Seismic Optimization Method Of RC Bridge Piers Based On Lifetime Seismic Loss In Chloride Ion Environment

In recent years,the importance of bridges in the entire transportation network has increased day by day.If a bridge is damaged due to an earthquake and can not be used normally,it will most likely cause traffic interruption,which will cause huge economic losses and casualties to the society.Therefore,it is necessary to evaluate the loss of the bridge during the entire service time.In the seismic process of the bridge,the bridge pier is one of the most vulnerable components in the entire bridge.Therefore,improving the seismic performance of the bridge pier will play a key role in improving the seismic performance of the entire bridge.At the same time,due to the complex terrain of our country,most of the bridges are in a relatively harsh environment,of which the chloride ion environment is one of its most severe environments.The erosion of the chloride ion on the bridge causes a significant reduction in the seismic performance.However,at present,it is rare to consider the influence of chloride ion erosion in the optimization of the whole life seismic design of bridge piers at home and abroad.Therefore,it is of great significance to optimize the seismic design of bridge piers based on the whole life earthquake loss under the environment of chloride ion.The main research contents are as follows:(1)The PEER earthquake risk assessment framework is described,and the basic theory and calculation model of bridge earthquake loss assessment are introduced.Taking a reinforced concrete continuous beam bridge as the research object,a nonlinear dynamic time history analysis is performed on it,and then the vulnerability and seismic loss are evaluated.(2)The chloride ion erosion,diffusion mechanism and the degradation law of material properties are introduced in detail,and the relevant calculation models for steel corrosion and initial corrosion time are described.A time-varying model of the performance degradation of materials such as concrete and steel bars has been established.The dynamic time history analysis of the bridge under the chloride salt environment is carried out,and then the vulnerability and seismic loss of the bridge are evaluated,and the seismic loss of the bridge is compared with the bridge without considering the corrosion of chloride ions.A comparative analysis of the influence of different discount rates on the expected seismic loss of bridges is carried out.(3)The mathematical model of seismic optimization of bridge piers under the chloride salt environment is constructed,and the basic theory of response surface is introduced in detail.Combining the response surface method,the functional relationship between life expectancy of earthquake loss and pier design parameters is established.Construct the objective function of the bridge pier seismic optimization,and carry out the optimization design.The comparison and analysis of the bridge pier optimization scheme and the initial design scheme under the chloride salt environment are carried out.(4)Consider the impact of the marine environment on the bridge,and optimize the seismic design of the bridge piers in the marine environment.A comparative analysis of the two optimization schemes under the chloride salt environment and the marine environment.The vulnerability of the two optimized piers in the chloride environment and the marine environment is analyzed and compared with the vulnerability of the pier in the initial design scheme.Through the above research,the chloride salt environment has more obvious effects on the severe damage state,complete damage state and indirect economic loss of the bridge;the bridge pier optimization scheme under the chloride salt and marine environment has improved seismic performance compared with the initial design scheme,However,the earthquake loss of the whole life has been reduced to varying degrees.Compared with the optimization scheme under the marine environment,the pier optimization scheme under the chloride salt environment is stronger than the pier optimization scheme under the marine environment in terms of seismic performance.From another analysis,this also shows that the chlorine salt environment the degree of erosion of the bridge will be more serious,so when optimizing the bridge piers,the chlorine salt environment optimizes the bridge piers to a higher degree.