Seismic Performance Evolution Analysis And Seismic Vulnerability Assessment Of RC Bridge Piers Based On Steel Bar Corrosion

As a hub for traffic interconnection,bridges are an important guarantee for economic development,social stability and disaster relief after the earthquake.The bridge structure is affected by the harsh environment of the outside world,and the problem of steel bar corrosion is becoming ever serious,which seriously affects the normal service performance and seismic performance,and meanwhile,shortens the service life of the bridge.The seismic damage of bridges is mainly the collapse of bridge piers.The research on the corroded reinforced concrete bridge piers is one of the focuses of seismic research on bridges.Taking a typical reinforced concrete single bridge pier model as an example,the ABAQUS software is used to establish the bridge pier model on the degradation of the effective section and yield strength of the steel bar.The influence of the corrosion location of the steel bar on the seismic performance of the bridge piers are explored,and the seismic strengthening analysis of the corroded bridge piers are carried out.Finally,the seismic vulnerability of the bridge piers are evaluated considering the chloride ion erosion effect.The main research contents are listed as follow:(1)The mechanism of steel bar corrosion is summarized according to the research results from home and abroad.The initial corrosion time of steel bar is determined based on Fick's second law,and the four influencing factors affecting the initial corrosion time of steel bar are discussed.The time-varying characteristics of corrosion current is considered finally to the expression for the diameter degradation of corroded steel bar,which laids a foundation for the evaluation of seismic vulnerability of bridge piers.(2)The pseudo static analysis and nonlinear seismic response analysis of the corroded reinforced concrete bridge piers are carried out considering the corrosion ratio of 5%,15%,25% and the four corrosion location of steel bar,and the horizonal displacement amplitude is applied reciprocaly during pseudo static analysis to analyze the hysteretic energy dissipation capacity and bearing capacity of bridge piers;while during nonlinear seismic response analysis,Taft wave,EL-Centro wave and Kobe wave are applied to the bottom of the bridge piers to analyze the maximum section curvature response along the height of the bridge piers and the change of the bottom shear force so as to explore the influence of the corrosion degree and the corrosion location of the steel bar on the seismic performance of the bridge piers.(3)It is known that the deformation of the bottom of the bridge piers is relatively large according to the maximum section curvature response along the height of the bridge piers.Taking the bridge pier with corrosion ratio of 15% as an example,the 6m range of the bottomof the bridge piers are strengthened with encased concrete method.The reinforced bridge piers are analyzed by pseudo static analysis and nonlinear seismic response analysis to analyze the hysteretic energy dissipation capacity,bearing capacity,stiffness,top displacement and bottom shear force so as to explore the seismic behavior of the corroded reinforced concrete bridge piers strengthened with encased concrete method.(4)The initial corrosion time of the steel bar in the bridge piers and the corrosion rate of the longitudinal steel bar and stirrup at 25,50,and 75 years of service can be obtained based on the previous research results considering the chloride ion erosion effect,so does the degradation of the effective section and mechanical properties of the corroded steel bar;based on which,the bridge piers models at 0,25,50,and 75 years of service are established,and the nonlinear dynamic time history analysis of the bridge piers is carried out by the cloud method to obtain the probability seismic demand model.Taking the drift rate of bridge piers as the damage index,the threshold values are determined by Pushover method,and then the seismic vulnerability curves of the bridge piers are drawn,and the seismic vulnerability of the reinforced concrete bridge piers are evaluated.Then the IDA analysis of the bridge piers are carried out for 0 year to obtain the seismic vulnerability curves of the bridge piers and thus compared with that of the cloud method.