Estimation of bending strength of structural glued laminated timber composed of homogeneous-grade finger-jointed lumbers of Japanese larch

摘要

It is known that bending strength (MOR) of a glued laminated beam (glulam) is decreasing when the depth of the glulam is increasing. The first study on this phenomenon in which the Weibull brittle fracture theory was applied to wood was reportedby Bohannan (1966). He studied clear wood beams and found that for geometrically similar beams MOR was proportional to the depth of the beam to the power 1/9 (B-model). On the other hand, Komatsu (1997) proposed the equation for predicting MOR of glulamscomposed arbitrary laminae without using the so-called "size-effect factor" (K-model). We attempted to compare these two models to the experimental results of Japanese larch gulams as reported by us. The types of used glulams were horizontally laminatedtimbers (H-type) and vertically laminated timbers (V-type).First, we compared two models to the experimental data of H-type. In higher grade, the estimates by K-model had good agreements with the data, but not in lower grade. Then, the estimates by using size-effect factor obtained from strength distribution offinger-jointed and without-joint laminae agreed with the data in lower grade. This differences between higher and lower grades may be caused by the quantity of defects excluding finger-joint. For V-type, the estimates by the "average model" proposed byHayashi (1992) agreed with the data in both grades.