PEDESTRIAN-INDUCED VIBRATION OF FOOTBRIDGES

This paper describes the critical loading effect which produced the excessive lateral vibrations of the Millennium Footbridge, London, UK, at its opening in June 2000. Pedestrians apply dynamic forces to the surface on which they walk, but the lateral loading effect seen on this occasion was due to the increasing synchronisation of footfalls, which applies the force at the resonant frequency of the bridge. Some other footbridges across the world are known to have been affected in a similar way. Knowledge of lateral loading effect is not extensive and further research is required in order to develop design rules. Statistical description and mathematical modelling could be used, and the correlated dynamic force could be quantified by back-analysis from actual bridge motions recorded during the passage of a crowd. The paper gives diagrammatic and brief descriptive information on the damping developed for the Millennium Bridge. Existing UK design standards do not adequately cover synchronous vertical excitation arising from groups, although European codes are being developed.