Pedestrian excitation of bridges

Abstract

This paper reviews the evidence on dynamic bridge loading caused by moving pedestrians. The phenomenon of ‘synchronization’ by which people respond naturally to an oscillating bridge when this has a frequency close to their natural walking or running frequency is a feature of this phenomenon. By increasing modal damping, synchronization can be prevented, but how much damping is needed in any particular situation? If some simplifying assumptions about how people walk are made, it is possible to predict analytically the minimum damping required to ensure that synchronization does not lead to high vibration levels. The main assumption is that the movement of a pedestrian's centre of mass has two components. One is its natural movement when the person is walking on a stationary pavement. The other is caused by movement of the pavement (or bridge) and is in proportion to pavement amplitude but with a time delay that is arbitrary. When the time delay is a ‘worst case’, pedestrians act as a source of negative damping. This theory supports the adoption of a non-dimensional number which measures the susceptibility of a bridge to pedestrian excitation. Although currently there are not many good bridge response data, predictions using this non-dimensional number are compared with the data that are available and found to be in satisfactory agreement. Both lateral and vertical vibrations are considered.