Short Video on the Miami bridge failure!!!

JD Seller · Mar 17, 2018

This gentleman does excellent videos on complex issues. The one that caused me to start watching his channel was the Orville Damn in CA. HE is a commercial pilot with his own plane too. He shots some really nice pictures of what was/is going on at the Orville Damn.

In this video he talks about the Miami bridge. He has pictures and explanations of how the bridge was supposed to work. He also has information from the NSB preliminary report.

Some facts that many of us Yters did not know are:
1) The bridge was NOT a suspension bridge. The central tower and cables where just for looks.
2) They where adjusting one of the cables on the bridge's center support structure when it failed. It appears the cable they were working on failed.

https://www.youtube.com/watch?v=sBDDQLcp6iI
Miami Bridge Failure preliminary analysis 17 March 2018

jeffcat · Mar 17, 2018

Also notice the concrete just turned into a big pile of korn flakes. Something was REALLY not right with this whole thing.

David G · Mar 17, 2018

I just watched the video, and did supporting research on it, yes cables were ornamental.

That sure sounds like a dumb idea to me.

gtractorfan · Mar 17, 2018

Sure seems to me the trusses (braces) and framework would have been steel, not concrete.

oldtanker · Mar 17, 2018

I don't see concrete as a problem. High quality concrete, properly reinforced is extremely strong. Heck they make highway bridges out it that carry hundreds of thousands of pounds at any one time. A foot bridge should be nothing. I suspect given that the cables were just for looks that substandard materials are going to come into play.

Rick

dpendzic · Mar 17, 2018

sure looks like a cable stayed bridge to me---perhaps the cables helped support the live load while the dead load was self supporting by the truss design that failed?

JD Seller · Mar 17, 2018

oldtanker: The issue is the "new" design in this bridge, which is the truss system used being concrete with imbedded cables. The most common truss bridges, Pratt or Warren bridges, use steel for the trusses. It is much stronger for its weight than concrete. Also steel is more flexible than concrete. Concrete is ridged for the most part. I do not see how you could "adjust" cables that are embedded in concrete.

Lots of questions on this whole thing. A big one is why would they be adjusting the cables on the main support trusses while traffic was still flowing under the bridge??

I see a lot of odd designed stuff that is made the way it is just to "look" pretty. I think this will come out as a contributing cause in this failure. They could have easily designed a more conventional bridge that would have been stronger/simpler/cheaper but it would have not looked "modern/pretty".

dpendzic · Mar 17, 2018

adjusting cables in the concrete is called "post Tensioning" the cables are actually run thru a void in the concrete or have a debonding material around them so you can tension them after the concrete has set to its required strength

David G · Mar 17, 2018

Northvale PA · Mar 17, 2018

I was listening to a radio talk show yesterday. The amount of people giving uneducated comments about bridges and structure failures was nauseating. Since I happen to be an engineer and work in the construction industry, here is my advice for anyone who cares: wait until the investigation determines the culprit. Seriously, it could be one of hundreds of design issues, material components or workmanship. I have seen all three problems and I am sure every one of you has too on various machines and autos, just for example . The failure was bad. The fact that the public was exposed to it was horrible. A good friend and Co-worker of mine tells me a saying his dad (construction superintendent) had: if it doesn?t fall down while you are building it, it probably won?t. Sobering wisdom from a guy who built high rises for most of his career.

Hoenes · Mar 17, 2018

Also, post tensioning is very time sensitive. Usually 3 to 5 days after the concrete is poured. Too early, cables tear up out of the concrete. Too late, the concrete is too brittle, and can crack. Testing labs take test cylinders out of the ready mix trucks. When they reach 3500 psi crush strength in a hyd. press, it's time to pull the cables. The cables would have been pulled, down in the parking lot,or wherever it was pre-fabbed. Whoever made the "field call" to pull the cables again,up in the air, is in serious trouble. Too hard, too brittle. (3500 plus or minus, been a few years)

gregww · Mar 17, 2018

I guess I am stupid. OP said the cables were for decoration only. So what does it matter what they were doing with the cables? Maybe I am misunderstanding.

dpendzic · Mar 17, 2018

tensioning is done when the strength of the concrete reaches around 80% of the 28 day design strength. I always used 5000 psi design strength so we transferred stress at 4000 psi. Much higher strength concrete is used these days--up to 10000 psi

dpendzic · Mar 17, 2018

the upper cables for looks or stays were not in place yet--they were speaking of the prestress cables inside the concrete truss elements

gregww · Mar 17, 2018

(quoted from post at 20:21:30 03/17/18) the upper cables for looks or stays were not in place yet--they were speaking of the prestress cables inside the concrete truss elements

eah Watched the video again...now I got it Thanks

Ozlander · Mar 17, 2018

Thanks for posting that.

Hoenes · Mar 17, 2018

d, your numbers sound more like it. Been a while since I was in the parking garage and high rise business. I'm a carpenter, not an engineer. One thing for certain, we NEVER proceeded until we got the "green light" from firms such as yours.

dpendzic · Mar 17, 2018

Yea--but remember no one is infallible!!! At least none of the prestress bridges I designed have fallen down!---YET

paul · Mar 17, 2018

Thanks.

Just for looks? Yikes. Tax money is free, right?

Paul

Ian Beale · Mar 18, 2018

A few extras here

http://www.smalldeadanimals.com/2018/03/the-fiu-bridge-.html

dr sportster · Mar 18, 2018

That thing really broke apart. The guy making the video must be trustworthy because he has a KTM motorcycle video.

JerryCPP(WA) · Mar 18, 2018

Maybe the people who designed this bridge were fans of Calvin and Hobbes . . . https://nnalert.com/ya86oasy

DoubleO7 · Mar 18, 2018

Not that it matters but I read elsewhere that the "cables" shown in the renderings are actually steel pipes with flanges at each end and bolted. Maybe there are tension cables inside as well.
Cosmetic, maybe but all that is a lot of work for cosmetics and a real lost opportunity to easily add some extra support to the entire structure for not much more effort.

Just sayin.

Short Video on the Miami bridge failure!!!

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