Field Validation of OMA-Based Damping Estimates for Evaluating Multiple Tuned Mass Dampers

Vortex-induced vibrations (VIVs) pose a significant serviceability and fatigue concern for long-span cable-stayed bridges, which are characterized by low natural frequencies and limited structural damping. Tuned mass dampers (TMDs) are widely used to mitigate VIVs, but evaluating their effectiveness requires accurate estimation of modal damping ratios. Operational modal analysis (OMA) using ambient vibration data has become a practical tool for in-service damping estimation, though its accuracy is often compromised by low signal-to-noise ratios, algorithmic sensitivity, and environmental variability. In this regard, this study presents field validation of OMA-based damping estimation using long-term structural health monitoring (SHM) data from a cable-stayed bridge equipped with a multiple TMD (MTMD) system. Ambient vibration measurements collected before and after the MTMD installation were analyzed using a displacement-reconstruction approach. Additionally, a field excitation test utilizing one TMD unit was conducted to obtain a reference damping ratio. The results demonstrate that OMA, when combined with displacement reconstruction, yields reliable damping estimates that closely align with the reference value. The findings further reveal the amplitude-dependent activation of the MTMD system, with effective damping achieved only under sufficient wind-induced excitation. These insights offer practical implications for evaluating damping and verifying the performance of passive control devices under operational bridge conditions. These findings highlight the applicability of OMA for in-service evaluation of passive vibration-control devices and provide practical implications for assessing bridge serviceability and MTMD performance under operational conditions.