Predicting flutter speed of a cable-stayed bridge

Cable-stayed bridges are prone to wind-induced instabilities owing to their smaller frequencies. Further, because of the closeness of torsional and vertical bending frequencies they are more likely to suffer from classical flutter. In this paper, empirical formulae have been proposed for estimating the basic frequencies as well as the flutter critical wind speed. Corroborative examples of a few cable-stayed bridges of different spans, namely, Karkinen, Nanpu, Yangpu and Oresund, have been considered. The flutter critical speeds of these bridges by the proposed method have been compared with those obtained from Selberg's formula and the Chinese method. Lastly, based on the safety margins with respect to the critical flutter speeds, cable-stayed bridges have been categorised into three groups, and the need for wind tunnel tests has been proposed. It is expected that the approach provided here will serve as a ready reckoner for cable-stayed bridge designers and will help reduce the project cost and time by assessing the flutter susceptibility of bridges.