Damping identification of MR-damped bridge cables from in-situ monitoring under wind-rain-excited conditions

The newly built cable-stayed Dongting Lake Bridge in Hunan, China has experienced wind-rain-induced cable vibration several times during the past months. A research/implementation project on using semi-active magneto-rheological (MR) dampers for cable vibration control of the bridge is in progress. As part of this ongoing project, one typical stay cable with 115 m length was installed with two MR dampers near the lower anchorage, and accelerometers were deployed on the damped cable and its two neighboring cables for long-term monitoring. After installing the dampers and sensors, wind-rain-induced cable oscillations were observed two times. This paper aims to investigate the vibration characteristics and to identify the equivalent modal damping of the cables with and without MR dampers in one wind-rain-excited event based on in-situ monitoring. In this wind-rain-excited event, the in-plane and out-of-plane responses of the damped cable and its two neighboring free cables were monitored. Equivalent modal damping ratios of the cables in both in-plane and out-of-plane motions are identified by means of spectral analysis of the measured data in conjunction with a curve-fitting technique. Such observed and identified results are beneficial to understanding the coupled motion of cables in wind-rain-excited conditions and the damping contribution of MR dampers to both in-plane and out-of-plane motions. The frequency-domain analysis of the wind-rain-excited responses of the damped and undamped cables also reveals the response characteristics under wind-rain excitation and the damping mechanism of MR dampers in suppressing such oscillation.