Florida bridge collapse solved... | GTAMotorcycle.com

Florida bridge collapse solved...

kwtoxman

Well-known member
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Horrible situation terrible terrible terrible...


But that guy is really fun and funny to watch...
 
A lot of the early speculative articles do not appear to be accurate. The structural folks on an engineering forum that I'm on have it mostly sussed out (and there was plenty of speculation early on there, as well; some of the early theories have been disproven).

http://www.eng-tips.com/viewthread.cfm?qid=436924

The current running theory is that the means of transporting the bridge from its construction location to the final location placed an element known as "member 11" - the outermost diagonal on the side that failed - into tension, which is the opposite of what its eventual loading would be with the bridge sitting on its piers. Concrete does not handle tensile loads well. This was evidently known, and was compensated for by pretensioning member 11 (steel cables apply tension that allows the concrete itself to remain in compression), but the process of setting the bridge down on its piers placed that element back into compression. This meant the concrete now had to take up not only the compression from the dead load but also the compression from the pretension. This is believed to have led to the initial crack that was thought not to be an issue, and it wasn't, until the pretension was removed and the joint between members 11-12 and the deck failed in the process of relieving the pretension.

In addition to all of this, concrete is a poor choice to make a truss from. When doing the structural analysis of a truss, one assumes that the joints are "pin joints" i.e. the joints do not transmit any moment loads (torque / twisting). Steel can approximate that by bending slightly. Concrete is unforgiving.

No one knows why this wasn't built as a steel structure with a concrete non-structural deck, and decorative cladding around the steel members if someone so desired the bridge to look the way it did ... in other words, the same way as thousands of other bridges that are still standing. There was evidently a lot of politics behind the construction of this bridge.

No one also knows why traffic was allowed under the bridge during pretensioning (or relieving pretension, as the case may be). Pretensioning is recognised as being a dangerous operation, and in structures that rely on pretensioning to achieve their load capacity, the structure is not functional "as designed" until that pretensioning is complete.
 
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I'm just catching up in that thread myself. Best post ... "Just a general blood pressure warning - do not search YouTube for videos of people explaining this. I would suggest cat videos instead."

LOL
 
Engineered to withstand Cat5 hurricane winds, forgot gravity. .

It's not at all clear if it would have remained standing for long even if the construction had been completed. Take a look at any normal bridge that uses a truss. There's a truss structure on each side of it. If load is applied to the left side of the bridge, the left truss takes most of the load; if load is applied to the right side of the bridge, the right truss takes most of the load, not a problem. This one had one in the middle. Any off-center loading would tend to twist the deck and there's not much to resist it over the length of that span. Any such attempt to twist the deck would try to twist the joints between the diagonals and the deck. Concrete doesn't like that.
 
Meanwhile in the inappropriate memes dept.

attachment.php
 
Looks like a bridge in China lol. I'm sure China is laughing & saying, haha, American bridges!
 
someone posted a dash cam of it collapsing right in front of them. some of those people were mere feet from being right under it. sorry for the ones that were. nuts...
 
The current running theory is that the means of transporting the bridge from its construction location to the final location placed an element known as "member 11" - the outermost diagonal on the side that failed - into tension, which is the opposite of what its eventual loading would be with the bridge sitting on its piers. Concrete does not handle tensile loads well. This was evidently known, and was compensated for by pretensioning member 11 (steel cables apply tension that allows the concrete itself to remain in compression), but the process of setting the bridge down on its piers placed that element back into compression.

So, in laymen's terms, the bridge was damaged during transport, they were aware of it, and chose to proceed with a jury-rigged solution. Is that a fair assessment, Brian?

via Tapatalk
 
You might wanna fact check a site that is used as gospel. They are not exactly politically neutral. The founders of snopes also had problems with the law. Just saying...


True. Snopes has been caught lying several times. In this case they're mostly right. But...the meme I posted wasn't claiming an "all female" company, just one of the chief engineers. The girl in the pic was involved, but men were too. Regardless, there's a point at which we take these things too seriously. There are lots of good female engineers.
 
So, in laymen's terms, the bridge was damaged during transport, they were aware of it, and chose to proceed with a jury-rigged solution. Is that a fair assessment, Brian?

via Tapatalk

It isn't clear if the crack happened during transport or when they set the bridge down on its supports. It was apparently spotted 2 days before collapse. The thread linked to above now has some rough-estimate back of notepad calculations concerning the joint between the deck and diagonal 11 and 12. This supports the view that the bridge was doomed by design.
 
You might wanna fact check a site that is used as gospel. They are not exactly politically neutral.

Care to point to some articles that prove that...or are you just upset because the facts they post don't always fit your political slant?

The founders of snopes also had problems with the law. Just saying...

An ownership debate after a divorce. Has zero to do with the legitimacy of the articles.

Anyhow, that aside, I also wonder why the hell the road was open during a stress test. Simple logic would dictate that any such test shoudl have been done with the road closed and surrounding area cordoned off for safety.
 
Care to point to some articles that prove that...or are you just upset because the facts they post don't always fit your political slant?



An ownership debate after a divorce. Has zero to do with the legitimacy of the articles.

Anyhow, that aside, I also wonder why the hell the road was open during a stress test. Simple logic would dictate that any such test shoudl have been done with the road closed and surrounding area cordoned off for safety.
http://www.dailymail.co.uk/news/article-4730092/Snopes-brink-founder-accused-fraud-lying.html
 

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