This paper presents the dynamic response/global performance of two types of submerged floating tunnels (SFTs) under survival wave and seismic conditions. Time domain numerical simulations are performed by the commercial program, OrcaFlex. Three buoyancy to weight ratios (BWRs) are considered as a design parameter. Two different configurations of mooring lines are considered to find a better solution to minimize dynamic responses of the SFTs in the extreme conditions. The floating tunnels are considered as a long/slender elastic cylindrical body clamped at both ends. Not only elastic responses including sway/heave motions at the mid span but also mooring tensions are evaluated and assessed. Modal analysis is performed to obtain the natural frequencies and mode shapes for different BWRs and mooring configurations.
The submerged floating tunnel (SFT), which is also known as Archimedes Bridge, is an innovative structure to solve the limitation of transportation in a waterway. The SFT is a submerged floating tunnel with positive net buoyancy and anchoring system using bars and/or cables (Xiang, Liu, Zhang, and Wu, 2010). Whereas there are several constructions for the traditional immersed tunnel mounted on seabed, there is no prototype construction of the SFT in the world yet (Di Pilato, Feriani, and Perotti, 2008). The first construction plan of the SFT has begun in Norway in 2016.
The SFT with an appropriate design can be better than the traditional immersed tunnel or bridge. While the traditional immersed tunnel has minimal dynamic responses against wave loads, it can be vulnerable to large seismic loads. In contrast, the SFT is prone to experience significant dynamic responses from hurricane-wave loads when submergence depth is not enough; however, it can provide much safer condition against the seismic load. Moreover, the significant dynamic response induced by large wave loads can be minimized by properly adjusting submergence depth, buoyancy to weight ratio (BWR), and mooring-line configuration. The length of the SFT can be long with no issue of ship passage (Indridason, 2013).
