Research On Seismic Behaviors Of CFST Columns Under Variable Axial Force

The research on seismic performance of concrete-filled steel tube column has been studied for many years and the depth and breadth of the research expand gradually both at home and overseas. However, subjected to the test conditions and the development of experimental methods,the experiments on seismic performance were often done under the condition of quasi-static test. Those of the previous quasi-static tests of research objects had been carried out in the terms of keeping the axial force unchanged and then applying reciprocating horizontal load to study the effect of different parameters on the seismic performance. Concrete filled steel tubular frame column should not only bear the effects of the horizontal earthquake, but also the effects of vertical earthquake function when the earthquake occurs. The overturning moment caused by structure lateral displacement have a significant impact on axial force of frame column. Relevant investigations show that the continuous changes of axial force will cause unexpected damages to columns, which play a large role in the stability of the whole structure. So we need to study the influence of the axial force on the structural seismic performance of frame column as long as failure mechanism under Variable axial force in the process of earthquake.In this paper, it is based on the Open Sees finite element software and external computing program combined with control program to accomplish the data exchange. And then complete the experimental research of seismic performance of concrete-filled steel tube under the variable axial force, comparing it with the results of Open Sees simulation calculation.(1) According to the actual engineering prototype,produced six circular concrete filled steel tube columns. It can be divided into three types according to the diameter of steel tube: 270 mm, 330 mm and 390 mm. The thickness of the steel tube is 6 mm.(2) Based on the substructure pseudo dynamic test method of Open Sees to study the hysteresis property, energy dissipation, ductility and seismic damage characteristics of concrete-filled steel tube column under the change axial force. The result shows full hysteretic curve and good energy dissipation capacity of concrete-filled steel tube column without obvious deflation "pinched" effect and axial force will produce much more influence on concrete-filled steel tube column which has already stepped into the stage of yield. Axial force change can reduce the ductility of concrete-filled steel tube column and also weaken the capacity of energy consumption. But when the axial compression ratio is 0.2, there will be less effect on the stiffness with the axial force change.(3) When use the Open Sees to simulate and analysis, the calculated results are in good agreement with experimental results, it indicate that the selection of steel and concrete constitutive relation and beam-column elements can better simulate the mechanical characteristics of the concrete-filled steel tube under the action of earthquake.(4) It is easy to select frame column as the research object to simulate stress pattern and mechanical properties of concrete-filled steel tube column based on the substructure pseudo dynamic test method of Open Sees under the seismic. Provide a new reference for the research of substructure pseudo dynamic test.