Probabilistic assessment of collapse in medium wind turbines under wind-driven multi-mechanism actions

This study investigates the structural reliability and collapse susceptibility of small- and medium-scale onshore wind turbines, which constitute a large portion of Europe’s installed capacity and are increasingly deployed under diverse environmental and geotechnical conditions. While tower–foundation systems are essential for overall stability, their collapse mechanisms remain insufficiently understood because they generally arise from the interaction of extreme wind events, soil–structure interaction, material degradation, construction deficiencies, and operational anomalies rather than from isolated causes. A comprehensive probabilistic framework is developed and applied to a representative medium-scale wind turbine supported by shallow foundations. The methodology combines a review of current design standards, detailed geometric and mechanical characterization of the prototype, site-specific modelling of wind and operational loads, calibrated finite-element analyses, and code-based global-to-local structural verifications. Multiple wind-driven degradation scenarios, including extreme gusts, control-system malfunctions, global and local fatigue, and soil-stiffness variations, are investigated to quantify the cumulative probability of collapse associated with each failure mechanism. Rather than generating fragility curves, the proposed framework directly compares the relative contribution of the investigated collapse mechanisms within a unified reliability-oriented assessment. The results identify the circumferential tower-to-base weld as the governing structural vulnerability, while excluding global tower fatigue as a plausible collapse trigger over the investigated operational period. The proposed methodology provides a transferable framework for structural assessment, maintenance planning, and risk-informed decision-making for small- and medium-scale onshore wind turbines.