Stochastic Stability of Bridges Considering Coupled Modes

Abstract

The stability of bridge structures in turbulent wind is investigated. The structural model is chosen to be a two‐degree‐of‐freedom system representing the first torsional and vertical bending modes of vibration of the bridge. These modes are assumed to be uncoupled structurally but coupled aerodynamically. The self‐excited loads are expressed in terms of convolution integrals with impulse‐response‐function type kernels. This formulation is shown to be equivalent to classical indicial function type representation. Assuming the random fluctuation of wind speed to be a random process with very short correlation time when carried by a high mean velocity, the equations of motion are converted to equivalent Ito equations. Based on these equations, moment stability boundaries in terms of mean wind speed and intensity of the turbulent fluctuation are derived. It is shown that turbulence can have a significant stabilizing effect if there is favorable aerodynamic coupling between the modes.