SEISMIC DESIGN FOR OFFSHORE WIND FARMS: CURRENT PRACTICES AND OPEN CHALLENGES

Over the past decades, wind farms have become increasingly important in the renewable energy sector, being one of the most innovative technologies that favor carbon-neutral energy production. Wind turbines are usually located offshore owing to both the better wind quality at sea and their structural and environmental advantages. Furthermore, a great number of wind turbines have been lately deployed in seismically active regions, where they should be designed against seismic hazards in addition to aero-and hydrodynamic loads. Although there is a common consensus in literature that seismic hazards play a crucial role for Offshore Wind Farms (OWFs), there are currently no specific regulations for their seismic design. Hence, seismic design procedures for ordinary buildings and/or critical infrastructures are actually adopted, even though main differences exist. Among the main issues to be accounted for in the seismic design of OWFs, the definition of relevant seismic intensity measure through seismic hazard assessment is of paramount importance. What are the current practices? How could they be improved to better meet the design purposes? Is there a balance between the cutting-edge science and the constraints of industrial applications? Motivated by the challenges experienced in industrial projects, the main aim of this paper is to present and discuss some crucial steps related to the estimation of seismic hazard of OWFs through a real case-study. In particular, the following aspects are addressed: (1) the definition of the ground motion vertical component, which is still a main issue in the framework of Probabilistic Seismic Hazard Assessment (PSHA), since it can generate significant effects on a wide range of wind turbines due to their high vertical natural frequencies, and (2) the inclusion of ground motion spatial correlation models to improve hazard estimates, being OWFs spatially distributed systems.