Comments on: Millennium Bridge, London http://googlesightseeing.com/2007/05/22/millennium-bridge-london/ Why bother seeing the world for real? Thu, 20 Nov 2008 17:56:26 +0000 http://wordpress.org/?v=2.6.3 By: Armageddon T. Thunderbird http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-144209 Armageddon T. Thunderbird Sun, 27 May 2007 21:23:18 +0000 http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-144209 Myth Busters, eh? If their bs improves a bit, they might be on par with Wikipedia. Google "Hyatt Regency collapse" for some scary stuff about the hotel walkway collapse in Kansas City, in '81. Myth Busters, eh? If their bs improves a bit, they might be on par with Wikipedia.

Google “Hyatt Regency collapse” for some scary stuff about the hotel walkway collapse in Kansas City, in ‘81.

]]> By: Gibbo http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143803 Gibbo Wed, 23 May 2007 17:17:29 +0000 http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143803 The whole vibrating bridges thing is almost always misunderstood. In this particular case, if was psychology that caused the problem. Any structural engineer in the world would have looked at the design of that bridge and said it would not have vibration problems. The bridge used a type of suspension that was (according to the Arup engineers describing it on TV) completely novel. Instead of having the suspension pylons going straight up (like the golden gate bridge) they went out at an angle. The vertical component of the tension in the cables is sufficient to hold the thing up. The horizontal component is balanced by the other pylon. Now there's nothing wrong with this. The same physics that governs other suspension bridges applies here. But why did this one wobble? The bridge is very light, so it can be set in motion by a comparatively small force. There's nothing wrong with that either. The Millenium bridge over the Tyne bounces when I jump up and down. The problems at the Millenium bridge in London were a combination of biomechanics and psychology that no-one (at least no structural engineer) had anticipated. Whenever we place a foot on the ground, it exerts a small sideways force. It is assumed that in a group of lots of people randomly milling about that these small forces will be randombly distributed and will cancel each other out. As it turns out, for a lightweight bridge, the random coincidence of a few people walking in step is enough to start the bridge moving very, very slightly. This small vibration then influences other people on the bridge to walk in step, and before long everybody is walking in step, and the bridge is vibrating like in the video. Other things: Soldiers break step on bridges because of the very regular impulsive vertical force that is transmitted into the structure, not the horizontal force. The tacoma narrows bridge was excited to resonance by quasi-periodic turbulent forces due to the wind travelling down the valley. Modern bridges are tested in wind tunnels and in software simulations to ensure they do not suffer similar fates. I think they might get damped, too. Finally, apologies to James and Alex for trolling up their nice website. The whole vibrating bridges thing is almost always misunderstood. In this particular case, if was psychology that caused the problem. Any structural engineer in the world would have looked at the design of that bridge and said it would not have vibration problems.

The bridge used a type of suspension that was (according to the Arup engineers describing it on TV) completely novel. Instead of having the suspension pylons going straight up (like the golden gate bridge) they went out at an angle. The vertical component of the tension in the cables is sufficient to hold the thing up. The horizontal component is balanced by the other pylon.

Now there’s nothing wrong with this. The same physics that governs other suspension bridges applies here. But why did this one wobble? The bridge is very light, so it can be set in motion by a comparatively small force. There’s nothing wrong with that either. The Millenium bridge over the Tyne bounces when I jump up and down.

The problems at the Millenium bridge in London were a combination of biomechanics and psychology that no-one (at least no structural engineer) had anticipated. Whenever we place a foot on the ground, it exerts a small sideways force. It is assumed that in a group of lots of people randomly milling about that these small forces will be randombly distributed and will cancel each other out. As it turns out, for a lightweight bridge, the random coincidence of a few people walking in step is enough to start the bridge moving very, very slightly. This small vibration then influences other people on the bridge to walk in step, and before long everybody is walking in step, and the bridge is vibrating like in the video.

Other things: Soldiers break step on bridges because of the very regular impulsive vertical force that is transmitted into the structure, not the horizontal force.

The tacoma narrows bridge was excited to resonance by quasi-periodic turbulent forces due to the wind travelling down the valley. Modern bridges are tested in wind tunnels and in software simulations to ensure they do not suffer similar fates. I think they might get damped, too.

Finally, apologies to James and Alex for trolling up their nice website.

]]> By: Cyre http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143728 Cyre Wed, 23 May 2007 00:19:42 +0000 http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143728 I believe that soldiers marching in step thing was mythBUSTED by the Mythbusters. I believe that soldiers marching in step thing was mythBUSTED by the Mythbusters.

]]> By: Alex http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143697 Alex Tue, 22 May 2007 18:32:53 +0000 http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143697 Oh, and cookie monster: <a href="http://dictionary.reference.com/search?q=nauseatingly" rel="nofollow"> nauseatingly</a> :) Oh, and cookie monster: nauseatingly :)

]]> By: mikeg http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143688 mikeg Tue, 22 May 2007 15:53:49 +0000 http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143688 Crazy stuff. Many years ago, when visiting San Francisco or some other city, I think a tour guide told us that the army was no longer allowed to march across the bridge because of the syncronized pounding of the feet caused similar vibrations in the bridge. Why do soldiers break step in marching over a bridge? http://www.answerbag.com/q_view/175566 Crazy stuff.

Many years ago, when visiting San Francisco or some other city, I think a tour guide told us that the army was no longer allowed to march across the bridge because of the syncronized pounding of the feet caused similar vibrations in the bridge.

Why do soldiers break step in marching over a bridge?
http://www.answerbag.com/q_view/175566

]]> By: Alex http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143673 Alex Tue, 22 May 2007 12:26:52 +0000 http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143673 That's a darn good point xman. That's what I get for believing something on Wikipedia... Post updated. That’s a darn good point xman. That’s what I get for believing something on Wikipedia…

Post updated.

]]> By: xman http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143669 xman Tue, 22 May 2007 11:47:17 +0000 http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143669 DHM caused by pedestrians not seen before? Huh? Why do you think soldiers break step when crossing suspension bridges? Any small suspension bridge will demonstrate this behaviour if enough people walk on it. Now gone, I think, but the Shacking Briggy over the River Dee near Aberdeen was a classic example of this in action. DHM caused by pedestrians not seen before? Huh? Why do you think soldiers break step when crossing suspension bridges? Any small suspension bridge will demonstrate this behaviour if enough people walk on it. Now gone, I think, but the Shacking Briggy over the River Dee near Aberdeen was a classic example of this in action.

]]> By: cookie monster http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143661 cookie monster Tue, 22 May 2007 10:34:36 +0000 http://googlesightseeing.com/2007/05/22/millennium-bridge-london/#comment-143661 'nauseatingly'? Good word (if a little bit made up maybe?). ‘nauseatingly’?
Good word (if a little bit made up maybe?).

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