Effect of Cyclic Long-Term Temperature Exposure on The Bending Strength of Lumber
Keywords:Lumber, high temperature, long-term exposure, cyclic temperature exposure, permanent effects, total effects
AbstractThis research evaluated the historical assumption that repeated exposure to elevated temperatures has a cumulative effect on wood properties. This recommendation was given in a paper by J. D. MacLean in 1951 and is a critical assumption when estimating the permanent effect of temperature on wood properties. No experimental results to support the recommendation were presented by MacLean. Approximately 670 southern pine and Douglas-fir solid-sawn 2x4's of two mechanical grades and one visual grade were subjected to cyclic and continuous exposure at 82°C and 30% RH for periods up to 30 mo. They were then tested after equilibration to room temperature and 20% RH. The cyclic exposure specimens alternated between 1 mo at 82°C and 1 mo at room temperature. The results show that there is no significant difference between the residual modulus of rupture (MOR) of the cyclic and continuously-exposed specimens for equivalent exposure periods. Trends in residual arabinose also supported this conclusion. Plotting the residual MOR of the cyclic specimens as the summation of the time they were exposed to the higher temperature provided a conservative estimate of the permanent effect of temperature. The results discussed in this paper are a small subset of a larger study and are not intended for use in general engineering design.
AF&PA (2005) NDS, National design specification for wood construction. American Forest and Paper Association, American Wood Council. Washington, DC.nASTM D 198-05 (2006) Standard methods of static tests of lumber in structural sizes. Annual Book of Standards, Volume 04.10. Wood. American Society for Testing and Materials. West Conshohoken, PA.nASTM D 1990-00 (2006) Standard practice for establishing allowable properties for visually-graded dimension lumber from in-grade tests of full-size specimens. Annual Book of Standards, Volume 04.10. Wood. American Society for Testing and Materials. West Conshohoken, PA.nASTM D 2395-02 (2006) Standard test methods for specific gravity of wood and wood-based materials. Annual Book of Standards, Volume 04.10. Wood. American Society for Testing and Materials. West Conshohoken, PA.nASTM D 4442-92 (2006) Standard test methods for direct moisture content measurement of wood and wood-based materials. Annual Book of Standards, Volume 04.10. Wood. American Society for Testing and Materials. West Conshohoken, PA.nASTM D 6570-04 (2006) Standard practice for assigning allowable properties for mechanically graded lumber. Annual Book of Standards, Volume 04.10. Wood. American Society for Testing and Materials. West Conshohoken, PA.nASTM D 6874-03 (2006) Standard test methods for non-destructive evaluation of wood-based flexural members using transverse vibration. Annual Book of Standards, Volume 04.10. Wood. American Society for Testing and Materials. West Conshohoken, PA.nCraig BA, Green DW, Gromala DS (2006) Flexural properties of structural lumber products after long-term exposure to high temperature. Proc of the 9th World Congress on Timber Engineering. August 6-10, 2006. Portland, OR.nFengel D, Wegener G (1984) Wood: Chemistry, ultrastructure, reactions. Walter de Gruyter, New York, NY.nFPL (1955) Wood handbook: Basic information on wood as a material of construction with data for its use in design and specification. Agricultural Handbook No. 72. USDA Forest Service, Forest Products Laboratory, Madison, WI.nFPL (1999) Wood handbook: Wood as an engineering material. General Technical Report FPL-GTR-113. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison, WI. http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm'>http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htmnGreen DW, Evans JW, Logan JD, Nelson WJ (1999) Adjusting modulus of elasticity of lumber for change in temperature. Forest Prod J 49(10):82-93.nGreen DW, Evans JW, Craig BA (2003) Durability of structural lumber products at high temperatures I: 66°C at 75% RH and 82°C at 30% RH. Wood Fiber Sci 35(4):499-532.nGreen DW, Evans JW, Hatfield CA, Byrd PJ (2005) Durability of structural lumber products after exposure at 82°C and 80% RH. Research Paper. FPL-RP-631 USDA Forest Service, Forest Products Laboratory, Madison, WI. http://www.fpl.fs.fed.us/documnts/fplrp/fpl_rp631.pdf'>http://www.fpl.fs.fed.us/documnts/fplrp/fpl_rp631.pdfnLeVan SL, Kim JM, Nagel RJ, Evans JW (1996) Mechanical properties of fire-retardant-treated plywood after cyclic temperature exposure. Forest Prod J 46(5):64-71.nLeVan SL, Ross RJ, Winandy JE (1990) Effects of fire retardant chemicals on the bending properties of wood at elevated temperatures. Res Pap FPL-RP-498, USDA Forest Service, Forest Products Laboratory, Madison, WI. http://www.fpl.fs.fed.us/documnts/fplrp/fplrp498.pdf'>http://www.fpl.fs.fed.us/documnts/fplrp/fplrp498.pdfnMacLean JD (1945) Effect of heat on the properties and serviceability of wood. Research Report 1471. USDA Forest Service, Forest Products Laboratory, Madison, WI.nMacLean JD (1951) Rate of disintegration of wood under different heating conditions. Am Wood Preserv Assoc 47:155-168.nMacLean JD (1953) Effect of steaming on the strength of wood. Am Wood Preserv Assoc 49:88-112.nMoore GL (1983) The effect of long-term temperature cycling on the strength of wood. J I Wood Sci 9(6):264-267.nMoore GL (2003) Personal communication.nPetterson RC, Schwandt VH (1991) Wood sugar analysis by anion chromatography. J Wood Chem Technol 11(4): 495-501.nPowell RM (1982) Discussion comment on the paper: Effect of temperature on the structural uses of wood and wood products by F. C. Beall. P 19 in Structural Uses of Wood in Adverse Environments. R. W. Meyer and R. M. Kellogg, Editors. Van Nostrand Reinhold Company, New York.nStamm AJ (1964) Wood and cellulose science. The Ronald Press, NewYork.nWinandy JE (1995) Effects of fire retardant treatments after 18 months of exposure at 150°F (66°C). Res Note. FPL-RN-0264. USDA Forest Service, Forest Products Laboratory, Madison, WI. http://www.fpl.fs.fed.us/documnts/fplrn/fplrn264.pdf'>http://www.fpl.fs.fed.us/documnts/fplrn/fplrn264.pdfnWinandy JE, Rowell RM (2005) Chemistry of wood strength. Chapter 11, Pages 303-347. in Handbook of wood chemistry and wood composites. R. M. Rowell (ed.). Taylor & Francis, New York.n
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