Study On Seismic Behavior Of Connections Between Beams And Special-shaped Column Composed Of Concrete Filled Steel Tubes Connected By Double Vertical Plates

The structure with L-shaped column composed of concrete-filled steel tubes connected by double vertical plates(L-CFST columns with double vertical plates)has outstanding advantages in structural performance and architectural effect,and has broad application prospects.Beam-to-column connections are the key force transfer area.The different structure of the joints on two sides of the L-shaped column will lead to the difference and complexity of the seismic performance on two sides.At present,there is no study on the seismic performance of the connections,and the theoretical basis for the design of the structure is lacking.In order to solve these problems,the seismic behavior of connections between H-beams and L-CFST columns with double vertical plates is systematically studied in this paper.The main work and achievements are as follows:1.Five full-scale specimens of L-CFST columns with double vertical plates to beam connections were tested under low cyclic loading at the end of the beam.The variation parameters of the specimens included the shape and position of vertical stiffener and whether concrete was filled in the column.The seismic performance of the connections,such as bearing capacity,ductility,energy dissipation capacity,strength and stiffness degradation,and the influence of different parameters on the seismic performance of connections were studied.The results show that the hysteretic curve is a full shuttle shape with good ductility and energy dissipation capacity,and the degradation of strength and stiffness is stable.The ultimate failure modes of connections include plastic hinge formed by beam flange buckling,cracking of the connecting plate at the end of vertical stiffener,etc.Concrete in steel tube can improve the stiffness,ductility and energy dissipation capacity of connections,and the weakening of vertical stiffener has little influence on the seismic performance of connections.2.The three-dimensional nonlinear finite element model of five specimens was established by using ABAQUS software.The material,contact and boundary conditions were reasonably set up.By comparing the results of numerical simulation with those of test,such as hysteresis curve,skeleton curve,phenomena and stress distribution,it is found that they are in good agreement,which proves that the finite element modeling method has good accuracy and reliability.Based on the experimental and numerical simulation results,the working mechanism of the connections were analyzed,the force transfer mechanism and deformation composition were clarified.The connections are determined to be rigid-jointed and full-strength joint.3.Parametric analysis was carried out by finite element method.The effects of thickness and strength of column steel tube,end plate thickness and strength on seismic performance of vertical stiffener-end plate connections were studied.Two seismic optimization measures were proposed and fracture risk evaluation index was introduced to evaluate their effects.The results show that increasing the thickness and strength of steel tube wall,the thickness and width of end plate in a certain range can improve the bearing capacity of connections to varying degrees.The optimum measures of reducing beam section and thickening vertical stiffener can reduce the fracture risk of the key parts of the connections and improve the seismic performance.4.Based on the structural characteristics of vertical stiffener-end plate connections,the calculation methods of yield and ultimate flexural capacity of the connections were deduced and compared with the experimental and finite element results.The results show that the error of flexural capacity calculated by the formula is less than 11% and slightly conservative,which proves the accuracy and reliability of the proposed method.