Optimal Design Of Seismic Isolation Bearings Of Bridge And Time-Dependent System Seismic Fragility Analysis

Bridge is an important part of transportation system.The damage of bridge structure caused by earthquake disaster will bring about social and economic losses.To reduce the earthquake-induced loss,it is necessary to effectively evaluate the seismic performance of the bridge structures and improve their seismic capacity.A highway bridge is used to study the influence of soil-pile-structure interaction(SPSI)and pile diameter on the seismic fragility of the bridge.The seismic fragility of bridge is used as the objective function to optimize the parameters of isolation bearing.And then,the time-dependent curves of bridge system fragility in its service life are explored.The main contents of this paper are summarized as follow:(1)The theory and method of bridge seismic fragility analysis are briefly introduced.The analysis steps of seismic fragility of components and system are introduced.The main methods to calculate the fragility of bridge structure system are compared.(2)The influence of pile diameter effect on bridge seismic fragility is fully studied.Three kinds of finite element(FE)models are established in Open Sees:model I considers both SPSI and pile diameter effect;model II only considers the SPSI;model III is a simplified model with pier bottom fixed.The incremental dynamic analysis(IDA)method is used to obtain the seismic response of bridge and establish the seismic fragility curves of bridge.The results of these three models are compared,which verifies the importance of considering pile diameter effect.(3)The objective function of seismic fragility of bridge system is established and the mechanical parameters of bridge isolation bearing are optimized.The characteristic strength and elastic stiffness of lead rubber bearing are adopted as optimization variables.By dynamic time history analysis,the reasonable ranges of bearing parameters are determined.The Gaussian process model is used to replace the time-consuming dynamic time history analysis,aiming to reduce the computational burden of the optimal design of the isolation bearing.(4)The time-dependent seismic fragility curves of bridge system considering chloride corrosion are established.Based on the diffusion mechanism of chloride ion in concrete,the material performance changes of steel and concrete under chloride corrosion are analyzed.Several FE models of bridge structures in different service periods are established.The moment curvature of the bridge pier is used to obtain the updated limit states and damage indexes of bridge pier at different service time,and then the fragility curves of bridge system at different time nodes are obtained.Gaussian process model is used to establish the time-dependent surface of seismic fragility of bridge system in the whole life cycle.