Research On Seismic Behavior Of Square Concrete-filled Tubular Columns With Stiffen Ribs And Binding Bars

Square concrete-filled steel tubular(CFST) column with stiffened ribs and binding bars is a new structure type which is strengthened with stiffened ribs and binding bars simultaneously. For the purpose of well understanding its mechanical performance and seismic behavior, in this paper the seismic response of the new kind of structure is studied and analyzed based on experiment, numerical simulation and theoretical study etc. And the main research contents and the achievements are summarized as follows:(1) 1 CFST stub column only with strengthened binding bars and another 15 ones strengthened with stiffened ribs and binding bars were tested under axial compression and reversed cyclic lateral load. The experiment parameters are mainly the influernce of the steel thickness, the axial compressive ratio and the ratio of the width to thickness of stiffened ribs to investigate the influence to the seismic behavior of the columns. It indicates from the experiment that the hysteretic curves of the columns with stiffened ribs and binding bars are very plump, the columns are of great bearing capacity and ductility, and its seismic behavior is better than that of nomal CFST column with binding bars only.(2) Compared to ordinary CFST columns, the square CFST columns with stiffened ribs and binding bars can provide more effective restraint for the core concrete. So the increase of the thickness of the tubular can significantly improve the initial stiffness, the strength and the ductility of the columns. This indicates that the seismic behavior of the columns can be effectively improve by increasing the thickness of the tubular.(3) With the axial compressive ratio increasing in reasonal range, the initial stiffness and load capacity of the columns increases, while the ductility decreases. It indicates the seismic behavior of columns with great axial compression ratio is relatively poor. Therefore, the effect of the compressive ratio should be considered synthetically in designing.(4) With the ratio of the width to thickness of the outer stiffen ribs increasing, the load capacity and the ductility of the columns increases. Therefore, the seismic behavior of the columns can be improved by appropriately increasing the ratio of the width to thickness of the outer stiffen ribs in designing. The incresing of the concrete strength can slightly increase the stiffness and load capacity of the columns, but can not affect its energy dissipation capacity and ductility factor obviously. So the influence of concrete strength should be taken into consideration comprehensively.(5) The numerical simulated models were established and the skeleton curves of each specimen were calculated based on the ABAQUS finite element platform, and the analysis results match the experimental results well. On the basis of the modeling, the mechanical mechanisms of square CFST column with stiffened ribs and binding bars were then analyzed, and the influences of some critical parameters on mechanical behavior were studied.(6) On the basis of skeleton curve of the experimental data, the simplified three broken line model for the load-displacement curve of the square CFST column with stiffened ribs and binding bars are obtained by test fitting methond, and further the hysteretic law was proposed.