Structural response of submerged floating tunnels with free-end boundary condition based on an analytical approach

Until now, the investigation of structural behavioral characteristics of submerged floating tunnels (SFTs) has primarily relied on numerical methods that demand intensive calculations. This preference stems from the challenges in deriving an analytical solution, given the complexity of the structural system and applied loadings. To address this, an analytical approach based on practical assumptions has been developed to assess the structural responses of SFTs. Mainly, to mitigate excessive internal forces in tunnel segments and facilitate an analytical approach, a free-end boundary condition is assumed. Under these assumptions, the analytical approach can effectively determine the structural response of SFTs in the time domain. The proposed approach was validated by a hydrodynamics-based numerical analysis using the finite element method program ABAQUS/ AQUA. In the harsh wave conditions of the Messina Strait, this approach matches well with numerical analyses, except in cases of extremely low submergence depth or exceptionally large tunnel diameter compared to mooring stiffness. This analytical approach can rapidly and accurately evaluate the structural behavior of SFTs, especially when considering the specific environment and design loads at the basic design stage. Therefore, this method is practically valuable. However, its application should be carefully exercised due to the several limitations.