Nonlinear dynamic analysis of a RC bridge with Gerber saddles: influence of material degradation on seismic response

In recent years, infrastructure management has encountered new challenges arising from evolving regulatory frameworks, in terms of increased traffic loads and progressive degradation of materials. As such, many bridges, designed prior to the establishment of modern seismic Standards, are now expected to meet performance requirements significantly higher than those originally envisaged. The introduction of recent Italian guidelines for the classification and management of seismic risk in bridges and viaducts has provided more sophisticated tools for vulnerability assessment. Nonetheless, several critical issues remain unresolved, especially concerning the accurate modelling of degradation mechanisms and their influence on the dynamic behaviour. This study presents the results of the detailed seismic vulnerability assessment conducted on an existing reinforced concrete bridge featuring Gerber saddles, located in Abruzzo region. The aim is to evaluate the impact of degradation, specifically reinforcement corrosion leading to bar cross-sectional reduction and concrete cracking, on the global seismic response of the structure. The analysis demonstrates that degradation, often underestimated in standard assessment procedures, can significantly reduce structural stiffness and energy dissipation capacity, increase deformations, and alter the natural frequencies of the system. As the degradation level grows, corresponding changes in the structural response are observed.