Research On Seismic Behaviour Of The Bottom Flange Bolted And Top Flange Welded Diaphragm-through Connection Between Concrete Filled Tube Column And Steel Beam

Frame joints are the main structure parts connecting horizontal force components and vertical force components,which play the role of transferring and distributing internal forces and ensuring structural integrity.Three types of joints configurations of rectangular steel tube concrete column and steel beam are recommended in “Rectangular Steel Tube Concrete Structure Technical Specification” and other norms.However,these joints have not taken into account the on-site construction,and they have still many shortcomings.In this paper,on the basis of the traditional bolt welding mixed joint,a new type of diaphragm-through joint was proposed.In this new joint,the steel beam bottom flange and the lower baffle plate were connected with bolts and the upper flange and the upper diaphragm were connected with weld.During the construction,the proposed joint can effectively reduce the risk that the steel beam cannot be in place due to the column inclination or the misalignment error,and it can reduces the precision sensitivity and speeds up the installation process.At the same time,because of the existence of the through diaphragm,the rigidity of the joint area is increased,the plastic hinge is moved out,and the damage of the steel beam is earlier than that of the joint.Therefore,the proposed joint is convenient and it meets the seismic criterion of "strong column and weak beam".In order to study the seismic performance of the proposed joints connecting the concrete-filled steel tubular column and steel beam,three full-scale joints including slot type,hole type and weld type were designed and tested under low cyclic loading.The effects of different web-connected structures on the seismic performance of the diaphragm-through joints were analyzed.The failure characteristics of each specimen were analyzed and the seismic performance indexes such as bearing capacity,stiffness,ductility and energy dissipation capacity were studied.The results show that different connection structures have little effect on the bearing capacity of joints,but have considerable influence on the ductility,stiffness and energy dissipation capacity.The stiffness of the nodal domain can be reduced to improve the energy dissipation performance of the joint.The slip of the bolt can increase the energy dissipation capacity of the joint,and it has little effect on the stiffness degradation.It is also found that the hole type joint and the weld type joint have better ductility and higher stiffness,especially for weld type joint,the stiffness degradation is more slowly which means it has better seismic performance.Based on ABAQUS,the three-dimensional finite element models of the three diaphragm-through joints were established.The material nonlinearity of steel and concrete,geometric nonlinearity and contact nonlinearity were considered.The deformations of the diaphragm-through joints under the low cyclic reversed load were analyzed.The results show that the finite element analysis results of the bearing capacity and failure characteristics of the joints are in agreement with the experimental results,which verifies the feasibility of the finite element analysis method.Through the finite element analysis,the stress-strain distribution rules of the diaphragm-through joints are obtained under the horizontal load,and the transmission path of the through joints is revealed.