Effects of Turbulence on Bridge Model Torsional Stability

A 1:64 scale section model of a recently constructed suspension bridge was tested in smooth and turbulent flow with and without an upstream obstacle. Testing was limited to determination of aerodynamic damping on a model confined to single-degree-of-freedom torsional motion. The upstream obstacle selected was a 1:64 replica of a cable-stayed bridge (basically a flat plate on a narrower box). The truss model (without an obstruction) showed little change in response due to turbulence intensity typical of an elevated open site. The upstream model produced high turbulence intensity levels even in smooth flow. In so far as catastrophic torsion was concerned the cable-stayed bridge model actually shielded the truss model producing some effect to a streamwise spacing of 10 times the truss dimension. Caution must be used in application of these results since different designs may produce different results. With any upstream structure, non-catastrophic buffeting is a possibility, with increased turbulence intensities possibly producing difficulties in vehicle control.