Torsional Rigidity of Rectangular Wood Composite Materials
Keywords:
Torsional rigidity, shear modulus, structural composite lumber, isotropic elasticity, orthotropic elasticityAbstract
The torsional rigidity of wood members is necessary for predicting lateral torsional buckling of laterally unsupported beams, and is useful for estimating the stiffness of two-way floor systems and the natural frequency for wood floors. Current estimations of torsional rigidity of composite wood materials are based upon elastic constant ratios of solid wood. Recently published work has found differences in the elastic constant ratios of solid wood versus structural composite lumber (SCL) materials. These differences in elastic properties may indicate differences in torsional rigidity. Rectangular sections of solid-sawn lumber and various SCL materials were tested to determine values of torsional rigidity. Torsional rigidity of solid-sawn lumber was significantly different (p<0.05) from laminated veneer lumber, while direct comparisons of parallel strand lumber and laminated strand lumber to solid-sawn lumber were not possible due to dimensional differences of test sections. Predictions of torsional rigidity based upon isotropic and orthotropic elasticity and shear moduli derived from bending tests were compared to the experimental results for each material. The solid-sawn lumber torsional rigidity was predicted best by the isotropic elasticity assumptions, while the parallel strand lumber and laminated strand lumber torsional rigidity values were predicted best by the orthotropic elasticity assumptions. The laminated veneer lumber torsional rigidity was predicted well by isotropic elasticity assumptions if shear moduli values derived from torsional testing were used. Torsional rigidity values for both solid-sawn lumber and SCL materials were not predicted well using an E:G ratio of 16:1 and isotropic elasticity assumptions.References
American Forest and Paper Association (AF&PA). 2001. Allowable Stress Design (ASD) Manual for Engineered Wood Construction. American Forest and Paper Association. Washington, DC, USA. 79 pp.nBradtmueller, J. P., M. O. Hunt, and S. R. Shook. 1998. Mechanical properties of laminated veneer lumber via five-point bending test. ASTM J. Testing Eval. 26(2):132-137.nFoschi, R. O. 1982. Structural analysis of wood floor systems. ASCE J. Struct. Div. 108(ST7):1557-1574.nHindman, D. P. 2003. Torsional rigidity and lateral stability of structural composite lumber and I-joist members. Ph.D. Dissertation. The Pennsylvania State University. University Park, PA. 222 pp.nHindman, D. P., H. B. Manbeck, and J. J. Janowiak. 2005. Comparison of ASTM D 198 and five point bending for elastic constant determination. Forest Prod. J. Submitted for publication.nJanowiak, J. J., and R. F. Pellerin. 1992. Shear moduli determination using torsional stiffness measurements. Wood Fiber Sci. 24(4):392-400.nJanowiak, J. J., D. P. Hindman, H. B. Manbeck. 2001. Orthotropic behavior of lumber composite materials. Wood Fiber Sci. 33(4):580-594.nLekhnitskii, S. G. 1963. Theory of elasticity of an anisotropic elastic body. Translated by P. Fern. Edited by J. J. Brandstatter. Holden-Day, Inc., San Francisco, CA. USA. 404 pp.nSmith, I., and Y. H. Chui. 1988. Design of lightweight wooden floors to avoid human discomfort. Can. J. Civil Eng. 15: 254-262.nTarnopol'skii, Y. M., and T. Kincis. 1985. Static test methods for composites. Van Nostrand Reinhold Company. New York, NY. 301 pp.nTimoshenko, S., and J. N. Goodier. 1930. Theory of elasticity. 2nd ed. McGraw-Hill, New York, NY. 506 pp.n
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