Pedestrian-induced torsional vibrations of suspended footbridges: Proposal and evaluation of vibration countermeasures

The aim of the paper is to propose and evaluate different design arrangements addressed to mitigate the in-service pedestrian-induced torsional vibrations of lightweight suspended footbridges. All the proposed structural countermeasures are characterised by the addition of few elements to the original structure, i.e. punctual masses and/or additional cables located in specific sections to reduce vertical and longitudinal relative displacements of the suspension cables, in order to preserve the bridge lightness and slenderness. An application to a test case footbridge is provided. Its structural nonlinear analysis is carried out by means of numerical simulations. On the basis of a preliminary modal analysis, a criterion for the localization of the vibration countermeasures along the span is proposed. The effectiveness of the localization criterion and of the proposed design arrangements is evaluated by comparing the structural responses obtained through step-by-step dynamic analyses with and without the countermeasures. The analysis of the results allows the design arrangements to be discussed and the best suited ones to be selected.