Civil Engineering Association

HUMAN INDUCED VIBRATIONS ON FOOTBRIDGES

The last few decades the community demands for more interesting bridges. Improvements in material properties, design methods, building techniques and the involvement of
architects led to longer and slender footbridges. These bridges tend to be more sensitive to dynamic forces induced by pedestrians, resulting in vibrations of the bridge deck. These vibrations can in some cases attain high proportions, especially when the walking pace of the pedestrians approaches the natural frequency of the bridge. Such a case could result in a situation where the pedestrian feel uncomfortable or even unsafe. This topic has thus become an important issue for the Serviceability Limit State of footbridges.
Some Codes of practice nowadays refer to this topic but it is still a developing field.
Dynamic analyses during the design phase have become inevitable. This report compares and evaluates three load models described in the codes (or proposal for the codes):
Proposal Annex C (to EN 1991-2:2003), the British National Annex (to EN 1991-2:2003) and the Australian Standard (AS 5100.2-2004). All three codes have different approaches to this topic. Proposal Annex C considers walking pedestrians (single and groups) and crowds and represent all of them by non moving harmonic loads. The British National Annex also considers joggers which have total different walking pattern. The fundamental difference with the load models described in Proposal Annex C is that the loads are represented by moving harmonic loads. So does the Australian Code, but this one only considers the model of a single pedestrian.