Evaluating Time-Dependent Reliability and Probability of Failure of Reinforced-Concrete Bridge Components and Predicting Residual Capacity after Subsequent Rehabilitation

The load-carrying capacity of reinforced concrete bridges can degrade over their service life through the initiation of deterioration mechanisms induced by fatigue, corrosion, cracks, and spalling. Analyses of residual capacity and time-dependent reliability of such bridges are significantly important information in the decision-making process of identifying the nature and timing of rehabilitation. It is noted in the literature that deterioration mechanisms such as chloride ingress, sulfate attack, and alkali-silica reaction have variable rates of deterioration governed by a large number of uncertain parameters. In such instances, a probabilistic approach provides a rational basis for estimating the uncertainties of residual capacity and reliability. In this paper, the authors present a probabilistic method to evaluate the time-dependent reliability and failure of concrete bridge elements. The probabilistic distribution of surface chloride concentration, diffusion coefficient, critical chloride concentration, and material variables were identified from literature. Monte Carlo simulation was employed for modeling the increases of live loads and the degradation of the component to obtain the time-dependent reliability curves for design service life. The methodology is further demonstrated by a pier column as an illustrative example. Results showed the reduction in resistance and the risk of failure periods. Further parametric studies showed that concrete cover depth and water-cement ratio have significant influence on the time-dependent probability of failure and reliability index. Overall, it has been shown that the methodology is generic and valuable information on residual capacity and time-dependent probability of failure can be applied to performance assessment and lifecycle for both new and existing structures.