Seismic Behavior Analysis And Experimental Study Of Damage Controllable Energy Dissipation Beam-Column Connection Joints

In the frame structure,the joints are connected with multiple components,whose configuration and stress are relatively complicated,and the joint destruction can easily cause the collapse of the structure,so it is very important to ensure its good seismic performance.Existing joints have problems such as uncontrollable plastic development and poor energy-dissipating capacity.In order to improve the seismic performance of the joints,the new frame beam-column joints have been extensively investigated.In this thesis,a damage controllable energy dissipation(DCED)beam-column joint is proposed.Low yield point steels are placed in predetermined areas and bolted to the embedded steel on both sides to make the areas enter plastic state earlier,dissipating seismic energy,and can be replaced after the earthquake,achieving the aim of controllable plastic development and reparability of the joint after the earthquake.Low cyclic reversed loading tests and finite element simulation of DCED joint was carried out to study the seismic performance of the joint,such as strength capacity,failure mode,energy dissipation capacity,strength and stiffness degradation.The parameters affecting the performance of DCED joints were analyzed.The main research contents are as follows:(1)Based on the design requirements of "strong column weak beam","strong shear weak bend",stiffness equivalence and plastic controllability,the configuration of DCED joint is proposed.The finite element model of the DCED joint is established to verify the rationality of the joint and study its seismic performance under low cyclic reversed loading.Result shows that the concrete and steel bars are still elastic when the low yield point steel is yielded.Compared with the cast in place joint,the positive and negative bearing capacity of the DCED joint increased by 41.13%and 14.51%,respectively,and the cumulative energy dissipation of the DCED joint is 2.03 times that of the cast in place joint.The initial stiffness of the two kinds of joints is basically the same.At the end of loading,the stiffness degradation is not obvious.(2)Low cyclic reversed loading tests of the DCED joint and the cast in place joint with a scale of 1/2 were carried out.The failure mode,strength and stiffness degradation and energy dissipation capacity of the DCED joint were studied and compared with the cast in place one.The test results show that the concrete in the core area of the cast in place joint is peeled off in a large area and damaged seriously,however the concrete column and the core area of the DCED joint are not damaged,Its damage only occurs at the interface between the steel and concrete and the loading end.Under the same loading displacement,when the steel bar in the core area of the cast in place joint yields,the reinforcement in the core area of the DCED joint is still in elastic state,indicating that the configuration form of the DCED joint can protect the core area of the joint and the main component such as the beam and the column.In the initial stage,two kinds of joints have similar stiffness,which can meet the design requirements of stiffness equivalence.The strength and stiffness degradation coefficients of the two joint during the positive and negative loading are consistent,but the overall strength and stiffness degradation coefficient of the DCED joint are smaller.The energy dissipation capacity of the DCED joint is greater.When the displacement is loaded to 30mm,the cumulative energy dissipation and the equivalent viscous damping coefficient of the DCED joint are 1.86 times and 2.14 times that of the cast in place joint,respectively.(3)The finite element models of the tested DCED joint and cast in place joint are built,and their seismic performance under low cyclic loading is analyzed and compared with the experimental results.The hysteresis curve obtained by the finite element simulation is close to the experimental results.The relative error of bearing capacity is small and the degree of conformity is high,which indicates that the finite element numerical simulation can accurately predict the hysteresis characteristics of the two kinds of joints.Base on that,the influences of the location and the length and the strength of the connecting steel on the seismic performance of the joints,such as bearing capacity,energy dissipation capacity and concrete damage in the core area are studied.The results show that the bearing capacity and energy dissipation capability of the DCED joint are less affected by the location and length of the connecting steel.Within a certain range,the initial stiffness during the positive loading increases with the length of the connecting steel,but the excessive length of the connecting steel will reduce the initial stiffness.The lower the strength of the connecting steel,the smaller the bearing capacity and the faster the stiffness degradation.The location of the connecting steel has no significant effect on the concrete damage in the upper part of the core area,but the damage of the concrete in the lower part of the core area is aggravated with the increase of the location of the connected steel.As the length of the connected steel increases,the concrete damage in the upper part of the core area is intensified,but the damage of the lower concrete is not affected.