Risk Assessment of Existing Bridge Structures: Evaluation of the Risk of Structural Collapse

A new comprehensive methodology is developed to evaluate the risk of structural collapse of existing bridges, where risk is defined as the product of the consequences and probability of failure. In the method proposed here, the key parameters influencing the risk of bridge collapse are identified and quantified. The five key risk indicators chosen are: (1) current safety, (2) future safety, (3) warning level (redundancy), (4) condition evaluation and (5) importance (consequences of failure). A novel graphic representation of the results, referred to as a risk spiderweb, is used to visually highlight the relative significance of each parameter and allows detection of the critical indicators. Finally a single performance measure combining the risk indicators is defined as well as a minimum acceptance criterion. By considering all risk indicators at the same time, the failure to meet acceptance thresholds by one or more of the risk indicators can in some circumstances be compensated for by higher values of the other indicators. This criterion helps to decide whether the performance of the bridge is adequate or whether intervention is necessary.