Research Information System
19th International Nondestructive Testing and Evaluation of Wood Symposium, Colombo, Brazil, 22 - 25 September 2015, pp.1, (Full Text)
Strength grading of the timbers according to their exterior appearance by a visual examination is extremely useful and has been widely used all around the world. In addition the predictive capability of nondestructive techniques to evaluate the mechanical properties of timber has been widely studied, based on the relationship between wave velocity and Young’s modulus. The objective of this study is to determine the compatibility between visual strength grading and mechanical strength grading performed by using nondestructive and destructive test methods in Turkish black pine (Pinus nigra var pallasiana Arnold.) structural timbers. Fifty-three structural timbers with the dimension of 6 × 8 cm (width × depth), 6 × 10 cm and 2-m-length were graded by visual inspection in accordance with three different visual strength grading standards; TS 1265, DIN 4074, and BS 4978. Following visual examination, dynamic modulus of elasticity (MOEd) was determined by using a longitudinal vibration nondestructive test method. Then, static modulus of elasticity (MOEs) and modulus of rupture (MOR) were determined on the timbers in structural size in accordance with EN 408. The relationship between visual, nondestructive, and destructive strength grades was determined in order to assess the compatibility between them. Results indicate that the visual strength classes determined using BS 4978 standard showed the best compliance with the MOEd determined by longitudinal vibration and the MOEs and MOR determined by destructive test. The visual strength class was increased by increasing the values of MOEd, MOEs, and MOR. However, the visual strength classes determined in accordance with DIN 4074 and TS 1265 showed weaker correlations with the MOEd, MOEs, and MOR than BS 4978. There were high correlations between MOEd and MOEs (R = 0.92) and MOR (R = 0.79). Mechanical grading was more reliable and more efficient than visual grading. It was also concluded that the best results can be achieved by combining visual evaluation with MOEd determined by longitudinal vibration nondestructive test.