SEISMIC DAMAGE OF WIND TURBINE TOWER UNDER MAINSHOCK-AFTERSHOCK EARTHQUAKE SEQUENCE

After the mainshock causes damage to the wind turbine tower, the occurrence of aftershocks may cause "secondary damage" to the tower, as a result, the wind turbine tower designed according to traditional seismic design code may be unsafe. In order to quantitatively analyze the additional damage caused by aftershocks to the wind turbine tower, firstly, 25 original mainshock-aftershock earthquake sequences were selected from the Pacific Seismic Center of the United States, and artificially constructed 75 mainshock-aftershock earthquake sequences using the repetition method, the random method and the attenuation method. Secondly, the finite element model of the wind turbine tower was established, and the additional damage coefficient of aftershocks was proposed based on the theory of steel fatigue cumulative damage to quantitatively analyze the additional damage caused by aftershocks. The three methods of artificially constructing mainshock-aftershock earthquake sequences were compared in term of the additional damage of aftershocks. Finally, combined with the incremental dynamic analysis, the influences of the peak acceleration and the ratio of the peak acceleration of the mainshock-aftershock earthquake sequences on the additional damage caused by the aftershock and the dynamic response of the wind turbine tower were discussed. The results show that, compared with the mainshock, the aftershock earthquake sequences have a wider interval of displacement sensitive region and a narrower interval of acceleration sensitive region. The artificially constructed mainshock-aftershock earthquake sequences using the attenuation method is the closest to the natural mainshock-aftershock earthquake sequences. The additional damage coefficient of aftershocks depends on the ratio of peak acceleration of mainshock-aftershock earthquake sequences and the main energy dissipation form of the wind turbine tower. The additional damage coefficient of aftershocks changes slightly at the non-main part of energy dissipating in the non-down-tower state, but surges at the main part of energy dissipating in the down-to-tower state.