Footfall-induced vibration: Prediction and control strategies

Footfalls can produce vibrations that are irritating to occupants, or disruptive to vibration-sensitive spaces in hospitals and research laboratories. This paper describes, using case studies, techniques that can be used to predict vibrations, and mitigation strategies to control them. Firstly, pedestrian loading on footbridges is described. Stochastic simulations are conducted in which a number of pedestrians with random weights, walking speeds, and walking paths cross a bridge with random spacing. The resulting vibration response of the bridge is determined to estimate the peak acceleration of the bridge. For the case considered, tuned mass dampers (TMDs) were subsequently installed on the bridge to increase the effective damping of two modes. Next, crowd loading on stadia and ballroom structures is considered. For these structures, the crowd-structure interaction must be considered since the mass of the crowd is a significant fraction of the mass of the structure, which alters the dynamic response of the system. In the case presented, TMDs are considered to reduce the vibrations associated with crowd excitation. Lastly, the vibrations associated with a pedestrian walking in a corridor adjacent to a vibration-sensitive room in a hospital or research facility are described. Maintaining low vibrations in these hospitals and laboratories is critical as the operation of equipment may be adversely affected by vibrations that are well below the threshold of human perception. Typical mitigation strategies for these vibrations include positioning sensitive equipment near columns or increasing the stiffness or mass of the floor.