| Nowadays, time-varying reliability analysis and assessment of existing RC bridge are urgent questions to be solved in bridge engineering circles. This thesis studies the fuzzy time-varying probability model of resistance of the structural member, the fuzzy probability model of load, the fuzzy time-dependent reliability and evaluation for ultimate load carrying capacity of main member for the existing RC bridges according to its characteristic. The main study works are as follows: 1)Based on the existing time-varying model of reinforcement strength and its area, and the time-varying model of concrete strength, this thesis introduces threshold value eulteriorly considering fuzziness to create fuzzy time-varying probability models of these factors. Accordingly, the fuzzy random time-varying functions of mean and standard deviation for resistance are deduced, and fuzzy time-varying probability model of resistance is established. 2)Because normal value and distribution statistic parameters of the existing RC bridges dead load are influenced some factors and difficult to describe with deterministic parameters, this thesis regards probability model of dead load as fuzzy normal distribution function, considers mean and standard deviation of bridges dead load as fuzzy random variable, and uses movement of threshold value αin selected membership function to solve variation of statistic parameter for dead load to compare existing bridges with proposed bridges. 3)In order to make live load of the existing bridges be close to practice, design reference period is altered into evaluation target period, maximum distribution of live load is chose as fuzzy extreme value I distribution pattern in target period, and the parameter is selected as fuzzy random variable described with a time-varying membership function to correct live load effect when random process of live load is transformed into random variable of its maximum value distribution in target reference period. 4)Considering fuzzy time-varying feature of resistance and live load, fuzziness of dead load and failure criterion, according to the character of fuzzy time-dependent reliability for existing bridge, the existing reinforced concrete bridge is regarded as series system, this thesis formulates load carrying capacity fuzzy limit state equation, and JC method is improved on to calculate the fuzzy time-dependent reliability index β|-(t ), and a computing program is developed to analysis variety of fuzzy time-dependent index with time and threshold value α. 5) Based on analysis of some factors resulting in reducing the ultimate load carrying capacity of bridge, this thesis uses fuzzing mathematics and analytic hierarchy process (AHP) to systematize these interrelated and interactional factors, quantifies qualitative description with fuzzy membership function, accordingly presents synthetical reduction coefficient, and then unites with finite element without considering material aging and damage to estimate the ultimate load carrying capacity of the existing RC bridge member. |
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