Nonlinear behavior of submerged floating tunnels accounting for seaquake effects

Submerged FloatingTunnels, also known asArchimedes Bridges, are a newstructural conceptual way for strait and waterways crossing, which are catching more and more worldwide attention. In this paper, a 3D finite element model is developed in a commercial finite element code, accounting for material and geometrical nonlinearities, soil-structure interaction and multiple-support seismic excitation, to give a broad angle view on the structural behavior under seismic motion. Elastic-plastic springs at tunnel shores, simulating passive control devices, are applied to reduce relative displacements between the tunnel and shores. Beside the traditional earthquake loading on the structure foundations' connections, the motion transmission from the seabed through the water (called seaquake) is newly introduced as an additional hydrodynamic pressure working on the floating tunnel. The velocity field due to seaquake is derived from its velocity potential which is deduced from the wave equation considering the boundary conditions. The force on the moving tunnel body in the oscillatory flow, simulating the seaquake, is modeled by using Morison's equations. A comparison between transient dynamic response in case of 'earthquake' and 'earthquake plus seaquake' is also given, which shows how seaquake loading affects the responses of anchor bars, shore connections and tunnel sections in terms of stresses, strains and displacements. The outcome indicates a larger displacement capacity is required to the control system in the mitigation of dangerous structural responses, as well as the significant role played by the seaquake loading source, and highlights the need of further investigations on seaquake effects. © 2013 Taylor & Francis Group, London, UK.