Experimental study and mathematical modeling on the unsteady galloping of a bridge deck with open cross section

Galloping instability can potentially threaten the modern launching of steel-concrete composite bridge girders, due to light weight and bluff shape of the steel box, which is normally launched first. A bridge deck with typical open cross section was selected and investigated in smooth flow through wind tunnel techniques. Aeroelastic tests showed that the classical instability arising from the interaction between vortex-induced vibration and galloping may occur for a mean flow incidence of 4 degrees, fixing the actual galloping onset at the Karman-vortex-resonance wind speed up to a high value of the mass-damping parameter. In contrast, a different and more complicated behavior was observed for a mean flow incidence of 0 degrees, where the actual galloping instability occurs at a wind speed clearly higher than the Karman-vortex-resonance wind speed even for a very low value of the mass-damping parameter. Static tests further 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. A rectangular cylinder with the same side ratio was also tested for the sake of comparison. Finally, Tamura's wake-oscillator model was implemented for the bridge deck at a mean flow incidence of 4 degrees, following a recently proposed parameter identification method. The mathematical model was found to be able to give some promising predictions even for a complex bridge deck profile.