Ensuring the Stability of Offshore Support Structures in the North Sea

Research project on load-bearing characteristics of wind turbines and wind farm platforms
Press release of the Leibniz University of Hannover

Support structures for offshore wind turbines and wind farm platforms are constantly affected by wind and waves. Heavy seas pose a significant risk - especially during the construction phase, where the support structure is connected to the foundation piles driven into the seabed, and the concrete that joins the foundation piles and the support structures hardens.

A pipe-in-pipe connector links the piles to the support structure. For this purpose, two pipes with different diameters are inserted into each other. The interspace is filled with grout, a fine-grained type of concrete, which takes up to 24 hours to harden. During this time, the properties that give concrete its rigidity and stability are developed. However, wave movement can interfere with the curing process and affect these properties permanently. The extent to which the properties of concrete are affected by waves requires further investigation.

Over the next three years, the GREAM research team at Leibniz University Hannover will undertake research on this topic. The project receives more than 1.5 million euros of funding from the Federal Ministry for Economic Affairs and Energy (BMWi). "The behaviour of concrete is of utmost importance for industry, certifiers, and planning bodies", explains Dario Cotardo from the Institute of Building Materials Science (IfB) at LUH (Head of Institute: Professor Ludger Lohaus). The project was initiated by the IfB in cooperation with the Institute of Steel Construction and the Test Center Support Structures (TTH) in Hannover. Project partners include industry members, the Federal Institute for Materials Research and Testing (BAM), as well as ForWind, the joint centre for wind energy research of LUH, Oldenburg University, and University of Bremen.

Scientific data regarding the effects of early age movement on the mechanical properties of concrete will facilitate the coordination of the construction process so that foundation structures can be planned more efficiently. "Presently, construction ships can only operate in good weather conditions. Unfortunately, there is a high risk of heavy storms in autumn and spring, which limits the time frame for construction", says Dario Cotardo. If research confirms that concrete can withstand stronger wave movement during the curing phase than anticipated, the time frame for construction could be extended by several weeks or even several months, if necessary. Thus, expensive special-purpose vessels could be used more economically. Furthermore, research data on the properties of concrete will help to predict the operating life of support structures.

In order to investigate the influence of early age movement, researchers have developed test facilities that simulate real sea conditions in the laboratory. The devices are up to 2.5 metres high and will be put into operation at the involved research centres over the next years. The generated data will be used for the numerical simulation of offshore support structures. All findings will be incorporated into extended offshore guidelines.

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