Abstract Summary
The Reduced Column Section (RCS) approach is a design approach proposed by the Authors to redesign the connection between the wind tower and its foundation. The proposed segment of hourglass shape is a passive vibration-control device that combines the advantages of several approaches used in seismic engineering, such as isolation, energy dissipation and the “rocking approach" design developed for shallow foundations. The proposed device can be designed to modify the first natural frequency of the wind turbine and to localize the maximum stresses onto the device, resulting in the dynamic protection of the wind tower and its foundation. Analytical formulas to design the proposed RCS device are established. The benefits of the proposed device are assessed on a real onshore wind turbine located in Italy. The wind turbine has been monitored to derive its modal properties and record the maximum accelerations induced by the wind. Real registrations have been used to verify a numerical 3D-finite element model, created for performing seismic and dynamic analyses. Direct integration analysis with spectrum-compatible real earthquakes and an incremental dynamic analysis are conducted to evaluate the dynamic mitigation induced by the proposed RCS device. Soil-structure interaction effects are also considered. This study shows that the proposed device can efficiently mitigate the effective stresses on the wind tower wall by up to 60% compared to the stresses computed on the existing structure.
