ROBUST VIBRATION SERVICEABILITY DESIGN OF A TUNED MASS DAMPER FOR THE PHÉNIX FOOTBRIDGE

Slender structures such as footbridges may be prone to human induced vibrations such that vibration mitigation devices as TMD's are adopted to increase the structural damping.Both the prediction of the structural response and the tuning of the TMD parameters rely on the modal parameters of the footbridge.These parameters are subjected to uncertainty in design stage, when only an estimation can be made for example using finite element models.After construction, the natural frequency and damping ratio can be measured but variations due to environmental effects such as temperature can result in parameter variations.Therefore it is important to take into account these uncertainties for the vibration serviceability assessment and the design of the TMD.The present paper proposes a robust TMD design which adopts a worst case approach to take into account uncertainties in design stage.The proposed approach is illustrated for the Phénix footbridge.Considering an uncertain natural frequency and damping value for the case study, a worst case approach is adopted to determine the optimal values of the TMD mass, stiffness and damping.A significant difference is found between the optimal TMD parameters of a nominal and robust tuned TMD.The mass and damping ratio of the robust TMD are found to be much higher than for the TMD tuned at nominal values of the natural frequency and damping ratio.This ensures that the comfort constraints are satisfied in all possible cases.