Seismic Fragility And Risk Assessment Of V-shaped Continuous Girder Bridge Based On Fuzzy Failure Criterion

Since the 1990s,performance-based seismic engineering theory and seismic design method have been widely accepted and gradually introduced into the relevant engineering seismic design codes of various countries.As an important part of performance-based seismic design,one of the advantages of seismic fragility analysis is that it can fully consider many uncertain factors,so as to comprehensively evaluate the seismic performance of bridge structures.However,for the influence of uncertain factors on the seismic fragility of structures,most scholars focus on the study of randomness,and ignore the influence of structural damage state fuzziness.In fact,the boundary between two adjacent damage states is not clear but fuzzy.Considering the fuzziness is more suitable for the real situation.Based on the fuzzy failure criterion,a set of seismic susceptibility assessment method and risk assessment process for a three span V-shaped continuous girder bridge were established by combining theoretical analysis and numerical simulation,based on the fuzzy failure criterion.The product of conditional marginal(PCM)method was further optimized and improved,namely the new improved PCM method.The new improved PCM method is used to establish the fragility analysis process of bridge system.The analysis process can establish the fragility curves of bridge system conveniently and quickly based on the correlation of various failure modes of components.This paper mainly completes the following work:(1)Taking a three span V-shaped continuous girder bridge as an engineering background,the dynamic analysis model of the bridge was established by using OpenSees finite element analysis software.On the basis of considering the randomness of earthquake and the uncertainty of bridge itself,the fragility curves of bridge components were formed by "Cloud Approach".(2)Considering the fuzziness of the failure criterion of bridge components,the fuzzy mathematics theory was introduced to describe the damage process of the structure.Membership function was used to describe the fuzziness of failure boundary,and the failure probability of components based on fuzzy failure criterion was derived by using reliability theory.At the same time,the influence of the membership functions and the size of membership interval on the seismic fragility curves of the bridge were studied.(3)The PCM method was further optimized and improved.The calculation accuracy of the new improved PCM method was verified from the number of failure modes,reliability index and correlation coefficient.Based on the new improved PCM method,this paper established a new set of bridge system fragility analysis method and analysis process which can simultaneously consider seismic randomness,bridge uncertainty and damage fuzziness are established,and established the fragility curves of bridge system based on fuzzy failure criterion.(4)A bridge seismic risk assessment method based on fuzzy failure probability was proposed.The influences of the distribution type of membership function and the size of membership interval on the seismic risk probability of the bridge supported by the project were studied,and the seismic risk assessment of the bridge supported by the project was realized.(5)According to the characteristics of V-shaped continuous girder bridge,the influence of the angle of V-angle on seismic fragility and risk of the bridge was studied by using the analysis method proposed in this paper,so as to reveal the influence law of V-angle on seismic performance and seismic risk probability of this kind of bridge.The research results can provide reference for the design of similar bridges.