Study On Lifetime System Reliability Of Long-span Cable Stayed Bridge Under Earthquake Diasaster

Long span cable-stayed bridge is widely used as a transportation hub in railway and highway trunk line because of its graceful shape and excellent spanning ability,which plays an important role in the development of national economy and society.China is loacated between the circum Pacific seismic belt and the Eurasian seismic belt,earthquakes occur frequently,and the earthquake disaster is the major natural disasters in China.The lifeline engineering,such as the long-span cable-stayed bridge,is extremely important for our life.The design life of this lifeline engineering is usually up to a hundred years and is inevitably affected by strong dynamic effects such as earthquakes during the service period.On the other hand,the structure is affected by natural environment factors(such as chlorine salt erosion)in long service period,and the stiffness and strength of structural each member will be degraded to different degrees in the early stage of service,and then the seismic performance of each member of the structure will be weakened.At the same time,as a high-order statically indeterminate structure,the failure of a certain member of the cable-stayed bridge does not mean the failure of the whole structure.The reliability of the structural system has always been the hot and difficult area in the latest research.Therefore,it is important and urgent to study the system reliability of long-span cable-stayed bridge in the whole life service period.In view of the above problems,the research content of this paper is as follows:(1)Aiming at the limitations and deficiencies about complicate calculation and insufficient accuracy of the current structural reliability analysis methods,a multiplier dimensional reduction method(MDRM)based on dimensional reduction theory and stochastic finite element theory was proposed to analyze the reliability of the actual engineering structure.Then,combining the analysis,the fractional moments of the structural response can be calculated quickly and accurately,and then the probability density function of structural response can be obtained based on the principle of the maximum entropy,which avoids the difficult problem that the random parameter joint probability density function is hard to get,while minimizing the number of finite element analysis,thus greatly reducing the calculation time.(2)Based on the OpenSees open source finite element platform,the 3D finite element model of cable-stayed bridge were established,and the uncertain parameters related to bridge modeling were summarized.Considering the actual site conditions of the cable-stayed bridge,the triangular series method was used to synthetic 30 random phase ground motions to consider the randomness of ground motions.At the same time,the common failure modes of cable-stayed bridges and the limit state equations of each component under earthquake disaster were summarized in the thesis,laying the foundation for the later reliability analysis.(3)Considering the randomness of both structural and the ground motions,the nonlinear time-history analysis models of the cable-stayed bridge were generated.Then,the OpenSees batch program was used to conduct a large number of numerical calculations to obtain the nonlinear seismic response and the fractional moment of the structural response.The maximum entropy principle was used to get the probability density function of the structural response,and then get the failure probability and the reliability index of each component.Considering the interdependencies between components,an improved probability conditional method(PCM)is used to obtain the system failure probability of cable-stayed bridges under earthquake disaster,not only the failure probability of components.(4)The diffusion and corrosion mechanism of chloride ions in concrete structures was expounded.Then,the time-varying probability models of the piers and towers,the performance degradation model of the rubber bearing,and the life-span corrosion curves and parameters of the cables under corrosive environment were given in chapter 5.Next,series of time-varying models were established to determine the nonlinear time-history analysis of cable-stayed bridges at five service-critical time nodes of 20 years,45 years,70 years,90 years and 100 years.At each service-critical time node,the OpenSees batch program was used to conduct a large number of numerical calculations to obtain the probability density function of the response,and then the failure probability and the reliability index of each component are obtained.The time-varying characteristics and the time-varying laws of the correlation coefficients between the various components of the cable-stayed bridge are summarized.The failure probability of cable-stayed bridge system at service time nodes is obtained by the improved conditional edge probability product method(PCM),and the time-varying characteristics of failure probability over the whole life of cable-stayed bridge are summarized.