Evaluation of the mechanical properties of Douglas-fir and Japanese cedar lumber and its structural glulam by nondestructive techniques

The objectives of this study were to investigate the effects of the configuration of the lamina on the bending properties of glulam made from Douglas-fir and Japanese cedar lumber. By using a visual grading method according to CNS 14631 and nondestructive evaluation techniques (including the ultrasonic wave technique, transverse vibration test and static bending test), lamina having both higher dynamic MOE and static MOE were chosen for the outside layers, in order to manufacture homogeneous and heterogeneous grade structural glulam lamina, with higher strength properties. The degrees of correlation, obtained from the different nondestructive testing methods, were then analyzed. The results indicated that the DMOEv, DMOEt and MOE values for both Douglas-fir and Japanese cedar lumber showed a decreasing order as follows: construction grade > standard grade > utility grade. It was also found that the transverse vibration test is a better nondestructive method of evaluating sawn lumber. The different configurations of the lamina within glulam can be used to fabricate glulams with different grades of bending strengths. The predicted values of glulam Eb(sp), were higher than those of the experimental values Eb(sc). Moreover, the value of Eb(sc) increased linearly with an increasing MOE of the outside layers of lamina (e3).