Anforderungen an die mechanische Fügetechnik für Türme von WEA in Stahlbauweise für große Nabenhöhen

Requirements for mechanical joining for application in the wind turbine towers for large hub height made of steel.

Modern wind turbines with high hub heights enable an economical energy production for locations with lower wind speed, complex terrain or in forests. High hub heights result in high requirements for the performance of turbine towers. For power production, the towers have to feature distinct static and dynamic properties. The feasibility of conventional, welded tubular steel towers faces technical and economical limits and alternative tower concepts are applied. For alternative steel towers concepts, friction connections with preloaded bolts have several advantages, but also raises new questions. The load bearing capacity of a friction connection depends on the coefficient of static friction and the applied pretension. During the turbine lifetime, the friction connection will be subject to a loss of pretension that needs to be considered. According to current design standards for steel constructions, the loss of pretension cannot be included in the design phase, but must be accounted for by means of maintenance.
This article presents an advanced design method for friction connection in steel constructions that is based on the VDI guideline 2230 for bolted connections in machinery structures and includes a possibility to consider loss of pretension. In addition, friction connections with drilled and punched holes are considered. It can be shown, that for preloaded friction connections, the punching of holes leads to no adverse effects for fatigue resistance. On the basis of this design method, it was possible to issue a type approval for a maintenance free steel shell tower that consists of steel plates, which are joined by friction connections.