Assessment of the Human Comfort of Pedestrian Footbridges Utilising Probabilistic Response Spectra

Resumo

Nowadays, the design of pedestrian footbridges is associated to light weight structures with low natural frequencies and low structural damping rates. These facts have generated slender footbridges, sensitive to human dynamic excitations, and consequently changed the serviceability limit states associated to the design. Thus, the current design codes and technical guides recommend the use of deterministic models to assess the dynamic structural behaviour of footbridges. On the other hand, the pedestrian walking is related to a stochastic phenomenon and the dynamic force generated at each step depends of the weight, the step frequency and the step length of each pedestrian. This way, this investigation aims to develop a probabilistic approach to assess the steel and steel-concrete composite footbridges dynamic behaviour, based on the use of design response spectra. To do this, the developed analysis methodology has considered the stochastic nature of the pedestrians walking, in order to evaluating the structural response having in mind excessive vibrations that may cause human discomfort. Based on the use of probabilistic methods, it becomes possible to determine the probability of the footbridges peak acceleration values exceeding or not the human comfort criteria. The results obtained in this research work reveal that the peak acceleration values calculated through the deterministic methods can be overestimated in project situations.