Probabilistic Approach based on Design Response Spectra to Evaluate the Human Comfort of Pedestrian Footbridges

Resumo

Nowadays, the structural project of pedestrian footbridges has been conceived based on the use of lightweight structures, with low natural frequencies and structural damping ratios. These facts have generated slender footbridges, sensitive to human dynamic excitations, and consequently modified the design serviceability limit states. Thus, current design codes and technical guides recommend the use of deterministic models to evaluate the footbridges dynamic structural behaviour. On the other hand, pedestrian walking is related to a stochastic phenomenon and the dynamic force generated at each step depends on the weight, frequency and length of each pedestrian’s step. This way, this research work aims to propose a probabilistic approach to assess the dynamic behaviour of pedestrian footbridges (steel; steel-concrete; and concrete footbridges), based on the use of design response spectra. The proposed analysis methodology considered the stochastic nature of pedestrian walking aiming to evaluate the structural response taking into account excessive vibrations that can induce human discomfort. Based on the use of a probabilistic approach, it is possible to determine the probability of the peak acceleration values of the footbridge exceeding or not the human comfort criteria. Therefore, it was possible to conclude that the 95% percentile values of accelerations calculated using the proposed design response spectra are lower when compared to the experimental tests peak accelerations. On the other hand, the results obtained in this study indicated that the peak acceleration values calculated through the deterministic methods can be overestimated in project situations.