Numerical assessment of a multi-span prestressed girder bridge under corrosion-induced degradation

In recent years, structural assessment of existing bridges and viaducts has grown in importance as most of these structures have exceeded their design service life and need detailed evaluations to inform maintenance, repair and strengthening. Following the 2018 Morandi Bridge collapse, Italy introduced guidelines to standardise bridge risk classification, safety assessment, and monitoring using a multi-level approach. Concrete bridges, particularly those with prestressed beams, form a significant portion of the national infrastructure, making their safety assessment crucial to prevent major disruptions and long-term impacts. Although experience has demonstrated that prestressed concrete bridges are particularly susceptible to deterioration, these phenomena are often largely overlooked in the assessment process. The present work addresses this problem with reference to a real multi-span prestressed concrete bridge, numerically modelled under traffic and seismic loading conditions following the procedure proposed by the Italian guidelines. Additionally, parametric analyses are conducted for various corrosion scenarios, considering both diffuse and localised phenomena. The behaviour of the piers under seismic loading is assessed through non-linear dynamic analyses. Established models from the literature are employed, incorporating the effects of reduced strength and ductility in both concrete and steel. In the investigated cases, the deterioration led to a reduction in strength up to 30-40% for beams with high corrosion rates, while for the piers, shear resistance decreased by 30%.