Influence of knots on tensile strength of sugi lamina

When timber is used as a building material, variability of the performance reliability is regarded as a big disadvantage. The performance of timber va ries piece by piece because wood is a natural material. The main cause that enlarges variability of the strength is defects such as knots. So far, how ever, any rational evaluation methods have not been established to give rel ations between the strength and knots, although the section deficit rate is often used to characterize knots. For improving the performance reliabilit y of timber, it is important to establish a new method by which the influen ce of knots on the strength is rationally evaluated. Once the performance r eliability of timber is remarkably improved, timber will be more willingly used as a building material. In this study, we tested laminae of the glulam under a tensile load, and in vestigated characteristics of the knot which might finally cause the ruptur e. Furthermore, the relation between the characteristics of knots and the p roperties of rupture was analyzed by using the finite element method. It is concluded that the size of a knot and the distance from the edge are impor tant parameters concerning the tensile strength of laminae. In particular, the highest stress concentration occurs when the knot is located near the e dge of the lamina, and consequently tensile strength decreases. Tensile str ength is able to be predicted approximately from these two parameters and t he modulus of elasticity.