Post Tension Failure Florida Bridge Collapse | Engineering EXPLAINED!

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CuriousMarc : First sensible and plausible engineering-based explanation I have seen so far. Quite a convincing argument teased out of the few clues that are available. Most people just speculate. You actually think, analyze, and even demonstrate with a simple experiment. There should be more of you around.

blancolirio : Great explanation at 14:33!

neo 71665 : What happens when aesthetics and cost are the priorities over form and function. Their lowest bid crew can now sweep up that pretty on paper bridge.

Runehorn : 950 tons for a fucking PEDESTRIAN bridge SECTION is what went wrong. No mystery there.

Anita Martini : fucking love this channel exactly as it is, let the man express himself for fuck’s sake

shubus : The big question to be answered is why traffic was allowed to flow under this bridge while these "adjustments" were being made. Gross negligence, IMHO.

Ranjit : Feel sorry for your wife ave, an inch of wood, not a very big stroke but the torque is amazing I bet.......

Clinton Andrews : "Under certain circumstances, urgent circumstances, desperate circumstances, profanity provides a relief denied even to prayer." — Mark Twain —

rhagerty1 : If your post tensioned member lasts more than four bours, contact a physician. 😀

Levi Stevenson : Interesting....I’m a construction inspector. Specializing in pre and post tensioning. I haven’t looked into this much yet. I’ve personally never seen a failure in my 20 years in the trade. At this point all I know is I’m glad I wasn’t the inspector on that project.

Hyena : *INVESTIGATE 3/11*

Rcbif : Having trouble understanding the forces the bridge saw. Would be cool to see an FEA showing the proposed lifting method and what they actually did and how it relates to the cable pensioning.

losing_myself 2571 : Foul language in construction jobs? Apparently the people complaining have never had to deal with this line of work. New subscriber I'll be waiting for the next f-bomb filled episode 👍

kingkongb1 : MADE BY FEMINIST


Jeff Irwin : This is a first of a kind for the ABC method: Accelerated Bridge Collapse.

Flavius : Engineers must use "mantalk". Their job is to poke holes in designs before they kill anyone. I worry that leftists can't be engineers because it is bullying and politically incorrect for them to criticize inferior work of fellow leftists.

Richard W : Good analysis and I am assuming you are correct or close to a root cause. I'm willing to bet the NTSB is focused on that post tensioning cylinder like a laser beam. This was basically a Warren truss structure which can be very strong when designed and fabricated correctly; this bridge doesn't appear to be. Redundant stress paths are a fundamental of sound Engineering. No competent Engineer would allow a single stress path, where a single component failure would allow complete collapse. This design should never have gotten off the drawing board. The entire project smells of environmental sensitivity and political correctness. Professional Engineers have legal responsibility and liability for their designs. The law suits over this will be amazing.

Robert Higgins : The mistake is in design or in fabrication. The former is found by examination of the stress report and the latter by hands-on examination of the materials in the remaining structure. if the cracks observed prior to the collapse were in areas of hi tension that would be a flag that collapse was imminent.

commonman80 : You're almost right.. However, what you got wrong was at 16:12 of this Video.. They put tension on the cables IN THE OPPOSITE DIRECTION.. (According to the NTSB.) Basically? Leaving every part of the Bridge to The Left? DANGLING... (So To Speak.) Leaving The Rest Of The Bridge WITHOUT ANY SUPPORT EXCEPT FOR THE STEEL RODS AND CONCRETE.. Think of it like putting a Brick on a LONG ROD at one end, And lifting it at the other end.. Except? The End with the brick? is tied to a platform.. Like your Glass Analogy? sooner or Later due to ALL THE STRESS/TENSION? IT BREAKS... Besides the fact that according to the design of the bridge? IT WASN'T MEANT TO BE MOVED AND STRESS TESTED/STRESSED IN THAT WAY..

Dada Fan : Oh yes, as a resident of the Tampa area I will think of this event every time I cross the Skyway Bridge, designed by the same engineering firm...

Bruno TaTa : It will turn out that: 1. Installation error created a stress on the ends that was too great and damaged the bridge 2. Materials were "eco friendly" and apparently not up to snuff. 3. Design was new and somewhat dangerous using concrete instead of steel for truss supports, and a single line rather than doubled, for asthetic reasons. 4. They were "testing" and "adjusting" bridge with cars under it, not wise. 5. At least one worker wasn't properly strapped into his harness. 6. Traffic should have been stopped during tensioning process. So, design, delivery, installation, and adjustment mistakes were made.

360MIX : Foulmouth Canadian! What did they say. (I love ya AvE).

ziptab : It didn't "collapse",it imploded just as the tension rod snapped. Check out the worker in the upper left of the bridge. The bridge went down faster than the worker,leaving him hanging for a moment like Wile E Coyote.

David Smurf : Excellent explanation , you are the man. You are the man, shedding some light on who fucked up. Great job

aussiebloke609 : Time to take a page from the Romans. I've heard that when building an aqueduct, the builders were made to stand under each arch as the forms were show that they really had confidence in its strength and in their workmanship. And possibly to rid the world of bad engineers and worse bureaucrats back in the office if it didn't hold up. I suspect the term "over-engineered" would be removed from the dictionary at that point, to be replaced by the phrase "standard operating procedure." :-D

SKULLS : All that heavy ass concrete for a pedestrian walk way??? And no center support columns? 950 tons worth that more than likely didn't cure long enough and on top of that you got engineers tightening the pretension cables while traffic is driving underneath?? A disaster in the making for sure. Next time use steal, with traditional supports, expensive or not, they tend to stay in one place. RIP to the victims and their families.

stxrynn : Those aren't true trusses, they are lined up with the angle of the suspension supports. If it were a true truss, it would be a stand alone structure with vertical members. Those and the angled members transfer the load to the supports on the end. I think that would have been the best design, with the suspension stanchion as a play pretty, not a support element. On legalities: Did the builder follow design to the nth degree? Did they have permits to have overhead cranes working above folks without safety gear (i.e. traffic)? I don't think OSHA allows overhead work without hardhats.... Did the city permit this construction technique? Folks need prison over this one.....

Michael Rosenthal : Three worst in the job swear words are : Should Easy And Fine. Somebody on that project said" it should be fine" amd wasn't Don't ever say 'easy' until the check clears.

Richard Warnock : That probably no dought a change order with engineers not or being involved to check stress factors due to the change and carefully checking this out before committing this change in the tested original design I had seen this hurry to get the job done before in construction oh yes their asses are in the ringer this is going to open a big O worms they might be the same smo's that did the collasping parking garage's in Tampa,Bradenton, Oh that built the Skywaybridge

Johnny B : Looks like you guys may have nailed it.

Kenneth Crips : I used to build pre-stressed panels such as this. What happened is the pre-stressed panel was not "harped" correctly. Harping puts an upward bow in the panel so when it is placed, it settles flat, I did not see any such bowing in the panel was dropped so it settled incorrectly. Consult with a person with experience this type of structure. I would have liked to see to the cable tensioning logs to make sure the cables were pulled at the same level. I would also like to see the results of the concrete test samples to see if the bag count was correct. I have peronally helped construct twin "T" panels at least as long as this for foot brigdes that have been in place now for over 30 years. The state highway officals that did not close traffic need to go to prison for manslaughter. The bottom line is the companies that pre-cast this brigde need to be sued out of business.

MrSpeedDemon72 : I still don't understand why it was deemed necessary to have a bridge this big and heavy for just foot traffic.

Internet Privacy Advocate : I see the rod failure as simply a side effect of a horribly poor design. Concrete is not a suitable material for a truss. Had the central single truss been fabricated entirely of steel it would have been more easily and more safely moved. The bridge would have been 90% lighter. The more you study this design the more you realize it was a complete POS. All hype, and no substance. It should have been removed from consideration early in the design concept stage as being totally unproven, and quite impractical. Blaming the collapse on a single bolt gives the engineers an out, but it doesn't excuse them from choosing a worthless design with absolutely no merrit in the fist place. Rather than blaming the catastrophe on a single overly stressed bolt, I put the blame on "group think" where common sense was not only ignored but shunned. All this said, your demonstration was quite informative, particularly when you show how the bolt shoots back out of the hole, and that is seen on the Rosenberg/Figg bridge as well.

Wesly Stanton : I think you may be right that it was the straw that broke the camels back, but the problem is that there was already too much straw on the camels back. This bridge should have not catastrophically failed due to one break in a post-tensioning rod. Bad bridge design overall. I don't think the concrete on the top deck was strong enough to take shear and bending forces. I also don't think they had enough shear reinforcements around the "anchor blister". Just my opinion.

Johnny B : So the mainstream media is getting closer to what AvE said a couple of days ago, they still haven't gotten it quite right yet methinks. From the Miami Herald: "While the cracking dominated media coverage on Saturday, experts appeared less concerned over that than with other factors, including the tensioning work going on at the bridge’s north end. Cracking in new concrete is not uncommon and not necessarily a sign of failure, they say. Tightening of steel cables, or tendons, that run through concrete structural elements is a delicate operation, and over-tightening can cause concrete pieces to twist and break apart, experts say."

Bryan Leuen : I’ve been in construction for 25+ years and this video makes sense .

Dave Newland : Here is the strain diagram that I was hoping for - The entry is at 18 Mar 18 23:32 The diagonal on the far right is the one in question (known as number 11 in other drawings). It is under compression when the span is in place. Interestingly it is under tension during transport from the nearby construction site. That is why there are tension rods inside it. This whole bridge design is an abomination. it is not a cable stayed bridge at all, the sixteen inch pipes "stays" are there to make it look like a real bridge. Why are they so fat says the voices in my head. They are so fat to make the concrete struts look more like cables! So you might ask - are the concrete struts extra thin for the same reason? Yikes! There are some NTSB photos in an entry at 19 Mar 18 03:23 that show the whole underside of diagonal 11 is gone and what was the lower end (now the upper end in the photo) of the diagonal and the lower end of the vertical are ruptured.

xariol : Internet famous now. congratulations Mr random lol

Kevin Willey : I question the wisdom of designing the trusses to line up with fake stays. This results in deformed trusses that had no vertical support on the end of the bridge that failed. From toothpick experiments, the truss configuration on the end that failed is much weaker than the one at the opposite end, which withstood the crash without pancaking.   When the bridge was moved using a method leaving the failure end unsupported, it created significant static and dynamic loads. Those loads would be magnified by the slanted truss configuration , and put alll the weight on the post tension rods(PTR ) in the truss member that failed. Perhaps those loads resulted in plastic deformation in the PTR leaving it permanently weakened. Whenthe PTR broke during tensioning, the member lost its tensile strength and crumbled. Thus it seems the causes are : A). slanted truss design was inherently weak,  B) movement of the poorly supported span overstressed and weakened the PTR in the end truss element C) weakened PTR allowed sag and cracks, and failed during tightening. D) failed PTR allowed truss member and bridge to crumble, Any thoughts on whether the truss design contributed to failure?

halnywiatr : So they transported an engineered structure, that was designed to be span-supported, as a cantilever. Would have been better to transport it upside down.

dykodesigns2yt : As a structural engineer in concrete design one of the first instinctive thing I thought of was that probably some post tensioning anchor had come loose. Looking at the truss design, the joins of the truss members are very critical in their reinforcement detailing. The members are quite slender, and considering the stresses in the joins there must be a lot of reinforcement in them to prevent splicing of the concrete. The high loads that these tension rods put on the concrete must be distributed some way. This requires a lot of strirrups and bend bars. Also I kind of expect the rebar cover to be around 50mm (allthough in some cases 35mm would suffice depending on the service life and envoirnmental conditions) and the bars to be at least 16-25mm, it would be quite challanging to fit them in such a slender join. Would be interresting to see the rebar detailling they used. Also this type of slender PT structure would need some self compacting concrete because of intricate mould shape. You certainly cannot use ordinary 20 mPa concrete for this.

Glenn Felpel : I freely admit that you are much smarter that I am on almost everything, except truss behavior. From the content of this video it shows that you do not understand the behavior of the members of a truss. This structure as it stood at the time of the accident can be described as a uniformly loaded simply supported truss. As such both of the outer diagonals (member 2 and member 11) are compression members, both of them. Using the reported structure weight of 950 tons it makes the reactions at each end 950 Kips. (1 kip=1000lb or 1/2ton) Using this information and the dimensions of the preliminary design the member force an Member 2 is around and approximately 2036 Kips compression. Member 11 (at a steeper angle from horizontal) is roughly at 1411 kips. Now remember both of these members are under compression for these conditions. They don't even need a prestressing cable or bolt. Actually prestressing these members is detrimental. If there was going to be a failure as you describe it should have occurred at member 2. I truly believe the cause is much more elusive to discovery than you present. I understand and agree they were working on the prestressing bolts of Member 11, but they should have been relaxing the bolts not increasing them. Actually they may have tightened the bolts for the move since at that time those outside members were actually under a tension load due to the cantilever effect of the supports. But that was small compared to their strength in my opinion. I do appreciate what you do overall in your videos but don't oversimplify this failure, I have the feeling it isn't what it appears at this time. I have designed many very heavy wood trusses but never a concrete one so there is much to be learned here. Thank you

a24396 : I really want AvE to narrate "seconds from disaster"

Sean Graham : I'd love to hear your analysis of the WTC building 7 collapse.

theguyjake : If you click on the video, then complain about the video, who is really at fault here?

Louis Ferreira : Looks like you're getting credit for the find in FL

100acrewood77 : they're citing your vid as a valid explanation. Good job AVE

Rustycowl L : at least he's trying to make some sense out of it. Some of the clear videos I saw initially! are no where to be found, now. And the few officials who are allowed to speak are either not saying anything, or saying stuff that most anyone can tell they're talking out of their ass. The bridge designer and builder companies' websites went dark shortly after the collapse. One thing I want to bring up is this so-called "design-build" fad that is sweeping public projects. Previously, most public projects were "design, bid, build". But in order to cut design, labor, supervision, & inspection costs and liability City and State are going to allow the Contractor to design, and build projects all by himself. In this endeavor the Public entities TRUST that the Contractor will rigorously design the project to standards, rigorously build the project to standards, and self inspect that the materials used meet specs, placed to specs, and all the quality controls meet standards. The Public entities think that by ceding the job to a private company, they are absolving themselves of any liability should something go wrong. Well, something went very wrong, but I can guarantee that when the lawsuits start flying, and they most definitely will in this case, the State, the University, and the City, will all be named as liable.

Guy Ligier : I believe the unloaded structure should have been strong enough to stand in place had everyone done everything perfectly by the book, but as was said, a disaster often is due to a series of errors. Error 1: This “first of its kind” bridge is made entirely of “self-cleaning” concrete which contains titanium dioxide. We’re not talking about titanium paint on the outside of the concrete structure, but titanium mixed right in with the concrete. There are many levels of purity for Titanium, and more pure is more expensive. I will bet the materials samples tests will come back that the titanium was substandard. Error 2: Also, I bet tests will show that the self-cleaning concrete was not mixed thoroughly, and uniformly, and long enough. This resulted in “veins” of overly brittle concrete. That, combined with the too short curing time, left brittle streaks so bad that the concrete’s overall compressive strength was not half of what was expected. (Also, isn’t a giant kiln usually used in making most self-cleaning pre-fab concrete sections?) Error 3: By not placing the transporter/crawlers at the very ends of the bridge truss, it caused the more slender top member of the truss to be in tension in ways the bridge designers had never intended. When the quickly constructed truss was moved/swung from the side of the road 90 degrees to across the road, the transporters were too far in towards the middle, so the ends of the truss were probably drooping. The crews were probably instructed to tighten the top tensioners more than they would have ever been had the truss been supported from the ends. This over-stressed the compressibility of the crumbly substandard concrete in the top member. The stress from drooping and then over tightening served to cause the brittle veins in the top member to develop deep cracks CLEAR THROUGH the top member like a series of seismic oblique slip faults. Error 4: Now remove the transporters and start supporting the truss by its ends, and the damaged top member with its slip faults of now powdered titanium concrete is still, remarkably, holding together. Yes, holding together like a half dozen bricks being suspended, held between your two hands. They’ll stay together as long as you keep pushing your hands together. Let up, even a little, and it all falls down. The workers were then probably instructed to loosen the top member tensioners (you can hear that on the video) back to spec, and boom, the top member catastrophically fails along its faults, and its weight and momentum break the truss’s bottom member…and you have 6 crushed to death.