Factors Influencing Bending Properties of White Spruce Lumber


  • Hui Zhou
  • Ian Smith


Bending properties, softwood lumber, drying defects, knot area


Influences of drying treatments, slope of grain, knots, juvenile wood percentage and other factors on strength properties of lumber were studied.

Conventional drying schedules, knots, warp, and juvenile wood significantly influenced the bending strength and stiffness of the lumber. Both modulus of rupture (MOR) and modulus of elasticity (MOE) decreased with any increase in the projected knot area (PKA). The mean MOR of specimens with PKA > 50% was only half of the mean MOR of specimens with PKA < 20%. The corresponding ratio for MOE was about 0.6. Both MOR and MOE decreased with an increase in warp or juvenile wood percentage. A clear dependence of strength on general slope of grain was not evident under the test conditions in this project.


ASTM. 1989. (D2915-88). Standard practice for evaluating allowable properties for grades of structural lumber. American Society for Testing and Materials, Philadelphia, PA.nASTM. 1989. (D4761-88). Standard test methods for mechanical properties of lumber and wood-based structural material. American Society for Testing and Materials, Philadelphia, PA.nBSI. 1988. (BS4978). British Standard specification for softwood grades for structural use. British Standards Institution, London.nCramer, S. M., W. B. Fohrell, K. A. McDonald, and D. C. Stahl. Exploring the relationship between local slope of grain angle and initial fracture in lumber subject to tensile load. Proceedings of 1988 International conference on timber engineering, Seattle, 2:566-575.nCech, M. Y., and F. Pfaff. 1977. Kiln operator's manual for eastern Canada. Eastern For. Prod. Lab. Ottawa xv + 198 pp.nForestry Branch, Forest Products Laboratories Division. 1981. Canadian woods: Their properties and use, 3rd ed. University of Toronto Press, Toronto, xviii + 389 pp.nGreen, D. W., and J. W. Evans. 1988. Moisture content-property relationships for dimension lumber. Proceedings Timber Engineering Group S 5.02 IUFRO Turku, Finland. 43 pp.nGreen, D. W., C. W. Link, A. L. DeBonis, and T. L. McLain. 1986. Predicting the effect of moisture content on the flexural properties of southern pine dimension lumber. Wood Fiber Sci. 18(1): 135-155.nGreen, D. W., J. W. Evans, J. D. Barrett, and E. N. Aplin. 1988. Predicting the effect of moisture on the flexural properties of Douglas-fir dimension lumber. Wood Fiber Sci. 20(1):107-131.nHoffmeyer, P. 1980. The moisture-mechanical property relationship as dependent on wood quality. Paper prepared for the 1980 IUFRO All-Division V conference, Oxford, England. 29 pp.nKuhnke, D. H. 1989. Silviculture statistics for Canada: An 11-year summary. North For. Prod. Res. Cent. Information Rep. NOR-X-301. 81 pp.nMadsen, B. 1975a. Duration of load test for wet lumber in bending. For. Prod. J. 25(5):32-40.nMadsen, B. 1975b. Moisture content-strength relationship for lumber subjected to bending. Proceedings of International Union of Forestry Research Organizations Wood Engineering Group. Houtinstitunt, Holland. Vol. 2, Paper 11.nMcGowan, W. M. 1968. Parallel-to-grain tensile properties of coast and interior grown 2 x 6-inch Douglas-fir. Information report VP-X-87. Western Forest Products Lab., Vancouver, B.C. 25 pp.nNational Lumber Grades Authority (NLGA). 1987. Standard grading rules for Canadian lumber. NLGA, Vancouver, B.C. 207 pp.nPearson R. G., and R. C. Gilmore. 1971. Characterization of the strength of juvenile wood of loblolly pine. For. Prod. J. 21(1):23-31.nRochester, G. H. 1938. The strength of eastern Canadian spruce timbers in sizes shipped to the United Kingdom. Canada Forest Service. Circ. 54.nSAS Institute Inc. 1985. SAS user's guide. Cary, NC.nSebastian, L. P. 1969. Investigation of some anatomical and physical properties of spruce sapwood and heartwood. Annual progress report. Forest Products Labs, of Canada Project at University of New Brunswick. Project No. EMR-F-29. 44 pp.nTaylor, F. W., E. I. C. Wang, A. Yanchuk, and M. M. Micko. 1982. Specific gravity and tracheid length variation of white spruce in Alberta. Can. J. For. Res. 12:561-566.nZhou, H. 1989. The influences of drying, knots and slope of grain on bending properties of white spruce. MSc.FE. thesis, University of New Brunswick, Fredericton.n






Research Contributions