Strength properties of Chinese fir timber collected from multiple sites

Abstract

Various strength tests of kouyouzan (Chinese fir: Cunninghamia lanceolata) obtained from multiple sites were conducted. The test results were used to evaluate strength property and verify the relationship with the current design strength. From the verification, the following conclusions were drawn. First, for mechanical grading of structural lumber under the Japanese Agricultural Standard for sawn lumber (JAS1083), it is appropriate to include the Chinese fir in akamatsu (Japanese red pine: Pinus densiflora) and other species groups for bending and compression. However, the shear should be equivalent to that of sugi (Japanese cedar: Cryptomeria japonica). Second, although only from the viewpoint of the select structural grade of A class structural lumber, for the Japanese Agricultural Standard for structural lumber and fingerjointed structural lumber for wood frame construction (JAS0600), it is appropriate to include JSIII for bending and compression and JSII for shear. Therefore, the current species groups are not applicable. For partial compression perpendicular to grain, all kinds of design strength are the same and will be equivalent to sugi. However, these results were obtained from a limited number of specimens, and neither JAS1083 was examined as visual grading of structural lumber nor JAS0600 was examined as no.2 grade for A class structural lumber. Additionally, for the shear strength and partial compression strength perpendicular to grain, some lumber had lower strength than the design strength of sugi. Moreover, some specimens with low density exhibited lower performance than sugi in terms of one-sided shear at nailed joints. As mentioned above, many issues remain, and data accumulation for further verification is essential.