Vibration Response due to Group Movements on a Footbridge

Footbridges can be susceptible to large vibrations when a group of people move across them. To evaluate the vibrations of a footbridge, the structural engineer usually computes the response of the structure due to one person crossing at the footbridge resonance frequency or its subharmonics. The response due to a group of pedestrians can then be found by magnifying the computed response using a so-called “enhancement factor”. Unfortunately, not much research has been conducted to define this factor. This study is an attempt to define the enhancement factor using an existing footbridge. It details the footbridge response when various groups of people marched in unison or walk randomly over it. Enhancement factors were computed for various group sizes and a closed form equation is proposed to compute enhancement factors for design purposes.