Assessment and risk mitigation techniques in critical bridge infrastructures

Bridges are key components of transportation infrastructure and, consequently, excessive deterioration or collapse may result in significant functional, social, and economic impacts. The progressive ageing of the existing bridge stock, together with the increasing exposure to more severe environmental actions, makes the definition of systematic and simplified assessment strategies to support risk management a priority. In this context, this dissertation proposes an integrated approach, suitable for large-scale applications, which links bridge assessment to the design of strengthening interventions. First, a national-scale retrospective analysis of bridge collapses and severe damage events in Italy was carried out through the development of a dedicated database and the classification of events by bridge typology, triggering cause, and damage level. The evidence derived from this analysis motivated a focused investigation on masonry arch bridges. Accordingly, a simplified assessment methodology was developed for large-scale applications, integrating information typically available within bridge management systems, particularly data from visual inspections. The methodology enables the estimation of the collapse load and the identification of the associated collapse mechanism for existing masonry bridges, explicitly accounting for the influence of defects commonly observed in such structures. Finally, within a risk-mitigation perspective, strengthening strategies were investigated as targeted actions to reduce vulnerability, with particular emphasis on external post-tensioning. Its effectiveness was evaluated using simplified tools supported by experimental evidence, establishing an operational link between assessment outcomes and intervention planning.