Study On Seismic Behavior Of Concrete-filled Thin-walled Stiffened Square Steel Tubular Columns

Concrete-filled thin-walled stiffened square steel tubular columns are formed by filling concrete in thin wall steel tubes,because of its advantages such as high bearing capacity,convenient construction,saving steel and so on,it has been paid more and more attention by domestic and foreign scholars in recent years.Under the action of earthquake,local buckling of concrete-filled thin-walled stiffened square steel tubular columns is easy to occur at the end,the restraint of steel tube wall on core concrete is weakened after buckling,its application in engineering is seriously restricted,in this paper,the seismic behavior of thin-walled square concrete-filled steel tubular columns with longitudinal stiffeners is studied in depth from the aspects of experiment and simulation.In this paper,the number of stiffeners(without ribs,single rib,double ribs),axial compression ratio(0.3,0.5,0.7)and length-fineness ratio(13.86,20.78,27.71)are taken as the main parameters,seven specimens with ribbed thin-walled square concrete-filled steel tubes are designed,the failure modes,hysteretic curves,bearing capacity,ductility,energy dissipation capacity and stiffness under low cyclic cyclic loading were studied.The results show that all the specimens show the phenomenon of weld crack or concrete being crushed in different degrees at the end.The end weld of the unribbed specimen cracked seriously and the internal concrete was crushed completely,the end weld of the ribbed specimen is relatively intact,and the bearing capacity,ductility and energy consumption of the steel tube concrete specimens with stiffeners inside are also obviously improved,and the seismic performance is better with the increase of stiffeners.Because of the internal stiffener's pulling action,the restraint effect of steel tube on concrete is improved,the specimen did not fail rapidly after reaching the bearing capacity,the specimen has good ductility,and the materials were put to good use;With the increase of axial pressure ratio,the crack degree of the weld at the end of the specimen increases,the bearing capacity of the specimen increases accordingly,but the ductility is weakened;With the increase of slenderness ratio,the failure degree of the specimen increases,and the end deformation of the specimen with the largest slenderness ratio is the most serious,the bearing capacity of the specimen decreases accordingly,but the effect of slenderness ratio on ductility is not obvious.The finite element software ABAQUS was used to simulate the test specimen,the stress distribution of steel tube and concrete,the bearing capacity of specimen and the failure mode of specimen are analyzed,the simulation results are in good agreement with the experimental results,the feasibility and reliability of the finite element model are verified.Based on the test results and simulation data in this paper,finite element software was used to expand the parameters,and the calculation formulas of bearing capacity enhancement coefficient and ductility enhancement coefficient of ribbed thin-walled square concrete-filled steel tubular column under the action of low cyclic loading are obtained by using software,the calculated results are compared with the simulated results,and they fit well,it can be used as reference for the following research and engineering practice.