Seismic performance of Ju-Yu joints in heritage timber structures

Among the diverse building styles of ancient China, Suzhou’s heritage timber architecture represents a typical tradition of the Yangtze River Delta (Jiangnan) region, featuring a variety of characteristic mortise-and-tenon joints. The Ju-Yu (Gathered-Fish) joint, named after the shape resembling two fishlike tenons approaching, is a distinctive representative of such joints. To effectively protect and restore historic timber structures using such joints, as well as to support the reconstruction of heritage-style buildings, it is essential to investigate and clarify their structural resistance under catastrophic loading conditions, especially earthquakes. However, there are still limited investigations available. In this context, the seismic performance of the Ju-Yu joint in Suzhou-style timber structures is determined as the main focus of this work. Scaled joint specimens were fabricated and tested under cyclic loading. The geometric characteristics of the tenons and the axial load ratio of the column were the key experimental parameters. The failure modes, moment-rotation hysteresis loops, skeleton curves, stiffness degradation, and energy dissipation capacity were recorded and analysed. A finite element (FE) model was developed, and then parametric studies were carried out. The experimental and analytical results indicate that the asymmetric design of the tenons results in a direction-dependency in seismic performance. The failure of the Ju-Yu joint initiates primarily in the tenon head region, then develops to tenon tip distortion, shear fracture, or tenon withdrawal. The hysteresis loops of the joint exhibit a significant pinching effect, as well as an increase in slippage with the rotation angle. With a fixed column cross-section, increasing the embedment length of each tenon within the joint leads to an improvement in the joint’s bearing capacity. The joint possesses relatively good comprehensive seismic performance under a balanced tenon dimension design and at an axial load ratio of 0.4. Increasing the interfacial friction coefficient is an effective and promising strategy for improving the seismic resistance of the Ju-Yu joints. The experimental observations and quantitative analyses in this work are anticipated to offer a scientific basis for protecting, preserving, and promoting the Suzhou-style heritage timber architecture, aiming to ensure both engineering safety and cultural heritage conservation.