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

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 👍

Glenn : The bridge identified as a sidewalk.

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.

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.

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.

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. 😀

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!.

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.

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.

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

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

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.

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.

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.

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

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

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

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

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.

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.

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

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?

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.

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.

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.

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

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.

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

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.

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.

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

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.

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

kingkongb1 : MADE BY FEMINIST

Steve Hennessy : I am not a structural engineer (a biomedical one), but when I saw the drawings on your vcast that showed 2-3 tendons terminating in a relatively small volume, each with a different force vector, I wondered that perhaps there might be local forces which compress correctly for strength in one dimension, but could interact with the other vectors to cause shear or weakening in other dimensions. Also, just the presence of three tendons and tensioning hardware in a restriced volume might weaken the material. Another observation — I’m thinking that the load on a pedestrian bridge could be handled pretty efficiently with a steel structure, and that the design was perhaps aesthetically driven towards the sculptural quality of post-stressed concrete — bringing in the large mass of the concrete. I’m wondering if a steel bridge would be less heavy and complex. Or was there something about the roughly 180 ft (and 100 ft) spans that posed difficulties for steel and pushed the choice towards concrete? Would appreciate your (and your followers) thoughts.

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.

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.

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.

TwennyGee : Ve jay o.... lmfao subscribed

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.

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

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

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.

CofRed1228 : When trusses are designed, all members within the truss are designed as tension/compression members only. No bending. So like you said, the original transport plan showed the supports at the panel points of the truss or the nodes of the truss. You always load a truss at the nodes...never between nodes. When they moved the SPMT to a spot between nodes, they were asking for trouble.

Ronald Rowe : When the bridge was moved the support system on the failed end was moved towards the middle. Leaving the failed end top slab under expansion instead of compression. It would apoears that the tensioning bolts would get additional loading and stretching into a plastics state. Retensioing it once placed would cause a failure. Is it possible that just improper supporting during the move caused this?