2001 ASD Supplements - unprotected PDF - American Wood Council

ASD TIMBER POLES AND PILES SUPPLEMENTPP-25and:where:∆T = T -T o-60°F ≤ T o≤ 130°FThe coefficient of thermal expansion of oven-drywood parallel to grain ranges from about 1.7x10 -6 to2.5x10 -6 per °F.The linear expansion coefficients across the grain (radialand tangential) are proportional to wood density.These coefficients are about five to ten times greater thanthe parallel-to-the-grain coefficients and are given as:Radial:e TE= [18(G) + 5.5] (10 -6 in./in.°F)Tangential:e TE= [18(G) + 10.2] (10 -6 in./in.°F)where:G = tabulated specific gravity for the speciesTable 6.1Coefficient of Moisture Expansion (e ME) and Fiber Saturation Point(FSP) for Solid Woods6Radial 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 316.3 Durabilitye MEOTHER CONSIDERATIONSDesigning for durability is a key part of the architecturaland engineering design of the building. This issue isparticularly important in the design of buildings that usepoles and piles. Many design conditions can be detailedto minimize the potential for decay; for other problemconditions, preservatively treated wood or naturally durablespecies should be specified.This Supplement does not cover the topic of designingfor durability in detail. There are many excellent textson the topic, including AF&PA’s Design of Wood Structuresfor Permanence, WCD No. 6, and designers are advisedto use this type of information to assist in designing“difficult” design areas, such as:• in moist or humid structures• where wood comes in contact with concrete or masonry• where wood members are supported in steel hangers orconnectors in which condensation could collect• anywhere that wood is directly or indirectly exposed tothe elements• where wood, if it should ever become wet, could notnaturally dry out.This list is not intended to be all-inclusive — it ismerely an attempt to alert designers to special conditionsthat have been found to cause problems when not designedwith durability in mind.Durability issues related to piles are generally bothmore critical and more easily accommodated. Since pilesare in constant ground contact, they cannot be “insulated”from contact with moisture — thus, the standard referencecondition for piles is to be preservatively treated.The importance of proper treatment processing of pilescannot be overemphasized.AMERICAN FOREST & PAPER ASSOCIATION