Case studies from the A24 highway bridges restoration, after the 2009 L’Aquila earthquake disaster

The A24 and A25 highways are strategic infrastructures, connecting the eastern and the western coasts of central Italy and they are located in one of the most seismic areas of the country. In 2009 a strong earthquake (Mw=6.1) struck L’Aquila city. The highway bridges were subjected to significant accelerations that, in some cases, exceeded design values, especially for those designed according to past national regulations (1962). The most critical situation was the collapse of the movable roller devices that sustained simply supported girder bridges, causing the longitudinal misalignment of adjacent spans. The breakdown of the bearings allowed dissipation of input seismic energy, limiting the force transmitted from the deck to piers and abutments and preventing understructures collapses. Immediately after the earthquake, the highway management company, Strada dei Parchi - Toto Holding, verified the static stability of the infrastructures and, after rapid and targeted interventions, authorized the transit of emergency vehicles for first aid operations. After this tragic event, the Italian Government classified the A24 and A25 highways strategically important for Civil Protection purposes, establishing the seismic restoration of the bridges (24th December 2012, n.228 - 2013 Stability Law). This work presents the main aspects of the disaster decision-making and management and describes three case studies belonging to the post-disaster restoration of >20 bridges placed along 15 kilometers (9 miles) between the L'Aquila and Tornimparte. The aim of the work is to present Seismic Isolation (SI) and Energy Dissipation (ED) systems adopted in new and existing bridges, in order to obtain the seismic retrofitting in compliance with Italian Technical Code NTC2018. The innovation of the study is linked to the large number of structures in such a limited site, that could definitively promote the use of these techniques for infrastructures.