Numerical models for the dynamic response of submerged floating tunnels under seismic loading

Submerged Floating Tunnels are a promising alternative to bridges and underground tunnels for crossing sea straits or, in general, waterways. The dynamic behavior of SFTs involves complex design and analysis issues, mainly related to the response to environmental actions. Within this context, the modeling of tethering elements of seabed anchored floating structures is here addressed, with particular reference to the crossing of deep waters; attention is devoted to the design solution encompassing slender bars as anchor elements. Two numerical tools are proposed: first, a geometrically non-linear finite element (NWB model), developed in previous work, has been refined in order to capture the effect of higher flexural modes of anchor bars. Secondly, a 3D beam element, based on the classical corotational formulation (CR), has been developed and coded. Both elements are implemented in a numerical procedure for the dynamic time domain step-by-step analysis of non-linear discretized systems; seismic loading is introduced by generating artificial time-histories of spatially variable seismic motion. An example of application of the NWB element is shown regarding the behavior of the dynamic model of a submerged tunnel proposed for the Messina Strait crossing. The model was subjected to extreme multiple-support seismic loading. The behavior under seismic loading is here illustrated and commented, especially in light of the effect of higher local vibration modes of the anchor bars.