Experimental Study On Axial Compression Behavior Of Spiral Stiffened Circular Thin-Walled Concrete Filled Steel Tube Columns

In order to solve the problem that the thin-walled steel pipe is prone to local buckling and the performance of the test piece degrades rapidly,a thin-walled circular steel tube concrete composite column is proposed.After the spiral stiffener is welded outside the thin-walled circular steel pipe,the outer concrete and the inner concrete are poured to form a superimposed column.The axial pressure performance test was carried out and the finite element verification was carried out.The mechanical properties of thin-walled concrete filled steel tube composite columns with different constraint forms were studied,which provided a reference for its application in practical engineering.According to the content of the experimental research,five thin-walled CFST composite columns were designed and fabricated,which are ordinary circular steel tubular concrete column C1,spiral rib circular steel tube concrete composite column C2,vertical plate-spiral rib round steel tube concrete composite column C3,spiral rib-vertical plate welded round steel tube concrete composite column C4 and steel spiral rib round steel tube concrete composite column C5.Through the axial compression test of each column,the failure process and failure characteristics of the superimposed column under axial compression conditions are mainly studied.The steel bars and stirrups of the steel spiral rib-concrete composite CFRP column are bound to the outer concrete.The effect is large.When the concrete is first cracked,the load has reached 62.7%of the ultimate load.At the same time,the load-displacement curve,load-strain curve and transverse deformation coefficient curve of the steel tube under the axial compression are analyzed.The research results show that the spiral stiffener can effectively restrain the thin wall buckling and enhance the restraining effect of the steel tube on the internal concrete.The outer concrete cracking of the steel spiral concrete reinforced concrete CFRP column is later than other columns,and the constraints can work together.The ultimate bearing capacity and ductility deformation capacity are greatly improved,and the ultimate bearing capacity and displacement ductility coefficient are increased by 17.4%and 18.6%,respectively,compared with spiral rib circular steel tube concrete composite column.Combining the mechanical properties of each thin-walled CFST stack test,selecting a reasonable constitutive relation,using a nonlinear calculation method to establish a reasonable and effective finite element calculation model,using ABAQUS software to optimize the mechanical properties of the spiral rib welding the calculation of the reinforced concrete CFST superposed column is carried out.The finite element calculation result is 6.04%different from the test result and can be well matched.On this basis,the thickness of the steel pipe wall and the thickness of the spiral stiffener are considered to further analyze the pressure performance of the laminated column axis.The theoretical analysis of the thin-walled CFST composite column under this constraint form is strengthened.The analysis results show that:As the thickness of the steel pipe wall increases,the bearing capacity of the test piece also increases,and there is no significant influence on the ductility of the test piece.When the wall thickness of the steel pipe is 3 mm,the ultimate bearing capacity is increased by 23.6%.The thickness variation of the spiral stiffener has little effect on the bearing capacity and ductility of the specimen.Through this research,we have a deep understanding of the axial pressure performance of the new type of confined thin-walled circular steel tubular concrete composite columns.Combining the test and finite element simulation analysis to verify the rationality and reliability of the thin-walled CFST composite columns under such new constraints,laid the foundation for its practical application.