Robust vibration serviceability assessment of footbridges subjected to pedestrian excitation: strategy and applications

The present paper proposes a strategy for the robust vibration serviceability assessment of footbridges. The response of the footbridge to vertical walking loading is predicted by simulating continuous flows of pedestrians on the structure. In the calculations, both variability in the walking characteristics and human-structure interaction effects are accounted for. Uncertainty in the modal parameters of the footbridge is considered in a multi-interval approach. The resulting range in predicted response levels is subsequently compared to vibration comfort criteria. A case study serves as illustration of the procedure. First, the response of the footbridge is evaluated in a multi-interval assessment showing how the predicted vibration levels are affected by uncertainties. The multi-interval approach allows understanding how uncertainties in the modal parameters of the structure affects the response. Second, the procedure is applied for the design of Tuned Mass Dampers (TMD). The TMD parameters are tuned by solving an optimisation problem such that an effective reduction of the accelerations under realistic walking scenarios is ensured. The total TMD mass is minimised, considered as the determining factor for the cost of the TMD. A higher TMD mass is needed to satisfy the vibration serviceability constraints for higher levels of uncertainty, showing the trade-off between cost and robustness.