 of a simply supported wale.

Thus, if a critical defect, such as a knot, occurred outside the middle

1/3 of a wale length (here "wale length" refers to either full length

or a 10' piece of a longer wale) the middle 1/3 was recorded as having

a GM3 grade higher than the G grade assigned to the entire wale. (Here

C-3
the GM3 grade is referred to as a partial length grade and the G grade

assigned to the entire wale (whether "full" or "10'") is referred to as

a full length grade.) Table C3 , based on 362 pieces assigned GM3 grades^

presents GM3 grade results for method B for wales in D.C. and Houston

combined

Table C4 presents, for methods A and B, the average strength ratio (SR)

for partial length (col. 1) and full length (col. 2) grades and the

average increase in SR due to partial length grading (col. 3). Both

methods clearly show that there was a significant increase in SR (col.

3 ) in those wales for which the partial length grade exceeded the full

length grade.

Table C4 (col. 4) also lists the percentage of wales for which the

partial length exceeded the full length grade. These percentages were based on all wales considered for regrading, including wales with full

length grades below No. 2. For wales in D.C. and Houston, method A (GIO)

resulted in considerably larger percentages of wales for which the

partial length grade exceeded the full length grade than did method B

(GM3). An explanation of one factor which may contribute to the larger

percentage for method A is as follows. For a single defect, such as a large knot, which controls the grade, method A - Type I will almost

always result in an upgrade on one of the two 10' pieces. Whereas in

method B, on the average, only 2/3 of the time will the defect fall

outside the middle third (resulting in an upgrade). Hence, based on this

crude model, the ratio of the number of pieces having improved quality

in Method A-Type I to method B would be 1/(2/3) or 1.5. A more thorough

study would be necessary to quantify the effect of defect type and

locat ion.

In col. 1-3 of table C4 , only wales for which SR values could be assigned

(i.e., having G grades of No. 2 or higher) were considered. Of the

eastern species wales that could be upgraded by partial length grading,

74 to 100 percent had G grades of No. 2 or higher, depending on the

geographic area and whether method A or B was used. All of the Douglasfir wales which could be upgraded by partial length grading had G grades

of No. 2 or higher. Thus, the average SR values for partial length

grading and their increase due to partial length grading should be a representative indication of a higher structural capability than that

indicated by full length grading.

REDUCTION OF CROSS-SECTIONAL AREA AND MOMENT OF INERTIA

Three methods were used to analyze the loss of cross-sectional area and

bending resistance (moment of inertia) due to missing cross-sectional

area. The first method used average end dimensions; the second method

was based on wane data (for example, wane on 1/3 of the thickness and

1/2 the width); the third method was based on the amount of downgrading

due to wane, even though the cross-sectional area and moment of inertia

reductions could not be determined quantitatively.

C-4
End Dimensions Method

A member width was determined as the average of two measurements taken, one at each end. Thickness was determined in the same manner. The crosssectional area and moment of inertia about the centroidal axis were com- puted using a rectangular cross-section. For comparison, the ratio of

the cross-sectional area based on the average actual end dimensions to

the area based on the nominal dimensions ("as sold" —given by "Member

Size" in Table 1) was computed and is referred to as the "area ratio,

A, based on end dimensions." Similarly a ratio (inertia ratio, I) of

the two corresponding moments of inertia was also computed.

Wane Data Method

As explained in appendix A, many wane configurations are possible for

a single wane data entry. Thus, due to the limited wane information,

an accurate analysis of the loss in cross-section was not possible.

This method was based on using data on the extent of wane occurring at

the worst affected corner and assumed that the wane was triangular in

shape. The fractional portion of a member°s cross-sectional area occupied by wane is given by 1/2 (WT), where W and T are wane measurements expressed as a fraction of the nominal ("as sold"— see table 1)

width and thickness. This expression tends to overestimate wane because

the wane surface is commonly convex rather than flat as assumed by

triangularity (for example, see figs. 11 and 16).

The expressions for the cross-sectional area, a, and moment of inertia,

i, about the centroidal axis for a section with wane are:

i = iAh/3) - ((1/12)(a3bWt3)) - ((a3b(0.5 - (WT^/e ) )2 ) / ( 1 - (WT/2))) (2)

where, as shown below, A and B are the nominal width and thickness of the

section.

a AB[1 - (WT/2)] (1)

CENTROIDAL

c-5
In a manner similar to the first method, the ratios of the reduced to

nominal area (A), and moment of inertia (I) were computed based on Eqns.

(1) and (2).

The average and coefficient of variation values for the area (A,CV^) and

inertia (I, CVj) ratios based on the end dimensions and wane data methods

are given in:

o Table C5 for full wales and for sheeting used as spot bracing

spot bracing refers to a single, separate, vertical upright

against the soil (fig. 1).

o Table C6 shows A and I for sheeting used as solid sheeting

solid sheeting refers to vertical sheeting which is continuous

(see fig. 1).

Both tables C5 and C6 show the range of values (minimum and maximum

ratios — see footnotes d and b, tables C5 and C6) which occurred when

several lumber sizes were analyzed separately; also shown is a combined

value for those same lumber sizes analyzed collectively.

Discussion of End Dimensions and Wane Data Methods

In interpreting the I and A ratio values there are several important

things to note. For the end dimensions method, the width and thickness

measurements taken at the ends of the lumber did not include bark. In

addition, if wane at the end was present, full section measurements were

taken at a location containing no wane, but as close to the end of the

member as possible. As a result, the "end measurements" did not represent wane. (For example, see figs. 11 and 16). Also, rectangular cross- sections were assumed, even though they were not always such.

If a piece had no wane, it was assumed that the actual and nominal

dimensions were identical. In other words the maximum value each ratio

could be was 100. In contrast, the ratios based on the end dimensions

reflect sections which had actual cross-sectional areas calculated from

dimensions larger and smaller than nominal. Thus ratio values in excess

of 100 were possible.

Further, the assumptions involved in the computation of the I and A

ratios in the wane data method can greatly influence the ratio values.

When interpreting the ratios based on wane, note that in some cases wane was relatively rare. As table C5 shows, the percentage of wales

which had wane were much less frequent in Douglas-fir (11%) than in the

eastern species (59%) material. Thus, the A and I ratios based on the

wane data would reflect only the low wane frequency; that is, the ratios

would not reflect the severity of the wane as measured only on the set

of pieces that had wane. Further, note that in the case of sheeting, wane data were not always recorded.

C-6
Finally, the end dimensions were recorded for almost all pieces. Thus,

the end dimension method is better than the wane method for comparing

eastern species with Douglas-fir, since wane was so relatively infrequent

in Douglas-fir.

Analysis of Wales

As Table C5 shows, there was a large range in the A, CV^, T, and CVj

values for eastern species for wales (D.C. and Houston) for both the

end dimensions and wane methods; this is in contrast to the smaller

range of values for the new Douglas-fir wales (end dimensions method).

Based on combined values for wales using the end dimensions method:

o I and A ratios for eastern species agree closely with the

Douglas-fir values

o CV^ and CVj values for eastern species are over three times

larger than for Douglas-fir

Analysis of Sheeting

Spot bracing which uses single, separate, vertical uprights against the

soil and solid sheeting, which uses continuous vertical uprights (see

fig. 1), were analyzed separately. This was done because the width of

the upright is used in determining the cross-sectional area and inertia

for spot bracing. For solid sheeting, however, only the thickness needs

to be- considered.

As Table C5 shows, for the e^astern j^pecies material using the end dimensions method, the range of A, CV^, I, and CVj values for spot bracing,

a_s for_wales, were also large. The combined (as previously defined)

A and I ratios for eastern species spot bracing considerably exceeded

those for Douglas-fir. Note that Douglas-fir sheeting is produced under

ALS standards whereas no standards exist for the eastern species

sheeting.

The ranges of values for A and I for eastern species solid sheeting

(Table C6) were again large; this is in contrast to the smaller ranges

for the Douglas-fir solid sheeting. Like spot bracing, the combined

A and I ratios, for eastern species solid sheeting exceeded^ those^ for

the Douglas-fir, with the exception of the relatively low A and I values

for the board road material (see appendix B). Again note that the

ALS standards were used for Douglas-fir, but not for the eastern species.

Excluding board road, there was very good agreement between the A and I values for spot bracing (end dimensions—table C5) and solid sheeting

(end thickness—table C6) for eastern species as well as for Douglas-fir.

C-7
Wane Downgrading Method

The third method involved comparing the amount of downgrading due to wane. If the grade was limited by wane, a grade for wane called GW

was assigned (damage and decay were disregarded when assigning the GW

grade). Not all full wales which could have been assigned a GW grade were given one—but many were. Often the GW grade was less than the

G grade assigned to the wale; at times the G and GW grades were the

same. Tables C7, 08 and 09 show the number of occurrences of GW as

a function of G for full wales observed in D.O., Houston, and D.O.

and Houston combined. When compared with the G grade (the grade without wane, damage, or decay), the GW grade provides a measure of the

downgrading caused by wane.

In the wane downgrading method only full wales (graded over their full

length) were analyzed. The wales were divided into two groups: those

wales with GW grades of No. 2 and higher and wales with GW grades less

than No. 2 (No. 3 and None).

Table 010 presents the number and fraction of full wales downgraded due

to wane (relative to their G grade-cols. 2 and 3) and a breakdown of

those wales into grades of No. 2 and higher (cols. 4 and 5) and, lower

than No. 2 (cols. 6 and 7). As shown in col. 3, 53% of the D.O. full

wales and 25% of the Houston full wales were dowgraded by wane. In contrast, the southern Oalifornia Douglas-fir had only 3% (col. 3) of

the full wales downgraded.

A quantitative analysis of the strength ratio reduction caused by the

GW grade was not done because over 75% of the wales assigned a GW grade

had GW grades of None or No. 3, for which a strength ratio could not be

assigned.

From an economic viewpoint and based on the SPIB grading rules used in

this study, if a No . 2 grade was chosen as a minimum grade then the

following percentages of the wales were downgraded from a G grade of

No. 2 or higher to a GW grade of No. 3 or None:

o D.O., table 07, 70% (39/56; 39 obtained as: 2 + 8 + 4 +

16 + 5 + 4 = 39)

o Houston, table 08, 71% (25/35)

o D.O. and Houston, table 09, 70% (64/91)

Note that the above percentages are based on the number of wales downgraded due to wane. Lower percentages, based on the total number of

wales (including those not downgraded due to wane), are:

o D.C.: 37% (39/106)

o Houston: 18% (25/142)

0-8
o D.C. and Houston: 26% (64/248)

Thus, there were high percentages of wales which would be downgraded

due to wane if a No. 2 wane restriction were required.

DECAY

When the amount of decay exceeded the limited decay around knot holes,

wormholes, etc. permitted in the strength ratio (G) grade (see

EXPLANATION OF DATA ENTRIES AND CODES , group No. 40, app. A) a decay

grade, called GDE, was assigned. For the GDE grade, wane and damage were disregarded. As in the wane downgrading analysis, only full wales

were analyzed for decay downgrading. About 7 percent of the eastern

species full length wales were downgraded to a non-stress grade status

relative to their G grade due to decay. Because decay is not acceptable

in significant quantity in high structural grades, the GDE grades generally were either No. 3 or None. No downgrade due to decay was observed

for the 37 new Douglas-fir full length wales.

Tables Cll, C12, and C13 show the number of occurrences of GDE as

a function of G for full wales for D.C, Houston, and D.C. and Houston

combined

.

DAMAGE

Very little mechanical damage, caused by handling or use, was observed.

Only 1 percent of the eastern species full length wales were downgraded

relative to their G grade. No hardwood sheeting was downgraded. For new and used Douglas-fir members, only 1 percent of the full length wales

and struts and 3 percent of the sheeting were downgraded. The Douglas-fir

sheeting percentage did not include brooming that could be eliminated

by trimming prior to reuse.

POTENTIAL FOR UPGRADING BY TRIMMING

A trimmed grade called GT, was assigned to a member if its G, GW, or GDE

grades could be upgraded by hypothetical trimming. Tables C14, C15, and

C16 show the number of occurrences of GT in terms of its minimum untrimmed

grade (minimum of G, GW, or GDE) for D.C, Houston, and D.C. and Houston

combined. As in the case of wane and decay downgrading, only wales

graded over their full length were considered.

The purpose of the trim analysis was to provide preliminary economic

information on the potential upgrading due to trimming. The following

trimming analysis is based on the choice of No. 2 as the minimum

acceptable grade. Of the full length wales graded in D.C. and Houston,

approximately 125 wales (about 50%) were less than No. 2 in quality

for strength ratio, wane, or decay. Of the 46 wales that could be

upgraded by trimming and which were less than No. 2 (Table C16), 38

(83%) of them could be trimmed to a grade of No. 2 or higher. Table C17

shows the analysis of these 38 full wales in terras of the frequency of

C-9
the trim length necessary to upgrade them. Table C17 shows that a trim

length of 2 feet was, by far, the most prevalent.

With all grades considered, only 11 percent (4 out of 37) of the new Douglas-fir full length wales could be upgraded by trimming; all of

these were No. 2 or higher before trimming.

It should be noted that the trimmed grade was a rough estimate made

under field conditions. It was not always consistent in definition.

For example, at times the effects of wane were ignored when assigning

the trimmed grade. Nonetheless, the analysis does at least provide

an indication of the effects of trimming in upgrading.

SPECIES

Table C18 shows the relative frequency of species for full hardwood

wales and sheeting for D.C., Houston, and D.C. and Houston combined.

As seen in table C18, in all cases, at least 50 percent of the pieces

sampled were either red or white oak. In addition to the above,

information on species, including approximate strength values, is given

in appendix B

Also, in a special study at a trenching jobsite in D.C, 17 out of 36

(47%) wales and struts sampled for species were yellow poplar —a significant increase compared with the 7.5 percent figure for full wales

found in D.C. This indicates that although the yard managers and contractors contacted claim to not "like" poplar, it still occurred and,

in this case, its occurrence was significant compared to the other

species

SLOPE OF GRAIN

A general slope of grain of 1:20 or straighter as measured in softwood

lumber grading was considered straight. As described in appendix A,

slope of grain was measured on two adjacent faces —1 and 2. Table C19

shows the relative frequency of the general slope of grain for all

eastern species full length wales and sheeting. As evident from

table C19, only about 5 percent of the members observed had a general

slope of grain of 1 in 10 or steeper (fig. 9). Similar trends are shown in table C20 for Douglas-fir full length wales, struts, and

sheeting. Thus, few pieces of No. 1 or 2 level were limited by slope

of grain in the grading process.

MOISTURE CONTENT

Almost all of the eastern species sampled were green. The moisture

content of the Douglas-fir varied from green to 10 percent.

C-10
Table CI. Summary of the Average and Coefficient of Variation Values

of the Strength Ratio for the Strength Ratio Grade (G)

Full Wales Sheet ing

Range of Values by Size^ Combined Value'' Range of Values by Size^ Combined Value''

(1) (2)

" (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)

Description sr'^ CVs/(%) SR CVsj^(%) P(%) SR CVsr(2) P(%) SR CVsr(%) P(%)

DC 55-60 19-24 72-97 58 22 85 57 20 74 57 20 74

HOUSTON 56-57 13-18 71-86 56 16 77 52-62 7.4-15 87-100 56 15 90

DC, HOUSTON 55-60 13-24 71-97 57 19 80 52-62 7.4-20 74-100 56 16 85

NEW DOUGLAS-FIR 56-60 8.0-23 100 58 19 100 54-57 14-18 67-80 55 16 74

USED DOUGLAS-FIR 52-53 8.1-12 72-100 52f 10^ 84f 57-59 12-15 90-95 58 13 92

NEW & USED DOUGLAS-FIR 52-60 8.0-23 72-100 56f 17f 93f 54-59 12-18 67-95 56 15 82

' Minimum and maximum values which occurred when analyzing the lumber sizes separately (see figs. CI to C4)-that is, the minimum is the smallest value for all sizes and the maximum is the largest value for all sizes.

'' Value for all lumber sizes taken collectively.

^ SR = Average strength ratio.

^ CVgg = Coefficient of variation of strength ratio.

^ P = Percent of pieces for which a strength ratio value could be assigned.

^ Includes struts and wales.

C-11
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C-15
Table C6. Analysis of Cross-Sectional Area and Moment of Inertia Ratios

for Solid Sheeting—Based on End Thickness

Description A(%) I(%)

D. C. and Houston

2x8, 3x12

Range of Values^

Combined Value^

14-30 88-102 69-107

94 96 91

Board Road

0 d 2x

o d 3x

65 83 57

65 55 17

Doug las- fir-New

3x12, 4x12

Range of Values

Combined Value

30-35 91-93 75-81

65 92 78

^ N = number in sample.

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were analyzed for the 3 x 12 size.

Value for all sizes taken collectively.

2x and 3x refer to 2" and 3" nominal thicknesses. Board road was reportedly sold as 3" nominally thick material (see appendix B); the

2" nominal thickness is included here for comparison.

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C-26
Table C17. Trim Length Necessary to Upgrade Full Length Wales

Number of Wales (Percent frequency in parentheses)

Trim*

Length

(Ft)

From a None Grade

to a No. 2 or Higher

From a No. 3 Grade

to a No. 2 or Higher

Fran Either a None

or No. 3 Grade to

a No. 2 or Higher

1 3 ( 12%) 1 ( 8%) 4 (11%)

2 16 ( 64%) 9 (69%) 25 (66%)

3 4 ( 16%) 3 (23%) 7 (18%)

4 2 ( 8%) 0 ( 0%) 2 ( 5%)

Totals 25 (100%) 13 (100%) 38 (100%)

* Includes trimming from both ends, if necessary; up to 20 percent of the

length of a piece was trimmable for upgrading purposes.

C-27
Table C18. Frequency (Percent) of Eastern Species Full Length Wales

and Sheeting by Species

i-Fiiu 1J- 1J- Wan d 1A, pqCO Sh eeting

DC Hous t on DC & Houston DC Houston DC & Houston

Sp ecies N*=107 N=148 N=255 N=25 N=69 N=9A

Red Oak 21.5 33.8 28.6 12 29.0 24.5

White Oak 28.0 29.0 28.6 88 47.8 58.5

Black Gum,

Tup el

9.3 11.5 10.6 1.5 1 -

i. • J.

R f>H Gum

Sweet Gum 2.8 3.4 3.1 0.0 0.0

Whit e Ash 0.0 4.7 2.7 10.1 7.4

Yellow Poplar 7.5 1.3 3.9 0.0 0.0

So. Yellow Pine 17.8 0.0 7.4 0.0 0.0

Sycamore 1.9 0.7 1.2 0.0 0.0

Hickory 3.7 0.0 1.6 0.0 0.0

Elm 0.0 0.0 0.0 1.5 1.

American Elm 2.8 0.0 1.2 0.0 0.0

Slippery Elm 0.0 3.4 2.0 1.5 1.

Ch erry 0.9 0.0 0.4 0.0 0.0

Sassaf ras 0.9 0.0 0.4 0.0 0.0

River Birch 0.9 0.0 0.4 0.0 0.0

B eech 1.9 1.3 1.6 0.0 0.0

P eca n 0.0 9.5 5.5 0.0 0.0

Hackberry 0.0 0.7 0.4 0.0 0.0

Mapl e 0.0 0.7 0.4 0.0 0.0

Mag nolia 0.0 0.0 0.0 1.5 1.1

Sugar Berry 0.0 0.0 0.0 5.8 4.2

Honey Locust 0.0 0.0 0.0 1.5 1.1

N = Number in sample.

C-28
Table C19. Frequency of General Slope of Grain for All

Eastern Species Full Length Wales and Sheeting

Slope of Grain

Fr equ ency

1

Face 1 Face 2

1 : J U e J U. U

1 • A U.J U . U

1 : J U • o U.J

1 .

"7 1 • ' U. U U.J

1:8 1.9 0.3

1: 10 1.3 1.0

1:11 0.0 0.3

1:12 1.6 0.7

1:18 0.6 0.7

1:20 93.3 96.4

or straighter

C-29
Table C20. Frequency of General Slope of Grain* for All

Douglas-fir Full Length Wales, Struts, and Sheeting

Frequency (%)

Slope of Grain Face 1 Face 2

n n

n n

1:8 2.3 0.6

1:9 1.2 0.0

1:10 1.8 0.0

1:11 0.0 0.6

1:12

f 0.6 0.0

1:13 0.6 0.0

1:15 1.8 0.0

1:20

or straighter

90.0 98.8

* SPIB NO. 2 SR grade permitted slope of grain of 1:8 or less.

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APPENDIX D

TRENCHING LUMBER:

STRESS DERIVATION AND

USE RECOMMENDATIONS

November 1979

Prepared by the

Forest Products Laboratory

Forest Service

U.S. Department of Agriculture

for the

National Bureau of Standards

U.S. Department of Commerce
ABSTRACT

Hardwood lumber and timber, which traditionally have not been stressgraded, are commonly used in trenching and excavation applications.

This paper presents a practical guide to the interpretation of ASTM

standards applicable to the derivation of allowable stresses for hardwood lumber.

A commentary on use recommendations that relate to the severe trenching

environment provides the basis for assuring structural integrity in

trenching when both new and used lumber are utilized.
CONTENTS

Page

Introduction D-1

Part I. Derivation of Allowable Properties--A Practical

Guide for Interpretation of ASTM Standards D-3

Basic Clear Hardwood Mechanical Property

Statistics and Timber Volume Estimates D-5

Species Combinations and Weighting Factors D-5

Clear Wood or Basic Stresses D-5

Clear Wood Property Summary D-13

Allowable Unit Stresses for Clear,

Straight-Grained Lumber D-13

Allowable Unit Stresses for Lumber Grades D-19

Bibliography I D-20

Appendix IA--Alternative Design Stresses for Compression

Perpendicular to Grain D-21

Appendix IB—Growing Stock Volume D-24

Appendix IC--A Computer Program for Calculating the

Exclusion Limit for a Combination of

Species D-27

Part II. Use Recommendations--A Commentary on Application D'»34

Use Environment and Mechanical Properties D-34

Exposure D-43

Storage D-46

Bibliography II D-51

TRENCHING LUMBER: STRESS DERIVATION

AND USE RECOMMENDATIONS

By

B. ALAN BENDTSEN, Forest Products Technologist

and

WILLIAM L. GALLIGAN, Engineer

Forest Products Laboratory,-^ Forest Service

U.S. Department of Agriculture

INTRODUCTION

The National Bureau of Standards (NBS) , in cooperation with the Forest

Products Laboratory (FPL) , is engaged in a study for the Occupational

Safety and Health Administration (OSHA) of the engineering and construction practices of excavation and trenching. The study will develop a technical basis for recommending revisions to existing standards where

technical weaknesses or ambiguities exist.

Lumber often is the key structural member in trenching, having to withstand soil pressure during excavation and subsequent construction. Thus

safe and efficient trenching requires a knowledge of lumber properties.

Apparently a high percentage of trenching lumber comes from hardwoods,

which traditionally are not stress graded. One FPL responsibility in

the cooperative agreement with NBS involves adapting a stress grading

system to both new and used trenching lumber, with emphasis on hardwoods.

Two existing ASTM standards provide the analytical basis for deriving

design properties of trenching lumber. These standards detail the procedures for determining basic clear wood mechanical properties and subsequently deriving allowable unit stresses using visual grading procedures.

These standards are ASTM D 2555-76, "Standard Methods for Establishing

Clear Wood Strength Values," and ASTM D 245-74, "Standard Methods for

Establishing Structural Grades and Related Allowable Properties for

Visually Graded Lumber." Hereafter, the standards are referred to as D 2555 and D 245.

Trenching lumber often is large in cross section, green, and marketed

locally. In addition, the lumber most commonly is used in contact with

soil and exposed to all types of weather. Consequently, the task of FPL

includes making use recommendations to reflect the unique circumstances

\l Maintained at Madison, Wis., in cooperation with the University

of Wisconsin.

D-1
of trenching. These recommendations are assumed to apply to lumber after

the visual grading standards have been considered.

Part I of this report covers the derivation of allowable properties;

Part II consists of the use recommendations. In combination, they

provide the basis for assigning use-oriented properties to trenching

lumber and for establishing application rules.

In Part 1, the procedures of D 2555 and D 245 are outlined in sequence.

Tables I-l to I-IO capsulize the procedures as referenced by the text.

The tables begin with a presentation of clear wood mechanical property

averages and variability statistics. Also included are estimates of

growing stock volumes for individual species or groups of species if

individual statistics are not available. Subsequent tables perform

successive operations that provide for species marketing combinations

and adjustments for variability, safety, duration of load, seasoning,

strength ratio, etc., as required for the derivation of design stresses.

Some additional comments concerning recent developments in the derivation of allowable properties in compression perpendicular to grain are given in appendix lA.

The text and tables I-l to I-IO do not cover all possible aspects of the

derivation procedures. (In fact, the ASTM standards fail to do that

also.) Traditionally, the lumber associations provide much more detail

in their derivation workbooks. However, this paper was prepared as a guideline for the NBS cooperative trenching lumber study. If the format

of Part I, including tables I-l to I-IO, is used by lumber associations

for other purposes, it is assumed that individual agencies will add

detail to their workbooks to cover unique circumstances and to satisfy

requirements not provided by this paper.

Part II discusses types of lumber defects that can be anticipated in

structural trenching lumber, including suggestions for categorizing

damage where reuse is of interest. Particular emphasis is placed on decay and insect damage, with recommendations on effective service life

under trenching conditions. The recommendations of Part II are specific

to trenching and should not be adopted for other uses without careful

review of the bases for the recommendations.

D-2
PART I. DERIVATION OF ALLOWABLE PROPERTIES--

A PRACTICAL GUIDE FOR INTERPRETATION OF ASTM STANDARDS

Allowable properties for visually graded lumber are based on clear wood

2/ properties as cataloged in D 2555 (3).- Three tables of properties are presented: Table 1 of D 2555 comprises properties derived by double

sampling procedures (5). This is designated in D 2555 as method "A."

Species sampled and analyzed by D 143 cruciform procedures (1^) or by

random methods (4) are designated method "B" and are listed in tables 2

and 3 of D 2555. D 2555 also provides rules and procedures for developing clear wood properties of species grouped for marketing purposes.

Once the clear wood properties of a species or market group are established, the steps necessary for allowable property derivation are found

in D 245.

Several sample property derivations are used in Part I to illustrate

procedures. Yellow-poplar demonstrates the derivation of stresses for

a single species; the "aspen" group demonstrates a combination (marketing

group) where the composite dispersion factor (CDF) for the group is not

limiting; the "maple" group illustrates a combination for which the CDF

is controlling; and "cottonwood" illustrates a combination involving both

a method A and a method B species. The aspen, maple, and cottonwood

groupings are not necessarily intended as official marketing groups but were selected arbitrarily to illustrate various possible combination

procedures

For accurate identification of species used in this part both common and

botanical names are included here:

Aspen, bigtooth--Populus grandidentata

quaking--P. tremuloides

Cottonwood, black--P. trichocarpa

eastern--P. deltoides

Maple, black--Acer nigrum

red--A. rub rum silver--A. saccharinum

sugar--A. saccharum

Yellow-poplarLiriodendron tulipifera

2/ Underlined numbers in parentheses refer to Bibliography I on page 20

D-3
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Basic Clear Hardwood Mechanical Property

Statistics and Timber Volume Estimates

Table I-l lists the average, standard deviation, and variability index,

obtained by double sampling, for mechanical properties of black cottonwood. Black Cottonwood is the only hardwood that has been evaluated by

double sampling. Table 1 of D 2555 is the data source for method A

species

Averages and standard deviations for method B species are also listed in

table I-l. Method B species are those for which mechanical property

estimates are established in accordance with D 143 or by random sampling

procedures. Tables 2 and 3 of D 2555 are the data sources for method B

species

Standing timber volume estimates are also listed in table I-l. Tables 4

and 5 of D 2555 are the primary data sources for volume data. Volume

data have been collected for some hardwood species not included in D 2555

and are tabulated in appendix IB.

Species Combinations and Weighting Factors

It is frequently desirable for marketing purposes to combine or group

species that have relatively similar properties. ASTM procedures seek

equitable treatment for each species in a group or combination by

weighting factors based upon standing timber volume. A species weighting

factor is the ratio of individual species volvune to the combined volume

of all species in the combination (D 2555, paragraph 5). Marketing

groups, species, and weighting factors are listed in table 1-2, in

which we have used the aspen, maple, and Cottonwood groups for demonstration purposes

Clear Wood Stresses

This section shows how stresses are assigned for clear unseasoned wood

for individual species and for marketing groups. Modulus of rupture (R)

compression parallel to grain (C |l ), and shear strength are near-minimum

property values (5 pet exclusion limits); compression perpendicular to

grain (Cj_) and modulus of elasticity (E) are average values. Tables 1-3

to 1-6 summarize procedures for assigning clear wood stresses. Further

application of procedures for assigning clear wood values to combinations

as outlined below and in tables 1-3 to 1-6 are given in D 2555, 5.5.

D-5
Table 1-2. --Combinations and combination weighting

factor

Combination Species Volume Weighting

factor

Million ft3

Aspen Bigtooth

Quaking

2,970

11,093

0.2112

.7888

Maple Black

Red

Silver

Sugar

1,801

6,037

5,507

8,566

.0822

.2755

.2513

.3909

Cottonwood Black

Eastern

394

5,000

.0730

.9270

D-6
Table 1-3 . --Assigned exclusion limits for modulus of rupture,

compression parallel, and shear (lb/in. ^)

Weighted CDF Species or o • ~ ttt i • r>r>r< u i Assigned

, . ^. Species X VI s exclusion CDF check ^ combination ^ i- i value limit value

MODULUS OF RUPTURE

Aspen Bigtooth

Quaking

5,400

5,130

864

821 3,814

1

1 .84.60

N.A. 3,814

Maple Black 7,920 1,267 2 .33

Red

Silver

7,690

5,820

1,230

931 4,963

2 .22

92 4,442 4,442

Sugar 9,420 1,507 2 96

Yellow-poplar 5,950 952 4,384 4,384

Cottonwood Black

Eastern

4,890

5,260

1 00 951

842 3,820

11 13

71 3,768 3 ,768

COMPRESSION PARALLEL

Aspen Bigtooth

Quaking

2,500

2,140

450

385 1,538

2

1 14

56

ILT A N.A. t COO

1 ,538

Maple Black 3,270 589 2 06

Red

Silver

3,280

2,490

590

448 2,056

2 07

97 1,827 1,827

Sugar 4,020 724 2 71

Yellow-poplar 2,660 479 1,872 1,872

Cottonwood Black

Eastern

2,200

2,280

1 00 360

410

SHEAR

1,606

1

1

.65

.64

N.A. 1 Cf\C

1 , oOo

Aspen Bigtooth

Quaking

732

656

102

92

512

2

1

.15

.56

N.A. 512

Maple Black 1,128 158 1 .55

Red

Silver

1,151

1,053

161

147

883

1

1

.67

.16

835 835

Sugar 1,465 205 2 .84

Yellow-poplar 792 111 609 609

Cottonwood Black

Eastern

612

682

1 .00 92

95

518

11

.02

.73

503 503

D-7
Table 1-4 . --Assigned averages for compression perpendicular (lb/in. ^)

Species or „ . — Weighting Weighted Check value Assigned

combination ^ factor x (x . • 1.10) value mm

Aspen

Maple

Yellowpoplar

Cottonwood

Bigtooth

Quaking

Black

Red

Silver

Sugar

Black

Eastern

206

181

601

405

369

645

269

165

196

0.2112

.7888

.0822

.2755

.2513

.3909

N.A.

.0730

.9270

186.3

505.8

N.A.

194

199.1

405.9

N.A.

181.5

186

406

269

182

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D-10
Exclusion Limits

Exclusion limits (EL) for individual species are calculated as

EL = X - 1.645 s (Note 9, D 2555)

where x and s are estimates of species averages and standard deviations

from table 1-1.

Exclusion limits for combinations are the 5th percentile of the volumeweighted frequency distribution (D 2555, 5.2.2.2 and 5.3.2.2). A computer

program for computation of a group exclusion limit (GEL) is given in

appendix IC. However, an estimate can be obtained by computing a volume

weighted average GEL for all species in the combination (D 2555, Note 8).

Method A species . --(D 245, 5.2.2.3.) GEL is limited by a composite dispersion factor (CDF) value of 1.18. CDF is calculated for each species in

the combination as

CDF _ (x/Vl) - GEL

(1)

where VI is the variability index from table 1-1. If CDF for one or more species in a combination is less than 1.18, the assigned value is

the minimum GEL calculated as

GEL = (x/VI) - 1.18 s (2)

for each species having a CDF less than 1.18.

Method B species .— (D 245, 5.3.2.3.) GEL is limited by a CDF value of

1.48. CDF is calculated for each species in the combination as

CDF = (x - GEL)/s (3)

D-11
If CDF for one or more species in a combination is less than 1.48, the

assigned value is the minimum GEL calculated as

GEL = X - 1.48 s (4)

for each species having a CDF less than 1.48.-

Both A and B species . --CDF limits are applied to method A species as per

equations (1) and (2); to method B species as per equations (3) and (4).

If CDF limitations are involved, the lowest result of equations (1), (2),

(3), and (4) is assumed for GEL (D 2555, 5.4.2.1).

Mean Values

Cj^ and E values for combinations are volume-weighted averages calculated

as

X =2 R X (5)

1

where

X = volume-weighted average for a combination,

n = number of species in the combination,

R = ratio of the volume of the ith species to the combined volume

of all species in the combination (D 2555, 5.2.1, 5.3.1,

and 5.4.1), and

X = average CJ^ or E value of the ith species.

Method A species . --Assigned E values may not exceed the minimum quantity,

1.16 (x/VI), calculated for each species. (D 2555, 5.2.1.1, 5.2.2) C|

is limited as for method B species.

Method B species . —The assigned C\_ and E values may not exceed the

minimum quantity, 1.10 x, in the combination. (D 2555, 5.3.1.1)

Both A and B Species . --For combinations containing both method A and

method B species, the limitations of method A and method B are applied

as appropriate.

D-12
Nonvolume Species

A species for which no volume estimates are available may be included

in a combination. Assigned values are determined for the combination

excluding the "nonvolume" species and for the "nonvolume" species as an individual. If the assigned values for the "nonvolume" species exceed

the combination values, the combination values are assumed. If not,

the assigned values for the "nonvolume" species are assumed for the

combination.

Clear Wood Property Summary

Table 1-7 summarizes the clear wood property assignments for individual

species and marketing combinations as derived in tables 1-3 through 1-6.

Modulus of rupture values listed in this table are assumed for clear wood

tension values.

Allowable Unit Stresses for Clear, Straight-Grained Lumber

Allowable unit stresses for clear straight-grained lumber are derived

from the clear wood values in table 1-7 by adjustment factors and modifications for seasoning effects and density (in our examples, modification

3/ for density is not applicable). The result is shown in table 1-8.—

values apply to lumber 2 inches wide only.

Adjustment Factors (D 245, 6.2, 6.2.1, and table 9)

Fi_ , F^ , F , and F Adiustment factors include a factor for normal durab t c' V

tion of load and a factor of safety.

The factor for E adjusts for span-depth ratio from 14 to 21 and from

concentrated centerpoint loading to uniform loading.

The factor for F^, includes adjustment for average ring position and a factor of safety.

F is derived as 0.55 F . (D 245, 4.2.5)

3/ Allowable properties are symbolized by the notation F^ for

bending, F^ for tension, F^ for compression parallel, F^ for shear,

F . for compression perpendicular, and E for modulus of elasticity.

D-13
Table 1-7. -- Clear wood values summary

Species Modulus Modulus

or of C|| Shear C| of

Combination rupture elasticity

Lb/ in.Lb/ in.Lb/ in.Lb/ in.

1,000

lb/in.

Aspen 3,814 1,538 512 186 915

Maple 4,442 1,827 835 406 1,037

Yellow-poplar 4,384 1,872 609 269 1,222

Cottonwood 3,768 1,606 503 182 1,018

D-14
Table 1-8 . --Allowable unit stresses for clear straight-grained lumber—1/

Species

or combination

-''f F F F F I b ^t V

Lb/in. 2 Lb/in. 2 Lb/in. ^ Lb/in. ^ Lb/in.

1,000

Lb/ in.

Aspen 1,658 912

Maple 1,931 1,062

Yellow-poplar 1,906 1,048

Cottonwood 1,638 901

UNSEASONED

732

870

891

765

114

186

135

112

124

271

179

121

973

1,103

1,300

1,083

19 PERCENT MAXIMUM MC

Aspen 2,072 1,140 1,098

Maple 2,414 1,328 1,305

Yellow-poplar 2,382 1,310 1,336

Cottonwood 2,048 1,126 1,148

123

201

146

121

186

406

268

182

1,109

-^1,257

1,482

1,235

15 PERCENT MAXIMUM MC

Aspen

Maple

Yellow-poplar

Cottonwood

2,238

2,607

2,573

2,211

1,231

1,434

1,415

1,216

1,281

1,522

1,559

1,339

129

210

152

127

FOR SEASONED MATERIAL THICKER THAN 4 IN. 3/

186

406

268

182

2/

1,168

1,324

1,560

1,300

Aspen

Maple

Yellow-poplar

Cottonwood

805

957

980

842

992

1,125

1,326

1,105

1/ F^ values apply to 2- inch depth only.

2/ Limited by dry-green ratio (table 1-6).

3/ F, , F^ , F , and F-, are the same as for unseasoned.

D-15
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D-17
Seasoning Modifications (D 245, table 11)

Table 1-8 contains unseasoned values which apply to lumber of all dimensions, except for values which apply to 2-inch depth only. Allowable

stresses, reflecting increases for 19 and 15 percent maximum moisture

content in use, are also given in table 1-8. These increases for seasoning are limited by the Dry/Green clear wood property ratios in tables Al

and A2, D 2555.

Provisions for handling seasoning increases for instances where D 2555

ratios are limiting are given in D 245 (7.1.2) when stresses for a single

species are being derived.

D 245 does not provide direction for handling seasoning increases when

the D 2555 ratios are limiting for one or more species in a combination.

However, the American Lumber Standards Committee (ALSC) Board of Review

has approved a procedure that performs seasoning adjustments prior to

forming a combination (WWPA Grading Rule, 3rd Edition effective

July 1, 1974 (8)). Seasoning adjustments are made to the averages and

standard deviations tabulated in table 1-1 for all species in the combination. For individual species or properties controlled by D 2555 ratios

(tables Al and A2), the adjustments are as per D 245 (7.1.2); other

adjustments are as normal (D 245, table 11), except that the seasoning

factor is applied to both the average and standard deviation. Using the

adjusted values, combination and derivation procedures are carried out

4/

as usual beginning with moisture-adjusted table I-l values.—

For lumber sizes thicker than 4 inches, a 10 percent increase over green

values is given for compression members and a 2 percent increase is given

for modulus of elasticity (D 245, 7.1.3 and 7.1.4). Compression members

must be sufficiently seasoned before the increase is applied, and

appreciable seasoning of the outer fibers must take place to benefit

from an increase in E. Stresses for seasoned lumber thicker than

4 inches are included in table 1-8.

Modification for Density

Strength properties may be increased by 17 percent and E by 5 percent

for lumber meeting dense requirements (D 245, 5.6 and table 8). All

^1 Because unseasoned properties are required in the "unseasoned"

part of 1-8, a supplemental table (table 1-6 is an example) should be

prepared showing property derivations for combinations where D 2555

ratios (tables Al and A2) are limiting. The supplemental table may be

limited to a single property if the D 2555 ratios (table Al or A2) are limiting in one property only. Table 1-8 should show by asterisk and

footnote those values derived in the supplemental table.

D-18
species other than Douglas-fir and southern pine must follow the provisions of paragraph 5.6.2 of D 245. Allowable unit stresses reflecting

a density increase can be shown by a second column for each property in

table 1-8 for the appropriate species or by preparation of a duplicate

table showing the dense values.

Allowable Unit Stresses for Lumber Grades

Allowable unit stresses for lumber grades are derived from table 1-8

values for clear lumber by application of strength ratios (D 245,

section 4 and tables 1-6) to strength properties and a quality factor

to E values (D 245, 4.2.4 and table 7). Special factors are applied to

values to adjust for depth effect, and an additional factor may be

applied where applicable for repetitive loading. Adjustments to

values conform to reductions recently recommended by the National Forest

Products Association (6) and approved by the ALSC Board of Review.

A strength ratio (D 245, 4) is the ratio of the strength of a piece of

lumber containing strength-reducing characteristics such as knots to its

expected strength if it were a clear, straight-grained piece. Strength

ratios for various lumber categories are given in table 1-9. The F^

strength ratios listed for grades of lumber in the Structural Light

Framing (SLF) , Light Framing (LF) , Studs (S), and Structural Joists and

Planks (SJ&P) categories are minimum ratios specified for these grades

by the National Grading Rule (NGR) as developed under PS 20-70 (7)

Strength ratios for other lumber categories are not covered by the NGR.

The strength ratios listed for these categories in table 1-9 are arbitrarily chosen for demonstration purposes only and do not necessarily

correspond to any grade description.

Table 1-9 also lists quality factors to be applied to modulus of elasticity values. The quality factors are related to F^ strength ratios

(D 245, 4.2.4, table 7). An example of stress-grade development comparable to the derivations outlined in tables 1-7 to I-IO is given in

D 245,8.0and table 13.

Size effect . --F^ values are adjusted for size effect by a multiplication

1/9 factor (2/d) , where d is the net surfaced depth or width (D 245,

6.3.1). For simplicity, a 11.25-inch depth adjustment factor (0.8254)

is commonly applied to members 5 to 12 inches in nominal width and a 3.5-inch depth factor (0.9397) is applied to nominal widths 4 inches and

less in SLF and LF categories. In this report (for demonstration only), we have assumed a 20-inch depth factor (0.7743) for grades of Beams and

Stringers and Posts and Timbers for actual widths (depth) greater than

12 inches and 12-inch depth factor (0.8195) for nominal widths 12 inches

and smaller.

D-19
Contiguous members . --An increase in of 15 percent is recommended for

design consideration for contiguous members because member interaction

provides greater load-carrying capacity than expected from predicted

individual member performance (D 245, 7.8.1). This adjustment may be

inappropriate for a majority of trenching applications.

Lumber grades . --Allowable unit stresses for lumber grades (table I-IO) are obtained by application of strength ratios and other adjustments

given in table 1-9 to clear lumber values given in table 1-8.

Rounding . --For publication, allowable unit stresses are rounded as per

D 245, 6.1.1. Rounded values are included in table I- 10.

Bibliography I

1. American Society for Testing and Materials.

1977. Standard methods of testing small clear specimens of timber,

D 143-52.

2. American Society for Testing and Materials.

1977. Standard methods for establishing structural grades and

related allowable properties for visually graded lumber, D 245-74.

3. American Society for Testing and Materials.

1977. Standard methods for establishing clear wood strength values,

D 2555-76.

4. Bendtsen, B. A., Frank Freese, and R. L. Ethington.

1970. A forest sampling method for wood strength. For. Prod. J.

20(ll):38-47.

5. Forest Service, U.S. Department of Agriculture.

1965. Western wood density survey. Report No. 1. U.S. Forest

Service Res. Paper FPL 27. For. Prod. Lab., Madison, Wis.

6. National Forest Products Association.

1977. National design specification for stress-grade lumber and

its fastenings. Washington, D.C.

7. U.S. Department of Commerce.

1970. American softwood lumber standard. Voluntary Product

Standard PS 20-70. National Bureau of Standards.

8. Western Wood Products Association.

1974. Grading rules for western lumber. Third edition,

effective July 1.

D-20
Appendix IA--Alternative Design Stress Derivation

Compression Perpendicular to Grain

In the evolution of structural lumber grades and associated allowable

design stresses, little emphasis was given to compression perpendicular

(C_[) or bearing stresses because they commonly were considered of little

or no significance. In fact, current CJ^ allowable stresses are derived

from average proportional limit values which have no apparent relevance

to design.

Recently, however, more efficient engineering design practices are resulting in instances where bearing stresses are limiting in design.

This has prompted research—^ at the Forest Products Laboratory directed

to developing a more appropriate CJ^ design basis.

Research is currently in progress at Forest Products Laboratory to

describe the stress-compression behavior in CJ^ for a number of species

and to develop models for predicting similar behavior in other species.

Figure A-1 shows a typical stress-compression result from the current

study for the 25 percent tolerance limit (75 pet confidence).

Similar tolerance limits can be estimated for D 2555 species with 75 per

cent confidence by

TL = a + bP - 0.711 1.111 +

(P - 311.1)'

1,020,000

(Al)

where TL = an estimated tolerance limit (lb/in. ^),

P = an average proportional limit from D 2555 (Ib/in.^), and

a,b,c = constants from table A-1.

To utilize equation (Al), an engineer must first decide how much compres

sion can be tolerated. Then, appropriate constants from table A-1 are substituted in the equations to obtain TL stresses for that design

compression level. TL stresses for intermediate compression levels can be obtained by straightline interpolation between stresses obtained for

the 0.03-, 0.06- , and 0.10-inch compression levels.

The estimated TL stresses do not make allowances for the effect of the

angle of the growth rings. Unpublished research at the Forest Products

Laboratory indicates that CJ_ strength at 45° to the annual rings may be

5/ Bendtsen, B. A., Haskell, J. H. , and Galligan, W. L. Characterizing the Stress-compression Relationship of Wood in Compression Perpendicular to Grain. Wood Science 10(3) : 111-121 . 1978.

D-21
1200

0.2 0.4 0.6 0.8 1.0

Compression (in.)

Figure A-1.--A typical 25 percent tolerance limit (75 pet confidence)

stress-compression behavior.

D-22
about 40 percent lower than the results obtained from standard tests.

Thus, we recommend that a reduction factor of 1.67 be applied to the TL

stresses.

Also, the TL stresses do not include a safety factor. However, the

consequence of exceeding Cj^ design stresses in wood structures is

commonly cosmetic failure only. In trenching and excavation, appearance

is not important and design with Cj^ can be quite liberal. Except for

the most critical design circumstances, a safety factor should not be

required considering that the Cj^ values obtained from (Al) are estimated

lower tolerance limits with associated confidence.

Table A- 1

. -

Parameters for estimating compression perpendicular

to grain tolerance limits

Compression level a b c

In.

0.03 36.05 1.098 1,905

.06 21.75 1.475 1,435

.10 27.19 1.677 7,263

D-23
Appendix IB--Growing Stock Volume

Timber growing stock volume data are used as weighting factors in the

derivation of allowable design properties for marketing combinations

consisting of two or more species. Volume data for many species are presented in tables 4 and 5 of D 2555. But timber of species other than

those in these tables are used in trenching and excavation. Volume data

for additional species were obtained from Resources Evaluation Research

(RER) , U.S. Forest Service, Washington Office, by species and State where

available. This information is summarized in table B-1 by four major

geographic regions: North Central, Northeast, Southeast, and Midsouth.

The States or portions of States in each region are as follows:

North Central . --Illinois , Indiana, Iowa, Kentucky, Michigan, Minnesota,

Missouri, and Wisconsin.

Northeast . --Connecticut, Delaware, Maine, Massachusetts, New Hampshire,

New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, and

West Virginia.

Southeast . --Florida , Georgia, North Carolina, South Carolina, and

Virginia

Midsouth . --Alabama , Arkansas, Louisiana, Mississippi, East Oklahoma,

Tennessee, and East Texas.

For many of the species listed in table B-1, volume data have not yet

been tabulated by the RER in every region. Thus, for these species,

total species volume estimates are not listed. Nevertheless, the data

should still be useful for making combinations within a region or between

two or more regions. For example, there may be interest in developing

design properties for a combination of all red oaks, all white oaks, or all oaks in the Midsouth region, the Southeast region, or the two regions

combined

The volume estimates in table B-1 should not be considered official in

the context of National timber inventories normally published by RER of

the U.S. Forest Service. Although there may be small discrepancies in

the data, we believe they are sufficiently accurate for use as weighting

factors for developing species combinations.

These discrepancies exist because the data received from RER contained

volume estimates for an "Other Hardwoods" category in each major region.

If the volume was not tabulated for a particular species in a region, we could not be certain whether the region contained no volume for that

species or whether the species was included in the "Other Hardwoods"

category. However, a species included in this category is likely to be

of minor importance (low volume) in the region. Also, a volume estimate

may contain more than one species; e.g., "basswood" estimates may contain

American and white basswood. In this case, however, white basswood most

likely does not make a significant contribution to the total basswood

volume. A similar conclusion would probably also apply where other

species estimates are combined.

D-24
Table B-1 . -- Growing stock volume for certain hardwood species

by major geographic regions (million ft^)

Species North

Central

NortheastMidsouth

Southeast

Total

Ash (Fraxinus):

Green (F. pennsylvanica)

White (F. Americana)

Balsam poplar

(Populus balsamifera)

Basswood (Tilia sp.)

Birch (Betula):

Gray (B. populifolia)

Paper (B. papyrifera)

River (B. nigra)

Boxelder (Acer negundo)

Cherry (Prunus sp .

)

Cottonwood eastern

(Populus deltoides)

Cucumber

(Magnolia acuminata)

Elm (Ulmus)

American (U. americana)

Rock (U. thomasii)

Slippery (U. rubra)

Holly (Ilex opaca)

Locust

:

Black locust (Robinia

psuedoacacia)

Honeylocust (Gleditsia

triacanthos)

Magnolia (Magnolia):

Southern

(M. grandiflora)

Sweetbay

(M. virginiana)

l/_

637

1,606

92

30

1,282

575

2/___

995 164

10

2,114 1,658

95 21

20

331 2,404

457

1 125

365

160

193

472

49

884

4

161

118

153

136

202 2,771

10

3,773

275

25

118

91

81

68

321

12

256

189

931

178

142 92 234

672 606 1,278

(Page 1 of 2)

D-25
Table B-1 . -- Growing stock volume for certain hardwood species

by major geographic regions (million ft-^) --Con.

Species North

Central

Northeast

Midsouth

Southeast

Total

Oak red (Quercus sp.)

Black (Q. velutina)

Cherrybark (Q. falcata

var. pagodaefolia)

Laurel (Q. laurifolia)

Northern red (Q. rubra)

Pin (Q palustris)

Scarlet (Q. Coccinea)

Shumard (Q. shumardii)

Southern red

(Q. falcata)

Willow (Q. phellos)

Oak, white (Quercus sp.)

Bur (Q. macrocarpa)

Chestnut (Q. prinus)

Chinkapin

(Q muehlenburgii)

Overcup (Q. lyrata)

Post (Q. stellata)

Swamp chestnut

(Q. michauxii)

Swamp white (Q. bicolor)

White (Q. alba)

Osage-Orange (Madura

pomifera)

Sassafras (Sassafras

albidum)

Tupelo (Nyssa):

Black gum (N. sylvatica)

Water (N. aquatica)

Walnut (Juglans nigra)

48

282

374

30

2,109

1,169

481

1,164

50

774

229

3,392

1,775

11

1,222

975

4,041

333

16

4,752

14

114

1,458

204

1,572

1,842

40

1,932

38

1,400

511

2,677

10

179

778

267

15

4,608

442 2,529 5,400

1,213 652

15

192

8,653

1,864

254 107

\l - Symbolizes that the volume for the species in the region is unknown.

2/ Symbolizes that there is no significant volume for the species in

the region.

(Page 2 of 2)

D-26
Appendix IC--A Computer Program for Calculating the

Exclusion Limit for a Combination of Species

ASTM D 2555, Section 5.2.2.2 and others, require calculation of a 5 percent exclusion limit for modulus of rupture, maximum crushing strength

parallel to grain, and shear by adding the areas under volume-weighted

frequency distributions of each species at successively higher levels of

strength until a value is obtained below which 5 percent of the area under the combined frequency distribution will fall.

This appendix presents a computer program for calculating the 5 percent

exclusion limit for three mechanical properties. The program is written

in Fortran V and has been executed on the Univac 1110. It should be

easily adaptable to other computers.

Numerical Procedure

The frequency distribution of a mechanical property for a combination

of species is, in general, a heterogeneous distribution. The numerical

procedure assumes the heterogeneous distribution is made up of two or more component normal distributions, having sample estimates of the

property mean and standard deviations as listed in table I-l, with each

component distribution weighted according to the volume estimates in

that table. These normal distributions overlap one another, and a value

of the property is sought such that 95 percent of the wood in the entire

combination will exceed it.

The property axis of the combined frequency distribution is subdivided

into a set of uniform classes of width (w) . Each component normal

frequency distribution is integrated from to an upper class limit (x^)

selected to be below the exclusion limit of the heterogeneous distribution. Then integration results are weighted to reflect the timber volume

of the species represented by each component distribution. Successive

classes are then integrated, the results weighted and accumulatively

summed until the summation exceeds 0.05. The last class integrated con- tains the 5 percent exclusion limit, which is then obtained by straightline interpolation between summations of integrations to the lower and

upper limits of the last class.

For successful operation of the program, x^ must be below the 5 percent

exclusion limit of the combined distribution. Also, w must be small for

accurate interpolation of the exclusion limit in the last class. Arbitrarily chosen dimensionless factors are entered as input to calculate

and w as a proportion of the lowest species property average (x) in

the combination. We have found factors of 0.5 and 0.005 appropriate

for calculating x. and w, respectively.

D-27
Additional details concerning the numerical procedures can be obtained

from the Forest Products Laboratory.

Program Input

There are two kinds of card inputs: (1) Species statistics and (2)

factors for calculating and w. Type (1) cards each describe one species and are limited to 50 in number. Figure C-1 is an example of

a set of cards for four species and the type (2) card. A species

statistics card includes estimates of the mean (x) and standard deviation is) for modulus of rupture, maximum crushing strength parallel to

grain, and shear; a volume estimate; and any convenient species designation code.

Program Output

The program output shown in table C-1 is self-explanatory.

D-28
Figure C-1. --S ample input cards

1 2 3| 4 |5 6 7 8 9 10 1 1 12 13 14 15 18 19 20 21 22 23|24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

TYPE (1) CARDS

^ g Modulus of rupture Compression parallel Shear Volume

•H 00

<u m X S X s xs

1 7 9 2 0 1 2 6 7 3 2 7 0 5 8 9 1 1 2 H8 1 5 8 1 8 0 1

2 7 6 9 0 1 2 3 0 3 2 8 0 5 9 0 1 1 5 1 1 6 1 6 0 3 7 3 5 8 2 0 9 3 1 2 4 9 0 4 4 8 1 0 5 3 1 4 7 5 5 0 7 —

1

4 9 4 2 0 1 5 0 7 4 0 2 0 7 2 4 1 4 6 5 2 0 5 8 5 6 6

Initial

integration

limi t Class

width

(w)

0

TYPE (2) CARD

4—I—I—

U

D-29
Table C- 1 .- -Program output.

MOR

SPECIES AVE PROP STD OEV EXCL LIM PEL WT COMBINED EXCL LIMIT

7920,

7690.

5820.

9a20.

1267,

1230.

<?31.

1507.

5836.

5667,

a289,

69«1 .

.0822

.2755

.2513

.3909

a963.

COMP PAR

SPECIES AVE PROP STD DEV EXCL LIM PEL WT COMBINED EXCL LIMIT

3270.

3280,

2a90.

a020.

589.

590.

aae.

72«.

2301 . 2309.

1753.

2829.

.0822

.2755

.2513

.3909

2056.

SHEAR

SPECIES AVE PROP STD DEV EXCL LIM REL wT COMBINED EXCL LIMIT

1 128,

1151,

1053.

ia65.

158,

161 , 1«7.

205.

868.

886.

811 . 1128,

.0822

.2755

.2513

.3909

883,

D-30
The Program

C

C A PROGRAM FOR CALCULATING PROPERTIES FOR GROUPS OF SPECIES

C DIMENSION STRAT (3,999) ,EXC (3) , JS0C51 ) ,XBAft(51 r 3) ,STD(5l ,3) , AVE (3)

#

.C(3,3),XM(3),V0L(5l)

DATA ASP/.S6ai8958/Al/,2258 36ea/A2/-,25212866/A3/l ,?596951/

DATA A^l/-l.?8 78224/A5/.9a06afe07/A6/.32759ll/

C

C READ FACTORS FOR CALCULATING INITIAL X AND CLASS WIDTH VALUES*

C FACTORS ARE MULTIPLIED BY THE LEAST AVERAGE PROPERTY OF A GROUP

C TO ARRIVE AT THE ACTUAL VALUES. DATA CARD FORMAT IS

C 2F10., RIGHT JUSTIFIED, INCLUDE DECIMAL POINTS.

C

1 READ 2,XFC,WFC

2 F0RMAT(2F10.0)

C DO a j=i,3

EXC ( J)xO.

AVE (J) = 0.

DO 3 K=l,999

3 STRAT(J,K)=0.

a CONTINUE

C

C READ A GROUP OF 2-50 DATA CARDS FOLLOWED BY A TRAILER CARD

C THAT HAS 99 PUNCHED IN CC 1-2, DATA IS RIGHT JUSTIFIED,

C WITHOUT DECIMAL POINTS, AS FOLLOWS

C

C COL 1-2 ANY NUMERICAL SPECIES DESIGNATION 12

C

C COL 3-9,16-21,27-52 SPECIES AVERAGE PROPERTIES

C

C COL 10-15,22-26,33-37 STANDARD DEVIATION OF PROPERTIES

C FOR THF SPECIES

C

C COL 38-aa TIMBER VOLUME

C

C COL a5-80 MAY BE USFD FOR REMARKS. NOT PROCESSED

C BY THE PROGRAM

C DO 7 J=l,52

READ b,JSQ ( J) , X8AR(J,1),STD(J,1),X8AR(J,2),ST0(J,2),X8ARCJ,3),

.STD(J,3),V0L(J)

6 FORMAT( 12, F7.0,F 6.0,2 (F6,0,F5.0) ,F7.0)

IF (JSQ(J) .EQ.99)G0 TO 8

7 CONTINUE

C 8 JN=J-1

AV0L=0.

DO 12 1=1,3

TV0L=AV0L

DO 10 J=l , JN

AVE(I)=AVE(I)+XBAR(J,I)*VOL(J)

10 TV0L=TV0L+V0L(J)

12 AVE (I ) = AVE(I)/TVOL

D-31
DEVELOP C-ARRAY

00 13 J»l,3

15 XM(J)s99999999,

DO 15 J«l,3

DO 15 K«1,JN

IF(XBAR(K,J) ,GE.XM(J))GO TO 15

XM(J)sXBAR(K, J)

15 CONTINUE

00 17 J«lr3

C(J, 1 )«XM(J)*XFC

C(Jr3)«XM(J)*WFC

17 C(J,2)«C(J,1)+997.*C(J,3)

PRINT 99

99 FORMAT(lHl)

DO 50 JJ«l,3

IF(AVE(JJ)),50,

00 32 IIslfJN

NsO

L«0

Y«C(JJ,1)

20 IF(Y-C(JJ,2)),21,2l

IF(N-998)22,21,22

21 L«l

22 NsNfl

X«(Y-XBAR(II» JJ) )/STD(II, JJ)

XXsX

IF{X),2a,2«

x«-x

2a X«X/1. 414214

Esl,/(l.+A6*X)

X2s-(X*X)

Q«2,*ASP*EXP(X2)

ERR3,5*(A 1*E+A2*E*E*A3*E*E*E+A4*E*E*E*E+A5*E*E*E*E*E )*Q

IF(XX),25,25

AREA2«ERR

60 TO 26

25 AREA2sl,-ERR

26 IF(Y-C(JJ,1))30,,30

STRAT(JJ,N) = 8TRAT (JJ,N)+AREA2*V0L(H)

28 YsY+C(JJ,J)

AREA1:AREA2

GO TO 20

30 STRAT(JJ#N)=STRAT(JJ#N)*(AREA2-AREA1)*V0L(II)

IF(L-1)28

NSN41

STRAT (JJ,N)sSTRAT(JJ,N)+ERR*VOL (II)

IF(Y-C(JJ,2)),J2,32

PRINT 33, JJ

33 FORMAT(« EXCLUSION LIMIT NOT REACHED FOR PROP', 12)

32 CONTINUE

00 38 Isl,999

38 STRAT(JJ,I)sSTRAT(JJ,I)/TVOL

CUMaO.

DO 46 Isl,999

D-32
IF(l-i)r,a?

IF{,05-STR4T(JJ,I)),,«^

PRINT ao,jj

00 FORMAT(/,« LOWEST CLASS CONTAINS EXCLUSION LIMIT FOP PR0P'»I3)

GO TO 50

02 IF(STRAT(jj,i)-.05"»-cuH),aa,aa

CUMsCUM+STRAT (JJ, I

)

GO TO ah

HH STEPSsI-2

EXC (JJ)=C (JJ, n*STEPS*C ( JJ,3)+C (JJ,3)*( .05-CUM)/STRAT (JJ, I

)

60 TO 50

Ub CONTINUE

50 CONTINUE

PRINT 99

DO 80 1=1,3

IF (AVE (I ) ) ,80,

IF(I-2),53,55

PRINT 52

52 FORMAT (

• MOR '

)

GO TO 63

53 PRINT 56

56 FORMATt////' COMP PAR')

GO TO 63

55 PRINT 58

58 FORMATC////' SHEAR')

GO TO 63

63 PRINT bU

bU FORMAT(/,' SPECIES AVE PROP STD DEV EXCL LIM REL wT COMBINED

.EXCL LIMIT',/)

JDsJN/241

DO 70 J=1,JN

FIVEPsXBAR ( J, I )-l ,6a5*STD( J, I ) t^TsVOL(J)/TVOL

KiJSQ (J)

IF(JO.EQ,J) GO TO 66

PRINT 68,K,XBAR(J,I),STD(J,I),FIVEP,WT

GO TO 70

66 PRINT 68,K,XBAR(J,I),STD(J,I),FIVEP,WT,EXC(I)

68 FORMAT (15, F 12,0, 2F9.0,F9,«,5X,F8,0)

70 CONTINUE

80 CONTINUE

PHIM 99

STOP

END

D-33
PART II. USE RECOMMENDATIONS--A COMMENTARY ON APPLICATION

Structural properties of lumber derived in Part I are predicated upon

controlled use in which no degradation of properties occurs. Trenching

lumber is a somewhat unique application for structural wood since, in

most cases, the lumber is in contact with the soil and is subject to an environment more severe than that for which most wood products are specified. The following sections consider various aspects of trenching

lumber applications assuming severe environment, some reuse of structural

members, and the need for structural integrity related to safety of both

life and property, for finite periods of time.

Use Environment and Mechanical Properties

Duration of Load

New lumber. —Increases in allowable stresses for short-term loading

conditions are justified as per paragraph 203 NDS (6) .2J Otherwise, normal

loading is assumed for all use not exceeding 10 years; 90 percent of

normal loading stresses are used where the duration exceeds 10 years.

Used lumber . --The uncertainty of actual loadings in trenching applications and the difficulty in accurately accumulating load duration history

suggest a conservative approach for used lumber. Thus, it is recommended

that normal loading stresses be used in all reuse applications not exceeding 10 years; 90 percent of normal loading where the duration exceeds

10 years.

Damage

All lumber is graded under the assumption that strength-affecting characteristics may be present in a piece if they do not reduce the strength

below the level predicted by the defect upon which the grade is based.

Mechanical damage may be tolerated without a grade change on this basis.

However, if the damage has the equivalent effect of a grade reduction,

the piece must be regraded. Thus, it is recommended that used lumber

with visible evidence of mechanical damage be regraded before reuse. Further guidelines follow.

Structural damage . --(1) Gouge--Minor scrapes or gouges on flat surfaces

will be subjected to the same limitations as "skips"; on corners, they

will be limited as wane. Major gouges, or those that exceed skip or wane limitations, will be treated as a knot as per D 245.

(2) Splits--Splits will have the same limitations as splits in new lumber.

6_/ Underlined numbers in parentheses indicate references in

Bibliography II, p. 51

D-34
(3) Punctures --Punctures have the same limitations as knots of equivalent

size

.

Severe structural damage . --Severe structural damage is defined as damage

potentially causing a loss in strength in excess of that expected solely

because of loss in section as graded under gouges, splits, or punctures.

Severe structural damage may not necessarily be visible; i.e., it may be

judged that the visible physical damage could not have occurred without

having caused more serious but less evident severe damage. An example

is a puncture wherein the average size of a hole is moderate but one side is much larger than that on the other. The extent of damage is

therefore difficult to accurately assess. A second example is a broomed

end on a strut. The actual extent of shear failure beyond the brooming

is difficult to assess. If a member is judged to have potentially severe structural damage, it should be (a) designated for resawing to remove damaged portions and then regraded, (b) designated for nonstructural use, or (c) discarded. Figure II-l shows examples of damage where the timbers

could be resawed and used as structural members.

Wane

Successful use of essentially full round timbers in much trenching lumber,

particularly wales and struts, suggests that wane may not be critical

unless a flat surface is required for fastening other materials. It is

desirable that wane restrictions for trenching lumber be related to

demonstrable need for cross sectional area as defined by the strength

ratio for the grade or by design requirements. Pieces not meeting wane restrictions may be treated as a smaller size. Figure II-2 shows an example of a timber that probably would not meet the wane restriction.

Bark

Traditionally, a substantial amount of trenching lumber is used with the

bark remaining on the piece. This practice is not recommended as the

bark will prevent the sapwood underneath from drying out, thus encour- aging decay and maintaining a haven for insect attack. Further, a removal

of bark is essential for adequate grading of the members. It is recom- mended, therefore, that bark be removed from trenching lumber.

Decay Attack

Wood kept constantly dry does not decay. If kept below approximately

20 percent moisture content, wood will last indefinitely. Further, if

it is kept continuously submerged in water (probably comparable to underground, below water table exposure) even for long periods of time, it

is not decayed significantly by the common decay fungi regardless of

the wood species or the presence of sapwood. Bacteria and certain softrot fungi can attack submerged wood, but the resulting deterioration is

D-35
Figure II-l . --Timbers that appear to have potential for resawing and

structural reuse. Resawing could remove the apparent bending failures near the end (top) or the brooming failures (bottom)

D-36

(M 145 664- lA)

(M 145 667-3)
Figure II-2 . --Extensive wane in trenching timber must be treated

structural defect or downgraded to a smaller size.

(M 145 667-11)

D-37
very slow (1_,2_) and is not a concern in trenching lumber even when

reused repeatedly.

The heartwood of some common native species has varying degrees of

natural decay resistance. Untreated sapwood of all species has low

resistance to decay and usually has a short service life under conditions conducive to decay. Decay resistance of heartwood is greatly

affected by differences in preservative qualities of the wood extractives, attacking fungus, and conditions of exposure. Considerable

difference in service life may be obtained from pieces of wood cut from

the same species or even from the same tree and used under apparently

similar conditions. Furthermore, in a few species, such as spruces and

the true firs (not Douglas-fir) , heartwood and sapwood are so similar in

color that they cannot be easily distinguished. Marketable sizes of some species, such as southern pine and baldcypress, are largely second

growth and contain a high percentage of sapwood.

Precise ratings of decay resistance of heartwood of different species

are not possible because of differences within species and the variety

of service conditions to which wood is exposed. However, broad groupings

of many of the native species based on service records, laboratory

tests, and general experience are helpful in choosing heartwood for use under conditions favorable to decay. Table II- 1 shows such groupings

for some domestic woods according to' their average heartwood decay

resistance. The extent of variations in decay resistance of individual

trees or wood samples of the species is much greater for most of the

more resistant species than for the slightly or nonresistant species.

Both resistant and nonresistant species can be utilized as trenching

lumber. However, if decay hazards are present, any sapwood and the

heartwood of nonresistant species should only be utilized for service

where the potential for decay is low or moderate or where the exposure

time is limited. Specific recommendations are given in a later section.

If a trench design defines certain members as not structurally critical,

sheeting perhaps, nonresistant material might be used even where decay

hazards are severe. Alternatively, nonresistant material can be treated

with preservatives for severe exposure conditions.

It is important to note that green lumber will support decay organisms

and that heavy timber dries very slowly. Thus, for green timbers, the

exposure period must include processing and storage times. Specific

recommendations regarding exposure periods for various geographical

locations are discussed in a later section ("Exposure")-

D-38
Table II-l . -- Grouping of some domestic woods according to

heartwood decay (taken from (8))

Resistant or Moderately Slightly or very resistant resistant nonresistant

Baldcypress

(old growth)—'''

Catalpa

Cedars

Cherry, black

Chestnut

Cypress, Arizona

Junipers

2/

Locust, black

Mulberry, red

Oak:

Bur

Chestnut

Gambel

Oregon white

Post

White

n 2/ Osage orangeRedwood

Sassafras

Walnut, black

2/ Yew, Pacific—

2/

Baldcypress

(young

growth)—'''

Douglas-fir

Honeylocust

Larch,

western

Oak, swamp

chestnut

Pine, eastern

1/

white

Southern pine:

Longleaf—

Slash

Tamarack

1/

Alder

Ashes

Aspens

Basswood

Beech

Birches

Buckeye

Butternut

Cottonwood

Elms

Hackberry

Hemlocks

Hickories

Magnolia

Maples

Oak (red and

black

species)

Pines (other

than longleaf, slash

and eastern

white)

Poplars

Spruces

Sweetgum

True firs

(western

and eastern)

Willows

Yellow-poplar

1^/ The southern and eastern pines and baldcypress are now largely second

growth with a large proportion of sapwood. Consequently, substantial quantities of heartwood lumber of these species are not available.

2/ These woods have exceptionally high decay resistance.

D-39
COo

OJ

u

(H +j «5 u o 0) >.

Ulm 1—1 P

iw •H Pn

•H 3

^3 •H OO a ns •H (U (U !-l u

+J (U +J +J

<U

a

O

IS •H 4-) I—

ft • d

>. R3 nju CO <U XI w •P00 >» nj CI

a

I—

(U (U o u 1 u «

+-> o o o si

!-i CO oi) CJ > •H

4-1 I—

•H »-l •H OJ

C/3 +J P

4-1 00 •H •H e 1—

I—

u o ft

•H

O CO P

«3 P

CO

CO

O

Si el XI

E-i 0) P 1 M p •H 1 P• M-l p

CO -H •H ci /—

1 I—

•H rH

1—

/~\ CO CM

t— P !-l P XI 00

0)m 00 <f ^ (L) •r-) <u

i-l si rH

oo ^ ' ^ ' P

•H
Unfortunately, sapwood is present in much trenching lumber, particularly

on edges and corners. Where decay resistance is essential, sapwood should

be treated as wane to take advantage of the natural decay resistance of

durable species (in critical service). If sapwood exceeds the wane limitation of the grade, a piece should be downgraded.

For most severe decay hazards pressure treatments are often required.

Even the very decay resistant species may require preservative treatments

for important structural uses. A general overview of preservation is

available in the Wood Handbook (8)

.

Decay is prohibited in members for all structural uses if identifiable

by visual inspection. An exception may be pieces in which decay occurs

in a knot but does not extend into the wood. Decay can usually be recognized by the appearance of brown or white spots or irregular zones and

the occurrence of collapsed or abnormally shrunken areas. If decay is

suspected but not visually confirmed, the toughness or brashness of

fibers should be tested by inserting a sharp probe (pick test) a short

distance into the wood in a suspected area and prying downward on the

probe to bring out a small section. Interpretation of the pick test

is given in figure II-3. Borderline cases should be judged to contain

decay, and along with pieces containing decay, should be designated for

nonstructural use or should be discarded. A more thorough discussion of

the pick test and its interpretation is given in (7)

.

Surface mold and stain is an indication that conditions are extremely

favorable for strength reducing decay to take place, although the extent

of the decay is difficult to assess (8) . The presence of the mold also

suggests the storage procedure is inadequate to prevent decay. Pieces

having extensive mold or stain should be examined with the pick test as described in the preceding paragraph.

Insect Attack

Insect damage can occur in seasoned or unseasoned lumber. In trenching

operations, the principal concern is where established large colonies of

insects are in existence. Where installation may exist for a year or more, control of insects, particularly termites, must be considered.

No method is known for estimating from appearance the amount of reduction

of strength from insect damage. If damage is evident, critical members

should be removed from service and the piece resawn and regraded or placed in a noncritical use. Detailed discussion of insect attack is

found in the Wood Handbook.

Grading rules for stress-rated lumber do not permit lumber containing

insect attack to be rated for critical structural use. In trenching,

a major concern would be attack subsequent to grading, during storage,

and during the trenching operation. Insect attack under these conditions

can include beetles and termites. Both hardwoods and softwoods are susceptible. Any evidence of attack should not be overlooked, as beetles

D-41
Figure II-4. --Levels of decay potential for wood exposed to the weather

in aboveground service based on a climate index derived from standard

temperature and rainfall data: Darkest areas , wettest climates, most

suitable for decay; index greater than 65. Lightest areas , driest

climates, least suitable for decay; index less than 35. Gray areas , moderately wet climates, moderately suitable for decay organisms;

index 35 to 65 (taken from (]_)).

(M 138 247)

D-42
can remain active while the lumber is in use. Timber commonly used for

trenching is not resistant to termite or beetle attack.

Inspectability

Members that are encased with mud or dirt or otherwise rendered nongradeable because growth characteristics and other defects are not visible

should be downgraded to nonstructural use or discarded. Alternatively

they may be hosed clean with water or surfaced clean (planed) if feasible and

then graded.

Exposure

Trenching lumber will often be exposed to decay organisms and insects in

the use environment. This use exposure determines the useful life of the

trenching material if, during the storage period, it was protected from

moisture and provided with adequate ventilation. If, on the other hand,

the trenching material is close piled and not shielded from rain or splash

during storage, this storage period then becomes part of the effective

life of the trenching material from a decay and insect exposure perspective. In essence, close piling and lack of moisture and insect control

during storage reduces the effective potential life of the trenching

lumber at the trenching site. Discussion of this aspect follows:

Decay

Decay in structural members is a function of species, temperature,

moisture content, and time. It is difficult, therefore, to make simple

quantitative observations on exposure for use guidelines. Generalizations, for example, are that fenceposts of substantially or very resistant

species may last 10 to 20 years, while those of nonresistant heartwood

may last 5 years or less (3,5,7). Fencepost use demands little bending

strength; structural trenching criteria must be more stringent.

Moisture and temperature, which vary greatly with local conditions, are the principal factors affecting rate of decay. When exposed to conditions that favor decay, wood deteriorates more rapidly in warm, humid

areas than in cool or dry areas. High altitudes are less favorable to

decay than low altitudes because the average temperatures as a rule are lower and the growing seasons for decay fungi are shorter. The relative

decay hazard by location is discussed further in later paragraphs.

Climatic and soil conditions at the trenching site provide environments

conducive to decay. If long exposure is anticipated in high moisture

content-high temperature environment, preservation may be a better option

than decay-resistant heartwood. The climate zones of figure II-4 may be

D-43
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used to estimate the seriousness of decay hazard. The decay potential

indicated is derived by a climate index (7):

Climate Index

Dec

Jan

(T-35) (D-3)

30

where T is the mean monthly temperature in degrees F and D is the mean

number of days in the month with 0.01 inch or more of precipitation.

The summation of the products for each month provides a yearly "index."

Clearly, there are local regions within figure II-4 in which, because

of elevation or other influences, the climate index formula is a more accurate estimation than the map.

Decay is very slow when the index is below 35; moderate at 35 to 65; and

rapid above 65.

Temperature alone is an indicator of decay under some conditions.

Little or no decay occurs below 32° F or above 100° F; very slow attack

occurs below 50° F and above 90° F. The most rapid attack occurs between

75°-90° F.

The choice of species or a requirement for treatment for structural

shoring requires judgment about anticipated exposure. Unfortunately,

no precise information is available concerning the time involved for

decay infestation to occur, to become established, and to progress to

the point of causing significant strength degradation. The climate

index is useful in identifying relative decay hazard zones in the

United States. Lacking, however, is a quantification of "expected

useful life" of timbers in the various hazard zones.

Based upon counsel with other Forest Products Laboratory staff

(researchers in the Protection of Wood in Use and Biodegradation of

Wood research teams), the following recommendations were developed:

These recommendations are for nonresistant to moderately resistant

species. If the anticipated exposure period (including storage during

processing at holding yards and onsite) exceeds the periods listed,

resistant or very resistant species (table Il-l) or pressure treatment

with preservatives is recommended. When trenching completion is delayed,

a plan must be developed for onsite inspection to assure that structural

integrity is maintained. Storage plans should include provisions for

Climate

index

Maximum

exposure

>65

35-65

<35

9 mo

.

12 mo. 24 mo.

D-45
proper handling of nonresistant or moderately resistant species if the

recommended exposure periods will be exceeded.

The exposure periods recommended above should be considered as rule-ofthumb. Additional interpretation may be appropriate for specific onsite

conditions, season of the year, and the geographical location within a broad hazard zone.

Insects

Protection from insect attack depends upon inspection procedures, good

housekeeping, and onsite treatment. Attack generally is not rapid, but

regular inspection for insect attack is recommended in critical regions

where exposure will be over 6 months on the job site. In reuse, any

evidence of attack should be regarded as damage and requires inspection

before use in critical applications.

Termite attack is influenced by climate and by natural habitat.

Figure II-5 illustrates the general boundaries of recorded damage. A

more specific illustration of the relative hazard of subterranean termite

infestation is seen in figure II-6.

Storage

If wood is dried below the fiber saturation point (FSP) , it generally

is immune from attack by decay fungi. The FSP varies between species

and between pieces, and the actual moisture content may be imprecisely

known; therefore, 20 percent moisture content is generally considered

the maximum "safe" moisture content.

Wood dried to 20 percent moisture content will not regain enough moisture

to render it susceptible to decay even in relative humidity conditions

approaching 100 percent, provided it is protected from rainwater and

other sources of free water. New lumber sold as dry should be checked

with a moisture meter to determine actual moisture content. Dry lumber

(20 pet moisture content and less) can be safely bulk piled under a roof or cover. Large timbers may require years to season and dry, permitting

decay to take place and promoting some insect attack as well. (See our comments earlier under " Exposure " concerning the necessity of including

storage time as a part of recommended exposure period.) As a general

rule, trenching lumber above the FSP should be stickered to permit adequate

ventilation and discourage surface decay and insect degradation. Stickering such as used for railroad ties may be a practical option.

The importance of proper lumber storage cannot be overemphasized. Rapid

deterioration of wood strength can be traced to incipient fungus infections originating during poor storage. Figures II-7, II-8, and 11-9

show examples of poor storage practices encouraging decay and insect

D-46
infestations. Trenching lumber should be protected against wetting

from the ground and, as noted, should be stickered to promote drying,

particularly after wetting from rain. In permanent or long-term storage,

lumber should be placed under a roof for protection or provided with

other protection from rain. Lumber at these sites should be above the

ground, preferably on foundations of concrete, asphalt, or treated wood.

These recommendations apply particularly when reuse is anticipated.

Figure 11-6 . --Relative hazard of termite infestation in United States is

indicated by density of stippling (taken from (4)).

(F-489264)

D-47
Figure II-7 . --Examples of how poor storage leads to problems. Top, solid

stacking of green timbers prevents drying and promotes decay infestation. Bottom, poor housekeeping and piling practices in a holding

yard

(M 145 666-11)

(M 145 665-7A) D-48
Figure II-8 . --Examples of decay in trenching lumber. Top, decay probably occurred because of close piling. Bottom, decay has occurred in

large green timbers before they seasoned.

(M 145 665-19A)

(M 145 667-7) D-49
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D-50
Bibliography II

1. Bendtsen, B. A.

1974. Bending strength and stiffness of bridge piles after 85 years

in the Milwaukee river. USDA For. Serv. Res. Note FPL-0229.

For. Prod. Lab., Madison, Wis.

2. Eslyn, Wallace E., and Joe W. Clark.

1976. Appraising deterioration in submerged piling. Sonderdruck

aus : Material und Organismen Beiheft 3. Verlag Duncker and

Humblot, Berlin 41.

3. Gjovik, Lee R. , and Harley L. Davidson.

1975. Service records on treated and untreated fenceposts. USDA

For. Serv. Res. Note FPL-068, rev. For. Prod. Lab., Madison, Wis.

4. Johnston, H. R. , Virgil K. Smith, and Raymond H. Beal.

1972. Subterranean termites, their prevention and control in

buildings. Home and Garden Bull. No. 64. South. For. Exp. Stn.

5. Miller, Donald J., and Robert D. Graham.

1977. Service life of treated and untreated fenceposts. 1976

progress report on the post farm. Res. Pap. 37. School of

Forest., For. Res. Lab., Oregon State Univ.

6. National Forest Products Association.

1977 edition. National design specification for stress-grade

lumber and its fastenings. Washington, D. C.

7. Scheffer, T. C., and A. F. Verrall.

1973. Principles for protecting wood buildings from decay. USDA

For. Serv. Res. Pap. FPL 190. For. Prod. Lab., Madison, Wis.

8. U.S. Forest Products Laboratory.

1974. Wood Handbook. U.S. Dep. Agric, Agric. Handb. No. 72, rev.

iz U.S. GOVERNMENT PRINTING OFFICE : 1980—0-3 14-654

D-51
NBS-114A (REV. 9-78)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. BSS 122

2,Gov'L Accession No, 3. Recipient's Acccbsirr No,

4. TITLE AND SUBTITLE

A Study of Lumber Used for Bracing Trenches in the

United States

5. Publication Date March 1980

$. PerfonsingOfganization Code

7, AUTHOR(S)

Lawrence Knab, Felix Y. Yokel, William L. Galligan;

B. Alan Bendtsen, John F. Senft

8. Performing Organ. Report No.

9. PERFORMING ORGANIZAI ION NAMt AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

18. Projed/Task/Work llftit No.

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS rsfree*. City, state, ZIP) Occupational Safety and Health Administration

Department of Labor

Washington, D<,C. 20210

13. Type of Report & Period Covered Final

|W. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 80-600015

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

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

literature survey, mention it here.) In certain areas of the United States, lumber is used extensively to brace

trenches against collapse. The life and safety of the workers in these trenches

therefore depends on the structural adequacy of the lumber bracing used. This report

presents a study of the properties and characteristics of trenching lumber which are critical to its structural performance. Using these properties and characteristics,

allowable stresses and use recommendations are proposed.

The National Bureau of Standards (NBS) conducted a field study of trenching lumber

and found that either ungraded eastern species, primarily hardwood, or graded

Douglas-fir is used. For graded Douglas-fir, allowable design stresses and other

properties are established by existing standards. The eastern species, however, are ungraded and no accepted guidelines are used to assign allowable design stresses

and other properties. The results of the field study indicate that 80 percent of the

eastern species trenching lumber, when graded by existing softwood grading rules

(Southern Pine Inspection Bureau Grading Rules, 1977 edition) is No. 2 grade or higher; 60 percent is No. 1 grade or higher. These percentages do not reflect the effects of wane (deficiency in cross- sectional area) and decay, which are additional

problems, NBS therefore recommends that, for hardwood wales and struts, allowable

stresses and other properties be based on a No. 2 minimum grade with appropriate

provisions to control wane and decay. (continued)

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)

Construction lumber; construction safety; excavation; hardwood; lumber grading;

shoring; softwood; timber engineering; trench bracing; trenching.

18. AVAILABILITY [x] Unlimited

1 1 For Official Distribution. Do Not Release to NTIS

[X~| Order From Sup. of Doc, U.S. Government Printing Office, Washington, DC

20402, SD Stock No. 003-003-02164-4

1

1 Order From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

221

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

$6

USCOMM-DC
16. ABSTRACT (continued)

Use recommendations were developed, which consider duration of load, mechanical

damage to lumber, presence of bark, decay, insect attact, inspectability , exposure,

and storage for various aspects of trenching lumber applications. These

recommendations reflect a severe trenching environment, possible reuse of structural

members, and the need for structural integrity to protect life and property.



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