In this paper, the modal coupling mechanism is studied of a single-span footbridge consisting of a suspended beam (i.e., bridge deck), two suspension cables (via hangers) and two wind guys (via wind ties). To start, the governing equations for the slender suspended beam are derived based on the linearized deflection theory for classical suspension bridges, which is followed by two parts. First, the free vibration analysis is conducted to obtain the modal frequencies and modal shapes of the suspended beam by Galerkin’s method, from which the key parameters dominating the flexural-torsional coupled vibrations are identified, along with measures for stiffness enhancement. Then, a virtual eccentrically moving vehicle is first attempted to scan (i.e. extract) the vibration messages of the suspended beam from a perspective that allows us to physically interpret the dominant mode of the flexural-torsional coupling of the beam in an easy way. The objective of this study is twofold: first to offer a complete nonlinear vibration theory for the suspension footbridge, and second to physically interpret the complicated mechanism of coupling involved.
