Three-Dimensional Flutter Characteristics of a Long-Span Shallow Stress-Ribbon Pedestrian Bridge

Earlier studies on stress-ribbon bridges showed that their natural modes of lateral vibration may be coupled with torsional motion; however the influence of coupling on flutter instability remains largely unexplored. This study aims to clarify the flutter mechanism of shallow stress-ribbon bridges and its implications on applicability of section model tests. Aeroelastic stability analysis of a 618 m long pedestrian stress-ribbon bridge is carried out by complex eigenvalue method. Several nominal flutter critical points are observed, corresponding to different torsional-mode branches. The fundamental flutter with the lowest critical wind velocity is originated from the coupled lateral–torsional mode branch; the corresponding flutter mode shape is characterized by the coupled vertical–torsional motion with a significant lateral component. The spring-mounted section model tests further confirm that the coupled lateral–torsional mode branch triggers flutter prior to the pure torsional mode branch. In addition, bimodal flutter analysis indicates that the multimode contribution effect is negligible for the fundamental flutter, but it becomes significant for the higher-mode flutter. When the self-excited drag forces and the forces (lift and moment) excited by lateral motion are considered, the critical wind velocity can decrease up to 11.1%, depending on the magnitudes of these forces. The wind-resistant cable scheme increased the flutter onset velocity by 115%, reaching 86.0 m/s. The present study underscores the importance of three-dimensional flutter analysis to select a suitable mode combination for wind tunnel tests, and highlights the contribution from drag forces and forces due to lateral motion that should be considered carefully.