Bridge Flutter Stability in Turbulent Flow

Despite the many studies on suspension bridge flutter stability, the influence of turbulence has not been completely understood yet. Experimental and numerical results have shown that atmospheric turbulence may have either a stabilising or a destabilising influence. This work investigates the alteration of the flutter stability threshold due to the parametric modulation of self-excited forces due to large-scale turbulence. Such an effect is considered through the 2D rational function approximation model for self-excited forces. First, a Monte Carlo method addresses the stochastic stability of a three-degree-of-freedom two-dimensional model of the Hardanger Bridge, Norway, subjected to different turbulent wind conditions. Such an approach highlights the sensitivity of flutter stability to turbulence parameters, but does not allow any interpretation of the instability mechanism. Then, Floquet multipliers are used to study the stability of the system obtained by assuming a harmonic slowly-varying angle of attack. This simplified scenario is particularly suitable to underline parametric effects that are often hidden in case of random broad-band parametric excitation. For the considered case study, the paper emphasises a significant destabilising effect of large-scale turbulence and a stabilising role played by the lateral degree of freedom in the simplified time-periodic system.