A Kriging-based Monte Carlo reliability analysis of an adriatic offshore jacket structure

The Italian offshore sector includes 138 platforms, most of which are jacket-type structures originally designed for gas production and transportation. The majority were installed between the 1960s and 1990s; consequently, many assets are now approaching or exceeding their original design life, with several wells depleted or operating at markedly reduced production rates. In this context, repurposing non-productive platforms as support structures for offshore wind turbines represents a potential alternative to relocation or decommissioning. This thesis investigates, within a structural reliability framework, the evolution of the reliability index over the service life of the primary structural members and its variation under a change of use to support an offshore wind turbine. The proposed approach provides a quantitative assessment of long-term structural performance and supports the interpretation of the governing failure mechanisms. The numerical workflow combines finite element modelling of the platform in ANSYS with a parametric definition of actions and model parameters in MATLAB. To enable a large number of simulations at an affordable computational cost, a Kriging-based surrogate model is trained and employed as a fast predictor within the state-based/snapshot reliability analyses. The results indicate that, for the current deck configuration, the structural performance remains satisfactory during the early service life but begins to deteriorate rapidly after approximately 27 years, as corrosion-induced loss of sectional capacity becomes increasingly significant. Under the offshore wind turbine configuration, the structure exhibits an acceptable reliability level in the initial years; however, reliability decreases markedly once aggressive corrosion mechanisms become dominant.