Vortex-induced vibrations of the Second Severn Crossing cable-stayed bridge—full-scale and wind tunnel measurements

In the first winter after opening, the Second Severn Crossing cable-stayed bridge exhibited occasional vortex-induced vertical oscillations. Vortex excitation had been detected by the wind tunnel tests on sectional models during design and an aerodynamic solution partly developed but, based on damping and turbulence assumptions from recognised design codes, it had been concluded that the probability of large vibrations occurring was small. Full-scale monitoring of both wind and structural response enabled the causes of the observed oscillations to be investigated. The structural damping and wind turbulence were found to differ significantly from the assumed values. Additional wind tunnel tests were undertaken using the full-scale measured values with a view to replicating the full-scale behaviour and developing a solution. Taking into consideration the revised damping and turbulence and an often-ignored factor to correct for the full-scale mode shape, good agreement between the model and full-scale measurements was obtained. Also, aerodynamic solutions were further explored, as a result of which baffle plates were installed under the bridge. Since their installation, no further signs of vortex-induced oscillations have been observed.