A simplified approach to bridge deck flutter

Flutter instability of flexible bridge decks is investigated in the framework of the semi-empirical Scanlan's approach based on flutter derivatives. The equations of the eigenvalue problem of stability are manipulated and simplified thanks to the analysis of a large number of dynamic and aerodynamic data. Simple expressions for critical reduced wind speed and coupling frequency are obtained. The major interest of this approximate method is the fact that only three or even two flutter derivatives are required to calculate the flutter instability limit. In addition, these aerodynamic functions are known to be quite reliable and the easiest to be identified through wind-tunnel tests. The proposed formulas seem to give accurate results in a wide range of cases, unless the frequency ratio is very close to unity. The method is shown to apply also in case of cross sections prone to torsional flutter. Finally, the paper offers a valuable insight into the flutter behavior of several types of bridges and investigates the role in the instability onset played by various structural parameters, such as frequency ratio and structural damping.