Vulnerability of a Damaged Bridge Abutment in a Seismic Area

The case of the abutment of a motorway urban viaduct damaged by human intervention is presented. Built in the 1960s, it lies in a critical seismic area and the human-induced damage involved the elements of the abutment foundation. The structure is geometrically complex and the evaluations of its structural safety were carried out by applying Italian codes from different times: those concerning the time of construction, those of a recent past (1996), and those of the present (2008), inspired by Eurocodes. A comparison between the safety checks performed and the requirements of all these codes is presented and discussed, especially regarding safety coefficients after the damage was done. Two different structural models were performed: a simplified one focused on the foundation plate and piles for a first approach of the analytical evaluations; and a complete three-dimensional finite-element model of the bridge on which numerical simulations were carried out for different load combinations and in which all structural elements were considered (deck, abutment, and foundation). The main aspects, believed to be the fundamental ones for specific evaluation of the global and local structural safety, are discussed. A hypothesis for restoration is presented, as well as the relevant technical and administrative items linked to the application and reliability of the Italian code on existing structures.