Non-linear finite element analysis of grouted connections for offshore monopile wind turbines

Grouted Connections (GCs) are vital structural components of Offshore Wind Turbine (OWT) substructures. On monopiles to achieve a GC, tubular hollow steel piles are in-situ attached with a high-strength grout. Monopiles are susceptible to large magnitude bending loads in offshore environments. Recently, following inspections the performance of GCs has been called into doubt when settlements were reported on several monopiles. To further comprehend the structural performance of GCs under large bending moments a nonlinear Finite Element (FE) analysis was conducted. Three-dimensional FE models were solved and validated against experimental and analytical data with good agreement. It is suggested that the presented models can be used to evaluate the global and local behaviour of a GC accurately. Finally, a comprehensive parametric study was carried out to investigate the influence of shear key numbers, shear key spacing and overlap lengths. It was shown that increased number of shear keys are advantageous for stiffness and reduce the gap at the interfaces, whereas the grout failure depends on the spacing between neighbouring shear keys. The ability of the numerical model to trace all relevant failure modes which are provoked by shear key spacing was also demonstrated.