Wobble of the London Millennium Bridge without synchronisation

Overview

Join us for an online lecture hosted by the ICE Europe Regional Committee.

On its opening day, the London Millennium Bridge experienced unexpected large oscillations due to crowd loading. This form of pedestrian-structure interaction has since been identified on many other bridges of various structural forms. The mechanism has commonly been attributed to ‘pedestrian synchronous lateral excitation’. However, some site measurements, including on the Clifton Suspension Bridge, show a lack of evidence of pedestrian synchronisation.

Modelling of the basic mechanism of human balance gives the surprising result that pedestrians walking randomly, keeping balance as normal, can effectively act as negative dampers to the bridge motion. This is in agreement with the empirical model developed by Arup from measurements on the London Millennium Bridge, leading to dynamic instability above a critical number of pedestrians. There is evidence that any synchronisation of footsteps that does occur is a consequence, rather than the cause, of the bridge vibrations. The significance is that pedestrians can induce large lateral oscillations of bridges with a wider range of natural frequencies than synchronisation models would suggest.

The event is dedicated to John Macdonald, Professor of Structural Dynamics, University of Bristol.