Abstract
To understand the failure modes and shear strength of glulam composed of different species and lamina compositions, we manufactured three kinds of glulam, i.e., sugi, Douglas-fir and a composite of Douglas-fir and sugi, and subjected them to shear tests using the three-point bending method. As a result, we found that bending failure occurred in almost all of the sugi glulam specimens, and shear failure occurred in most of the Douglas-fir and composite glulam specimens. Various factors appeared to be involved with the failure modes, such as the lamina composition of the glulam, outermost lamina grade, compression and tensile strength of the outermost lamina, performance in compression perpendicular to the grain, and species and tissue structure. Calculations were made of shear strength using two kinds of equations : a homogeneous beam equation in which the material was considered homogeneous and failed in the neutral axis, and a composite beam equation. The effect of the position of shear failure was greater than the differences in shear stress of the various lamina compositions in the neutral axis. Therefore, not only lamina composition of the glulam, but also failure position in the cross section should be considered.
