Control of vortex-induced oscillations of a suspension foot bridge by tuned mass dampers

The across-wind oscillations due to vortex-shedding from the deck are often of concern in the design of suspension and cable-stayed bridges. This kind of oscillations may cause cumulated damage to the structural elements due to fatigue and discomfort to the users. The vortex-shedding can arise for wind velocities usually lower, and therefore more likely to occur, than those corresponding to other aeroelastic phenomena, like flutter or torsional divergence. In this paper, the control of vortex-induced oscillations of a suspension bridge by Tuned Mass Dampers (TMDs) is dealt with; namely, a procedure for the design and location of the control devices is implemented and applied, as a case example, to a suspension footbridge with a span of 252 m. The evaluation of the structural response is obtained in time domain by a finite element model, that allows the optimal location of the TMDs, according to the modal shapes involved in the vortex-shedding excitation, as well as the calibration of their characteristics. The dynamic parameters of the TMDs are optimised through a parametric analysis, that considers the main aspects of the dynamic response of the coupled system. The ef-ficiency of the control system is proved by comparison of the responses of the bridge deck with and without TMDs.