Abstract
Although the existence of a size effect for timber strength has been internationally acknowledged, no size effect factor has yet been adopted as a domestic standard for structural timber, when intended for structural members used in domestic post and beam structures. Fundamental knowledge concerning the size effect must be clarified to secure structural safety, when large cross-sectional timber is used, e.g. in public buildings. The effect of the depth or width of the timber on bending strength was examined to clarify the size effect of sugi (Japanese cedar) timber in bending strength, using a method of cutting the timber with a side- and/or end-matched pattern from a log. The bending strength was compared among 3 kinds of depth, 300, 170 and 105mm with a fixed 140mm width for the effect of timber depth, and among 2 kinds of width, 150 and 105mm with a fixed 150mm depth for the effect of timber width, under a bending test condition of a standard span-depth ratio. Consequently, the average bending strength rose with decreasing timber depth, and the size effect parameter value calculated in accordance with the size effect factor was 0.25-0.35. Conversely, no effect of timber width on bending strength was found.
