Estimation of Damping Ratio from Operational Monitoring of Cable-Stayed Bridge

Abstract

Estimation of Damping Ratio from Operational Monitoring of Cable-Stayed Bridge

Interference Vortex-Induced Vibration (VIV) has been observed for Second Jindo Bridge. A previous study with wind tunnel tests suggests that VIV was due to low structural damping ratio (0.2%). Multiple Tuned Mass Damper (MTMD) has been installed in Second Jindo deck to mitigate amplitude of vibration. This study verifies the assumption of low structural damping ratio for the first vertical mode of vibration with field measurements. Based on monitored data, modal parameters are obtained using NExT-ERA time domain method. Results of damping ratio are in good agreement with the wind tunnel tests (average 0.3%). However, this structural damping ratio is lower than the recommended value by Korean Design Guidelines. Estimation of modal parameters for First Jindo Bridge shows a higher damping ratio than second bridge (average 0.5%). As expected, the acceleration monitored with the MTMD operating in Second Jindo Bridge provides a higher damping ratio. When wind conditions create VIV, larger RMS accelerations can be observed, while MTMD is kept under fixed conditions. On the other hand, after releasing the MTMD, the amplitude of vibration is within the usual range and damping ratio increases with an average of 3.4%. In the present investigation, it has been successfully demonstrated that MTMD design is an efficient method to mitigate VIV.