Buffeting-Induced Resonances of Hangers at a Long-Span Suspension Bridge and Mitigation Countermeasure

Abstract

Buffeting-induced oscillations of hangers at a suspension bridge have been addressed in this work. The buffeting is obtained by a dynamic finite-element analysis procedure in the time domain, with simulated turbulent wind fields and experimentally obtained load parameters. Wind loadings inherent to the hangers are neglected intentionally to exclude potential interference. Dynamic properties of hangers are simulated by discretizing them into a number of elements. The numerical results show that a number of long hangers can experience large-amplitude oscillations due to the main structure’s buffeting at a moderate wind speed. Motions of the hangers are mainly contributed by their first-order modal shapes. The hangers oscillate in both directions in the horizontal plane, with motions in the longitudinal direction being more violent than in the lateral direction. Moreover, it is found that the dominant frequency of a single hanger in one direction differs slightly from that in the other, thereby causing an ever-changing phase angle between the two motions. Fourier transforms of the time series indicate that excitations resulting in the resonances are from the main cables. The functional motion component at cable-hanger intersections can be as small as a couple of millimeters, which can result in hangers’ motions as large as 300 mm. Replacement of steel wire hangers with carbon fiber-reinforced polymer (CFRP) ones can restrain effectively the resonance. However, replacements over an insufficient range of hangers may result in transferring of the resonance to neighboring ones, and a comprehensive mitigation necessitates replacements over quite a wide range along the bridge deck.