In this paper the structural response of Submerged Floating Tunnels (SFTs) to severe seismic events is investigated. The Submerged Floating Tunnel (SFT, also known as Archimede's Bridge) is an innovative structural solution for the realization of waterway crossings, consisting in a tubular structure placed underwater and anchored to the seabed by means of cable systems having a fixed inter-axis along the tunnel. SFTs seem to be particularly suitable to cross waterways located in high seismicity zones: due to their large transversal flexibility and to the additional damping and inertia arising from the water-structure interaction, a reduced amount of the earthquake input energy can be transferred to the tunnel, provided that its connections with the shores are equipped with proper seismic joints.

The behaviour of SFTs during strong earthquakes features peculiar aspects that deserve to be studied, such as the influence of the asynchronous ground motion and of the propagation of vertical ground motion in the upper water layer. In order to adequately investigate the structural response of SFTs to strong ground motion produced by a large size earthquake, the 1908 Messina (Italy) earthquake is simulated by means of a flat-layered ground-water model. Several SFT structural configurations, differing for the set up of the anchoring system, and different values of the crossing length are considered. The structural behaviour of SFTs during the simulated seismic event is then studied through F.E. analyses and the main outcomes thoroughly discussed.