Mystery behind London Millennium Bridge 'wobble' solved

Washington, December 17 (ANI): Civil engineers at the University of Bristol say that the reason behind the wobbling that people experienced on the opening day of the London Millennium Bridge lies in the way humans stay balanced while walking.

The researchers say that the same pedestrian-structure interaction has also been identified on several other bridges, including Bristol's famous Clifton Suspension Bridge.

They point out that humans achieve balance by changing the position of foot placement for each step, based only on the final displacement and speed of the centre of mass from the previous step.

The team say that they applied the same balance strategy as for normal walking on a stationary surface to walking on a laterally swaying bridge.

The researchers observed that pedestrians could effectively act as a negative damper to the bridge motion without altering their pacing frequency.

Thus, they said, the pedestrian could inadvertently feed energy into bridge oscillations.

"It is clear that the motion of the bridge affects the force from the pedestrian, rather than the pedestrian simply applying an external force," said Dr. John Macdonald, Senior Lecturer in Civil Engineering.

While it has been though that the Millennium Bridge 'wobble' was due to pedestrians synchronizing their footsteps with the bridge motion, it was not supported by measurements of the phenomenon on other bridges.

The researchers observed that pedestrians walking randomly, keeping balance as normal, could cause large bridge sway.

They say that their observations may help understand why the Millennium Bridge wobbled, and that they give new insight for designing bridges to avoid vibration problems.

A research article on their study has been published in the Royal Society journal Proceedings of the Royal Society A. (ANI)