Time-Dependent Reliability Assessment Of Existing Reinforced Concrete Bridge Under Fuzzy Information

The enough samples and accurate statistical characteristics of parameters aredifficult to be obtained for reliability assessment of the existing reinforced concrete(RC) bridges. A reliability assessment method under fuzzy informations for existingRC bridges is developed by combining detection results and expert experiences. Theinfluencing parameters of structure resistance are considered as the fuzzy variablesand time-varying variables.The main contents can be drawn as follows:(1) Research results for random reliability and fuzzy reliability theory aresummarized combing with a lot of literatures. The limitation of random reliabilitytheory and the applicability of the fuzzy reliability theory is pointed out. Basicknowledges of fuzzy mathematics and fuzzy reliability theory are introducd. Basedonλcut set concept, the fuzzy reliability computation method is developed.(2) Common method for determining the fuzzy variable membership functionis introduced. The specific method and steps for deteriming the fuzzy variablemembership function is developed in the reliability caculation of exsiting RCbridges. Two different methods are used to transform the fuzzy variables intoequivalent normal fuzzy variables. The process that the determination and equivalentnormalization of membership function for reinforcement corrosion rate demonstratesfeasibility and correctness of the developed method in this thesis.(3) The fuzziness and time-effect variation existed in the various influncingparameters of structure resistance of exsiting RC bridges is introduced. Thetime-varying model of various parameters is established considering the fuzzinessexisted in the various influncing parameters of structural resistance. Then, thetime-varying model of structural resistance under fuzzy informations is built. Thesturctural limit state equation is eventually established combining the thoery offuzzniess and time-effect variation, and the revised load model.(4) The general formula that the fuzzy variables are transformed intoequivalent random variables of the existing RC bridges is derived. The fuzzy limitstate equation is transformed into equivalent limit state equation after acquiring theexpression of probability density function and distribution function of equivalentrandom variables. An example of a fabricated RC bridge is employed to demonstratethe developed method. The time-dependent reliability index is calculated out in thereliability assessment of the existing RC bridge. Meanwhile, the structurual parameter sensitivity of fuzzy and time-varying reliability is analysed. The resultsshow that the effect of mean value of annual average reinforced cossion rate onstrucutal reliability is obviously significant.