2006 Volume 55 Issue 4 Pages 367-372
In Japan, the shapes of traditional wooden joints are based upon carpenters′ experiences. However, in terms of strength, it is not revealed whether these shapes are optimum or not. For dovetail joints (ari-tsugi in Japanese), which have been frequently used in traditional timber constructions, an inclination of 1/6 is empirically and often used. In this paper, we conducted the tension tests with dovetail joint specimens of various inclinations and base widths, and examined whether empirical shape is optimum or not. Then strain distributions were calculated by digital image correlation (DIC). The results were as follows : (1) Joints with the inclination of 1/3 were 25∼35% stronger than that of 1/6, therefore empirical shape was not optimum. In comparison with the inclination, the effect of the base width to tensile strength was not significant. (2) Radial tensile strain concentrated on the corner of notches in the mortise side (female part of joint), where more than 2% of tensile strain was observed just before the fracture occurred. However, there was little difference between radial strain distributions whether inclination and base width were large or small. On the bottom of the mortise, approximately 0.7% of tensile strain observed in early wood just before the fracture occurred, but there was little strain in late wood. (3) On shear strain, concentration on the notch was remarkable with inclination increase. Consequently, the fracture of dovetail joints was caused due to the complex stress state, though the main factor of it can be radial tensile stress or strain.
