Assessment and comparative study of design method for onshore wind power plant foundations
Övrigt - Master's thesis, 2017
In recent years the demand for renewable energy has increased significantly, resulting in a large number of wind power plants being built. There has also been an increase in size of these towers and due to that an increase in the foundation size. The design of these foundations is a complicated process due to the complex loading on these towers. Especially the cyclic loads results in potential fatigue damage which gives cumbersome calculations with a lot of uncertainties.
The company WSP has designed several foundations over the years using a method developed by a professor at the Royal Institute of Technology in Stockholm. There was however a wish within the company to investigate the process and increase the knowledge. Another aim was to make the design process more efficient and for this a document capable of designing a foundation in little time was developed.
The aim of this study was to present a method that fulfills the standards set by the norms. In addition, some of the more problematic concepts will be discussed in more detail. The two major concepts analyzed in detail were wind loads and fatigue verification. The wind loads are often provided by the manufacturer of tower and are maybe not known in an early stage. Fatigue is one of the areas where designers have limited knowledge and it is an area where a lot of assumptions needs to be made in the design. Therefore, a more thorough investigation was done into this for both Eurocode and Model Code 2010. A comparison between the methods presented was also conducted to investigate potential improvements in the design process.
With the developed method three different case studies were made using three different wind towers. The studies concerned the influence of tower height, the life span of the foundation and the difference between using different partial safety factors, taken from Eurocode and IEC. The first study showed a clear relationship between the height and the design forces on the tower, and a moderate correlation between the height and the dimensions of the foundation. This study also showed that the influence of fatigue on the reinforcement increases with height and has a larger influence on the reinforcement in the top of the foundation. The second study showed that there is no major gain in designing a foundation for a 20-year life span instead of 50 years which is the value determined from Eurocode. Finally, the third study showed that there is little difference when designing according to IEC instead of designing according to Eurocode.
Wind power plant foundations