Zeno's Paradox
While critical thinking may not make up for a lack of knowledge, it is essential for gaining knowledge.
Wednesday, November 02, 2005:  
Revealed: Why London's Millennium Bridge wobbled

A natural phenomenon rather than a design fault caused London's Millennium Bridge to wobble and sway, forcing its closure just two days after opening in 2000...

In the case of London's wobbly bridge, it was large crowds walking across a flexible footbridge that vibrated at a frequency of one cycle per second, which just happened to be the same frequency as humans walking.
What?! The bridge had a natural frequency of one cycle per second! That frequency didn't raise any concerns? Maybe they forgot to post a sign on how to properly cross the bridge? ;)

This article caught my attention not only because the vibrational resonance problems reminded me of the famous Tacoma Narrows Bridge, but also because it was people walking that caused the problem. So, unlike the Tacoma Narrows Bridge, the Millennium Bridge's displayed a classic resonance problem: it's normal environment subjected it to an oscillating force (people walking) that was close to one of its natural frequencies.

Also, am I the only one that thinks it ironic that the bridges failure is attributed not due to a "design fault" but to a "natural phenomenon" that future pedestrian bridges will have to be designed to accommodate? I'm guessing that it's not a design fault in the legal sense. The designers used the proper materials and properly tested their design. They weren't required to test the case that a large number of people walking across it would be walking fairly close in step.

I wonder how quickly structural engineers will be required to test for this problem?

Update: Science Blog has a nice article on the bridge.

    -  Ron  12:00 PM

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