Abstract Summary
Among the load scenarios considered for the serviceability assessment of human-induced footbridge vibrations, is that of the transient action of a single pedestrian or a small group of pedestrians. Although such action is stochastic due to the variability of gait parameters, Standards and Guidelines assume it is deterministic, and equal to that coming from the “worst pedestrian ever” for the given footbridge. Such approach is sound from an Engineering point of view, but does not allow control of the probability of failure. It also has the advantage that it can be applied to footbridges with any structural system. In this paper, firstly the analysis of peak accelerations is developed according to prEN1991-2:2018 (Eurocode 1 - Actions of structures, Part 2: Traffic loads on bridges) for a number of simple supported footbridges, for which a closed-form acceleration response is available, both in vertical and lateral directions. Then, a probabilistic procedure by the authors is used to evaluate the probability of exceedance of the calculated acceleration. The procedure uses empirical cumulative density functions of the peak acceleration obtained through Monte Carlo simulations. To this aim, a European Standard Population of walkers is defined based on literature data, to account for the variability of pedestrian and gait characteristics. It is found that the probability of exceedance of the acceleration calculated according to prEN1991-2:2018 is not uniform among the footbridges considered. A comparison between the peak acceleration evaluated in accordance with prEN1991-2:2018 and the characteristic values obtained by the probabilistic procedure is also performed. Finally, a probability-based model is proposed for the evaluation of the characteristic value of the footbridge peak acceleration due to single pedestrians or groups of pedestrians. The latter is easily codifiable, and has the advantage of allowing control of the probability of failure; on the other hand, it has the drawback of being limited to footbridge with sinusoidal mode shapes.
