Soil-structure reliability assessment of fixed monopile offshore wind turbine based on modified environmental contour method

This paper aims to develop a reliability assessment method for monopile offshore wind turbines, focusing on a serviceability limit state wherein the rotation of the pile head should not exceed a specified threshold. The modified environmental contour method is used to estimate the 50-year extreme distribution of the pile head forces. The finite element method is utilized to calculate the pile head rotation, taking into account the pile-soil interaction through the p-y curve method. Given the uncertainties associated with the extreme pile head forces and soil conditions, the First Order Reliability Method (FORM) is applied to evaluate the reliability of the monopile offshore wind turbine. The findings indicate that the short-term extreme pile head forces conform to the generalized extreme value distribution, and that the extreme bending moment and extreme shear force do not necessarily occur simultaneously. For a comprehensive reliability assessment, it is crucial to consider the 50-year extreme bending moment and the corresponding shear force that occur concurrently.