| The concrete-filled steel tube（CFST）structure is rising gradually in the reinforced concrete structure.The composite steel tube concrete is formed by adding steel tubes inside the ordinary steel tube concrete structure.Because in the concrete-filled steel tube structure,the steel tube has a stronger confinement effect on the concrete,so the structure can give full play to its mechanical properties.construction process is convenient and quick,and self-weight is reduced,the national “13th five-year plan”is promoting green energy-saving building,using industrial waste steel slag to replace part of concrete aggregate,under the condition of ensuring bearing capacity,saving the cost of raw materials,has a good application prospect.In order to study the seismic behavior of steel slag concrete filled composite circular steel tube,the experimental study is carried out in this paper,the failure mode,failure process and parameter analysis are compared and studied.The research work of this paper consists of the following parts:Under the condition of 9% steel content,a total of 3 specimens with circular cross-section were designed for repeated low-cycle test,it consists of 1 concrete-filled circular steel tube specimen,1 concrete-filled composite circular steel tube column specimen and 1 concrete-filled composite steel tube specimen mixed with steel slag coarse aggregate.The diameter ratio of inner and outer steel tubes and the ratio of steel slag substitution were taken as the variable parameters during the test.The failure positions and failure modes of the specimens were observed and the hysteretic curves of the specimens were recorded and analyzed under low cyclic loading test,the bearing capacity,stiffness,ductility and energy dissipation of the specimen,and the stress variation at the base of the column are analyzed.The test results show that after low cyclic loading,local bulging occurs at the bottom of the column,and the crack appears at the push-pull side of the common concrete filled steel tube,but the height and radius of the bulging are different,the common concrete filled steel tubular（CFST）column is the first to appear the heave,and the heave radius is larger and the height of the top surface of the foundation is higher,while the inner steel tube in the CFST provides the circumferential restraint to the core concrete,which makes the heave radius smaller.At the lower end of the push-pull side of the specimen,there will be a slight bulge of the outer steel pipe at first.The bearing capacity of composite concrete filled steel tubular column mixed with steel slag coarse aggregate does not decrease obviously,but decreases slowly after reaching the limit load,and the bending height of steel tube is the same when the specimen reaches the limit load,the yield displacement and the yield load of the composite steel tube concrete specimen and the steel slag specimen are nearly the same,which can be used to study the steel slag concrete and promote the secondary utilization of the waste slag.On the basis of the experimental study,the failure mode of three specimens was observed by finite element analysis under low-cycle cyclic loading with ABAQUS software,the stress distribution nephogram of steel tube and concrete in the specimen is viewed,and the simulated results are analyzed.Compared with the experimental data of the member,the finite element analysis shows that the simulated curves are in good agreement with the experimental ones on the whole,validation of simulation.It is found that the diameter ratio of the inner and outer steel tubes is the main factor that affects the CFST column.With the increase of axial compression ratio,the bearing capacity increases and the ductility decreases,while with the increase of slenderness ratio,the ductility increases. |
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