Vibration analysis of footbridges due to vertical human loads

Pedestrian footbridges have been constructed with increasingly daring structures encompassing the experience and knowledge of structural designers by using newly developed materials and technologies. This fact has generated very slender structural footbridges and, consequently, changed their associated serviceability and ultimate limit states. A direct consequence of this design trend was a considerable increase of structural vibration problems. In the particular case of pedestrian footbridges this phenomenon occurs when the structural fundamental frequency is near the load excitation frequencies, or higher frequencies multiples. This was the main motivation for the development of a design methodology to better evaluate the footbridge user’s comfort and safety. Considering all these aspects a linear elastic finite element analysis contemplating the dynamical response of pedestrian footbridges focusing on critical acceleration values was conducted. The investigated model was based on an existing footbridge located at the city of Rio de Janeiro, Brazil. Four different loading models were developed to incorporate the dynamical effects, induced by people walking, in the dynamical response of pedestrian footbridges. The results indicated that this footbridge can reach high vibration levels hat could compromise the user’s comfort limit state.