Abstract:

The offshore wind industry needs to move towards floating offshore wind turbines (FOWTs) that are secured to the seabed with anchoring systems in order to harness the more substantial amounts of offshore wind resources available in deep waters. The design of the anchoring system for FOWTs is crucial to ensure stability and safety in challenging offshore conditions. As a simplified reliability-based design approach, the partial safety factor method remains important in current offshore foundation design practice, but its effectiveness in achieving the required target safety level still needs to be examined. To achieve this end, a reliability analysis is performed for the uplift limit state design of strip plate anchors embedded in sand subjected to vertical loads, and a wide range of load cases are considered in the analysis. The failure probabilities of strip plate anchors designed with the partial safety factor method are estimated and then compared to the target safety levels. The results show that the estimated reliability index decreases rapidly with the increasing of permanent to variable action ratio and gradually converges to a relatively steady state. In addition, the current partial safety factor method has been shown to be conservative for offshore plate anchor design over a wide range of permanent to variable action ratios. The results provide probabilistic insights into the effectiveness of the partial safety factor method and may aid in the further development of reliability analysis for offshore anchors.

Key words: reliability analysis, partial safety factor method, uplift limit state, offshore plate anchors, drainage conditions