Damage Detection and Identification in a Column under the Effect of Axial Load Using Modal Properties and Mode Shape-based Detection Index

From the past until now, monitoring the health of structures and identifying different locations of damage to their elements have always been one of the basic requirements of maintaining structures and ensuring the safety of residents. Damage is defined as any modification to the shape or material characteristics of a structure that could impair its overall performance. Irreversible damages to structures can be avoided by promptly identifying, repairing, and replacing any damaged components in early stages. Damage to columns, one of the most vital elements of building structures and bridges, can pose serious concerns about the overall health of the structures compared to damage to other elements. This study proposes a detection index based on the slope and curvature of the mode and explores its usefulness in identifying distinct sites of column damage under axial load. The preliminary findings of this research revealed that as the axial load increases, the value of the natural frequency of all modes drops in both healthy and damaged conditions. Considering that the given columns may buckle and become unstable under the impact of axial load less than the design axial load due to damage, this underlines the necessity of addressing the problem of damage detection in columns under this load. The results also demonstrate that the frequency values of healthy and damaged conditions are different due to damage. Damage detection using the suggested index indicates that it is sensitive to the position of the damage, and that by establishing relative maxima in the damaged area, it is possible to recognize the location of the damage with an error less than one percent. In addition, the findings demonstrated that while the amount of axial load affects frequency values, it does not have any effect on the values of the damage detection index.