For offshore wind turbines (OWTs) the design of connections of parts of the support structure is an essential and limiting topic. Within this paper some specific issues of grouted connections between tubular structural members are described with a focus on the peculiarities of offshore wind turbines in contrast to "conventional" offshore support structures and monopile foundations especially. Intermediate results of the ongoing research project "GROW- Grouted Structures for Offshore Wind turbines" are presented.
Within the last few years, a number of offshore wind farms have been put into operation in European countries like Denmark, the UK and the Netherlands. They all have in common that they are situated in shallow water, i.e. less than 25m and relatively close to the shore. For many of these projects the foundations are designed as driven monopiles. Peculiarities in context with wind turbines are the predominant bending loading in combination with high cycle fatigue loading induced by the rotor and waves. The diameter of these piles usually lies in a range of 4 to 5 m. The connection between the foundation piles and the tower of the wind turbine is executed with an overlap connection of these two tubular members filled with high performance grout. For the combination of these factors no comparable experience could be derived from constructions of the offshore oil & gas industry. Further applications of grouted connections for OWT support structures for deeper water are pile sleeve connections of jacket or tripod structures where the grout is used to connect piles and support structure. Germanischer Lloyd (GL) is taking part in a joint research project named GROW together with the industry partners SIAG AG and Oevermann GmbH and lead by the Institute for Steel Construction, Leibniz Universität Hannover (Germany).