Abstract
No strength data existed for keyaki (Zelkova serrata) full-sized timber because the keyaki used had dimensions of around 180×180mm or more, even in common houses. Due to the lack of full-sized strength data, the validity of the design strength requirement value of keyaki as full-sized timber was unclear. Moreover, no fundamental data existed to determine the grading method, because the effect of timber quality and defects such as knots on the strength properties also remained unclear. In this study, bending and compressive tests were conducted using full-sized keyaki timber, and these problems were examined. Strength tests using small clear specimens of keyaki were also conducted and compared with the results for full-sized timber and the design strength requirement value. As a result of bending tests using full-sized timber, it was found that the visual grading method and the machine grading method could be applied to keyaki timber as well as to coniferous timber. However, additional study is needed on the effect of grain angle. Based on the results of bending and compressive tests using full-sized timber and strength tests using small clear specimens, it was found that the design strength requirement value of keyaki now in use is reasonable.
