Hexabase

Offshore wind turbines in great depths of water require disintegrated foundation structures such as jackets and tripods. As an alternative to these variants, the Maritime Offshore Group GmbH (MOG) from Bremen has developed the so-called "HEXABASE". This foundation structure has a hexagonal layout and is to be realised with identical pipe diameters. Only the wall thickness of the pipes is to be varied in order to cope with the different stresses in the various truss levels. Depending on the market situation, HFI steel pipes (high-frequency induction welding process) or spiral-welded pipes are to be used.

The design can be used as „Pre-Piling“- oder als „Post-Piling“-Variante be planned. In the pre-piling variant, the piles are first driven into the seabed and then the support structure is lifted into place. A force-fit connection between the jacket legs and the piles is created by grouting with a high-strength grout.

The force is transferred from the tower to the supporting structure via a transition piece known as the central pipe node. At the base of the HEXABASE, the loads are transferred from the grouted pipe-in-pipe connections, also known as pile-sleeve connections, to the driven piles and finally transferred into the ground.

The SKI engineering company has carried out numerical structural analyses of various connection techniques in order to obtain a load-optimised geometry for these design details. The central tube node, the grouted pile-sleeve connection and the snake node were analysed.