35W bridge in minneapolis collapses

[radou]

Excuse me, I am going to go hide in my closet now with my duct tape.

Short off-topic comment: at some point, you'll have to get out of the closet, though. :tongue:

 

[Cyrus]

Here I found the animation.

http://video.wnbc.com/player/?id=138456

wow, did I really need this animation to see what happened.

 

[russ_watters]

Isn't there any resistance from the connecting roads? I was just wondering if it would take slightly longer to begin a drop because of the steel beams (or stiffening girders?) running horizontally underneath, connected to the ends of the bridge and the anchorage blocks or abutments. If so, perhaps that would explain the "earthquake" descriptions, that the bridge has to pull away from the ends?

Yeah, and of course, parts of the roads never detatched, so those sections only fell at one end. So perhaps the outer third on each side was slowed by that. But the center of the span would have fallen at near freefall acceleration. Also, though, supporting a falling object from one side makes half of it fall slower than g, but the other half faster than g because the center of gravity is trying to accelerate at g. That's why smokestacks that are demolished by toppling them break while they are falling - the different accelerations cause them to bend.

 

[Mallignamius]

(I only a few minutes ago saw the animation. I didn't know it broke up.)

So then could a connected end quickly snap upwards (following a detachment)? I suppose under such circumstances, cars could go flying if they're on those sections.

 

[Cyrus]

Not according to the animation! LOL

 

[russ_watters]

They have video of the actual collapse online now...

 

[ranger]

Yea, you should watch the video on cnn's website instead of those crappy animations.

As I was reading the morning papers, they were saying that the bring had an inspection in 1990. To sum it up, it was given "structurally deficient".
http://www.courant.com/news/nationworld/nation/wire/sns-ap-bridge-collapse,0,1159498.story?coll=hc_features_outdoors_util

 

[chief]

I like how the newspeople are asking, "well, they were jackhammering near the bridge, do you think that might have been a cause?"

Actually the jackhammering could have played a part in the collapse. If there were already corrosion problems and fatigue cracking in the welds, it is very possible that the vibration from the jackhammer amplified the problem and was the immediate cause of a truss connection failure... which in turn caused the rest of the bridge to come down.

 

[Cyrus]

A jackhammer is not really going to put a stead sinusoidal vibration on the bridge at exactly the resonant frequency of the structure. Could it play a role, possibly. The point is, it was a stupid question/statement for the reporter to make. I have seen a few clips of reportes saying stuff without knowing what there talking about, such as: "I know in a suspension bridge that if one section fails the whole bridge fails" and the expert told him, "well, that's not true". Quite sad.

Bumper to bumper traffic twice a day for 40 years of loading and unloading the bridge will fatigue crack it appart though.

 

[Alkatran]

The coverage makes me believe everyone should be forced to play armadillo run, or a similar game, in school at some point. It's amazing how small the difference between all-ok and near total collapse is.

 

[chief]

A jackhammer is not really going to put a stead sinusoidal vibration on the bridge at exactly the resonant frequency of the structure.

You don't have to have steady vibration at the resonant frequency of the truss to cause fatigue stress in the connections. I'm a licensed structural engineer by the way.

 

[Cyrus]

Interesting, you think jackhammers would have an effect on such a large structure? Personally, I find it rather hard to believe. I would expect the vibrations of the cars and tractors trailer going up and down the bridge to wash out the noise from a jack hammer.

 

[chief]

Interesting, you think jackhammers would have an effect on such a large structure? Personally, I find it rather hard to believe. I would expect the vibrations of the cars and tractors trailer going up and down the bridge to wash out the noise from a jack hammer.

I'm not saying the jackhammer caused the collapse, but it could have contributed. I think corrosion and fatigue were the main problems... but since only 2 of the 6 lanes were open at the time of collapse, something else must have played a part. Otherwise it would have collapsed on a day when it was more heavily loaded (all 6 lanes full).

 

[Cyrus]

Cheif, you should get a copy of the New Yorker, June 25, 2007, pg. 70. They have a nice article on Cecil Balmond.

He is one of the top structural engineers in the world right now.