In the paper a numerical procedure is described for the dynamic analysis of seabed anchored floating structures, with particular reference to the so-called Archimedes bridge solution for deep water crossings; attention is devoted to the design solution encompassing slender bars as anchor elements. A geometrically nonlinear finite element, developed in previous work, is here refined extending its capabilities to full 3-D analysis and to nonlinear modelling of hydrodynamic loads due to steady current and wind waves. The element is implemented in a numerical procedure for the dynamic time domain step-by-step analysis of nonlinear discretized systems; consistently, hydrodynamic and seismic loading are introduced by generating artificial time-histories of spatially variable seismic motion and wind waves. An example of on application is shown regarding the behavior of the dynamic model of a submerged tunnel proposed for the Messina Strait crossing. The model is subjected to an extreme multiple-support seismic loading having a PGA equal to 0.64g and to an extreme wave loading with significant wave height of 16 m. The dynamic behaviour in the two loading situations is illustrated and compared, showing interesting facets, especially in terms of interaction between the tunnel and anchoring bars oscillations.
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