The Failure Mode Of RC Piers And Seismic Fragility Of Bridges Subject To The Chloride-induced Corrosion

In recent decades,our economy has developed rapidly,and the infrastructure of transportation has been deepened continuously.The whole country will face the problem of “aging” of bridge generally.Chloride ion erosion is one of the most important factors affecting the durability of reinforced concrete structures.From the perspective of seismic resistance,steel corrosion will not only weaken the bearing capacity and ductility of RC pier,but also change its dynamic characteristics and seismic response.More importantly,the corrosion of steel bar will cause the non-uniform degradation of flexural and shear properties of pier,leading to the change of failure mode of pier under earthquake.Therefore,the seismic capacity and dynamic characteristics of Bridges are different from those of newly built Bridges.Obviously,the traditional seismic analysis method has great limitations in evaluating the seismic performance of Bridges in service.In order to provide technical support for seismic performance assessment of many Bridges in service and reduce the risk of seismic damage of Bridges,the seismic performance of corroded RC bridge piers and service Bridges was systematically studied in this paper considering the material degradation and failure mode evolution characteristics of bridge piers under chloride ion erosion environment.The main research work is as follows:(1)Pearson correlation coefficient was used to analyze the corroded and non-corroded RC pier column samples,and the significant influencing factors between different failure modes of RC pier column were determined.Based on Fisher discriminant analysis theory,a two-stage discriminant model for the failure mode of corroded pier was established,and its accuracy was compared with that of existing discriminant methods.Combined with the mechanism of chloride ion erosion and reinforcement corrosion,the evolution characteristics of failure modes and the influence of parameters of the calculation pier during its service were analyzed.(2)Study the mechanical properties of corroded pier under the combined action of compression,flexural and shear.The modified pressure field theory was introduced into the fiber section model to analyze the shear characteristics of the section elements,and a simulation method considering the combined action of compression-flexural and shear was established.The deformation capacity and energy dissipation capacity of the example pier were analyzed according to skeleton curve and hysteresis curve,and the influence of shear action on the corroded pier was studied by comparing with the traditional pressure-bending simulation method.(3)Combined with the compression-flexural-shear model of pier and the nonlinear characteristics of other components,the refined dynamic analysis model of bridge is established.The time-varying seismic vulnerability analysis is carried out on the example bridge,and the time-varying damage law of different components and bridge system is studied.(4)Based on the time-varying recoverability theory,a mathematical model for multi-objective seismic optimization of bridge piers was proposed,and an efficient multi-objective seismic optimization design process was established by introducing response surface method and improved non-dominated sorting genetic algorithm(NSGA-II).The proposed method is applied to the lifetime seismic optimization design of the example bridge.