Influence of the piers' height on the fragility assessment of Italian R.C. Link slab bridges

Recent seismic events occurred in Central Italy drew the attention towards the resilience of the Italian road network, which is characterized by a significant number of old reinforced concrete bridges and viaducts. In this context, the fragility assessment of existing bridges is crucial, since their collapse or loss in functionality after earthquakes may lead to significant economic and social consequences. This work focuses on the fragility assessment of reinforced concrete multi-span continuous bridges, which is a widespread structural typology in Italy. The study aims to individuate fragilities relevant to both local and global mechanisms, considering bridge components such as piers, bearings and deck members, in order to highlight the most vulnerable ones compromising the whole structural response under the seismic action. A probabilistic framework is developed considering both the site-dependent seismic hazard and the most important Engineering Demand Parameters (EDPs) characterizing the structural response. The first one accounts for the record-to-record variability as well as the parameters governing the seismic scenario in which the structure is located, while the latter ones are individuated depending on the structural typology and the identified vulnerabilities. Multiple Stripe Analyses are performed with the aim of providing insights about the seismic response of the bridge class at hand and of furnishing the fragility curves for all the response parameters relevant for the structural system. Starting from a real case study located in Centre Italy, a couple of reinforced concrete bridge models is developed in order to consider the influence of different heights for the piers and to provide a forecast for the structural behaviour of the selected bridge class. The models are able to capture the failure mechanisms most likely to occur. Performance thresholds are chosen for each bridge component considering the relevant limit state demands according to the current codes and literature. As a result, fragility curves provide useful insights about the main structural deficiencies of the system at hand.