Summary and conclusions
This paper has presented a brief history of the development and growth of wind turbines and OWTs. It has also presented the state of practice in seismic design of offshore wind turbines and existing design cods. In addition, the paper has addressed, among others, the use of foundation macro-elements for earthquake response of wind turbines under lateral earthquake excitation and has highlighted the vulnerability of wind turbines to vertical earthquake excitations due to their high vertical natural frequencies. It has also been shown that for such loading conditions, use of radiation damping is a key to a more economical design. Moreover, the paper has demonstrated how soil nonlinearity and pore-pressure generation could lead to settlement and permanent tilting of offshore wind turbines on mono-bucket foundations. Using these cases, the paper has clearly highlighted the importance of performance-based analyses in seismic design of OWTs.
