Issues in the Upgrade of Italian Highway Structures

The last 15 years have seen fundamental advances in both the definition of the hazard and on the criteria in codified seismic design, creating a situation whereby even relatively modern constructions may represent an unchecked risk. This article deals with a case of particular relevance, i.e., the seismic risk of bridges and viaducts on the Italian highway network. After a brief outline of the present state of the network, the article concentrates on the solutions adopted in the upgrading, for increasing both the traffic and the seismic capacities, through the illustration of two case studies. The second, main part of the article deals in more detail with one of the case studies, examining alternative design options and the corresponding analytical aspects. Finally, the opportunity is taken to investigate the relevance of two aspects not commonly taken into account in design practice, i.e., differential support motion and soil-structure interaction.