Study On The Bond-slip Constitutive Relations Of Square Concrete-Filled Steel Tube

Square Concrete-Filled Steel Tube is main development of residential structure. It is in high deformability, tennsibility and earthquake-resistance performance. It overcomes the difficulty of design, construction and application for special section of circular CFST structure. The shear bond problems at the interface of CFST are a basic theory. This research is very important for accuracy of connected calculation and connection of finite element analysis mode among steel tube and core concrete. At the present time, theory research is not complete and standard is shortage, so it rejects the development of square CFST.9 axis push-out tests of CFST are completed in this paper. Stress and longitudinal slip distribution and bond stress of interface among steel tube and concrete are also tested. Bond -slip constitutive relations is researched as follow:1. According to the analysis of stress, test method of CFST interface bond stress is shown. Distributed function ε(x) 和 τ(x) for strain ε and bond stress τ is got. Before limit load P_u is reached, ε(x) and τ(x) are distributed as exponential form; otherwise, ε(x) tend to be linearity and τ(x) is adequate distribution in all interface.2. Relative slip on the interface is measured during all the push-out tests by setting slip sensing units and its regularities of distribution also are shown. The conclusion is before limit load appears, s(x) is distributed as conical section; otherwise, tends to be linearity.3. Considering flakiness ratio and slenderness ratio, expression of average bond-slip constitutive relations and position function related bond stress F(x) and slip G(x) are obtained. Bond-slip constitutive relations are created on different lengthwise direction, as the foundation for finite element simulation.