Amplitude and Turbulence Effects on Bridge Flutter Derivatives

The paper refers to established theory for the flutter of long-span bridges. Within that theory it is shown that the assumption of a spanwise diminution of coherence in the flutter derivatives can account for the observed phenomenon that turbulence in the cross wind raises the critical speed of instability. This finding is supported by data from two recent model studies of the aerodynamic stability of the Golden Gate Bridge. In this illustrative case the flutter instability condition is uniquely dependent upon a single torsional mode, the aerodynamic damping of which is influenced in a pronounced manner as changes in spanwise coherence effects are postulated. Overall, an observed increase of flutter velocity by 10 to 20% over that under smooth flow is theoretically accounted for.