Seismic analysis and risk assessment of wind turbines

The seismic analyses of two different sizes of wind turbines are investigated in this thesis. The first turbine is a relatively short wind turbine previously subjected to a shake table test. The main objective of this part is to evaluate the accuracy of the finite element model based on the experimental results. Effects of adding the blades to the FEM are investigated. The effects of a detailed model are observed on higher natural frequencies of the structure; however, for this case, those frequencies do not fall into a critical range with regards to the tower's seismic response. The structure is then subjected to a magnified ground motion and nonlinear time history analysis is conducted in order to observe its failure modes. The wind turbine tower is observed to buckle in the vicinity of the lower joint of the tower. The second wind turbine is a modern wind turbine currently operating in one of the campuses of Bo\u{g}azi\c{c}i University. A detailed finite element model is constructed using available information such as the mass distribution. The structure is analyzed using nonlinear time history analyses under earthquakes selected from the Los Angeles, California earthquake suit. The turbine tower is observed to buckle around the areas where there is a thickness change in the wall thickness; however, the level of seismic motion that leads to such failures is significantly high. The base moment demands calculated on the surface of the foundation are significant, and there is a possibility that seismic loads may govern design.