2001 ASD Supplements - unprotected PDF - American Wood Council

ASD STRUCTURAL GLUED LAMINATED TIMBER SUPPLEMENTGL-57∆MCwhere:= M - M o[6.2]M o= initial moisture content % (M o≤ FSP)For more information concerning the effects of moisturechanges on glued laminated timber, refer to APA EWSTechnical Note Y260.M = new moisture content % (M ≤ FSP)FSP = fiber saturation point, as given in Table 6.2 forselected speciesTable 6.2Coefficient of Moisture Expansion, e ME, and Fiber Saturation Point,FSP, for Solid WoodsRadial Tangential Volumetric FSPSpecies (in./in./%) (in./in./%) (in. 3 /in. 3 /%) (%)Alaska Cedar 0.0010 0.0021 0.0033 28Douglas Fir-Larch 0.0018 0.0033 0.0050 28Englemann Spruce 0.0013 0.0024 0.0037 30Redwood 0.0012 0.0022 0.0032 22Red Oak 0.0017 0.0038 0.0063 30Southern Pine 0.0020 0.0030 0.0047 26Western Hemlock 0.0015 0.0028 0.0044 28Yellow Poplar 0.0015 0.0026 0.0041 316.4 Dimensional Changes Due to TemperatureThe thermal expansion of solid wood, including gluedlaminated timber, is computed by the relationship:X = X ( ∆ T)e[6.3]where:oX oe TETE= reference dimension at T oX = computed dimension at T= coefficient of thermal expansion (in./in./°F), seeTable 6.3e MEsoftwoods, the parallel-to-grain values have ranged fromabout 1.7x10 -6 to 2.5x10 -6 per °F.The linear expansion coefficients across the grain (radialand tangential) are proportional to the density of wood.These coefficients are about 5 to 10 times greater than theparallel-to-grain coefficients. The radial and tangentialthermal expansion coefficients for oven-dry wood in theoven-dry specific gravity (SG) range of about 0.1 to 0.8can be approximated by the following equations.Radial:6OTHER CONSIDERATIONS∆Twhere:∆T = temperature change (°F), as defined as follows:= T-T o[6.4]T o= reference temperature (°F), -60°F ≤ T o≤ 130°FT = new temperature (°F), -60°F ≤ T o≤ 130°F.e TE= [18(SG) + 5.5] (10 -6 in./in./°F) [6.5]Tangential:e TE= [18(SG) + 10.2] (10 -6 in./in./°F) [6.6]where:SG = specific gravity provided in Table 6.1The coefficient of thermal expansion of oven-drywood parallel to grain appears to be independent of specificgravity and species. In tests of both hardwoods andAPA – The Engineered Wood Association