Non-Flutter Design Principle for long Span Bridges

The case of flutter on a sharp edged flat plate section model, with a height-to-width ratio of 1:10, has been investigated at four different torsional-to-vertical frequency ratios equal to 0.71, 0.88, 1.19 and 2.10. At a torsional-to-vertical frequency ratio of approximately 1.1 the flutter wind velocity for a thin airfoil shows an asymptotical behavior. In traditional bridge design the torsional-to-vertical frequency ratio is increased to obtain higher flutter wind velocities. In the present study, we investigate, what we will label the non-flutter design principle, in which the torsional-to-vertical frequency ratio will deliberately be smaller than 1. Two cases with frequency ratios of 1.19 and 2.10 showed classical and torsional flutter, respectively. Within the maximum wind velocity obtainable in the wind tunnel the two cases with a frequency ratio below 1 did not show any sign of aerodynamic instability. The results are a first indication the non-flutter design principle could be applicable in future design of slender structures.