Research On Influence Of Dry Shrinkage Deformation On Seismic Behavior Of Through-tenon Joints

The wood structure is a significant part of Chinese ancient architecture and Chinese civilization is accompanied by its development.So the wood structure is an important carrier of Chinese civilization,with high historical,cultural,artistic and scientific value.The existing wood structures of ancient buildings have accumulated different degrees of damage over time and the looseness of joints caused by drying shrinkage deformation is a typical damage type.Therefore,it is of great significance to study the influence of dry shrinkage deformation on the seismic performance of through-tenon joints for the repair and reinforcement of existing ancient timber structures.In this paper,the dry shrinkage deformation of through-tenon joints is simulated by reducing the height of tenon to produce a gap between tenon and mortise.The seismic behaviors of through-tenon joints such as the failure characteristics,strain distribution on mortise,hysteretic loops,skeleton curves,degradation of rigidity and energy dissipation were studied through low-cycle reversed loading experiment on 2 groups of through-tenon joints with different degrees of dry shrinkage and sizes.The results indicate that the through cracks at the variable section of the tenon will develop under small moment,making a big difference in the stress mechanism of the joint during its positive and negative rotation.As the significant deflection of the tenon during rotation,the energy dissipation performance of the specimen is significantly weaker in positive rotation than in negative rotation.The dry shrinkage deformation of the through-tenon joints will weaken the seismic performance of the specimens,with the gap between the tenon and mortise increased,the compression area will reduced and concentrated to the end,causing insufficient compression between the tenon and mortise.The energy dissipation capacity of the joint decreases with the increase of dry shrinkage deformation,and the energy dissipation capacity will be significantly weakened when the gap between the mortise and tenon increases slightly,for example,the energy dissipation capacity of the specimen will be weakened to 50%that of the intact specimen when the gap value increases to 3%height of the mortise.In the deduction of the moment-rotation equation for the through-tenon joints with different degrees of dry shrinkage deformation,the rotation model of the joints is set up by the relative rotation and displacement between the tenon and the mortise,the force model of the joints is according to the distributed force actually applied on the tenon by the mortise,and adopt bilinear to match the deflection of the tenon.In the solution it can be found that the center of rotation in the joint is on the section where the direction of shear on tenon changes and on the same section the moment in the tenon reaches the peak value,equal to the value of the resisting bending moment of the joint,but in the opposite direction.When the loading position is determined,the relative displacement between the tenon and mortise can be eventually expressed as a function of their relative rotation.When the relative rotation between the tenon and mortise is determined,the resisting bending moment of the joints can be approximated by the numerical calculation method.Some of the specimens were analyzed by ABAQUS,and the simulation results of the joints with different degrees of dry shrinkage deformation were compared with the experimental results.The comparison shows that the simulation results can analyze the failure characteristics and stress distribution of the joints accurately.Due to the abrasion and damage accumulation of the joints exist during the experiment,the hysteretic loops of the simulation results are numerically different from the experimental results,but the simulation results can reflect the slip characteristics of the joints and the asymmetry of the hysteretic loops during positive and negative loading.When a gap exist between the tenon and mortise or the construction size of the joint changes,the simulation results can reflect the changes of seismic performance of the specimens sensitively.After correcting the data of the simulation,the skeleton curves of the simulation results fit well with those of the experiment.