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Wood structural members are frequently subjected to loads resulting in multiaxial stress. Failure criteria ordinarily used for isotropic materials do not apply to orthotropic and anisotropic materials and their use may result in incorrect stress state interpretation. This paper summarizes the current state of the art in applying phenomenological failure criteria to wood and wood-based materials.

Current compression perpendicular-to-grain (C H ) design values for wood members are based on mean stress obtained from ASTM D143 specimen. The standard ASTM test with metal on wood bearing has limited applicability in modern construction assemblies with C H loading scenarios. Previous work has shown that end-bearing conditions and wood-onwood C H bearing is a more severe case as opposed to load applied over central area and metal-on-wood bearing. This study evaluated C H behavior of typical assemblies used in construction, in which members experience C H stresses near their longitudinal-end through wood-on-wood contact. These included assembly of the bottom chord of a truss bearing on the top plate of a wall (BC assembly) and assembly of the compression chord of a shear wall bearing on the bottom plate (BP assembly) of a wall. Three different BC assemblies were tested with varying aspect ratios (height/width) of the bottom chord (B.C.) member. For each test assembly, paired ASTM tests of the main member (bottom chord member in BC tests, and bottom plate member in BP tests) were conducted. The assembly stresses at 1 mm deflection were always lower than the corresponding ASTM stresses at the same deflection. Due to varying assembly depths, 1 mm deflection was a poor criterion for determining C H stress values. For B.C. members, when loaded tangentially, they buckle in the direction of annual ring curvature. High aspect ratios accentuate this effect. Expectedly, the tendency to buckle and the probability of total failure in the assembly increase with increasing aspect ratio. This behavior was not observed in the ASTM tests.

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