Concrete fatigue of onshore wind turbine foundations

Abstract

Climate challenges have led to greater focus on renewable energy sources and the development of wind turbines has become increasingly popular. There are both advantages and disadvantages with the use of wind turbines. The wind turbines offer major advantages in the production of renewable energy, while at the same time causing interference in nature.

Wind turbines are continuously affected by varying wind forces that create cyclic stresses in the foundation. Over a typical 20-year life, a foundation can be exposed to up to 109 load cycles. These cyclic loads can lead to fractures in the concrete at stresses lower than the static breaking limit.

By using one year of wind measurements, a spectrum of fatigue loads applied to a foundation for a 100-meter-high wind turbine have been created. This spectrum has been used to control the concrete fatigue capacity in the foundation for compression and shear forces according to three different standards, NS-EN 1992-1-1:2004, Model Code 2010 and DNV-OS-C502. In addition, the expected lifetime of the foundation due to concrete fatigue has been calculated according to two of the standards.

After analysis of the results, it turns out that DNV-OS-C502 is the most suitable standard to use for concrete fatigue verification of wind turbine foundations, for both compression and shear forces.

Huge deviations in the results between the standards for both compression and shear were found, which indicates that concrete fatigue needs further development and better standardization.