EXPERIMENTAL STUDY ON BENDING STRENGTH PROPERTIES AND PRESUMPTION INDEX OF MEDIUM SIZE LOG OF SUGI (CRYPTOMERIA JAPONICA) GROWN IN WAKAYAMA PREFECTURE

Abstract

Flatwize bending tests were conducted after a measurement of the visual grading factors and dynamic modulus of elasticity for a full scale rectangular-cut lumber sawed from Sugi (Cryptomeria japonica D.Don) mediumsize logs grown in Wakayama Prefecture. The purpose is to verify the applicability of machine stress grading of JAS (Japanese Agricultural Standards) and to examine utilization of the materials as structural lumber under flatwize bending. Main results are as follows. 1) As visual features rectangular-cut lumber whose ratio of knot size to face depth exceeded more than 60%, and which had dead knot showed brittle fracture. 2) Although visual stress grading and machine stress grading were both effective as stress grading system, the machine stress grading was more effective than the other. 3) Very strong linear relationships are observed between bending modulus of elasticity and dynamic modulus of elasticity. From these results in the above, the strong standard characteristic values of lumber by the machine stress grading using bending modulus of elasticity of the standard size of 45mm, were calculated. Therefore, the rectangular-cut lumber, of which quality is controlled by the present method, is available as structural lumber, since stiffness, strength, and ductility are guaranteed.