Efeitos de carregamentos cíclicos multidirecionais em estacas de fundação de turbinas eólicas flutuantes

Abstract

One solution for anchoring Floating Offshore Wind Turbines (FOWTs) is the use of open-ended steel piles connected by catenary mooring lines. This setup mainly results in horizontal loading on the piles. Due to metocean conditions, these structures must withstand complex loading, including cyclic forces. Using shared anchor piles between turbines can reduce costs, but increases the complexity of the loads applied, resulting in multidirectional solicitations. Understanding how these loads affect pile behavior is essential for ensuring safety and optimizing design. The usual p-y design method for laterally loaded piles can be questioned for multidirectional loadings and also for thin tubes. In this method, the pile behavior is derived based on classical beam theories, such as Euler-Bernoulli Beam Theory. These theories assume simplified structural responses that may not be valid in such piles. To provide some insights into pile behavior, an analysis of an experimental study was carried out. The experimental campaign consisted of a reduced-scale pile embedded in sand, which was tested under three loading conditions of increasing complexity. It was instrumented with nine head displacement sensors and 32 strain gauges to measure its response. In parallel, a 3D finite element simulation was performed to evaluate the validity of classical beam theory for thin-walled piles. The results showed that these assumptions do not hold, especially due to stress concentration and cross-sectional ovalization. This indicates that the current formulation to experimentally obtain p-y curves is not suitable for such piles. Experimentally, it was observed that the pile’s response to cyclic loading depends on both the average load and the load amplitude. Furthermore, multidirectional loading increased soil disturbance around the pile, allowing more particle rearrangement, which led to greater displacement. These findings highlight the need for improved modeling approaches to capture the real behavior of short piles under complex offshore conditions.