Study On Practical Models Of Relationship Between Moment And Rotation Of Mortise Tenon Joints Of Traditional Timber Structures

The traditional timber structure is the main type of Chinese ancient architectures,which has rich cultural significance and scientific research value.Many of the ancient wooden buildings that survive for hundreds of years have been damaged so seriously that it is urgent to reinforce them.Besides,with support of the national policy for timber structures and the strategy of the development of tourism,new or rebuilt traditional timber structure projects are also increasing now.In order to protect and rebuild traditional timber structures,it is necessary to study their mechanical performances.The main connection form of traditional timber structures is mortise tenon joints,which become the weak parts of structures because their cross sections are weakened.What’s more,the working mechanism of mortise tenon joints is very complex.They are semi-rigid joints whose rotational stiffness plays an important role in the lateral stiffness and stability of structures.Therefore,it is very important to establish practical mechanics models of mortise tenon joints for the integral structure analysis of timber buildings.In this paper,several typical mortise tenon joints including straight joints,dovetail joints and penetrate joints were studied further by combining experiment study,numerical simulation and theoretical analysis.According to the existing test data,the differences caused by test conditions are identified and the characteristics of mortise and tenon joints are concluded.Based on that,the mechanism of mortise tenon joints was analysed,which provided the basis for numerical simulation and establishing the theoretical models of mortise tenon joints.The results show that the tenon pull-out is proportional to the joint angle and the proportion coefficient is slightly less than half of the tenon height.The small part of penetrate joints has obvious bending deformation,while the large part as well as straight joints and dovetail joints have little bending deformation.The finite element models of mortise tenon joints were established with the help of ABAQUS and verified by test data.Then the finite element models were applied to analyze contact conditions of mortise and tenon,local compression effect,the distribution of compressive stress and the failure modes of penetrate joints,which provided reasonable assumptions for establishing theoretical models of mortise tenon joints.The numerical simulation results show that the extrusion stress of tenons is only distributed in a certain height range along the extrusion direction and their distribution is not linear,which can be equivalent to uniform stress distribution through the equivalent compression height coefficient.Besides,the maximum transverse tensile stress occurs at the corner of the variable section when the penetrate joint is bent clockwise and the normal stress of the tenon root section can be simplified into triangular stress distribution when the penetrate joint is bent anticlockwise.Based on the analysis of test results and numerical simulation,relationship between moment and rotation of mortise tenon joints were theoretically analyzed under rational assumptions.The theoretical models of mortise and tenon joints were established,which simultaneously satisfied three conditions,namely the moment,horizontal force and vertical force equilibrium.Abandoning the limited assumption of fixed rotation center,the models are more universal and reasonable.On the base of theoretical models,the practical models of mortise and tenon joints were finally established by defining the characteristic points.The models exclude empirical parameters determined by test and only include quantifiable parameters such as material properties,the size of joints and the thickness of gaps.Generally,the practical models,with simple form and good accuracy,are easy to be applied in engineering practice.