Rotational behaviour of the Zuo-Dou joint in Taiwanese traditional Dieh-Dou timber construction and the efficiency of reversible reinforcement

This paper is mainly to assess the rotational behaviour of the beam-to-column joint, named Zuo-Dou, in Taiwanese traditional Dieh-Dou timber construction and to evaluate the structural efficiency of the feasible reinforcement for the Zuo-Dou joint. The appraisal is based on full-scale static test. The rotational stiffness and ultimate moment of Zuo-Dou in horizontal plane are appraised and the failure modes are analysed. The mechanical characteristics of Zuo-Dou are highly associated with the geometric profiles of the entire connection, particularly the depth of the mortice and the direction of the wooden fibre. While the depth of the channel over the join influences stiffness, the orientation of wooden fibre of Zuo-Dou itself determines the failure modes. Depending on the results from the first series of testing, various retrofitting strategies are figured out in order to enhance the critical structural deficit of Zuo-Dou joint. As demonstrated by former research, self-tapping screw (STS) is reliable fastener for not only modern timber construction but also the wooden cultural heritage. Different ways to apply STS to constrain the crack are taken into account in this study and then the second series of testing is intended for evaluating the structural retrofitting efficiency of STS. The testing demonstrates that STS can slightly improve the ultimate moment and considerably ensure the sufficient plastic deformation, which is a positive factor for the seismic behaviour of the connection. In the case of total failure of the original wooden dowels in the joints, STS contributes to remain the structural performance of the entire connections. The results demonstrate the adaptability of STS as retrofitting strategy.