It was reported that sugi (Japanese cedar, Cryptomeria japonica) boards with pith had a greater partial compression strength perpendicular to the grain (σ e) than sugi boards without pith. However, the reason for the superior strength of sugi boards with pith remains unclear. In this study, as the first step to elucidate the reason, we report the effects of loading direction (tangential and radial), density, microfibril angle (MFA) of earlywood and latewood tracheids, latewood tracheid length and cross-sectional parameters of earlywood tracheids (CE) on σ e in sugi wood. There was no significant effect of loading direction on σ e , and the specimens with pith had significantly larger σ e values than the specimens without pith. A larger density, larger MFA, and smaller cross-sectional dimensions with a square shape in earlywood tracheids significantly increased σ e in the radial loading direction. By multiple linear regression, it was recognized that density and MFA was the effective parameters, and MFA had a larger effect than did density in the predictor equation for σ e. This is the first study that reported the positive effects of MFA on σ e in sugi wood.

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Bending creep tests for sugi (Cryptomeria japonica D.Don) glulam with extremely low Young's modulus laminae (3-4GPa) for the inner layer, along with the tests for hybrid glulam with the Douglas-fir (Pseudotsuga menziesii Franco) laminae (14-15GPa) for the outermost layer and the sugi laminae including 3-4GPa laminae for the inner layer, have been carried out since October, 2005. For the test, eight different composition glulam beams with the dimensions of 105mm in width, 210mm in depth and 3980mm in length were prepared. The results are summarized as follows. (1)There was no big difference between the Young's modulus or bending creep of glulam with L30 (Laminae with 3-4GPa Young's modulus) for the inner layers and that of glulam with L50 (Laminae with 5-6GPa Young's modulus) for the inner layers regardless of the glulam types.(2)Hybrid glulam with sugi laminae for the inner layers and the Douglas-fir laminae for the outermost layers showed higher Young's modulus and lower creep deflection than the glulam composed of only sugi laminae. However there was no big difference between their relative creep in 50 years, showing the values of approximately "2". (3)The relation between the change of humidity and that of creep deflection was not clear for the symmetry composite glulam, while it was very clear for the asymmetry one.