Author Topic: New Miami Foot Bridge Collapse Bad Engineering?  (Read 11494 times)

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Offline Quarlo KlobrigneyTopic starter

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New Miami Foot Bridge Collapse Bad Engineering?
« on: March 15, 2018, 09:15:28 pm »
« Last Edit: October 26, 2019, 03:49:17 am by Quarlo Klobrigney »
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Offline floobydust

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #1 on: March 15, 2018, 10:08:29 pm »
My condolences to the families and loved ones of the dead, in this tragedy.

The pedestrian bridge was not finished, it is a cable-suspension bridge without the suspension support installed.
It's early but I question the span design could ever support its own weight. There was a crew working at the end that broke.

It was supposed to showboat "Accelerated Bridge Construction methods".

It seems like a fat, obese bridge at 950 tons, for this collapsed section.
 

Offline Kjelt

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #2 on: March 15, 2018, 10:20:02 pm »
My sympathies for those involved.
Here in Holland last year a brand new carparking collapsed.
The experts couldn't believe what they found, some concrete plate building technique already in use for decades and in the building community accepted as proven was the cause.
Now every building using this technique has to be investigated and perhaps toredown.
It shows that design errors can be hard to surface.
 

Offline Cerebus

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #3 on: March 15, 2018, 10:36:23 pm »
It was supposed to showboat "Accelerated Bridge Construction methods".

That's not a good thing to hear. There was a movement to use "Accelerated Construction" methods for high rise dwellings in the UK in the 60s and it lead to this:

The Ronan point Disaster


Anybody got a syringe I can use to squeeze the magic smoke back into this?
 

Offline Quarlo KlobrigneyTopic starter

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #4 on: March 15, 2018, 10:38:22 pm »
I can only speculate that the top section weight, without the proper end support, cracked the small vertical(s) and fell to the lower part.
I wish that they would remove some of the sections, not just walk around.
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Offline Quarlo KlobrigneyTopic starter

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #5 on: March 15, 2018, 10:42:42 pm »
The Ronan point Disaster
And then there's the Grenfell Tower..Someone's bright idea of flammable cladding.
This is not just a mistake made by one but by committee.
« Last Edit: March 15, 2018, 10:46:09 pm by Quarlo Klobrigney »
Voltage does not flow, nor does voltage go.
 

Offline raptor1956

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #6 on: March 15, 2018, 11:15:43 pm »
Too soon to say for sure, but it should be pointed out that bridge was set in place just this past Saturday and they were still working on it.  Roughly speaking, there's about four areas of interest:  the design, the materials, the construction, and the environment.  They will look into everything, they have to, but I'd bet the design was OK and the weather wasn't an issue leaving material and construction as the two most likely.  I doubt the materials are the issue, though this is an area that contractors have frequently cut corners on -- they had no live load on it at all so it would have had to have been really poorly designed and/or really cut enormous corners for it to fail from a materials problem without any live load on it.  Finally, the fact that they were still working on it is key and I'd bet that is what will be the outcome. 


Brian
 

Offline Stray Electron

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #7 on: March 16, 2018, 03:35:23 am »
   The local Miami news said today that the bridge was undergoing some kind of stress test when it collapsed.   :palm:
 

Offline floobydust

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #8 on: March 16, 2018, 04:15:01 am »
"If workers were adjusting cables once the bridge was in place, the cables should not have connected to the bridge’s structural integrity, Verrastro said. “Once you’re done tensioning those cables, you’re done,” he said.
It’s possible the cables were over-tightened, causing the bridge to elevate slightly in what’s called a camber. Adjusting the cables to address camber would be appropriate, but that would not impact the structural strength.
“If they were adjusting the structural cables, it was to try to put more or less camber,” he said.

Still, adjusting the camber — called tuning the bridge — can be tricky. Robert Bea, a University of California Berkeley engineer and catastrophic risk expert, has studied hundreds of structural failings including the BP Deepwater Horizon. According to Bea, when workers adjusted the camber on a bridge in Australia in the 1970s, it also collapsed. {West gate bridge} “The steel buckled while they were attempting to tune this camber, so it’s very plausible,” he said.
...
The bridge’s superstructure was something Verrastro said he’s not seen in 42 years of designing bridges. Rather than using steel trusses, it employed heavier concrete trusses. The bridge also had a concrete roof, adding even more weight. “This was a very long span and then they used very heavy material,” he said. “The majority of pedestrian bridges are steel.” Steel bridges are about one-tenth the weight of concrete, he said.

copy pasta from http://www.miamiherald.com/news/local/community/miami-dade/article205422719.html
 

Offline ez24

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #9 on: March 16, 2018, 04:34:54 am »
"If workers were adjusting cables

Human error
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Offline jonovid

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #10 on: March 16, 2018, 05:22:44 am »
if it feels right? when engineers get it wrong
is this a warning to all engineering school graduates?
Hobbyist with a basic knowledge of electronics
 

Offline DG41WV

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #11 on: March 17, 2018, 01:22:58 am »
Bit of a different point of view by AvE.

 

Offline floobydust

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #12 on: March 17, 2018, 02:21:52 am »
First fail: "Advanced Bridge Construction" - leaving out the support tower and cables  :palm: so you can install the bridge span.
You couldn't swing the span into position with a tower in the way. With no support cables, it's under a lot of stress to support its deadweight.

Second fail: It has absolutely minimal steel, it's all concrete. Massive cheap bloated design is unable to support it's deadweight. 950 tons to support pedestrians?

Third fail: "Stress test" while traffic is flowing underneath. Video of the collapse show the work crew broke (a cable?) before it fell.

Fourth fail: Engineering design review
 "...FIU picked a firm that was not pre-qualified to check the design of the bridge, which was required because it was such a long pedestrian bridge and other unique characteristics. The firm selected, Louis Berger, was not FDOT pre-qualified for this service, which is required under FIU’s agreement with the state. FIU’s design build team is responsible for selecting a pre-qualified firm and ensuring this process is followed,” the governor said in a statement. "
 

Offline lordvader88

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #13 on: March 17, 2018, 03:57:01 am »
Not the type of thing most people would be cautious of. Likewise I 'assume' my roof is not going to fall in on my head.
 

Offline tooki

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #14 on: March 17, 2018, 05:52:49 am »
FYI, AvE has posted a second video explaining what he and the Hive Mind believe to be the smoking gun.
 

Offline llkiwi2006

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #15 on: March 17, 2018, 06:01:01 am »
FYI, AvE has posted a second video explaining what he and the Hive Mind believe to be the smoking gun.

Link here for convenience: https://youtu.be/KtiTm2dKLgU
 
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Offline jmelson

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #16 on: March 17, 2018, 04:46:01 pm »
   The local Miami news said today that the bridge was undergoing some kind of stress test when it collapsed.   :palm:
Our paper said the tension on "the cables" had slipped, and they were being retensioned when the collapse happened.  From the photos, this looks a lot like post-stress construction, where they put steel cables in with the rebar before pouring the concrete in.  About 2 weeks later, they use a hydraulic gadget to tension the cables and then lock them into big steel plates with conical grippers.  Then they cut the end of the cables off.  Once the cables are cut, I don't think they can be retensioned.  But, maybe there is new technology.  Anyway, where I've seen this done (parking garage at my work) they tension the cables BEFORE removing the support and concrete forms.

And, it was reported the engineering firm saw cracks in the concrete a day before the collapse and reported it to the highway department, but nobody heard his message until after.

And, although I'm not a structural engineer, or anything like it, it SEEMS to me that adjusting the tensioning cables while traffic is driving below the bridge is the HEIGHT of insanity.  There are so MANY opportunities for something to go wrong, and it the cable tension is lost, the bridge WILL collapse.

Jon
« Last Edit: March 17, 2018, 07:07:06 pm by jmelson »
 

Offline amyk

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #17 on: March 17, 2018, 05:07:44 pm »
I can't help but think of this thread also happens to be close by... https://www.eevblog.com/forum/chat/feminist-professor-thinks-'rigor'-is-evil/

 
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Offline tooki

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #18 on: March 17, 2018, 05:51:00 pm »
I can't help but think of this thread also happens to be close by... https://www.eevblog.com/forum/chat/feminist-professor-thinks-'rigor'-is-evil/
Everybody knows structural engineering is a social construct!
 

Online Marco

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #19 on: March 17, 2018, 09:48:56 pm »
Presumably the bridge was just a truss, with the stays purely cosmetic. Making the web out of tensioned concrete seems a bit cutting edge though. If you have to hold up the hydraulic jack with a crane to tension the tendons I can't help but feel it's all a bit experimental, not suited for doing with traffic.

Making the web out of steel and the top/bottom out of tensioned concrete would be the easy way out. No need to tension all those awkwardly angled tendons with lots of setup time. The top/bottom also have far more tendons sharing load than the web, so if one breaks the bridge might not immediately self destruct.
 

Online chris_leyson

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #20 on: March 17, 2018, 10:14:48 pm »
I got the impression it was just a truss but made to look like a suspension bridge. Having to post stress all the concrete members after the bridge has been partially erected, I don't know, it just seems crazy. Wish I had kept some my old structural engineering text books but I dropped out of civils in the 80s when the recession hit, I don't think they would have been a lot of use anyway certainly not in this case. Prefabricating bridge sections off site and just dropping them in place is nothing new. Just have to wait for the final report.
 

Offline raptor1956

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #21 on: March 18, 2018, 03:00:53 am »
Boy, I gotta say, if the whole cable-stay look was just for show then the entire concept gives me reason to worry about the thinking that went on to design and build this bridge.  I think the analysis the AvE has so far done, though far from conclusive, does seem to point to the work on the post tensioning.  In my first post on this I suspected workmanship and the evidence seems to confirm that.  Six dead for a show horse!


Brian
 

Online BrianHG

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #22 on: March 19, 2018, 03:07:09 am »

A cloud of smoke shoots out from under the bridge in front of the crane on the left at around 6 seconds in, then, half a second later, it collapses breaking just to the right of that smoke.
« Last Edit: March 19, 2018, 03:09:27 am by BrianHG »
 

Offline Quarlo KlobrigneyTopic starter

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Re: New Miami Foot Bridge Collapse Bad Engineering?
« Reply #23 on: March 19, 2018, 04:29:30 am »
    ^^^^^^^^^
I've yet to find a clear video of the live "event". All I get is the one with people in front of a screen or very low res. Do you have a valid clear link to one?
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