New developments in bridge flutter analysis

The first part of this paper is devoted to an approximate approach to flutter, which is attained through simplification of the flutter equations. The critical wind speed and the flutter frequency can be calculated with the proposed formulas by employing only three flutter derivatives instead of the usual eight coefficients. This approach may be seen as an easy engineering tool for a better tailoring of bridge structures at early design stages. In addition, the simplicity of the equations allows better understanding of the mechanism of flutter instability and the role played by structural parameters such as damping. In particular, an explanation is provided for soft- and hard-type flutter. The second part of the paper outlines a model to take into account the uncertainty in the measurement of self-excited forces in a flutter analysis. Ad hoc wind tunnel tests allowed determination of the statistical properties of the measured flutter derivatives. These coefficients are treated as independent normally distributed random variables and Monte Carlo simulations are performed in order to determine the probability distribution function of the critical wind speed. The paper concludes with an example of application of the proposed probabilistic flutter assessment method.