Experimental Study On Bond Stress-Slip Relationship Of Concrete Filled Steel Tubes

This paper analyzed the mechanism of bond between the circle steel tube and the concrete in the Concrete-Filled Steel Tube. By a series of CFST (Concrete-Filled Steel Tube) push-out test, the relations between the bond stresses and slip, which was usually called bond-slip constitutive relations, were analyzed and studied to solve the problem on bond-anchoring design and the problem on numerical simulation of the bond-slip in FEM(Finite Element Method) analysis of CFST structure. The bond problem between steel tube and concrete is one which is further concerned by more and more construction engineers and managers. Many experiments are tested at domestic and external, most of which are about bond strength, but bond stress-slip relationship was little researched. At present, concrete and steel's constitutive relations is obvious and the bond stress-slip relationship is uncertain, which restricted the application of FEM analysis of CFST structure. In this paper, the equations of stress of steel tubes, bond stress, and relative slip of steel tubes and concrete were deduced through theoretical analyses, and mathematical model of bond stress-slip relationship is established, which may be contribute to the further analysis of bond-slip relationship of concrete filled steel tubes.9 axis push-out tests of CFST are completed in this paper. Stress and longitudinal slip distribution and bond stress of interface between steel tube and concrete are also tested. Bond -slip constitutive relations is researched as follow:According to the analysis of steel tube stress, test method of CFST interface bond stress is shown. Distributed functionε(x)andτ(x) for strainεand bond stress r is got. Before limit load P_u is reached,ε(x)andτ(x) are distributed as exponential form; otherwise,ε(x) tend to be linearity andτ(x) is adequate distribution in all interface.Relative slip on the interface is measured during all the push-out tests by setting slip sensing units and the regularities of distribution also are shown. The conclusion is as follows: before limit load appears, s(x) is distributed as conical section; otherwise, tends to be linearity.Considering flakiness ratio and slenderness ratio, expression of average bond-slip constitutive relations and position function related bond stress G(x) and slip F(x) are obtained. Bond-slip constitutive relations are created on different lengthwise direction, as the foundation for finite element simulation.