Moment-resisting properties of post-to-sill joints connected with hardwood dowels

Moment-resisting properties of post-to-sill joints made with glued-in hardwood dowels were studied. Dowels of 12 mm in diameter made of hard maple (Acer saccharum) are glued into post and sill members of sugi (Cryptomeria japonica) glulam with polyurethane adhesives to make joint specimens. Assuming that joints fail by withdrawal of dowels, moment-resisting strength and stiffness of joints were predicted by considering withdrawal force of dowels and compressive stress perpendicular to the grain in a sill members. Withdrawal strength and stiffness of single dowels were derived from previous reports. Tests of joint specimens showed the possibility of controlling moment-resisting strength and stiffness by choosing proper arrangements of dowels in the joint area. The greatest strength was obtained by arranging dowels in the outer section of the joint area. In this case, predictions of strength and stiffness agreed well with experimental results. For example, the joint of 105-mm squares with 6 dowels in the outer section showed a maximum moment of 3.49 kNm at a rotation angle of 38.9 X 10-s radian, compared to a calculated strength and stiffness of 3.69 kNm and 38.6 X 10-3 radian, respectively. However, strength and stiffness for joints with dowels in the inner section were overestimated by the calculations. The reason may be explained as follows : The compressive stress at the edge of the joint area exceeded the elastic limit_ and the neutral axis moved toward the tension side, which caused a larger pull-out force for the dowels than calculated assuming elastic behavior on the compression side. Furthermore, bending forces would act on dowels when a joint rotated significantly. Racking tests of dowel-connected frames were conducted to verify their 贔performanceas shear walls. The test results of frame specimens without braces showed good agreement between experimental strengths and calculated estimations based on moment distribution among joints assuming rigid-joint frames. Test specimens with braces failed by buckling of the braces, which showed sufficient withdrawal strength of the dowels comparable to metal fastners for post-to-sill joints