Seismic fragility curves assessment of corroded RC bridges

The Italian infrastructure network of roads and bridges is one of the most complex in the world, due to the orography of the territory. Italy is strongly interested by seismic and hydrogeological hazards and, in addition, degradation and obsolescence phenomena are common on infrastructures approaching the end of their nominal life. Furthermore, these infrastructures are subjected to continuous traffic load increase over time. In 2020, the Italian Ministry of Infrastructure and Transport (MIT) published the Guidelines for risk classification and management, safety assessment, and monitoring of existing bridges, as an attempt to unify the multiple procedures of inspection, monitoring, and maintenance of infrastructures. An important phase of the risk classification regards the analysis of the typical defects that may occur on structural elements of reinforced concrete and prestressed reinforced concrete bridges. Among them, various studies on the deterioration of the structural elements of these types of bridges have been conducted both in Italy and abroad, highlighting that one of the most widespread defects is the corrosion of reinforcement. The corrosion process evolves over time, leading to a reduction of the rebar cross-section that in turn is reflected into a decrease in the deformation capacity and strength of steel. In the most advanced stages of the process, concrete cover spalling may also take place, with a consequent reduction of the confinement action exerted on longitudinal rebars, and a possible risk of rebar buckling. In this work a typological case study bridge in marine environment is created according to gravity loads design. The seismic assessment of the bridge structural elements, caused by the design seismic action, is first shown, with reference to the initial uncorroded situation. Then, the seismic assessment is repeated for different time periods, by taking into account the effects of corrosion, which depend on the assumed corrosion rate. Finally, an interesting comparison in terms of fragility curves is proposed between the safety condition of the infrastructure expected in both cases, with or without the consideration of the corrosion of the reinforcement.