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This study investigates the structural health of bridges by introducing the appearance frequency harmonic (AFH) coefficient, a novel parameter for monitoring structural stability. The research encompasses the analysis of vibration data from 14 bridges, including 11 simply supported bridges, 2 cable-stayed bridges, and 1 steel-truss bridge, over multiple measurement sessions conducted across two years. By utilizing the circle power spectrum density (CPSD) method, the study evaluates harmonic frequency appearances under varying live traffic loads and environmental conditions. The findings highlight the critical role of structural stiffness, with increased stiffness correlating to higher appearance frequencies of fundamental vibrations. In contrast, older bridges with reduced stiffness exhibit significant variability in the appearance frequencies of harmonic vibrations. Importantly, the fundamental frequencies of all surveyed spans remained stable throughout the research period, underscoring their limited sensitivity to minor structural changes. This study demonstrates the practical value of the AFH coefficient and CPSD, which go beyond traditional monitoring methods by enabling early detection of structural degradation and offering cost-effective, scalable solutions for regular bridge monitoring. These findings provide a strong foundation for integrating AFH into bridge health monitoring protocols and underscore the necessity of continuous monitoring to ensure long-term structural integrity and functionality.
Nguyen et al. (Fri,) studied this question.