Modelling of pedestrian-induced load in serviceability limit state analysis of footbridges

Abstract

The last few decades new trends in the design of pedestrian bridges have resulted in lighter and more slender structures. This leads to a reduction in natural frequencies and increased flexibility, and thus a greater possibility for structures to become more exposed to excessive vibrations caused by pedestrians. The lager amplitudes of vibrations occur if the pace frequency of excitation load approaches one of natural frequency of footbridge. The vibration of high proportions may cause pedestrians to feel uncomfortable, sick or unsafe while crossing the bridge. In modern pedestrian bridge design, human-induced vibrations have become an important issue. Footbridge vibrations occur in vertical, lateral and longitudinal direction, and torsion of the bridge deck is also possible. The main types of pedestrian action on the bridge are walking and running, while jumping, bouncing, swaying are considered to be intentional, or sometimes even vandal excitation. Pedestrian-induced loads are difficult to model since pedestrians may have different weight, various number in the groups randomly distributed over the bridge deck. Also, the walking velocity may vary from a pedestrian to a pedestrian. The load models appropriately set up are of great importance for understanding the response of the bridge. Principles of modeling of the human-induced load and some characteristic models of pedestrian loads, described in proposals and codes, are presented in this paper. Some results of Serviceability Limit State analysis, in terms of human-induced vibration, of the pedestrian bridge over the Nisava River in Nis, are also presented.