MECHANICAL STRESS GRADING OF LARCH SAWN TIMBER FROM NORTHEASTERN CHINA

摘要

In this research, the mechanical properties in full size were tested to evaluate structural properties of dahurian larch (Larix gmelini), a major softwood species that grows in the Northeast China. The results showed a good relationship between bending strength and static and dynamic modulus of elasticity (MOE). The good correlation of dynamic MOE and static MOE indicated that vibration method could be used as an effective mechanical stress grading indicator for larch timber. When combinations of the indicating properties such as dynamic MOE, timber density, and so on are applied, mechanical grading model could be improved to achieve the required strength properties as for relatively higher grades. Timber was sorted into three or four grades including M22, M26, M30, M35 and M40 using mechanical stress grading. The grades were equivalent to the European machine grade of C22, C27, C30, C35 and C40, respectively. It was found that the mechanical graded timber had a higher design value than the existing general design value of larch timber according to China design code for timber structures GB50005-2003.