Study On The Basic Theory Of Bond-Slip Between Steel Tube And Concrete In CFT Structures And Numerical Simulation By ANSYS Program

Based on the domestic and abroad researches, the mechanism of bond between steel tube and concrete in CFT (Concrete Filled Steel Tube) structures was analyzed in this paper,. By a series of CFT push-out test results, both the bond strength and the relations between the bond stresses and slip, which was usually called bond-slip constitutive relations, were analyzed. And theoretical analysis on the bond behaviors was carried out.According to the former researches, initial understanding on the CFT structures was established, and the importance of interface conditions to bond behavior and the distribution of bond stresses along the CFT column were noted. The constitute of bond force, including chemical bond action between the steel and the concrete, the bond action provided by the mechanical interlocking of the concrete and steel, and the bond action that depends on the interface pressure and the coefficient of friction. According to the load-slip curves (P-S curves), every stage of relationship between bond stress and slip was analyzed, including initial slip stage, accelerated slip stage, descending stage and residual stage. The characteristics of P-S curves were summed up. In some ones, there were ultimate stage and descending stage, and in the others there was only ascending stage, not reaching the peak point. The bond strength was defined on the basis of the distributions of the steel tube strain. Factors and shear connectors, affecting the bond strength, were analyzed, involving many aspects, such as materials, the specimen shape and size, curing conditions and loading methods. And how the behavior of the structure was influenced by the bond strength and slip between the steel tube and the concrete core was also studied. According to linear regression analysis, both the bond strength and the bond-slip constitutive relations were presented in this paper.The push-out test specimens were numerically simulated by ANSYS program. In order to take the interaction between the steel tube and the concrete core into account, combination 39 elements were used to simulate the three directional interactions. The simulation results were compared with the experimental results, from which the established bond-slip constitutiverelations model was verified. The methods and skills of nonlinear FEM numerical simulation by ANS YS program used in CFT structures were summarized and presented.