Great video. The official report also called out that the calculations were assuming a redundant structure, but it was a single load path. So the bridge was underdesigned from the get-go. Also, the shear line between the truss member and bridge deck was a cold joint, and was supposed to be roughed up to 1/4" before the truss pour. It was not. So the genesis of the failure started in the design phase, moved into the construction phase, and continued right into the installation phase. A complete breakdown of engineering discipline all around.
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.
Except he is wrong. The cable snapping was just a symptom of a greater failure, which was likely due to improperly transporting an extremely fragile bridge.
Just found this channel. 20 years heavy lift. 3 bridges among many other industrial projects. Seen lot of folk not pay attention to safety. Folk get hurt at minimum, dead some times, all cause some folk do not listen, cost/time issues, bad construction practise and yep ego. I retired when a project manager was so incompetent he told me(general crane and rigging and iron worker superintendent) to fuck off he knew better. I did. he cost a guy an arm and another both hands. Shit happens. Never an "accident". Thank you
I say we should push our legislators to pass laws that forbid these bridges from carring more than ten rounds in their magazines, then people wouldn't die so often from these damn bridges!
In Germany we have a saying: "Der Fisch stinkt vom Kopf" (A fish rots from head) ... My thesis: It's a teamwork failure in all kind of aspects. I got the impression that the are more than one failure. First there was a changing of lifting support locations caused by a bad trackway preparation for the lifter. Then a tension rod breaking and last no safety closure of the road underneath after getting problems with the structurals. This is typical for a "weak" management with bad communication between front site workers/foremans and backside engineers/management when nobody is trusting each other. From each ones point of view the other one is not a problem solver but a trouble maker.
rkalle66 in the usa engineering management is often promoted pseudo engineers. Ie folks who are great at dog and pony shows. Folks who are great in dealing with folks. Folks who often have giant holes in their engineering sense. Thus many so called engineering failures are management failures. Ie shoot all the engineers and process to meet schedule.
3beltwety, Hi ... I'm not complaining in general. We're talking here of the situation on this specific construction. For example, why is it that nobody in charge at the construction site was closing the road after structurals problems occur? It looks like the captain is not on board.
The construction firm was no doubt in a rush to complete the project over the few days that the road was closed. That could have played a role in the disaster, especially as they came upon challenges that required them to deviate from the original design.
it's like the bread and butter of any engineering firm. XD seriously, working in an engineering firm where a meeting hasn't had an f-bomb dropped is like having steak without the seasoning - it's bland XD
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
Is this in the land of wooden huts too? Anyone ever heard of 'metric'? No? Like in Megabytes or kiloWatts? If you would use a 20th century system of scales then you would maybe be successful in creating a bridge in the 21st century which doesn't fall and kill people. 'Inches' and 'miles' or 'horses' are not suitable for serious things which kill when they fail, and how many bridges fail every day in hut land? Probably too many to report on and who cares? A cow-boy is someone who came out of a cow and can make noises similar to 'English', but no one would give a cow-boy a job dealing with things which could fall apart and kill people. No one would do that. So where does that type of thing happen? Aha, in the big hut land. "Shucks, wadda ya no?"
@@tbelding Yup. I'm a capitalist. What I don't want is a corporatocracy- which we're already in. Multi-national companies run goverments, and can silence dissidents.
@@tbelding Ask the NRA and Trump Org how that's going for them. Not saying those cases necessarily deserve priority over the countless others, but kudos to NY state prosecutors for occasionally bringing criminal charges against corporations when they're due. Scares the flock at least. As far as I'm aware it's just a question of electing the right AG and DAs, gotta wake up for the boring elections.
I worked for over thirty years at a Nuclear Power Station. Our containments were tensioned to the point that they were six inches smaller when tensioned then when completely relaxed. I understand the concepts you are covering, and appreciate the job you are doing.
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.
I would imagine that two guys from the year 1900, who could not even spell "geometry" could have designed and installed a walkway that would still be safely in use today.
Overbuilt and under engineered, except back then they over engineered and overbuilt (in the majority of still standing structures) **** the shittier ones aren't around anymore, the others will fall after neglect of course
I have 3 words for you that contribute to failure, "bridges as art." Sometimes a bridge just needs to be a bridge. Or, in AvE speak, do not forget the prime directive.
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.
When I worked for W.M. Barr, (think Kleen-Strip), we had an engineer who didn't show up until about 11 o'clock one morning. He had been the engineer who signed off for the Fire Department for the Wal-Mart that had burned to the ground the night before. He didn't come in until he found out that Wal-Mart installs the required sprinklers, then turns them off and chains the valve wheel.
I would almost guarantee the crane was to move the tensioning cylinder and other gear for the guys working on the bridge. I say that as a mobile crane operator. Hooking onto a failing bridge not only isn't going to help, but just feeds more shit into the fan. That crane is no where even near the ballpark big enough to make a difference on something that size.
I was watching the collapse video and thinking to myself where these guys would have tied off to. Anchoring to the bridge would be like putting your seat belt on in a sinking ship, just not fucking smart.
I was thinking that, because an “eye witness” claimed that a blue piece of equipment was attached to a crane and that it broke off from the hook it was attached to and hit the bridge. He was saying that’s what caused the collapse, obviously not, but could it have been part of it?
Yah at least a two or three given the length of the structure and the need for it to be supported on the ends as well as in the middle once it started failing. You generally only pick around half a cranes maximum rated capacity. This is because as the boom telescopes out and the load gets further away from the crane, it's capacity drops very quickly. A 500 ton capacity crane cane only lift that weight over top of rear of the machine. So by the time you have enough boom out to reach the top of the load and to accommodate the necessary rigging, that 500 ton is only picking about 400k. And that's with only 90-100 for of boom. In order to rig the whole span to pick with one crane you need rigging as long as the span. That means 120 foot span has at a minimum of 120 foot rigging on each end, creating a 60 degree angle up to the hook. That means more boom stuck out and as such, a lower capacity. There are defiantly cranes capable of lifting that span whole. They are the size of the road that bridge is built over, and take weeks to assemble. Look up Lampson transi lift.
The pretensioning of these rod assemblies is becoming a common theme in structural bridge failures and mirrors a similar finding that investigators found in the Northern Ontario 2015 Nipigon River Bridge failure near Thunder Bay. In this case, (which also used ABC construction techniques) 24 pretensioned bolts installed near the abutment pillar at the east end were incorrectly tightened and as a result, 14 failed from improper tensioning. The pretensioning of the bolts, used a different installation (vertical instead of diagonal) method than the FIU bridge. Both bridge designs used a shoe plate anchor design. Interestingly, when tested at the University of Waterloo, the bolts did pass the ASTM A490 specifications. Tests conducted indicated low cycle fatigue between 50 and 140 cycles, cracks began (in the bolts) and then a final fracture, snapped all 14 failed bolts simultaneously. Testing on the remaining bolts that did not shear showed the same cracks but had not fully fractured as the fatigue fractures found on the same spots of the failed bolts. Like AVe shows using an oscilloscope, the Waterloo team tests methods included determination of the elemental composition of the bolts by glow discharge mass spectrometry and wavelength dispersive x-ray fluorescence mass spectrometry. Investigators now had the smoking gun with the evidence that lack of proper pretension and tightening of the bolts attributed to the cracks and fatigue as the reason for the failure because if the pretension was not set correctly, the condition of the bolts was the evidence needed. Many early arm chairs experts initially believed wind and the sub-zero temperatures were to blame, which the investigating team clearly proved otherwise. I'm not sure if the setup for temporary supports under the span would be the cause of the bolt / tensioning failure that stretched the bolt shaft and or shoe plate or not, but AvE's analysis is a valid angle that investigators will have to pursue. But there can be no doubt, based on what is known so far (cracks found and reported, etc.) that there was a pretension bolt issue.
it is baffling (in preliminary plans) that the structure members #9 and #11 show no PT bars... I would assume that PT bolts should be tensioned symmetrically, it appears the might have had ram only on one side?
It could be that the crack heard some time before the collapse was due to the misplaced supports, that crack putting a lot more tension on whatever rods were involved. I have to say, I'm not sure why a failure in tensioning the trusses would lead to the failure of the bridge. Aren't those always under compression all the time? Wouldn't it be the tensioning on the bottom portion that would have to fail? Maybe I've misunderstood something here.
Doug Hanchard I bet you those bozos "fixed an issue" on the fly (the supports that couldn't be placed where they were supposed to, in their calculated position) without notifying the designer of the (now) changed construction site situation impeding the original plan. That would have meant delays and possibly expenses and it would have probably changed the whole sequence of tensioning and repositioning. Oh boy the clusterf@ck...
The guy hearing a crack has a 50:50 chance of being a red herring. It's likely enough that someone dropped his hammer and the guys memory decided it was 10x as loud as it actually was.
macbeth2354 makes a valid point....and a damn good one. But what Dougie hear has clearly mentioned is what can be related in Waterloo. To recall what AvE mentioned, that the PT rod has clearly yielded into cyclic failure due to improper pretensioning, maybe sometime before [the installment] has seem to be a discontinuity along side with the Wheatstone bridges (for Strain gauges) may have also been a factor. Or I could just be rambling because it's 4:45 in the morning and Im fucking exhausted from the PSVR.
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.
Man this was awesome. I don't mean to overshadow the lives that were lost and negatively impacted in any way by this event, but I really enjoyed figuring this problem out.
Yeah. Interestingly, the crane seems to have something dark hanging down the boom and angling off to the roof of the span - which drops to hang from the crane when the bridge drops. Makes me wonder what it was...and it also tells me that the crane boom must have been pretty close to the span. Wonder if it hit the edge with the boom in just the right (or just the wrong) spot and pushed or weakened a crucial area.
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 👍
Great Video! As a metallurgical/materials engineer, I have been involved in failure analyses of turbine engine parts and, although design is a factor, we always look at material properties. With turbine component failure, it is generally a fatigue failure, but in this case there were no fatigue modes. In that light, has anyone conducted mechanical property testing on the tensioning rods? Maybe to cut corners, they purchased some steel rods of "dubious character"? Checking their tensile yield and ultimate should tell you if there was a tensioning material problem. Also, if the photographs of the collapsed bridge I noticed that the concrete had "crumbled" versus fractured. Properly mixed and cured concrete generally is somewhat brittle and it fractures and not crumbles. Has anyone done any testing on the concrete itself? Also, in the dash cam video, you can see the cable on the crane snapping at the precise moment that the bridge started to collapse. Was it connected to the bridge? Was it holding up the bridge? Did it snap before the bridge collapse or when it collapsed?
Excellent analysis. The penny dropped when you said the yield curve. The contractors doing the tightening must have wondered why it was not tightening. Perhaps the engineer in charge was not contactable as they must have contacted someone about whether to keep adding tension.
Stephen Gloor ...There should have been a deputy inspector on site for a project like this. Why did the deputy inspector not put a stop to this before the failure? The deputy inspector works for local city or county agency.
THANK YOU SIR! You have achieved what I spent half a lunchtime failing to. I've been an enginerd for a couple dozen trips around the sun, and failure analysis has always been one of my favorite parts. You've found the evidence I didn't, and interpreted it excellently IMHO. I heard on the news that day that at the time of the fall, they were tightening 'cables' that had loosened, and that was a big red flag to me right off. Something just spontaneously 'loosened' and you just try to tighten it without looking into why? That's exactly how a couple of guys got killed a few years ago in my industry. The news people must have been talking about that rod, which was probably yielded to the point that it was never going to hold load again. The really tragic thing is, if anything's not 100% plus safety factor, the FIRST thing you're supposed to do is Get The Bipeds The Hell Out Of The Danger Zone! Aaaaaagh! How many oafs were standing around scratching their butts not thinking of that? A series of mistakes were made, which is invariably the case in disasters like this, but keeping the road open while they were tinkering with that sucker was the worst. Concrete and steel can be replaced, lives can't. I have been enjoying your vidjeos for some time now, but this is on a whole other level. Your words are strange, O Wise One, but your insights are most skookums. And as you so eloquently point out, if anyone can't handle a man talking like a man, fukkum.
As an FIU student who easily could have been one of the cars under that bridge, I just wanted to say thank you to all the people trying to find answers to why this happened. A lot of us are hurt, confused and traumatized and the waiting for an answer makes it even harder.
In the slow motion shot of the bridge collapsing , the end diagonal beam was crushed under compression. I am not an engineer , however even common sense dictates just one beam there under compression holding up 900 tons is really wishful thinking. There was zero redundancy built in to the span. As far as the kids at FIU i am sorry you had to go through all this. Our thoughts are with you.
I’m back here a year+ later for a refresher while reading the official OSHA report that was released. A great video and demonstration of the failure of this bridge.
This is the sticking point, even if the cable stays were just cosmetic and thus thing was designed as a truss ... never no fucking way should they have retensioned the steel with traffic underneath. Trusses aren't exactly known for their redundancy.
My money's on 1) electric brake system failure, plus 2) simultaneous failure of the drive, letting the chairlift freewheel. The weight of all the skiiers on the uphill side pulled that half of the cable downhill... faster and faster, and pulled the empty chairs uphill. All backwards.
Don't they have a sprag clutch on such a thing to prevent reversal? Any load carrying conveyor belts on an incline are fitted with sprag clutches to stop them running away in reverse due to the weight,if the drive stops powering the drive drum/s. That said they more than likely have fancy electro and electromechanical braking and anti reverse systems. I dare say they may want to run in reverse certainly during maint/service/repair.
In North America ski lifts have three brakes. The service brake works on the motor. This is the brake that is normally used to slow and stop the lift. The motor is connected to the bull wheel spindle via a transmission. The second brake works directly on the spindle. This brake may be manually activated by the operator, via a valve lever. Sometimes the spindle brake also has automatic activation when a roll back is detected. The last stop is a ratcheting dog clutch normally located on the non-drive bull wheel. Google “devils head ski lift accidents” for a good account of a roll back incident in Wisconsin.
“Go fuck yer hat” made my day. People aren’t REALLY offended, they just think they’re SUPPOSED to feel offended, and then complain about what they think are their feeling. We’re living in a strange time of: “I’m not uptight, but I think I’m supposed to be”
Been around thousands of cables being tensioned during new home slab construction. Failures do happen when streching but are rare. Have seen 100' cables shoot out 300' whipping and snapping as they go. Another point to consider, and I haven't seen, is the cable restraint on the opposite end of the tension pulling device, the anchored end.
Coming from experience, when it comes to traffic control on projects like these, politics start running deep. Shutting down lanes is almost never in the cards, thus the prefab of the whole project. Of course when it comes down to public safety on stuff like this, it is still on the engineers and boots on the ground, but foregoing traffic control and shutting down lanes for cribbing wouldn't surprise me if it was motivated by a politician. Of course there will never be proof of that.
Work in real estate development in a core city. When I say we have to have traffic control for the most remedial thing would be an understatement. Hell, we have to have traffic control for a truck to come to pump out the blue rooms while double parked.
The more performance you wring out of a material and the closer you push it to its edge through the use of "smart" engineering the less robust the resulting construction will be. If you build something to be super stiff then it's failure mode will be catastrophic brittle failure. I prey that those that died did not suffer and that those they left behind will find a way to forgive. Thanks for the great analysis.
This explanation makes good engineering sense. Though I'm a EE, I have experience with this technology. And yes, having traffic under the bridge when they are increasing the tension on the rods is astronomically stupid.
Expect more accidents like this to happen in the future, as depressing as it sounds. Engineers and workers are constantly pushed harder and harder, and in this case the work was ongoing while the traffic was still moving I assume because they didn't want to take the extra time, effort and money to block off traffic...
If the public knew the problems associated with these affirmative action contractors.. They'd be scared to death to ride on any road/bridge they had a hand in constructing.
The pressure by central governments to not inconvenience the motoring public is insane today. Especially with many of these contracts being let with time-sensitive incentives for the contractors as an effort by the DoTs to speed up the work. It appears an adjustment to the erection plan is what may have set this thing in motion. And that adjustment was partially down to not wishing to add time dealing with some problematic locations for the supports.
Add to that most jurisdictions will require a permit for lane closures which are costly, and fines for delays of re-opening the road by the specified time. Even though the city/town does nothing for traffic control, they still want their piece of the pie. It's hard to say whether they would have been able to close the road, or if someone made the mistake of considering the risk negligible and continued work with traffic moving underneath.
So (from a completely non engenerding POV) did someone say "gnnnnnnnahh-click" after engaging safety squints. Possibly followed by "she'll be right might" ?
A Pratt type steel through truss bridge would have been much more practical, but when you get involved with government contracts, efficiency and often with it safety, goes out the window.
There'll be months (years?) of discussions, committees, congressional hearings, etc....and in the end, all the fishbone diagrams and failure reports will basically be a mostly verbatim (less the f-words) transcript of this video ;)
There's always civil litigation - and I hope the families make the people/corporations responsible pay - this is ridiculous, brazen, irresponsible, etc....someone was probably about to lose a bonus so rules were "bent"
Although, settlements to the victims via civil actions will be forthcoming. Government imposed "fines" in a case like this are not meant to compensate victims, they are meant to cover the cost of the investigation and, more importantly, to punish the sloppy behavior and incent others not to repeat the behavior.
Discussions from a construction standpoint on projects like this is half F-bombs in the field. Did it for 40 years. Not for the Meek. Great explanation and will follow. Thanks.
thanks AvE , lives could have so easily been avoided by someone stepping up and saying stop! Let's re-evaluate this before proceeding. I worked in a very dangerous profession for many years and survived, always instructed and encouraged my subordinates to speak up if they ever felt there was a safer or more productive way to complete any tasks at hand. An idea being submerged in ego's and the all mighty $. Very, very sad indeed.
14:40, anybody whos over tightened a engine head bolt (which are mostly torque to yield bolts) knows EXACTLY what this feels like. You putting pressure on the torque wrench but shes just not clicking. Keep going and you FEEL something is wrong, then pop..
TTY is not garbage, it has a purpose its because TTY is a more reliable, accurate way of attaining a set clamp load, using a torque setting to clamp load is inaccurate as too many factors are at play such thread, bolt head and washer friction. I won't lie though, I HATE tightening TTY bolts, just feels like a regular bolt does just before the threads pull out! 😂 😂 😂
Yes but I don't think it has to yield to get that benefit. You can do torque+angle below yield strength on a bolt and still get a much more accurate clamp force than torque alone. The idea is that you just torque until all of the slack is taken up and you know that you are beginning to elongate the bolt itself. From there on the only variables going into the clamp load are the thread pitch, the number of degrees turned, and the effective spring constant of the bolt.
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.
Trusses should always be designed for bending on top and/or bottom chords to resist bending as load application dictates. Clearly the difference in pedestrian load between node points and the bending/shear from supporting approx half the bridge weight is substantially different
@@BillySnowball In practice the Truss will undergo some bending but they are supposed to be designed in such a way that the moment generated is almost negligible because the members are supposed to carry only axial forces. If the moments are huge they should accounted for in the design but Why take on this extra headache to begin with.
We had a road bridge in Edmonton that was being constructed too fast with pre-engineered beams....they didn't cross-brace them as fast as they loaded them up in place and the steel beams fell over under their own self weight....no traffic was under the bridge at the time, and nothing fell to road below. My point is, why was there traffic under it at that critical point.
I couldn't fathom why they were allowing traffic under the bridge while work was being done. Hearing they were using post tensioning equipment it really baffles me. They should have had the area clear of all non essential personal while stressing any post tension member. It makes me wonder how much political pressure was on the contractor to have the street open for traffic? This project was politically driven from the get go. It was funded through the T.I.G.E.R. program from the previous administration. It was supposed to be proving a more economical method of bridge building.
It's Florida. The way traffic is here, people would scream if the area was closed off to traffic for too long, and local and state government would be under intense pressure to keep it open. Do not be surprised if local FDOT knew it was unsafe but forced it open anyway.
FDOT, according to them, did not receive a request to close off any lanes. While the failure itself may have been unavoidable, there was no reason for the traffic under the bridge. The collapse resulted in the entire area being rerouted. Certainly would have been easier to reroute traffic for a few hours just to be safe.
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.
Kenneth Crips ay im from a similar industie used to weld in the stressheads bild/setup the molds for this kind of tearoff beam . the stress heads i installed were mounted on UB's 1200mm hi 32mm thick and concreated 10meters in the ground ,basicly down to bedrock, 4 of theas each end wot to hold up to 30 cables each with around 100tn load on. i was just a suby so i never saw the tentioning ever happen but. wot i wonna know is how the hell did thay do that "onsite" im with u mate i recon the cables were badly arsed up
MrRoughNutz There’s a huge difference between an accident and negligence. An accident is accidentally locking your keys in the car with your child in it and then immediately calling for help, negligence is leaving your child in the car during the middle of summer to go inside a store and then to come out and the child is passed out or unconscious.
People who can't handle a fbomb clearly have never been stuck outside in - 10c, at night, 16hrs into a 8hr shift trying to solve a problem on some piece of 'mission critical equipment' for a client. Just saying....
Post tension members are plastic covered tendons (cable not a rod) in order to be unbonded otherwise when you pull the tendon the cured concrete around the bare cable is going to adhere to the member and wont let it move/transfer the load.
First time I ran into post tension was on foundations on houses for a new subdivision. With the framing, roof and exterior siding done, one of the houses was found with the patio door glass busted. The floor had popped during the night and threw chunks. The second house had a big buckle all the way across the living room floor but the 3rd was OK. Mysteriously, all 3 caught on fire and the insurance paid up. Replacements had conventional footings.
Thanks AvE, I have no knowledge on these things but you have explained it in such a way as a "civilian" like myself could understand it...thank you again!!!!
Steel goes into a plastic state under tension. Learned that in college. Also the transporter should have been under the truss. I'm sure during the short time after the transporters were removed and they de-tentioned the the members they were over stretched. I also agree that they should have had some false work under it until they put the cables on top. Triangles are our friends.
At least you made sense and prove while everyone else is trying to prove it wasn't their fault. Common sense says the traffic should have been rerouted until it was finished and inspected. I applaud you.
This would end up in the "Engineering Diasters" episodes of Modern Marvels... if that was even still a thing. I cut cable a long time ago, last time I watched the History channel it was nothing but dudes arguing with chainsaws, alligators, and big rigs with snow chains. Plus alien/conspiracy theory bullshit Bad Engineerding, it has claimed many peoples lives over the years. Want to know why airplanes only have oval windows and not square windows? Guess what, some engineer did try to use square windows... The corners were weak, a window broke and people died. Forever forward. Always learning. These types of things are travesties, but at least the professional people figure out how to not make the same mistakes again.
That would have been the de Havilland Comet. The frame and skin panels around the square windows exhibited stress fractures from repeated pressurization/depressurization cycles and that led to failure of the airframe and subsequent crash of the plane.
So to sum it up, the plan changed where as the transporter to hold the bridge up was moved, because it was moved the post tention rod yielded. They tryed to fix it by tightening it and it broke causing the bridge to fall.
brendan454 Looks that way, the modular construction moved in sections method is sound. I guarantee this was all perfectly calculated but at the last minute a change was made to the plan (moving the location of the SPMT), calculations rushed and the rest is tragic history.
You and I distort a lot of words the same way. If I was a student of yours I may have stayed in school past grade 9.7. I agree with your diagnosis of how things failed! Your a great fella to listenate too, Mcgoo.
Sure so from what Ave said that sound was reported before the collapse, like an hour or so if memory serves. Wouldn't that rod have ejected itself from the housing in spectacular fashion as soon as that failure occured and not sometime later?
Cracked could have been stress on any of the other members. Also remember that bolts will make noise before they break. If you check out the FIU dashcam video(just search that on youtube) you can see the rod eject at 8 seconds in. It's clearly there.
You were name dropped on a Florida radio station this morning. "An engineer in Canada discusses this and seems to sound like he knows what he's talking about"
I am not an engineer and there are times when I have no clue what you are saying. But you make it interesting none the less. Just goes to show what some knowledge, investigation, and a little open minded-ness can get you. Keep up the great work.
Looks like you found the point of failure, NOT what went wrong. What went wrong is who thought it was ok to remove those spreader plates and reposition the equipment. Then who failed to spot it was seriously weakened and still allowed traffic to move under it. This is a clear failure of design and management of the assembly of the bridge and those responsible should be sent to prison for manslaughter.
Looked good in Cad all complete huh? Maybe ABC needs to be Slightly-ABC That tower & suspension should have been ready for the deck it was ment to hold up. why a half supported bridge goes over head in the frist instance makes nosense
It was a first of its kind in another way too. That being the all female diversity hire engineering firm that designed it, and the media were singing their praises a week ago. If the fault in its failure turns out to be an engineering problem we will never hear another word about that fact.
Respectfully, I think you have this wrong and I think the rod demo in your video demonstrates why. If you'll allow me to explain: At @11:24, your test rod goes whippin' out of the hydraulic cylinder (HC) when the spring tension on it was released at the failure point. In your video, at @11:46, you can see the SFU bridge HC still attached to the rod and the rod still embedded in the concrete. This shows that the rod did not fail! Had it failed, the rod would've been found buried in the side of a building, 1.6 km away from the bridge, not intact on the end of the HC. Now, this location is also definitely the source of the failure. Take a look at the animated GIF (4 images down) in the Miami Herald article (below) from the exact moment of failure. Specifically, look at the base of the vertical south end pillar. At the moment of collapse, in about two frames, you can see the base of that pillar shoots to the right a couple of feet. This is because the spring tension in the rod pulled it in that direction! If the rod had failed, the release of the spring tension would have shot the rod into the air and that pillar would have remained standing while the bridge toppled over to the right as the in-span fracture and collapse occurred. www.miamiherald.com/news/local/community/miami-dade/article212571434.html This same article identifies that some unassociated structural engineers examined the plans and felt that the final truss-member was undersized for the load. I haven't done the math, so I'll take their word for it. This bridge construction technique also used an Accelerated Bridge Construction (ABC) method. it's my assessment that the final diagonal concrete strut suffered a catastrophic failure in compression. This is particularly unusual in concrete construction, but this was a particularly unusual bridge design and I think this explanation best suits the available evidence. Regardless of why the diagonal strut truss member failed, it certainly failed and led to the collapse. Additional evidence: Looking to the right of the lower deck failure point, the rest of the truss remained intact during the bridge fall, so the collapse had nothing to do with that section. In contrast, on the left, the upper truss deck pancakes on the lower deck before the bridge has even hit the ground, so that truss section (end pillar and diagonal strut) was structurally demolished before the bridge started to fall. In the Reddit thread you posted, "Tomfh" included a few CCTV frames from the other side where it seems pretty clear that the last diagonal strut suffers a couple of sudden fracture failures, one toward the top of the strut and one about 2/3 of the way down. in the view from the opposite direction, I thought the column had crushed toward the base (and it might have, as well), but in this "reverse" angle, the strut clearly suffered a compression fracture and folded up. Unfortunately, concrete does not generally abide by requests to expedite its curing time without sacrificing some strength and if the bridge was designed at the limit of material strength, instead of with a 3x (or 10x) safety margin, then defects in either the design, the concrete specification, or the concrete mix could well explain the compression failure of the diagonal concrete truss member. There have been additional reports of concrete cracks reported to engineers prior to the collapse that should have alerted them to a problem with either the concrete or the design. Instead, due to pressures to complete the bridge on time, they chose to ignore these omens. The best question you asked, here, was "why were they attempting to reinforce the bridge while traffic was passing underneath it" and while the concrete was exhibiting stress cracks and still curing. And then there's the loud bang that a pedestrian observed shortly prior to the collapse that the workers should have been trained to understand was a sign for them to exit the scene with the greatest alacrity. In general, the designers and builders put expedited construction ahead of worker safety and public safety. Engineers are explicitly trained to not permit anything to come ahead of design safety because mistakes like this can (and do) kill people. The people running and implementing this project displayed a criminal lack of integrity and professionalism and held insufficient regard for human safety ahead of their own hubris. EDIT: Check out the size and location of the "cracks" in the bridge at one month and at two days prior to the complete collapse. They're enormous! The preliminary report indicates that the concrete samples taken from the bridge met the expected specs. Everything I've now read seems to point to a catastrophic design flaw and pressure to ignore the error and continue to install the bridge anyway. www.ntsb.gov/investigations/AccidentReports/Reports/HWY18MH009-investigative-update.pdf Thank you for making these videos. They're a f'n pleasure to watch. ;-) And, yes, I'm still keeping my stick on the ice.
Re: "Bad language?" The British building industry is full of extremely capable men who all use cursing in everyday speech. You cannot walk into a building which was put together by "godly vicars" so fucking deal with it!
if we cant swear on a YouToob videos, let switch to subsitutue words as placeholders. Red Dwarf comes to mind with creative uses for smeg. "Rimmer, you are such a smeghead". Self appointed censorship boards can smeging well smeg off!
on your first video my thought was some thing had to go wrong with tension cables and or the PT rods. I've worked in rail road construction for a few years in project oversight for most of the big class five railroads. when it comes to bridge building with the rail road it unreal the design loads they use "E-80" I've seen a handful of bridges they have used Pretension deck panels. the amount of testing data that is needed and paper work that go with each panel. theirs no way the railroad would even consider letting a contractor build pretensioned concrete onsite to many variables.
Tommy Petraglia I would agree this not some basement foundation. in the railroad if the batch is an hour old the truck is rejected. in ACI they want you to check the batch in the middle of the truck if it was over 90 degree we rejected the truck. the contractor always want use to check the batch before they poured just in case it didn't paas. the railroad has some hard rules but they can't afford a bad batch of concrete.
Bridge collapses are very rare. The whole point was to have the road open for traffic, and it's safer for the workers to build it off-site as well. Occasionally someone dies in an elevator, but it isn't necessary to go back to taking the stairs. If it's unsafe for traffic below, then it's unsafe period. But nobody knows that ahead of time.
NegatingSilence 1 death per $million spent on bridge; an old algorithm. You are correct, they are rare because of a leaning curve. Often being "Better safe than sorry" is inconvenient, but is in place for the sake of safety.
It seems crazy to me that structures would be created that are entirely reliant on a few bolts to stay up. There should be enough redundancy that these botls can be entirely unbolted and replaced if damaged without the entire structure collapsing.
Munilla Construction Management, the contractor that built the bridge, is buddy-buddy with Paul Manafort. therealdeal.com/2017/08/31/meet-paul-manaforts-real-estate-fixer/ So yeah, the potential for obfuscation and shifting of blame is high on this one.
Very interesting, and thanks for offering a cogent and testable hypothesis. I deal (in part) with early concrete bridges, like bowstring arches, and despite much cracking they retain their integrity quite well, even those dating to the 1910s and 1920s. My father-in-law, who specialized in bridges, far preferred cast-in-place over prestressed: none of his have collapsed, to date. YMMV.
The crane they had over the failure point. Was more than likely there just to move the hydraulic tensioner machine. That crane was way to small to lift any part of bridge.
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.
that bridge was doom the moment they decide to change the mobile support placement under the bridge before moving it into place ! the posttensioning was calculate to be support at the end so all the weight was hanging in the center but they carry it a full thrust nearer the center so all the pressure they put in tension was already breaking the bridge before it was in place so when they drop it on the piers at both end it was already to late the tension rod that you see with the tensioner was overstretch by the weight of the unsupported end of the bridge i hope it make sense because it is not easy to explain something in English when you are French canadian
Gil B Nearly all these disasters are caused by some last minute half-baked change to the plan/procedure. Usually because of budget/politics. I agree with you, they relocated the SPMT because traffic infrastructure was in the way, so they come up with a quick solution to avoid the extra cost and disruption to traffic instead of moving what was in the way. Where are the cost savings now? And six souls have lost their lives as a result.
It's easy to say that now but these type of adjustments are common in big construction projects. Its not like they just wing it, every factor is recalculated and either someone fucked up a calculation or there was a material flaw.
These type of field adjustments are common sure, but this type of construction technique is a) new, and b) requires at least three different sets of load calculations (fully installed, partially installed, while being moved). Maybe what happened is they recalculated the force for the wrong scenario. Or, maybe a construction company hired because they're minority owned and had a connection to the school wasn't very good.
Yup. They moved the support away from the end yet left the tension rod tightened as if it the end were still supporting most of the bridge. Unfortunately it was actually being stressed in the opposite direction. Nothing good came from that.
deezelfairy They saved $-15 million and -6 lives with that "shortcut". But adjusting tension bars when you've already seen cracks and heard bad noises is the truly criminal part.
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
That has a ring of truth - a more complex sequence of changes was performed than originally planned due to different placing of the supports, with noone going back to the drawing board and seeing what the consequences could be. It also seems to me that they skimped on the rod size/number with no wiggle room. A heavy brittle structure like that is unforgiving of error.
Also notable that the original drawings show no post-tensioning in the end diagonal (no.11) which would be in compression in the final position but probably in tension during the installation due to the temporary support position. Maybe this had to be changed to allow the support position.
Mark Tillotson Shocking lack of redundancy. Probably Dywidag bars - they're skookum, but very brittle. Even a nick on them can cause failure due to point stress issues - think cables would have been a better option. Transporting mid span seems a massive mistake without some sort of load transfer mitigation. A series of preventable errors. Four culpable parties- owner, engineer, contractor and transporter. Should be multiple jail terms and license revocations.
As reported by NTSB, the crew that was working on the section that collapsed had just previously completed the same exercise on the other end of the bridge.
Also not only did the PT areas need tension, but they were supposed to be supported holding weight off the anchor points. By removing the mobile supports they broke it the moment they added the extra load to the anchor points. It just needed the time it took to yield.
You hit the nail on the head when you mentioned the fact that the crew was working to remediate the situation with the PTM, but NO ONE thought to close the road to traffic! Crazy!
I love this guy, holy shit! Finally, someone with a sense of logic and how to use language to make cogent points. Great great video, thanks for posting and keeping it objective.
I seriously have to add, this video is extremely entertaining as well. You have a funny way of intentionally playing with words, and your analogous references are hilarious! When a person is qualified and smart enough to explain something with total competence, only idiots become critical and offended out of a duty to fend off their own insecurities by whining about the use of "fuck", regardless of how perfectly placed it is for emphasis and humor. You must have a hard time dealing with idiots on the road, listening to politicians, and listening to vehicle advertisements. Once you start using logic and reason at this level, there's zero turning back. You can't dummy yourself back down to the societal level, especially socially. It's a frustrating existence my friend. It would be awesome to see you walk into a room with the parties and agencies involved in this investigation and see you tear some assholes with your humor and knowledge, especially the moment when you would point to the dipshits who were responsible. "That cunt sitting right there!!!!" "Wearing the ostrich boots!!!!!"
It make you appreciate even more the work of John Augustus Roebling, Thomas Telford, Isambard Kingdom Brunel, and Abraham Darby. Not a computer in sight when they designed their bridges. They may have been over engineered by today's standards, but their structures are still standing after all these years. Take the Forth Road Bridge in Scotland. Opened in 1964. They have now opened a second road bridge. Not just because of capacity, but because the 1964 bridge is failing due to corrosion, and will be closed and eventually dismantled. J A Roebling's Brooklyn Bridge is still standing, even though it was later found that the supplier of the steel cables supplied sub standard materials. Sadly though, design mistakes and blunders still occur to this day. As the Grenfell Tower fire in London tragically proved in 2017. I know in the demolition industry, post stressed concrete is treated with great respect. It can explode when the concrete is broken and the stress/tension in the reinforcement is released. As for leaving the road live to traffic below the bridge, while it's still being tensioned and hasn't been load tested. Total madness.
No not Irresponsible! A lot of people are CRIMINALLY HOMICIDE NEGLIGENT , and should be place under a 950 ton Hydraulic press for it ... let them die horribly as those who die under their greed,ignorance,arrogance!!!
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.
Good job. One point....the truss member that they were tensioning is by design in pure compression. You'll see on the drawing you were showing that they did not initially plan to have any PT bars in that member and three others. I dislike the whole concrete truss scheme. When you build a truss out of steel, you know exactly how the material and joints will behave. Not so much with concrete.
Just the very act of relocating that support/transporter from the end of the span to midspan changes the load on the canopy from the now last transporter out from compression to tension as that unsupported end wants to sag down, which could certainly overload the rod in that member...
Very good description of what may have caused this collapse. I believe you are correct in saying it failed where the workers were tightening the post tensioning rods. Why that work was necessary will be revealed during the investigation. What you said about the absence of support beams (load spreaders) between the transporters I believe is valid. I agree what others have said about how stresses change when supporting such a thing from different points along the beam. Why officials and the construction firm allowed traffic continue during the remediation is anyone's guess. But...it sure seems negligent.
Original concept drawings show a tower with support cables that would have supported the weight of all the concrete and steel. Because the truss is not uniform means the stresses on each individual web member is different. I am not an engineer, but it looks like a terribly complicated design.
