An index-based method for risk assessment of existing bridges subjected to multiple hazards

Recent bridge collapses have highlighted the urgent need for rapid risk analysis methods to support infrastructure managers in the selection and prioritization of disaster risk mitigation measures. As far as existing road bridges are concerned, their construction was mainly carried out between the 1960s and 1980s, implying that many of those structures have exceeded or are reaching their typical 50-year nominal lifespan. Previous studies have shown that bridges often fail due to a range of natural and human-induced hazards, including floods, vehicle impact, and overloading. Such hazards together with earthquakes should be duly considered into disaster risk assessment of existing bridges. Therefore, the identification of critical structures within a large bridge portfolio should rely upon comprehensive multi-hazard risk assessment approaches. This study presents an index-based methodology for disaster risk assessment of existing bridge portfolios, accounting for a variety of natural and human-made hazards and their potential impact on the roadway network. The proposed risk-based methodology considers various factors that influence structural vulnerability and potential consequences of bridge failure, depending on the specific nature of each hazard. Additionally, the structural condition of the bridges is taken into account when computing single-hazard risk indicators for traffic, seismic, fire, and vehicle impact. These indicators are then integrated into a multi-hazard risk measure using multiple formulations. The final part of the study shows the application of the methodology to a set of road bridges located in northern Italy. The analysis results are compared with those provided by methods available in the literature, discussing the benefits of the proposed methodology.