Analysis of the influence of cumulative damage on the structural fragility of medium-height wind turbine towers

Abstract

This study analyzes the influence of cumulative fatigue damage on the structural fragility of medium-height steel wind turbine towers (70, 75, 80, and 85 meters). The proposed methodology is applied to representative towers located in the region of "La Ventosa" in Oaxaca, which is known for its high wind power. The analysis focuses on the progressive accumulation of damage at the base of the towers, where critical stress concentrations develop due to dynamic loads induced by wind. The methodology is developed in three stages: 1) determination of acting forces, 2) fatigue analysis, and 3) structural fragility analysis over time. In the first stage, turbulent wind speeds are simulated to characterize forces acting on the tower and at the rotor center. In the second stage, a transient dynamic analysis is conducted to obtain the stress values at the base of the tower. Subsequently, the Rainflow counting technique is applied to quantify cumulative damage through fatigue analysis. Finally, in the third stage, incremental dynamic analyses (IDA) are performed to generate fragility curves considering two scenarios: 1) towers without cumulative damage, and 2) towers with cumulative damage after 35 years of operation. The results of this study indicate that wind turbine towers exceed a service life of 20 years. Furthermore, it was observed that fatigue damage primarily impacts the structural fragility of shorter towers, as these are subjected to a higher accumulation of load cycles and greater damage compared to taller towers.