The Gravagna Viaduct is over fifty years old. It was designed at a time when Italian engineering was experimenting with new, increasingly daring construction models, some of which have shown over time various characteristics capable of being improved. Additionally, the works were originally designed to withstand significantly lower traffic volumes than today.

Despite the interventions carried out over time, the viaduct does not currently fully meet the requirements of the NTC 2018 in terms of seismic performance and, in static terms, thanks to the “struts” supporting it from below, is in an operational condition according to the recent Bridge Guidelines, i.e. in need of adaptation within 5 and 30 years.

Considering both the temporary nature of the portals underneath the viaduct and uncertainties around the tensile status of the prestressing bars in the concrete structure of the caisson, it was deemed appropriate and a priority to start the works in September 2023. These structural reasons were also encouraged by the opportunity to carry out the first 6 months of work as part of other worksites already in place, thus limiting inconvenience to users, due to similar demolition and reconstruction work on two other viaducts located a few hundred metres from the Gravagna Viaduct.

The impressive and particular nature of the structure means that explosives must be used to demolish the supporting metal arches and that the decks must be dismantled segment by segment, in the same sequence in which they were built, then the decks must be rebuilt one by one. The work requires continuous and prolonged contraflow lane reversals for each of the two decks.