According to political goals, electricity from offshore wind farms in Germany will amount to 15 GW by 2030. Most of the wind farms will be located far offshore in water depths larger than 30 m. For such water depths, lattice substructures like jackets or tripods are the preferred solution. The substructures are founded on piles and connected to these by submerged grouted joints. In lattice substructures grouted joints are predominantly loaded by cyclic axial loads. Even though, this connection is well known from the offshore oil and gas industry, comparatively few results on effects of attrition due to water for grouted joints are available.
At the Institute for Steel Construction of the Leibniz University Hannover, Germany, within the joint research project ‘GROWup’ investigations focus on the fatigue performance of grouted joints under predominant axial loading. As part of this research project, cyclic loading tests on small scale grouted joints with shear keys were conducted. The specimens were filled with industrial grout products and tested in a water basin to evaluate the influence of water to the fatigue performance of the connection at small scale. These test results show that the water effect leads to a significant reduction of the fatigue performance of the connection compared to results from tests in dry conditions. Moreover, the impact of water is proportional to the applied test frequency. The results of the structural tests differ from results of pure material specimen tests, on which current code provisions are based.
This paper presents results from the small scale tests on grouted joints with shear keys in dry and submerged conditions. Effects of attrition due to water are shown and their effect is quantified. The results are compared to other published findings. In conclusion the presented investigations underline the importance of the water effect to the fatigue performance of small scale grouted joints. In conclusion, this paper will stimulate discussions on the demand for research on large- and real-scale grouted joints.