Why did millenium bridge wobble

Their latest study looks at a different biomechanical principle. Human beings are so-called "stable" walkers. We want to walk without falling, and will make adjustments based on the feedback we receive from our environment. Since "humans are top-heavy objects, often modeled as an inverted pendulum," the authors write, we need that feedback to stabilize us; otherwise we'd lose our balance pretty quickly.

So they incorporated that feedback into their simulations. The improved model correctly predicts some phenomena that the model couldn't account for, like the wobbling of footbridges even in the absence of this crowd synchrony. Also, the onset of crowd synchrony and the onset of bridge wobbling are not simultaneous. They occur at different numbers of pedestrians. The bridge can begin to wobble even at lower numbers of pedestrians, in which case the crowd does not synchronize, yet the bridge spontaneously begins to move.

As for the metabolic energy cost, once the virtual bridge began to shake, the simulated walkers widened their steps—a much less energy-efficient gait.

But the authors argue that perhaps over time, people would figure out how to minimize the energy expenditure. They next hope to incorporate crowd dynamics into their simulations. In reality, people try to avoid colliding with others, or suddenly change directions, for example. Ultimately, he hopes to learn more about the biomechanics of how we can adapt so quickly to unusual situations, like a moving surface.

Engineers fixed the Millennium Bridge's swaying issues by retrofitting the structure with 37 energy dissipating dampers to control the horizontal movement, and another 52 inertial dampers to control the vertical movement. The bridge hasn't had a significant wobble problem since it reopened in February Start your Independent Premium subscription today.

Already subscribed? Log in. Hence the pedestrian can inadvertently feed energy into bridge oscillations. Dr John Macdonald, Senior Lecturer in Civil Engineering, said: "It is clear that the motion of the bridge affects the force from the pedestrian, rather than the pedestrian simply applying an external force.

It has generally been thought the Millennium Bridge 'wobble' was due to pedestrians synchronizing their footsteps with the bridge motion. However, this is not supported by measurements of the phenomenon on other bridges. The researchers found, to their surprise, that pedestrians walking randomly, keeping balance as normal can cause large bridge sway.

This finally seems to explain the initiation of the Millennium Bridge 'wobble' and gives new insight for designing bridges to avoid vibration problems. The Millennium Bridge was retrofitted with an additional 89 dampers to reduce the wobble to a safe level.

This included 37 energy dissipating dampers to control the horizontal movement and 52 inertial dampers to control the vertical movement. If you are interested in learning more about an example where a bridge was destroyed by wind, check out our case study of the Tacoma Narrows Bridge. Katie Wohlust Mar 4, What Causes Bridge Wobble At first, it was widely believed that the wobble was caused by a synchronized pedestrian footstep pattern in response to a slight movement in the bridge.

Original Design The Millennium Bridge was built to accommodate approximately 5, pedestrians at one time. To view a Cause Map of the Millennium Bridge incident, click on the thumbnail below.