Study On Bond Behavior Between Stell Bar And Concrete Under Sustained Load And Dry-wet Cycles

The bond performance between steel bar and concrete is an important factor that influencing the bearing capacity,usability and durability of the reinforced concrete structure.Nowadays,many domestic and foreign researchers studied the factors that influencing the bond performance of reinforced concrete But,the stress conditions and the bond values developed in the concrete specimen during pull-out tests differ from those in the actual work.Therefore,it's difficult to predict the failure mechanism and service life of reinforced concrete structures scientifically.Based on the above reasons,This paper examines the bond behavior between steel bar and concrete under different conditions(i.e.Dry-wet cycles action,sustained load action(25%,50% and 75%ultimate load),combined action of sustained load and dry-wet cycles,reinforced concrete beam specimen without transverse reinforcement).(1)The relationship between the relative slip of reinforced concrete with time,the ultimate bearing capacity of concrete beam specimens and the bond slip constitutive model between steel bars and concrete were studied.The mechanism of various factors on the mechanical properties of concrete beam specimens was discussed.(2)The function of bond slip constitutive relation of reinforced concrete after sustained loading conditions is established,in this paper.Results show that:(1)The relative slip increment decreases exponentially with time,and approaches to zero.The total amount of slip is increases in logarithmic form,and tends to be stable,gradually.(2)The limit slip of reinforced concrete is obviously reduced after the action of sustained load and combined action of sustained load and dry-wet cycle.The bond strength and bond stiffness of reinforced concrete will be reduced after the high level of sustained load and these were improved after low level sustained loading and dry-wet cycles.(3)The relative slip between steel bars and concrete decreases and the bond strength of the beam specimen was increased by 40% after the dry-wet cycles alone,and the bond stiffness increased significantly as well.(4)Transverse stirrup can constraint core concrete,and enhanced the bond strength between steel bar and concrete to a certain extent.The deformation capacity andductility of reinforced concrete beam specimen were improved significantly for the configuration of stirrup.