Advanced vs Simplified Design Approaches for Monopiles in Seismic Areas

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As part of a rapid global wind energy growth, offshore wind farms are being developed in moderate to high seismic active areas. The geotechnical design of monopiles, in non-seismic environments, is now typically based on detailed 3D finite element analysis (FEA) for the optimisation of foundation geometry and provision of required soil reaction curves (SRC). Despite this advanced design philosophy being well-established, simplified but accurate approaches for seismic input definition and soil-structure interaction for seismic design during early stages of developments are limited to date. This paper aims at presenting a simplified approach accounting for kinematic soil-structure interaction during earthquake loading, that could be used for the design of next generation 20 MW wind turbines founded on large diameter monopiles. The simplified approach is compared against an advanced one, to establish its performance. The advanced approach considered in this paper includes 3D FE time-domain modelling of the monopile in linear and non-linear soil materials subject to different real earthquake time histories. The simplified approach consists of a 1D soil column propagating earthquake time histories and connected to a stick model of the monopile through springs and dashpots. Results of the two approaches are compared and a sound yet efficient way to define an equivalent uniform ground motion input including kinematic soil-structure interaction is described.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

9 - Monopile design to cyclic loads: quasi-static, dynamic and seismic loads