Evolution of Standardized 

Procedures for Adjusting 

Lumber Properties for 

Change in Moisture 

Content

David W. Green 

James W. Evans 

United States

Department of 

Agriculture

Forest Service 

Forest

Products

Laboratory

General

Technical

Report

FPL−GTR−127
Abstract

This paper documents the development of procedures in 

American Society for Testing and Materials standards for 

adjusting the allowable properties of lumber for changes in 

moisture content. The paper discusses the historical

context of efforts to establish allowable properties on a 

consensus basis, beginning in the 19th century. Where

possible, the reasons for proposed changes in the standards 

are presented. The goal of this work is to foster a better 

understanding of how current standards have evolved and to 

promote reconciliation of conflicting property assignment 

procedures between current standards. 

Keywords: Moisture content, modulus of elasticity, modulus 

of rupture, compression parallel to grain, compression

perpendicular to grain, tension parallel to grain, shear

parallel to grain, American Society for Testing and Materials

September 2001 

Green, David W.; Evans, James W. 2001. Evolution of standardized

procedures for adjusting lumber properties for change in moisture content. 

Gen. Tech. Rep. FPL-GTR-127. Madison, WI: U.S. Department of

Agriculture, Forest Service, Forest Products Laboratory. 50 p. 

A limited number of free copies of this publication are available to the 

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Acknowledgments

The authors thank Dr. John Senft of Purdue University for 

pictures and information on W.K. Hatt; Walter C. Sturm, 

past president of the American Railway Bridge and Building 

Association, for pictures and information on W.G. Berg; 

Brian Brundige of Simmons–Boardman for a picture of

W. G. Berg from Railway Track & Structures; Carol

Severance, historian, USDA Forest Service, Forest History 

Society (Duke University, Durham, North Carolina) for a 

picture of H. Betts from American Forests; Hurworth IT 

Consultants for a picture of and information on W. Emerson; 

Vicki Herian, USDA Forest Service, Forest Products

Laboratory, for assistance in obtaining biographies and 

pictures of pioneers in the development of standardized 

procedures for lumber properties (App. I); and William 

Galligan, Dr. Edward King, Douglas Rammer, and especially Dr. Robert Ethington for their extensive comments

on the draft manuscript. 

Cover: Class at Yale University, around 1906.

Harry D. Tiemann is second from right. 

Conversion factors 

Inch–pound unit 

Conversion

 factor SI unit 

inch (in.) 25.4 millimeter (mm) 

foot (ft) 0.3048 meter (m) 

pound force/square inch (lb/in2

) 6.894 kilopascal (kPa) 

pound force/square foot (lb/ft2

) 47.88 pascal (Pa) 

temperature, °F (TF) [TF − 32]/1.8 temperature, °C
Preface

Of the environmental factors that affect structural design 

with wood, one of the most important is moisture content. 

Although the mechanical properties of small clear specimens 

generally increase with drying, the properties of structural 

lumber may not. In the United States, differences of opinion 

over the objectives of a lumber testing program, and therefore over whether to base allowable properties on tests of 

small clear specimens adjusted for grade and other factors or 

directly on tests of full-size structural members, have influenced efforts to establish lumber property standards since the 

19th century. Efforts to harmonize the benefits of the two 

approaches have sometimes led to confusion as to the basis 

for adjusting allowable properties for change in moisture 

content and to inconsistencies between different standards.

The primary objective of this paper is to document the historical development of procedures in American Society for 

Testing and Materials (ASTM) standards for adjusting the 

allowable properties of lumber for changes in moisture 

content. Our goals are to foster a better understanding of 

how current standards have evolved and to promote reconciliation of conflicting property assignments.

We first review the historical context for establishing lumber 

properties on a consensus basis, beginning in the 19th century. Then, we follow the development of factors for adjusting allowable properties for change in moisture content, 

beginning with ASTM D245, which was established in 

1926. Where possible, we try to document reasons for these 

developments. We also try to chronicle and explain the 

development of adjustment factors in ASTM D2915, established in 1970, and ASTM D1990, established in 1991. 

Current editions of these standards show some significant 

differences in adjustment factors for dimension lumber when 

properties are adjusted from green to 12% moisture content. 

These factors are shown in a table following this text. 

We recognize that moisture adjustment procedures are not 

the only differences between these ASTM standards, but 

they are a significant difference. Because both ASTM 

D1990 and D2915 start with test results on full-size lumber, 

these may be the easiest standards to reconcile. 

Ratio of property at 12% moisture content to that of green 

dimension lumber by various ASTM standardsa

Standard MOR UTS MOE UCS Shear C–perp 

D245–99 1.35 1.35 1.20 1.75 1.13 1.50 

D2915–98b 1.33 1.33 1.20 1.91 1.17 1.00 

D2555–98c

 1.69 — 1.25 1.99 1.47 2.03 

D1990–97 1.18 — — 

6,000 lb/in2

 1.39 1.09 1.18 NA — — 

5,000 lb/in2 1.33 1.07 1.18 NA — — 

4,000 lb/in2 1.26 1.04 1.18 1.65 — — 

3,000 lb/in2

 1.13 1.00d 1.18 1.53 — — 

2,000 lb/in2

 1.00d 1.00d 1.18 1.30 — — 

1,000 lb/in2 1.00d 1.00d 1.18 1.00d — — 

a

MOR is modulus of rupture, UTS ultimate tensile stress,

 MOE modulus of elasticity in bending, UCS ultimate

 compressive stress, C-perp compression perpendicular to grain, 

 and NA not applicable. NA indicates that the green value is

 higher than the applicable range of adjustment (9,600 lb/in2

 for

 MOR, 8,400 lb/in2

 for UTS, and 4,400 lb/in2 for UCS);

 significant error may occur. Arrow ( 

 under D1990–97 may vary with initial green strength. Refer to

 strength values listed in the table. 

b

Adjusting over this moisture content range may not be within

 the intent of the standard (see text). 

c

D2555 values are the average for all softwood species, for

 small clear specimens (App. E). 

d

Adjustment is 1.0 below 2,400 lb/in2 for MOR, 3,150 lb/in2

 for UTS, and 1,400 lb/in2

 for UCS. 
ii

Contents

 Page

Introduction ...........................................................................1

Scope .....................................................................................6

Modulus of Rupture...............................................................6

Development of Fundamental Concepts............................6

ASTM D245 ......................................................................8

ASTM D2555 ..................................................................12

ASTM D2915 ..................................................................12

ASTM D1990 ..................................................................13

Modulus of Elasticity...........................................................15

ASTM D245 ....................................................................15

ASTM D2915 ..................................................................16

ASTM D1990 ..................................................................16

Ultimate Compressive Stress Parallel to Grain....................16

ASTM D245 ....................................................................16

ASTM D2915 ..................................................................17

ASTM D1990 ..................................................................17

Ultimate Tensile Stress Parallel to Grain.............................18

ASTM D245 ....................................................................18

ASTM D2915 ..................................................................18

ASTM D1990 ..................................................................18

Compressive Strength Perpendicular to Grain.....................19

ASTM D245 ....................................................................19

ASTM D2915 ..................................................................20

ASTM D1990 ..................................................................20

Shear Strength Parallel to Grain ..........................................20

ASTM D245 ....................................................................20

ASTM D2915 ..................................................................21

ASTM D1990 ..................................................................21

Summary of Changes to Standards......................................21

Recommendations................................................................23

References ...........................................................................24

Page

Appendix A—First Consensus Recommendations for 

Strength of Bridge and Trestle Timbers ............................. 27

Appendix B—Moisture Content Effects on Flexural 

Properties of ≥5-in.-thick Timbers...................................... 29

Appendix C—Chronology of ASTM D245 ....................... 31

Appendix D—Allowable Properties in Bending of

Select (S2) Grade in Early Documents ............................... 32

Appendix E—Dry-to-Green Ratios for U.S. Hardwood

and Softwood...................................................................... 38

Appendix F—Derivation of Moisture Content–Property 

Adjustment Models for D1990–91 .................................... 40

Basic Model.................................................................... 40

Simplified Model ............................................................ 40

Normalization ................................................................. 40

Wet Use Factors.............................................................. 41

Appendix G—Research on Effect of Moisture Content

on Compression Perpendicular to Grain............................. 44

1949 to 1957 ................................................................... 44

Later Research ................................................................ 45

Appendix H—Potential Source of Dry-Green Ratio for 

Shear in ASTM D245 ......................................................... 46

Calibration of Allowable Shear Stresses......................... 46 

Tests of Full-Size Members as Basis for Adjustments.... 46 

Appendix I—Profiles of Early Pioneers ............................. 48

Walter Gilman Berg (1858–1908) .................................. 48

Harry D.Tiemann (1875–1966) ...................................... 48

John A. Newlin (1872–1943) ......................................... 49

Robert Pilson Albert Johnson (1888–1962) ................... 49

William Emerson (1701–1782)....................................... 49 
Evolution of Standardized Procedures

for Adjusting Lumber Properties for

Change in Moisture Content 

David W. Green, Supervisory Research General Engineer

James W. Evans, Supervisory Mathematical Statistician

Forest Products Laboratory, Madison, Wisconsin

Introduction

Most properties of small clear specimens of wood increase 

significantly as moisture content decreases (Fig. 1). The 

properties of structural lumber may or may not increase with 

drying (Fig. 2). Historically, allowable properties in the 

United States were based on tests of small clear specimens in 

American Society for Testing and Materials (ASTM) standard D245. However, moisture adjustment procedures in 

D245 were not necessarily based on clear wood tests. The 

combination of basing properties on clear wood data and 

basing some adjustment procedures on tests of full-size 

members with defects has created confusion in the literature 

(Madsen 1992) and could lead to erroneous decisions in 

future engineering standards. Furthermore, the adoption of 

ASTM D1990 for deriving allowable properties based on 

tests of full-size structural members resulted in three ASTM 

standards (D245–99, D1990–97, and D2915–98) with procedures for adjusting lumber properties for change in moisture content. These procedures do not always produce

identical results, and any consistency between them in

regard to moisture content adjustment procedures is not 

apparent.

The primary objective of this paper is to document the historical development of procedures for adjusting the allowable properties of lumber for changes in moisture content in 

ASTM standards. First, we describe the early development 

of standardized procedures for assigning allowable lumber 

properties as a basis for understanding why some moisture 

adjustment procedures have evolved in different ways. We 

then present the history of standardized moisture content 

adjustment procedures for six properties for which allowable 

properties are currently assigned: modulus of elasticity in 

bending and strength in bending, tension parallel to grain, 

compression parallel and perpendicular to grain, and shear 

parallel to grain. Finally, we present recommendations to 

improve the consistency of adjustment procedures between 

different standards. 

Figure 1—Traditional model for predicting effect of

moisture content on mechanical properties of small

clear specimens (Panshin and de Zeeuw 1970). 

Figure 2—Quadratic surface model for predicting

effect of moisture content on bending strength of

lumber parallel to grain (Green and Evans 1989). 
2

It is important to consider the assumed adjustment factors 

within the historical context of when the decisions were 

made. Early emphasis was placed on standardization of 

allowable properties for what today is primarily considered 

“heavy timber.” Over much of the past century, “framing 

lumber,” lumber primarily intended for use in housing, did 

not have assigned properties. Beginning in the late 1950s, 

the development of engineered roof systems, the metal-plate 

wood truss, and more recently, the wood I-joist, have 

changed the focus of standards and the ways in which adjustment procedures are handled in ASTM standards. In the 

1960s, lumber dimensions were standardized for green and 

dry lumber (Wood 1964). All these changes interacted with 

changes proposed for moisture content adjustments. 

Research on the properties of wood and the effect of moisture content on these properties did not originate in the 

United States. For example, 

in ancient Greece, Theophrastus (372–287 B.C.) 

conducted comprehensive 

investigations into the properties and utilization of wood 

(Tsoumis 1995). Although 

Theophrastus apparently did 

not discuss the effect of 

moisture content on mechanical properties, he did 

comment on its effect on 

shrinkage and utilization. 

Booth (1964) summarized 

developments in Europe 

during the 17th and 

18th centuries to determine 

the mechanical properties of timbers (Table 1). Galileo is 

often called the “father of strength of materials,” and Booth 

recommended that Petrus van Musschenbroek be bestowed a

similar title for undertaking 

the first comprehensive work 

to determine the properties 

of timber. Some previous 

researchers had concluded 

that “dryness” could affect 

wood properties. Booth, 

however, credited William 

Emerson (in 1758) as the 

first to correctly conclude 

that “wood is likewise 

weaker when it is green and 

strongest when thoroughly 

dried,” a conclusion with 

which Musschenbroek disagreed. Georges Buffon 

(1707–1788) performed one 

of the most comprehensive 

series of tests that had been 

undertaken on the mechanical properties of wood. 

Included were a series of 

tests to compare the properties of small clear specimens 

with those of large members. 

After carefully testing more 

than 1,000 small specimens 

and being extremely careful 

to ensure that the specimens 

contained no knots or other 

defects, Buffon concluded 

that it was not possible to 

predict the properties of full-size timbers containing defects 

from tests of small specimens, and he began a series of tests 

on full-size structural members. His conclusion that tests of 

small specimens (without further adjustment) cannot be used 

to predict the properties of full-size members raised a

Theophrastus

William Emerson 

Georges Buffon 

Table 1—Summary of timber testing developments in Europe in the 17th and 18th centuriesa

Name Topic Date

Galileo Description of tension test 1638 

Mariotte Ultimate load of small cantilever beam and small tension specimens 1680 

Hooke Load–deformation behavior of cantilever 1678 

Parent Ultimate load of small oak and fir beams fixed at one end, fixed at both ends, and simply supported 1707 

Musschenbroek Development of tensile test machine; tension tests of various free parts; tension strength of various 

species; drawings of failures; effect of moisture content and density on strength; buckling of a column 

1729–1762

Buffon Effect of growth rate on density; tabular recording of test results; tests of large beams; load–deflection 

behavior of beams; effect of duration of load 

1740, 1741 

Duhamel Distribution of stresses in a beam 1742 

Emerson Correct effect of moisture on strength 1758 

Girard Development of test machine for large bending and compression specimens; tests on large compression specimens 1798

a

Booth 1964. 
3

question that was to continue into the 20th century. Early 

researchers in the United States conducting tests on

wood properties would have been aware of European developments.

Prior to 1895, grading procedures and property assignment 

procedures for solid-sawn structural lumber sold in the 

United States were not standardized. Rather, lumber testing 

procedures, visual grading procedures, and procedures for 

derivation of allowable properties were proprietary procedures developed by consulting engineers, college professors, 

and government scientists active in the field of timber engineering. The primary impetus for standardization of these 

procedures was the design of 

railway structures. In 1895, a 

committee of the American 

International Association of 

Railway Superintendents of 

Bridges and Buildings presented a report on the 

strength of bridge and trestle 

timbers (Berg and others 

1907). This report included a 

summary, compiled by the 

chairperson, of all available 

property data collected from 

many sources from about 

1870 to 1895. It also presented 15 recommendations 

by leading authorities on the strength of timbers, which 

included design equations. Three of these recommendations 

may be paraphrased as follows (App. A): 

• Recommendation 4: As a rule, a reduction of moisture 

content is accompanied by an increase in strength. 

• Recommendation 5: Structures should generally be designed for the strength of green or moderately

seasoned lumber of average quality, and not for a

high grade of well-seasoned material. 

• Recommendation 9: Beams cut from heartwood frequently 

season-check along their center and fail by

longitudinal shear. 

The committee recommended ultimate breaking stress for 

selected species based on their review of the available data 

(App. A). These properties were for the average conditions 

existing in railroad timber structures. The committee also 

recommended the following safety factors for converting the 

breaking stresses to allowable properties: 

 Tension, with and across grain 10 

 Compression, with grain 5 

 Compression, across grain 4 

 Transverse (bending), extreme fiber stress 6 

 Transverse (bending), modulus of elasticity 2 

 Shear, with and across grain 4 

In the discussion of the existing data, the committee was 

highly critical of those using small specimens of clear wood 

to derive allowable properties, and complimentary of those 

using tests of full-size members (Berg and others 1907). 

In 1886, Bernard E. Fernow was appointed chief of the 

Division of Forestry, the predecessor of the Forest Service. 

Fernow conceived a forestry program that contained as one 

of its major objectives a more comprehensive determination 

of the strength properties of the most important species of 

trees (Nelson 1971). Efforts to develop standardized procedures on a broader basis shifted toward this program. At this 

time, there was no general agreement in the United States on 

the purpose of timber test programs. Generally, the proponents of timber testing fell into one of two groups (Newlin 

1927).

Some strongly felt that the primary purpose of timber test 

programs is to develop data needed by engineers and architects. These proponents thought that tests should be conducted on full-size structural members selected from the 

marketplace.

Others, including foresters, felt equally strongly that the 

primary purpose of a timber test program should be to reveal 

the average strength properties of various species and the 

effect of conditions of growth and other factors on these 

averages. This group became intimately associated with the 

idea that many tests of small specimens should be used to 

establish average values for the species. They thought that a 

large program to test full-size members would be quite 

expensive and impractical. 

Each group tried to meet the demands of the other group to 

some extent. The testing program of the Division of Forestry 

from 1891 to 1909 generally incorporated both approaches.

In 1891, J.B. Johnson of Washington University in St. Louis, 

Missouri, formulated the first detailed testing program under 

Fernow’s general plan. Although an engineer, Johnson 

emphasized the forestry aspects of the problem and primarily 

focused on tests of small (4- by 4-in.) specimens. His work 

ceased after about 5 years when the Division of Forestry 

appropriations for research 

were reduced. 

In 1902, Harold Betts joined 

the Division of Forestry and 

organized the first timber 

testing laboratory in Washington, D.C. (Nelson 1971). 

Later that year, Betts helped 

organize a second laboratory 

at Yale University in New 

Haven, Connecticut. In 1903, 

he organized laboratories at 

Purdue University in Lafayette, Indiana, and the

Walter G. Berg 

Harold Betts 
4

University of California at 

Berkeley. The Washington 

laboratory emphasized tests 

of Southern Pine. At Yale, 

Harry Tiemann began a 

comprehensive program of 

the influence of moisture on 

strength. At Purdue, William 

Kendrick Hatt emphasized 

the development of improved 

test methods and the testing 

of hardwoods from the

central region of the United 

States. At Berkeley, Loren 

Hunt conducted tests on 

California structural timbers.

In 1905, another timber testing program was established at 

the University of Washington in Seattle, where Rolf Thelen 

conducted tests on western hemlock and Douglas-fir structural-size timbers. The following year, a laboratory was 

established at the University of Oregon in Eugene, where 

J.B. Knapp tested structural timbers for species native to the 

region. In 1908, a laboratory was established in Denver to 

test the strength of fire-killed timber.

By 1905, W.K. Hatt of Purdue was in charge of the overall 

timber test program of the Division of Forestry. He trained 

several timber test engineers 

who later entered the Forest 

Service, including McGarvey 

Cline, the first director of the 

Forest Products Laboratory 

in Madison, Wisconsin, and 

John Newlin, who was in 

charge of timber mechanics 

at the Forest Products Laboratory. Hatt was of the opinion that the proper function 

of a government laboratory 

was to pursue both full-size 

tests of commercial timbers 

to provide engineering design data and tests of small 

specimens to provide insight 

into the relationship between management practices and 

wood properties (Newlin 1927). To incorporate all knowledge gained over the last 14 years and to standardize the 

program at the various laboratories, the Forest Service published Circular 38, Instructions to Engineers in Timber 

Tests, in 1905 (Hatt 1905). 

The American Society for Testing and Materials (ASTM) 

was organized in Philadelphia on June 16, 1898, to consolidate the American membership in the International Association of Testing Materials, which had been organized in 

Munich in 1895 (ASTM Proceedings 1905). The ASTM was 

formed to promote the knowledge of the materials of engineering and the standardization of specifications and methods of testing. By 1905, ASTM had 21 committees, including the newly formed Committee Q on “Standard 

Specifications for the Grading of Structural Timber.” Committee Q (which became Committee D7 in 1910) described

their objective as follows: 

It is believed that the time has come for a comprehensive 

study and analysis of the grading of structural timbers, so as 

to arrive at a general understanding of the qualities of the 

various woods used for structural purposes, in order to standardize as far as possible, for the use of lumber manufacturers 

on one hand, and architects and engineers on the other hand, 

the various grades and qualities of woods. (ASTM Proceedings 1905)

The report further notes that one of the most important practical results of such a study would be to reduce the enormous 

waste that results, even in the practice of the most competent 

engineer. The work of the committee was to be organized 

into three areas: definition of structural timbers, standardization of trade names, and grading. Hermann Von Schrenk was 

chosen as chairperson. By 1907, the committee was organized into five subcommittees: Bridge and Trestle Timbers, 

Car Sills and Car Framing, Framing for Buildings, Ship 

Timbers, and Cross-Arms for Poles (ASTM Proceedings 

1907).

Hatt was Committee secretary and a member of the Bridge 

and Trestle Timbers subcommittee (as was Fernow, then at 

Ithaca, New York). The 1908 meeting of Committee Q was 

held in conjunction with the meeting of the Bridge and 

Trestle Timber Committee of the American Railway Engineering and Maintenance of Way Association in Chicago 

(ASTM Proceedings 1908). Of particular note are three 

papers presented by Forest Service researchers: McGarvey 

Cline, Harry Tiemann, and Rolf Thelen. 

Cline’s and Tiemann’s

papers dealt primarily with 

the relationship between 

loading rate and properties. Cline’s paper, Forest

Service Tests to Determine 

the Influence of Different 

Methods and Rates of 

Loading on the Strength 

and Stiffness of Timber,

included strength at different rates of loading in an 

ordinary universal testing 

machine, strength under 

dead load, and resistance 

of wood to impact loads.

Tiemann’s paper, The Effect of the Speed of Testing Upon 

the Strength of Wood and the Standardization of Testing for 

Speed, provided more details on this subject and also

William K. Hatt 

McGarvey Cline 

Harry D. Tiemann 
5

included contemporary information on results obtained by 

non-Forest Service researchers. His own data were for small 

clear specimens, including both wet and kiln-dried material. 

Tiemann observed that the moisture–strength relationship in 

bending and in compression parallel to grain is a function of 

the speed of testing, with green specimens being more sensitive to rate of loading than are dry specimens.

In Thelen’s paper, The Structural Timbers of the Pacific 

Coast, the test data on full-size timbers included both green 

and partially air-seasoned timbers. Thelen concluded the 

following:

It has been found that in large timbers the seasoning process 

causes not only the loss of moisture but also the checking of 

the timber. Since it is impossible to determine the exact effect which this checking has on the strength of the timber, it 

is impossible to reduce the strength of the tested timber to 

that at some other conditioning of seasoning, even though 

we know exactly the effect of the moisture on the strength.

(ASTM Proceedings 1908)

A more detailed discussion of this topic is given in Forest 

Service Circular 115 (Hatt 1907). 

In 1910, the Forest Service timber testing program was 

centralized in the new Forest Products Laboratory in

Madison, Wisconsin. A new work plan was formulated

with the cooperation of Hatt. This work plan included an 

exhaustive study of the properties of clear wood for many 

American species. The plan was submitted to ASTM Committee D7, approved as a tentative standard in 1922, and 

established as standard D143–27, Standard Methods of 

Testing Small Clear Specimens of Timber, in 1927.

The dual emphasis on testing of full-size lumber was also 

maintained. A number of individual reports had been generated by the Division of Forestry since 1891 on the properties 

of individual species of structural timbers. A re-summary 

and correlation of all the major data available from the Forest Service test program on full-size timbers was published 

in 1912 as Forest Service Bulletin 108 (Cline and Heim 

1912). The results of this phase of the program were felt to 

be particularly valuable in determining safe working stresses 

(allowable properties) and in preparing and revising grading 

rules. Bulletin 108, and some individual previous reports, 

contained some test data on the properties of both green and 

dry timbers. A standard testing procedure for full-size timbers (Fig. 3) was proposed to the ASTM D7 Committee and 

accepted as a tentative ASTM standard in 1924. In 1927, the 

tentative standard was approved as standard D198–27.

Figure 3—Testing of lumber at Forest Products Laboratory, around 1915.
6

World War I also brought attention to the need to standardize lumber grades, sizes, moisture content, and nomenclature 

(Shelley 1992). In 1922, the American Lumber Congress 

passed a resolution that a committee meet with Secretary of 

Agriculture Herbert Hoover to discuss standards and related 

matters. Their efforts resulted in the establishment of the 

Central Committee on Lumber Standards (predecessor to the 

American Lumber Standard Committee) by the Department 

of Commerce in 1922. In 1924, the Committee issued Simplified Practice Recommendation No. 16, the first national 

standard for lumber sizes and grades. This standard dealt 

primarily with nomenclature and grade descriptions. It did 

not deal with allowable design properties for lumber. 

Scope

The history of standardized moisture content adjustment 

procedures is presented for the six mechanical properties for 

which allowable properties are currently assigned: flexural 

strength (modulus of rupture, MOR) and flexural modulus of 

elasticity (MOE), ultimate tensile stress (UTS) parallel to 

grain, ultimate compressive stress parallel to grain (UCS), 

ultimate compressive stress perpendicular to grain, and shear 

strength parallel to grain. Recommendations are provided for 

improving the consistency of adjustment procedures between 

different standards. 

Modulus of Rupture 

Early investigators understood that lumber was primarily 

used structurally in bending or in compression parallel to 

grain. They viewed strength in bending as more important 

than compression parallel to grain because failure in bending 

is likely to be catastrophic. Therefore, the amount of research effort placed on bending studies far outweighs that 

for other stress modes.

Development of Fundamental Concepts

Forest Service Bulletin 10 (Roth and Fernow 1895) provides 

a discussion of the influence of weight and moisture content 

on the strength of clear wood, but provides little information 

not previously known. In his pioneering research at the Yale 

laboratory on how moisture content affects the properties of 

small clear specimens, Tiemann (1906) established the concept of a fiber saturation point—the moisture content at 

which the cell walls are completely saturated with (bound) 

water, but no (free) water exists in the cell lumen. He also 

established that only those changes in moisture content that 

occur below the fiber saturation point affect properties. 

Although these concepts were vital to the implementation of 

moisture content–property adjustment procedures for lumber, the clear wood property increases established by

Tiemann were never proposed for adjusting the properties

of large members containing defects.

Moisture content was also included as a variable in the fullsize testing program of the Forest Service that was summarized in Bulletin 108 (Cline and Heim 1912). Using data for 

beams tested in bending and in compression parallel and 

perpendicular to grain (Table 2), the researchers concluded 

that although seasoning results in a significant increase in 

strength for small clear specimens, for timbers the increase 

in bending strength resulting from drying may be offset by a 

weakening of the timber, which is caused by the formation 

of splits (see Apps. B, H). Grading rules for structural timbers proposed by the Forest Service in 1915 show no allowable increase in strength properties as a result of seasoning 

(Betts 1915). This is consistent with the 1895 recommendations for railway structures (Berg and others 1907).

A system of grading lumber much like that currently in use 

is described in USDA Circular 295 (Newlin and Johnson 

1923). Grade descriptions were developed for four grades 

using the test results summarized in Bulletin 108.1

 The 

grades were designated S1, S2, S3, and S4, which were later 

associated with Extra Select, Select Structural, Standard, and 

Common, respectively. The minimum strength ratios of S1, 

S2, S3, and S4 were limited to, respectively, 88%, 75%, 

62%, and 50% that of clear wood. In Circular 295, allowable 

properties (called “working” properties) for these grades are 

for all widths of timbers, with no special rules for lumber

4 in. and less in thickness (hereafter referred to as ≤4 in. 

lumber). No specific rules for seasoning adjustments are 

given in Circular 295. However, working stresses are 

1

The green and dry timbers tested were not necessarily of equal 

quality. The data in Bulletin 108 were used to develop the visual 

grading system that we now use to describe “quality,” and thus 

these were ungraded timbers by current definition. See Appendix B 

for other early data on the effect of moisture content on timber 

properties.

Table 2—Ratio of average mechanical properties for full-size,

air-seasoned timbers to those of green timbersa

Species MOR MOE 

Horizontal

shear

Compression

parallel to 

grain

Compression

perpendicular to grain 

Douglas-fir 1.06 1.02 1.33 1.22 1.12 

Western larch 1.18 1.14 1.18 1.64 1.31 

Longleaf pine 0.94 1.16 0.77 1.00 1.01 

Shortleaf pine 1.19 1.17 1.10 1.76 2.26 

Loblolly pine 1.19 1.07 1.30 1.46 1.31 

Western hemlock 1.21 1.20 1.07 1.73 1.09 

Tamarack 1.21 1.10 1.15 1.34 –– 

Norway pine 1.57 0.25 1.20 1.66 –– 

Redwood 0.87 0.85 –– 1.16 1.21 

a

Adapted from Cline and Heim 1912. MOR is modulus of rupture;

 MOE, modulus of elasticity. 
7

presented for three different moisture conditions (shown in 

Table 3 for bending):

Continuously dry—“Continuously dry” refers to use in 

interior or protected construction not subject to conditions of excessive dampness or high humidity. 

Occasionally wet—“Occasionally wet but quickly 

dried” assumes use in such exterior structures as 

bridges, trestles, grandstands or bleachers, and exposed 

framework of open sheds. 

Continuously wet—“More or less continuously damp 

or wet” applies to material exposed to waves or tidewater, placed in contact with earth, or used in building 

components that are more or less continuously exposed 

to water. 

The values for modulus of 

rupture (MOR), compression 

parallel to grain, and compression perpendicular to 

grain vary by exposure condition; the values for horizontal shear (as determined 

from bending specimens) 

and modulus of elasticity 

(MOE) do not. It would be 

easy to assume that these 

were property decreases for 

increases in moisture content. However, this is not the 

case. The clearest example of 

the calculation of allowable 

properties in this period was given in a paper presented by 

John A. Newlin (1927) to the American Society of Civil 

Engineers in 1925. Newlin calculated a “safe stress for a 

Select (S2) grade of spruce structural timber” as 

5,760(3/4)(3/4)(9/16) = 1,820 lb/in2

Newlin stated that

the starting point would be 5,760 lb/in2, which would be the 

average modulus of rupture of small, clear stock tested green 

at standard speed. Reduce this by one-fourth to take care of 

variability of the clear wood; make another reduction of onefourth to take care of the maximum defect permitted in the 

grade; then take off about seven-sixteenths for the dead load 

effect over a number of years (elsewhere stated as a 10-year 

load duration).2

 (Newlin 1927) 

Newlin said that this is the “stress under long-term loading at 

which an occasional timber, possibly 1 in 25, would be 

expected to fail” and notes that “the recommended stress of 

1,100 lb/in2

 gives a factor of safety of 5/3 for this bad timber 

and this worst loading condition (1,820 × 3/5 = 1,100).” The 

value of 1,100 lb/in2

 is the value listed in Circular 295 for 

Sitka spruce for S2 grade used under shelter in dry locations 

(Table 3). Thus, the working stress for the continuously dry 

exposure is based on test results for green specimens.

In an unpublished memorandum, Newlin and Johnson 

(1924) discussed the factors involved in determining the 

working stresses given in Circular 295. They noted that 

“timber in wet or damp locations is subject to deterioration 

from decay. Under such conditions lower stresses have been 

recommended in order to avoid too frequent renewals.” 

2 Note that a reduction of 7/16 means that 9/16 remains.

Table 3—Early versions of working stresses in bending for Select (S2) grade of spruce 

Extreme fiber stress (lb/in2

) for different

exposure conditions 

Continuously dry Occasionally wet Continuously wet 

Publication and spruce species Timber 

Joist & 

plank Timber 

Joist & 

plank Timber 

Joist & 

plank

Horizontal

shear

(lb/in2

)

Modulus of 

elasticity 

(×103 lb/in2)

Circular 295 

Red, white, Sitka 1,100 — 900 — 800 — 85 1,200 

Engelmann 750 — 650 — 500 — 70 800 

Newlin and Johnson 1924 

Red, white, Sitka 1,100 1,280 900 — 800 — 85 1,200 

Engelmann 750 880 650 — 500 — 70 800 

ASTM D245–27 

Red, white, Sitka 1,100 — 900 800 800 710 85 1,200 

Engelmann 750 — — 580 — 440 70 800 

John A. Newlin 
8

Thus, the different allowable 

properties at three exposure 

conditions are really a response to decay hazard and 

are not indicative of the 

effect of moisture content on 

strength. The reasoning for 

the amount of the reductions 

is not stated.

After reviewing all the data 

collected at Forest Products 

Laboratory to date on flexural strength of green and dry 

full-size lumber, Newlin and 

Johnson (1924) did recommend some increase in flexural 

strength with seasoning for lumber ≤4 in. thick (which they 

called Joist and Plank). The memorandum stated that the 

authors had observed “an increase of about 20% for S1, 15% 

for S2, 8% for S3, but no increase for the S4 grade.” The 

appendix to the memorandum includes the following statement (under Modifications of and Additions to Circular 295 

developed in conference with Forest Products Laboratory):

The working stresses for dimension (lumber) not thicker 

than 4 in. may be increased proportionally over those for 

timbers in dry locations with corresponding defects from 

equal stresses in a grade having one-half the strength of 

clear wood to stresses 25% greater than in timbers in a

grade of clear wood strength. (Newlin and Johnson 1924)

For green lumber with a strength ratio of 50% or more, this 

rule can be written as: 

SRdry = SRgreen + (SRgreen – 50)/2 (1)

where SR is strength ratio (%).

Newlin and Johnson’s memorandum clearly shows that for 

dry joist and plank, this is an increase for decreasing moisture content (Table 4). Although slightly more conservative 

than the increases cited by the authors in the main text of 

Circular 295 (Newlin and Johnson 1923), this “25% rule” 

closely approximates the experimental results reproduced in 

Table 4. 

Circular 296, Standard Grading Specifications for Yard 

Lumber, was also published at this time (Ivory and others 

1923). This publication contained recommendations on 

lumber sizes and adjustments to size for changes in moisture 

content. At this time, there were no recommended design 

values for dimension (yard) lumber. Yard lumber was recommended for framing uses such as residential housing, 

which was not considered a structural use requiring design 

values (Shelley 1992). 

ASTM D245

The Formative Years 

The development of ASTM D245 is chronicled in Appendix C. ASTM D245, Standard Methods for Establishing 

Structural Grades for Visually Graded Lumber, was established as a tentative standard in 1926 and as a full standard 

in 1927 to “offer a means of selecting structural material for 

strength” and “that appropriate working stresses may be 

assigned for its use.” The appendix of D245–26T (ASTM 

Proceedings 1926) gives the same working stresses for 

timbers, for the three exposure conditions, given in Circular 

295 (Table 3). However, the special increases proposed in 

the unpublished memorandum for pieces ≤4 in. thick and 

used continuously dry are not included. Instead, only the 

allowable property for green timbers is listed for the continuously dry exposure condition. Rather than allow a higher 

allowable property for dry dimension lumber (≤4 in. thick) 

used in a dry location, D245–26T lists lower allowable 

properties for occasionally wet and continuously wet hazard 

conditions.

To this point, the seminal work of Newlin and Johnson 

clearly provided the basis for the early versions of D245. 

From their unpublished memorandum (Newlin and Johnson 

1924), it is clear that these authors intended allowable properties for members >4 in. thick to be based on the properties 

of green wood. However, they also recognized an increase in 

allowable bending strength for ≤4-in.-thick lumber that was 

used continuously dry. Moreover, it is clear that they intended the properties of lumber of all widths to be reduced 

for expected decay hazards if not used in a continuously dry 

environment. Table 3 is an attempt to show the evolution of 

these concepts in a clear manner. The actual format, terminology, and, sometimes, the allowable properties themselves 

also evolved over time. Appendix D gives the properties of 

S2 grade lumber as originally presented in three “foundation 

documents:” Circular 295, Newlin and Johnson’s unpublished memorandum, and ASTM D245–27. 

The next revision of ASTM D245 occurred in 1930. With 

only editorial changes, the 25% rule discussed in the appendix of the unpublished memorandum by Newlin and Johnson 

(1924) is included in the 1930 revision and repeated in the 

1933 revision: 

Robert P. Johnson 

Table 4—Results of FPL tests on effect of moisture

content on MOR of ≤4-in.-thick lumbera

Increase in strength for 

dry location 

Grade

Minimum

strength

ratio, green 

condition

Experimental

evidence

25%

rule

S1 (Extra Select) 88 20 22 

S2 (Select) 75 15 17 

S3 (Standard) 62 8 10 

S4 (Common) 50 0 0 

a

Adapted from Newlin and Johnson (1924).
9

In dimension sizes 4 in. and less in thickness...and

in these sizes used in dry locations, working stresses in extreme fiber in bending are increased proportionately from 

equal values with timbers, and dimension not continuously 

dry, in a grade having 50% of the strength of clear wood, 

to values 25% greater in clear wood. (Newlin and Johnson 

1924)

With the 1936 revision of D245 (D245–36T, ASTM Proceedings 1936), the format of the standard changed dramatically. Much discussion of the derivation of properties was 

dropped. Included in the text were grade descriptions, but 

only those “recommended by the Forest Products Laboratory.” The appendix included standard stress grades and 

working stresses. The appendix stated that “the detailed 

reasoning basic to these grades will be found by a report of 

the U.S. Forest Products Laboratory...Miscellaneous

Publication 185” (Wilson 1934). It also stated that “reference should also be made to the ‘Working Stresses’ appearing in the appendix of...D245–33.”

The revised standard was very brief, primarily a collection of 

grading rules. The format was maintained in D245–37 and 

until the next revision (D245–49T), which did not occur 

until the end of World War II. The adoption of the reference 

to Miscellaneous Publication 185 (Misc. Pub 185) complicates tracking the dates when a “modification” was made to 

D245. As will be seen, two revisions (supplements) to Misc. 

Pub. 185 were made before a new version of D245 was 

issued. We assume that because Misc. Pub. 185 is referenced 

in D245–37, any subsequent changes to Misc. Pub. 185 were 

directly incorporated into D245, even without a new edition 

of that standard. 

Attempts Toward a Comprehensive Document 

Miscellaneous Publication 185 (Wilson 1934) was an attempt to provide a comprehensive document on structural 

grading. According to this 

publication, Circular 295 

(Newlin and Johnson 1923) 

presented the principles of 

grading for strength, but it 

did not show how to determine appropriate working 

stresses. With respect to 

seasoning, Wilson noted that 

although drying greatly 

increases the strength of 

wood fibers, “in large timbers this increase is largely 

offset by the checking that 

occurs in seasoning.”

He concluded the following:

The minimum strengths in any group of large pieces are increased so little by seasoning that beams and stringers and 

posts and timbers (except pieces 4 by 4 in.) are given no 

higher working stresses for continuously dry than for continuously wet service. The increase in strength of pieces 

4 in. and less in thickness with seasoning is sufficiently 

great, and is uniform enough, that it is given recognition in 

working stresses for material that will be continuously dry 

in service. (Wilson 1934) 

For lumber ≤4 in. thick, the 25% rule discussed previously

is restated. For continuously dry use, Misc. Pub. 185 gives 

working stresses for various lumber association grades.

With reference to Circular 295, Wilson stated that

the tables previously published by the Forest Products Laboratory included values for three types of exposure. Ratios 

among stresses for the different exposure conditions as given 

in these tables varied somewhat with species but averaged 

approximately as... (Wilson 1934) 

The average ratios among stresses for different exposures in 

Circular 295 are given in Table 5. The discussion again 

makes clear that lower stresses for lumber not used continuously dry were responses to decay hazard, not reduction in 

strength resulting from increased moisture content. These 

decay hazard classes are also clearly presented in the 1935 

edition of the Wood Handbook (FPL 1935). However, how 

the reductions for decay hazard were originally determined 

is not discussed.

A supplement to Misc. Pub. 185, issued in 1940 (Wilson 

1940), extended the concept of strength ratios to grades with 

strength ratios below 50%; for ≤4-in.-thick lumber, restrictions on knots and slope of grain were extended to the full 

length of the piece. This supplement also introduced restrictions on moisture content for specifications based on 

T.R.C. Wilson 

Table 5—Average ratio among stresses for different decay hazard 

exposures in Circular 295a

Stress ratio (%) for various 

 types of exposure 

Type of stress 

Continuously

dry or

submerged 

Continuously

wet, but

quickly dried 

More or less 

continuously

damp or wet 

Stress in extreme fiber in bending 100 85 71 

Stress in compression perpendicular to grain 100 70 58 

Stress in compression parallel to 

grain

100 92 78 

Stress in horizontal shear 100 100 100 

Modulus of elasticity 100 100 100 

a

Wilson 1934. 
10 

satisfactory performance (as opposed to property increases) 

for lumber to be used for house framing. For such material, 

the supplement stated that “material shall be seasoned to a 

moisture content of not to exceed 19% in any individual 

piece.” The intent was clarified in a footnote: “Since seasoning to an average moisture content well below 19% is desirable for house-framing material, this figure should be regarded as a maximum, subject to revision downward as 

increased drying facilities become available.” 

A second supplement to Misc. Pub. 185 was issued in 1948 

(FPL 1948). The purpose of this supplement was to document conclusions on working stresses drawn from favorable 

performance of wooden structures constructed during World 

War II, when certain restrictions on wooden buildings had 

been relaxed. No changes in moisture adjustments for MOR 

were made in this supplement, but some changes were made 

in other properties, which will be discussed in subsequent 

sections of this report.

Extending the 25% Rule 

The basic idea expressed by the 25% rule that the effect of 

moisture content on the bending strength of lumber ≤4 in. 

thick was somehow dependent upon the quality (or strength) 

of the lumber was retained in ASTM D245 from 1930 

through 1968. However, the interpretation of how this adjustment could be applied began to change. According to 

ASTM D245–49T, “in these sizes used in dry locations, 

higher working stresses in extreme fiber in bending can be 

permitted with the same size defects as in pieces of larger 

size, or greater defects can be permitted with the same working stress” (D245–49T, table X, footnote a). The standard 

further stated that the increase in strength caused by seasoning is “commonly taken into account by increasing the 

strength ratio by half its excess over 50%.” In addition, 

when one takes “advantage of the increase in strength from 

drying by increasing permissible sizes of knots or other 

characteristics rather than by increasing the working 

stress...the working stress may have to be reduced if the 

material is to be used under wet conditions.” This interpretation is much more complex than the original principles given 

by Newlin and Johnson (1923) and was therefore more 

difficult to implement in practice. Footnote b of table X in 

D245–49T states that “modification for seasoning in current 

commercial practice is accomplished by liberalizing defects 

in grade rather than increasing working stresses.”

By the early 1950s, there was an increasing trend to market 

2-in.-thick lumber separately from lumber of other thicknesses. It therefore appeared logical to question whether the 

25% rule developed for lumber 2 to 4 in. thick could be 

liberalized for 1-in.-thick lumber. After a review of published U.S. data and then unpublished Canadian data (later 

presented in Jessome (1971)) for 1- and 2-in-thick lumber, 

Wood (1953) concluded that stresses for green material with 

a strength ratio of 50% or more could be increased by 25% if 

used under continuously dry conditions. This adjustment 

was judged to be “conservative enough” for most species. 

The increase of 25% in the allowable bending strength of

1-in.-thick boards was recommended in the 1955 edition of 

the Wood Handbook for all grades and adopted in ASTM 

D245–57T for lumber 1 or 2 in. in thickness. This acrossthe-board 25% increase was not, strictly speaking, an extension of the 25% rule.

By the mid-1950s, some Southern Pine manufacturers produced a class of lumber with 15% maximum moisture content. Western producers and others were drying lumber to 

the 19% maximum moisture content specified in Misc. 

Pub. 185 (Wilson 1940). Thus, ASTM D245–57T retained 

the statement of D245–49T for lumber 2 to 4 in. thick, but it 

noted that “working stresses for all grades of 1 or 2 in. lumber dressed at 15% or lower moisture content and is fabricated and used under conditions where that moisture content 

is not exceeded may be increased...by one-quarter in bending.” That is, working stresses may be increased over the 

values for already-dry lumber at 19% maximum moisture 

content.

This increase in working stresses did not depend upon the 

grade (strength ratio) of the lumber. The 25% gradeindependent increase was not taken in addition to the 25% 

rule increase, but rather in place of it. Thus, a 1-in.-thick 

board could take the grade-independent 25% increase and a 

2-in.-thick board could take either the 25% rule increase (the 

magnitude of which depended upon grade) or the gradeindependent 25% increase. Note that the implementation of a 

property increase for dry material was becoming even more 

complex. ASTM D245–57T also retained the option for 

liberalizing grade characteristics given in D245–49T. 

In the early 1940s it became clear that it would be necessary 

to establish standard widths and thicknesses for both green 

and dry lumber sold under the American Lumber Standard 

system and to tie the standard dry sizes to a specific moisture 

content (Wood 1964). However, reaching a consensus on 

this standardization proved exceedingly difficult and agreement was not reached until 1963. The agreement based dry 

sizes for 2-in.-thick dimension lumber and boards on a 

maximum moisture content of 19%, with dry width and 

thickness based on shrinkage to an average moisture content 

of 15%. This consensus agreement helped spur the 1964 

revision of D245. 

ASTM D245–64T retained both the 25% rule from D245–

57–T for 2- to 4-in.-thick lumber and the grade-independent 

25% increase from D245–57T for 1- to 2-in.-thick lumber 

surfaced and used at ≤15% moisture content. However, a 

15% increase in working (allowable) stresses was added for 

1- to 2-in.-thick lumber with moisture content of not more 

than 19% at time of manufacture and that was used in dry 

conditions. The option for liberalizing grade characteristics 

instead of increasing allowable properties was also retained. 
11 

With these changes, the moisture adjustment procedures for 

bending strength in ASTM D245 reached their maximum 

complexity.

Changes After 1965 

The late 1960s were another period of major transition for 

ASTM standards for assigning lumber properties. During 

this time, a major public–private research and development 

effort focused on obtaining new, independent estimates of 

mechanical properties for clear wood (FPL 1965, Wahlgren 

and others 1975). Emphasis was on the major species of 

Southern Pine, Douglas-fir, western hemlock, and certain 

true firs. Solid-sawn lumber and plywood were both key 

interests. The strategy involved systematically studying the 

geographic variation in properties, using the more easily 

measured specific gravity as the indicator of mechanical 

properties. The result of this effort was a new standard, 

ASTM D2555, which included tables of clear wood properties for green wood by individual species, obtained from the 

new density studies or from the procedures of ASTM D143. 

Ratios of dry to green properties were also calculated and 

included in D2555. The new standard was intended to provide a starting point for applying ASTM D245. 

To make ASTM D2555 and D245 work systematically in 

tandem, it was necessary to address numerous anomalies. As 

the history of standards development has indicated, many 

early procedures for assigning properties involved judgments, often based on limited data. In the procedures proposed in Circular 295, and later adopted in D245–26T, 

judgment factors (sometimes referred to as Newlin factors) 

were sometimes applied to individual species because the 

properties of the species were judged to be more or less 

variable than those of the average species. For some species, 

the basic clear wood stresses were sometimes reduced because of drying behavior that Newlin had observed in the 

laboratory. Thus, there was an effort to revise D245 to treat 

all species by a common set of well-defined decision rules 

(Robert Ethington, personal communication).

The 1960s were also a time of fairly intense testing of fullsize lumber, for the first time since the early studies of Cline 

and Heim (1912). These more contemporary studies were 

based entirely on 2-in.-thick lumber (Doyle and Markwardt 

1966, 1967; Doyle 1968), and they generally showed higher 

strength values than those calculated from D245 procedures. 

At the time, the ASTM task group attributed much of the 

higher strength values to drying effects greater than those 

traditionally assumed (Robert Ethington, personal communication).

The 1969 revision of D245 contained neither of the two 

provisions for increasing the bending strength by 25% for 

dry lumber (25% rule for 2- to 4-in.-thick lumber or gradeindependent 25% increase for 1- or 2-in.-thick lumber). 

However, the concept of two maximum moisture content 

levels, 15% and 19%, was clearly identified. For bending of 

dimension lumber, the increases were 35% and 25%, respectively, provided that the proper allowances were made for 

shrinkage (Table 6). D245–69 explicitly assumes that lots 

(batches) of lumber dried to a maximum moisture content 

19% have an average moisture content of 15%, and lots of 

lumber having a maximum moisture content of 15% have an 

average moisture content of 12%. Adjustments of properties 

were traditionally adjusted to the average moisture content 

of the group, rather than the maximum.

The new adjustment factors for 19% and 15% maximum 

moisture content were qualified by the addition of the statement that “the increases in allowable properties given...at 

15% maximum moisture content shall not exceed the ratio

of dry to green clear wood strength shown in...D2555”

(App. E). This statement is apparently the introduction of 

dry-green moisture ratios for small clear specimens as a 

limiting factor for adjusting lumber strength. For certain 

properties of a few species, concern was expressed about 

cases in which the increase for drying lumber (25% and

35% increases of D245) would exceed that measured on 

small clear specimens, a situation considered to be indefensible. For most species, the clear wood dry-green ratios 

exceed the adjustment based on experimental results with 

lumber. The D245–69 adjustment procedures have been 

maintained through the current edition (D245–99). 

Table 6—Modification of allowable unit stresses for seasoning effects for ≤4-in-thick lumber in D245–69

Increase (%) in allowable stress and MOE for 

different maximum

moisture contentsa

Property 19% 15% 

Extreme fiber in bending 25 35 

Tension parallel to grain 25 35 

Horizontal shear 8 13 

Compression perpendicular to grainb

 50 50 

Compression parallel to grain 50 75 

Modulus of elasticity 14 20 

a

Above that of green lumber properties, the increase for 15%

 maximum moisture content shall not exceed ratio of dry to green 

 clear wood strength shown in Ratios of Dry to Green

 Clear Wood Properties in D2555. Where ratios in D2555 are

 less than those shown in this table, proportionate reductions

 shall be made for lumber at 19% maximum moisture content.

b

Increase in compression perpendicular to grain is the same

 for all degrees of seasoning below fiber saturation because

 outer fibers that season rapidly have the greatest effect on

 this strength property regardless of extent of seasoning of

 inner fibers. 
12 

ASTM D2555 

ASTM D2555, Standard Methods for Establishing Clear 

Wood Strength Values, was approved in 1966 as a tentative 

standard to provide an “authoritative compilation of clear 

wood strength values for commercially important species.” 

However, the edition of D245 in effect that year, D245–64T, 

still provided the traditional “basic stresses.” When D2555 

was accepted as a full standard in 1969, D245–69 referenced 

D2555–69 for clear wood stresses (called unit stresses). The 

1969 version of D2555 also contained, for the first time, the 

dry-green ratios by species for the properties that were included in D245. During the 1970s, the Forest Products 

Laboratory conducted clear wood studies of 10 eastern and 

western softwood species (Bendtsen 1970, 1972, 1973, 

1974) using a random procedure for selection of trees. These 

studies used an equal number of green and dry observations 

per property. The new dry-green ratios for the study species 

were incorporated into D2555 in the 1988 revision (App. E) 

and remain the values listed in the current edition

(D2555–98).

ASTM D2555–67T also marked the introduction of the 

concept of calculating a clear wood “5th percentile” for 

derivation of allowable properties. The 1955 edition of the 

Wood Handbook introduced coefficients of variation, by 

property, for green clear specimens. D245–67T built on this 

concept to account for the variance of strength within a 

species or species group. Historically, Newlin had accounted 

for within-species variability of bending strength by multiplying the clear wood mean value by a factor of 0.75. This is 

approximately the 5th percentile for most species, assuming a 

normal distribution for clear wood strength properties and a 

coefficient of variation for MOR of 16%. With the exception 

of moisture content adjustments using the 25% rule, most 

adjustment factors had historically been applied to mean 

trends or had been applied as constant percentage adjustments (per the 25% and 35% moisture content adjustment 

factors in D245–69T). As will be discussed in the section on 

ASTM D1990, this explicit assumption of a lower tail property eventually led to questioning the application of moisture 

content adjustment factors without regard to quality level 

(grade).

ASTM D2915 

ASTM D2915, Standard Methods for Evaluating Allowable 

Properties for Grades of Structural Lumber, was approved as 

a tentative standard in 1970 and as a full standard in 1974. 

This standard was established for “assessing the appropriateness of the assigned properties, and thus for occasionally 

checking the effectiveness of grading procedures.” The 

introduction to D2915 stated that

when making an evaluation of the entire marketed production of a grade, it is intended that this method will supply...a 

high degree of confidence. It may also be used for less

broad purposes, for example, to evaluate the properties of 

individual lots of lumber, or the output of a single grading 

machine. For situations where repeated sampling is likely to 

take place, or the lot size is small, this method is not particularly efficient. (ASTM D2915) 

For the first time in the history of Committee D7, this new 

standard provided guidelines for independent establishment 

of allowable properties based on testing lumber. One of the 

first applications of D2915 was in calculating allowable 

properties for Machine Stress Rated lumber. The standard 

states that “properties shall be adjusted to a single moisture 

content appropriate for the objectives of the testing program...” and provides the following adjustment formula: 

[ ] ( )( ) P2 = P1 − M 2 − M1 (2) 

where P1 is property measured at moisture content M1, P2 is

property predicted at moisture content M2, M1 and M2 are

coefficients (Table 7). 

The standard states that the equation “yields adjustments 

consistent with the moisture factors given in...D245.” It also 

suggested that “adjustments for more than five percentage 

points of moisture content are to be avoided.” 

The original intent of the moisture adjustment procedure was 

apparently to have a standard for deriving properties of dry 

lumber, with no intent of using it to adjust these properties to 

a green moisture content level (Robert Ethington, personal 

communication). It was also felt that for relatively small 

changes in moisture content, a straight line would adequately 

describe property changes around the 12% to 15% expected 

target levels (Robert Ethington, personal communication). 

With this philosophy, Equation (2) predicts no change in 

allowable compressive stress perpendicular to grain. This is 

consistent with the D245 assumption that perpendicular-tograin compressive strength is increased 50% in going from 

green to dry, regardless of the actual dry moisture content 

(that is, no change in compression perpendicular to grain in 

going from one dry level to another). 

In the years following the adoption of D2915–70T, there 

developed within Committee D7 a concern that obtaining the 

precise increases for drying recommended in D245 would 

require implied maximum values of M1 that varied with 

property (Table 7). In 1984, D2915 was modified with an 

explicit statement that “moisture contents M1 greater than 

22% are taken as 22%” and that “M2 must be less than or 

equal to 22%.” This change remains in effect in the current 

version of D2915 (D2915–98). 

The introduction of the 22% maximum value for M1 implies

a major change in the intent of the use of Equation (2). 

Despite the “suggestion” that adjustments for changes in 

moisture content be held to less than a 5% moisture content 

adjustment, the implication is that it is all right to use

Equation (2) to adjust to a green property level. Using the
13 

22% maximum value, current versions of D245 and D2915 

are therefore implied to have major differences for some 

properties when adjusting from green to an average moisture 

content of either 15% or 12%, and the recommendations on 

adjustments for compressive strength perpendicular to grain 

would appear totally inconsistent (Table 7). It may be appropriate to reconsider the intent of D2915 and resolve 

apparent differences with D245 and D1990. 

ASTM D1990

ASTM D1990, Standard Methods for Establishing Allowable Properties for Visually Graded Dimension Lumber 

From In-Grade Tests of Full-Size Specimens, was established in 1991. This standard provides guidelines for sampling, testing, and deriving allowable properties for large 

lumber populations. D1990 is intended to be consistent in 

philosophy with D2915, but it is applicable only to visually 

graded lumber and is therefore more prescriptive than 

D2915. Unlike D2915, methods are also given for estimating allowable properties for untested grade–size combinations and for calculating allowable properties for species 

groups.

ASTM D1990 evolved from the joint U.S.–Canadian InGrade testing program. An overview of this program was 

presented at an ASTM workshop in 1988 (Green and others 

1989). Because some lumber sampled in the In-Grade program was to be tested in the field using portable equipment, 

it was recognized that equations to adjust properties for 

change in moisture content would be critical to the 

conclusions.

In 1979, the existing standardized procedures were reviewed 

and a work plan was formulated to develop new procedures 

(Green 1980). This resulted in two studies being conducted 

in virtually identical fashion (McLain and others 1984, 

Aplin and others 1986). In each study, green 2-in.-thick 

lumber in three commercial grades was obtained from one 

mill (Green and Evans 1989). Each grade of lumber was 

divided into four samples of about 120 specimens; three 

samples were equilibrated to 10%, 15%, and 20% moisture 

content and the fourth sample was tested green. The specimens were tested on edge in one-third-point bending using a 

span-to-depth ratio of 17:1.

As had been assumed by the 25% rule, results of these studies showed that change in strength with change of moisture 

content is a function of lumber quality. Higher quality 

(strength) lumber is more sensitive to change in moisture 

content than is lower quality lumber (Fig. 2). The studies 

also showed that strength does not necessarily increase with 

decreasing moisture content.

Numerous analytical models, including models based on 

ASTM D245 and D2915 principles, were compared to determine how close the corresponding percentiles of the four 

moisture content distributions were to each other after adjustment to a common moisture content. As in the research 

conducted by Wilson (1932), the intersection moisture content, Mp, for each model type was determined analytically 

using a curve fitting technique.3

 The resulting “best” model 

types in terms of versatility and accuracy for MOR were 

quadratic surface models (Green and others 1986, 1988). 

The model chosen to adjust data in the In-Grade program 

was a quadratic surface model with an assumed Mp value 

(called “assumed green value” in D1990) of 23% (Evans

3

Mp is defined as the moisture content at the intersection of a 

horizontal line representing the strength of green wood and 

an inclined line representing the strength of dry wood.

Table 7—ASTM D2915 moisture content adjustment procedures for ≤4-in.-thick lumbera

Coefficients of P2 = P1 – M2 – M1)] 

Increase (%) in allowable property above that of green 

lumber for two average moisture content levelsb

 Max value of M1 15% 12%

Property 1970Tc 1984 D245–99 D2915–98 D245–99 D2915–98 

Modulus of rupture 1.75 0.0333 22.5 22 25 22.9 35 32.7 

Modulus of elasticity 1.44 0.0200 22.0 22 14 14.0 20 20.0 

Tensile strength 1.75 0.0333 22.5 22 25 22.9 35 32.7 

Compression

parallel to grain 

2.75 0.0833 21.0 22 50 63.6 75 90.8 

Shear strength 1.33 0.0167 19.8 22 8 12.1 13 17.3 

Compression perpendicular to grain 1.00 0 NR NR 50 0 50 0 

a

P1 is property measured at moisture content M1; P2, property predicted at moisture content M2;

M1 and M2, moisture contents (%); an b

Assumes maximum value of M1 is 22% moisture content in D2915–98. c

Implied maximum value of M1 to obtain D245 adjustments. Implications of adjusting from green values not valid by intent of

 task force in 1970 (see text). 
14 

and others 1990, Green and Evans 1989, Green and

Evans 1992). 

The development of ASTM D1990 moisture adjustment 

procedures began with the methodology used in the InGrade program. However, concern was raised about the 

complexity of using the model since it required finding the 

roots of a cubic equation (Evans and others 1990). Compromises, such as stipulating the use of “an appropriate 

adjustment procedure” rather than naming a specific adjustment model or using the model in D2915, were also unacceptable to many.

The D1990 task group proposed a simplified version of a 

linear surface model that was accepted by Committee D7. 

The form of the model is 

 P2 = P1 if MOR ≤ 2,415 lb/in2

 (3)

( ) 40

2,415 1 2

1

1

2 1 M M

M

P

P P −













−

− = + if MOR > 2,415 lb/in2

where P1 is property measured at moisture content M1, P2 is

property predicted at moisture content M2, and M1 and M2

are moisture contents (%). 

This adjustment equation was “assumed valid for moisture 

contents between 10% and 23% (assumed green value).” 

The rationale for this decision began by noting that the 

linear surface models fit to the data were almost as good as 

the quadratic surface model (Table 8). Here, the smaller the 

average maximum absolute difference between the model 

and data at a given percentile level the better the fit of that 

model.

In a note to the D1990 task group, Green and Evans developed a simplified version of the linear model; the major 

elements of their original derivation are presented in Appendix F. A lower limit of 10% moisture content was chosen 

because this is the lowest moisture content tested in the 

studies that formed the basis for the models (Green and 

Evans 1989). Limiting the adjustments to moisture content 

above 10% also avoided the regions where the quadratic 

surface model and the simplified model showed substantially 

different trends (Fig. 4). Equation (3) shows the lower limits 

of MOR below which the model assumes that no adjustment 

with change in moisture content is needed. Fitting the model 

on the upper end of the data was also of concern. If the data 

are too sparse, then the model might become too sensitive to 

a few data points. Generally, the 95th percentile of the highest grades was used to set upper limits, beyond which the 

predictive relationship between MOR and moisture content 

was forced to remain parallel to the last valid fitted line. For 

MOR, this upper limit is 9,600 lb/in2

 for green lumber. 

Although seldom used in practice (Evans and others 2000), 

ASTM D1990 allows strength properties (MOR, ultimate 

tensile stress, ultimate compressive stress) of a species to be 

“normalized” relative to the properties of Douglas Fir and 

Southern Pine used to develop the moisture content adjustment models (Green and Evans 1989). The concern that led 

to this option was that the moisture content–strength models 

tended to flatten out and show no change in properties at 

low strength levels. Without some type of adjustment, a 

significant portion of the strength distribution of a much 

weaker species might be below this lower limit. Therefore, 

the concept was to “scale” the data for a lower strength 

species relative to that of Douglas Fir and Southern Pine. 

The equation is given in Appendix F. 

Table 8—Moisture content adjustment models for MOR at 15% moisture content used to select adjustment model

for D1990–91 

 Average maximum absolute difference (lb/in2

) for mean and different percentiles

Species Modela Mean 5th 25th 50th 75th 95th

Douglas Fir No adjustment 2,277 727 1,662 2,201 3,182 4,075 

 Quadratic surface 574 529 664 721 868 973 

 Linear surface, linear 815 681 813 999 1,116 1,197 

 Linear surface, quadratic 823 517 801 1,013 1,170 1,224 

 Linear surface, cubic 826 455 804 1,013 1,187 1,209 

 Simplified model 797 458 801 999 1,116 1,197 

Southern Pine No adjustment 2,593 1,073 1,663 2,586 3,698 4,788 

 Quadratic surface 535 801 759 766 778 893 

 Linear surface, linear 531 1,005 872 833 783 1,037 

 Linear surface, quadratic 549 949 861 824 844 1,189 

 Linear surface, cubic 534 945 875 850 839 1,069 

 Simplified model 535 939 860 819 811 1,009 

a

All models were fit using both Douglas Fir and Southern Pine data and assuming the intersection moisture content to be 23%. 
15 

As the preceding discussion indicates, D1990 procedures 

result in a larger increase in MOR when drying high quality 

lumber and less (or no) effect when drying low quality lumber. Thus, the basic idea that moisture effects on bending 

strength are somehow dependent on lumber quality, as first 

expressed in the 25% rule of Newlin and Johnson, was again 

confirmed. Moreover, although D1990 applies these factors 

only to 5th percentile levels, the research clearly shows that 

within a given grade, the higher the percentile level the 

larger the adjustment (Green and others 1986, 1988, 1990). 

ASTM D1990 also contains “wet use” factors for adjusting 

allowable properties derived from the characteristic values at 

15% moisture content using Equation (3) to green (Table 9). 

The allowable properties derived at 15% moisture content 

and the adjustment factors of Table 9 account for the normal 

shrinkage and swelling of lumber with changes in moisture 

content, as well as the changes in mechanical property values with change in moisture content. The basis of the adjustment factors is discussed in Appendix F. 

Two other decisions that were made during deliberations 

about adopting D1990–91 are worthy of mention. The 

D1990 task group first discussed the application of adjustment procedures developed from tests of 2-in.-thick lumber 

to lumber 4 in. thick. A comparison of the results predicted 

for 2-in.-thick Southern Pine (Green and others 1986) with 

experimental results from 4-in.-thick Southern Pine 

(Gerhards 1968, 1970) does suggest that the MOR of 4-in.-

thick lumber is slightly less sensitive to changes in moisture 

content than is the MOR of 2-in.-thick lumber. However, the 

studies by Gerhards were based on a very limited number of 

specimens. It was the task group’s opinion, confirmed by 

Committee D7, that the differences were not large and that to 

promote simplification of the standard it was appropriate to 

apply the new adjustment model to all 2- to 4-in.-thick

lumber. 

The moisture content on which to base the “characteristic 

value” of D1990–91 was also a topic of discussion. A moisture content level of 15% was chosen because it seemed to 

represent the most common moisture content level for which 

lumber was produced across the United States. After 

D1990–91 was adopted, only the allowable properties at 

15% moisture content were published in the grading manuals 

of the various rules-writing grading agencies and in the 

National Design Specifications (NDS) (AF&PA 1991). 

There was no indication from the research, or in ASTM 

discussions, that the properties at 15% maximum moisture 

content should be discontinued. Rather, this was a decision 

by the industry to simplify the presentation of properties in 

the NDS.

Modulus of Elasticity 

ASTM D245 

Early discussions did not recognize any increase in flexural 

modulus of elasticity (MOE) as a result of seasoning. In 

1957, provisions were added to ASTM D245 (D245–57T) 

for a 10% increase in MOE for dry lumber of all grades of 

joist and plank and of timbers. For 1- and 2-in.-thick lumber 

that was planed and used at ≤15% moisture content, the 

allowable increase as a result of seasoning was also 10%. 

We could find no documentation as to exactly why the MOE 

adjustments were added in 1957. As discussed in the section 

on MOR, more highly engineered systems were beginning to 

be used, 2-in.-thick lumber was gaining in usage, and work 

was being conducted on shrinkage–moisture content relationships as part of the effort to standardize lumber dimensions throughout the United States (Wood 1964). Thus, 

perhaps there was a growing need to have a more precise 

MOE value for dry lumber. Certainly, the data available at 

the Forest Products Laboratory and elsewhere would have 

justified taking an increase in MOE for dry lumber (Jessome 

1971, Wood 1953) (App. B).

Figure 4—Effect of moisture content on bending

strength of lumber as predicted by quadratic surface

model and ASTM D1990 model.

Table 9—Modification of allowable property 

values in ASTM D1990 when wood moisture

content exceeds 19% 

Property Adjustment factor 

Fb < 1,150 lb/in2 1.0 

Fb > 1,150 lb/in2 0.85 

Ft 1.0 

Fc < 750 lb/in2

 1.0 

Fc > 750 lb/in2

 0.8 

MOE 0.9 
16 

In the 1964 revision of D245, an increase of 10% was still 

allowed for dry lumber of all thicknesses. For 1- and 2-in.-

thick material dressed and used at a maximum moisture 

content of 15% or less, the allowable increase was raised to 

20%. However, this factor was to be used in place of, not in 

addition to, the general 10% increase for all thicknesses. For 

1- and 2-in.-thick lumber dressed and used at a maximum 

moisture content of 19%, an increase of 14% was allowed.

ASTM D245–69 extended the 20% increase for lumber 

manufactured and used at 15% and the 14% increase for 

lumber at 19% maximum moisture content to all lumber 4 in. 

or less in thickness (Table 6). The standard reduced the 

increase allowed for dry lumber of all widths in D245–67T 

to a 2% increase for lumber >4 in. thick based on net size at 

time of manufacture, providing the lumber was seasoned to a 

“substantial” depth before full load was applied. These are 

the moisture adjustment factors still given in the current 

edition of D245 (D245–98). 

ASTM D2915 

As previously discussed for MOR, D2915–70T made provisions for adjustments to MOE for changes in moisture content that were consistent with those of D245 (Eq. (2),

Table 7). The explicit addition of 22% moisture content as

a maximum value for M1 in D2915–84 did not alter this

comparison. 

ASTM D1990 

As discussed for MOR, moisture content adjustment procedures for MOE in ASTM D1990 were developed from studies on Douglas Fir and Southern Pine (McLain and others 

1984; Aplin and others 1986; Green and others 1986, 1988; 

Green and Evans 1989). Unlike the strength models in 

D1990, the model for MOE developed as part of the InGrade Program (Green and others 1989) was adopted

directly into D1990–91. The model is a constant percentage 

adjustment model of the following form (Fig. 5): 

( )

( )



 





−

− =

1

2

2 1 1.857 0.0237

1.857 0.0237

M

M

P P (4) 

where P1 is property measured at moisture content M1, P2 is

property predicted at moisture content M2, and M1 and M2

are moisture contents (%). 

This equation is assumed to be valid from 10% to 23% 

moisture content. The D1990 model predicts changes in 

MOE that generally agree with those of D245–98 (Fig. 5). 

ASTM D1990 also contains “wet use” factors for adjusting 

allowable properties derived from the characteristic values at 

15% moisture content using Equation (4) to green (Table 9). 

The allowable properties derived at 15% moisture content 

and the adjustment factors of Table 9 account for the normal 

shrinkage and swelling of lumber with changes in moisture 

content, as well as the changes in mechanical property

values with change in moisture content. The basis of the 

adjustment factors (Table 9) is discussed in Appendix F. 

Ultimate Compressive Stress 

Parallel to Grain 

ASTM D245 

As with MOR, ultimate compressive stress (UCS) parallel to 

grain increased with each of the three exposure conditions 

given in D245–26T. Like MOR, the compressive stresses 

were derived from green clear-wood mean values and were 

to be used without regard to the actual moisture content of 

the piece. These green values were listed for the continuously dry exposure condition and reduced for the occasionally wet and usually damp or wet condition to avoid too 

frequent removals because of possible decay hazard. These 

recommendations were not modified through D245–30. 

As previously discussed in the section on MOR, D245–36T 

references Misc. Pub. 185 (Wilson 1934) for the development of working stresses. Without discussion, Misc.

Pub. 185 states that for material ≤4 in. thick that is to be 

used under continuously dry conditions, the strength ratio for 

stress in compression parallel to grain is first increased by 

one-half its excess over 50%. Thus, the 25% rule is extended 

to parallel-to-grain compression for joist and plank. 

According to ASTM D245–49T, studies had confirmed that 

increases in strength of timbers are largely offset by drying 

degrade. As in earlier versions of the standard, no increase

in compression was allowed for timbers ≥ 4 in. thick; the

standard again stated that the 25% rule was applicable to

Figure 5—Effect of moisture content on modulus of

elasticity of lumber in bending as predicted by the 

D1990 and ASTM D245 bending MOE models. 
17 

2- to 4-in.-thick lumber stressed as short columns.

Supplement 2 to Misc. Pub. 185 (FPL 1948) indicates that 

the increase is not applicable to long columns in the Euler 

class. Table IX of the standard also noted that for parallel-tograin compression in joist and plank, “modifications in 

current commercial practice is accomplished by liberalizing 

defects in grade rather than by increasing working stresses.” 

ASTM D245–57T allowed a 10% increase for >4 in. thick 

lumber. For 2- to 4-in.-thick lumber, the 25% rule was retained, but an additional 10% increase could be taken. This 

latter increase was independent of grade. For 1- to 2-in.-

thick lumber manufactured and used at a maximum moisture 

content of not more than 15%, D245–57T allowed working 

(allowable) stresses in compression parallel to grain to be 

increased 3/8 (37.5%) over stresses for green lumber. However, these increases were in place of, not in addition to, 

seasoning increases resulting from the 25% rule. The footnote to table IX of the standard was retained for parallel-tograin compression of joist and plank, but stipulated that 

“modifications in seasoning in joist and plank may be accomplished either by liberalizing grade limitations or by 

increasing working stresses.” 

ASTM D245–64T retained the provisions of D245–57T but 

added an adjustment for 1- and 2-in.-thick lumber manufactured and used at a maximum moisture content of 19%. For 

compression parallel to grain, the increase over the green 

strength was 22%. Again, this increase was in place of, and 

not in addition to, other increases. The note on liberalizing 

grade limitations was retained. 

The 10% increase for dry lumber ≥4 in. thick without regard 

to grade was continued in ASTM D245–69. For lumber

≤4 in. thick, D245–69 introduced the strength ratio independent factors still used in the current (2000) edition of 

D245 (Table 6). The drying factor at 15% maximum moisture content more than doubled, apparently because of the 

adoption of an average ratio based on clear wood. In addition, as noted in previous discussions of properties, for the 

first time these increases could not be more than the drygreen ratio from compression tests on clear wood specimens. 

These ratios were not available in D2555 until the 1970 

version. Also, the note on liberalizing grade limitations in 

joist and plank was dropped from the standard. 

ASTM D2915 

ASTM D2915-70T was established to provide a method of 

assessing the appropriateness of assigned properties. As 

discussed in detail in the section on modulus of rupture, it 

was “suggested” in the standard that the moisture adjustment 

procedures reproduced in Equation (2) of this paper not be 

used for more than a 5% moisture content change. There was 

apparently no intent that this equation be used to adjust 

properties to (or from) green moisture content. However,

the addition of a maximum value of 22% moisture content

in D2915–84 could imply that such an adjustment were 

possible. The moisture content adjustment procedures of

D2915–84 are unchanged in the current version (D2915–

98); the standard continues to suggest the limitation on a 5% 

maximum moisture content change. Table 7 compares adjustments from green to 15% and 12% average moisture 

content by current procedures given in D245 and D2915. 

These procedures could imply a significant difference in

the change in predicted ultimate compressive stress parallel 

to grain. 

ASTM D1990 

As in the case of MOR, studies were conducted and models 

developed to predict changes in UCS parallel to grain associated with changes in moisture content (Barrett and Lau 

1994). As with MOR, these models were judged too complex (Evans and others 1990), and the model chosen for 

ASTM D1990 was a simplified linear surface model of the 

following form (Fig. 6): 

 P2 = P1 if UCS ≤ 1,400 lb/in2

 (5) 

( ) 2 1

1

1

2 1 34

1,400

M M

M

P

P P −













−

− = + if UCS > 1,400 lb/in2

where P1 is property measured at moisture content M1, P2 is 

property predicted at moisture content M2, and M1 and M2

are moisture contents (%).

As discussed for MOR, the lower limit of the model, below 

which UCS is assumed independent of moisture content, is 

1,400 lb/in2

. The upper limit, above which the slope of the 

relationship between UCS and moisture content (UCS–MC) 

Figure 6—Effect of moisture content on compressive

strength of lumber parallel to grain as predicted by

quadratic surface model and ASTM D1990 model. 
18 

is held constant, is 4,400 lb/in2 for green lumber. The “normalization” option discussed for MOR is also available for 

UCS (App. F). Equation (5) is assumed to be valid from 

10% to 23% moisture content. 

ASTM D1990 also contains “wet use” factors for adjusting 

allowable properties derived from the characteristic values at 

15% moisture content using Equation (5) to green (Table 9). 

The allowable properties derived at 15% moisture content 

and the adjustment factors of Table 9 account for the normal 

shrinkage and swelling of lumber with changes in moisture 

content, as well as the changes in mechanical property values with change in moisture content. The basis of the adjustment factors (Table 9) is discussed in Appendix F. 

Ultimate Tensile Stress

Parallel to Grain 

ASTM D245 

Until the late 1950s, testing of full-size lumber specimens in 

ultimate tensile stress (UTS) parallel to grain was thought to 

be impossible because of the difficulty in gripping the 

specimen without causing premature failure near the grips. 

The ASTM D143 necked-down specimen for small clear 

members showed very high tensile strength for such specimens, but this was believed to be representative of the 

strength of large members. In fact, so little data were available that parallel-to-grain tensile strength of clear wood is 

not even discussed in the 1935 edition of the Wood Handbook. Given the familiar model of stresses in a bending 

specimen and the observation that in almost all bending tests 

of full-size lumber catastrophic failure occurred on the tensile side, it was assumed that MOR would be a reasonable 

measure of tensile strength. Thus, for the first half of the 20th

century, no tests of lumber in tension were conducted. Researchers assumed that the allowable tensile stress equaled 

the allowable bending stress for all conditions of grade, 

moisture content, and other factors that affect strength. 

ASTM D245–26T states that for “direct tension, the same 

values as for extreme fiber stress in bending may be used.” 

Nothing is specifically stated about moisture adjustments to 

tensile strength, but presumably these would be the same as 

those for bending. The same statement is made in D245–27. 

This statement would imply that the 25% rule applicable to 

bending members ≤4 in. thick would also be applicable to 

tensile strength. However, this assumption is not specifically 

stated in the first version of D245 (D245–26T) or later in 

Misc. Pub. 185, nor is the effect of moisture content on 

tensile strength discussed in the two supplements to Misc. 

Pub. 185. Moreover, moisture content adjustment to tensile 

strength is not stated in D245–49. 

ASTM D245–57T specifically extends the use of the 25% 

rule to UTS. Although the technical justification for linking 

the moisture adjustments for tension with those for bending 

is not apparent, this change was consistent with the historic 

practice of deriving tensile strength from bending strength. 

Unpublished clear wood data available at the time (see 1974 

and later editions of the Wood Handbook, which summarize 

clear wood tensile strength based on historical data) would 

have suggested an average increase of about 13% in the UTS 

of softwood species dried to 12% average (15% maximum) 

moisture content. 

ASTM D245–69 continued the practice of assuming that 

bending strength is a conservative estimate of tensile 

strength and introduced the percentage increases currently 

(D245–99) allowed for lumber ≤4 in. thick manufactured 

and used at moisture content less than 15% or 19%

(Table 6). Again, no test data appear to have been used to 

justify allowing the increases in MOR to be applied to UTS. 

Although ASTM D2555 does not contain dry-green ratios 

for tensile strength parallel to grain, UTS was assumed to be 

limited by the same percentage as was MOR. 

ASTM D2915 

ASTM D2915-70T was established to provide a method of 

assessing the appropriateness of assigned properties. As 

discussed in detail in the section on modulus of rupture, it 

was “suggested” in the standard that the moisture adjustment 

procedures reproduced in Equation (2) of this paper not be 

used for more than a 5% moisture content change. There was 

apparently no intent that this equation be used to adjust 

properties to (or from) green moisture content. However, the 

addition of a maximum value of 22% moisture content in 

D2915–84 could imply that such an adjustment were possible. The moisture content adjustment procedures of D2915–

84 are unchanged in the current version (D2915–98); the 

standard continues to suggest the limitation on a 5% maximum moisture content change. Table 7 compares adjustments from green to 15% and 12% average moisture content 

by current procedures given in D245 and D2915. These 

procedures could imply an approximate 2% difference in the 

change in predicted UTS parallel to grain. 

ASTM D1990 

In support of the In-Grade program, a study was conducted 

on the effect of moisture content on the UTS of lumber 

parallel to grain of Douglas Fir dimension lumber (Green 

and others 1990). Green lumber in two commercial grades 

was obtained from one mill. Each grade of lumber was 

divided into four samples of about 120 specimens; three 

samples were equilibrated to 10%, 15%, and 20% moisture 

content and the fourth sample was tested green. As in the 

case of MOR, D1990 moisture content adjustments for UTS 

evolved from a quadratic surface model developed from the 

study used to adjust In-Grade data (Evans and others 1990).

As with MOR, the concern was that the quadratic model 

predicted loss in strength with drying below approximately 
19 

13% to 15% moisture content and that the model was too 

complex for use in the standard.

The model chosen for ASTM D1990 was again a simplified 

linear surface model:

P2 = P1 if UTS ≤ 3,150 lb/in2

 (6) 

( ) 2 1

1

1

2 1 80

3,150 M M

M

P P P −













−

− = + if UTS > 3,150 lb/in2

where P1 is property measured at moisture content M1,

P2 is property predicted at moisture content M2, and

M1 and M2 are moisture contents (%).

The performance of this model, as compared with the more 

precise linear surface model, can be seen in Table 10 and is 

plotted in Figure 7. As with MOR, the model was limited to 

moisture contents above 10% because this was the lower 

limit of the data on which the model was based (Green and 

Evans 1989). As discussed for MOR, the lower limit of the 

model, below which UTS is assumed independent of moisture content, is 3,150 lb/in2

. The upper limit, above which 

the slope of the UTS–MC relationship is held constant, is 

8,420 lb/in2

 for green lumber. As presented in the standard, 

Equation (6) is applicable to the lower tails of lumber 

strength distribution. As can be seen from Table 10, it may 

not be appropriate for adjusting UTS values at higher percentile levels. At the mean, the maximum absolute difference 

between the simplified model of Equation (6) and that of the 

more precise quadratic surface model is 128 lb/in2

 when 

adjusting from green to 12% moisture content; the quadratic 

surface model is more precise by about 36%. Thus, the 

ASTM model is appropriate only for adjusting lower tail 

properties of data from visual grades of lumber. The

normalization option, as discussed for MOR, is also available for UTS (App. F). 

ASTM D1990 also contains “wet use” factors for adjusting 

allowable properties derived from the characteristic values at 

15% moisture content using Equation (6) to green (Table 9). 

The allowable properties derived at 15% moisture content 

and the adjustment factors of Table 9 account for the normal 

shrinkage and swelling of lumber with changes in moisture 

content, as well as the changes in mechanical property values with change in moisture content. The basis of the adjustment factors (Table 9) is discussed in Appendix F. 

Compressive Strength 

Perpendicular to Grain 

ASTM D245 

As previously discussed for MOR, ASTM D245–27 provides working stresses at three moisture content levels: 

continuously dry, occasionally wet, and usually damp or 

wet. However, as previously discussed, these changes in 

properties were a response to decay hazard and not a change 

in compression perpendicular to grain strength values resulting from change in moisture content.

Also, as previously discussed in the section on MOR, ASTM 

D245–36T references Misc. Pub. 185 for a discussion of the 

development of working stresses. No specific changes related to moisture content effects on compression perpendicular to grain were made in the original publication or in the 

first supplement. However, the 1935 edition of the Wood

Handbook does recommend a 30% reduction for members 

that will be continuously wet in service. Supplement 2 to 

Misc. Pub. 185 (FPL 1948) notes the following:

The evaluation of fiber stress at proportional limit in compression perpendicular to grain is based largely on test 

specimens with the direction of growth rings, either parallel 

or perpendicular to the direction of applied force, while in 

Table 10—Moisture content adjustment models for UTS at 

15% moisture contenta

 used to select adjustment models for 

ASTM D1991–91 

 Average maximum absolute difference (lb/in2)

Model Mean 5th 25th 50th 75th 95th

No adjustment 617 545 434 582 789 1,504 

Quadratic surface 332 482 272 302 634 1,077 

Linear surface, linear 460 553 385 452 633 1,172 

Linear surface, cubic 460 519 349 461 641 1,155 

Simplified model 460 541 402 450 626 1,172 

a

Based on data for Douglas Fir lumber.

Figure 7—Effect of moisture content on tensile 

strength of lumber parallel to grain as predicted by 

quadratic surface model and ASTM D1990 model. 
20 

the majority of structural timbers, the rings are at some intermediate angle. In view of the fact that bearing at an angle 

to the rings may be substantially less than those with rings 

parallel or perpendicular, the existing design values appear 

to be amply liberal, and no increase is recommended except

for material which will be dry in service. (FPL 1948)

Supplement 2 also states “it is recommended that the basic 

stress values in compression perpendicular to grain...be 

increased 20% for seasoned material used under continuously dry conditions. Material surface dry when installed 

may be given stress values 10% higher....” Thus, a 20% 

increase was allowed if lumber was fully seasoned, but the 

increase was limited to 10% if only the surface of the lumber 

was dry.

Table X of D245–49T states that adjustments are to be made 

to perpendicular-to-grain compression for seasoning, but the 

standard includes no provisions for making these adjustments. Footnote c of table X states that “modifications of 

stresses in compression perpendicular to the grain for seasoning or moisture content are now under further study at 

the U.S. Forest Products Laboratory.”

The next edition of ASTM D245 was D245–57T. Table IX 

of this version again states that seasoning adjustments are to 

be made and indicates that these increases apply to all sizes 

of lumber (that is, both dimension lumber and timbers). 

Paragraph 16f states that “working stresses in compression 

perpendicular to the grain may be increased by 50% above 

the value in table VIII (clear wood basic stresses) for lumber 

that will be continuously dry in use.” This increase applied 

to lumber of all thicknesses. We have been unable to document the basis for this adjustment. Some information on 

research available on the effect of moisture content on 

strength in compression perpendicular to grain is given in 

Appendix G.

ASTM D245–69 does not provide an increase because of 

seasoning for compression perpendicular to grain of lumber 

5 in. and more in thickness. The standard does provide a 

50% increase in compression perpendicular to grain for 

lumber ≤4 in. thick regardless of the degree of seasoning. A 

footnote to table 8 of D245–69 states the following:

The increase in compression perpendicular to grain is the 

same for all degrees of seasoning below fiber saturation 

since the outer fibers which season rapidly have the greatest 

effect on this strength property regardless of the extent of 

the seasoning of the inner fibers. (ASTM D245) 

The reasoning for the 50% increase was apparently that it 

was conservative relative to the dry-green ratio of small 

clear specimens (Robert Ethington, personal communication), which averages about 2.0 for softwoods and hardwoods (App. E). The moisture factors for compression

perpendicular to grain of D245–69 (Table 6) still appear in 

the current version of the standard (D245–99). 

ASTM D2915 

ASTM D2915–

(Table 7). This has the effect of making the dry values equal 

to the green values, yet ASTM D245 allows a 50% increase 

regardless of the degree of drying. As discussed for MOR, 

this may be an example where the original intent of those 

that first established this standard was lost in revisions. If the 

original intent was simply to provide an equation for making 

changes in compression perpendicular to grain resulting 

from small changes in moisture content (later defined as

+5%), then assuming a factor of 1.0 made some sense 

(Robert Ethington, personal communication), especially if 

there were originally no intent to provide for adjusting values from dry to green (or vice versa). ASTM D245–70 

assumed that a factor of 1.5 should be used to increase compression perpendicular to grain from green to dry, for all 

levels of dryness. Thus, the assumption that the factor was 

1.0 between one dry level and another was consistent with 

D245. However, by 1984, when the equations were changed 

slightly to make a consistent assumption with regard to an 

assumed green moisture content, this original intent would 

seem to be forgotten. In the current form of the standard, 

users are not specifically prevented from making adjustments for moisture content changes greater than 5%. Thus, 

the apparent differences between the adjustments shown in 

D245 and D2915 can lead to confusion in the application of 

these standards. 

ASTM D1990 

Compressive strength perpendicular to grain is not determined in ASTM D1990. Rather, it is referenced to D245. 

Shear Strength Parallel to Grain 

ASTM D245 

Prior to 1949, ASTM D245 included only one allowable 

shear strength for all moisture content levels, and no decrease was taken for decay hazard in the occasionally wet 

and usually wet service conditions. However, larger shake 

and checks were allowed for dry material than for green 

material in Circular 295 (Newlin and Johnson 1923) and in 

D245–26T. Thus, changes in performance because of seasoning were accounted for not by increasing the allowable 

shear strength but by changing the grade description for dry 

material, a practice to be followed for many years. The ratio 

of permitted shake for green and dry material is not a

constant factor in the tables, and no further guidance is given 

in these two documents. The 1930 edition of D245 retains 

one shear value, but it adds the explicit statement that “shake 

in green material is assumed to reduce shearing stress in 

direct proportion to its extent. A greater amount of shake is 

permitted in seasoned material, made up for by the increased 

resistance of the remaining cross-section when seasoned.”
21 

As previously discussed in the section on MOR, ASTM 

D245–36T references Misc. Pub. 185 (Wilson 1934) for a 

discussion of the development of working stresses. This 

publication provides separate strength ratio tables for 

checks, shake, and splits for both green and dry lumber. The 

strength ratio tables for dry lumber are approximately 9/8 

those for green lumber. Forest Products Laboratory report 

GTR–23 (Ethington and others 1979) identifies Misc. 

Pub. 185 (Wilson 1934) as the first to recommend an increase in working stresses in shear for dry material. As 

previously discussed, this is not strictly true, but Misc.

Pub. 185 was the first to suggest a specific relationship 

between green and dry shear values. We did not find an 

explicit statement of a 9/8 factor in Misc. Pub. 185. Rather, 

the factor was deduced by comparison of the formula for 

deriving the permissible size of shake given in footnotes (a) 

and (b) to table 5 of Misc. Pub. 185: 

Sgreen = (100 − Rgreen)/100

 (7) 

Sdry = (900 − 8Rdry)/900

where S is permissible size of shake as a fraction of nominal 

width and R is strength ratio (%). 

Equating the two values for S in Equation (7) yields 

Rdry = (9/8) Rgreen

Misc. Pub. 185 does not explain the data, or logic, behind 

the 9/8 increase. A factor of 9/8 (or 1.125) is considerably 

less than the average value of the dry-green ratio obtained 

from block shear tests on small clear specimens. It seems 

likely that the 9/8 factor was based on differences between 

dry and green shear strength of beam specimens that failed 

in shear (App. H). 

ASTM D245–49T was the first revision of the standard since 

1936. It included the dry and green strength ratio tables of 

Misc. Pub. 185 and thus the 9/8 factor for all thickness of 

dry lumber. Footnote b of table X in D245–49 noted that 

“modifications for seasoning (for joist and plank) in current 

commercial practice is accomplished by liberalizing defects 

in grade rather than increasing working stresses.” 

In ASTM D245–57T, the 1/8 increase in the strength ratios 

for shake in dry lumber of all sizes was retained, but the 

footnote (now to table IX of the standard) was replaced by 

“modifications for seasoning in joist and plank may be accomplished either by liberalizing grade limitations or by 

increasing working stresses.” Separately, D245–57T also 

stated the following:

Working stresses for all grades of 1- or 2-in. (nominal) 

lumber that is dressed at 15% or lower moisture content 

and is fabricated and used under conditions where that 

moisture content is not exceeded, may be increased...by 

one-eighth in horizontal shear.... (ASTM D245)

ASTM D245–64T retained the provisions of D245–57T and 

added an 8% increase in horizontal shear with 1- or 2-in.-

thick lumber if the maximum moisture content were 19% 

and the lumber were used under continuously dry conditions. 

In D245–69, the footnote to the table (now table 7) vanished, 

as did the strength ratio table for shake or splits in dry lumber. A new table showed allowable increases in allowable 

stress for seasoning for lumber ≤4 in. thick (Table 6). The 

1/8 increase for lumber with maximum moisture content of 

15% was rounded to 13%, and the 8% increase for lumber 

with maximum moisture content of 19% was maintained. 

The restriction that “the increase for 15% maximum moisture content shall not exceed the ratio of dry to green clear 

wood strength shown in...D2555” was added to the standard. Furthermore, the standard states that “where ratios in 

D2555 are less than above, proportionate reductions shall be 

made in lumber at 19% maximum moisture content.” No 

factors for seasoning are given for lumber 5 in. or more in 

thickness. These adjustments are retained in the current 

version of the standard (D245–99).

ASTM D2915 

As with other properties, adjustments to increase shear 

properties of dimension lumber consistent with those of 

ASTM D245 were provided in D2915–70T (Eq. (2),

Table 7). In 1984, modification of D2915 to assume lumber 

moisture content was no higher than 22% for all properties 

resulted in a higher increase for shear than was provided by 

D245 (Table 7). The ASTM committee apparently decided 

that these differences were justified. However, as discussed 

for MOR and compression perpendicular to grain, this may 

have also been an instance where the original intent of the 

1970 version of the standard was lost to future generations 

of ASTM members. 

ASTM D1990 

Shear strength parallel to grain is determined by reference

to ASTM D245.

Summary of Changes to 

Standards

The chronology of changes to ASTM standards presented in 

this report particularly focuses on ASTM D245 because it is 

the oldest standard for adjusting the allowable properties of 

lumber for changes in moisture content. ASTM D245 bases 

allowable properties on tests of small clear specimens, but 

procedures for adjusting lumber properties for change in 

moisture content are not always based on clear wood data. 

Table 11 summarizes changes to moisture content adjustment procedures in D245. This table enables the reader to 

follow potential logical changes over the years and to see 
22 

Table 11—Summary of changes in adjustment procedures to allowable properties in ASTM D245 as a result of moisture 

content changesa

Nominal thickness of lumberb

Property Edition of standard >4 in. 2 to 4 in. 1 to 2 in. 

MOR 1926T None 25% rule — 

 1957T None 25% rule or 25% if ≤15% MC 

 1964T None 25% rule or 15% if ≤19% MC 

 or 25% if ≤15% MC 

 1969 None 35% if ≤15% MC same as for 2 to 4 in. 

 25% if ≤19% MC same as for 2 to 4 in. 

MOE 1926T None None — 

 1957T 10% 10% or 10% if ≤15% MC 

 1964T 10% 10% or 14% if ≤19% MC 

 or 20% if ≤15% MC 

 1969 2% 14% if ≤19% MC same as for 2 to 4 in. 

 20% if ≤15% MC same as for 2 to 4 in. 

UCS 1926T None None –– 

 1936T None 25% rule –– 

 1957T 10% 25% rule + 10% or 37.5% if ≤15% MC 

 1964T 10% 25% rule + 10% or 37.5% if ≤15% MC 

 or 22% if ≤19% MC

 1969 10% 75% if ≤15% MC same as for 2 to 4 in. 

 50% if ≤19% MC same as for 2 to 4 in. 

UTS 1926T None 25% rulec

 –– 

 1957T None 25% rule or 25% if ≤15% MC 

 1964T None 25% rule or 15% if ≤19% MC 

 or 25% if ≤15% MC 

 1969 None 35% if ≤15% MC same as for 2 to 4 in. 

 25% if ≤19% MC same as for 2 to 4 in. 

C–perpd 1926T None None –– 

 1937e

 20% if thoroughly dry 20% if thoroughly dry –– 

 10% surface dry 10% surface dry –– 

 1949T NR NR NR 

 1957T 50% 50% same as for 2 to 4 in. 

 1969 None 50% same as for 2 to 4 in. 

Shear 1926T (f) (f) — 

 1957T (f) or 12.5%f or 12.5% if ≤15% MC 

 1964T (f) or 12.5%f or 12.5% if ≤15% MC 

 or 8% if ≤19% MC 

 1969 None 13% if ≤15% MC same as for 2 to 4 in. 

 8% if ≤19% MC same as for 2 to 4 in. 

a

In some periods, it was possible to liberalize the grade description for dry lumber rather than increase the allowable property.

 Beginning in 1969, adjustments could not be greater than the dry/green ratio for the species as given in ASTM D2555.

b

NR designates no recommendations provided. 

c

Beginning with D245–26T, it was assumed that UTS was equal to MOR. It is assumed that the 25% rule applied to UTS,

 but this was not stated. 

d

Compression perpendicular to grain. 

e

ASTMD245–37 changed automatically with modifications to Misc. Pub. 185. Such a change occurred with Supplement 2 

 (FPL 1948) (see text). 

f

From 1926 through 1933, the increase in strength ratio for shake in dry lumber varied somewhat with width. Beginning with

 1936T, the increase in strength ratio for dry lumber was 9/8 (a 1/8 or 12.5% increase). 
23 

how these changes were made for each of the six properties 

currently used in design specifications. The alternative of 

liberalizing the grade description instead of increasing a 

specific allowable property is included in Table 11 only as a 

footnote. As discussed in the text, this option was historically taken by grading agencies, especially with respect to 

shear strength. Also note that D245 is the only ASTM standard that contains provisions for adjusting the properties of 

≥4-in.-thick lumber for changes in moisture content. For 

timbers, these provisions have remained unchanged for at 

least 30 years. 

This report also includes discussion of the development of 

two relatively new standards for deriving allowable lumber 

properties based on tests of lumber containing defects and 

naturally occurring growth characteristics. These standards 

are D2915 (first adopted in 1970) and D1990 (first adopted 

in 1991). Table 12 presents a simplified summary of how the 

current versions of these standards handle moisture adjustment procedures for ≤4-in.-thick lumber. Because the D2555 

dry-green ratios were adopted as an “override” in D245 in 

1969, Table 12 also includes average values from these 

results for softwood species as points of comparison. In 

D1990–97, the adjustments for MOR, UTS, and UCS depend upon the initial green strength of the lumber. Thus, for 

green lumber with MOR of 6,000 lb/in2

, the property would 

be increased 39% when the value was adjusted to an average 

moisture content of 12%, while a lower quality piece with 

MOR of 2,000 lb/in2

 would get no adjustment. 

Recommendations

As the text indicates, the procedures in D245, D2915, and 

D1990 show some very significant differences. As D2915 

and D245 evolved, some of their apparent differences may 

have resulted from ASTM task group members reading 

inferences into D2915 formulas in a manner not intended by 

the original framers of this standard. Some differences between D1990 and D245 are the result of failure to update 

D245 in light of more recent information on the effect of 

moisture content on the properties of 2- to 4-in.-thick dimension lumber. Note that differences also exist between the 

standards in how other adjustment procedures are handled.

The challenge is not to simply use the same adjustment 

procedures in all three standards, but rather to have each 

standard produce equivalent allowable properties for the 

same material. Although they have different objectives, both 

D2915 and D1990 start with test data generated from tests of 

full-size structural lumber. Thus, adjustment procedures in 

these two standards would seemingly be the easiest to reconcile, and perhaps this is where the first attempts should be 

made. Once consensus is reached on adjustment procedures 

in D2915 and D1990, the greater challenge of modifying 

D245 might be somewhat easier. D245 presents a greater 

challenge because it starts with test data from small clear 

specimens. There are many alternatives to modifying this 

standard so that it produces results consistent with the other 

two standards. Which approach is the best from a technical 

perspective or which would be the easiest for reaching a 

consensus opinion is not clear.

Table 12—Ratio of property at 12% moisture content to that of green dimension lumber by various

ASTM standardsa

Standard MOR UTS MOE UCS Shear C–perp 

D245–99 1.35 1.35 1.20 1.75 1.13 1.50 

D2915–98b 1.33 1.33 1.20 1.91 1.17 1.00 

D2555–98c

 1.69 — 1.25 1.99 1.47 2.03 

D1990–97 1.18 — — 

6,000 lb/in2

 1.39 1.09 1.18 NA — — 

5,000 lb/in2

 1.33 1.07 1.18 NA — — 

4,000 lb/in2

 1.26 1.04 1.18 1.65 — — 

3,000 lb/in2

 1.13 1.00d 1.18 1.53 — — 

2,000 lb/in2

 1.00d 1.00d 1.18 1.30 — — 

1,000 lb/in2

 1.00d 1.00d 1.18 1.00d — — 

a

NA indicates that the green value is higher than the applicable range of adjustment (9,600 lb/in2 for MOR,

 8,400 lb/in2

 for UTS, and 4,400 lb/in2 for UCS); significant error may occur. Arrow ( 

 property under D1990–97 may vary with initial green strength. Refer to strength values listed in the table. 

b

Adjusting over this moisture content range may not be within the intent of the standard (see text). 

c

D2555 values are the average for all softwood species, for small clear specimens (App. E). 

d

Adjustment is 1.0 below 2,400 lb/in2 for MOR, 3,150 lb/in2 for UTS, and 1,400 lb/in2 for UCS. 
24 

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Wilson, T.R.C. 1932. Strength–moisture relations for wood. 

Tech. Bull. 282. Washington, DC: U.S. Department of

Agriculture, Forest Service. 

Wilson, T.R.C. 1934. Guide to the grading of structural 

timbers and determination of working stresses. Miscellaneous Pub. 185. Washington, DC: U.S. Department of

Agriculture.

Wilson, T.R.C. 1940 (corrected December 1943). Guide to 

the grading of structural timbers and determination of working stresses. Supplement to USDA miscellaneous pub. 185. 

Memo R1225. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 

Wood, L.W. 1953. Increase of strength with drying of

2 inch lumber. Memorandum to R.P.A. Johnson (unpublished). Madison, WI: U.S. Department of Agriculture, 

Forest Service, Forest Products Laboratory. 

Wood, L.W. 1964. History of yard lumber size standards. 

Unnumbered rep. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 

Youngs, R.L. 1957. The perpendicular-to-grain mechanical 

properties of red oak as related to temperature, moisture 

content, and time. Res. Rep. 2079. Madison, WI: U.S.

Department of Agriculture, Forest Service, Forest Products 

Laboratory.
27 

Appendix A—First Consensus 

Recommendations for Strength 

of Bridge and Trestle Timbers 

Recommendations for timber strength were presented in 

1895 by a committee of the American International Association of Railway Superintendents of Bridges and Buildings 

(Berg and others 1907). The committee’s report, reproduced 

in part here, included a summary of all available property 

data collected from many sources from about 1870 to 1895 

as well as design equations. 

Report of Committee on “Strength

of Bridge and Trestle Timbers” 

 Your committee appointed to report on “Strength of Bridge and 

Trestle Timbers, with special reference to Southern Yellow Pine, 

White Pine, Fir, and Oak,” desire to present herewith, as part of 

their report, the very valuable data compiled by the chairman of the 

committee, relative to tests of the principal American bridge and 

trestle timbers and the recommendations of the leading authorities 

on the subject of strength of timber during the last twenty-five 

years, embodied in the appendix to this report and tabulated for 

easy reference in the accompanying tables I to IV. 

 The uncertainty of our knowledge relative to the strength of 

timber is clearly demonstrated after a perusal of this information, 

and emphasizes, better than long dissertations on the subject, the 

necessity for more extensive, thorough, and reliable series of tests, 

conducted on a truly scientific basis, approximating, as nearly as 

possible, actual conditions encountered in practice. 

 The wide range of values recommended by the various recognized authorities is to be regretted, especially so when undue influence has been attributed by them in their deductions to isolated 

tests of small size specimens, not only limited in number, but 

especially defective in not having noted and recorded properly the 

exact species of each specimen tested, its origin, condition, quality, 

degree of seasoning, method of testing, etc. 

 Great credit is due to such investigators and experimenters as 

Professors G. Lanza, J.B. Johnson, H.T. Bovey, C.B. Wing, and 

Messrs. Onward Bates, W.H. Finley, C.B. Talbot, and others, for 

their experimental work and agitation in favor of full size tests. 

Professors G. Lanza, R.H. Thurston, and William H. Burr have 

contributed valuable treatises on the subject of strength of timber. 

The extensive series of small and full size United States government tests, conducted in 1880 to 1882, at the Watertown arsenal, 

under Col. T.T.S. Laidley, and more recently the very elaborate and 

thorough timber tests being conducted by the United States Forestry Division under Dr. B.E. Fernow, chief, and Professor J.B. 

Johnson of Washington University, St. Louis, afford us to-day, in 

connection with the work of the above-mentioned experimenters, 

our most reliable data from a practical standpoint. 

 The test data at hand and the summary criticisms of leading 

authorities seem to indicate the general correctness of the following 

conclusions.

 1. Of all structural materials used for bridges and trestles timber 

is the most variable as to the properties and strength of different 

pieces classed as belonging to the same species, hence impossible 

to establish close and reliable limits of strength for each species.

 2. The various names applied to one and the same species in 

different parts of the country lead to great confusion in classifying 

or applying results of tests. 

 3. Variations in strength are generally directly proportional to 

the density or weight of timber.

 4. As a rule, a reduction of moisture is accompanied by an 

increase in strength; in other words, seasoned lumber is stronger 

than green lumber. 

 5. Structures should be in general designed for the strength of 

green or moderately seasoned lumber of average equality and not 

for a high grade of well-seasoned material. 

 6. Age or use do not destroy the strength of timber, unless decay 

or season-checking takes place. 

 7. Timber, unlike materials of a more homogeneous nature, as 

iron and steel, has no well defined limit of elasticity As a rule, it 

can be stained very near to the breaking point without serious 

injury, which accounts for the continuous use of many timber 

structures with the material strained far beyond the usually accepted safe limits. On the other hand, sudden and frequently inexplicable failures of individual sticks at very low limits are liable to 

occur.

 8. Knots, even when sound and tight, are one of the most objectionable features of timber, both for beams and struts. The full size 

tests of every experimenter have demonstrated, not only that beams 

break at knots, but that invariably timber struts will fail at a knot or 

owing to the proximity of a knot, by reducing the effective area of 

the stick and causing curly and cross-grained fibers, thus exploding 

the old practical view that sound and tight knots are not detrimental 

to timber in compression. 

 9. Excepting in top logs of a tree or very small and young timber, the heart-wood is, as a rule, not as strong as the material farther 

away form the heart. This becomes more generally apparent, in 

practice, in large sticks with considerable heart-wood cut from old 

trees in which the heart has begun to decay or been wind-shaken. 

Beams cut from such material frequently season-check along 

middle of beam and fail by longitudinal shearing. 

 10. Top logs are not as strong as butt logs, provided the latter 

have sound timber. 

 11. The results of compression tests are more uniform and vary 

less for one species of timber than any other kind of test; hence, if 

only one kind of test can be made, it would seem that a compressive test will furnish the most reliable comparative results.

 12. Long, timber columns generally fail by lateral deflection or 

“buckling” when the length exceeds the least cross-sectional dimension of the stick by twenty, in other words, the column is 

longer than twenty diameters. In practice the unit stress for all 

columns over fifteen diameters should be reduced in accordance 

with the various rules and formulae established for long columns. 

 13. Uneven end-bearing and eccentric loading of columns 

produce more serious disturbances than usually assumed. 

 14. The tests of full-size, long, compound columns, composed of 

several sticks bolted and fastened together at intervals, show essentially the same ultimate unit resistance for the compound column as 

each component stick would have if considered as a column by 

itself.

 15. More attention should be given in practice to the proper 

proportioning of bearing area; in other words, the compressive 

bearing resistance of timber with and across grain, especially the 

latter, owing to the tendency of an excessive crushing stress across 

grain to indent the timber, thereby destroying the fiber and increasing the liability to speedy decay, especially when exposed to the 

weather and the continual working produced by moving loads. 
28 

 The aim of your committee has been to examine the conflicting 

test data at hand, attributing the proper degree of importance to the 

various results and recommendations, and then to establish a set of 

units that can by accepted as fair average values, as far as known 

to-day, for the ordinary quality of each species of timber and corresponding to the usual conditions and sizes of timber encountered in 

practice. The difficulties of executing such a task successfully 

cannot be overrated, owing to the meagerness and frequently the 

indefiniteness of the available test data, and especially the great 

range of physical properties in different sticks of the same general 

species, not only due to the locality where it is grown, but also to 

the condition of the timber as regards the percentage of moisture, 

degree of seasoning, physical characteristics, grain, texture, proportion of hard and soft fibers, presence of knots, etc., all of which 

affect the question of strength.

 Your committee recommends, upon the basis of the test data at 

hand at the present time, the average units for the ultimate breaking 

stresses of the principal timbers used in bridge and trestle constructions shown in the accompanying table. 

 In addition to the units given in the table, attention should be 

called to the latest formulae for long timber columns, mentioned 

more particularly in the Appendix to this report, which formulae 

are based upon the results of the more recent full-size timber column tests, and hence should be considered more valuable than the 

older formulae derived from a limited number of small-size tests. 

These new formulae are Professor Burr’s, App. I.; Professor Ely’s, 

App. J.; Professor Stanwood’s, App. K., and A.L. Johnson’s App. 

V.; while C. Shaler Smith’s formulae will be better understood after 

examining the explanatory notes contained in App. L. 

 Attention should also be called to the necessity of examining the 

resistance of a beam to longitudinal shearing along the neutral axis, 

as beams under transverse loading frequently fail by longitudinal 

shearing in place of transverse rupture. 

 In addition to the ultimate breaking unit stress the designer of a 

timber structure has to establish the safe allowable unit stress for 

the species of timber to be used. This will vary for each particular 

class of structures and individual conditions. The selection of the 

proper “factor of safety” is largely a question of personal judgment 

and experience, and offers the best opportunity for the display of 

analytical and practical ability on the part of the designer. It is 

difficult to give specific rules. The following are some of the 

controlling questions to be considered.

 The class of structure, whether temporary or permanent, and the 

nature of the loading, whether dead or live. If live, then whether the 

application of the load is accompanied by severe dynamic shocks 

and pounding of the structure. Whether the assumed loading for 

calculations is the absolute maximum rarely to be applied in practice, or a possibility that may frequently take place. Prolonged 

heavy, steady loading, and also alternate tensile and compressive 

stresses in the same place, will call for lower averages. Information 

as to whether the assumed breaking stresses are based on full-size 

or small-size tests, or only on interpolated values averaged from 

tests of similar species of timber, is valuable, in order to attribute 

the proper degree of importance to recommended average values.

The class of timber to be used, and its condition and quality.

Finally, the particular kind of strain the stick is to be subjected to, 

and its position in the structure with regard to its importance and 

the possible damage that might be caused by its failure.

 In order to present something definite on this subject, your 

committee presents the accompanying table showing the average 

safe allowable working unit stresses or the principal bridge and 

trestle timbers, prepared to meet the average conditions existing in 

railroad timber structure, the units being based upon the ultimate 

breaking unit stresses recommended by your committee and the 

following factors of safety, viz.: 

 Tension, with and across grain................................. 10 

 Compression, with rain .............................................. 5 

 Compression, across grain.......................................... 4 

 Transverse, extreme fiber stress ................................. 6 

 Transverse, modulus of elasticity............................... 2 

 Shearing, with and across grain.................................. 4 

 In conclusion, your committee desires to emphasize the importance and great value to the railroad companies of the country of 

the experimental work on the strength of American timbers being 

conducted by the Forestry Division of the United States Department of Agriculture, and to suggest that the American Association 

of Railway Superintendents of Bridges and Buildings endorse this 

view by official action, and lend its aid in every way possible to 

encourage the vigorous continuance of this series of government 

tests, which bids fair to become the most reliable and useful work 

on the subject of strength of American timbers ever undertaken. 

With additional and reliable information on this subject, farreaching economies in the designing of timber structures can be 

introduced, resulting not only in a great pecuniary saving to the 

railroad companies, but also offering a partial check to the enormous consumption of timber and the gradual diminution of our 

structural timber supply.

 WALTER, G. BERG, Chairman,

 J. H. CUMMIN, 

 JOHN FOREMAN, 

 H.L.FRY, 

 Committee.
29 

Appendix B—Moisture Content 

Effects on Flexural Properties 

of ≥5-in.-Thick Timbers

As discussed in the text, analysis of data from Bulletin 108 

(Cline and Heim 1912), as well as engineering judgment, led 

to the conclusion that although the strength of timbers increases with seasoning, this increase may be offset by weakening of the timber as a result of the formation of splits. 

Later versions of ASTM D245 maintained this philosophy 

for modulus of rupture (MOR), but they allowed a 2% increase in modulus of elasticity (MOE) for lumber dried to a 

maximum moisture content of 15% (average 12%). However, the data in Bulletin 108 (summarized in Table 1 in the 

text) is not the best place to determine the possible magnitude of property increases for timbers. This is because the 

green and dry pieces in the data sets for any given species 

are not necessarily of equal quality, and the green and dry 

data sets may have much different sample sizes. Other historical data are available that are better suited to making 

judgments about the effect of seasoning on changes in properties. Such information may be useful to those making 

decisions on the degree of conservatism incorporated into 

ASTM standards and to those conducting research on the 

properties of timbers. 

Data on approximately 50 green and dry Sitka spruce and 

western hemlock 8- by 12-in. timbers cut in Alaska were 

reported in USDA Technical Bulletin 226 (Markwardt 

1931). Each of the selected logs was 32 ft long. Half of each 

log was used to obtain a dry timber and the other half to 

obtain a green timber. The dry timber was obtained from the 

butt log of half the trees (25 trees) and from the top log of 

the other half. By current standards, the timbers were generally of high quality. Approximately 86% of western hemlock 

timbers and 95% of Sitka spruce timbers were graded as S2, 

later called Select, by the rules of USDA Circular 295 

(Newlin and Johnson 1923).4

 Thus, most of these timbers 

would have been graded as Select Structural by current 

grading rules. 

The timbers were shipped to the Forest Products Laboratory, 

cut in half, and the green beams immediately tested. The 

remaining members were then air dried for several years 

prior to testing. All timbers were tested as simply supported 

beams, on edge in one-third point bending, using a span-todepth ratio of approximately 11:1. The MOE of both species 

increased approximately 12% in drying to about 17% moisture content. Mean MOR increased about 20% and 5th percentile MOR by about 9% (Table B1). 

4

 The minimum estimated strength ratio for this historical 

grade was 75%. 

An earlier study (Cline and Knapp 1911) on ten 32-ft-long 

Douglas-fir 8- by 16-in. timbers had been conducted in a 

manner similar to that described in Bulletin 226, except that 

dry specimens were not taken alternately from butt and top 

logs (Table B1). In this study, MOE increased about 13% in 

drying the lumber to about 16% moisture content and mean 

MOR increased about 24%. 

Betts (1909) presented data on loblolly pine timbers seasoned slowly under cover for 21 months. Mean MOE of 

these pieces increased 16% in drying to 18% moisture content and mean MOR about 20% (Table B1).

Littleford (1967) presented the results of tests conducted in 

Canada many years earlier on Douglas-fir nominal 6- by

12-in. lumber. These beams were tested on edge in onethird-point bending with a span-to-depth ratio of approximately 15:1. Mean MOE of these timbers increased about 

9% in drying to a moisture content of about 17% (Table B1). 

Mean MOR increased about 23% in drying and the 5th percentile MOR about 17%. 

These data demonstrate the increases in properties that might 

occur when timbers are dried slowly to a moisture content of 

about 17%, as, for example, might occur with timbers that 

were installed green in a building and then dried in place. 

The data also show the degree of the conservative assumptions of D245. As with dimension lumber, the increase in 5th

percentile MOR with drying is less than that of the mean 

value.
30 

Table B1—Historical data on the effect of moisture content on flexural properties of slowly dried timbers 

 MOR

Moisture content (%) Mean MOE Mean 5th percentile Species, timber 

size, and referencea

 Condition 

Sample 

size Mean Low High GPa ×106 lb/in2

 MPa ×103 lb/in2 MPa ×103 lb/in2

Sitka spruce Green 20 34.4 29 53 8.569 1.243 29.823 4.326 23.00 3.48 

8 by 16 (1) Dry 20 17.3 14 23 9.660 1.401 36.614 5.311 25.00 3.77 

 Dry/green –– –– –– –– 1.127 1.127 1.228 1.228 1.08 1.08 

Western hemlock Green 28 41.6 31 59 9.362 1.358 33.636 4.879 25.78 3.74 

8 by 16 (1) Dry 29 17.5 16 19 10.486 1.521 39.620 5.747 28.47 4.13 

 Dry/green –– –– –– –– 1.120 1.120 1.178 1.178 1.10 1.10 

Douglas-fir Green 10 31.0 26 36 9.907 1.437 37.503 5.440 –– –– 

8 by 16 (2) Dry 10 16.4 15 17 11.175 1.621 46.466 6.740 –– –– 

 Dry/green –– –– –– –– 1.128 1.128 1.239 1.239 –– –– 

Douglas-fir Green 26 35.1 –– –– 11.203 1.625 42.240 6.127 33.73b

 4.89 

6 by 12 (3) Dry 28 17.4 –– –– 12.182 1.767 51.996 7.542 39.61b

 5.75 

 Dry/green –– –– –– –– 1.087 1.087 1.231 1.231 1.17 1.17 

Southern Pine Green 12 50.9 36 79 10.000 1.450 38.744 5.620 –– –– 

8 by 16 (4) Dry 12 19.7 22 18 11.637 1.688 46.335 6.721 –– –– 

 Dry/green –– –– –– –– 1.164 1.164 1.196 1.196 –– –– 

a

References: (1) Markwardt 1931, (2) Cline and Knapp 1911, (3) Littleford 1967, (4) Betts 1909.

b

Calculated using an assumed normal distribution. 
31 

Appendix C—Chronology of ASTM D245 

Date Title of standard 

1926T Tentative specifications for structural wood joist and planks, beams and stringers, and posts and timbers 

1927 Standard specifications for structural wood joist and planks, beams and stringers, and posts and timbers 

1930 Standard specifications for structural wood joist and planks, beams and stringers, and posts and timbers 

1933 Standard specifications for structural wood joist and planks, beams and stringers, and posts and timbers 

1936T Tentative specifications for structural wood joist and plank, beams and stringers, and posts and timbers 

1937 Standard specifications for structural wood joist and planks, beams and stringers, and posts and timbers 

1949T Tentative methods for establishing structural grades of lumber 

1957T Tentative methods for establishing structural grades of lumber 

1962T Tentative methods for establishing structural grades of lumber 

1964T Tentative methods for establishing structural grades of lumber 

1968T Tentative standard methods for establishing structural grades and related allowable properties for visually 

graded lumber. This standard does not appear in either the 1968 or 1969 Annual Book of Standards. 

1969 Standard methods for establishing structural grades and related allowable properties for visually graded lumber 

1970 Standard methods for establishing structural grades and related allowable properties for visually graded lumber 

1974 Standard methods for establishing structural grades and related allowable properties for visually graded lumber 

1981 Standard methods for establishing structural grades and related allowable properties for visually graded lumber 

1988 Standard practice for establishing structural grades and related allowable properties for visually graded lumber 

1992 Standard practice for establishing structural grades and related allowable properties for visually graded lumber 

1993 Standard practice for establishing structural grades and related allowable properties for visually graded lumber 

1998 Standard practice for establishing structural grades and related allowable properties for visually graded lumber 

1999 Standard practice for establishing structural grades and related allowable properties for visually graded lumber 
32 

Appendix D—Allowable 

Properties in Bending of Select 

(S2) Grade in Early Documents 

Appendix D includes data from two seminal documents by 

Newlin and Johnson for establishing working stresses and 

grading rules: Circular 295, published in 1923, and an unpublished memorandum of 1924. Circular 295 provides 

grade descriptions for the four grades (S1, S2, S3, and S4) 

later associated with Extra Select, Select Structural, Standard, and Common grades. In the unpublished memorandum, Newlin and Johnson discuss the factors involved in 

determining the working stresses provided in Circular 295.

This appendix also includes data from ASTM D245–27, the 

first standard specifications for structural wood joists and 

planks, beams and stringers, and posts and timbers. 
33 

Circular 295 (Newlin and Johnson 1923) 

Table 1—Working stresses permissible for structural timber of Select (S2) gradea (pounds per square inch)

 Bending Compression

Allowable stress in extreme fiber 

for Select (S2) grade 

Allowable stress parallel 

to grain “Short Columns”c

for Select (S2) grade 

Allowable stress 

perpendicular to grain 

for all grades 

Species

Damp or 

wet location (docks, 

piling, and 

sills)

Outside, not in 

contact with 

soil (bridges 

and open 

sheds)

Under shelter 

in dry location 

(factories and 

warehouses)

Allowable

horizontal

shear stress 

Select (S2) 

grade—all

locations

Allowable

modulus of 

elasticity

for all 

grades—all

locations

Wet

location

Dry

outside

location

Dry inside

loca-tion

Wet

location

Dry

outside

location

Dry inside

location

Ash, black 800 900 1,000 90 1,100,000 500 550 650 150 200 300 

Ash, commercial white (green,

 Biltmore, white) 

1,000 1,200 1,400 125 1,500,000 900 1,000 1,100 300 375 500 

Aspen and large-tooth aspen 500 650 800 80 900,000 450 550 700 100 125 150 

Basswood 500 650 800 80 900,000 450 550 700 100 125 150 

Beech 1,000 1,300 1,500 125 1,600,000 900 1,100 1,200 300 375 500 

Birch, paper 600 750 900 80 1,000,000 450 550 650 100 150 200 

Birch, yellow and sweet 1,000 1,300 1,500 120 1,000,000 900 1,100 1,200 300 375 500 

Cedar, Alaska 800 900 1,000 90 1,100,000 650 750 800 150 200 250 

Cedar, western red 750 800 900 80 1,000,000 650 700 700 125 150 200 

Cedar, northern and southern

 white 

600 650 750 70 800,000 450 500 550 100 140 175 

Cedar, Port Orford 900 1,000 1,100 100 1,200,000 750 825 900 150 200 250 

Chestnut 700 850 950 90 1,000,000 600 700 800 150 200 300 

Cottonwood, common and black 500 650 800 80 900,000 450 550 700 100 125 150 

Cypress, bald 900 1,100 1,300 100 1,400,000 800 1,000 1,100 225 250 350 

Douglas fir (western

 Washington and Oregon)b

1,000 1,300 1,500 90 1,600,000 850 1,000 1,100 200 225 325 

Douglas fir (Rocky Mountain

 type) 

700 900 1,100 85 1,200,000 700 800 800 200 225 275 

Elm, cork 1,000 1,300 1,500 125 1,300,000 900 1,100 1,200 300 375 500 

Elm, slippery and white 800 900 1,100 100 1,200,000 650 750 800 125 175 250 

Fir, balsam 600 750 900 70 1,000,000 500 600 700 100 125 150 

Fir, commercial white (white,

 noble, grand) 

800 900 1,100 70 1,200,000 650 750 800 150 200 300 

Gum, black and cotton 800 900 1,100 100 1,200,000 650 750 800 150 200 300 

Gum, red 800 900 1,100 100 1,200,000 650 750 800 150 200 300 

Hemlock, western 900 1,100 1,300 75 1,400,000 800 900 900 200 225 300 

Hemlock, eastern 800 900 1,000 70 1,100,000 600 700 700 200 225 300 

Hickory, true and pecan 1,200 1,500 1,900 140 1,800,000 1,000 1,200 1,500 350 400 600 

Larch, western 900 1,100 1,200 100 1,300,000 800 1,000 1,100 200 275 325 

Maple, sugar and black 1,000 1,300 1,500 150 1,600,000 900 1,100 1,200 300 375 500 

Maple, red and silver 700 900 1,000 100 1,100,000 600 700 800 200 250 350 

Oak, commercial red and white 1,000 1,200 1,400 125 1,500,000 800 900 1,000 300 375 500 

Pine, southern yellowb 1,000 1,300 1,500 110 1,600,000 850 1,000 1,100 200 225 325 

Pine, white, sugar, western

 white, western yellow 

750 800 900 85 1,000,000 650 750 750 125 150 250 

Pine, Norway 800 1,000 1,100 85 1,200,000 700 800 800 150 175 300 

Poplar, yellow 800 900 1,000 80 1,100,000 600 700 800 125 150 250 

Redwood 800 1,000 1,200 70 1,200,000 750 900 1,000 125 150 250 

Spruce, red white, Sitka 800 900 1,100 85 1,200,000 650 750 800 125 150 250 

Spruce, Engelmann 500 650 750 70 800,000 450 550 600 100 140 175 

Sycamore 800 900 1,100 80 1,200,000 650 750 800 150 200 300 

Tamarack, eastern 900 1,100 1,200 95 1,300,000 800 900 1,000 200 225 300 

a

Working stresses for Extra Select (S1), Extra Select (S1) Dense, Standard (S3), and Common (S4) grades are obtained by multiplying the basic

 stress by 7/6, 8/6, 5/6, and 4/6, respectively. 

b

The working stresses of any grade of timbers of Douglas fir and southern yellow pine, which meet the density requirements of the American Society of Testing 

Materials shall be increased one-sixth the allowable stress given in the table for the basic or Select (S2) grade. 

c

The influence of knots on compressive strength of columns of constant cross section decreases as the length increases. When the length reaches 30 times the 

least dimension, knots such as are allowable in Select (S2) timbers have no appreciable effect on the strength as a column. 
34 

Newlin and Johnson 1924, unpublished memo 

Working stresses permissible for structural timbers of Select (S2) gradea (pounds per square inch) 

Bending Compression

Stress in extreme fiber 

Under shelter in dry locations 

Stress parallel to grain, short 

columns,c

 all sizes (location) 

Stress perpendicular to 

Damp or grain, all sizes (location) wet locations

(docks,

caps,

and sills) 

all sizes 

Outside

locations

(bridges

and open 

sheds)

all sizes 

Beams

(factory and 

warehouse)

6 in. thick 

and over 

Joists (houses, stores, and

light warehouses) 4 in. thick

and under 

Allowable horizontal shear 

stress, all 

locations, all 

sizes

Average

modulus of 

elasticity for 

all locations 

and sizesb Wet

Dry outsideDry inside Wet

Dry

outside

Dry

inside

Species Select (S2)b S1 S2 S3 S4 Select (S2) All grades Select (S2) grade All grades 

 (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15) 

Ash, black 800 900 1,000 1,420 1,170 920 670 90 1,100,000 500 550 650 150 200 300 

Ash, commercial white (green,

 Biltmore, white 

1,000 1,200 1,400 1,980 1,630 1,280 930 125 1,500,000 900 1,000 1,100 300 375 500 

Aspen and largetooth aspen 500 650 800 1,130 930 730 530 80 900,000 450 550 700 100 125 150 

Basswood 500 650 800 1,130 930 730 530 80 900,000 450 550 700 100 125 150 

Beech 1,000 1,300 1,500 2,120 1,750 1,370 1,000 125 1,600,000 900 1,100 1,200 300 375 500 

Birch, paper 600 750 900 1,270 1,050 820 600 80 1,000,000 450 550 650 100 150 200 

Birch, yellow and sweet 1,000 1,300 1,500 2,120 1,750 1,370 1,000 120 1,600,000 900 1,100 1,200 300 375 500 

Cedar, Alaska 800 900 1,000 1,420 1,170 920 670 90 1,100,000 650 750 800 150 200 250 

Cedar, western red 750 800 900 1,270 1,050 820 600 80 1,000,000 650 700 700 125 150 200 

Cedar, northern and southern white 600 650 750 1,060 880 690 500 70 800,000 450 500 550 100 140 175 

Cedar, Port Orford 900 1,000 1,100 1,560 1,280 1,010 730 100 1,200,000 750 825 900 150 200 250 

Chestnut 700 850 950 1,350 1,110 870 630 90 1,000,000 600 700 800 150 200 300 

Cottonwood, common and black 600 650 800 1,130 930 730 530 80 900,000 450 550 700 100 125 150 

Cypress, bald 900 1,100 1,300 1,840 1,520 1,190 870 100 1,400,000 800 1,000 1,100 225 250 350 

Douglas fir (western Washington

 and Oregon)d

1,000 1,300 1,500 2,120 1,750 1,370 1,000 90 1,600,000 850 1,000 1,100 200 225 325 

Douglas fir (Rocky Mountain type)d

 700 900 1,100 1,500 1,280 1,010 730 85 1,200,000 700 800 800 200 225 275 

Elm, cork 1,000 1,300 1,500 2,120 1,750 1,370 1,000 125 1,300,000 900 1,100 1,200 300 375 500 

Elm, slippery and white 800 900 1,100 1,560 1,280 1,010 730 100 1,200,000 650 750 800 125 175 250 

Fir, balsam 600 750 900 1,270 1,050 820 600 70 1,000,000 500 600 700 100 125 150 

Fir, commercial white (white, noble,

 grand) 

800 900 1,100 1,560 1,280 1,010 730 70 1,200,000 650 750 800 150 200 300 

Gum, black and cotton 800 900 1,100 1,560 1,280 1,010 730 100 1,200,000 650 750 800 150 200 300 

Gum, red 800 900 1,100 1,560 1,280 1,010 730 100 1,200,000 650 750 800 150 200 300 

Hemlock, western 900 1,100 1,300 1,840 1,520 1,190 870 75 1,400,000 800 900 900 200 225 300 

Hemlock, eastern 800 900 1,000 1,420 1,170 920 670 70 1,100,000 600 700 700 200 225 300 

Hickory, true and pecan 1,200 1,500 1,900 2,690 2,220 1,740 1,270 140 1,800,000 1,000 1,200 1,500 350 400 600 

Larch, western 900 1,100 1,200 1,700 1,400 1,100 800 100 1,300,000 800 1,000 1,100 200 275 325 

Maple, sugar and black 1,000 1,300 1,500 2,120 1,750 1,370 1,000 150 1,600,000 900 1,100 1,200 300 375 500 

Maple, red and silver 700 900 1,000 1,420 1,170 920 670 100 1,100,000 600 700 800 200 250 350 

Oak, commercial red and white 1,000 1,200 1,400 1,980 1,630 1,280 930 125 1,500,000 800 900 1,000 300 375 500 

Pine, southern yellowd 1,000 1,300 1,500 2,120 1,750 1,370 1,000 110 1,600,000 850 1,000 1,100 200 225 325 

Pine, white, sugar, western white,

 western yellow 

750 800 900 1,270 1,050 830 790 85 1,000,000 650 750 750 125 150 250 

Pine, Norway 800 1,000 1,100 1,560 1,280 1,010 730 85 1,200,000 700 800 800 150 175 300 

Poplar, yellow 800 900 1,000 1,420 1,170 920 670 80 1,100,000 600 700 800 125 150 250 

Redwood 800 1,000 1,200 1,400 1,200 1,000 800 70 1,200,000 750 900 1,000 125 150 250 

Spruce, red, white, Sitka 800 900 1,100 1,560 1,280 1,010 730 85 1,200,000 650 750 800 125 150 250 

Spruce, Engelmann 500 650 750 1,060 880 690 500 70 800,000 450 550 600 100 140 175 

Sycamore 800 900 1,100 1,560 1,280 1,010 730 80 1,200,000 650 750 800 150 200 300 

Tamrack, eastern 900 1,100 1,200 1,700 1,400 1,100 800 95 1,300,000 800 900 1,000 200 225 300 

a

Working stresses for Extra Select (S1), Standard (S3), and Common (S4) grades are obtained by multiplying the basic stress by 7/6, 56, and 4/6, respectively, except in

 case of joints 4 in. thick and under in dry locations, stresses for which are given in the table. 

b

Values under modulus of elasticity are averages for species. For long columns a factor of 4 must be applied to them in order to obtain safe loads. c

The influence of knots on compressive strength of columns of constant cross section decreases as the length increases. When the length reaches 30 times the least

 dimension, knots such as are allowable in Select (S2) timbers have practically no effect on the strength as a column. 

 dThe working stresses of any grade of timbers of Douglas fir and southern yellow pine, which meet the density requirements of the American Society for Testing Materials,

 may be increased one sixth of the allowable stress given in the table for basic or Select (S2) grade. Working stresses for any grade of Douglas fir, exclusive of Rocky

 Mountain type, and southern yellow pine, timbers not graded for density, but containing not less than six or more than twenty rings per inch measured over same portion 

 of cross section as prescribed for density determinations may be increased one-fifteenth of basic stress.

Note: Stresses cannot be given for the grades of yard and dimension stock on account of manner in which the knots are limited on edges and narrow faces. 

The standard S3 grade is in general more lenient for knots than the No. 1 common grade of yard dimension. This grade can, therefore, be selected from No. 1 and No. 2 common dimension.

 The same comparison holds between No. 2 common and the S4 grade. 

U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, Wisconsin Project L-256 (Revised) November 9, 1923. Not for distribution. 
35 

ASTM D245–27

Table I.—Working stresses for joist & plank and beams & stringersa

Continuously dry (pounds per square inch)

Species

Extreme fiber in 

bending

Compression

perpendicular

to grain 

Maximum

horizontal

shear

Modulus of 

elasticity

Select Grade 

Cedar 

Western red 900 200 80 1,000,000 

Northern and southern white 750 175 70 800,000 

Port Orford 1,100 250 90 1,200,000 

Alaska 1,100 250 90 1,200,000 

Cypress 

Southern 1,300 350 100 1,200,000 

Douglas Fir 

Coast Region 

Select 1,600 345 90 1,600,000 

Dense Select 1,750 380 105 1,600,000 

Rocky Mountain Region 1,100 275 85 1,200,000 

Fir 

Balsam 900 150 70 1,000,000 

Golden, noble, silver, white 1,100 300 70 1,100,000 

Hemlock 

West Coast 1,300 300 75 1,400,000 

Eastern 1,100 300 70 1,100,000 

Larch 

Western 1,200 325 100 1,300,000 

Oak 

Red and white 1,400 500 125 1,500,000 

Pine 

Southern 

Select 1,600 345 110 1,600,000 

Dense Select 1,750 380 128 1,600,000 

California, Idaho and Northern white, 

Pondosa, sugar 

900 250 85 1,000,000 

Norway 1,100 300 85 1,200,000 

Redwood 1,200 250 70 1,200,000 

Spruce 

Red, white, Sitka 1,100 250 85 1,200,000 

Englemann 750 175 70 800,000 

Tamarack 

Eastern 1,200 300 95 1,300,000 
36 

ASTM D245–27

Table I.—Working stresses for joist & plank and beams & stringersa—(Continued)

Occasionally wet but quickly dried (pounds per square inch) 

 Extreme fiber in bending 

Species

4 in. and 

thinner

5 in. and 

thicker

Compression

perpendicular

to grain 

Maximum

horizontal

shear

Modulus of 

elasticity

Select Grade 

Cedar 

Western red 710 800 150 80 1,000,000 

Northern and southern white 580 — 140 70 800,000 

Port Orford 890 1,000 200 90 1,200,000 

Alaska 890 — 200 90 1,200,000 

Cypress 

Southern 980 — 250 100 1,200,000 

Douglas Fir 

Coast Region 

Select 1,240 1,385 240 90 1,600,000 

Dense Select 1,370 1,515 265 105 1,600,000 

Rocky Mountain Region 800 900 225 85 1,200,000 

Fir 

Balsam 670 — 125 70 1,000,000 

Golden, noble, silver, white 800 — 225 70 1,100,000 

Hemlock 

West Coast 980 1,100 225 75 1,400,000 

Eastern 800 — 225 70 1,100,000 

Larch 

Western 980 1,100 225 100 1,300,000 

Oak 

Red and white 1,070 1,200 375 125 1,500,000 

Pine 

Southern 

Select 1,240 1,385 240 110 1,600,000 

Dense Select 1,370 1,515 265 128 1,600,000 

 

California, Idaho and Northern white, 

Pondosa, sugar 

710 — 150 85 1,000,000 

Norway 890 — 175 85 1,200,000 

Redwood 890 1,000 150 70 1,200,000 

Spruce 

Red, white, Sitka 800 900 150 85 1,200,000 

Englemann 580 — 140 70 800,000 

Tamarack 

Eastern 980 — 225 95 1,300,000 
37 

ASTM D245–27

Table I.—Working stresses for joist & plank and beams & stringersa—(Continued)

More or less continuously damp or wet (pounds per square inch) 

 Extreme fiber in bending 

Species

4 in. and 

thinner

5 in. and 

thicker

Compression

perpendicular

to grain 

Maximum

horizontal

shear

Modulus of 

elasticity

Select Grade 

Cedar 

Western red 670 750 125 80 1,000,000 

Northern and southern white 530 — 100 70 800,000 

Port Orford 800 900 150 90 1,200,000 

Alaska 800 — 150 90 1,200,000 

Cypress 

Southern 800 — 225 100 1,200,000 

Douglas Fir 

Coast Region 

Select 950 1,065 215 90 1,600,000 

Dense Select 1,050 1,165 235 105 1,600,000 

Rocky Mountain Region 620 700 200 85 1,200,000 

Fir 

Balsam 530 — 100 70 1,000,000 

Golden, noble, silver, white 710 — 200 70 1,100,000 

Hemlock 

West Coast 800 900 200 75 1,400,000 

Eastern 710 — 200 70 1,100,000 

Larch 

Western 800 900 200 100 1,300,000 

Oak 

Red and white 890 1,000 300 125 1,500,000 

Pine 

Southern 

Select 950 1,065 215 110 1,600,000 

Dense Select 1,050 1,165 235 128 1,600,000 

California, Idaho and Northern white, 

Pondosa, sugar 

670 — 125 85 1,000,000 

Norway 710 — 150 85 1,200,000 

Redwood 710 800 125 70 1,200,000 

Spruce 

Red, white, Sitka 710 800 125 85 1,200,000 

Englemann 440 — 100 70 800,000 

Tamarack 

Eastern 800 — 200 95 1,300,000 

a

For material complying with structural grades of the American Society for Testing Materials. 

 Values are those recommended by Forest Products Laboratory, U.S. Forest Service. 
38 

Appendix E—Dry-to-Green 

Ratios for U.S. Hardwood

and Softwood

The tables in Appendix E provide dry-to-green ratios for 

clear wood properties of softwood and hardwood species 

grown in the United States, as specified in ASTM D2555, 

1988 to current edition (2000). 

Table E1—Dry-to-green ratios for U.S. softwood species

Species MOR MOE UCS Shear C–perp Species MOR MOE UCS Shear C–perp 

Baldcypress 1.60 1.22 1.78 1.23 1.81 Pine 

Cedar Eastern white 1.74 1.24 1.97 1.33 2.01 

Alaska 1.73 1.25 2.07 1.35 1.78 Jack 1.64 1.27 1.92 1.55 1.95 

Atlantic white 1.44 1.24 1.97 1.16 1.67 Lodgepole 1.70 1.24 2.06 1.28 2.41 

Eastern red 1.25 1.36 1.69 1.32 Monterey 2.00 1.27 2.22 1.69 2.11 

Incense 1.28 1.24 1.65 1.05 1.59 Ponderosa 1.84 1.30 2.17 1.61 2.05 

Northern white 1.54 1.24 1.99 1.39 1.32 Red 1.88 1.27 2.22 1.77 2.31 

Port Orford 1.93 1.31 1.99 1.62 2.38 Sugar 1.67 1.16 1.81 1.58 2.32 

Western red 1.46 1.18 1.64 1.29 1.89 Western white 2.06 1.22 2.07 1.54 2.45 

Douglas-fir Loblolly 1.75 1.28 2.03 1.61 2.04 

Coast 1.62 1.25 1.91 1.25 2.08 Longleaf 1.70 1.25 1.96 1.45 2.01 

Interior north 1.76 1.27 1.99 1.48 2.16 Pitch 1.59 1.19 2.01 1.58 2.23 

Interior south 1.75 1.28 2.00 1.59 2.20 Pond 1.56 1.37 2.06 1.48 2.06 

Interior west 1.64 1.21 1.92 1.38 1.82 Sand 1.54 1.38 2.01 0.96 1.86 

Fir Shortleaf 1.76 1.26 2.06 1.54 2.31 

Balsam 1.66 1.16 2.01 1.43 2.16 Slash 1.87 1.29 2.13 1.74 1.93 

Calfornia red 1.81 1.28 1.98 1.36 1.82 Spruce 1.73 1.23 1.99 1.66 2.63 

Grand 1.53 1.26 1.80 1.22 1.85 Virginia 1.77 1.25 1.96 1.52 2.32 

Noble 1.74 1.25 2.03 1.31 1.90 Redwood 1.34 1.15 1.68 1.25 1.93 

Pacific silver 1.71 1.24 2.04 1.64 1.98 Spruce 

Subalpine 1.76 1.23 2.11 1.54 2.01 Black 1.77 1.16 2.10 1.67 2.27 

White 1.67 1.29 2.00 1.46 1.89 Engelmann 1.98 1.26 2.06 1.89 2.06 

Hemlock Red 1.80 1.25 2.04 1.71 2.09 

Eastern 1.39 1.11 1.76 1.25 1.81 Sitka 1.81 1.27 2.10 1.51 2.07 

Mountain 1.83 1.28 2.24 1.65 2.32 White 1.89 1.25 2.20 1.53 2.06 

Western 1.71 1.25 2.14 1.49 1.94 Tamarack 1.62 1.33 2.06 1.49 2.07 

Larch, western 1.70 1.28 2.03 1.56 2.32 

 Average 1.69 1.25 1.99 1.47 2.03 

 Minimum 1.25 1.11 1.64 0.96 1.32 

 Maximum 2.06 1.38 2.24 1.89 2.63 

 5th percentile 1.30 1.15 1.66 1.09 1.42 
39 

Table E2—Dry-to-green ratios for U.S. hardwood species

Species or Region MOR MOE UCS Shear C–perp Species or region MOR MOE UCS Shear C–perp 

Alder, red 1.50 1.18 1.97 1.40 1.73 Magnolia 

Ash Cucumbertree 1.66 1.16 2.01 1.35 1.74 

Black 2.10 1.53 2.60 1.82 2.20 Southern 1.66 1.27 2.02 1.47 1.86 

Green 1.49 1.18 1.69 1.52 1.78 Maple 

Oregon 1.67 1.20 1.72 1.50 2.36 Bigleaf 1.45 1.32 1.84 1.56 1.68 

White 1.57 1.21 1.86 1.41 1.73 Black 1.68 1.22 2.04 1.61 1.69 

Aspen Red 1.75 1.19 1.99 1.61 2.48 

Bigtooth 1.68 1.27 2.12 1.48 2.19 Silver 1.53 1.21 2.10 1.41 2.00 

Quaking 1.64 1.37 1.99 1.30 2.04 Sugar 1.67 1.18 1.95 1.59 2.27 

Basswood, American 1.76 1.41 2.13 1.65 2.16 Oak 

Beech, American 1.74 1.25 2.06 1.56 1.86 Red oak 

Birch Black oak 1.69 1.39 1.88 1.56 1.32 

Paper or white 1.92 1.36 2.41 1.45 2.20 Cherrybark 1.67 1.27 1.89 1.51 1.63 

Yellow 2.01 1.34 2.42 1.70 2.26 Laurel 1.59 1.21 2.20 1.55 1.85 

Sweet 1.80 1.32 2.28 1.80 2.29 Northern red 1.72 1.35 1.97 1.46 1.65 

Butternut 1.51 1.21 2.11 1.55 2.08 Pin 1.69 1.31 1.85 1.61 1.42 

Cherry, black 1.54 1.14 2.01 1.51 1.91 Scarlet 1.67 1.30 2.04 1.34 1.34 

Chestnut, American 1.53 1.32 2.15 1.36 2.00 Southern red 1.58 1.31 2.01 1.49 1.60 

Cottonwood Water 1.72 1.30 1.81 1.63 1.65 

Black 1.73 1.18 2.05 1.69 1.82 Willow 1.96 1.48 2.35 1.40 1.85 

Eastern 1.62 1.35 2.15 1.36 1.95 White oak 

Elm Bur 1.43 1.18 1.84 1.35 1.78 

American 1.65 1.20 1.90 1.51 1.95 Chestnut 1.65 1.16 1.94 1.23 1.58 

Cedar 1.47 1.27 1.61 1.70 1.57 Live 1.54 1.25 1.64 1.20 1.39 

Rock 1.56 1.29 1.87 1.51 2.02 Overcup 1.57 1.24 1.84 1.52 1.50 

Slippery 1.62 1.21 1.92 1.48 1.97 Post 1.63 1.39 1.90 1.44 1.67 

Winged 1.61 1.36 1.83 1.82 1.61 Swamp chestnut 1.64 1.31 2.05 1.58 1.93 

Hackberry 1.70 1.25 2.05 1.49 2.23 Swamp white 1.80 1.28 1.97 1.54 1.56 

Hickory White 1.83 1.43 2.09 1.60 1.59 

Bitternut 1.66 1.28 1.98 1.58 2.10 Poplar, balsam 1.76 1.47 2.38 1.57 2.18 

Mockernut 1.74 1.41 2.00 1.36 2.13 Sweetgum 1.76 1.37 2.08 1.61 1.70 

Nutmeg 1.83 1.32 1.74 1.79 2.06 Sycamore, American 1.55 1.33 1.84 1.47 1.91 

Pecan 1.40 1.26 1.97 1.40 2.22 Tupelo 

Pignut 1.71 1.37 1.91 1.57 2.15 Black, black gum 1.36 1.16 1.82 1.22 1.92 

Shagbark 1.83 1.38 2.01 1.60 2.08 Water 1.32 1.19 1.76 1.33 1.81 

Shellbark 1.72 1.41 2.04 1.78 2.23 Walnut, black 1.54 1.18 1.76 1.13 2.08 

Water 1.65 1.30 1.85 1.75 Yellow-poplar 1.70 1.29 2.08 1.50 1.85 

Honeylocust 1.44 1.27 1.70 1.36 1.60 

Locust, black 1.40 1.11 1.50 1.41 1.58 Average 1.65 1.28 1.98 1.51 1.88 

 Minimum 1.40 1.11 1.50 1.30 1.32 

 Maximum 2.10 1.53 2.60 1.82 2.48 

 5th percentile 1.40 1.16 1.65 1.22 1.40 
40 

Appendix F—Derivation of 

Moisture Content–Property 

Adjustment Models for

D1990–91

Basic Model 

The simplified model was developed from the linear surface 

models, which start with the assumption that the strength of 

a specimen is a linear function of its moisture content: 

P = b0 + b1M

Thus, in going from moisture content M1 with strength S1 to 

moisture content M2, the resulting strength is 

P2 = P1 + b1( M2 – M1) (F1) 

To use the model, one must be able to predict b1. The three 

methods considered were to use a linear, quadratic, or cubic 

function of the strength property at 15% moisture content to 

predict b1; that is,

1. b1 = C0 + C1P15

2. b1 = C0 + C1P15 + C2P152

3. b1 = C0 + C1P15 + C2P152

 + C3P153

P15 is obtained by finding the strength at 15% moisture 

content that when adjusted to moisture content M1 gives 

strength P1. From Equation (F1), this means solving 

P1 = P15 + b1(M1 – 15) (F2) 

This process is complicated by the fact that b1 is a function 

of P15 (option 1, 2, or 3). When option 3 is used, the roots of 

a cubic equation must be solved to get P15. It is possible to 

solve this equation in closed form, but the equation would be 

so messy that no one would use it. Thus, a computer program is the only viable solution for option 3. Both options 1 

and 2 are more tractable to a closed-form solution. 

Simplified Model 

Because all three linear surface models perform relatively 

the same, a simplified model could be developed. Consider 

the linear surface model with option 1. In this case, we can 

substitute for b1 in Equation (F2) using option 1; that is, 

P1 = P15 + (C0 + C1P15)(M1 – 15) 

which implies 

( )

( ) 



 





+ −

+ − = 1 1515

1 1

1 0 1

15 C M

P C M

P

Combining this equation with Equation (F1) and option 1 

gives

( )

( ) ( ) 2 1

1 1

1 0 1

2 1 0 1 1 15

15 M M

C M

P C M

P P C C  −



 





+ −

+ − = + +

which can be rewritten as 

( )

[ ] ( ) ( ) 2 1

1 1 1

0 1 1

2 1 1 15

M M

C C M

C C P

P P −













− +

+ = +

The coefficients of this equation are obtained from the moisture content data and are as follows: 

Bending Tension 

C0 100.93534538 48.15270011 

C1 –0.04179655 –0.01541423 

Thus, for bending the equation becomes 

P2 = P1 + [(P1 – 2414.92)/(38.93 – M1)](M1 – M2)

and for tension, 

P2 = P1 + [(P1 – 3123.91)/(79.88 – M1)](M1 – M2)

For simplicity,

P2 = P1 + [(P1 – 2415)/(40 – M1)](M1 – M2) for bending 

P2 = P1 + [(P1 – 3150)/(80 – M1)](M1 – M2) for tension 

To prevent the model from showing a decrease in strength as 

moisture content drops, it was decided to take no change 

below 2,415 lb/in2

 in bending and 3,150 lb/in2 in tension. 

Normalization

As discussed for MOR, normalization is an option that will 

allow the properties of a lower strength species to be scaled 

relative to those of Douglas Fir and Southern Pine prior to 

adjusting their strength to a common moisture content level. 

The concern was that without some type of adjustment, a 

significant portion of the distribution of a much weaker 

species might fall below the lower limit of the stronger 

species where the species showed no change in strength with 

change in moisture content. Normalization was an attempt to 

fit the data to the model so that the weaker species had the 

same percentage of the lower tail below the lower cut-off as 

the percentage for the stronger species used to formulate the 

model. To “normalize,” the data are first adjusted to 15% 

moisture content and the mean of the 2 by 4 Select Structural 

values at 15% is calculated. The data at the original moisture 

content is then adjusted to “fit” the model using 
41 

P = [ ] ( ) P1 − C ( ) A B + C *

1

where

A is the mean property of 2 by 4 Select Structural 15% moisture content values of the species used to create the 

model (lb/in2

),

B the mean property of 2 by 4 Select Structural 15% moisture content values of the species being adjusted (lb/in2

),

and

C a constant (lb/in2

).

This “adjusted property value” * P1 at the original moisture 

content M1 is then modified to an “adjusted property value” 

* P2 at 15% moisture content using the standard procedure. 

This “adjusted property value” * P2 must then be “unadjusted” or scaled back to its original scale using 

P = [( ) P − C ( ) B A ]+ C * 2 2

where A and C are the following for MOR, UTS, and UCS: 

A C 

MOR 10,120 1,000 

UTS 7,452 0 

UCS 5,785 0 

In practice, normalization has been found to have little effect 

on allowable property estimates. 

Wet Use Factors

The factors in Table 9 of the text are based on the change in 

capacities of lumber with moisture content relative to a 15% 

moisture content base. The factors selected provide acceptable estimates in the range of allowable property values 

normally assigned for lumber design (that is, 5th percentile 

strength levels, not necessarily strength values throughout 

the strength distribution). Changes in property values with 

change in moisture content were calculated using a property 

adjustment model, and dimensional changes were calculated 

using the equations of Appendix X1 of ASTM D1990–91 

(see also Green 1989). 

In some earlier drafts of D1990 that were balloted in Committee D7, the quadratic surface model of Green and Evans 

(1989) (see computer programs of Evans and others 2000) 

were used to develop the wet use factors relative to a base of 

12% moisture content. These capacities by this approach are 

shown in Table F1, where the strength properties are given 

in terms of characteristic values. The wet use factors using 

this approach differed from those of Table 9 only in the 

factor for Fc (UCS in Table F1), which was judged to be 0.7 

for Fc values > 750 lb/in2

.

As previously noted, concerns developed during the ASTM 

balloting process about the complexity of the quadratic 

surface model. This led to adoption of the simplified version, 

the linear surface model (Eq. (3) in the text), which is applicable only to the lower tails of strength distributions. During 

the balloting process, the basis for the wet use factors was 

also changed from 12% to 15% moisture content. Table F2 

reproduces the capacities given in Annex X10 of D1990–91. 

These capacities formed the bases for the judgments that led 

to the wet use factors of Table 9. Note that the properties of 

Table F2 are shown as the characteristic values divided by 

the general adjustment factors (e.g., Fb = MOR/2.1). 
42 

Table F1—Relative capacity of lumber at three moisture content (MC) levels based on quadratic surface model for 

adjusting lumber properties (Evans and others 2000) and shrinkage formulas given in ASTM D1990–91 

Ratio of property to 

property at 12% MC 

Ratio of dimensions to 

dimensions at 12% MC 

Ratio of capacity to capacity at 12% MC 

Property

Value at 

12%

MC

12%

MC

15%

MC

23%

MC

Comparative

section

12%

MC

15%

MC

23%

MC

12%

MC

15%

MC

23%

MC

MOR 1000 1.00 0.993 0.973 Section 1.00 1.019 1.071 1.00 1.012 1.042 

 2000 1.00 1.024 0.920 modulus (Z) 1.00 1.019 1.071 1.00 1.043 0.985 

 3000 1.00 1.031 0.844 1.00 1.019 1.071 1.00 1.051 0.904 

 4000 1.00 1.019 0.796 1.00 1.019 1.071 1.00 1.038 0.852 

 5000 1.00 1.002 0.762 1.00 1.019 1.071 1.00 1.021 0.816 

 

UTS 500 1.00 1.062 1.164 Area (A) 1.00 1.012 1.045 1.00 1.075 1.217 

 1000 1.00 1.073 1.128 1.00 1.012 1.045 1.00 1.086 1.179 

 1500 1.00 1.085 1.057 1.00 1.012 1.045 1.00 1.098 1.105 

 2000 1.00 1.081 1.017 1.00 1.012 1.045 1.00 1.094 1.063 

 2500 1.00 1.072 0.989 1.00 1.012 1.045 1.00 1.085 1.034 

 3000 1.00 1.062 0.968 1.00 1.012 1.045 1.00 1.075 1.012 

 3500 1.00 1.052 0.951 1.00 1.012 1.045 1.00 1.065 0.994 

 4000 1.00 1.042 0.937 1.00 1.012 1.045 1.00 1.055 0.979 

 4500 1.00 1.033 0.924 1.00 1.012 1.045 1.00 1.046 0.966 

 5000 1.00 1.026 0.914 1.00 1.012 1.045 1.00 1.038 0.955 

 

UCS 500 1.00 0.974 0.768 Area (A) 1.00 1.012 1.045 1.00 0.986 0.803 

 1000 1.00 0.974 0.768 1.00 1.012 1.045 1.00 0.986 0.803 

 1500 1.00 0.974 0.768 1.00 1.012 1.045 1.00 0.986 0.803 

 2000 1.00 0.974 0.768 1.00 1.012 1.045 1.00 0.986 0.803 

 2500 1.00 0.974 0.768 1.00 1.012 1.045 1.00 0.986 0.803 

 3000 1.00 0.949 0.732 1.00 1.012 1.045 1.00 0.961 0.765 

 3500 1.00 0.927 0.700 1.00 1.012 1.045 1.00 0.938 0.732 

 4000 1.00 0.909 0.674 1.00 1.012 1.045 1.00 0.920 0.705 

 

MOE 0.5 1.00 0.954 0.834 Moment of 1.00 1.026 1.097 1.00 0.978 0.915 

 1.0 1.00 0.955 0.834 inertia (I) 1.00 1.026 1.097 1.00 0.979 0.915 

 1.5 1.00 0.955 0.834 1.00 1.026 1.097 1.00 0.979 0.915 

 2.0 1.00 0.955 0.834 1.00 1.026 1.097 1.00 0.979 0.915 

 2.5 1.00 0.955 0.834 1.00 1.026 1.097 1.00 0.979 0.915 
43 

Table F2—Relative capacity of lumber at three moisture content (MC) levels based on simplified surface model for

adjusting lumber properties (Eq. (3), Evans and others 2000) and shrinkage formulas given in ASTM D1990–91 

Ratio of property to 

property at 15% MC 

Ratio of dimensions to 

dimensions at 15% MC 

Ratio of capacity to capacity 

at 15% MC 

Property

Value

at

15%

MC

10%

MC

12%

MC

23%

MC

Comparative

section

10%

MC

12%

MC

23%

MC

10%

MC

12%

MC

23%

MC

Fb 1000 1.000 1.000 1.000 Section 0.978 0.987 1.036 0.978 0.987 1.036 

 2000 1.085 1.051 0.864 modulus (Z) 0.978 0.987 1.036 1.061 1.037 0.895 

 3000 1.123 1.074 0.803 0.978 0.987 1.036 1.099 1.060 0.831 

 4000 1.143 1.086 0.772 0.978 0.987 1.036 1.117 1.071 0.800 

 5000 1.154 1.092 0.754 0.978 0.987 1.036 1.129 1.078 0.781 

 

Ft 500 1.000 1.000 1.000 Area (A) 0.979 0.988 1.033 0.979 0.988 1.033 

 1000 1.000 1.000 1.000 0.979 0.988 1.033 0.979 0.988 1.033 

 1500 1.000 1.000 1.000 0.979 0.988 1.033 0.979 0.988 1.033 

 2000 1.019 1.012 0.969 0.979 0.988 1.033 0.998 0.999 1.002 

 2500 1.031 1.018 0.951 0.979 0.988 1.033 1.010 1.006 0.983 

 3000 1.038 1.023 0.938 0.979 0.988 1.033 1.017 1.010 0.970 

 3500 1.044 1.026 0.930 0.979 0.988 1.033 1.023 1.014 0.961 

 4000 1.048 1.029 0.923 0.979 0.988 1.033 1.027 1.016 0.954 

 

Fc 500 1.000 1.000 1.000 Area (A) 0.979 0.988 1.033 0.979 0.988 1.033 

 1000 1.069 1.042 0.889 0.979 0.988 1.033 1.047 1.029 0.919 

 1500 1.134 1.080 0.786 0.979 0.988 1.033 1.111 1.067 0.812 

 2000 1.166 1.100 0.734 0.979 0.988 1.033 1.142 1.086 0.759 

 2500 1.186 1.111 0.703 0.979 0.988 1.033 1.161 1.098 0.727 

 3000 1.179 1.119 0.682 0.979 0.988 1.033 1.174 1.105 0.705 

 4000 1.215 1.129 0.657 0.979 0.988 1.033 1.190 1.115 0.678 

 

MOE 0.5 1.079 1.047 0.874 Moment of 0.967 0.980 1.054 1.044 1.027 0.921 

 1.0 1.079 1.047 0.874 inertia (I) 0.967 0.980 1.054 1.044 1.027 0.921 

 1.5 1.079 1.047 0.874 0.967 0.980 1.054 1.044 1.027 0.921 

 2.0 1.079 1.047 0.874 0.967 0.980 1.054 1.044 1.027 0.921 

 2.5 1.079 1.047 0.874 0.967 0.980 1.054 1.044 1.027 0.921 
44 

Appendix G—Research on

Effect of Moisture Content on 

Compression Perpendicular

to Grain 

1949 to 1957

ASTM D245–49T states that “modifications for seasoning in 

compression perpendicular to the grain are now under study 

at the U.S. Forest Products Laboratory.” Some studies in the 

period 1949 to 1957 were found in published and unpublished research files at the Forest Products Laboratory. However, it is unclear to what extent this research led to the 

recommendation given in D245–57T (paragraph 61f) that 

“working stresses in compression perpendicular to the grain 

may be increased by 50 per cent above the values given in 

Table VIII (a table of basic stresses) for lumber that will be 

continuously dry in use.”

One of the most prominent studies in this period was that of 

Dr. Robert Youngs on the perpendicular-to-grain properties 

of red oak (Youngs 1957). Compression perpendicular-tograin specimens were obtained using a 4 × 3 ×4 factorial 

design (4 logs, 3 temperatures, and 4 moisture content levels). The target moisture content levels chosen were 6%, 

12%, and 18%, as well as green, and temperatures were 

80°F, 130°F, and 180°F. The tests were conducted on

0.5- by 0.5- by 2-in.- long specimens, with the load applied 

tangential to the growth increments. Eight specimens were 

used per treatment condition (two specimens per log). Both 

proportional limit stress and stress at 2.5% strain were calculated (Table G1). The change in proportional limit stress was 

found to be less than that of the stress at 2.5% strain, but 

the change in both stresses was a function of the degree of 

dryness. At 80°F, the change in stress at 2.5% strain of dry 

oak was plotted relative to the stress at 2.5% stain for green 

oak (Fig. G1). The relationship continued to increase from 

green to about 5.5% moisture content. At 12% moisture 

content, the dry stress was about 60% higher than that for 

green oak. 

Unpublished records also indicate that a second study was 

begun on the perpendicular-to-grain properties of ponderosa 

pine. Apparently, the intent of the study was to virtually 

repeat Young’s experiments, but with a softwood species. 

Although several researchers worked on this problem over 

the years, the study was never completed. The portion dealing with the effect of moisture content and the reversible 

effect of temperature on compression perpendicular to grain 

was completed but never published. These results show a 

much larger percentage of change in compression perpendicular to grain with drying than did the oak study (Fig. G1). 

At 12% moisture content, the increase in stress was about 

100% that of the green wood.

A study on American beech was also published during this 

period (Ellwood 1954). Logs obtained from six locations in 

the eastern United States were cut into 0.5- by 0.5- by 2-in.- 

long specimens. Specimens were tested green or after conditioning to moisture contents of 6%, 12%, and 18%. Tests 

were conducted at 80°F, 100°F, 120°F, 140°F, and 160°F. 

Specimens were tested parallel to growth increments. The 

stress proportional limit and at 2.5% stain were calculated 

(Table G1). The percentage of change in stress at 2.5% strain 

for dry beech, relative to that for green lumber, is plotted

in Figure G1. At 12% moisture content, the increase in 

compression perpendicular to grain was about 85%. 

Table G1—Results of compression perpendicular to grain of northern red oak and American beecha

 Stress (lb/in2

) at Percentage of change due to seasoningb

Species

Moisture

content

(%) Proportional limit 2.5% strain Proportional limit 2.5% strain 

Northern red oakc 6 806 1,504 75.2 110 

 12 574 1,130 24.7 75.1 

 18 383 765 –16.7 6.8 

 green 460 716 0 0 

American beechd 6 1,045 1,773 135 135 

 12 780 1,402 75.7 86.2 

 18 583 989 31.3 31.4 

 green 444 753 0 0 

a

Tests were conducted at 0° angle to growth rings at 80°F. b

Percentage of change calculated as 100 (dry − green)/green. c

Youngs 1957. 

d

Ellwood 1954. 
45

Later Research

In the research discussed in the text, results were presented 

for only two deformation levels: proportional limit and stress 

at approximately 2.5% strain. Research Paper 337 (Bendtsen 

and Galligan 1979) compares ratios of stress for green lumber and lumber with 12% moisture content at 20 levels of 

strain for eight hardwood and softwood species (Fig. G2). 

For most species, the ratio stabilized for deformation levels 

over approximately 0.02 to 0.03 in. Because all test specimens were standard 2 by 2 in. in cross section, the change 

was stable for stresses past approximately 1.0% to 1.5% 

strain.

 This page revised May 2002

Green and Kretschmann (1994) studied the properties of 

clear Southern Pine as a function of moisture content from 

green to 4% moisture content. At 4% strain, the change in 

stress increased continuously with decreasing moisture 

content (Fig. G1). At 12% moisture content, the change in 

stress was about 150% that of green wood.

Figure G1—Effect of moisture content on compressive 

stress perpendicular to grain at 80°F, relative to green 

values. Data sources: ponderosa pine, Forest Products 

Laboratory unpublished data; Southern Pine, Green 

and Kretschmann 1994; beech, Ellwood 1954; red oak, 

Youngs 1957. 

Figure G2—Dry/green ratios for compressive stress 

perpendicular to grain of eight species (adapted from 

Bendtsen and Galligan 1979). 
46 

Appendix H—Potential Source 

of Dry-Green Ratio for Shear in 

ASTM D245 

ASTM D245–98 permits allowable shear values of dimension lumber to be increased 13% for lumber with maximum 

moisture content of 15%. As discussed in the text, this factor 

apparently originated in 1934 with a 9/8 factor developed 

from information in Misc. Pub. 185. In ASTM D2555, the 

dry-green ratio obtained by block shear tests (ASTM D143–

94) on small clear specimens averages about 2.0 for softwood species and about 1.9 for hardwood species (App. E, 

Table E1). If block shear tests were the basis for moisture 

adjustments in Misc. Pub. 185, why was the factor (drygreen ratio) only 1.125? One potential explanation is that 

this low ratio is based not on clear wood tests but on observations from tests of full-size beams that failed in shear.

We have found no direct evidence of this assumption,

but it is supported by the following concepts:

1. Original allowable shear stresses were really 

“calibrated” to bending members that failed in shear. 

2. Initial seasoning increases in extreme fiber in bending 

for dry dimension lumber were based on test results

from full-size members, not on clear wood data. 

Calibration of Allowable Shear 

Stresses

In an unpublished letter to Alex R. Entrican in 1933, John 

Newlin explains some of the reasoning behind the derivation 

of working properties in the United States:

Our assigned stresses in horizontal shear are primarily the 

results of tests of structural timbers. A part of these bending 

tests were made on short, high stringers with symmetrical 

loads placed three to four times the height of the beams from 

the support.

Here we should point out that Newlin is not talking about 

some special series of beam shear tests, but rather inferences 

made from the standard bending tests at the time on timbers. 

Since 1906, the standard test conducted by the Forest

Service had used a simply supported beam with symmetric 

loads placed at one-third points of the span. However, the 

standard span was approximately 15 ft, regardless of the 

depth of the beam. Thus, the standard test provided an “a/h” 

ratio between 3 and 4. Moreover, prior to 1906, the standard 

test was conducted using a 15-ft span, but with a single load 

applied in the center of the span. 

Newlin is thus indicating that allowable properties for shear 

were determined from an evaluation of failure stresses for 

beams that first failed in shear. Given this fact, it seems 

plausible that moisture adjustments might also be based on 

observations of full-size tests. 

Tests of Full-Size Members as

Basis for Adjustments 

As was discussed in the text for MOR, the “25% rule” first 

discussed in the unpublished memorandum of 1924 by 

Newlin and Johnson was based on test results for graded 

lumber tested green and dry. In this instance, the resulting 

moisture content adjustments for dimension lumber were 

also much lower than those found from tests of small clear 

specimens. Thus, the idea of basing property–moisture content adjustments on results from tests of full-size specimens 

would not have been novel in 1934. 

One source of information that was available in 1933 was 

the data summarized in Bulletin 108 (Cline and Heim 1912). 

However, despite the large numbers of timbers tested, in 

very few timbers was the first failure judged to be due to 

shear (or occurring at checks and splits). Another problem is 

that the range of moisture contents of beams considered 

green sometimes overlapped with the range of moisture 

contents of beams considered dry. Also, there is no assurance that the beams that failed in shear were of equal quality 

in the green and dry groups. These were the data used to 

develop the initial grading system proposed by the Forest 

Products Laboratory, and specimens were therefore not 

selected on the basis of “grade.” However, the data published in Bulletin 108 were the primary data that would have 

been available to Newlin and Johnson, and thus it is instructive to look at what they may have evaluated.

Two of the largest data sets within the various species and 

beam sizes reported in Bulletin 108 are the green and dry 

bending data from tests on Douglas Fir–Larch and Southern 

Pine 6- by 16-in. timbers. Using the data from only those 

beams identified as having initial failure in shear, we calculated the shear stress at time of failure using the VQ/IT 

concept. Average values from these calculations are summarized in Table H1. For Douglas Fir–Larch, the dry-green 

ratio is 1.32; for Southern Pine, the ratio is only 0.96. For 

both species groups, the average moisture content of the dry 

group was only approximately 20%. Thus, these two sets of 

results are contradictory. From the information available, it 

is not possible to further investigate reasons for the difference in performance. However, a limited amount of other 

timber data that are not part of Bulletin 108 are available that 

can shed additional light on dry and green beam shear

failures.

In 1931, Markwardt published results from tests on 8- by

16-in. western hemlock and Sitka spruce timbers sampled in 

Alaska. Markwardt carefully selected 32-ft-long logs of 

approximately uniform quality along their length. Each log 

was cut in half and one-half tested green. The other half was 

carefully air dried under cover for a long time before testing. 

Testing was conducted over a 15-ft span with loads at the 

one-third point of the span. Because only one green Sitka 

spruce beam failed in shear, those results are not useful.
47 

The average dry-green ratio for western hemlock judged to 

have failed in shear was 1.4 (Table H1). 

As part of a study on Douglas-fir timber properties, Cline 

and Knapp (1911) used a simply supported beam loaded by a 

single load at mid-span, the older Division of Forestry procedure. Study material consisted of 171 green beams and 81 

“air dry” beams (no moisture content given). No attempt was 

made to match quality of green and dry timbers. Three green 

beams and five air-dry beams failed in shear. The dry-green 

ratio of these members was 1.33 (Table H1). 

Finally, Betts (1909) evaluated failures in center-pointloaded Southern Pine 8- by 16-in. beams for green and two 

dry exposure conditions. Again, timber groups were not 

matched for quality. For beams dried outdoors under shelter 

for 21 months, the dry-green ratio based on calculated shear 

stress at time of failure was 1.31; for beams dried in the open 

for 3.5 months, the dry-green ratio was 0.97 (Table H1). 

These studies suggest that the shear strength of carefully 

dried beams might increase about 30% when the beams are 

dried to an average moisture content of about 20%. However, the data also support the judgment given in Circular 

295 that excessive checking, which can occur when green 

beams dry quickly, may result in much lower values. This 

type of reasoning could have resulted in the adoption of the 

more conservative 9/8 factor. It is also interesting to note 

that for softwoods, a factor of 1.125 (later rounded to 1.13) 

is not far from the 5th percentile dry-green ratio tabulated in 

D2555 (App. E). 

Table H1—Effect of moisture content on calculated shear strength at failure of timbers judged to have failed 

initially in sheara

 Green lumber Dry lumber 

Load point and species group Refb n

MC

(%) Shear n

MC

(%) Shear 

Dry-green

ratio

One-third-point load 

Douglas Fir (1) 7 46 287 15 20 380 1.32 

Southern Pine (1) 13 33 362 9 20 348 0.96 

Western Hemlock (2) 5 42 281 18 17 394 1.40 

Center-point load 

Douglas Fir (3) 3 ? 166 5 ? 211 1.33 

Southern Pine (4) 12 51 375 12 20 493 1.31c

 4 23 364 0.97d

a

Timbers were 8 by 16 in.

b

References: (1) Cline and Heim 1912, (2) Markwardt 1931, (3) Cline and Knapp 1911, and (4) Betts 1909. 

c

Air dried under shelter for 21 months 

d

Air dried in the open for 3.5 months. 
48 

Appendix I—Profiles of

Early Pioneers 

Early pioneers had a tough job: to devise the first national 

consensus system for grading and property assignments in 

the United States. Later contributions may have been just as 

sweeping, but these were changes to an existing policy. The 

following individuals each contributed to the first set of 

procedures for adjusting lumber properties for change in 

moisture content. For all of them, this was but one of many 

contributions to wood engineering.

Walter Gilman Berg (1858–1908) 

Walter G. Berg was born in the United States, but received 

most of his education in Europe. At university, Berg was 

awarded a Gold Medal by the King of Wurtemberg for a 

treatise on spherical conic sections. In recognition of this 

award, the Polytechnic Institute of Stuttgart awarded Berg a 

scholarship and employed him for government surveys.

In 1878, Berg received a Civil Engineer degree from the 

Institute.

Berg returned to the United States in 1879 and entered a 

career with the railroads. His first job was office assistant 

and shop inspector of railroad bridges of the Delaware 

Bridge Company. In 1880, he joined the engineering department of the Richmond and Allegheny Railroad; in 1882, 

he became principal assistant engineer of the East Tennessee, Virginia, and Georgia Railroad; and in 1883, he joined 

the Lehigh Valley Railroad Company where he was to spend 

the rest of his career. 

At Lehigh Valley, Berg was initially in charge of design and 

construction of shop buildings and roundhouses. In 1886, he 

designed and constructed a creosote treatment plant at Perth 

Amboy, New Jersey, and was put in charge of the operation. 

This plant was among the earliest of its kind to be operated 

by an American railroad. By 1890, Berg had become chief 

engineer.

Berg was very active in a number of professional organizations and served as president of the Association of Railway 

Superintendents of Bridges and Buildings and of the American Railway Engineering and Maintenance of Way Association. For his engineering standing and prominence he was 

selected to serve on the jury of awards on railroad exhibits at 

the St. Louis World Fair in 1904. In 1908, he was appointed 

a delegate to the conference on conservation of natural 

resources held by President Theodore Roosevelt. Berg died 

suddenly on May 12, 1908. 

Berg authored many books and publications. The recommendations of the committee (App. A) that he chaired on the 

strength of bridge and trestle timbers, presented in New 

Orleans in 1895, is discussed in the committee’s report on 

the early development of standardized procedures (Berg and 

others 1907). This report contained a comprehensive review 

of the available test data on wood properties by the leading 

authorities of the day. It also included recommendations on 

specific design concerns such as bolted connections and 

column design. The report was published in whole or part by 

a number of technical outlets, including incorporation in the 

appendix of Economical Designing of Timber Trestle 

Bridges by A. L. Johnson (1902). Because of the demand for 

this information, in 1899 Berg also published the report as 

Berg’s Complete Timber Test Record (B. S. Wasson and 

Co., Chicago, IL). We found it easier to obtain a copy of the 

original committee report than Berg’s Test Record. The Test

Record differs from the committee’s report by the addition 

of six pages, which discuss the distribution of the committee’s report and list publications since October 1895. The 

Test Record also includes an interesting diagram prepared by 

Berg of test data on full-size “yellow pine” columns and 

formulas for column strength. 

Harry D.Tiemann (1875–1966) 

Dr. Harry Tiemann was born in Brooklyn, New York, on 

March 26, 1875. The son of a Civil War veteran and chemist, he completed his engineering degree from Steven’s 

Institute of Technology in 1897 and a master of forestry 

degree from Yale in 1903. In 1900, Tiemann was hired by 

the Division of Forestry to conduct research on wood moisture relationships at the new testing laboratory established at 

Yale University. He conducted an extensive and exhaustive 

study of the effect of moisture content on the physical and 

mechanical properties of clear wood. Even if he had done 

nothing else of note in his professional career, Harry Tiemann would be remembered as the first to articulate the 

concept of the “fiber saturation point” (Tiemann 1906). In 

1903, he became head of the New Haven laboratory, a post 

he held for 6 years. He spent the winter of 1909 in Washington, D.C., perfecting his design for a water spray dry kiln 

and obtaining a patent. In the spring of 1910, Tiemann came 

to the new Forest Products Laboratory (FPL) in Madison, 

Wisconsin, and remained there until 1945. 

In honor of Tiemann, a Douglas-fir tree was planted and a 

memorial plaque placed at FPL in May 1976. In an article in 

the FPL newsletter Chips following the dedication ceremony, FPL scientist Bill Feist wrote of Tiemann’s accomplishments:

During World War I, he developed the first practical wood 

drying kiln used in this country. His water-spray kiln saved 

the United States from what might have been a disastrous 

shortage of seasoned wood during the war. During the war, 

300 of these kilns were built to dry everything from gunstocks to airplane wing beams. His kilns were the only ones 

officially accepted by the War Department for the drying of 

war materials. He was the chief of FPL’s first Timber Physics section, and retired in 1945. When he died in 1966, he 

was survived by a son, Dr. Theodore D. Tiemann, Professor 

of Metallurgical and Mining Engineering at the University 

of Wisconsin, Madison. At that time, as is still true, this
49 

engineering department occupied the original Forest Products Laboratory building on University Avenue. 

John A. Newlin (1872–1943) 

John Newlin was born February 2, 1872, in Plainfield, Indiana. He graduated from Purdue University with a bachelor of 

science degree in civil engineering. For 4 years, Newlin 

served as a civil engineer with the Chicago, Indianapolis, 

and Louisville Railroad and the Pittsburgh, Cincinnati, Chicago, and St. Louis Railroad. In 1904, he joined the USDA 

Division of Forestry as an engineer in timber testing on a 

cooperative project then under way with Purdue University. 

A short time later he was placed in full charge of this work, 

which was shifted to Madison in 1910.

Newlin was chief of the Timber Mechanics Division at FPL 

from 1910 to 1939, when he was relieved of administrative 

duties so that he could devote full time to research and consultation. He died March 27, 1943, 4 weeks after his retirement. The following is an excerpt from a profile written by 

L. J. Markwardt: 

John A. Newlin was the first Chief of the Division of Timber 

Tests, later named Timber Mechanics, and then Wood Engineering. He was transferred from Purdue University when 

the Laboratory was organized, where he worked on Forest 

Service projects under Dr. William Hendrick Hatt, Dean of 

Engineering.

In my first FPL appointment in September 1912 as Assistant 

Engineer, I assumed duties as Assistant Chief of the Division, and worked under Newlin until his retirement [from 

Administration] in the 1930s, when I was appointed Chief

to succeed him. I thus had a long tenure with Newlin, and 

probably knew him as well or better than anyone else. 

Newlin was both competent and modest. He thrived on

details of technical analysis, and had an uncanny ability to 

develop sound conclusions from seemingly conflicting data. 

He could clearly visualize the distribution of strain in members under stress, which led to refinements and modifications of the usual formulas used in stress analysis. This was 

his preferred area of operation in which he achieved eminent 

success.

He preferred to turn administrative duties over to me, so he 

could devote practically full time to research. I was also 

delegated to take charge of the testing personnel and operation of the testing floor. In preparing reports and publications, he did little longhand writing or stenographic dictating. He preferred to work with an assistant to whom he gave 

notes, which were converted to draft form and then reviewed. He was author of numerous papers and publications. 

He did not care to give speeches or take part in society meetings. He was a member of the American Society for Testing 

and Materials and the American Railway Association. For 

many years he was Secretary of ASTM Committee D–07 on 

Wood of which Dr. Herman von Schrenk was Chairman. 

Robert Pilson Albert Johnson

(1888–1962)

A native of Alexandria, Virginia, R.P.A. Johnson graduated 

from Virginia Polytechnic Institute and State University with 

a bachelor’s degree in engineering and then earned a master’s degree from the University of Wisconsin, Madison. In 

June of 1918, he joined the FPL as an engineer in the Division of Timber Mechanics under the direction of John 

Newlin. Specializing in lumber properties and grading, 

Johnson helped establish the first systems for lumber property assignment developed at FPL. During his career he was 

often honored for his contributions to the safe and efficient 

utilization of wood, and he ultimately became chief of the 

Division of Physics and Engineering at FPL. He was an 

active member of the American Institute of Timber Construction, Committee D7 of the American Society for Testing and Materials, the American Lumber Standards Committee, and the Committee on Bridge and Trestle Bridges of the 

American Railway Engineering Association. With the exception of 2 years on the War Production Board during World 

War II, Johnson spent his entire career at FPL and retired in 

1958 with over 50 years of government service. The following is excerpt from an article in Chips by D.G. Colman: 

“Johnny,” as he was affectionately called by all who knew 

him, was a personal friend of all who worked at the Forest 

Products Laboratory. Endowed with a warm, friendly, and 

sincere personality, probably no other person in the Forest 

Service has made more lasting and genuine friendships than 

Johnny. He was a firm supporter of “esprit de corps.” 

Johnny did many big things—authored bulletins, delivered 

speeches, headed a Laboratory Division—but it was the little 

things that set him apart—a simple form for a legal will, a 

diagram of Government salaries compared with well-paid 

industry, a pocket lens for wood identification, a gentle Virginia drawl noticeable on nationwide radio hookups. These 

are but a few of the things that made Johnny a friend of 

mankind, a champion of wood, and a truly uncommon man. 

William Emerson

(1701–1782)

William Emerson, of Hurworth on Tees–County Durham, 

England, wrote several influential books in astronomy, 

physics, navigation, and mathematics. The Principles of 

Mechanics is described as “explaining and demonstrating the 

general laws of motion, the laws of gravity, motion of descending bodies, projectiles, mechanic powers, pendulums, 

centers of gravity, &c. strength and stress of timber, hydrostatics, and construction of machines.” This book is characterized as “a work very necessary to be known by all gentlemen and others that desire to have an insight into the 

works of nature and art, and extremely useful to all sorts of 

artificers, particularly to architects, engineers, shipwrights 

millwrights watchmakers &c. or any that work in a mechanical way.” Emerson described the organ of the middle 18th

century and rightly concluded that “wood is likewise weaker 
50 

when it is green and strongest when thoroughly dried.” He 

designed sundials that show both the time and line of latitude. Emerson was offered the opportunity to join the Royal 

Society, but he turned down the offer in objection to paying 

dues for the right to place FRS after his name. He died on 

May 21, 1782, and is buried in the churchyard of All Saints 

Church in Hurworth. 

It was a challenge to find pictures of the early pioneers who 

made important contributions to our understanding of the

effect of moisture content on lumber properties. Some pictures, like the one of Walter Gilman Berg, required a long 

search and a measure of luck. The most unusual source was 

for the picture of William Emerson. We were told that a 

portrait of Emerson hangs in the Emerson Arms, a pub in 

Hurworth that overlooks the river, possibly in recognition

of his fondness for ale and fishing. Thanks to the Internet, 

we managed to contact Hurworth IT Consultants, who 

kindly went to Emerson Arms and photographed

Emerson’s portrait. 
51