Disastrous Effect of Earthquakes on Monopole and Hybrid Wind Turbine Towers: An Analysis Incorporating Soil-Structure Interaction

With the increase in scale of wind power generation, seismic stability of large turbine support structures, especially monopole and hybrid towers, is becoming central, in areas with varying soil profiles and high seismic activity. This study uses nonlinear time-history analysis based on finite elements to compare the dynamic behavior of such towers under earthquake loading with explicit consideration of soil-structure interaction (SSI). The models were subjected to the ground motions induced by the 2001 Bhuj and 2015 Nepal earthquakes and the displacement at the top of the nacelle, base shear and the bending moments were evaluated with different soil profiles. It is found that the hybrid towers have significantly superior performance, having lower displacements, significantly lower base shear and moments compared with monopole towers. In monopoles towers, SSI increased displacements (e.g. 57.9 % increase in fore-aft nacelle displacement during the Bhuj event), but decreased base forces (e.g. 20 % decrease in base shear). Interestingly, side-to-side responses in case of base moment were larger than fore-aft motions in both towers. SSI and variation in soil profiles have no effect on hybrid towers. Earthquakes are a disaster risk for wind turbine towers through shaking of the ground, failure of foundations and interaction with operational loads and can cause tilting and buckling or operational shutdowns in wind farms. The findings strengthen the case of hybrid towers in terms of earthquake resistance and provide valuable information in relation to improving the safety and sustainability of wind turbines in earthquake prone regions to prevent failure of structure and disaster.