Research On Seismic Behavior Of Concrete-Filled Steel Tube Column Under Cyclic Tension And Compression Loads

With the continuous development of the economy,the high-rise buildings have rapidly constructed,meanwhile,faced much challenge.As the building height increases,the role of lateral displacement becomes particularly important.Under such circumstances,the diagrid structure of concrete-filled steel tube made from obliquely-arranged columns of concrete-filled steel tubes(CFST)has emerged and been applied successfully at home and abroad due to its large anti-lateral stiffness and efficient transfer of force.The inclined CFST columns,as the main force components,are mainly bearing axial forces under both horizontal and vertical loads.At present,the research on the uniaxial compression behavior of CFST column has become more mature,however,there has been little research on its seismic behavior under the cyclic axial tensile and compressive load has been done.Therefore,in view of the above insufficiency,this paper studied the seismic behavior of CFST columns under cyclic axial tension and compression load by means of experimental research,Finite element(FE)simulation,and theoretical analysis.The calculation formula of the bearing capacity under cyclic tension and compression load was modified.The work are as follows:(1)The seismic behavior of CFST was analyzed under cyclic axial tension and compression load.Through the analysis of hysteretic curves,skeleton curves,bearing capacity and stiffness degradation,deformation characteristics,and energy dissipation capabilities and so on,the test results showed that the CFST column has a higher bearing capacity.After entering the elasto-plastic stage,the concrete and steel both could perform their combined effects well,mainly manifested as better post-buckling bearing capacity,good ductility and energy dissipation,meanwhile strength and stiffness degradation were relatively slow as well.Combined with the strain gauge data and the deformation of the specimen,provided the stress mechanism of CFST column under cyclic axial tension and compression load.(2)On the basis of simulating the CFST columns by ABAQUS software and comparing with the test results,analyzed the influence of variable parameters on the hysteretic properties of CFST columns.The results showed that the FE results agreed well with the test results.The concrete strength had little effect on the initial stiffness and the tensile strength of the CFST column,however it had a great influence on the compressive strength.With the increase of the slenderness ratio,the initial stiffness and compression bearing capacity of the model decreased,while,the tensile bearing capacity was almost unchanged.Besides with the increase of the strength of steel,the initial stiffness of the model was almost unchanged,and the tensile bearing capacity and the compressive bearing capacity increased.With the increase of the steel content,the initial stiffness and the compressive bearing capacity of the model was almost unchanged,the bearing capacity under tension increased yet.(3)Based on the previous research on the calculation formula of the bearing capacity of CFST columns subjected to uniaxial compression or tension,combined with the results of FE analysis,and took into account the cumulative damage of CFST columns caused by cyclic axial load,the bearing capacity reduction factor was proposed,finally set up a design formula for the bearing capacity of CFST columns subjected to cyclic axial load.Compared with the test results,the results showed that the theoretical values were all lower than the experimental values,and the errors are within 10%,so it could provide a reference for the design of CFST columns.