Analysis Of Time-dependent Seismic Effect Of RC And UHPC Piers Under The Chloride Ion Corrosion

With the further increase of regional economic exchanges in China,bridge projects extend to the ocean,saline alkali land and other chloride rich environment.However,the corrosion of chloride ion to reinforced concrete(RC)bridges can not be ignored,which leads to the degradation of structural material performance and the shortening of service life.Especially for bridges in the marine environment,the construction cost is high,the environmental impact is significant,the maintenance and reinforcement work is difficult,and the maintenance cost is higher and higher with the structural degradation.Pier is the key connecting component between superstructure and foundation,which is connected with the external water environment,and is most significantly affected by chloride ion erosion.As the main lateral force resistant component,its performance under earthquake is the control factor of the overall safety of the bridge.In order to solve the problem of RC bridge pier caused by chloride ion erosion,it is an ideal scheme to replace conventional concrete with UHPC,a new material with excellent durability.However,there are few researches on the degradation process of UHPC piers under the action of chloride ion erosion at present,so this paper takes a three span continuous beam in an ocean environment as an example to compare and analyze the degradation process of RC and UHPC piers under the action of chloride ion erosion.Based on the vulnerability,the time-varying seismic performance of both piers are analyzed.The specific contents are as follows:(1)Two kinds of pier sections,RC and UHPC,are designed with reference to the actual engineering and specifications.The Duracrete model is used to analyze the initial corrosion time of the reinforcement of RC pier considering the uncertainty of the parameters.The environmental parameters of chloride ion corrosion of UHPC pier are selected conservatively with reference to the data of conventional concrete,and the initial corrosion time of the reinforcement is analyzed by the standard chloride ion diffusion model.Based on the standard formula,the cracking time of the protective layer of two kinds of piers are analyzed,and the degradation curve of the material properties of the reinforcement and concrete are calculated.(2)In view of the problem that the conventional damage state does not consider the crack of the marine bridge structure sufficiently,the durability damage state is defined with the crack of the protective layer as the defining condition,and the pier damage state is divided into no damage,durability damage,slight damage,medium damage,serious damage and complete damage with the displacement of the pier top as the damage index.100 earthquakes for seismic analysis are selected,the intensity index of ground motion for the example bridge is analyzed.(3)The nonlinear finite element analysis model of the example bridge is established by Open SEES software;the index value of each damage state are calculated by pushover analysis;the seismic demand of RC and UHPC piers under five different time is calculated;the time-dependent seismic fragility curves of two piers are established;the seismic fragility analysis results of the two piers are compared quantitatively.Based on the above study,the degradation degree of seismic performance of RC and UHPC piers under Chloride Erosion is compared quantitatively based on vulnerability,which provides a reference for the solution of durability problems of bridges in harsh environment.