Wind turbines deal with significant loads that limit the lifetime of the blades. To aid in this, blades can be designed to be compliant in a manner that reduces the peak loads it experiences. One such approach is to use bend–twist coupling. However, as this paper documents, the behavior of blades with bend–twist coupling can be very sensitive to manufacturing tolerances. Understanding these sensitivities allows for better design and manufacturing practices to be developed.

In this research, a cyclic p–y overlay model for monopiles in sand soils could be developed via comparison of numerical simulations of monopile behaviour: once under monotonic and once under cyclic loading with a defined number of load cycles (utilizing the stiffness degradation method). The new cyclic overlay model gives plausible results and can be applied to any monotonic p–y approach for monopiles in sand.

A brief summary of current regulations and recommendations for the serviceability limit state dimensioning of offshore monopile foundations in sand for wind turbines is given. Results from a large number of small-scale model experiments are presented, discussed and compared to the findings of other research groups to contribute to a better understanding of the complex processes associated with the cyclic load-bearing behaviour of piles and to the development of improved calculation approaches.