Stability analysis of wind-induced torsional motion of slender bridges

The paper presents a numerical, simulation-based approach to investigate th e stability of torsional motion of slender suspension bridges under stochas tic wind turbulence. The torsional bridge motion is represented by a linear , single degree of freedom oscillator. Stochastic turbulence in wind veloci ty is considered in the form of a periodic excitation with random phase mod ulation. The stability condition refers to the asymptotic sample stability, for which the necessary and sufficient condition is that the largest Lyapu nov exponent be negative. Monte Carlo simulation is performed to evaluate t he largest Lyapunov exponent, and stochastic differential equations of moti on are integrated in polar coordinates using Euler's scheme. Unlike earlier analytical approximations, a quadratic noise term is retained in the prese nt analysis. The turbulence intensity is shown to have a small stabilizing effect on the bridge stability in a sense that an increase in the turbulenc e intensity moderately increases the critical mean wind velocity beyond the deterministic flutter velocity. The stabilization effect is limited to the case of narrowband detuned excitation. In the proximity of the parametric resonance frequency, an increase in the bandwidth of the excitation process tends to stabilize the bridge motion. (C) 1999 Elsevier Science Ltd. All r ights reserved.