Study On Life-cycle Seismic Behavior Of Reinforced Concrete Piers In Service Under Chloride Ions

Bridges are the throat of traffic and play an important role in the process of earthquake relief.However,with the passage of service time,the material performance of bridge structure will deteriorate under the influence of many factors,especially under the erosion of chloride ions in the environment,the deterioration of reinforced concrete material performance will be more serious.As an important bearing member of bridge,the stability of pier under earthquake will directly affect the safety of the whole bridge.Therefore,based on the erosion effect of chloride ion in deicing salt environment,this paper explores the seismic performance of reinforced concrete piers in service in the whole life cycle,and evaluates their time-dependent seismic vulnerability.In this paper,the existing bridge of Qilin Expressway in Shanxi Province is taken as the research object,and combined with field investigation,bridge detection and theoretical analysis,the deterioration law of material properties of typical existing piers of Qilin Expressway and the aging vulnerability of piers in the whole life cycle are studied.Based on the data of chloride ion content measured on site,a modified chloride ion diffusion model under deicing salt environment is proposed.The deterioration law of mechanical properties of reinforced concrete materials under deicing salt environment is studied.The seismic resistance of in-service piers under chloride ion erosion is analyzed.The seismic vulnerability analysis model of in-service piers considering deterioration of material properties is established,and the pier achieves under earthquake action is calculated.Or more than the failure probability of aparticular damage state.The main research contents and results are as follows:(1)The on-site investigation of existing bridges on Qilin Expressway in Shanxi Province has been carried out.It is found that the girder bridge accounts for 93% of all bridge structure systems on Qilin Expressway.The average winter temperature of Qilin Expressway in Shanxi Province is below 0 C.The phenomenon of snow and ice on roads is serious in winter.Spraying deicing salt is the main measure to remove snow on roads.The chloride ions contained in deicing salts cause serious damage to bridge structures.The concrete protective layer peeling,steel corrosion and concrete cracking occur in piers and cap beams.(2)The Duracrete model is modified based on the chloride ion content detection data of the bridge in service on Qilin Expressway in Shanxi Province.The environmental impact correction coefficient kie=0.845 of the chloride ion diffusion model under deicing salt environment is obtained.The chloride ion diffusion correction model under deicing salt environment is proposed.Based on the modified chloride ion diffusion model,the formula for calculating the initial corrosion time of steel bars is derived,and the degradation model of material properties of steel bars and concrete is proposed.(3)Taking Hongshan overpass,a typical bridge in service on Qilin Expressway,as the research object,the initial corrosion time of reinforcing steel bars is calculated,and the time-varying deterioration law of material properties is studied.The finite element model considering material deterioration is established by OpenSees,and the nonlinear dynamic time history analysis is carried out to compare and analyze the seismic response results of piers with service time of(0-100)years.The results show that the corrosion of longitudinal reinforcement mainly decreases the flexural capacity of piers,while the corrosion of stirrups mainly decreases the ductility of piers.(4)Based on the deterioration model of reinforced concrete material performance under chloride ion erosion,the deterioration indexes such as diameter and yield strength of corroded steel bar,compressive strength of protective concrete,peak strain and ultimate strain of confined concrete are introduced.The seismic vulnerability analysis model of bridge pier considering deterioration of material performance is established,and the time-dependent vulnerability buckling of bridge pier in service for(0-100)years is drawn.Line.The vulnerability probability curves of piers in different service times are compared and analyzed,and the vulnerability evaluation of piers in the whole life cycle is completed.