Shake Table Testing of a Utility-Scale Wind Turbine

Abstract

Shake table tests were undertaken on a full-scale wind turbine (65-kW rated power, 22.6-m hub height, and 16-m rotor diameter) using the Network for Earthquake Engineering Simulation Large High Performance Outdoor Shake Table at the University of California, San Diego. Structural response characteristics and modal parameters are presented for base shaking imparted in two configurations, both parallel (configuration 1) and perpendicular (configuration 2) to the axis of rotation of the rotor. Results are summarized for a series of progressively stronger motions imparted in configuration 1, with analysis identifying damage sources leading to an overall loss in stiffness. Two sources of observed softening are identified and quantified: (1) degradation of grout at the tower base, and (2) loss of bolt torque at the connections between tower segments. Results showed that the two configurations had little difference in structural response and demand parameters. For the tested turbine, with appropriate consideration of boundary conditions and modal characteristics, linear theory for a single degree-of-freedom system can explain most of the observed dynamics. Although not significant for the tested turbine, it was observed that higher mode behavior may be important for large turbines.