The structural safety assessment of existing bridges is a topic of growing relevance, as many infrastructures in Italy were designed according to outdated standards without adequate seismic and durability provisions. To address these issues, the 2020 Italian Guidelines by the Ministry of Infrastructure and Transport (MIT) introduce a multi-level approach for risk classification, structural verification and asset management.

This study applies the Level 4 procedure proposed by the Guidelines to an existing reinforced concrete bridge through finite element modeling (FEM). Linear and nonlinear static and dynamic analyses are carried out to the purpose. The effects of the corrosion-induced degradation are also investigated, by incorporating two distinct scenarios into the structural model.

Results show a seismic safety index of ζ_E= 0.33 from linear analyses and of ζ_E = 0.22 from nonlinear analyses. In the degraded models, the index further decreases to ζ_E = 0.10, highlighting a significant loss of ductility and  a pronounced shift toward brittle collapse.

The findings emphasize the necessity of explicitly considering degradation phenomena-particularly reinforcement corrosion-within seismic vulnerability assessments. Such considerations are essential for producing realistic safety evaluations and informing the prioritization of retrofitting strategies and structural health monitoring programs.