Wind tunnel test on the galloping instability of a bridge deck with open cross section

The galloping instability was experimentally investigated for a bridge deck with open trape-zoidal cross section, representing a typical cross section type during the construction phase of steel-concrete composite bridge girders. In smooth flow, unsteady galloping due to a strong interaction with vortex-induced vibration was observed for this bridged deck around a wind angle of attack of 4°, being the actual galloping onset fixed at the Kármán-vortex-resonance wind speed when the Scruton number is not higher than 70. This interaction was not encoun-tered at the null wind angle of attack. Aerodynamic force measurements on stationary model indicated that the most evident difference between the two cases is the magnitude of the vortex shedding force, which is much lower for a null angle of attack. First results in turbulent flow with an intensity from 8.7% to 13.9% were also reported.