Reducing the wobbles in pedestrian bridges Monday, 27 November 2017

Many pedestrian bridges around the world have experienced dramatic vibrations and dangerous wobbling when crowds of pedestrians have tried to cross them, including the London Millennium Bridge, the Clifton Suspension Bridge in Bristol, England, the Squibb Park Bridge in New York and Singapore Airport’s Changi Mezzanine Bridge. An army marching over a bridge will often break the march so that the rhythmic synchronised impacts of marching don't create dangerous vibrations in the bridge which can lead to the bridge's collapse. A new model has been developed to predict the effect of large crowds of people on bridges.

The study led by Georgia State University found that the dangerous wobbling of pedestrian bridges could be reduced by using biomechanically inspired models of pedestrian response to bridge motion and a mathematical formula to estimate the critical crowd size at which bridge wobbling begins.

“We challenge the widespread view that increasing the crowd size will gradually increase the bridge wobble," said Dr Igor Belykh from Georgia State.

"The current view is the more pedestrians we add to the bridge, the wilder the oscillations will be. This is true, but only for crowd sizes above this critical size. There is an important threshold effect."

He said the paper he and colleagues Russell Jeter and Vladimir Belykh published in Science Advances gives an explicit guideline and formula of how to estimate this critical crowd size, which can be used to limit the carrying capacity of an existing bridge and to help designers build better bridges.

"The biomechanical models we’re developing are particularly important for understanding the role of crowd dynamics on a wobbly bridge because the US code for designing pedestrian bridges does not contain specific guidelines that account for collective pedestrian behaviour," he said.

"The industry standard programs used by bridge designers only use linear models. We’re working on the inclusion of biomechanical models like ours into the standard tools and software programs used by bridge designers to better predict the nonlinear effects associated with the interaction between crowds of pedestrians and bridges.”

[Image: George State]