Study On The Key Issues Of Reliability Assessment Of Existing Bridges

More and more attention on the problems of poor reliability, inaccurate reliability evaluation and excessively high maintenance cost of bridges in service has been attracted by many bridge researchers, which accompanies the rapid development of bridge construction. Study is expanded enclosing to the subject“Study on the key issues of reliability assessment of existing bridges”. Based on the international research results, system reliability updating method and the determination method of time-variant target reliability of existing cable-stayed bridges were analyzed systematically. Taking the system reliability as the starting point, the reliability assessment of the existing bridges was also considered in this dissertation. The main content is summarized as following:1. The component reliability and system reliability calculation method were summarized systematically and compared their advantages and disadvantages. The calculation method of system reliability based on the approximate formula that suggested by Dong Cong was proposed in this paper.2. Method on system reliability updating through inspection information for existing cable-stayed bridges was proposed: On the basis of the comprehensive analysis method that fully utilized the advantages ofβ-unzipping method, finite element method(FEM), first order second moment method(JC) and the response surface method (RSM), the modified model of cable-stayed bridge random variables was established based on monitoring information, the reliability of failure candidate elements of cable-stayed bridge components were updated by using Bayesian method. Therefore the system reliability was updated. Finally a project sample was analyzed in this paper to verify the validity of the method.3. Calculation models of all the life-cycle cost aspects of existing bridges were established, the major maintenance and reinforcement method were summarized systematically and their advantages and disadvantages were compared. The determined target reliability indexes by the home and broad related standards and the crruent determination methods of the target reliability indexes were summarized.4. Method on the determination of time-variant target reliability based on the life cycle cost optimization for existing bridges was proposed: Based on the life cycle cost, the effect on the system reliability and target reliability after repair and reinforcement was considered. Using the optimal life cycle cost as the object function, time-variant system reliability and target reliability as the constraint condition, through establishing the time varying reliability-cost-life of the multi-objective optimization model, the parameter in the time-variant target reliability index evolution formula was determined by adopting the improved NSGA-II multi-objective optimization algorithm. Finally, the feasibility of the proposed methods of the determination of time-variant target reliability evolution rule in this paper were verified through an engineering example, and the determined target reliability index by present study was more rational than that determined by existing codes.