Behaviour Of A Typical Multi-layer Beam-column Joint In Heritage Tibetan Wooden Structures

Heritage structures represent the value of human history,culture,art and science.They are the important components of the world civilization.These structures have been under the adverse effects of the environments,such as earthquake,temperature and effect of fungus,etc.,the load-carrying,stability and safety of the structures are all weakened.Existing heritage wooden structures in China have a common type of beam-column joint which composes of layers of wooden beam to resist the vertical applied load.The stiffness of this beam-column joint is an important parameter in the safety analysis of the structure.The performance of this type of joint under loads is not clear,at present,particularly under the seismic effect.It is,therefore,essential to have an efficient finite element model of the layered beam-column joint for evaluating the performance status of these heritage structures under load.This thesis presents a finite element model for reproducing the performance of a typical layered wooden beam-column joint under pseudo-static loading conditions.The main works are as follows:With reference to the beam-column joint of Tibetan heritage structures,a nonlinear analytical model of a cantilevered two-layer wooden beam system is developed based on the Euler-Bernoulli beam theory and the Timoshenko beam theory separately.The proposed model takes into account the effect of the friction-slip-shear between the two individual layers with a specified range of slip at the connector(tenon).There are four deformation scenarios to describe the load resistance based on the state of friction between the beam layers and the state of shear at the tenon.The behavior of the tenon with the friction-slip-shear mechanism is significant to the mechanical behavior of the cantilevered two-layer beam system.The proposed analytical model can be used to evaluate the stiffness of a cantilevered two-layer wooden beam.An equivalent finite element model of the two-layer beam system with the external uniformly distributed vertical load on the top of the element is developed.This equivalent beam element is derived from consideration of deformations under different load with the proposed cantilevered two-layer analytical beam system.The derivation of the equivalent beam element is validated against by traditional Euler-Bernoulli beam element.This proposed method can be applied to obtain equivalent finite element for various systems with different physical and geometric parameters directly without experiment.The above model is extended to the case of a three-layer beam system in the heritage wooden structures.The three-layer beam system is taken as consisting of several two-layer beam systems.This approach of analysis is verified with the equivalence of strain energy and the deformation in the initial beam and those in the equivalent two-layer beam systems under the same load.A general finite element model is adopted to model a cantilevered beam-column joint with three layers considering the structural symmetry of the beam-column joint.This joint model can reproduce the nonlinear performance of friction-slip-shear between the individual beam layers.A frame with the three-layer beam-column joint is studied to evaluate the performance of heritage timber structure under pseudo-static load with evaluation of the energy dissipation.Due to the general nature of the development of the cantilevered three-layer joint finite element model,the finite element model for any multi-layer composite joint can be obtained easily.The proposed models are developed by the Euler-Bernoulli and Timoshenko beam theories separately,and they can be introduced into the analysis of most composite structures accordingly.