Study On Hysteretic Behavior Of Special-Shaped Concrete-Filled Steel Tubular Columns Under Diagonal Loading

The special-shaped concrete-filled steel tubular(CFST)columns(L-shaped,T-shaped and +-shaped)are becoming more and more popular in structural engineering,because they can avoid the appearance of corners and make full use of indoor areas when they are used in the buildings.At present,many achievements have been made in the research on the static and hysteretic behavior of the special-shaped CFST columns.However,there are few studies on seismic behavior under diagonal loading.In this paper,the seismic performance of special-shaped CFST columns(L-shaped,T-shaped and cross-shaped)are studied under diagonal loading.The main work includes the following aspects:(1)Tests on the total of 35 special-shaped CFST columns subjected to constant axial load and lateral cyclic load were carried out.The columns include 12 L-shaped specimens,14 T-shaped specimens and 9 +-shaped specimens.The main parameters explored in the tests were: axial compressive load level(0,0.25 and 0.5),loading angle(0°,45°,90° and 135°),concrete strength(fcu=54.1MPa and fcu=76.2MPa)and section form(section without stiffeners,section with stiffeners and multi-cell section).The failure process and failure mode,load-displacement hysteretic curve,envelope curve,stiffness degradation,ductility,energy dissipation capacity and deformation of the special-shaped CFST columns under cyclic loading were obtained.The effects of parameters on hysteretic performance were investigated.(2)The constitutive models of steel and core concrete were determined reasonably.The models of L-shaped,T-shaped and +-shaped columns were developed by using the finite element software ABAQUS.The predicted results are in good agreement well with the test results,which proves the reliability of the finite element models.(3)The working mechanism analysis of the L-shaped,T-shaped and +-shaped CFST columns including the section with stiffeners and multi-cell section under diagonal loading was conducted with the aid of the verified finite element models.The loading process and the stress distribution of the special-shaped CFST columns was deeply understood.(4)The parameters influencing the lateral load-lateral displacement curves of the L-shaped,T-shaped and +-shaped CFST columns were analyzed by ABAQUS.The main parameters are: steel yield strength,concrete compressive strength,sectional length-width ratio,axial compressive level,slenderness ratio,loading angle,length-to-thickness ratio and presence of stiffener or not.Based on the parametric analysis,simplified calculation methods for different section forms were proposed.