Toward performance-based evaluation for offshore wind turbine jacket support structures

This paper introduces a framework for the assessment of damage of offshore wind turbines (OWTs) supported by jackets under extreme environmental loadings. Performance levels/damage states, ranging from operational/undamaged to near collapse/severely damaged, are defined based on static pushover analyses. An example performance assessment is presented for an OWT supported by a jacket based on environmental conditions for a site off Massachusetts along U.S. Atlantic coast. The environmental conditions are characterized based on two methods for estimating wind and wave conditions, one on extrapolation of NOAA buoy measurements and one on a stochastic hurricane catalog, and two models for extreme wave height, one on the crest height and one on the zero-up-crossing height. Using probabilistic models for demands and capacities, two curves of fragility, one estimating the initiation of yielding and the other estimating the onset of collapse, are developed to distinguish between the three damage states. The curves are applied to four combinations of two environmental hazard models and two extreme wave height models, and significant differences are found in the probability of damage among the four combinations of models. The findings have potential implications for the evaluation of the overall risk profile and associated performance for offshore wind farms.