Motion of Suspended Bridge Spans under Gusty Wind

The buffeting response of suspended-span bridges can be calculated if certain wind-tunnel section model data, plus wind spectral information, are provided. The needed wind tunnel data are the self-excited aerodynamic (flutter) coefficients. The meteorological data required are vertical and horizontal gust spectra of the natural wind at the bridge site. The natural mechanical modes of vibration in bending (vertical and lateral) and torsion are assumed known, and the response of each of these with postulated negligible aerodynamic coupling between modes, is calculated. Some examples are then given of the calculated vertical and torsional buffeting responses of a flexible long-span bridge (Golden Gate type) and a stiff, medium-span type (Sitka Harbor). The wind velocity range covered is 60 mph to 90 mph (27 m/s to 40 m/s).