Risk and Reliability Based Calibration of Design Codes for Submerged Floating Tunnels

Submerged floating tunnels (SFTs), also known as Archimedes' bridges, allow crossing waterways where common bridges, underground tunnels or immersed tunnels are not feasible. In spite of this, no SFTs have been built yet in the world except for a prototype in China. The reasons are numerous and widely discussed in literature. The lack of past experience and ad hoc design codes or guidelines represents a great challenge in design. In fact, the direct use of target reliabilities and design codes, which are specifically developed for common structures and adapted through the years based on the gained experience, is questionable. This is because STFs might be characterized by different failure consequences and marginal safety costs. Optimal target reliabilities can be estimated through a full-risk assessment following the ISO standard 2394:2015 guidelines. Successively simpler design approaches and assessment of decisions such as reliability-based and semi-probabilistic design can be calibrated.