Abstract
A nailed steel gusset was developed and applied to truss assemblies to evaluate the structural performance of a Japanese cedar roof truss system. Sawn lumber from plantation trees was graded with a tap-tone approach, and E90 and E110 grade lumber was selected for truss fabrication. A shear capacity of 1.88~2.0 kN per nail was obtained for the Japanese cedar lumber joint in tension, which was 5.7-times the design value. The truss assembled with 45×120-mm members showed a 24.3% higher in ultimate bending load capacity than that assembled with 45×90-mm members. The Howe truss system showed a 13.6% higher ultimate loading capacity than that of the Fink truss system, but the difference was insignificant. The bending stiffness of the 45×120-mm wood roof truss system was 26.5% higher than that of the 45×90-mm wood roof truss system, and the bending stiffness of the Howe truss was 14.0% higher than that of the Fink truss. Critical failures of the Japanese cedar roof trusses were located at the heel joints, and reached 75% due to a combi¬nation of nail withdrawal and gusset failure. Flexural deflections of the Japanese cedar roof trusses measured at the design load level were within 3.5~7.5% of the design limitation. Furthermore, the designed roof load was only 6.9~10.2% of the ultimate equivalent distributed loads measured at truss rupture, which assured the safety of Japanese cedar roof trusses in service.