Grouted Connections on Monopiles: A Numerical Study

The installed capacity of offshore wind turbines (OWTs) has rapidly grown during the past decades around the globe. Monopiles are the most common substructure employed in the majority of the current operating OWTs. A monopile is usually formed by tubular steel tubes which are connected in-situ by means of an ultra-high strength grout. Monopiles differ from common jacket offshore structures as the main loading action is bending caused by environmental loads. Their structural performance principally relies on the grouted connection (GC). Particularly for this type of substructure, the connection is of critical interest due to several unexpected issues that were recently reported in wind farms around Europe. The latter were mainly related to sliding between the tubular steel piles of the substructure causing settlements.

In the present study an investigation of a grouted connection with shear keys by means of Finite Element Modelling (FEM) is presented. The FE model is validated against experimental data. An explicit quasi-static solution of the numerical model is conducted. A comprehensive description of the numerical model is provided, focusing on the representation of the cementitious grout and the failure modes. A sensitivity analysis and discussion on the associated parameters of the material model is given. Finally, an evaluation of the results from the numerical simulations is presented including the cracking behaviour of the grout.