Original paper(Vol.46 No.4 pp.395)
Properties of bending strength of full size structural glued laminated timber composed of homogeneous-grade MSR lumbers of Japanese larch
Hashizume Takeo; Saito Takeshi; Takeda Takashi; Ishihara Shigehisa
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 (MGEAVG) and the minimum of MOE were obtained on 6400 lumbers of Japanese larch. The average of the difference (=MGEAVG-MGEMIN) was 0.92 GPa and MGEMIN was extremely lower than MGEAVG 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 MGEMIN, because it was supposed that MGEMIN 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 laminate, 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 MGEMIN instead of MGEAVG.
Key Words:continuous mechanical grading-machine, bending strength, homogeneous-grade composition, horizontally laminated glulam, vertivally laminated glulam, minimum of Young's modulus