Multi-support seismic input and response of submerged floating tunnels anchored by cables

The modeling and seismic analysis of Submerged Floating Tunnels moored by cables is addressed with particular attention to spatial variability of the excitation. A uniformly modulated random process is deemed adequate to model the spatial variability of the seismic input for the given structure. A novel method to obtain response spectrum compatible accelerograms is proposed, that is based on the explicit expression of the median pseudo-acceleration response spectrum induced by the adopted power density function (PSD), which is then used to identify the parameters of the PSD function that minimize the difference with the elastic response spectrum prescribed by EN 1998. The minimization process is discussed and parameters for the PSD spectra are obtained. Samples of the free-field motion are then generated using a proved and theoretically sound approach and reach a satisfactory agreement with the prescribed response spectra. To model the cables, a 3 node isoparametric cable element, formulated in the coordinates of the dynamic model, is enriched, by including hydrodynamic loading, within a numerical procedure for the dynamic time domain step-by-step analysis of non-linear discretized systems. Cables discretization and dissipation modeling issues are addressed. An example of application is shown, that makes reference to the bed profile of Qiandao Lake (People’s Republic of China), where the first SFT prototype should be built; additional analyses tend to assess the sensitivity to soil parameters.