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.

Paul Phillips : You referenced the collapse of the Ironworkers Memorial Second Narrows Bridge in Vancouver B.C. in your presentation above was due to falsework failure. My father knew the first engineer who designed the falsework support for the bridge construction. The base was originally designed using 12X12s laid tight, in four layers to support the upper falsework. The powers in charge considered the design too conservative and used too much timber. The engineer was let go from the project and another engineer was installed to finish the project. The second engineer's design used four layers of 12X12s on 24 inch centers to save materials costs, against the strong objections of the first engineer. After the bridge collapse, my dad found out that the first engineer encountered his replacement in a bar shortly thereafter and beat the living crap out of him. Apparently no charges were laid as a result of the altercation. Thought you'd like to know some background on a bit of B.C. engineering history. Paul

Glenn : The bridge identified as a sidewalk.

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

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 👍

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.

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

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.

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

Mark Henry : I did pre-stressed concrete and also construction in Florida and construction in Texas. The Pylons are done in forms-bout 6 at a time [[dpends on length/use but my bed had 6 on each side. About 20' long each.]] Metal plates with holes separate each Pyl. We pull the cable off big drums in the morning, snake it thru the end forms to the next. The cables are tensioned to 22k pounds [IIRC]] then the 'slinkies' are pulled from each end and tied in with metal wire. Cement poured the vibrated and it sits overnight and craned out in the morning. This is not going to be PC but I've witnessed what happens when you have lazy people or people fresh from Mexico [[I noticed the guys accent in the vid]], shit gets done ass-backwards [[water faucet knobs and electrical in houses]], roofing materiel needing to be kept dry until placed and tarred left out then used to save a penny. [[Research what happened at Leesburg Fl H.S. in the late 90's]] I worked on the roofing crew there and witnessed the stupidity done. Then you add in kids no longer having the option to take shop or vo-tech and getting degrees in women's lib lesbian studies or degrees in researching some hockey players life [[that's from Canada btw]] and you have a society destined to fail-especially with infrastructure.

Aussie50 : While the news media says bugger all on the incident, CNN is probably grooming David Hogg to blame it all on the NRA or Aliens, we have our good man AvE here to sum things up professionally and accurately!, well done my Canadian friend!.

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

smakfu : Look, I don't have a problem with the language, and your analysis is very interesting. However, this dick in a vise thing really seems like a bad idea. I am definitely NOT keeping mine in a vise.

Ob Fuscated : Should have been all steel. There are WWII Bailey bridges still in daily use in Europe for vehicle traffic, and they'll hold tanks. Concrete is fine for pavement but if it were as expensive as steel we'd see no concrete pedestrian bridges because it is inferior in every way.. Bailey bridges are still produced. One would have done the job this cheap concrete grenade failed to do. Steel properly used fails gracefully.

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.

satburn : Although the content is very interesting i'm actually here for the foul language.

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.

metaforest : If you are offended by what this man says, it is YOU that have a problem, not him!

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.

Harley guy 68 : 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.

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 removed...to 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

z3dsdead : Back in about 1991, I worked for a year at a little company that manufactured various gaskets and seals. Of those items I know nothing of the boss and his greed in terms of selling shoddy materials. I myself was tasked at the bottom rung of the structure, mostly using a hydraulic press and spending mindless hours stamping out little circles and squares from rubber, butyl, aluminum and whatnot. Other more interesting tasks would be when I was given a set of calipers, various green plastic templates, a pencil and instructed to design and build the tool that would later be used to cut out a gasket for some kind of widget. Usually it was something like a 1936 Ford carburetor or valve cover. I would draw and measure everything to certain allowed tolerances, and then set about to make a dye out of plywood, stainless steel strips that were the cutting edge and a jigsaw.This was a fun and often challenging way to earn my minimum wage, way better than the regular shitwork.But one day the underboss, (the BOSS rarely ever came directly to me, only later when he fired me I think.) told me to go way back into the noisy place, a place I didn't like because it was very loud (like a forge perhaps, but lots of hammer and anvil violence!) dark and the guy who worked back there was said to be dangerous as well as insane! (Not really, he was fine, just always blackened from head to toe under a caking of grease and soot)Back there, I was sent to assist on a project that from the immediate get-go I knew was a REALLY REALLY BAD fucking thing. What I was instructed to do was use a largish sledge hammer and a tool for stamping letter/numbers into iron, and change the markings on the KOREAN or THAILAND or CHINA or wherever the fuck the giant barrel of NUTS (Or a pallet which had a dozen 6" diameter type bolts. The size isn't important, the fact only matters that they were BIG FUCKING bolts FOR SHIT LIKE BRIDGES ETC!!)The markings on the bill of lading were generally something like GRADE 3 steel.The EVIL BOSS was changing the markings and RESELLING this shit as GRADE 8 or similar. TO companies around the world or just the country. Selling weak Grade 3 shit, but passing it off as GRADE 8!When I asked the underboss Eric about this bullshit, he said (whatever main boss-mans names was I can't recall)was already planning to sell this company inside the next 5 years and didn't give a shit. A few weeks later I met a girl who was a little sister of a friend of mine, she was a paralegal, and when I told her I worked with a lot of asbestos, she told me her companies main area of litigation was class action lawsuits for old workers and the families of people who were suing for mesothelioma and so on. I told my boss one day I was sick and would be staying home one day, instead I spent the day in the library this girl had sent me to to learn about this mesothelioma thing. Later, when I mentioned to my boss I wanted proper respirator type stuff to use for work, he laughed and said all I would get was what they provided. Paper painters masks. So I went to the BIG BOSS and stated I knew a little something something about Asbestos and alluded to the lawyer shit, and of course two weeks later, he used my lie about being sick as the reason to fire me. Several years later, right before I got married I happened to drive past the shop where I had worked, and it was an empty building. For Sale signs.Two or three years later, when I met my wife's parents in Minneapolis, don't recall the year, but it was the same year that the big bridge somewhere in the Twin Cities had collapsed.For the next couple years I would speculate that it was quite possible, those fucking bolts my boss had us alter, could've been used in that bridge.This is a fucking true story.

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.

tonymak88 : Yes, I like your analysis and foul language. When the temporary supports were put underneath the intersection of the second diagonal (from the left) and the bottom bridge deck (ie. the bridge ends cantilevered from the temporary supports), the second diagonal was put into compression. The post-tensioning rods would have been found loosen. If the rods were tightened up at that time, later when the temporary supports of the second diagonals were removed, the second diagonal became in tension. It was possible that the post-tensioning rods were overstressed by having been tightened twice. The engineer might have realised it too late and started to de-stress the rods in the second diagonal. The tension released from one rod was taken up by the remaining rods, which led to even more over stressing of the remaining, then the rods broke progressively. As the second diagonal failed in tension, the truss action was gone, bridge failed by shear at the end

R.Peter Reinhardt : "That's odd... The dead-end anchor that you pointed out, appears to be a structural discontinuity and should cross over the more vertical PT cables, like the PT cable it is paired with. Need to check the 'Approved for Construction' drawings and go from there.

robhimself79 : I wasn't expecting this series of videos but wow do I appreciate it.

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.

R. Andrew K. Reed : All woman designed , all women built, all woman supervised...Three smoking guns...

OldKawH1 : Excellent analysis of why this bridge failed. I've have experience using similar methods tensioning steel structures. Most cables and bolts depending on the length, size, and temperature are expected to stretch over a given distance. An example might be 4 inches over a 50 ft span. If these cables were pre-tensioned, someone should have documented the stretch and hydraulic pressure. When they discovered cracking and loose pre-tensioned cables, it should have been a red light that something was failing. I've seen 2 inch thick rods go through walls after breaking. They could have cribbed under the suspected area while inspections and or repairs occurred. I think there was a lot pressure to not interrupt traffic. I believe the university and contractors involved are promoting this new accelerated bridge technology to replace aging bridges world wide. The new concrete tech is great when manufactured in controlled environments where no mistakes are made. This bridge was built on the side of road.

kingkongb1 : MADE BY FEMINIST

Eric Gulseth : Anybody that's offended by swearing on these videos have never gotten their hands dirty for a living.

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

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.

kurt phillips : Great Video, Total disregard for safety and human life. Big lawsuits to follow.

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

Justin Leeds : The official investigation will take months if not years and cost tens of millions to come up with the same result as the hive mind did in a few hours and for free.

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.

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?

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.

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.

zolt : When AvE puts dad jokes about wood and members aside you know shit got real.

david schneider : AVE ... that's what we love about you ... tell it like it is including the f-bombs. I like your attitude, if they are so sensitive that they can't handle the language ... go watch something else.

rickterfied : I found it interesting that this was on the wikipedia page for a couple of hours: In many bridge truss designs, the triangulated supports are arranged into two or more parallel walls. Among other benefits, this gives some redundant load-bearing paths to help the overall structure survive if any one member fails. In the FIU bridge, there is only a single vertical plane of diagonals along the centerline. There is no backup for any strut. The entire structure is threatened If any one diagonal or joint were to fail. Collapse can be avoided if the remaining joints and members were overbuilt stiffly enough to accept the shifting emergency loads without breaking. Otherwise, the structure continues to sag unchecked to the point where more things fracture or buckle, and the structure folds. Such bridges are called [National Bridge Inventory fracture critical] with each strut being a potential [single point of failure]. That vulnerability is avoided in most new bridge designs. But not in this case.

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.

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.

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...

Russell Higgins : Brilliant You noted the one PT that could only be tensioned have tension released from bottom Unless men were working top & UNDER THE BRIDGE which was not shored at all putting workers under it at huge risk well if not wkg t & b You'd induce asymtric load ACROSS CONCRETE SECTION I'd say that's insane but so was using conc , MOVING brittle conc, no shiring , working w traffic flowing , not knowing curb cut bank etc to miss on far side, then changing on fly day of move PT for that change, ignoring cracking on failure end which was reported to DOT who don't CK phone msgs wkend work was done after they extended span after design, and to top it design is utterly asymetric top to bottom every truss chord & they didn't try to use suspension rods to at least allow for graceful failure or canal section tied to main section to slow it's fall in case of failure... IDIOTS were building this EVERY firm needs to go out of business.

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

TwennyGee : Ve jay o.... lmfao subscribed

MastaRob : I literally dont understand how an engineer could do this. If you are tightening it and not "seeing stress", then doesnt that mean it is no longer elastic but has moved into inelastic deformation? Which is bad. And if it stops stretching at all then it is work hardening = very bad place to be. But if there are strain gauges all over the place, wouldnt this be obvious?! Shouldn't they be charting all the strain values? I mean FFS this is basic yield curve engineering, me no comprende how bridge engineers could screw up something like that.... Of course, been a few years since I was in engineering school so maybe I am missing something???