Why did millennium bridge wobble

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Newest articles Information Technology. The spontaneous synchrony of the crowd was similar to what happens with the highly synchronized flashing of fireflies or firing of neurons in the brain. As for this latest paper, "The authors use a much more realistic and biomechanically inspired model of human walking than my colleagues and I were able to muster back in ," says Strogatz. In a simulation , Joshi and his co-author, Manoj Srinivasan—both of whom have backgrounds in studying human locomotion—found that people walking in synchrony with a sideways-swaying bridge lowers the metabolic energy cost of the motion.

So it was a natural reaction, they reasoned, for people to start to synchronize their gaits with the bridge's motion. However, this model didn't factor in the energy cost of stabilizing one's gait. 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