Schädigungsmodell für hybride Verbindungen in Offshore-Windenergieanlagen

Damage approach for hybrid connections in offshore wind turbines.

During the service life of an offshore wind turbine, the connection between monopile and tower, the so-called grouted joint, is exposed to high dynamic loadings from wind and wave actions. Additionally the connection, which is filled with a high performance grout, has to withstand extreme load situations. Within the last years vertical settlements between the connected steel pipes have been detected. This non-redundant failure mode underlines the necessity for an optimization of the axial load bearing capacity. One possible solution is the application of shear keys, which are weld beads installed in circumferential direction of the connection on the surfaces of pile and sleeve. This additional mechanical interlock leads to compression struts and an increased axial strength. Unfortunately these geometric notches lead to local stress concentration and reduce the fatigue resistance of steel and grout. The fatigue design for the steel members can be performed acc. to well known local approaches. For plain grouted joints usually uniaxial S-N-curves for the grout layer are considered, which is not appropriate in cases of shear keys. Taking the multiaxial stress space around the weld beads and suitable S-N-curves into account, the fatigue design of the connection can be conducted.