Fatigue Sensitivity Analysis to Piles Fixity length in Offshore Wind Turbines Jacket Substructures

Fatigue damage has always been a significant concern for engineers regarding offshore structures applications. This phenomenon is investigated, especially for lattice structures such as jackets in which tubular welded connections are the most critical points threatened with fatigue failure. Fatigue damage, moreover, for jacket-type offshore wind turbines have relatively been examined in literature focusing on structural considerations. However, since most offshore wind turbines simulation programmes use simplified soil-pile interaction models such as Apparent Fixity model; fatigue analyses concerning such models, especially the Apparent Fixity model, have not been investigated so far. More specifically, the impacts of different apparent fixity lengths on fatigue damage in jacket-type offshore wind turbines have not been taken into account. In this study, fatigue analysis of the jacket-type offshore wind turbine supported by "Upwind" reference jacket for different pile fixity lengths is carried out considering both wave and wind loads applied on the structure. Apparent fixity model is used herein for soil-pile interaction. Ultimately, a sensitivity analysis for fatigue damage to different pile fixity lengths is carried out in order to find how accumulated fatigue damage is changed. It is concluded that fatigue life of a connection - the most vulnerable one to fatigue damage - in jacket substructures of the offshore wind turbines is considerably sensitive to pile fixity length when applying Apparent Fixity model for soil-pile interaction.