Probabilistic Assessment of Ice Environment and Ridge Loads for the Norströmsgrund Lighthouse

Abstract

Structural reliability analysis requires statistical distribution of the loads. One such case is ice load calculation for offshore structures. Ice-structure interaction is a highly stochastic phenomenon due to the natural variability of sea ice (aleatory uncertainties) and lack of knowledge about the processes that are taking place and long-term data needed for ice load calculation (epistemic uncertainties). Ice ridges are typically the ice features that govern the quasi-static ice load calculations in areas without icebergs. This is the case for Gulf of Bothnia, where Norströmsgrund lighthouse is located. This paper investigates how to utilize a Monte Carlo simulation for probabilistic assessment of ice environment and ice loads on the Norströmsgrund lighthouse. Information found in literature about sea ice growth, ridge formation and ice drift in Gulf of Bothnia (and in general) are used to simulate the ice environment parameters (e.g., ice ridge frequency of occurrence, ridge keel depth, consolidated layer thickness). Simple and generally accepted load models are used to avoid involving additional uncertainties that arise with more advanced models. The final result of the simulation is the probability distribution of the ridge horizontal load acting on Norströmsgrund lighthouse, from which loads with specific return period can be extracted (e.g., 100-year load).