Experimental And Theoretical Study On The Interfacial Bond Behavior Of Steel Reinforced Recycled Concrete

The steel reinforced recycled concrete structure can not only achieve the recycling and utilization of waste aggregates,but also has good seismic performance of steel reinforced concrete.It is a steel-concrete composite structure that takes into account energy conservation,environmental protection,and structural performance.Good interface bonding is the foundation of the collaborative work between steel and recycled concrete.In order to more accurately study the bonding performance of the interface between steel and recycled concrete under different influencing factors.This paper designed and manufactured beam type-specimens of steel reinforced recycled concrete,and developed a beam test device with spherical hinges.Static tests were conducted with the critical parameter of replacement ratio of recycled coarse aggregate to study the bond-slip behavior and bond-slip constitutive relationship of steel reinforced recycled concrete.Fatigue tests were conducted with the critical parameters of replacement rate of recycled coarse aggregate,loading frequency,and stress level to investigate the fatigue life and bond performance degradation of the interface between steel reinforced recycled concrete.The main research contents of this paper include:(1)Based on the static test results,the distribution rule and calculation formula of the steel strain are obtained.According to the steel strain and the theory of material mechanics,the calculation formula of the bond stress has been derived.In the load raising stage,the bond stress increased with the load increasing,the closer to the loading end,the greater the bond stress was.In the load reducing stage,the bond stress reduced with the load decreasing.Based on the analysis of the interface slip,the change rule and distribution behavior of the slip were obtained.In the the load raising stage,the slip increased exponentially with the load increasing,and it was negative exponentially along the anchorage length.In the load reducing stage,the slip increased continually with the load decreasing,and showed a negative linear distribution along the anchorage length direction.The calculation formula for slip was obtained through statistical regression of slip data.(2)Based on the load-slip curve of the specimen under static load,the corresponding bond-slip curve was obtained,and the characteristic bond strength was defined.By analyzing the characteristic bond strength of each specimen,the influence law of replacement ratio of recycled coarse aggregate on the characteristic bond strength was obtained.Based on statistical regression of static test data,the calculation formulas of the characteristic bond strength and characteristic slip were derived,and the bond-slip constitutive relationship at the loading end was established.The position functions were proposed based on the bond stress and slip at different positions,and the local bond-slip constitutive relationship with the consideration of the position function was established.Combined with the conclusion of the pull-out test,a unified model of the bond-slip constitutive relationship with consideration of position function under different stress states was proposed,which took the replacement ratio of regenerated coarse aggregate as the parameter.(3)Based on the results of fatigue tests,the influences of various factors on fatigue life were analyzed,and a fatigue life prediction formula considering the replacement ratio of recycled coarse aggregate was proposed.By analyzing the steel strain and slip under fatigue loads,the variation laws of steel strain and slip with the number of load cycles were obtained,and the calculation formulas of steel strain and slip were proposed.Based on the steel strain and material mechanics theory,the degradation law of bonding stress was obtained.An interfacial damage model was established based on the degradation law of bonding stiffness under fatigue load.The Weibull distribution function was verified to be suitable for the fatigue life distribution of interfacial bonding through research.(4)Based on the static test results of specimens with fatigue loading history,the influence law of fatigue loading history on interfacial bonding strength was obtained by analyzing the remainder bonding strength.Within a certain range,increasing the loading frequency and stress level led to a decrease in interfacial bonding strength.By analyzing the steel strain and slip of the specimen,the distribution laws of steel strain and slip were obtained,which were similar to the original static test results.Based on the characteristics of the load-slip curve at the loading end and the conclusion of the original static test,the calculation formula for characteristic average bonding strength and characteristic slip considering loading frequency and stress level were established,and a basic bond-slip constitutive relationship with the consideration of fatigue loading history was proposed.(5)Based on experimental results and theoretical analysis,a bond-slip failure criterion was proposed,which corresponds one-to-one with the failure morphology of the specimen.According to the actual engineering requirements,the calculation formula of the protective layer thickness of steel reinforced recycled concrete structures had been determined,and the minimum reinforcement ratio of steel reinforced recycled concrete structure had been derived.Based on the reliability analysis principle and reliability indicators of bonding anchorage for steel reinforced recycled concrete,combined with statistical data,an expression for the critical anchorage length of steel reinforced recycled concrete was established.According to the calculation formula of the bond-slip constitutive relationship obtained in this article,a method for determining the values of F and D was proposed of the spring element which was suitable for finite element analysis.In this paper,the research contents and research results are of great significance to improve the calculation theory and design method of steel reinforcement recycled concrete structure,and are also of great value in promoting the promotion and application of steel reinforced recycled concrete structures.