Shaking table test on seismic responses of a wind turbine tower subjected to pulse-type near-field ground motions

Near-field records with long-period velocity pulses can be considered as a most important factor in causing structural damage. In order to understand the effects of near-field records on the seismic behavior of a 2.0 MW land-based wind turbine, a 1/20-scaled model is designed and investigated by shaking table test. Two pulse-type near-field records (Westmorland record, Chi-Chi record) and two far-field records (Taft record, El-Centro record) are chosen as the input ground motions. The dynamic characteristic, acceleration, displacement, strain and shear force of this structure are measured and compared. The experimental results show that the wind turbine remains in elastic stage during this test. The pulse-type near-field records generally has an amplification effect on the acceleration response at the bottom and top of the tower. The effects of Chi-Chi records on the acceleration and displacement response of the tower top, nacelle and hub are particularly obvious. The vertical displacements at the tower top under Chi-Chi excitation are almost 5.6 times that under El-Centro record excitation. The maximum circumferential and vertical strains appear in the middle and lower part of this tower under the horizontal earthquake excitation, which occur at 1/2-3/4 height of the tower under the vertical earthquake. This study emphasizes the importance of incorporating the pulse-type near-field effects into seismic design of wind turbines, especially for those located in near active fault.