Millennium Bridge wobble blamed on walkers

[RubyToogood]

There are some very impressive bits of footage of the Tacoma Narrows bridge waving in the wind, looking more liquid than solid, until the concrete gave way.

I looked this up... http://uk.youtube.com/watch?v=j-zczJXSxnw

 

[RubyToogood]

How do marchers 'break step'? Is it like a 'shuffle' every fourth step or soemthing? Or every other row adjusts to they are doing the 'other' step?

It means they should break step which each other, rather than all march in unison, ie just walk naturally.

 

[WouldBe]

this was an entirely new design of bridge. by far the flattest suspension bridge ever. this resonance mode had never been seen before.

designer didn't do utterly exhaustive dynamic structural analysis with 100's of AI walking agents. because that's the only thing that would have predicted this behaviour

You've already pointed out that kids know how to get a swing to go higher so clearly architects must know about positive feedback mechanisms in suspended structures unless they have all lead such a sheltered life they have never been on a swing.

 

[weltweit]

... What happenned with the millenium bridge is slightly different. The motion of one person walking would make the bridge move sideways a bit. Unconsciously, someone else on the bridge has to adjust their own motion to compensate. This resulted in a feedback mechanism, like kicking legs on a swing to make it go higher - each person compensating for the side-to-side motion of the bridge only made it worse.

This was a novel case because the millenium bridge has such a slender profile. Most bridges are vertical structures and horizontal forces have little effect. The millenium bridge is so flattenned out that horizontal forces can come into play.

Aha, but surely the designers not taking into account the horisontal moment of walkers or perhaps not making the bridge strong enough horisontally against the force exerted by walkers or a number of walkers perhaps walking in time is still their mistake.

 

[Crispy]

*shrug*
You do new things, you make mistakes, you fix them. That's innovation for you.

 

[weltweit]

... Innovation isn't without mistakes, and the bridge and Eye were attempts to do something new in engineering, something this country used to excel in...

I think it is to be expected that people want things like bridges to be built on principles which are proven and well known about rather than as a process of testing by trying new things until one fails catastrophically perhaps when people are actually crossing on it.

 

[weltweit]

Hmm,

innovation, yes, the Tacoma Narrows Bridge ..

That one sure found a limit!

 

[Crispy]

Like I said, this is a different type of bridge, that had a novel resonant mode.

If you only want bridges built to 'proven' principles, then you're limited to a simple beam.

 

[Bahnhof Strasse]

Did I hear or dream that whilst this bridge was being built a similar one was opening in Paris and was also wobbly. The builders of the London bridge, instead of looking and learning from Paris' mistake, simply pointed their finger and went, Ha Ha!



Doh!

 

[weltweit]

Like I said, this is a different type of bridge, that had a novel resonant mode.

If you only want bridges built to 'proven' principles, then you're limited to a simple beam.

Havent we had enough twin tower suspension bridges yet to class them as "proven" ?

 

[kyser_soze]

'The desire for safety stands before every noble and grand activity'

Tacitus

Havent we had enough twin tower suspension bridges yet to class them as "proven" ?

The MB was a completely different type of suspension bridge tho, so it was using old principles in a new way.

 

[5t3IIa]

It means they should break step which each other, rather than all march in unison, ie just walk naturally.

Oh. They 'break' the leeeft right leeeft right stuff and just stroll over?

But what happens when a wobble starts they all start compensating in the same way and the harmonics go batshit? Or would that only happen if the harmonics were wrong in the first place?

 

[Sneaky Rushton]

I looked this up... http://uk.youtube.com/watch?v=j-zczJXSxnw

I seem to remember a documentary about this phenomenon on one of those Discovery Channel Mage Structures Docs... wind alone wouldn't make the bridge wobble, but beads of rain water on the supporting cables were the crucial factor... to counter this they covered the cables with a spiralling wire which somehow stopped the vibrations... I’ll try to find the clip...

 

[cybertect]

I walked across the Milennium Bridge at about 7pm on the day after it opened, and after most of the big crowds had dispersed. It was a bit wobbly, but it didn't bother me too much.

I think they closed it an hour or two later.

*shrug*
You do new things, you make mistakes, you fix them. That's innovation for you.

Quite. Beauvais Cathedral collapsed twice during its construction. The distinctive scissor arches of Wells Cathedral's central crossing were a remedial measure to prevent the tower collapsing.

 

[aylee]

I think the architects simply fucked up.

Jazzz in "looks for simplest and most rational explanation" shocker!

 

[hash tag]

It is closing again, for yet more repairs

Millennium Bridge: 'Wobbly' pedestrian crossing to close for repairs

Parts of the central London pedestrian crossing are beginning to degrade and need replacing.

www.bbc.co.uk