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The Ordinary Engineering Behind the Horrifying Florida Bridge Collapse (wired.com)
An anonymous reader quotes a report from WIRED: The people of Sweetwater, Florida were supposed to wait until early 2019 for the Florida International University-Sweetwater University City Bridge to open. Instead, they will wait about that long for an official assessment from the National Transportation Safety Board of why it collapsed just five days after its installation, killing at least six people. In the immediate aftermath of the disaster, many queries have centered on the unconventional technique used to build the bridge, something called Accelerated Bridge Construction, or ABC. But ABC is more complicated than its acronym suggests -- and it's hardly brand new. ABC refers to dozens of construction methods, but at its core, it's about drastically reducing on-site construction time. Mostly, that relies on pre-fabricating things like concrete decks, abutments, walls, barriers, and concrete topped steel girders, and hauling them to the work site. There, cranes or specialized vehicles known as Self-Propelled Modular Transporter install them. A video posted online by Florida International University, which helped fund the bridge connects to its campus, showed an SPMT lifting and then lowering the span into place.
In a now-deleted press release, the university called the "largest pedestrian bridge moved via SPMT in U.S. history," but that doesn't seem to mean much, engineering-wise. SPMTs have been around since the 1970s, and have moved much heavier loads. In 2017, workers used a 600-axle SPMT to salvage the 17,000 ton ferry that sank off the coast of South Korea in 2014. The ABC technique is much more expensive than building things in place, but cities and places like FIU like it for a specific reason: Because most of the work happens far away, traffic goes mostly unperturbed. When years- or months-long construction projects can have serious effects on businesses and homes, governments might make up the money in the long run. Workers installed this collapsed span in just a few hours. These accelerated techniques are also much safer for workers, who do most their work well away from active roads. The report goes on to note that the bridge collapse is still under investigation and the search for a culprit is ongoing. "The answers could run the gamut, from design flaws to fabrication flubs to installation issues," reports WIRED. As of publication, The Washington Post is reporting that an engineer called the state to report cracking two days before its collapse.
In a now-deleted press release, the university called the "largest pedestrian bridge moved via SPMT in U.S. history," but that doesn't seem to mean much, engineering-wise. SPMTs have been around since the 1970s, and have moved much heavier loads. In 2017, workers used a 600-axle SPMT to salvage the 17,000 ton ferry that sank off the coast of South Korea in 2014. The ABC technique is much more expensive than building things in place, but cities and places like FIU like it for a specific reason: Because most of the work happens far away, traffic goes mostly unperturbed. When years- or months-long construction projects can have serious effects on businesses and homes, governments might make up the money in the long run. Workers installed this collapsed span in just a few hours. These accelerated techniques are also much safer for workers, who do most their work well away from active roads. The report goes on to note that the bridge collapse is still under investigation and the search for a culprit is ongoing. "The answers could run the gamut, from design flaws to fabrication flubs to installation issues," reports WIRED. As of publication, The Washington Post is reporting that an engineer called the state to report cracking two days before its collapse.
Like every engineering disaster, somebody found the problem, and failed to communicate its severity. In this case, they decided it wasn't a safety issue (cracks in a brand new bridge!) and left a voice mail with somebody else who was out of the office for a few days.
There's no substitute for risk assessments by fully qualified engineers, of course. But those engineers also need communication skills â" including persuasive skills. Engineers who can find somebody in authority and convince them to take action save lives.
The engineering drawings I have seen show a tall tower with suspension supports coming down to support the span. Was the tower complete and the suspension in place when it broke or was that for completion later? Also the suspension when to both sides of the tower so it was balanced. Are there any pictures of the bridge while it was "good" to compare with the engineering drawing?
See here for a 3d view of the design. As far as I could tell the tower, the section over the water and the suspension lines were not in place when it collapsed.
https://youtu.be/Q2A1wS09p0k?t=5
To start, it was a truss bridge, self-supported. The stays shown in final drawings are pipes for stiffening and harmonics in high winds.
The structure was non-redundant. A failure of any truss was near guaranteed to lead to collapse. It's theorized by some that truss member #11 at the junction of the pier was initial failure point.
In preliminary drawings, #11 is shown with no post-tensioning bars, but the actual construction shows it with two. While those bars in #11 may have been necessary due to the move, since the ends of the bridge were cantilevered (which is different than shown in the preliminary drawings), they likely weren't needed after placement; not needed to be post-tensioned, since #11 would be in high compression.
It appears workers were post-tensioning #11 using a crane and other equipment attached to one of the post-tension rods. It appears tensioner (blue) and part of the bar is sticking out several feet in photos of the collapse. According to some, this likely lead to the collapse.
The ABC technique is much more expensive than building things in place, but cities and places like FIU like it for a specific reason: Because most of the work happens far away, traffic goes mostly unperturbed.
Nope!! That span was assembled right next to the road where it was placed. I drive by it every day and I can assure you, even though it wasn't on the road, it disrupted traffic due to rubbernecking for over a year.
"Hello, I'm an American. As such I have some sort of pathological need to reference my personal political beliefs in every single interaction I have with anyone and anything. No matter how unrelated the discussion at hand is."
It will be interesting as one of the prime's MCM, has had issues in the past. MCM gives generously to Christie and Rubio.
In my town we have a footbridge that was installed this way, several years ago. It was factory-built in Phoenix, hauled 100 miles up I-17 using one of the smaller roadable version of the SPMT, and installed overnight to cross a creek. There hasn't been a problem since.
Offsite construction should be safer than site-built, so in this disaster let's focus on the design itself, rather than rushing to judgement on the offsite construction.
Here is a story of another seemingly similar bridge. Tower with stays pedestrian bridge. The deck was originally planned to be concrete but design revisions changed it to steel. Would be interesting to look into that decision.
http://johnsankey.ca/path2014.html
From the 13 April link in above: http://www.davidmckie.com/airport-parkway-bridge-undergoes-new-design-after-pricey-deficiencies/
"Delcan reviewed the partially completed structure and found that there were many deficiencies, including cracks in the concrete tower and in the bridge deck-these are obvious safety concerns."
It's much more likely the fault of a diversity hire.
Sure, xe couldn't pass algebra, but xis skin color raised our minority numbers. It was well worth it, being this woke.
I know right. And we even had to wait for the first comment to correctly make it political and blame Trump.
engineering-wise. SPMTs have been around since the 1970s, and have moved much heavier loads
Depends what you call a SPTM. Bridges have been prefabricated and moved into place since pre-historic times, starting with carved tree trunks. It does not matter how the bridge gets put there, what matters is its strength and that of its supports. Here is a much more ambitious construction, overseen by Robert Stephenson and Brunel no less, over dangerous water too, 150 years ago :- Britannia Bridge, Menai Strait
It was not a cable-stayed bridge. It's a truss. See my other posts for details. Hopefully, someone can mod them up for visibility. Thanks in advance!
The complexity and risk of the intermediate stages of a project are the most impressive things to me about civil engineering. It's one thing to design a dam, it's another to build that dam in the middle of an actual river; you need a dam to build a dam. It's one thing to draw a bridge that's perfectly stable once built, it's another to ensure the partially completed structure is in perfect equilibrium at every point from the time the moment the ground is cleared until the last cable is tightened.
If you think about what ABC involves, it really ought to make bridge construction safer, but I think in this case people simply put too much faith in it. Any time you put something heavy over someone's head, you're taking a terrible risk. For a completed bridge, engineering reduces that risk to negligible, but if you're going to be building that bridge while people pass under it every intermediate step has to be as safe as the completed structure. I wonder if that's even possible.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
I've been wondering about that ever since I saw the first images of its proposed shape. "Where's the pylon? Where are the supports?"
Obviously it wasn't strong enough to span the distance without them. Doh. But not a word from the media yet about that missing pylon or supports.
It seems that the tower+cables were a mere cosmetic thing, they were not supposed to support the bridge.
Miami bridge that collapsed was a truss design, despite the cosmetic tower, support cables
It was in the process of being constructed, they hadn't got to that bit yet. It was engineered from day 1 to be put up without the supporting pylon. However some things were changed from the initial design.
AvE does his best to analyse what went wrong.
https://www.youtube.com/watch?v=ioC61QW7SHQ&t=0s
https://www.youtube.com/watch?v=KtiTm2dKLgU&t=0s
Obviously it wasn't strong enough to span the distance without them
That isn't obvious at all. That's why we do incident investigations. Just because it's final design was to have cables doesn't mean that during construction this wasn't taken into account. There is a lot of reasons why this incident could have happened.
They slide this 950 ton slab onto the pilings and congratulated themselves. Great job of building a suspension bridge without you know the suspension part that holds it up.
Only the State obtains its revenue by coercion. - Murray Rothbard
Now imagine what would happen if enough people say "Fuck this, I am not voting for any shitty candidate."
One of the two losers still wins. There is no quorum requirement in American elections.
I doubt it. The span itself weighs 950 tons. It seems improbable they have to add extra support to ensure the bridge can carry an additional 5-10 tons, especially given the usual engineering rule of thumb that you build to support twice the forces you expect.
You are not alone. This is not normal. None of this is normal.
Is there any huge advantage to making something out of concrete/rebar when it's designed to handle only foot traffic?
I think this could be a case of style over substance.
You know, you'd be more visible if you didn't post AC.
They were tightening the cables that run through the structure - it's called post tension concrete - Concrete is strong in compression but weak in tension, so the idea is to preload the structure with large cables under tension - which squeezes the concrete.
This is extremely common with slab on grade houses these days.
If you consider a beam supported between two supports, there's a bending moment - the top is in compression, the bottom is in tension. If you externally apply a force to squeeze the ends together then you can make it so that the bottom is in compression and the top is in even more compression, both of which are easily handled by the concrete.
In this bridge that is done by cranking cables through the bridge. In something like, say, the Roman Arch, it's done by having massive side supports. In Gothic cathedrals, it's flying buttresses.
This isn't exactly new engineering - although the details change over time.
Concrete is cheap and easy to make withstand things like hurricane winds.
Other alternatives are steel beam truss (very expensive for the span)
or some sort of suspension bridge (requires a strong vertical support and often more room for the backstays on the support) - Calatrava's bridge in Chico, CA, or the Golden Gate.
The possible explanation to the failure (over tightening of one or more post tension rods) as detailed in this AvE video, seem to make sense. https://www.youtube.com/watch?...
Like supporting it's own weight, perhaps?
Faster! Faster! Faster would be better!
If people here listen to personalities first and reason second, they do not deserve the latter.
Have gnu, will travel.
The Reason Foundation has published an article about the bridge was funded by a federal program that has come under repeated fire for awarding money based on politics rather than merit:
Collapsed FIU Bridge Was Funded by Federal Grant Program Criticized for Shoddy, Politicized Review Process - The TIGER grant program has come under fire for putting politics ahead of technical concerns.
AvE over on youtube did a very good commentary on how and why the bridge collapsed. Video 1 (overview): https://www.youtube.com/watch?... Video 2 (technically in depth): https://www.youtube.com/watch?...
Mod this up, The AvE analysis covers changes from the original design and the pretensioning cables embedded in the deck that where over tensioned till failure due to those changes as evidenced by what can be seen in the rubble and the video of the collapse. It was made all the worse that they where doing this while there was still traffic going beneath it.
This bridge had to withstand hurricane force winds, thunderstorms and salt water erosion, plus not get in the way of traffic
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If 6 people died while we were inventing a new technique that improves construction for a decade, it's a sad growing pain. If 6 people died because of a fuckup in traditional design, it's horrific.
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or SMPTE (Society of Motion Picture and Television Engineers).
In my opinion, it was wrong to keep the road open until the 1000 tons bridge was fully functional and well tested.
But they could not close the road because there are basically no other modes of transportation. No bicycle routes worth mentioning, no pedestrian alleys, no trams.
Close the road for two days and the town collapses.
"Imagine this, they KNEW that pylon and support was to added later. Gee, duh. You don't think they planned for that?" What is more plausible: The team of engineers and contractors 'forgot' the cable stays, or the people who think they 'forgot' the cable stays are morons?
...which means, obviously, why did they need to do any cable tightening to begin with? If it was to ensure the structure that supports the bridge was capable of supporting 1,000 tons, then that suggests it was never safe to begin with
No. Concrete under compression behaves much differently than concrete under tension. A concrete span of that length couldn't possibly survive on it's own; gravity would cause the centre to sag more than the ends, which would put a tensile force on it and literally pull the concrete apart. To avoid this you add cables which compress the concrete, eliminating the tension. With the tension gone your span goes from fail-under-its-own-weight mode to being able to support several times it's own weight.
People filter zero-score (where AC posts start) due to shit like GNAA.
Circumcision is child abuse.
man you are a fucking moron.
i could live a little longer in this prison
Were they sure EVERYONE working on the project knew it was a truss bridge?
Laws are rules for the court, but merely a bottom bar to hit for life. Think beyond laws in your actions always.
I read at -1, showing all posts. I'd still like to suck on some of that dick, though. I hope I'm not ineligible.
https://youtu.be/KtiTm2dKLgU
In GOD we trust, all others we monitor.
I thought corporate taxes in the US were insanely high, compared to Europe for instance. Or is this a classic case of high taxes and numerous loopholes that are only available to a happy few megacorps?
If construction was anything like programming, an incorrectly fitted lock would bring down the entire building...
One of my favorite youtube personalities has a couple interesting things to say about this, and presents a well reasoned conclusion....
https://www.youtube.com/watch?...
and
https://www.youtube.com/watch?...
I don't know many details about this canadian fellow but he's he's no idiot and funny af.
enjoy...
chris watts íë¦ìS ì(TM)ì
In other words, if the cable tightening were to ensure the structure that supports the bridge was capable of supporting 1,000 tons, then that suggests it was never safe to begin with.
You are not alone. This is not normal. None of this is normal.
I would argue that there should be enough cable redundancy so that one or two failures wouldn't bring down the whole bridge, which IMO makes it at least partially a design issue, too, but....
Check out my sci-fi/humor trilogy at PatriotsBooks.
It's not even about political beliefs anymore. It's about emotions, and more specifically virtue signaling. And it's not only with Americans, it's with most people living in Western societies, particularly white people. "Hello, I live in the West, I'm white, let me virtue signal."
or build the bridge. Instead, only woman or minority owned business were picked from. The president of FIU even bragged about that during the ground breaking ceremony. I bet he already regrets saying that.
Your comments look like the rantings of an angry white male. First, we don't know that was true, second why cast aspersions at someone because of their sex. You know nothing about that. How about if you said that about a black engineer? It would be obvious racism. Somehow you don't seem to see that. See AvE on youtube for a breakdown. It looks very clear it was a problem with assembly, where they had to move something and weren't able to adjust it. By the way, there appear to only be men standing in front of it, working on it, leading the team. Nothing wrong with men, I'm one myself. But your comment looks doubly idiotic.
Are you incapable of understanding what the concept of being number one is?
Those who do not learn from commit history are doomed to regress it.
Any evidence that this bridge was built on diversity hiring practices?
Those who do not learn from commit history are doomed to regress it.
It was not a cable-stayed bridge. It's a truss. See my other posts for details. Hopefully, someone can mod them up for visibility. Thanks in advance!
They claimed it was a struss, and not a suspension bridge. They lied-by-telling-the-truth, it is not a truss. Look at the struts ... carefully!
8-)
We had good will? Way back in the 1990s, I thought BILL Clinton squandered all of that with his reality show and response to the beginning of WWII by blowing up a couple of tents with cruise missiles (for those who haven't noticed, WWIII started with the bombing of the USS Cole and has been accelerating ever since; but the United States Government has been *very* careful to hide our involvement and culpability for it).
SJW: a person who perceives an injustice, and while correcting it, commits a greater injustice.
Cracks are so common you can't do that or you could never build a bridge. And an internal flaw is likely impossible to detect. Sometimes you can detect it with an xray, or sound test, but not always.
OTOH, further down the thread it looks as if someone has come up with a plausible reason having to do with over tensioning a support member.
I think we've pushed this "anyone can grow up to be president" thing too far.
Reason is usually pretty even-handed in placing blame on both Republicans and Democrats. They've also been known to blame private companies as well. There is probably plenty to go around in this instance.
It was a federal grant for improving transportation. It would have only improved pedestrian transportation for students at a single university. Hardly an appropriate use of federal funds... In addition, it was a massively over-expensive artistic bridge instead of a simple, practical one. But hey, I guess you need a gateway to the expensive luxury apartments for those broke college students saddled with unsustainable debt right?
http://myinvestmentbrokers.com...
Yes it's an anecdote! Were you expecting original research in a Slashdot comment?