Failure of footbridges in England and France due to excessive vibrations from marching soldiers in the nineteenth century resulted in many fatalities and injuries. The unexpected lateral vibrations of the Millennium Bridge over the Thames River in London was a watershed event as large number of research studies were conducted on this subject following this incidence. However, there are still a number of issues related to vibration serviceability of footbridges that require further studies. Among these are: the amplification of structural response when a group of pedestrians cross a footbridge as compared to a single individual (group effects). This is important as footbridge vibrations are usually computed when subjected to one pedestrian’s crossing and are magnified to estimate those generated by a group of people. Therefore, it is important to conduct vibration testing of footbridges to better define the group effects. This paper presents an experimental study of a footbridge susceptible to vibrations due to human movements. With the help of a group of volunteers, the group effects were computed as a function of the group size. It was found that the results were not completely consistent with those in the literature. Conclusions are made based on the results of the data analysis.
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