Stiffness and shrinkage of green and dry joists

Abstract

This report gives information on the edgewise modulus of elasticity, stiffness, and shrinkage of 360 joists in three species, three grades, and two sizes, each species obtained from two sources. Each joist was evaluated nondestructively at four moisture content values ranging from the green condition to about 11 percent. Information is also given on specific gravity, strength ratio, hardness, and direction of the annual rings. The work showed a relation of modulus of elasticity to grade, with the highest grades having about the same value as that for clear wood. Increases of about 14 percent were observed in drying to 15 percent moisture content and about 20 percent in drying to about 11 percent moisture content. The stiffness showed little change with drying. Shrinkage values to 15 percent moisture content averaged 2.8 percent in width and 2.5 percent in thickness. Douglas-fir and western hemlock had a predominance of flat grain and greater shrinkage in width than in thickness. Southern pine had a more uniform distribution from flat to edge grain and greater shrinkage in thickness than in width.

Citation

Wood, Lyman W.; Soltis, Lawrence A. 1964. Stiffness and shrinkage of green and dry joists. Res. Pap. FPL-RP-15. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 26 pages