A simple macroelement for predicting cyclic rotations of suction caissons in sand

Abstract

Suction caissons are widely adopted as foundations for offshore wind turbines, due to their capability to resist high lateral forces and overturning moments. A critical aspect for their design is the accumulation of irreversible rotations under cyclic loads, which can compromise the functionality of the turbine over its service life. Advanced Finite Element (FE) models provide detailed insights on the cyclic foundation response, but require unfeasible computational costs for practical applications due to the large number of lifespan load cycles. To address this challenge, this work presents a novel macroelement model developed to predict the cyclic accumulation of irreversible rotations of suction caisson foundations in sand. Its constitutive features are inspired by the memory and bounding surface plasticity framework and by the results of 3D FE analyses carried out with SANISAND-MS model. By describing the soil-foundation interaction with a small set of generalized load-displacement/rotation variables, the proposed macroelement significantly reduces computational time compared to FE analyses, while maintaining the capability of predicting cyclic ratcheting and rotation accumulation. The model captures the effects of caisson geometry, load eccentricity and sand relative density. Validation against FE results establish the macroelement as a practical and efficient alternative for integrating soil-structure interaction effects into the design of offshore wind turbines.