Behaviour Of Typical Joints And The Structure Of Yingxian Wood Pagoda

Built in the 2nd year of Qingning, Liao Dynasty (1056 AD) of approximate a thousand years ago, the Yingxian Wood Pagoda is located in the Town of Yingxian County, Shanxi Province, China. It is the oldest and highest standing ancient wood structure and the only storeyed wood pagoda of China. With vicissitudes of nearly a thousand years, the pagoda has undergone times of severe earthquakes and some human-induced disasters. Yet it is still towering there with majesty, showing the world the glory of the ancient Chinese civilizations. Meanwhile, it should be noted that significant deformation of compression, both overall inclination and torsion of pagoda and local inclination of columns have happened. The situation is serious for some wood components with large deformation and even damage due to compression perpendicular to grain and bending, some with fractures and property-deteriorations due to aging, some even with damage from shelling in the war. The distortions of pagoda and deteriorations of wood are worsening and can become critical any time. It is, therefore, of urgent need to evaluate the structural safety of Yingxian Wood Pagoda and to undertake repairing accordingly. However, the structure of the pagoda is rather complicated, the structural system and the load-transfer paths are not quite clear, and the structure and load-carrying mechanism of joints and connections of the pagoda are not quite clear either. This study aims to undertake thorough on-site survey of the pagoda, undertake analysis and understanding of the structural system, conduct tests of structural performance of the typical joints, and finally conduct refined FE analysis of the whole structure of the pagoda, thus providing basis for evaluation of the structural safety and reinforcement and repairing of the pagoda.By the on-site survey and the analysis and understanding of the structural system, the Yingxian Wood Pagoda can be regarded as a layered multi-storey structure with semi-rigid connections and high degrees of indeterminacy. The Dou-Gong Brackets, beam-column joints and column-base joints were classified from a structural point of view. The structural virtues of Column-Lean and Column-Raising, unique in ancient Chinese wood structures like the pagoda, were investigated by means of engineering mechanics. Tests on models of the typical Dou-Gong Brackets, beam-column joints and column-base joints under monotonic vertical and cyclic lateral loads, respectively, were conducted, the structural performance in terms of load-carrying capacity, stiffness and failure modes of these joints were investigated. Based on the test results and the theory of similarity, the load-carrying capacity and stiffness of the prototype joints in the true pagoda were deduced. Under vertical load from the column, a Dou-Gong Bracket transfers load down mainly via Shua-Tou, Hua-Gong, Gong-Fang, San-Dou and Lu-Dou, the structural behaviour is basically similar to wood under compression perpendicular to grain. Under cyclic lateral load, a Dou-Gong Bracket transfers load mainly via bending of the several Gong-Fang's, the structural behaviour is basically similar to wood under bending. A beam-column joint transfers lateral load to Lan-E via compression perpendicular to grain between tenon of Lan-E and mortise of column. Lan-E is thus under torsion and local compression perpendicular to grain, column under tension perpendicular to grain at the mortise and Pupai-Fang under compression perpendicular to grain. Whist a column-base joint transfers lateral load to the several Gong-Fang's via compression perpendicular to grain between the mortise of column and Gong-Fang. Gong-Fang is thus under bending and torsion, column under tension perpendicular to grain at the mortise, Gong-Fang and Di-Fu under compression perpendicular to grain. Tests also showed that, the lateral resistance and stiffness of Dou-Gong Brackets, beam-column joints and column-base joints increase with the axial compressive load applied to the column. The lateral performances of all joints are enhanced with reinforcement of column to prevent propagation of the fracture perpendicular to grain.In consideration of the anisotropy, constitutive relationships of wood under complex stresses, suitable for EF modelling of the structures, were developed and incorporated into ABAQUS via encoding a user-defined subroutine VUMAT. FE models of the Dou-Gong Brackets, beam-column joints and column-base joints were developed based on the true geometric structure of the joints, the complex constitutive relationships and the kinematic friction formulation between the components. The structural performance of these typical joints was simulated, and good agreement between FE modelling and tests was obtained. Based on the FE modelling and tests, simplified mechanics models of Dou-Gong Brackets transferring vertical load were developed, and the load-transferring paths clarified. Two refined FE models of the structure of Yingxian Wood Pagoda, with and without considering damage, were developed incorporating ABAQUS, respectively. The natural vibration frequencies and modes of both FE models were obtained by the numerically dynamic analysis, and analytical results from the FE model with considering damage correlated with test reported by literature. The structural performance and load-transferring paths of the pagoda were investigated via conducting FE modelling of the structure under gravity and static lateral earthquake actions, respectively. FE modelling of the structure of the pagoda under frequently occurring earthquakes was also conducted, and the structural responses obtained. The index for evaluating the overturning of the pagoda was suggested, and the safety of Yingxian Wood Pagoda under earthquakes assessed. The structural weaknesses of the pagoda, such as inclinations both overall and local, poor torsional stiffness, poor inter-storey and local lateral stiffness of the apparent storeys and low compression strength perpendicular to grain, were reviewed and analysed, and measures to reinforce the structure of the pagoda and to alleviate detrimental effect of gravity were proposed.