Enlarge / London’s Millennium Bridge had issues with excessive shaking and swaying when it first opened in June 2000. (credit: Alberto Pezzali/NurPhoto/Getty Images)
London’s Millennium Bridge is notorious for its “wobble” when this first opened in June 2k, as thousands of pedestrians streamed across. Londoners nicknamed it “Wobbly Bridge. ” The accepted explanation has been that the swaying was due to a weird synchronicity between the bridge’s lateral (sideways) sway and pedestrians’ gaits—an example of emergent collective phenomena.
But that explanation turns out to be a bit more complicated, according to a recent paper published in the journal Nature Communications. “This [old] explanation was so popular, it has been part of the scientific zeitgeist, ” said co-author Igor Belykh , a mathematician at Georgia State University. “Our work shows that very tiny vibrations from each person walking can get amplified significantly. ” People adjust their footsteps to keep their balance in response to the wobble, which only makes things worse. Eventually the bridge becomes unstable.
As we’ve reported previously , this phenomenon is not limited to the Millennium Bridge. There’s a sign dating back to 1873 on London’s Albert Bridge warning military troops in order to break their usual lock-step motion when crossing, since the bridge is wont to shake and wobble—hence its nickname, “The Trembling Lady. ” Other similar “unstable” bridges include the Clifton Suspension Bridge in Bristol, UK; the particular Squibb Park Bridge in Brooklyn, New York; and the Changi Mezzanine Bridge in Singapore’s airport.
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