The innovative elastometric spring bearings designed to improve the vertical load carrying capacity of the wind turbines of the Sheringham Shoal Offshore Wind Farm, have now been installed on each of the 90 foundations at the site, 20 kilometres off the coast of the Norfolk in the UK.
Trelleborg Offshore Norway AS, has recently completed its contract to install the 552 bearings before the start of winter. They worked with project team members from owner Scira Offshore Energy and operator Statoil to design, manufacture and deliver the bearings following reports of grouting failures on other wind farms.
The bespoke steel and rubber bearings were designed to reduce the vertical load on the grouted connection between the inner monopile pipe and the outer transition piece, which together make up the foundation on which the wind turbine will sit.
Each of the wind farm’s monopiles are between 44 and 61 metres long, have a 4.2 to 5.2m diameter, weigh from 375 to 530 tonnes and have been piled between 23 and 37m into the seabed. The bright-yellow transition pieces were fitted over the top of the monopiles and secured with the cement grouting, in preparation for the installation of the turbines
The grouting filling the gap between the monopile and the slightly larger diameter transition piece has to withstand both the vertical weight of the tower and the lateral force of the wind.
Statoil’s company representative for the bearings contract, Mr Sigmund Lunde said examples of failing grout connections elsewhere led certification authority Det Norske Veritas (DNV) to reduce acceptable loads which could be placed on grouted connections required by offshore wind farms.
”The bearings developed by Trelleborg had to be compatible with the design of our wind turbines, which were already under construction, while also being able to significantly reduce the load on the grouted connections,” he said. “This solution can also be adopted retrospectively by other existing wind farms if they have grouting issues.”
Sheringham Shoal Offshore Wind Farm is owned equally by Statoil and Statkraft through joint-venture company Scira Offshore Energy Limited. Statoil is operator for the project during the development phase and Scira will be the wind farm operator.
Source: scira ,October, 20. 2011;