Properties of Bending Strength of Full-Size Structural Glued Laminated Timber Composed of Homogeneous-Grade MSR Lumbers of Japanese Larch

Abstract

With a continuous mechanical grading-machine (MG) which can be used to measure Young's modulus (MOE) of lengthwise portion of a lumber, the average of MOE (MGE_AVG) and the minimum of MOE were obtained on 6400 lumbers of Japanese larch. The average of the difference (=MGE_AVG-MGE_MIN) was 0.92GPa and MGE_MIN was extremely lower than MGE_AVG in some cases.
Next, horizontally (H-type) and vertically (V-type) laminated glulams of homogeneous-grade composition were made to examine the bending strength of glulams. They were composed of lumbers classified according to MGE_MIN, because it was supposed that MGE_MIN should be useful for estimating the bending strength (MOR) of glulams.
In V-type glulams, the laminating effect which lowers the variation of MOR distribution was evidently observed. On the contrary, MOR of H-type glulams was almost independent of the number of laminae, because it depends on the quality of lumber in the outermost layer. Particularly, this result suggests that lumbers for the outermost layer of H-type glulams should be classified according to MGE_MIN instead of MGE_AVG.