Experimental Study On Bond Strength And Degradation Of Steel Recycled Reinforced Concrete Under Cyclic Loading

In the composite structure of steel recycled reinforced concrete,the bond-slip effect on the joint surface between steel shape and recycled concrete is the key to work together.At present,the experimental study on bond strength of steel recycled reinforced concrete is mostly carried out through push-out test and short-column test,while there is little research on the bond strength and degradation under cyclic loading.Under cyclic loading,the bond strength between steel shape and recycled concrete has obvious degradation characteristics.Therefore,six factors,including loading mode,replacement rate of recycled concrete,protective layer thickness of steel shape,volume ratio of stirrups,strength of recycled concrete and different bond interfaces were considered comprehensively.Seventeen specimens were designed to study the bond strength and degradation behavior of steel recycled reinforced concrete.The bond-slip behavior of some specimens were simulated and analyzed by using finite element software ABAQUS.The results of the finite element model were compared with the experimental results.The main work of this paper is as follows:(1)The internal local slip between steel shape and recycled concrete was measured directly by the inductive bond-slip sensor.The strain distribution along the anchorage length of profiled steel was obtained by measuring the strain at different positions of flange and web of steel shape.(2)The failure modes and processes of the specimens were observed and summarized.The hysteretic curves and the skeleton curve of the specimens were measured by the displacement meter under cyclic loading.The variation rules of thehysteretic curves and skeleton curves were summarized,and the degradation of bond strength of the specimens was analyzed under cyclic loading.(3)The initial bond strength,ultimate bond strength and residual bond strength of steel recycled reinforced concrete were obtained from the skeleton curves of the specimens under cyclic loading.The relationship between the influencing factors and the characteristic bond strength of steel recycled reinforced concrete was analyzed.The calculation formula for characteristic bond strength of steel recycled reinforced concrete was established by statistical regression under cyclic loading,and the calculation methods of critical protective layer thickness and minimum stirrup ratio of steel recycled concrete were introduced.(4)The degradation mechanism of bond strength of specimens was analyzed under cyclic loading.The bond interface between steel shape and recycled concrete was divided into three regions along the anchorage length.The development law of characteristic bond strength degradation coefficient with the number of load cycles was summarized,and The calculation formula for bond strength of steel recycled reinforced concrete considering degradation was given.(5)Based on the results of cyclic loading test,some specimens were simulated and calculate by finite element software ABAQUS.The whole process of finite element simulation of bond slip of steel recycled reinforced concrete was introduced under cyclic loading,and the hysteresis curve and skeleton curve of the specimens were obtained by finite element calculation.(6)Comparing the finite element simulation results with the test results,the results showed that the calculated values were close to the experimental values,which verifies the feasibility of the bond-slip modeling technology proposed in this paper,and provides a certain reference value for the anchorage design and modeling analysis of the composite structure of steel recycled reinforced concrete.