Seismic fragility curve development of an onshore wind turbine incorporating soil structure interaction effects

Abstract

In this study, a 900 kW onshore wind turbine supporting structure was modelled with finite elements in ANSYS software to perform nonlinear time history analyses. The structure has a tubular steel tower of 54 meters high, foundation with 26 rein forced concrete piles. The mass from rotor, nacelle and hub were applied to tower top as point mass with eccentricity. To incorporate soil-structure interaction effects, three different modelling approaches were used. Firstly, the soil medium was modelled explicitly together with piles and superstructure. The uncertainty related with the elasticity modulus of the soil was discussed by comparing the mode frequencies from finite element model with varying soil elasticity modulus values to those obtained by FDD of ambient vibration response from the accelerometers on the tower. In the sec ond model, the load-deformation relationships obtained by static nonlinear pushover analysis were defined in soil springs under the tower. Lastly, py, tz and qz springs attached to the piles were used to model soil properties. Three ground motion records were selected in accordance with 2018 Turkish Earthquake Resistant Building Design Guideline. Nonlinear time histories were applied to the three models and their re sponses were compared. Then, choosing one of the modelling approaches, fragility curves for the structure were constructed with limit states being tower drift and steel local buckling. The results showed tower drift to be the governing limit state. The failure probabilities for local buckling for the same PGA values were found to be much lower than for tower drift.