This document has been scanned from hard-copy archives for research and study purposes. Please note not all information may be current. We have tried, in preparing this copy, to make the content accessible to the widest possible audience but in some cases we recognise that the automatic text recognition maybe inadequate and we apologise in advance for any inconvenience this may cause.

Technical Report No 2 ODe 811 2 812 7(048 1)

Sloping Grain and the Strength of

Structural Timber -A Selective

Annotated Bibliography

Therese 0' Hara

Dennis Grant

N.S.W. TIMBER ADVISORY COUNCIL

Sydney 1985

Member ATRI

SLOPING GRAIN AND THE STRENGTH OF STRUCTURAL TIMBER: A SELECTIVE ANNOTATED BIBLIOGRAPHY

The rese 0 I Ha ra Dennis Grant

N.S.W. TIMBER ADVISORY COUNCIL Sydney 19R5

-------------------------------------------------------------------

- 2 -

Published by N.S.W. Timber Advisory Council, P.O •. Box 100, BEECROFT. 2119. Tel: (02) 871 1458.

Compiled by Therese O'Hara and Dennis Grant, Wood Technology & Forest Research Division, Forestry Commission of N.S.W., P.O. Box 100, BEECROFT. 2119.

Technical Report No. 2 - published 1985

Australian National Library ISSN 0813-5134 ISBN 0 9599030 6 2

- 3 -

FOREWORD

The literature searched for this bibliography covers the period

1921-1984. Although not exhaustive, the major texts for this period have been covered. The primary source was the Forestry Commission of New South Wales plus abstracting services. References marked with an asterisk (*) are not held in the New South Wales Forestry Commission Library. Call numbers are those for Library holdings.

p

- 4 -

INTRODUCTION

Slope of grain in structural timber can result from diagonal sawing,

sawing a log with significant taper, sawing logs with poor form or with spiral

or twisted grain.

Definitions of slope of grain as given in AS 01 (27) are firstly for

sloping grain:

"An arrangement of fibres or other longitudional elements at an angle to the

longitudinal axis of the piece."

and secondly for spiral grain:

"An arrangement in which fibres or other longitudinal elements take a spiral

course about the axis of the tree."

Slope of grain is measured by the angle between the direction of the fibres and

the edge of the piece, with the angle being expressed as a slope. When both sloping grain and spiral grain. are present the combined slope of grain is taken

as the effective slope (i.e. the square root of the sum of the squares of the two slopes). Grading rules generally allow the slope of grain associated with a permissible knot to be ignored. The method of determination of slope of grain by the commonly used scribe method is described in AS 1080.2.1 (26).

Commonly used strength ratios corresponding to various slopes of grain are given in ASTM 0245 (1) and reproduced in Table 1. The strength ratio is the percentage reduction that is applied to permissible stresses for pieces with a

particular slope of grain relative to pieces with zero slope of grain.

- 5 -

TABLE 1. Strength Ratios Corresponding to Various

Slopes of Grain

Maximum Strength Ratio,

percent

Slope of Grain

Bending or Compression

Tension Parallel Parallel to

to Grain Grain

1 in 6 40 56

1 in 8 53 66

1 in 10 61 74

1 in 12 69 82

1 in 14 74 87

1 in 15 76 100

1 in 16 80

1 in 18 85

1 in 20 100

Data from ASTM 0245-74 (1)

1 •

2.

3.

- 6-

BIBLIOGRAPHY

AMERICAN SOCIETY FOR TESTING MATERIALS.

1981 Annual book of ASTM standards. Part 22. Wood;

Adhesives.

UDC R.389.6(73)

AME

0245-74. Standard methods for establishing structural grades and related allowable properties for visually

graded lumber.

Strength ratios associated with slope of grain in bending

members, and in members subjected to compression parallel to grain. (see section 6). Section 4.1.2. plus table

p. 158.

AMERICAN SOCIETY OF ENGINEERS.

Wood structures: a design guide and commentary. Compiled by Task Committee on Status-of-the-Art: Wood Committee on Wood. ASCE Structural Division.

New York, 1975.

The influence of fiber direction on mechanical properties can be approximated by Hankinson's formula. Graphical and tabular information (pp.40-43).

OOC 833 AME

BACH, L.; ROVNER, B. SER/C

Stress relaxation in wood at different grain angles. Canada. Forest Products Laboratory, Information Report VP-X-14.

Vancover, 1967.

An exploratory study of uniaxial compression stress relaxation of Douglas-fir was made to survey the relative influence of grain angle to direction of restraint. Fractional stress relaxation was found to increase with increasing grain angle.

Graphs.

4.

5.

6.

7.

- 7 -

BAMBER, R.K.; BURLEY, J. ODC 811:174.7

The wood properties of radiata .pine. Slough, Commonwealth BAM Agricultural Bureau, 1983.

Slope of grain is important in grading timber and in the

Australian grading rules for structural use of radiata pine timber slope of grain exceeding one in five is excluded from

the weakest grade and slope exceeding one in ten is excluded from the highest grade.

BOOTLE, K.R. ODC 8(94)

Wood in Australia types, properties and uses. Sydney. BOO McGraw-Hill, 1983.

The strength of sawn beams can be reduced approximately 20 percent by a grain slope of 1 in 16, 30 percent by 1 in 12 and 50 percent by 1 in 8. (p. 46).

BRITISH STANDARDS INSTITUTION.

Code of Practice CPl12 : Part 2:1971. The structural use of timber. Part 2. Metric Units. London, 1971.

Tabular information for maximum slope of grain of softwood and hardwood (p.111). Where spiral grain occurs, the slope of grain should be determined by measuring the worst slopes of grain on the faces and on the edges and taking the square root of the sum of the squares of the slopes (p.112).

BROWN, H.P.; PANSHIN, A.J.; FORSAITH, C.C.

STD

ODC 100

Textbook of wood technology: the physical, mechanical, 4 and chemical properties of the commercial woods of the United States. Vol.2. First Edition. New York, McGraw-Hi 11, 1952.

pz

8.

9.

- 8 -

Tabular information recommending reductions with respect to slope of grain in the values for basic stress in

extreme fiber in bending and in compression parallel to the grain for beams and stringers; joists and planks; posts and timbers (p.478).

C.S.I.R.O. DIVISION OF BUILDING RESEARCH.

Fundamentals of timber engineering, Part 1. Melbourne, 1974.

*

Tabular data on the effects of various amounts of sloping

grain on the strength of beams. The modulus of elasticity also decreases with increasing slope of grain although the effect on Young1s modulus or stiffness is less than that on strength. Graphs showing the effects of slope of grain on the bending strength and stiffness of jarrah beams. The maximum crushing strength parallel to the grain is unaffected at slopes of up to 1 in 10, with a reduction of only 5-10% at a slope of 1 in 5.

C.S.I.R.O. DIVISION OF FOREST PRODUCTS.

Technical Paper No.28. The properties of Australian timbers. Part 3. Pinus radiata D.Don (Pinus insignis Doug.) Insignis, Monterey, or remarkable pine.

Table showing the loss of bending strength for various slopes (p.19-20).

ODC P219.02

6

10. C.S.I.R.O. DIVISION OF FOREST PRODUCTS. SER/C

Trade Circular No.48, 1952. Sloping grain in timber.

Graphs of the effect of sloping grain on the stiffness and bending strength of structural members. A slope of grain greater than 1 in 12 should not be permitted in beams. In flooring and in the smaller sizes of joists and rafters, stiffneis is usually of more

- 9 -

importance than strength, and a slope of 1 in 8 is usually

permissible. Posts and columns generally depend on stiffness, and the slope of grain should not exceed 1 in 8. However, short columns such as struts and stumps are not seriously affected by sloping grain unle;s slope exceeds 1 in 5.

11. DINWOODIE, J.M. PER/J

Timber - a review of the structure - mechanical property relationship. Journal of Microscopy, Vol.104, Pt.1, 1975, pp. 3-32.

Since timber is an anisotropic material it follows that the angle at which stress is applied relative to the longitudinal axis of the cells will determine the strength of failure. Strength in tension appears to be much more sensitive to angle of grain than either bending or compression and at angles exceeding 8% there is a marked decline in tensile strength. Table showing anisotropy in strength in Douglas-fir timber for moisture content, tension and compression (p.22-23).

12. FORESTRY BRANCH, FOREST PRODUCTS LABORATORIES DIVISION.

Canadian woods: their properties and uses. Second Edition. Ottawa, 1951.

ODC Q810(71)

CAN

While cross or spiral grain is responsible for considerably fewer failures in structural timbers.than are knots, the magnitude of the strength reduction may be considerably greater. As shown in Table 9, approximately 9 per cent of failures were due to cross or spiral grain. However, the strength reductions, below that for joists failing through no apparent cause, were 40 percent. (p.114-116). Effect on compressive strength less severe than on tensile strength.

- 10 -

13. HAYGREEN, J.G.; BOWYER, J.L.

Forest products and wood science an introduction. Iowa, Iowa State University, 1982.

The strength of wood is affected whenever there is a

slope of the grain greater than about 1 in 20. The percent of strength loss in bending and compression resulting from grain deviation Table 10.6 (p.245-248).

14. G.G. KARLSEN. (edit).

Wooden Structures. Moscow, Mir Publishers, 1967.

Graphical data showing influence of slope of grain on the strength of timber. The amount of sloping grain for members under tension according to the existing standards must not exceed 7cm for 1m of length (pp.27-28, fig.8).

15. KLOOT, N.H.; SCHUSTER, K.B.

The effect of cross-grain on the bending properties of jarrah scantlings. Australian Journal of Applied Science,

Vol.9, No.1, 1958. pp.9-17.

Bending tests have been conducted on 118 green jarrah scantling specimens of nominally 4 by 2 in. sections containing various degrees of cross-grain. The results indicate a significant linear trend of both modulus of

rupture and modulus of elasticity on grain angle. The effect of cross-grain has been found to be substantially lower than has hitherto been assumed in formulating grading rules for this timber.

ODC

8

HAY

833 KAR

PER/A

- 11 -

16. KOLLMANN, F.F.P.; COTE, W.A.

Principles of wood science and-technology. Vol.1, Solid wood. New York, Springer-Verlag, 1968.

Relationship between grain angle and the elastic

properties of wood for spruce, beech and basswood (p.302-304).

Tensile strength in relation to grain angle. Tensile strength is much more reduced by cross grain than

bending or compressive strength (p.326-327). Grain

ODC 81(021)

KOL

angle affecting the bending strength (modulus of rupture). Tabular and graphical data showing fir, basswood, pine, ash (p.365-366). Slope of grain reduces the shock resistance of wood. Angle of 5° causes 10% decrease in toughness, 10° leaves only 50% shock resistance. Graphical data for beech (p.385-386).

17. KUBLER, H.

Wood as building and hobby material. New York, Wiley, 1980.

Low strength in a piece is mostly caused by fiber deviation - slope of grain, cross grain. In tension, slopes of 1 in 25 can already have significant effects, while in compression a substantial drop begins at slopes of 1 in 10. Graph showing effect of fiber-load-angle on strength of clear wood. (p.73-74).

18. LOWERY, D.P.; ERICKSON, E.C.O.

The effect of spiral grain on pole twist and bending strength. Intermountain Forest and Range Experiment Station. Research Paper INT-35. 1967.

Table 5 shows that for Douglas-fir and Western larch moderate right spiraled grain with a slope of 1:12 or more has a negligible effect on the strength of a pole, and poles with a spiral grain of 1:8 or less have 75%

*

SERf I

~- --- - -------

- 12 -

of the strength of straight grained poles. Poles with left spiral grain of 1:8 to 1:12 slope may not be more than 50 to 60% as strong as comparable straight-grained poles.

19. MULLINS, E.J.; KNIGHT, T.S.

Canadian Woods: their properties and uses. University of Toronto Press, Canadian For. Serv., Canadian Govt. Publ. Centre. Third Edition. Toronto, 1981.

A brief description of the nature of cross-grain, its

detection and effects or stiffness, strength and seasoning defect and limitations on its use (p.56-57). Effect on compressive strength less severe than on tensile strength. Definition and determination of slope of grain, p.77.

20. PANSHIN, A.J.; de ZEEUW, C.

Textbook of wood technology. Volume 1. Structure, identification, uses, and properties of the commercial woods of the United States and Canada. Third Edition. New York, McGraw-Hill, 1970.

Graphical data showing change in compression strength for Scotch pine [Pinus sylvestris L. (from Sweden)] at 12 percent moisture content, as related to the angle between direction of load application, grain angle, and growth­ring orientation. The tensile behaviour of wood is the most sensitive to cross-grain and decreases for any slope

ODC : 81

PAN

of grain greater than 1 in 25, i.e. deviations of grain whose fractional representation has a larger value 1 in 20, 1 in 10. Bending strength is not reduced until the grain slope is greater than 1 in 20. Compression strengths are the least sensitive and show no change until the grain slopes become larger than 1 in 15. The loss of strength becomes large for cross-grain which exceeds the critical limits given above. A slope of 1 in 8 reduces the bending strength approximately

one-half and the compressive strength one-third.

\ ,

- 13 -

21. PEARSON, R.G.; KLOOT, N.H.; BOYD, J.O. ODC 833

Timber engineering design handbook. Second Edition. PEA Melb., C.S.I.R.O. 1962.

Tabular information on the effect of sloping grain on strength of beams (p.21). Nomograph of Hankinson's formula for bearing strength of wood at angles to the grain (p.56-57). Nomograph of Hankinson's formula for joint strengths at angles to the grain (p.135-136).

22. RADIATA PINE ASSOCIATION OF AUSTRALIA. ODC P854.2

Grading rules for radiata pine timber. Fourth Edition. RAD Adelaide, 1977.

Tabular information showing modulus of rupture across

the grain and ultimate strength in compression along the length of piece for timber with various grain angles

(p.98-99).

23. REID, J.S. SER/N

Notes on structural grading and use of timbers. New Zealand. Forest Service. Information Series No.50, 1964.

Defect provisions for the select structural grade Tawa, hard beech, red beech, silver beech and rimu that sloping grain will not exceed 1 in 12 in middle third of length in special length joists for single spans and 1 in 10 towards ends; not exceeding 1 in 15 in middle third of length of beams ordered in special lengths and 1 in 12 towards ends. Maximum admissible defects of sloping grain on the poorer face or edge for standard structural grades: N.Z. Douglas fir and N.Z. European larch 1 in 10; Radiata pine and Corsican pine 1 in 10; tawa, hard beech, red beech, silver beech and rimu 1 in 10.

- 14 ~

24. SCHNIEWIND, A.P.; LYON, D.E. PER/F

Tensile strength of redwood dimension lumber. 11. Prediction

of strength values. Forest Produ~ts Journal. Vol.21, No.8, 1971. pp. 45-55.

Relationship between tensile strength and slope of general

cross-grain. Graph.

25. SILVESTER, F.D. OOC 812

Timber: its mechanical properties and factors affecting SIL its structural use. Oxford, Pergamon, 1967.

Graphical data showing the effect of slope of grain on strength (pp.33-34). Graphical data showing effect of grain angle on strength for Douglas-fir and Sitka spruce as measured by ultrasonic pulse technique together with

comparative curves for compressive tensile strength. (p.40-41). Tabular information giving maximum slope of grain for the permissible gross features for sawn timber.

(p.79). Measurement of slope of grain and tabular detail of permissible combined slopes for diagonal and spiral grain

(p.93-95).

26. SLIKER, A.

Young1s modulus of wood as affected by strain rate, grain angle, and stress level. Wood Science, Vol.7, No.3, 1974,

pp. 223-231.

PER/W

Pinus lambertiana tests show that as the angle between load and grain increased, there was an increase in the rate of change of Young1s moduli with strain rate and an increase in the change of Young1s moduli with stress.

- 15 ,-

27. STANDARDS ASSOCIATION OF AUSTRALIA.

AS01 - 1964. Glossary of terms used in timber standards.

Defines technical and descriptive terms used or likely to

to be used in Australian timber standards.

28. STANDAROS ASSOCIATION OF AUSTRALIA.

AS 1490-1973. Visually stress-graded radiata pine for structural purposes.

Sloping grain limitations for structural timbers. In F5, not exceeding 1 in 5; to F11, not exceeding 1 in 10; F14, 1 in 15.

29. STANDARDS ASSOCIATION OF AUSTRALIA.

AS 2082-1977. Visually stress-graded hardwood for structural purposes.

Sloping grain limitations for four structural grades of hardwoods. Structural grade No. 1, not exceeding 1 in 15 (jarrah 1 in 12), to Structural Grade No. 4, not exceeding 1 in 6 (all species).

30. STANDARDS ASSOCIATION OF AUSTRALIA.

AS1080.2.1-1981. Determination of slope of grain by scri be.

Sloping grain is often difficult to detect by visual

examination of the surface. This method is suitable for use on timber articles with dressed surfaces and

which do not exhibit surface checks.

STD

STD

- 16 -

31. SUNLEY, J.G.

Grade stresses for structural timbers. Great Britain.

Forest Products Research Laboratory. Bulletin No. 47. 1968, pp. 8-9.

SER/G

Effect of slope of grain on strength properties is much

greater in structural sizes than in small clear specimens. Grading rules for slope of grain in relation to strength of Hardwood/Softwood.

32. WILSON, T.R.C.

The effect of spiral grain on the strength of wood. Journal of Forestry. Vol.19, No.7, 1921 pp. 740-747.

Tabular and graphical data for Douglas fir, Sitka spruce and white ash (Fraxinus americana) relating slope of grain to strength variables in static bending. Stiffness appreciably decreased at a slope of 1:15; strength in bending decreased 10% at a slope of 1:20 and 20% at 1:15. Shock resistance was deficient at slopes of 1:25. It was concluded that slopes greater than 1:20 should not be permitted in highly stressed parts.

33. WILSON, T.R.C.

U.S. DEPARTMENT OF AGRICULTURE. Guide to the grading of structural timbers and the determination of working stresses. Miscellaneous Publications No. 185, Washington, D.C., 1934.

Tabular information giving strength ratios for stress in extreme fiber in bending for various values of slopes of grain (p.9).

PER/J

SER/U

- 17 -

34. U.S. DEPARTMENT OF AGRICULTURE. FOgEST SERVICE, FOREST PRODUCTS LABORATORY.

Wood handbook: wood as an engineering material. Agriculture Handbook No. 72, 1974.

Tabular information on the strength of wood members with various grain slopes compared to strength of a straight-grained member expressed as percentages. Graphical information on the effect of grain angle on mechanical property of clear wood according to a Hankinson-type formula (pp.4-27 - 4-29).

8

UNI