Probabilistic analysis of ship-bridge allisions when designing bridges

The advances in civil engineering with novel bridge designs between islands and across fjords with long spans, increasing ship traffic density and larger ships in coastal areas, have resulted in an increased frequency of ship-bridge allision accidents worldwide. It is thus essential to have reliable models and methods for engineers to create safe designs of these new bridges to simulate and analyse early pro-active mitigation measures. This study presents a new ship traffic allision probabilistic simulation mid fidelity model (STAPS), which includes a ship's manoeuvrability and motion physics and uses the Monte Carlo simulation method in the probabilistic calculations. It is compared with the low fidelity model IWRAP Mk2, which is used to analyse the risk of ship allisions with structures. Two case studies with ship-allision scenarios are presented to compare how the model fidelity levels of STAPS and IWRAP Mk2 affect the calculated probability levels of ship-bridge allision events. On a general level, the results show that IWRAP Mk2 overestimates the accident probability, for example IWRAP Mk2 predicts a 4.5 times higher probability of allisions compared to STAPS in the base case, and that the failure's duration and route layouts significantly influence both models. The study concludes that IWRAP Mk2 is preferred in the early phase of bridge design and STAPS is preferred in later stages.