Cyclic pullout behavior of helical anchors for offshore floating structures under inclined loading condition

Abstract

Helical anchors are an effective option to support offshore floating structures with mooring and anchoring systems, where wave and tidal forces are the predominant load components leading to cyclic and inclined loading conditions. In this study, the cyclic and inclined pullout load carrying behavior of helical anchors was investigated. Large-deformation finite element (FE) analysis using the coupled Eulerian–Lagrangian (CEL) method was performed to simulate the cyclic pullout load response of helical anchors. Various configuration conditions of the helical anchor and loading direction, including the number and diameter of helical plate, plate arrangement and load inclination angle (θ), were considered in the analysis. Induced displacements were most significant during the first loading cycle, whereas those for subsequent loading cycles were relatively small. The geometry condition of the helical anchor less affected the pullout load carrying behavior as θ increased. The horizontal displacements (δh) were larger than the vertical displacements (δv) when θ was larger than 30°. When θ was smaller than 30°, δv was more dominant component. It was found that the configuration with top-down increasing diameter was more effective to enhance the pullout load carrying behavior than the conventional bottom-up increasing diameter configuration.