Titel: Three-dimensional strut-and-tie modelling of wind power plant foundations
Författare: Nicklas Landen, Jacob Lilljegren
Utgivare: Chalmers University of Technology
Årtal:2012
Sökord: wind power plant foundation, gravity foundations, 3D, three-dimensional, strut-and-tie model, fatigue, equivalent load, concrete
Rapport (Pdf)
Sammanfattning/Abstract:
With an increasing demand for renewable energy sources worldwide, a promising alternative is wind power. During the last decades the number of wind power plants and their size has increased. Wind power plant foundations are subjected to a centric load, resulting in a 3D stress distribution. Even though this is known, the common design practice today is to design the foundation on the basis of classical beam-theory.There is also an uncertainty of how to treat the fatigue loading in design. Since a wind power plant is highly subjected to large variety of load amplitudes the fatigue verification must be performed.
The purpose with this master thesis project was to clarify the uncertainties in the design of wind power plant foundations. The main objective was to study the possibility and suitability for designing wind power plant foundations with 3D strutand-tie modelling. The purpose was also to investigate the appropriateness of using sectional design for wind power plant foundations.
A reference case with fixed loads and geometry was designed according to Eurocode with the two different methods, i.e. beam-theory and strut-and-tie modelling. Fatigue assessment was performed with Palmgren-Miners law of damage summation and the use of an equivalent load. The shape of the foundation and reinforcement layout was investigated to find appropriate recommendations.
The centric loaded foundation results in D-regions and 3D stress flow which make the use of a strut-and-tie model an appropriate design method. The 3D strut-and-tie method properly simulates the 3D stress flow and is appropriate for design of Dregions. Regarding the common design practice the stress variation in transverse direction is not considered. Hence the design procedure is incomplete. If the linearelastic stress distribution is determined, regions without stress variation in transverse direction can be distinguished. Those regions can be designed with beam-theory while the other regions are designed with a 3D strut-and-tie model.
Further, clarifications of fatigue assessment regarding the use of an equivalent load for reinforced concrete need to be recognized. The method of using an equivalent load in fatigue calculations would considerably simplify the calculations for both reinforcement and concrete.
We found the use of 3D strut-and-tie method appropriate for designing wind power plant foundations. But the need for computational aid or an equivalent load are recommended in order to perform fatigue assessment.