Time-Varying Seismic Performance Analysis Of RC Column In Chloride Ion Environment

When reinforced concrete（RC）columns are exposed to chloride ion attack,corrosion will gradually occur over time.The corrosion of stirrup will affect the stress-strain of the confined concrete,which in turn will cause cracking of the cover concrete and deterioration of the restraint effect on the rebar,resulting in a decrease in the bond between the rebar and concrete,leading to more severe damage than expected under the action of extreme events such as seismic.Therefore,it is particularly important to evaluate the seismic performance of RC columns undergoing different corrosion times in chloride ion environments.However,the existing confined concrete stress-strain model ignores the effect of pitting in the theoretical analysis and calculation,cause insufficient consideration of the degradation of confined concrete stress-strain performance;meanwhile,the stirrup confined rebar-concrete bond-slip model relies mainly on empirical formulas obtained by fitting experimental data,so it is difficult to determine the effect of stirrup corrosion on the degradation mechanism of the restraint effect on the steel reinforcement.In addition,the size of the specimens used in different experimental studies is different,cause a large dispersion between different models.In view of this,this paper base on theoretical analysis and numerical simulation and existing research to analyze the seismic performance of RC columns with different corroding times under the chloride ion environment.The main research contents include:（1）Firstly,based on the existing research results,the time-varying damage model of corroded reinforcement considering the coupling effect of uniform corroding and pitting was obtained by analyzing the development process of pitting pit depth and its distribution probability on the surface of reinforcement with the corroded time.The model is further modified to establish a time-varying stress-strain model for confined concrete with stirrup considering the effect of pitting corrosion;and the reliability of the model is verified by comparing the simulation results with the corresponding test results.（2）Based on the damage model in the research content（1）,the confined stresses of the rebars at different corroding times are determined by combining the previous research results,and then the calculation methods of the confined stresses at different corroding times are obtained;subsequently,by studying the mesomechanics model between the rebars and concrete,the stresses between the stirrup confined rebars and concrete at different corroding times are determined,and the corroding stirrup confined rebars-concrete bond-slip model is established.Finally,on this basis,different paper experimental data are selected to verify the validity of the model proposed in this paper,and further compare it with proposed models to analyze its applicability.（3）Based on the existing RC column specimens,OpenSEES finite element software was used to establish a finite element model of the RC column with material parameters equivalent to those of the specimens with different corrosion times in the experimental and loaded with equal transverse cyclic loading;then the simulated data were used as the basis to analyze the hysteresis and skeleton curves,stiffness and ductility of the model at different corrosion times to obtain the seismic performance of RC column.The results show that the seismic performance of the RC column increases slightly with the stirrup corrosion time when the corrosion time is short.As corrosion time go on,the seismic performance starts to deteriorate gradually,and this process is accelerated by the influence of the stirrup,and more serious performance deterioration occurs than expected.