Modeling Of Concrete Cover-cracking And Bond Behavior Of Corroded Steel Bars Under Transverse Constraints

The bond stress between concrete and steel bar is a necessary condition for the common work of reinforced concrete members,and the stress between the reinforcement and the concrete is transmitted through the bond and the deformation is coordinated.The bond problem of reinforced concrete structure have great significance in theory and engineering practice.Deterioration of bonding between steel bar and concrete due to corrosion of steel bar is one of the important factors affecting the durability of concrete structures.Many scholars have studied the bonding properties of corroded steel bar and concrete,but most of the previous studies have been based on the central pull test and have not fully considered the lateral confinement of the stirrups.The change of the position of the steel bar in the drawing specimen changes the constraint of the concrete around the steel bar,and thus presents different mechanical properties.In this paper,the eccentric drawing specimens are taken as the research object,and the following research work is carried out around the bond performance between corroded steel bar and concrete:(1)The corrosion cracking behavior of reinforced concrete members under transverse confinement was studied.The critical corrosion rate of the longitudinal steel bar at the time of the crack initiation of the concrete protective layer under different stirrups was measured.The influence of the stirrup spacing and the stirrup diameter on the critical corrosion rate was analyzed.Based on the theory of elasto-plastic mechanics,a theoretical model for predicting the critical corrosion of steel at the cracking time of the protective layer is proposed,considering the uniform corrosion of the steel bar and considering the restraint effect of the stirrups on the surrounding concrete.The results of this model are in good agreement with the experimental results,which can be used to predict the corrosion rate of the longitudinal reinforcement at the time of crack initiation of the stirrup structure,and further extend the applicable range of the model.(2)The bond mechanism and macroscopic mechanical properties of eccentric pull members under transverse restraint are studied.The bond strength and bond-slip curve of the corroded member under eccentric tension are measured under the condition of transverse restraint,and the change of the bond between the two kinds of reinforcement is obtained.The differences in the bonding properties between round steel bar and ribbed steel bar are compared.The mechanism of'the bond slip between the round steel bar and ribbed steel bar is explained.The effects of longitudinal reinforcement type and stirrup spacing on ultimate bond strength and bond-slip constitutive curves were analyzed.An eccentric pull ultimate bond strength model with transverse constraints is established.(3)The macroscopic mechanical properties and acoustic emission characteristics of the eccentric drawing members are studied.A new positioning method is designed to determine the position of the acoustic emission source during the pull-out process of the specimen and its development trend.The evolution of the acoustic emission characteristics of the eccentrically drawn specimen with the corrosion rate is analyzed.The concept of the damage factor is introduced into the bond behavior.The microstructural evolution of the bond between the steel and the concrete is discussed.The damage evolution model based on the relative variation of acoustic impact number is established.