Research On Behavior Of Axially Loaded Composite-sectioned Concrete-filled Square Steel Tube Column

The CFSST(concrete-filled square steel tube) has the advantages of high bearing capacity, good ductility, rapid construction speed, regular shape, simple connections between columns and beams. Due to it's good behaviour, it is used more and more widely in engineering practice. But the confinement effect of square steel tube is not obvious, the bearing capacity of column improves little. In order to overcome the disadvantages of CFSST, a new type composite section CFSST column is designed in this paper. The behaviour and mechanism of this composite section CFSST column under axial load were investigated, including theoretical and experimental studies.By the axial compress experimentation of two CFSST specimens and six composite section CFSST column, the differences of mechanical properties between CFSST and composite section CFSST and the influence law of section type, steel ratio, strength of concrete and confinement index on the behavior of composite section columns are studied. The internal force of square steel tube and concrete were analyzed and the mechanism of two materials of CFSST were studied under axial load.Load-deformation curve of CFSST column and composite section CFSST column under axial load was analyzed by ABAQUS, which is a common analysis software of finite element method(FEM). The results of calculation coincide well to experimental data. It shows that the finite elements model established in this paper could be used to calculate the bearing capacity of CFSST column and composite section CFSST column under axial load. Bearing capacity of twenty-seven CFSST and twenty-seven composite section CFSST short column under axial load were calculated by finite element method. The formulas of ultimate axial compressive strength of the column of CFSST and composite section CFSST are obtained form the analysis results. Theoretical results are verified by tests results, and the formulas have clear mechanics concept, simple form, which can supply reliable references to practical engineering and specifications.