Study On Bond-slip Behavior Of Steel Bar And Concrete Subjected To Freezing-thawing And Stirrup Corrosion

The foundation of reinforcement and concrete work together is bond stress between them.Bonding stress achieves compatible deformation between the them to reach ultimate limit state.Therefore,the sdudy of the bond behavior of reinforced concrete has important theoretical and practical significance.This paper analyzes the problem of bond degradation of reinforced concrete.On the one hand,it is due to the continuous low temperature weather environment,on the other hand,chloride ion and sulfate ion invade concrete and cause steel bar corrosion.These two factors have a serious impact on the durability of concrete.In previous researches at home and abroad,the bond behavior of reinforcement and concrete is not related to the restraint of stirrup,so most of the tests are center pull-out tests.However,the influence of stirrups is often ignored in the central drawing.The change of stirrups ratio will change the mechanical constitutive properties of surrounding concrete,and the ring compressive stress can improve the bonding performance.Based on eccentric pull-out specimens,this study discusses the influencing factors of corrosion stirrups and freezing-thawing concrete on bond performance,mainly including the following three aspects:Firstly,by comparing the existing test schemes at home and abroad,and by comparing and analyzing the existing test schemes of pull-out specimens,the test loading scheme that can accurately describe the freezing-thawing cycles and stirrup corrosion is finally established.Secondly,this test is a monotonic pull-out test of reinforced concrete specimens.It mainly studies the variation of bond strength,slip between steel bars and concrete under the coupling of three key factors:corrosion rate,freezing-thawing cycles and stirrup spacing.The 1000kN microcomputer controlled electro-hydraulic servo test machine was used to observe and analyze the destructive form,and the three key indexes of ultimate bond strength?_u,ultimate bond slip _uS and residual bond strength?_r were obtained.The empirical formula of strength is constructed to consider the bond-slip constitutive model under the three factors of stirrup spacing,stirrup corrosion rate and concrete freezing-thawing.Further,the bars are instrumented with strain gauge placed in a machined axial cavity.And the influence of the anchoring position on the changes of the stress and strain is observed and analyzed by the strain change of the strain gauges in the grooves.Finally,the ABAQUS simulation is used to establish a refined finite element model,which mainly analyzes the effects of stirrup spacing,stirrup corrosion rate and freezing-thawing concrete on the ultimate bond strength and slip,and will simulate the test results which are compared with the actual test results to compensate insignificance in the test and lay the foundation for further analysis with finite elements.