Segmented Monobucket Foundation

Abstract

Large-diameter monobucket foundations are a promising alternative for offshore wind turbines in cases where monopiles are not suitable. However, during installation, the induced underpressure leads to compressive stresses in the thin-walled shell, making these structures susceptible to buckling. This is further amplified by the need for slender designs to remain cost efficient. This study investigates an alternative monobucket geometry in which the cylindrical shell is replaced by a segmented configuration composed of multiple curved sections. Two concepts are studied: the Outward Segmented Bucket (OSB) and the Inward Segmented Bucket (ISB). These geometries either increase local curvature or fundamentally alter the load application, both with the aim of improving buckling resistance.

A two-step finite element approach is applied, consisting of Linear Buckling Analysis (LBA) and Geometrically and Materially Nonlinear Analysis with Imperfections (GMNIA). The results show that segmented geometries achieve significantly higher buckling capacities, compared with a conventional cylindrical design. For OSB configurations, this improvement is driven by the increased local curvature, for which a clear relationship with the limit pressure is observed. In contrast, ISB configurations exhibit a different failure mechanism, where buckling is governed by local instabilities at segment edges due to stress concentrations, rather than global buckling. Furthermore, the results show that the buckling limit strongly depends on the eigenmode used as an imperfection, and that higher-order modes should also be taken into account. The improved buckling performance allows for substantial reductions in required shell thickness, demonstrating clear material and thus cost savings.