Frequency characteristics in various flutter instabilities of bridge girders

Since flutter is one of the divergent-type oscillations, the onset of flutter directly induces structural failure. Therefore, in the design of super-long spanned bridges, flutter stability has to be carefully investigated not to excite the flutter oscillation below the designed wind velocity. It has been reported that the change of the geometrical shape of the bridge girder makes various types of flutter, since it characterizes the flow field around the body, such as flow separation, separated-flow reattachment and so on. Each flutter type has different frequency characteristics; however, little is known about the relation between the flutter type and the frequency characteristics. The aim of this paper is to clarify the flutter mechanism from the point of frequency characteristics related with the aerodynamic derivatives.