Efficient modal flexibility signal processing methodology for innovative identification of debonding zones in concrete-filled steel tubes

• Proposes MFIDI as a robust metric for delineating intermediate and end debonding zones in CFST columns. • Highlights interfacial debonding-induced decorrelation in primary and secondary vibration mode shapes. • Demonstrates amplified irregularity peaks with increasing damage intensity across debonding regions. • Establishes independence in identifying multiple debonding zones with negligible mutual interference. • Enables concurrent detection of critical debonding zones, prioritizing end-region damage in CFST columns. This study introduces a damage index to identify interfacial debonding in CFST composite columns, which is a damage type that impacts modal characteristics in the form of changes in frequency values. Moreover, the existence of damage is further approved by the lack of correlation between the primary and secondary shapes of vibration modes measured through the asymmetry of the angle matrix ( θ ) and Modal Scale Factors ( MSF ). To identify single and multiple debonding regions, a Modal Flexibility-Irregularity Detection Index ( MFIDI ) is suggested based on modal flexibility signal processing using the concept of curvature and considering the signal of impact factors 0 < I f ≤ 1 . The results indicate that by utilizing 2D MFIDI signals, the accumulation of negative and positive irregularity peaks occurs in the form of elevated peaks in debonding locations. Moreover, the heights of irregularity peaks are either zero or minimal in undamaged locations. Furthermore, using MFIDI , it is possible to identify the locations of debondings in the end regions of the column.