0 species of wood, only 20 species are used structurally.? 比如,在美国,在超过600个木材品种中,只有20种在结构中使用。РTimberР9РThese are generally the conifers,or softwoods,both because of their abundance and because of the ease with which their wood can be shaped.? 这些通常是针叶松,或软木,是因为它们产量丰富并容易成型。? The species of timber monly used in the United States for construction are Douglas fir,Southern pine,spruce,and redwood. ? 在美国更通常被用于建筑的木材品种是美国松,南方松,云杉和红木。? The ultimate tensile strength of these species varies from 5,000 to 8,000 psi(350 to 560 kg/sq cm). ? 这些品种的极限抗拉强度从5000变化到8000psi。? Hardwoods are used primarily for work and for interior finishes such as floors.? 硬木最初是被用作细木家具和内部的成品,比如地板。? Because of the cellular nature of wood,it is stronger along the grain than across the grain.? 因为木材多孔的特征,它沿纹理方向的强度比跨纹理方向的强度要大。РTimberР10
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