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!
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?"
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.
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
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.
@@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.
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 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.
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 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.
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.
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.
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.
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?
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 👍
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.
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.
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.
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.
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.
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.
So (from a completely non engenerding POV) did someone say "gnnnnnnnahh-click" after engaging safety squints. Possibly followed by "she'll be right might" ?
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.
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.
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.
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.
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.
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.
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.
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.
“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”
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.
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.
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....
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.
I believe the design was correct for the design condition on the plan. But as usual the site conditions did not follow the plans and they never will. An onsite engineer is essential on these projects. It is not code mandated in this case- only on wood truss placement in high velocity zones. Inspector Jeff state inspector
I never realized engineers have such a potentially life impacting job or rather, I didn't think about it that way. I don't know if the buck stopped with someone on this screw up, would be interesting to know, probably a lot of finger pointing .
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.
As a retired Florida general contractor, we were always taught that the greatest loads are at the supports of a beam and not in the center. Your explanation makes all the sense in the world. Even placing such a heavy load on the pylon with a misplaced lifting jack could over stress the post tensioning rods and break them.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
I am a civil engineer and I would like to express some points. These actual super duper structures are based on calculations of advanced mathematic techniques, These computer programs take in consideration so many variables that it makes almost impossible to control in construction sites. Every element is affecting the next one and so on, the stress and shear forces are dynamically calculated in the computer model . As already mentioned, a structural collapse is a sum of multiple failures, and it's very hard to manipulate those structures in situ. Once you make a change in one support, you are changing the whole model, affecting the tensions in all elements, the tensions tend to travel to less stressed elements that are not supposed to handle it. If the model is supposed to be supported with on only 2 nodes, when you put another support in the middle, it start to act like a continuos beam.creating all kinds of different tensions in the element. It's an unfortunate case of mishandle the the tensions on the site. Once one or more? rods were subject to tensions above the limit, the steel would break after passing the fluidity limit ( when it loose it's traction capacity ). And I guess that they were already working almost on the limit of their capacity, the security loads for this kind of elements are very high.
Jon O , for sure. The variables are just too demanding in this kind of project. And we did’nt even talk about the constraints required by the contract to install the bridge.
Jon Wiebold there is not such a thing. The structure is very interesting and very complex. Still , these structures are almost like machines. Thanks to this channel I could peek on the designs , they are very challenging.
Jon Wiebold nothing wrong with type of bridge so many experts out there .This could have been just a bad gauge on the tensioner we don't know yet.this bridge type has been built for years with no problems let's not speculate let's wait for the word.
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.
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.
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.
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.
The first diagonal web member was designed to be a compression member in the completed structure. It was designed to absorb the high shear forces that develop near a support. A late in the game change (Which happens on just about all fast track over budget past schedule projects) required the transporter to be moved one more web panel toward the center of the span. This changed the first diagonal member into a tension member to support the shear of the newly created cantilever end of the bridge. They likely call the engineer and need a "quick" analysis to see if they can do this even though the bridge was analyzed to hell and back in it's permanent position AND "planned" transport position, which unfortunately changed at the ninth hour. The very large tensile forces created in the first diagonal must pass through the post-tensioning tendons. As you see in the video, one of the tendons in the member (The one that has to be tightened from the bottom 12:20) terminates PRIOR to the "node" or intersection of the rest of the tendons at the blister. The tension in this dead end tendon is resisted by primarily concrete and requires a much lower load to "breakout or crack the concrete." A crack formed and opened over straining and stretching the remaining cable (The one being tightened when it fell). After the bridge was placed back onto its permanent support, the first diagonal goes back into compression and the adjacent web goes back into tension. They go to tighten the cable from the top that was found to be loose (because it had yielded.) They unknowingly over tighten the loose cable beyond it's strain limit. The imbalance of force causes the crack created earlier to propagate behind "dead end" plate on the first diagonal and a shear failure occurs causing the top deck to fold almost instantly followed by complete loss of shear and bending capacity. PT concrete is not supposed to crack. The pre-compression cause by the steel rods/strand are there to maintain compression or at the very least limit tensile stresses in the concrete to very low values. If a crack forms in through /adjacent to a "node" where intersection forces occur then it could entirely screw up the post-tensioning calculations since the forces have to travel within the material until equilibrium and the guys in the field could be chasing their tail trying to hit target values that can't be achieved without straining the steel past it's breaking strength. Trusses are generally not redundant. All of the members are critical. The job should have been stopped, budgets and schedules blown further, the road should have been shut down until a complete and a thorough analysis of all of the potential failure mechanisms were flushed out. This decision requires GUTS since it could cost a person or Company their jobs. If you can't get ahold of the State when they are on break, then you call the police and have them shut the road down until things can be evaluated and then peer reviewed (Time, money, inconvenience)...No loss of life.
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.
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!
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!
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.
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.
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!!!!!"
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.
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.
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.
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!!!!
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.
Good Work! Cool Shop. As a simple truss the end member being adjusted would be in compression (designed for) under normal service loading. Note on the tensioning table that that member 11 has no Pre Tension Force entry compared to the mid truss members. They probably tensioned it to move it, as the truss would experience completely different loading in transit as you indicated. This member probably failed in tension during transit over bumps and uneven surfaces causing unanticipated deflection. These were the cracks they were concerned about after install. Members 2 and 3 on the other end were also subject to the same design, loading, and circumstances. Those were probably the ones tensioned earlier. They were probably trying to close the cracks in 11 just to keep the thing together, oblivious to the fact that they were increasing the compressive loads already in the member. This resulted in the explosive failure (fell faster than the poor guy) as you noted, at the upper joint, as the lower section of the member appears to be intact. Engineering 101. What a design; no redundancy, no design for installation, and wasted taxpayer $ for a cosmetic suspension display above which carries no load. Looks like the Taggert Bridge from Atlas Shrugged!
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.
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.
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!!!
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.
I'd be more concerned about what the contractors have built who the engineers were. Unless it comes out that the firm was responsible for giving the OK on the changes outlined in the video. What it looks like is someone on site changed up the support plan without giving a thought to the de-tensioning.
Guys, I agree it was likely the contractors. On the one hand, I expect that the firm would demand a review of a change but that leads down one rat-hole. If they didn't demand it, well, that's a different rat hole.
REPORT: "2. The bridge had structural design deficiencies that contributed to the collapse during construction stage III. The cracks on the bridge occurred due to deficient structural design. 3. The morning of the incident, EOR held a meeting with project participants after evaluating the cracks over the course of the previous two days. At that meeting, the EOR acknowledged that his computations could not replicate the cracks and therefore, he did not know why the cracks were occurring. The Construction Engineer and Inspector (CEI) of the project advised the EOR at this meeting that the cracks were lengthening daily. Despite these admissions and the knowledge that the cracks were growing in size, EOR stated more than once that the cracks did not present any safety concerns. 4. The magnitude of the cracks warranted that SW 8th Street be immediately closed, and the concrete truss be shored and supported at multiple intermediate locations to reduce the loads in the north diagonal and the node until final evaluations were done and remedial measures implemented. " "11. EOR should have known that the truss was a non-redundant structure and if one diagonal member failed, the entire bridge could collapse. Given the nature and extent of the cracking and the non-redundancy of the bridge design, necessary safety precautions should have included closing the roadway below the bridge and immediately providing shoring to the bridge at suitable locations until a complete evaluation was done." www.osha.gov/doc/engineering/pdf/2019_r_03.pdf At the time of the collapse, they were pretensioning a member, but that was not the cause of the collapse.
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!
So the mainstream media is getting closer to what AvE said a couple of days ago, they still haven't gotten it quite right yet methinks. From the Miami Herald: "While the cracking dominated media coverage on Saturday, experts appeared less concerned over that than with other factors, including the tensioning work going on at the bridge’s north end. Cracking in new concrete is not uncommon and not necessarily a sign of failure, they say. Tightening of steel cables, or tendons, that run through concrete structural elements is a delicate operation, and over-tightening can cause concrete pieces to twist and break apart, experts say."
Have any concrete bridges near you? Or even ones with the concrete parapet walls along the side (barrier, so you don't drive off the edge). Walk out on one and look at the parapet or roadway up close. You will see thousands of spiderwebbing and microcracks. The bridge is constantly flexing, especially on a roadway bridge with traffic imparting massive live moment force every time it crosses onto the bridge from the approach slab. These are superficial cracks and mean little to the concrete's compressive strength. And on the parapets, that are non-load bearing, it means nothing. If the steel cables inside the concrete beams underneath the bridge fail...you lose all tensile strength and the bridge is in trouble.
Allowing folks to drive under that bridge while knowing full well their was trouble lurking is beyond negligent. You really have to freaking wonder sometimes what folks are smoking on the job these days. lawsuits galore, stupidity has no bounds.
![KSI - Dirty [Official Visualiser]](http://i.ytimg.com/vi/VoDh1h1dPUE/mqdefault.jpg)
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.
Robert, thanks for your comment. I've just watched this video again after many years. Your comment adds a lot to the story.
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.
CuriousMarc please not, my day only has so much time to watch videos.
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.
@john handcock You should listen before you talk... you say "he is wrong" and then offer up your own theory which agrees with his 100%.
And yet there are so many people that hate the way AvE thinks. They hate people who think for themselves and try to figure stuff out.
You're debating talking about the precise point of failure vs. root cause. Not to mention, he did talk about the transportation!
"Under certain circumstances, urgent circumstances, desperate circumstances, profanity provides a relief denied even to prayer." - Mark Twain -
What about uncertain circumstances?
Whiskey Tango Foxtrot(!?)(Click)
Well hell, then, it;s mandatory.
love this quote
Mark Twain apparently said a lot of stuff, and the more I learn about the cooler he becomes. His name is the first 'Mark' that pops up in Googoo
Anybody that's offended by swearing on these videos have never gotten their hands dirty for a living.
Eric Gulseth straight up
Anyone offended has never gotten their hands dirty at all. Hands up those who hasn't sworn when they injuried themselves.
Just straight up bitches
That is so true
YOU get a fuckin thumbs up!
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
Welcome aboard, my man! Sorry bout your mates.
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!
@@SkuzzelB8 High capacity assault bridges!
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?"
The engineer in charge of the falsework died in the collapse. Musta been a higher up?
Whenever you are fed a story by an elder, be aware that there might be some creative editing taking place.
the song London bridge is falling down with be changed in honor of the university & engineering company...
I seem to recall another video where AvE said if you want an unknown answer not to post a question but post the wrong answer to the question. Hmmmmm
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.
charles streeter good point. The bridge was around the 900t mark wasnt it? Would expect a couple cranes would you?
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.
stewart fowler you not tied off in case the structure fails. You tie off so you don't die from tripping on an extension cord.
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.
I wasn't expecting this series of videos but wow do I appreciate it.
robhimself79 Exactly!!
"Partner, if ya can't handle an F-bomb, go fuck yer hat." Subscribed!
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.
I have learned lmra everybody is entitled to stop the work at any time when there is a safety issue. At least on refinaries and platforms it is.
So in that sense. Everybody there is to blame.
Although the content is very interesting i'm actually here for the foul language.
satburn I knew there were others like me 😆😆😆😆
Quick satburn get the popcorn!
I don't understand why AvE didn't give you a heart on this one. Maybe he is asleep.
fackin a
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
There’s an article somewhere on the inter webs with the tittle:
“A Foulmouthed Canadian RUclipsr Might Have Solved the FIU Bridge Collapse”
There are subreddits where journalists are asking if anyone known AvE's contact information so they can contact him about this video.
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.
The fact that they knew something was wrong and still let people drive under it is so negligent it’s sickening.
This is the bottom line. It will all come down to this fact. Negligence.
Murder , or at least depraved indifference.....criminal charges should be brought
@@tbelding Thank you for the update. Well said.
@@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.
The bridge identified as a sidewalk.
Glenn And it failed.
yes its more of a pedestrian crossing now
But for some reason, we're having trouble getting over it.
Laughed so fucking hard I almost forgot the diesel coal roller that identified as a prius
😂😂😂😂
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.
@@PeterWolfe2012 so its not his fault?
I'm really glad I wasn't on this job, some hack at a desk really screwed the pooch on this one! FOR SURE
@@PeterWolfe2012 I assure you Walmart does not chain sprinklers shut
@@nealinnc I assure you, they did.
When AvE puts dad jokes about wood and members aside you know shit got real.
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.
Guy Ligier I think the drooping end is key. Looks like they were trying to carry the load on that end while they came up as you said on the hydraulic.
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 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.
There were plenty of spectacular failures back then.
@@joetrapp9187 As there are structures still is use (Brooklyn Bridge) today.
Survivorship bias, plus todays cheap "value engineering".
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.
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.
You were right. The NTSB called out the non-redundant design in their report.
The design just looks wrong with 'unsupported' triangles that appear to be random sizes.
@@gyrfalcon23 All in the efforts to save some spring steel and concrete
Well done sir, cribbing and traffic control would have saved lives!!!
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.
Tj Smyth I'm
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.
Traffic Control....near the top of the list for the lawsuits....
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.
Apparently, the university was doing all of the inspection with limited oversight from the DOT.
HE RAN OUT OF HIS MEDS ON THAT DAY.
+ Yeti Dan: In other words, the fox was guarding the henhouse.
Also, given the short length of the cable, the room for error was smaller. T
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?
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 👍
That's why it collapsed.
Course language is the primary source of communication on the job site.
I'm disappointed in the swearing. There's fucking not enough!
Barry Britcher I totally agree with you. I'm a shop guy, we cuss.
You guys need to watch your goddamn mouths, I'm fucking tired of all this fucking cussing
I'm actually kinda befuddled that there are apparently some shop guys who don't speak French.
That's gotta be a fun place to work.
Locker room talk? Wait till they hear shop talk!
This channel is improved by embracing the parlance of the building site.
The fact they continued to let traffic pass underneath that bridge is Unforgivable!!
American arrogance!
@tomrogers9467 European Ego! Things collapse there all the time, get over yourself.
Seems like the enginerds forgot to "back it off a half turn"
That's for matting surfaces. Still u torque from the center out. They must have messedup the order do you think?
More likely the contractors that fucked it up.
FIGG/MCM diversity hires in action at FIA bridge: "Hey, Jose... how's that go again? Righty tighty, lefty loosey? Which way's left?"
I’ve see a post tension cable shoot 400 feet out off a 260 foot building
Billy Strong was it launched from a trebuchet by any chance?
CreamTea did it weigh 90kg
Thered a lot of energy in those cables, they're nothing to fool with.
That would have been a brown moment for everyone in the area!
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.
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.
Do the Georgian Ski Resorts run-away Chair Lift next....
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.
God, I saw that video it was horrific. I just wanted all the skies to jump off before they got ran into the mess of lifts towards the end...
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.
I was stumped about that. I didn't think they would be designed to be reversible. Running free makes all the sense.
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.
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.
Six months ago, I couldn't spell anganear...now I are one!
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.
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.
1:49 you can see the bridge fail on the left side, almost dead nuts in front of the crane
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.
So (from a completely non engenerding POV) did someone say "gnnnnnnnahh-click" after engaging safety squints. Possibly followed by "she'll be right might" ?
Last time I worked in South Florida, it was "is good ok amigo?" Same-same but different the whole world over.
AvE Cuban for gnnnnah-click. Direct translation. I speak fluent shopaniese.
My learnings from a long time ago were to count the fingers of to guy who delivers the "she'll be right mate".
AvE shee'll be right mate!
Maybe they were using torque-to-yield fasteners? :-P
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.
Given that RPM is pronounced 'rippem', shouldn't PSI be pronounced 'pissie'?
It is right?
Example: I added anothr 5 pissies to my motorcycle tire as it was a little low.
AGREE!
AvE has pronounced it in exactly that way in older videos.
How do things fail? Like everything else, slowly, then all at once.
SnarkyPosters except drunks off of a bar stool. Its rather elegant. Like an inverted ballerina.
I believe the drinking itself is the slow part of the failure process in that scenario!
once at peak intoxication the man has enough potential booze energy to overcome the chairs stability point
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
this wasn't just an accident, it was gross negligence to have Joe Blow driving under a bridge that hadn't had it's final testing complete.
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.
@Mr. Gandalf Because there is no such thing as an accident, someone is always at fault.
@Mr. Gandalf So the "accident" won't happen again.
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.
so correct. they want to squeeze every dollar out of a project.
I *pray* that if these companies are found negligent, that they are sued into nonexistence.
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.
1320fastback agree its like in plumbing you need two wrenches to tighten one end of compression bolts to squeeze two sides together common sense
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.
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..
Ugh, TTY garbage! ARP replacements(ideally head studs) ALL DAY
Yep. Even on stock rebuilds I mostly use ARP now
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! 😂 😂 😂
You know you're there when tighter gets easier.
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.
Is "AVECAD" the same as "DAVECAD", only with the D still in the vice?
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.
They should have used steel UNDER the concrete or made it entirely steel.
Didn’t blame it on a bolt, blamed it on poor field engineering.
Here's the thing, there was no redundancy. Any bolts fail, and the entire thing goes.
G - damn right
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.
If you click on the video, then complain about the video, who is really at fault here?
Wojcicki
Clearly, Obama.
Sticks and stones may break my bones, but I'll eat my hat if words won't kill me.
Russia
Trump! its all trumps fault.
“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”
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...
sad but true .
Plus diversity hiring
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.
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 ;)
We'll get the official official findings in 18 months. That's my bet anyway.
I get the feeling (as you said in the video) they already know....they just have to go through the motions, to show "due dilligence" and such...
And not a cent of ensuing fines will go to those who need it.
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.
"This thing'll kill ya right dead quick fast in a hurry if'n you're not careful." Quote of the day right there.
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....
Right? If an F-bomb offends you over engineering/political incompetence that killed people your priorities are really fuckin' out of whack.
Couldn't *fuckin* agree more.
I’m sure he did a proof of concept in Minecraft and it worked
Jordan Bjork LMFAO
The engineer did for sure.
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.
I believe the design was correct for the design condition on the plan. But as usual the site conditions did not follow the plans and they never will. An onsite engineer is essential on these projects. It is not code mandated in this case- only on wood truss placement in high velocity zones.
Inspector Jeff state inspector
I never realized engineers have such a potentially life impacting job or rather, I didn't think about it that way. I don't know if the buck stopped with someone on this screw up, would be interesting to know, probably a lot of finger pointing .
So how fucked are these guys for letting traffic continue?
Really fucked
construction company has admitted this was an oversight
Very
I think these guys will REALLY have all their dicks in a collective vice. Along with their balls.
they have been working on developing this rapid install system at that school for like 5 years as to minimise traffic interruption
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.
As a retired Florida general contractor, we were always taught that the greatest loads are at the supports of a beam and not in the center. Your explanation makes all the sense in the world. Even placing such a heavy load on the pylon with a misplaced lifting jack could over stress the post tensioning rods and break them.
This deserves same amount of likes as views. AvE has found the smoking gun.
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.
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.
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.
Excellent explanation.
You gotta be a Canajun
This is a first of a kind for the ABC method: Accelerated Bridge Collapse.
Built, installed and demolished in record time!
Always Be Careful (afterwards)
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
No, this is not first of its kind.
This method of construction has been in practice for slightly over a decade.
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.
I still don't understand why it was deemed necessary to have a bridge this big and heavy for just foot traffic.
Have you seen the size of people these days?
A steel truss bridge would have solved the problem easily. High strength to weight ratio.
Who constructs a truss with concrete? Does it work well?
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.
It's all about the way she looks man.
They wanted it to be a hang out area able to host events like concerts.
Absurdly negligent to have this road open for traffic.
That's the biggest take on this tragedy for sure! :(
The negligence was removing temporary supports before the overhead suspension cables could be installed.
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.
D N the laws of common sense. Across the board, the lack of structural support is a theme.
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.
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.
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.
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.
This is why in the West Coast, if one wants to let traffic pass below, falsework is required before all structural parts are installed.
I am a civil engineer and I would like to express some points. These actual super duper structures are based on calculations of advanced mathematic techniques, These computer programs take in consideration so many variables that it makes almost impossible to control in construction sites. Every element is affecting the next one and so on, the stress and shear forces are dynamically calculated in the computer model . As already mentioned, a structural collapse is a sum of multiple failures, and it's very hard to manipulate those structures in situ. Once you make a change in one support, you are changing the whole model, affecting the tensions in all elements, the tensions tend to travel to less stressed elements that are not supposed to handle it. If the model is supposed to be supported with on only 2 nodes, when you put another support in the middle, it start to act like a continuos beam.creating all kinds of different tensions in the element.
It's an unfortunate case of mishandle the the tensions on the site. Once one or more? rods were subject to tensions above the limit, the steel would break after passing the fluidity limit ( when it loose it's traction capacity ). And I guess that they were already working almost on the limit of their capacity, the security loads for this kind of elements are very high.
Jon O , for sure. The variables are just too demanding in this kind of project. And we did’nt even talk about the constraints required by the contract to install the bridge.
Jon O tight schedule?
I think they've been working on it for 5 years
No. Back up six steps and look at the big picture. It is the wrong kind of bridge. Period.
Jon Wiebold there is not such a thing. The structure is very interesting and very complex. Still , these structures are almost like machines. Thanks to this channel I could peek on the designs , they are very challenging.
Jon Wiebold nothing wrong with type of bridge so many experts out there .This could have been just a bad gauge on the tensioner we don't know yet.this bridge type has been built for years with no problems let's not speculate let's wait for the word.
Just think. The NTSB will spend 36 months to reach the same conclusion Uncle reached by crowd sourcing (and his own peculiar genius) in 36 hours!
Depending on if they publish the real results or not. You never know when someone wants their ass saved.
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.
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.
From what I'm seeing around my city, post-tensioning used a lot here.
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.
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.
The first diagonal web member was designed to be a compression member in the completed structure. It was designed to absorb the high shear forces that develop near a support. A late in the game change (Which happens on just about all fast track over budget past schedule projects) required the transporter to be moved one more web panel toward the center of the span. This changed the first diagonal member into a tension member to support the shear of the newly created cantilever end of the bridge. They likely call the engineer and need a "quick" analysis to see if they can do this even though the bridge was analyzed to hell and back in it's permanent position AND "planned" transport position, which unfortunately changed at the ninth hour. The very large tensile forces created in the first diagonal must pass through the post-tensioning tendons. As you see in the video, one of the tendons in the member (The one that has to be tightened from the bottom 12:20) terminates PRIOR to the "node" or intersection of the rest of the tendons at the blister. The tension in this dead end tendon is resisted by primarily concrete and requires a much lower load to "breakout or crack the concrete." A crack formed and opened over straining and stretching the remaining cable (The one being tightened when it fell). After the bridge was placed back onto its permanent support, the first diagonal goes back into compression and the adjacent web goes back into tension. They go to tighten the cable from the top that was found to be loose (because it had yielded.) They unknowingly over tighten the loose cable beyond it's strain limit. The imbalance of force causes the crack created earlier to propagate behind "dead end" plate on the first diagonal and a shear failure occurs causing the top deck to fold almost instantly followed by complete loss of shear and bending capacity. PT concrete is not supposed to crack. The pre-compression cause by the steel rods/strand are there to maintain compression or at the very least limit tensile stresses in the concrete to very low values. If a crack forms in through /adjacent to a "node" where intersection forces occur then it could entirely screw up the post-tensioning calculations since the forces have to travel within the material until equilibrium and the guys in the field could be chasing their tail trying to hit target values that can't be achieved without straining the steel past it's breaking strength. Trusses are generally not redundant. All of the members are critical. The job should have been stopped, budgets and schedules blown further, the road should have been shut down until a complete and a thorough analysis of all of the potential failure mechanisms were flushed out. This decision requires GUTS since it could cost a person or Company their jobs. If you can't get ahold of the State when they are on break, then you call the police and have them shut the road down until things can be evaluated and then peer reviewed (Time, money, inconvenience)...No loss of life.
Meanwhile in a pandemic in 2020... (not what meanwhile means)
TL;DR This is what happens when the design is a class 2 lever but you build it as a class 3 lever.
A snapping PT rod would explain that "bullwhip cracking" sound... (2:33)
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?
I guess there are more than one of those in parallel. When one fails the others get a lot more stress and would fail soon, but maybe not immediatly.
I wonder if it was being acoustically monitored?
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.
It's easy for something to fail to the point of being useless, while optically things only shifted an inch or so.
appreciate all your videos . also the more censored youtube seems to get, the more i enjoy the foul language. keep them coming buddy
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!
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!
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.
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.
MarcAFK
Im with you 100%. This is progress?
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!!!!!"
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 worker was harnessed to it. in slow motion his harness failed and it looks like he hits the fallen bridge
Jim K and he died
www.google.com/amp/s/amp.local10.com/news/florida/miami-dade/pedestrian-bridge-collapse-victim-navaro-brown-was-37
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.
Did you watch the video? He's asserting, with reason, that the failure was the post-tensioned cable. The concrete didn't fail.
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.
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.
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!!!!
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.
Horseshoe nail ?
Good Work! Cool Shop. As a simple truss the end member being adjusted would be in compression (designed for) under normal service loading. Note on the tensioning table that that member 11 has no Pre Tension Force entry compared to the mid truss members. They probably tensioned it to move it, as the truss would experience completely different loading in transit as you indicated. This member probably failed in tension during transit over bumps and uneven surfaces causing unanticipated deflection. These were the cracks they were concerned about after install. Members 2 and 3 on the other end were also subject to the same design, loading, and circumstances. Those were probably the ones tensioned earlier. They were probably trying to close the cracks in 11 just to keep the thing together, oblivious to the fact that they were increasing the compressive loads already in the member. This resulted in the explosive failure (fell faster than the poor guy) as you noted, at the upper joint, as the lower section of the member appears to be intact. Engineering 101. What a design; no redundancy, no design for installation, and wasted taxpayer $ for a cosmetic suspension display above which carries no load. Looks like the Taggert Bridge from Atlas Shrugged!
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.
It hasn't gotten better.... Probably worse. It's all worthless reality tv and sitcom trash on tv.
God I miss that show. At the very least it was truly educational. Learned a ton from it
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.
Could not agree more with everything you've said.
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.
@GlennL the tower & cables are purely decorative... this isn't a suspension bridge.
Yes, I did find that out. The tower and the support cables were not to have any function, other than to provide aesthetics and some sway protection.
This helped with my Engineering Ethics course!
Irresponsible to have traffic passing under it, especially when they knew there was a problem.
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!!!
One track minds in action
Is that the pencil you used to charge your phone forever ago?
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.
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...
DaDa Fan engineering was done right, it's the contractor who built the bridge that is most at fault for their bad decisions in building it.
DaDa Fan
Just don't park under the Skyway bridge and you'll be fine.
I'd be more concerned about what the contractors have built who the engineers were. Unless it comes out that the firm was responsible for giving the OK on the changes outlined in the video. What it looks like is someone on site changed up the support plan without giving a thought to the de-tensioning.
Guys, I agree it was likely the contractors. On the one hand, I expect that the firm would demand a review of a change but that leads down one rat-hole. If they didn't demand it, well, that's a different rat hole.
Life is a risk, even in the bathroom.
Your language is rather course. But love how you invent your own vocabulary as you go along. Carry on.
REPORT: "2. The bridge had structural design deficiencies that contributed to the collapse during
construction stage III. The cracks on the bridge occurred due to deficient structural
design.
3. The morning of the incident, EOR held a meeting with project participants after
evaluating the cracks over the course of the previous two days. At that meeting, the EOR
acknowledged that his computations could not replicate the cracks and therefore, he did
not know why the cracks were occurring. The Construction Engineer and Inspector
(CEI) of the project advised the EOR at this meeting that the cracks were lengthening
daily. Despite these admissions and the knowledge that the cracks were growing in size,
EOR stated more than once that the cracks did not present any safety concerns.
4. The magnitude of the cracks warranted that SW 8th Street be immediately closed, and the
concrete truss be shored and supported at multiple intermediate locations to reduce the
loads in the north diagonal and the node until final evaluations were done and remedial
measures implemented. "
"11. EOR should have known that the truss was a non-redundant structure and if one diagonal
member failed, the entire bridge could collapse. Given the nature and extent of the
cracking and the non-redundancy of the bridge design, necessary safety precautions
should have included closing the roadway below the bridge and immediately providing
shoring to the bridge at suitable locations until a complete evaluation was done."
www.osha.gov/doc/engineering/pdf/2019_r_03.pdf
At the time of the collapse, they were pretensioning a member, but that was not the cause of the collapse.
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!
So the mainstream media is getting closer to what AvE said a couple of days ago, they still haven't gotten it quite right yet methinks.
From the Miami Herald:
"While the cracking dominated media coverage on Saturday, experts appeared less concerned over that than with other factors, including the tensioning work going on at the bridge’s north end. Cracking in new concrete is not uncommon and not necessarily a sign of failure, they say.
Tightening of steel cables, or tendons, that run through concrete structural elements is a delicate operation, and over-tightening can cause concrete pieces to twist and break apart, experts say."
Wow. "Cracking in new concrete is not uncommon and *not necessarily a sign of failure* " Well if that statement doesn't take the cake.
The people who were close to this project knew immediately it was because of one or maybe two things and said oh fuck.
Exactly. It may be months or years before they pin down exactly what happened.
Have any concrete bridges near you? Or even ones with the concrete parapet walls along the side (barrier, so you don't drive off the edge). Walk out on one and look at the parapet or roadway up close. You will see thousands of spiderwebbing and microcracks. The bridge is constantly flexing, especially on a roadway bridge with traffic imparting massive live moment force every time it crosses onto the bridge from the approach slab. These are superficial cracks and mean little to the concrete's compressive strength. And on the parapets, that are non-load bearing, it means nothing. If the steel cables inside the concrete beams underneath the bridge fail...you lose all tensile strength and the bridge is in trouble.
alternative media. This youtube channel is a form of media.
Allowing folks to drive under that bridge while knowing full well their was trouble lurking is beyond negligent. You really have to freaking wonder sometimes what folks are smoking on the job these days. lawsuits galore, stupidity has no bounds.
Thanks AVE, just saved millions in investigation bills.
Andrew Roxby those milions still need to be spent, someone needs a new house or two