Mechanical Properties and Design Values of Hinoki (Chamaecyparis obtusa) Dimension Lumber from Japan

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Abstract

This study evaluates the mechanical properties of Hinoki (Chamaecyparis obtusa) from Japan to determine reliable design values for its application as structural dimension lumber species in the United States. A comprehensive experimental program was conducted on 1464 (approximately 240 per grade/size) dimension lumber in-grade specimens sourced from prominent Hinoki-growing regions of Japan. These specimens were tested in bending, compression perpendicular to the grain, and horizontal shear. Tests were conducted, and the results were subjected to statistical analysis and adjustment factors to determine base reference values in accordance with ASTM International standards. The four-point bending tests showed moderate numerical variation across growing regions; however, one-way ANOVA confirmed no statistically significant regional effect on MOR or MOE. Compression parallel to grain and tensile strength were estimated from the MOR values using empirical relationships per ASTM D1990. The base design values after adjustments for 15% moisture content, specimen size, and volume effects fall within the expected range for high-quality structural species and support the acceptability of Hinoki as a load-carrying wood species. The results constitute the first complete, statistically verified dataset for Hinoki, and provide a basis for its use in wood design specifications such as the National Design Specification (NDS) for Wood Construction (NDS). Wider recognition of Hinoki as a viable structural species could expand its commercial use and support sustainable forest management practices in Japan.

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