Automated crack detection in axially loaded grouted connections of offshore wind turbines using embedded Fibre Bragg Grating sensor data

Grouted connections are critical components in offshore wind turbine foundations subjected to cyclic axial loading. Understanding their fatigue degradation is essential for structural integrity. This paper presents an application of a frequency-based method for automated crack detection and evaluation in grouted connections using embedded Fibre Bragg Grating (FBG) sensors. The method identifies mechanical response reversal, from grout compression to elongation at load peaks, linked to crack initiation, using short-time Fourier transform (STFT) analysis of FBG signals. Validated through fatigue testing, it enables robust, automated, and spatially resolved crack detection throughout the fatigue life. Statistical evaluation revealed typical crack progression from outer regions towards central shear key levels. A correlation was found between crack formation and displacement behaviour, segmented into stable, incremental, and progressive degradation phases. Rapid displacement increases in the progressive phase occurred only after cracks formed across all shear key levels, offering insights for damage detection and monitoring strategies. • Frequency-based method for internal crack detection • Short-time Fourier analysis identified crack phases in FBG sensor signals. • Polarity reversal in sensor response as robust crack initiation marker • Crack progression followed typical path from outer to central shear key levels. • Global displacement phases strongly correlated with internal cracking.