Security Assessment Based On Time-dependent Reliability For Bridges

Reliability is an important technical specifications for the existing bridges to maintenance and strengthening, but the reliability of bridge is varying with time due to the influence of vehicle load, environment and materials degradation. Therefore, security assessment and residual service life prediction of long-span bridge can be accurate considering time-dependent characteristic of reliability. Processing of long- term monitoring data from WIM with probability statistic method, establish vehicle load effect model. Probabilistic model of structural resistance model is established by considering the time-dependent property of concrete carbonization and prestressed bar. Based on the minimum incremental loading principle to establish the failure tree model of structural system, and propose a computational method for time-dependent reliability of bridge structure combining JC and narrow reliability bounds methods. Finally, the method is applied to a continuous rigid-framed bridge to provide bridge security assessment a new method support.The main task and result of the research are concluded as follow:(1) Based on the statistical analysis of long-term monitoring data which are from WIM, the results show that the vehicle weight of all lanes follow the lognor ma l distribution and the speed and vehicle spacing are in normal distribution after statistica l analysis about vehicle weight, vehicle spacing, speed and other vehicle parameters under probability statistics and examination.(2) Measuring motorcade moving loading on the influence line, getting the section distribution of vehicle load effect at the current time and selecting the maximum value of vehicle load effect in one day as the maximum sample, vehicle load effect time-dependent model can be established basing on the classical extreme value theory extrapolation.(3) Choosing the deterioration model of concrete strength and prestress loss, the time-dependent model of structural resistance can be established under independent increment model.(4) Establishing structural failure tree model which is based on the minimum incremental loading principle, according to the failure probability and correlation coefficient of each failure mode and establishing the time-dependent reliabilit y calculation method of structural system by means of JC method and Ditlevsen boundary method, the remaining service life of structure can be obtained from extrapolation of vehicle load effect time varying model and resistance time-dependent model.(5) Applying the time-dependent reliability calculation method of structural system into one continuous rigid frame bridge, the results shows that the current reliability index of the bridge was 5.1769 after using 15 years, which meets the requirements of the load carrying capacity. The remaining service life of bridge structure is 82 years.