Vibration Control of a Long Span Cable-stayed Bridge Tower Using Pendulum Mass Damper

The configuration of long span cable-stayed bridge varies at different construction stages and so does its natural frequencies. The vibration control performance of a multi-stage pendulum mass damper (MPMD), whose natural frequency can be altered by controlling the pendulum wire length, was studied for mitigation of the wind-induced vibration of a long span cable-stayed bridge tower during construction. A theoretical framework for predicting the buffeting response of the coupled MPMD-bridge system was first developed. Four different construction stages of the bridge were selected for study. The effectiveness of MPMD was further examined by an experimental investigation. A 1:100 scale model of the bridge tower together with a two-stage pendulum mass damper were designed and manufactured. Two kinds of excitations, harmonic and white noise excitation, were applied respectively in the lateral direction of the bridge tower (ie in the direction normal to the bridge longitudinal axis), which was considered as the most critical loading direction. The effect of various parameters, including damping ratio, mass ratio, and frequency tuning ratio of the damper, was considered in this study. Both the theoretical and experimental investigations showed that the MPMD can significantly reduce the displacement responses of the bridge tower for the concerned construction stages and the total damping of the tower was enhanced significantly by the MPMD.