Fatigue–Chloride Time‐Sequential Effects on UHPC Fatigue Performance for Nearshore Wind Turbine Towers

ABSTRACT This study investigates the fatigue degradation mechanism of ultra‐high‐performance concrete (UHPC) in nearshore wind turbine towers under the time‐sequential effects of wind‐induced fatigue and chloride erosion. Through a comprehensive experimental program, UHPC specimens were subjected to initial fatigue loading, chloride erosion, and secondary fatigue loading (up to 2 million cycles). Results show that chloride ion concentration peaks in the mid‐span tensile zone and decreases with depth and distance. Initial fatigue damage significantly increases diffusion by forming microcrack networks. Scanning electron microscopy (SEM) analysis highlights severe steel fiber corrosion, interfacial debonding, and pullout damage, driven by fatigue–chloride interaction, which reduces fiber bridging capacity and accelerates fatigue damage. A chloride diffusion model based on Fick's second law was developed, achieving an average prediction error of 5.10%–8.93% against experimental data. Additionally, a modified fatigue damage model incorporating a “fatigue–erosion” time‐sequential damage index was proposed, conservatively enveloping experimental damage curves. The findings underscore the synergistic deterioration from fatigue‐induced cracking and chloride corrosion, providing critical insights for enhancing the durability design of UHPC in chloride‐rich coastal environments.