Research On Seismic Behavior Of Outer Stiffening Ring Plate Joints With T-Shaped Concrete-Filled Steel Tube Frames

Special-shaped concrete-filled steel tube(CFST)structure not only has the superior performance of ordinary CFST structure,but also can be made the same thickness of wall,avoiding the corner edges and increasing usable area of room.Special-shaped CFST structure has been researched by domestic and abroad scholars owing to these outstanding advantages in recent years.However,the current research is mainly focused on special-shaped CFST column,and there is little literature on column-beam joint of special-shaped CFST structure.Moreover,most of them only focus on the research of column-steel beam joint.It is basically in the blank state on the research of column-reinforced concrete beam joint.Based on the experimental research on seismic behavior and finite element analysis of the extended-end-plate joints and stiffening ring joints of T-shaped CFST column with reinforced concrete beam which Dr.Liu Jixiong completed,outer stiffening ring plate joints of T-shaped CFST column with reinforced concrete beam were put forward and 33 models of this joints were designed.Using the finite element analysis software ABAQUS,the seismic behavior of 15 joints and the orthogonal experiment of 18 joints were studied.The main contents and results are as follows:(1)The model of outer stiffening ring plate joints of T-shaped CFST column with reinforced concrete beam was established by ABAQUS,and the working mechanism of joints was analyzed.There are 4 processes of crack development of joints,which are the initial crack,the crack,the limit and the damage.In the process of load transfer on beam,the corbel is the role of bridge.The failure of joints is finally derived from the development of plastic hinges formed at the connection of corbel and beam,which accords with the seismic design idea of "strong-joint and weak-member".(2)Seismic behavior of joints was analyzed under the low-cycle reciprocating load.The stress concentration is formed in the core area of joints.However,the stress concentration and the degree of diffusion to the surrounding are different,which is caused by the variation of parameters.The shape of hysteresis curves of all models of joints is full and have no pinch phenomenon,which indicates good hysteretic behavior.The displacement ductility factors are greater than 1.93,equivalent damping factors are greater than 0.180 and energy dissipation factors are greater than 1.134.These seismic behavior indicators largely exceed the requirements of ordinary reinforced concrete structure,and some even exceed the requirements of steel reinforced concrete structure.Moreover,the stiffness degradation curve of joints is basically in line with the standard normal distribution.Due to the hooping effect of steel tube to the core concrete,the stiffness degradation trend gradually slows down.This kind of joints has good lateral resisting ability.(3)The variational laws of seismic behavior indicators of joints with the parameters were revealed by parameter analysis.Increasing reinforcement ratio of frame beams not only can improve the bearing capacity,but also improve the seismic behavior of joints.Increasing length of corbel can improve the bearing capacity,but has few influences on seismic behavior of joints.(4)The effect of 3 performance indexes which are the bearing capacity,the displacement ductility factors and the energy dissipation factors was arrived by orthogonal experiment of joints.The results show that the reinforcement ratio of frame beams plays a significant role in 3 performance indexes.Increasing concrete strength grade of frame beams can improve the bearing capacity,but increase too much goes against seismic behavior of joints.Hence,the concrete strength grade of frame beams should be reasonably selected in engineering design.Finally,on the basis of summarizing the work,the prospects of the research on this topic are put forward.