Study On Bond-Slip Relationship Of Concrete-Filled Steel Tube Based On Interface Damage

The bond strength between steel and concrete is the foundation of its can working together in concrete filled steel tubular structures. But internal or surface initial damage will be existence in the production process. With the development of interface bonding ability damage, the service life of concrete filled steel tubular structure will be shortening. In the nonlinear finite element analysis, must establish the bond slip constitutive relationship. However, there is still no perfect bond slip constitutive relationship between steel tube and concrete. It is necessary to establish suitable bond-slip constitutive relationship considering the interfacial damage between the steel tubule and concrete. This paper carried out the following work:By the energy method, the push-out test process was analyzed, and obtains the distributions of bond stress along the length of steel tubule.4 specimens of push-out tests were carried out. using the theoretical analysis and experimental results, obtained the bond-slip curve, and established the bond-slip constitutive relationship.According to the steel and concrete to produce the initial debonding of the reasons, analysis the interfacial debonding stress under vertical load, temperature variation and shrinkage of concrete, and the columns in practical engineering were calculated. For 7 different ratios of initial debonding push-out tests, obtained the relationship of ultimate bearing capacity and debonding ratio, interfacial bonding force and its composition.The steel and concrete interface bonding and debonding stress were calculated under cyclic compressive load; the maximum pressure and fatigue load cycles as parameters, the 13 specimens bond slip test were carried out and established the interface fatigue life prediction method.The creep deformation of core concrete were analyzed, load holding time as parameters, the long-term load were applied to the core concrete,7 specimens push-out test after long term loading were carried out, calculate the relaxation of core concrete, the relationship of interfacial bond strength and hoop force.Based on the principle of damage mechanics, the interface damage model of concrete-filled steel tube was established, with the secant modulus of P-s curve as damage variable, analyzed the various factors under the effect of interface bond damage rule, established containing damage variable bond-slip constitutive relationship.With ABAQUS working as the platform, establish the finite element analysis of interface bond-slip of CFST model. And verify the correctness of the model, the analysis results and test results are coinciding each other.By analyzing the various causes interface damage factors, In the design stage from the inner surface of steel pipe and concrete composition look for the way to reducing the interfacial damage.