Behavior Of Concrete Filled Steel Tubular Columns With Hollow Steel Balls Under Axial Compression

Concrete-filled steel tubular(CFST)columns are widely used in various high-rise and long-span structural engineering because of their advantages such as high bearing capacity,good seismic performance and good economy.However,due to construction,maintenance and testing reasons,there are often defects such as cavities in CFST columns,which affect the mechanical performance of the structure.In this paper,a concrete-filled steel tubular column with hollow thin-walled steel balls is designed.On the one hand,the hollow steel balls can be used to simulate the cavities in the concrete,and the influence of different size defects on the mechanical properties of the concrete-filled steel tubular column can be discussed.On the other hand,the hollow thin-walled steel balls can be used to replace part of the concrete,and the concrete-filled steel tubular can be discussed under the condition of reducing the weight of the structure Mechanical properties of concrete columns.At the same time,in order to carry out the comparative study,this paper also designed the same parameters of solid CFST columns.In this paper,the influences of void ratio,slenderness ratio and hoop coefficient on the mechanical properties of the specimens are analyzed by axial compression test and numerical simulation method based on ABAQUS finite element,and the calculation formula of bearing capacity of CFST columns with hollow steel balls inside is proposed.The main contents of this paper are as follows:(1)60 CFST columns were designed,including 45 CFST columns with hollow steel balls,18 short columns and 27 long columns,15 solid CFST columns,6 short columns and 9 long columns.Through the axial compression test,the failure mode,load displacement curve,initial stiffness and ultimate bearing capacity of two types of CFST columns are obtained,and the results are compared and analyzed.The results show that the failure of the short concrete-filled steel tubular columns with hollow steel balls is concentrated in the middle and upper part,and there is obvious ring-shaped buckling;the ultimate bearing capacity of the concrete-filled steel tubular columns with hollow steel balls is slightly lower than that of the solid concrete-filled steel tubular columns,and it decreases with the increase of the void heart rate,increases with the increase of the wall thickness of the steel tubes,and changes slightly with the increase of the slenderness ratio.(2)Based on ABAQUS finite element,the model of CFST columns with hollow steel balls under axial compression is established to simulate the influence of different variable parameters on the mechanical properties of the specimens.The failure mode,ultimate bearing capacity and load displacement curve are in good agreement with the test.(3)Referring to the formula of bearing capacity of concrete-filled steel tubular columns in domestic and foreign regulations,the formula of bearing capacity of concrete-filled steel tubular columns with hollow steel balls is fitted by introducing the influence coefficient of void ratio,and compared with the test value,the results show that the formula is in good agreement.