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Was The Florida Pedestrian Bridge Collapse Triggered By Post-Tensioning? (enr.com)
A new lawsuit claims post-tensioning triggered the collapse of the pedestrian bridge at Florida International University, killing five motorists and one worker. Engineering News Record reports
According to the lawsuit, the March 15, 2018 collapse occurred while a crew was post-tensioning bars in a diagonal member at the north end of the concrete truss that was the bridge's main element. The post-tensioning compressed the diagonal so that it overstressed a joint in the top chord, the lawsuit claims, triggering hinge failure at a connection in the lower chord and resulting in the catastrophic failure of the rest of the 174-ft-long structure. Post-tensioning that modifies the stresses in a structure is inherently risky and should be performed "in the absence of traffic," the lawsuit claims. [The lawsuit] draws heavily on video of the collapse, a voice message about cracks in the structure that were deemed superficial at that time by the engineer of record and design drawings in the design-build joint venture's proposal.
Slashdot reader McGruber writes: Interestingly, just two days after the collapse, an Anonymous Coward posted that post-tensioning likely led to the collapse of the bridge... A March 21, 2018 NTSB News Release said "The investigative team has confirmed that workers were adjusting tension on the two tensioning rods located in the diagonal member at the north end of the span when the bridge collapsed. They had done this same work earlier at the south end, moved to the north side, and had adjusted one rod. They were working on the second rod when the span failed and collapsed. The roadway was not closed while this work was being performed."
The Miami Herald reports that "how and where precisely the bridge broke apart likely won't be known for months, until the National Transportation Safety Board issues an official finding." While summarizing the leading theories, they're also calling it "the sort of baffling accident that makes structural engineers break out in sweats."
Slashdot reader McGruber writes: Interestingly, just two days after the collapse, an Anonymous Coward posted that post-tensioning likely led to the collapse of the bridge... A March 21, 2018 NTSB News Release said "The investigative team has confirmed that workers were adjusting tension on the two tensioning rods located in the diagonal member at the north end of the span when the bridge collapsed. They had done this same work earlier at the south end, moved to the north side, and had adjusted one rod. They were working on the second rod when the span failed and collapsed. The roadway was not closed while this work was being performed."
The Miami Herald reports that "how and where precisely the bridge broke apart likely won't be known for months, until the National Transportation Safety Board issues an official finding." While summarizing the leading theories, they're also calling it "the sort of baffling accident that makes structural engineers break out in sweats."
Seems like a rather large error.
- and all the anxiety!
Is this figure correct:
Panagos, who seeks $15,000 in damages for physical and emotional injuries...
I'd imagine that any of the insurers would be happy to pay her $15K (or even more) if she'll accept that as their final liability.
In the elastic region, increasing strain increases stress / tension. When the member enters the plastic region, steel under tension starts to neck. In this region, increasing strain can result in decreased stress. Eventually, the member fails and you have lots of strain and no stress / tension.
When tensioning, the question every structural engineer must ask is: Am I in the elastic region? For sure?
Structural engineers tend to use ridiculously small assumptions for material strength to guarantee being in the elastic region. However, one good crack or subsurface fracture, and fracture can occur. High performance work tends to use fea to predict areas of stress concentration, and then eddy current, magnetic and x-ray inspections to prevent these failures. This is not common in structural applications.
For those of us who are not structural engineers, here's an good easy-to-read article (pdf) that explains it.
I eat only the real part of complex carbohydrates.
It seems less 'baffling' and more 'inevitable' that this sort of life ending tragedy would happen.
Way to go, armchair engineers!
Stop it, please. Slashdot is going down the slope faster than ever.
AvE (crusty canadian enginerd on youtube) had a couple of interesting videos on this:
https://www.youtube.com/watch?...
https://www.youtube.com/watch?...
If you go back and look at the first Slashdot story on this when it happened, a number of people were thinking is was related to incorrect tension settings on the bridge (which had been pre-tensioned if I remember right, then they were trying to stress it even more...).
"There is more worth loving than we have strength to love." - Brian Jay Stanley
"...they're also calling it "the sort of baffling accident that makes structural engineers break out in sweats."
Uh, how exactly is this some kind of "baffling" mystery here? Instead of summarizing theories, let's review the facts:
"The investigative team has confirmed that workers were adjusting tension on the two tensioning rods located in the diagonal member at the north end of the span when the bridge collapsed...They were working on the second rod when the span failed and collapsed."
Seems pretty damn clear to me as to the cause of the collapse. Let's review the fuck-ups that lead to disaster and lives lost:
"...a[n ignored] voice message about cracks in the structure that were deemed superficial...Post-tensioning that modifies the stresses in a structure is inherently risky and should be performed "in the absence of traffic,"...The roadway was not closed while this work was being performed."
Seems pretty damn clear who fucked up and who should be held accountable here. Of course, this also happened in the United States, which means insurance companies are going to drag out pointless "investigations" for the next 2-3 years in order to keep millions in their coffers for as long as immorally possible.
Post-tensioning that modifies the stresses in a structure is inherently risky and should be performed "in the absence of traffic," the lawsuit claims.
As they say, it it was really common sense everyone would have it.
Before we ban Bridges.
This actually highlights the problem with our legal system more than it does what caused the collapse. Lawyers have filed a lawsuit (i.e. are certain who is blame) while the investigation has barely started and is still collecting evidence, and is probably a year away from reaching a conclusion.
If you want to argue that the lawyers aren't certain, they just want be first to get their speculative lawsuit in, then that's yet another problem with our legal system. That the penalty for filing a frivolous lawsuit is so lacking that lawyers can file speculative lawsuits with impunity without a shred of evidence to back up their claim, gambling that such evidence might turn up in the future. Thereby forcing countless innocent defendants to waste money preparing a defense against lawsuits which never should have been filed in the first place.
If you know how this process works, and watch the video of the bridge falling apart like a stack of cards, it is kind of obvious.
https://www.vdare.com/posts/th...
There is a lot or pressure to give contracts to minority owned firms. If you ever enter into one of these government bidding competitions, the number of questions devoted to the diversity of your business is greater than questions related to your ability to fulfill the contract.
These fucking doofus civil engisneers got licensed just like their paper-pushing process pukes demanded, and they still managed to fuck it up. Meanwhile, unlicensed software developers create a thousand times the value in the economy and manage not to crush anybody.
I guess it's either building worthless bridges we don't need or cleaning toilets, and at least with these ignoramuses building bridges I don't have to look at other people's shit when I go to the bathroom.
The reason for this event was pretty clear. This is what happens when you deviate from the original design without the proper testing.
the Florida Department of Transportation in October 2016 ordered Florida International University (FIU) and its contractors to move one of the bridge's main support structures 11 feet north to the edge of a canal, widening the gap between the crossing's end supports and requiring some new structural design.
I'd expect from from Slashdotter's. Well, maybe not.
https://www.cbsnews.com/news/florida-bridge-collapse-fiu-florida-state-university-project-behind-schedule-over-budget-updates-2018-03-20/
Seems to me the stress tensioning on top sort of caused a imbalance of lower structure causing a sort of bowing effect. Its also possible weakness occurred when moving the structure into place. I think one thing learned is that when testing a structure like this you better block off all public access while testing is taking place.
Bad engineering - from office to execution.
If Post-tensioning is needed... it is easy execute but not trivial to be managed by non-experienced people.
I have been looking for a slow motion video of the failure to see where the first break was and the progression of the failure. Also was the bridge subject to a any loading at the time. The best I can tell is that left side failed away from the left end and might have been a shear failure. Concrete is generally stronger in compression in static loading than either tension or shear.
This picture from the Miami Herald article shows a design with no redundancy. If any one of those diagonal elements fails, the whole thing comes down.
And one did fail.
As SJW hires amplify in engineering, these types of 'accidents' will multiply. And the reason is simple. Proper engineers understand fundamental principles. SJW hires do not, and thus rely purely on what the computer tells them.
This concrete structure could NEVER have been safely self-supporting. It's principle was the same as trying to correct the sag on a washing line when wet washing is hung out. To moronicly attempt to ramp up the tension in the line till it is horizontal again.
Look at any previous concrete spans like this one and you'll see arches, or columns, or cable support above. NOT to support the entire weight of the span- but to prevent it bowing under its own weight, at which point the strength of the reinforced concrete is lost as compression changes to expansion.
But on the computer, when a no-nothing SJW hire plays with the parameters, it SEEMS that if one simply ramps up various factors beyond any used in the past, reinforced concrete suddenly gains magical properties.
Beneath the lead enginner, chosen cos of her sex or colour of her skin, are proper engineers, competent and skilled in their own fields. When asked to do something stupid, they check their liabilty, and upon finding themselves safe for later blame, happily (for money) go along with the idiot plans to over-stress the concrete by using 'better' steel ropes, or thicker, or with more strands or whatever, and the same with the joints- as if OVER-ENGINEERING can fix the fatal design flaw.
You'll hear a LOT of crap about 'imperfections' in the span that failed, as if more 'perfect' manufacture would have solded the real issue. You see a really BAD engineer will claim her design is great even if it requires impossible manufacturing to meet it. Cos manufacturing can always be done better, don't ya know.
An old stone arched bridge stays up forever, even if the stones used deviate from the ideal shape by 10%, so long as the original builder compensated for that 10%. And that's the entire point. A design that doesn't need 'magic' anything- and therefore will never blame the lack of perfection in those that supplied the parts' THAT is why we always used arches, or columns, or above cables. So no 'magic' CAD values were needed to prevent the span bowing under its own weight.
But today America is an IDIOCRACY, where the dribbling idiots are taught that the SJW hire that leads the disater is never to blame.
It seems strange to me that the pylon and its cables were not in place to provide support for the span. I've been reading that the pylon and suspension system weren't there for support... that's hard to understand. You don't build the suspension part of a suspension bridge just for kicks...it holds the thing up. I think they built the thing backwards.
Dumbing down of Universities is the reason because of the student loan programs. Create a system with a gov bureaucracy profiting , banks profiting and school administrators more concerned with asses-on-seats rather than higher learning. Good job leftists - again.
AvE first posted this on YouTube and should get the credit.
Quick!
Since we had an all female team design the bridge. and named it the 'bridge to the global future'.
It's all one big circlejerk virtue signal.
Turns out you can't build a bridge like that.
So we gotta find some man to blame. Fast.
When I was eight or nine years old and playing with hot wheels cars and tracks, it became apparent that it was better to at least finish the track layout before sending cars down the new design.
No. Wait what! Betteridge was wrong? Yes actually the answer is clear that post-tensioning activities were quite likely what the collapse. That is pretty evident from the video footage showing small explosions either side of support member 11 followed about 2 frames later with the bridge starting to fall, along with the fact that crews were working on top of the member (and the only thing up there are the ends of the tensioning rods).
But that's the end of what we know. There's nothing about the root cause of the incident. Nothing about if this was a routine exercise that exposed some other flaw or that they screwed up the process itself, or maybe the designer screwed it up, who knows. That's what investigation teams are for and the many variables are why investigations generally take a long time.
I would say it's a bit premature for a lawsuit, but this is America. I'm surprised they don't just pre-emptively sue all engineering companies at this point and then just drop lawsuits if nothing goes wrong.
Its what happens when you give feminazis the job and no based off merit to the best contractor.
Design and build this bridge.
I've seen little focus on the concrete, other than the observation of some "minor cracking," prior to the failure.
One notable feature of the bridge is that it was THE FIRST IN THE WORLD built with "self cleaning concrete," most frequently done by adding TiO2 (Titanium dioxide) to the mixture. A little research suggests that concrete strength is negatively affected, on the order of 10% weaker with 6% TiO2, according to http://www.cipremier.com/e107_... Does someone know more precisely what concrete was used?
While most are focusing on a failure of the tensioning members, another cause may be a hinge failure at the point where the posts meet, where the concrete strength may be an important factor. In addition to the self-cleaning mix being weaker in general, other problems in the concrete pour or the concrete mix could create even weaker points, and as the hinge failure is at the top of the structure, presumably at the end of the pour, using the "bottom of the barrel" of the concrete mix which may differ from majority of the concrete produced.
the real failure here which cost the lives was not an engineering failure.
This was a failure of basic common sense, probably backed-up by bad engineering. What failure of common sense? It is an act of complete irresponsibility to be doing ANY tensioning or stressing on a structure while uninformed innocent members of the public are passing beneath it. It's even a bigger error in basic judgement to allow members of the public to be passing beneath a cable-stayed bridge BEFORE THE SUPPORT CABLES ARE IN-PLACE AND VERIFIED GOOD.
The people managing that mess must have been denser than lead.
Nothing gives an engineer the moral right to expose the uninformed public to such a hazard - no matter how many times he may have gotten away with it before or which government idiot gave it a green light.
The finding of facts in the report can be used. It is the interpretation of those facts which is out of bound of the court. E.g. if NSTB find out there was tension work of the rod that day, that there was a 21 inch V form crack on member 11/member 12, and that the road was not closed contrary to best practice, it can be used as a fact in the court. But any interpretation of those facts ("it was likely involved in the failure" / "it was not likely involved in the failure") will not be admissible.
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visit randi.org
and it will cost them a fortune anyway..
I wholeheartedly agree. The people who allowed traffic near the bridge while post-tensioning activities should (as a minimum) have their licenses revoked and be put on trial for manslaughter.
The bridge collapsed because American government spent all the money was spent on funding, training and arming ISIS in Syria. Now, American infrastructure is collapsing because USA can't afford to maintain it. Let's hear it, proud patrios-- USA! USA! USA! AMERICA SO STRONK! *salutes flag and claps*
If it can be proven that a crew was still working on the bridge while they allowed motorists to use the bridge that is a SMOKING GUN!!! Bottom line the people installing the bridge are responsible for the safety of motorists who use that bridge.
They hired for diversity instead of skill/competency. Building something good under those conditions was a bridge too far.
It is easy to see that it was a tensioning cable that failed. If you watch the video of the collapse, there is a worker on top of the bridge. If the collapse was a failure due to weight, the entire structure would have landed on the ground at the same time, including the worker standing on top of it.
But if you watch the slow motion video, there is a one to two foot gap from when the top of the bridge hit the ground to when the worker standing on the top of the bridge hit the ground. That means there was some force other than gravity pushing the structure down.
The only thing that could make that happen is a tensioning cable snapping forcing the smaller section down faster than gravity would let it fall. The smaller section imparted it's increased downward speed to the larger section, forcing the larger section downward faster than gravity would let it fall, leaving the worker on top hanging in the air.
By the time the tensioning cable released all of its tensioned energy into the bridge downward, there is a one to two foot gap between the worker that was standing on top of the bridge and the top of the bridge.
I think that there is a good reason why concrete truss bridges of this type are rare. The connections are fundamentally difficult to analyse correctly, although the member forces can be simply calculated by hand in a few minutes. I believe that an over-reliance on computer generated outputs may be an underlying cause of this failure. And a desire for "innovation" without wanting to pay the price in terms of thorough design reviews.