Large Diameter Monopile Buckling Due to Localized Force

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The study uses finite-element simulations to investigate local buckling and damage at the tip of large-diameter offshore wind monopiles struck by localized forces, such as impacts from boulders during driving. This risk may increase as cost-optimized piles become wider and thinner.<br /><br />The authors model eight steel-pile geometries with outer diameters of 6–12 m and diameter-to-thickness ratios of 80 or 100. They apply displacement-controlled loads at the pile-base edge at five inclinations, from horizontal to vertical, and use nonlinear analyses to capture instability. The study also examines geometric imperfections and alternative shell reference surfaces. Soil and detailed boulder–pile contact are not modeled.<br /><br />Results show that force inclination is the main influence on normalized load capacity. For a given inclination, capacity is nearly independent of pile diameter and wall-thickness ratio after normalization. Horizontal loading produces a comparatively simple bending response, while vertical loading triggers more complex local instabilities and is more sensitive to imperfections and other local disturbances. Imperfections generally alter load factors only partly, tending to smooth peak loads. Because peak resistance occurs at small displacements, post-peak strength may better represent practical residual capacity. The simulated post-buckling response is generally hardening, even at substantial tip deformation; diameter reduction is driven mainly by bending and horizontal force components.<br /><br />The resulting charts may support assessment and mitigation of pile-tip damage, although the analysis does not directly represent surrounding soil or impact contact conditions.

Keywords

finite-element simulations

local buckling

offshore wind monopiles

boulder impact

pile-tip damage

steel pile geometries

diameter-to-thickness ratio

force inclination

nonlinear analysis

post-buckling response