Study On Axial Compression Behavior Of Multi Cavity Concrete-filled-steel-tube Columns With Rectangular Section

This paper adopts the method of combining experimental research,numerical simulation and theoretical calculation to study the axial compression performance of rectangular multi-cavity concrete-filled-steel-tube(CFST)columns.The research contents are as follows:1.Taking the number of cavities,concrete strength and section steel content as the main parameters,16 specimens were designed and fabricated,including 2 ordinary CFST columns,8 rectangular multi-cavity CFST columns with "Ri" type and 6rectangular multi-cavity CFST columns with "Tian" type,and their axial compression tests were conducted.2.The ABAQUS of rectangular multi-cavity CFST column was established and nonlinear numerical simulation was carried out.3.The theoretical calculation of the ultimate bearing capacity of rectangular multi-cavity CFST columns under axial compression is carried out by using five relevant calculation methods at home and abroad.The main factors affecting the bearing capacity and their related parameters are analyzed,and the calculation formula of axial compression bearing capacity is established.Main conclusion:1.Compared with ordinary CFST columns,the axial compressive bearing capacity of Ri and Tian rectangular multi-cavity CFST columns is increased by 15%and 35%,and the ductility index is increased by 72% and 143%,respectively.The axial bearing capacity of rectangular multi-cavity CFST columns increases with the increase of concrete strength.Concrete strength has little effect on residual bearing capacity.2.The reliability of the finite element model of rectangular multi-cavity concrete-filled steel tubular columns is verified by comparing the load-displacement curves of numerical simulation and test.The analysis of concrete stress cloud diagram shows that the construction of "Ri" and "Tian" can effectively improve the restraint area of concrete.Expansion analysis of finite element parameters shows that the bearing capacity of specimens with inner diaphragm increases greatly when concrete strength is increased compared with specimens with ordinary steel tube.With the same number of cavities,the specimens with high steel content in section will have higher bearing capacity when the strength grade of concrete is increased than those with low steel content in section.The steel strength increases with the increase of concrete strength,in which the higher bearing capacity can be obtained when the concrete strength is low.3.The formula for calculating the axial compressive bearing capacity of rectangular multi-cavity CFST was established.The average error and variance of the formula were 0.34% and 0.001 respectively,which showed high accuracy.