Influence of low-frequency wind speed fluctuations on the aeroelastic stability of suspension bridges

Starting from the standard multimode approach to the aeroelastic instability of a long span suspension bridge, that gives the critical flutter speed in the ideal case of a wind constant both in time and in space (turbulence neglected), this paper describes a procedure to evaluate in a closed form the worst effects that can ever be expected as a consequence of a turbulence with a given spectrum. To this respect, only low-frequency wind speed fluctuations strongly correlated along the span are taken into account, neglecting the beneficial effects due to a loss of coherence or to higher frequency components. This allows to obtain a flutter speed certainly safe in comparison with any realistic turbulence field. The proposed formulation is then applied to the current design of the bridge on the Messina Strait (Italy).