PROBABILISTIC LIMIT STATE ASSESSMENT OF CONCRETE BRIDGES CONSIDERING NON-STATIONARY FACTORS

To develop a probabilistic limit state assessment method for concrete bridge components, a probabilistic transformation principle was introduced to analyze the rating period and rating reference period. The individual risk criterion, social risk criterion, life quality index and cost optimization principle were employed to determine the target reliability index in an operation stage. Both non-stationary and stationary probabilistic models were considered to derive the rating values of load effect and resistance. In addition, the reliability theory was adopted to conduct the calibration of partial factors and an existing bridge was used to complete a case study. The results show that the rating period and rating reference period can be taken as 6 years and 10 years, respectively, considering the actual bridge maintenance conditions. For the ductile components with safety level I, II, and III, the target reliability index of safety assessment is suggested as 3.37, 3.13 and 2.85, respectively. When the stationary-probabilistic-vehicle load effect models of a general operating state and an intensive operating state are employed, the characteristic value of safety assessment can be taken as 0.705 and 0.805 times of design vehicle load effect, respectively. When the non-stationarity of vehicle load process is considered in the safety assessment, the extreme value distribution within a rating reference period can be modeled by a generalized extreme value distribution based on the discretization of continuous stochastic process, and the corresponding 0.95 fractile can be adopted. For the ductile component of safety level I, the partial factors of dead load effect and resistance are proposed as 1.056 and 1.194, respectively, and the partial factors of vehicle load effect corresponding with general operating state and intensive operating state are proposed as 1.081 and 1.054, respectively. The achievements mentioned above can be referenced for the adjustments of the current safety assessment method of existing bridge component specified in the standard.