On the choice of seismic retrofitting strategies for bridges – Case studies on the Italian Highway

Italy is the 4th European country for highway km extension after Spain, Germany and France, with 85% of the network built before the 1980s. The first Italian modern code, Ordinance No. 3274, was issued in 2003 only after a school in San Giuliano di Puglia collapsed in 2002 due to a M 5.7 earthquake. Therefore, most of Italian infrastructures have been designed according to basic, or none, seismic consideration, even those that fell in high seismic risk zones. Thus, most of the structures show structural deficiencies against seismic actions. In 2003, the Ordinance introduced a new zonation according to a probabilistic seismic hazard analysis (PSHA) and imposed the verification, following the Eurocode 8 principles, of the strategic buildings/infrastructures. The recent (2022) Italian ‘Guidelines for risk classification and management, safety assessment and structural health monitoring of existing Bridges’ addresses specifically non‐seismic conditions leaving to the manager of the relevant asset the retrofitting strategy. Bridges seismic retrofitting can be achieved by different solutions, adoption of seismic isolation being one of the most efficient. In this paper, the retrofitting selection criteria adopted for 2 bridges in high‐seismicity zones are presented, emphasizing design issues.