From Reuters:
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.
The elegant pedestrian walkway was conceived as a blade of light linking the south bank of the River Thames to the City of London.
But as large crowds walked across the steel structure on opening day in June 2000, the 320-meter long bridge swayed from side to side because of a phenomenon known as collective synchronisation.
“The phenomenon was that people who were walking at random, at their own favorite speed, not organized in any way spontaneously synchronized,” said Steven Strogatz, of Cornell University in Ithaca, New York.
“That’s the phenomenon. Why did they all start moving in step? They did it unconsciously. That is what nobody had thought about and engineers did not anticipate.”
The applied mathematician and expert on the phenomenon said collective synchronisation is now something engineers will have to consider when designing bridges.
He and colleagues at Cornell and other universities in the United States, Britain and Germany have devised a theory based on what happened to the Millennium Bridge to estimate how much damping or stabilization is needed in footbridges.
Their findings are published in the science journal Nature.
[…]
Certain coincidences must occur for collective synchronisation to occur. 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.
“The people were resonating with the bridge,” said Strogatz.
As the bridge started to move, people would get in step with the sway to steady themselves. They widened their stance to make it more comfortable to walk and inadvertently made the wobbling worse.
“A lot of people were blaming it on the beautiful innovative structure, the design of the Millennium Bridge itself, which was a radical design,” said Strogatz.
“But that is not true.”
Collective synchronisation occurs in nature when crickets start chirping in unison. In some parts of the world, fireflies blink on and off in perfect synchrony like a Christmas tree. The monthly cycles of women living together have also been known to synchronize.
“It is always very striking and almost spooky because it is like order coming out of chaos,” said Strogatz.
I find this kind of stuff is fascinating—newly discovered engineering problems concerning utilitarian architectural structures that’ve been around ever since some crafty hominid first felled a tree across a span of river. For my part, I encountered this phenomenon of collective syncronization in the wilds a couple of times myself—the first being in 1989, when a bunch of Ruby Tuesday’s waiters and bartenders spending the day at my parents’ pool skinny-dipping suddenly broke into a kind of postmodern water ballet, all groping arms and legs and tongues and lubed-up waterwings; and the second six years later, when a group of about 14 PhD students in literature got drunk on Goldschlager and a keg of Busch Light and suddenly broke into a remarkably offkey rendition of the Eagles’ “Seven Bridges Road.”
So yeah. Spooky is right, Dr. Strogatz…
(h/t Tom Pechinski)
Ever since the Tacoma Narrows bridge in Washington state collapsed, natural frequency analysis has been part of any bridge design. And yet someone designs a footbridge with the natural frequency of people walking. Way to score an auto-goal on yourselves, chaps.
Speaking of “Seven Bridges Road,” when it would come on the juke-box at the college annex when I was a Freshman the entire gathered throng would spontaneously sing slong. I’ve tried the same thing recently with some Eminem. It hasn’t been the same.
and, I suspect, blog together.
Any guesses whether Jesse and Amanda are in sync?
—
The above comment was completely gratuitous and sexist, probably, at some level, advocates rape, which in no way dimishes its accuracy.
or that Michelle Malkin called Jeff G. ‘trenchant’ … which means ‘Joooooish’ in Tagalog.
Goldschlager and a keg of Busch for PhD English students? Sound more like the basement of Zeta Psi or DU.
I’m of the opinion that “Seven Bridges Road” be stricken from the list of acceptable spontaneous sing-alongs.
That’s because my roommate at CU insisted on playing it repeatedly in hopes that I might eventually appreciate it on the level that he did.
God how I have grown to hate the Eagles. I even met Bernie Leadon when I first moved to Nashville. Nice guy too. Take it to the limit indeed.
“collective synchronisation”…
might this explain the behavior of the U.S. Senate?
Gamer is right. What a bunch of idiots!
Anybody who’s ever walked across a rope bridge or small suspension bridge knows this. Walkways have been falling for decades due to this phenomenon (Vegas comes immediately to mind). Yet the Brits didn’t learn until 2000?
This is not a newly discovered engineering problem. The engineers of this bridge should have design for such a well known phenomenum. For ages, armies have always broken there marching cadence when they cross a bridge in order to prevent resonance with the bridge’s natural frequency. I certainly hope the owners can recoup at least some of the costs of fixing the problem from the engineering firm.
Ditto on the not-new thing. The design of ANY structure should consider resonance, and what might excite the structure at its resonant frequency.
Not saying these guys were completely clueless for failing to anticipate collective synchronization (not saying they weren’t, either, just not speaking to that at all), just that a quick Google on “damping coefficient” might have saved them a rework of the structure.
Slaretibartfast, you speak truth more than you know. You—well, not you, because you already know, but others—would be amazed at how many problems in my life I have solved by Googling “damping coefficient.”
Ditto ditto on marching armies. One of the first things we learned during “Drill and Ceremony” was to ALWAYS break cadence when crossing any bridge. Failure to do so can cause structural damage or failure of the bridge. All of this is caused by simple harmonic motion at a natural resonating frequency, said motion being induced by the simultaneous impact of marching soldiers. Or, in London, strolling pedestrians.
I recall a science fiction novel which used this phenomnen to defeat an army of evil (but literal minded) robots.
I find the offkey rendition of “Seven Bridges Road” to be of more scientific interest, myself. How many of the PhD literature students were female?
Collective synchroniation? So that’s why the moonbats always all start barking and howling at the same time!
And here I thought it was the phase of the moon. Guess we’ll have to rename the species.
But will “barking collectively-synchronizedbats” really catch on?
Han Solo and the Lost Legacy?
Ich erklärte ihnen, daß diese Brücke zu meinen Zwecken unbrauchbar sein würde. Aber sie hörten nicht. Sie hören nie! Britische Schweine!
I’m just trying to guess how long this will take to become an episode of “Numb3rs”.
My guess is March.
Corvan,
I don’t have any experience with spontaneously singing slong…but it intrigues me while still making me feel a little grimy…
It was already an episode of “Mythbusters”.
This sounds like a job for the Ministry of Silly Walks.
Here’s how it works: you give people tickets to cross the bridge, each with a number on it from 1-10.
If you get a 1, you have to walk like John Cleese did in that skit (all British people should have this memorized anyway).
If you get a 2, you have to do a rendition of “shuffle off to Buffalo” all the way across. And so on.
See? Simple.
Stupid engineers … always making things so complicated.
I can absolutely vouch for this phenomenon having experienced it on the Brooklyn Bridge after the blackout in 2003. It is kinda scary. The funny thing is, its also kinda obvious…I guessed they missed it because it was a new bridge.
Guess this is why we don’t often see productions of Riverdance on bridges…
Yeah… the designers of the bridge sure got away clean here. This looks like an obvious design error.
Resonance is nothing new and is always taken into account, particularly for foot bridges because they are less robust than vehicular bridges and have to deal with the cyclical movements of pedestrian traffic.
VW,
Singing slong is one of those things I do late at night while I touch my “special” place. Of course on the post above I meant to say sing along, but singing slong is alot more fun in a private, guilty sort of way.
Jeff G. (I can call you “Jeff G.”, can’t I? Because we have met, and all….),
I love ya, man. But sometimes…sometimes, mind you– you scare me.
The term “collective synchronisation” apparently comes from biology, but in this case it sounds like a contrived excuse for an engineering mistake. I seriously doubt the engineers overlooked resonant frequency as an issue, but were thinking more in terms of wind and maybe traffic flow. I’d like to know how many people were on the bridge and how much it actually moved. Maybe they had Sousa on the loudspeakers. The easy fix would be to suspend weights along the length of the bridge and spaced appropriately to dampen harmonics.
Damn!! The things you can learn at 5:15AM just by getting your Protien Wisdom!
TW: set I guess I’m all set now. Or for Frist: Hey! Grow a set, will ya?
Of course you break step when you go over a bridge. The whole problem with this bridge wasn’t that people were marching over it in step. They were walking normally. That’s what the whole article is about. The natural phenomenon that people subconciously push out horizontally in the direction of the sway making it worse. And they don’t balance each other out which is what the engineers thought would happen. It’s a new kind of design which is always going to have teething problems.