Influence of pedestrians on the effective damping of a footbridge

The realistic evaluation of the serviceability of footbridges in regard to pedestrian-induced vibrations requires a comprehensive load model, a correct model of the random pedestrian stream and finally a thorough understanding of the dynamic behaviour of the coupled system structure-users. For passive persons, a probabilistic model is available which allows the prediction of the change in the natural frequency and the effective damping. However, an equivalent approach for active persons is not available. Based on field experiments with a shaker, the present study identifies the induced additional damping for a single person walking on a pedestrian bridge which has a natural frequency of 1.8 Hz. It is shown that the induced damping exceeds that of a passive person and depends on the step frequency. The influence of pedestrian groups is studied based on simulations modelling in a first and conservative approach the additional damping in accordance to a passive person. For the chosen example bridge, the reduction of the mean maximum experienced acceleration is in the range of 10% to 15% for groups of 10 to 16 persons.