Analysis of grouted connections for offshore wind turbines

In offshore wind turbines grouted connections are generally used to install a transition piece between the steel tower and the monopile foundation. The transition piece is plugged on to the monopile, aligned vertically and the annulus in between is filled with high-strength grout. During service operations unexpected settlement of the transition piece has been observed at several wind turbines. The serious findings have called for additional, extensive numerical analyses for the detailed design of the London Array offshore wind farm. The advanced non-linear finite-element analyses provide a more detailed insight into the structural behaviour of grouted connections. Important effects and a possible mechanism for the settlement at existing wind turbines are detected. The previous practice of designing separately for bending moment and transverse force on the one hand and axial force and torsion on the other hand leads, among other things, to the overestimation of capacity. The interaction has to be taken into account.