The dynamic behaviour of Archimede’s Bridges: numerical simulation and design implications

In the paper the activity of the research group in the field of the dynamic behaviour of Archimede’s Bridges is reviewed. The scope is twofold; on one hand the implications, in terms of structural analysis and design, of the results of this activity are summarized and discussed. On the other hand the needs for future research are defined. The general criteria adopted in the simulation of the dynamic response of the Archimede’s Bridge are first summarized. Attention is focused on “slow” dynamic actions; loading conditions due to impacts and internal or external explosions are thus not considered. The problem of seismic response is subsequently addressed; the problem of transverse response is discussed, especially in light of the anchoring system typology. It is then commented how another critical issue can be represented by the longitudinal motion of very long tunnels and, on design grounds, by the way of providing adequate restraint. Finally the aspects related to hydrodynamic excitation due to seabed motion (tsunamis and “seaquake”) are briefly presented especially in light of research development. The dynamic behaviour under wave and current excitation is addressed in the second part; the adopted wave models are briefly described along with the criteria for defining hydrodynamic forces; some results are shown illustrating the response to exceptional wind waves, with particular reference to the motion of the anchoring elements. The issue of vortex induced vibration is then treated, showing how long anchoring elements can be dangerously prone to activation of large oscillations, with the additional problem of high Reynolds numbers characterizing the fluid-structure interaction. The numerical procedure which has been developed for simulating the phenomenon is illustrated along with some example of application to simple problems. Finally, some general considerations relating dynamic performance and basic design choices are proposed.