Time-Dependent Fault Tree Analysis And Service Time Prediction Of Existing Prestressed Concrete Bridges

In modern highway communication, prestressed concrete bridge is widely used because of its good integration, high stiffness, and good crack resistance, especially the smooth curve of the main beam deflection. With the growth of the bridge service time, because of affection of all kinds of corrosive medium, the durability and bearing capacity of the bridge structure which is exposed in the open air started to decline. This has affected the bridge structure normal use enormously. So, the bridge assessment base on the prediction of bridge service time has the vital significance.The thesis takes the structure system reliability theory and structural material's time-dependent characteristic as a foundation and studies the time-dependent bridge system reliability. The thesis proposes a way of predicting the bridge's service time through comparing structure system reliability index in every reference period with the target reliability index. The correlation theories about the thesis are divided into three parts: the first part is structure durability analysis, which lists a variety of factors affect the prestressed structure's durability through the structure durability analysis. The second part is structure members' reliability analysis, in this part the basic theory and computational method of structure member reliability,the process of structure component reliability completely and introduce the time-dependent analysis will be introduced, at last the probability and statistical model about bridge structure resistance,loads of actions and bridge structure probability limit states analysis are put forward. The third part is structure system reliability analysis, it introduces the basic problem of structure system reliability, the structure system main failure mode recognition and Ditlevsen boundary method for structure system failure probability computation in turn. And the structure system fault tree is established through the main failure modes' recognition; the probability of the structure system failure is calculated through the Ditlevsen boundary method. At last, the bridge's service time is predicted through computing the structure system time-dependent reliability index base on the structure system reliability analysis and time-dependent structure members' reliability analysis.Base on the above theoretical analysis, the article carries on the time-dependent system reliability analysis to some prestressed concrete continuous beam bridge. Combined with the analysis results gained by structure finite element method and time-dependent of structure's resistance, the dominate failure modes for structure are hunt for by branch-unzipping method of overall cases, and then the failure tree model is built too; the reliability index of dominate failure mode is worked out by JC method; the failure probability of structure system is worked out by Ditlevsen boundary method; combined with the result of time-dependent analysis and system reliability analysis, the reliability index in the design reference period will be worked out. Compared with the target reliability index, the service time of bridge will be obtained.The resulting of computing can server as a basis in the process of bridge design and evaluation of use, and improve bridge in maintaining work in future.