After reading the proposal it states that the cable stays will provide added stiffness and pedestrian load... so they were not only an aesthetic feature.. the cable stays were actually intended to provide some support. After watching the video and looking at pictures what I see is the lower deck became disconnected from the last column / diagonal support.. when that happened the lower deck fell causing the total collapse. The lower deck likely had ether pre or post tensioned cables. If they are post tensioned there are wedge sockets that secure the cables and it's possible that the wedges failed or the strength of the connection at that point was inadequately designed / engineered. If that's the case review of the design / calculations should have caught it, but maybe not... I've suggested this book before... not sure if you or any of your followers have read it but it's a really good read for folks who are interested in this sort of thing. www.goodreads.com/book/show/271495.To_Engineer_Is_Human
Interesting that the drawing of the deck shows that member 11 (the end diagonal) did not have post-tensioning bars. Maybe these were added to accommodate the temporary support position which was in from the span end during the installation?
Damn, in 10 min you gave a more insightful presentation than all the cable channels combined. No interviews of people about what they thought, how sorry they were. I'm sure a lot what you presented is in the hours of blather, you distilled it down perfectly. As Joe Friday would have said "Just the facts Ma'am"
Samual Whittemore, while the designers could be found to be at fault also, someone in charge ordered those people to adjust the tensioning without closing traffic. I don't fault the construction guys who were following orders. I blame the people responsible as I said.
So the FIU bridge was a truss design made to look like a cable-stayed bridge - resulting in one of the most moronic truss layouts I've ever seen. Juan describes it as a Warren truss but it actually morphs from half-ass Warren on the north failure end to half-ass Howe on the south end, with absolutely ZERO redundancy! Were this span designed in steel it could have been done at one-third the weight, half the cost, a redundancy factor of at least three, and WITH NO LOSS OF LIFE!!! Did FIU engineering dept go through any what-if worst case analysis? If not it should be shut down permanently.
I'm guessing that FIU has an "engineering" department which provided the original concept as a class project. I"ve seen it before in other colleges. Modifying the truss design to appear to be part of a suspension system was the first serious mistake. Using friable concrete throughout was the second big mistake. Erecting an untensioned truss was the third mistake. All in the name of "Accelerated Bridge Construction" so they could brag about closing the street for only one weekend. Heads need to roll.
if an engineering company can't build a walkway then no sidewalk is safe from those guys...the students have little to fear until the next project is started
This was an "all-female no men allowed feel-good safe-space" project. She said "it just felt right" the design just felt right. That is proper engineering, just feelings....
The question of why traffic was allowed while they were allegedly tightening cables was one of my first questions. Thanks for the report Juan. Look forward to next report...if there will be one. 😎
Juan, I understand that you are being cautious and reporting only the facts, but others have made a much more in depth analysis, and come to preliminary (but unproven) conclusions that mainstream media haven't touched, and the NTSB will take months to release.
Excellent analysis as always! Minor correction: in your credits at the end, you state that it happened in March 2017. It’s 2018. I am not an engineer, but the whole design concept and the way it was executed seems like a disaster waiting to happen.
I discovered your RUclips channel a couple few days after the spillway failure at the Oroville Dam and have been watching your excellent videos since them. Your new videos are one of the small handful that I genuinely anticipate. Thank you for the informative service that you are providing the public. The mainstream media is a complete failure when it comes to most MAST related subjects. You are becoming the “goto guy” that the public turns to for better information on Civil Engineering disasters - you are becoming the Neil deGrasse Tyson of Civil Engineering. As proof of what I observe, you are now attracting professional engineers such as Barry Gerbracht, Bob Crosby and bcbloc02. (Ok, Brian - bcbloc02 - is not a Civil Engineer, he’s a MSME. But unfortunately, he can tell you all about catastrophic structural failure.) The reason that I mention this, is that whether or not you chose this ‘profession spokesman role’ or it just fell into your lap (which is what I suspect happened), you now occupy this spot by simple RUclips viewership. If you want to further explore this path (which I sincerely hope you do), then someone should probably point out who some of your viewers are. Again thanks for all of the exceptional videos, and I eagerly look forward to seeing many more.
All the holes in the cheese lined up that day. Several key decisions led to this chain of events, any one of which could've been changed. Decision to transport and support bridge in a different position than engineered (mid span between truss hard points). Decision to not install or leave falsework/cribbing in place after initial bridge placement during critical post tensioning/ final inspection works. Decision to rush the initial process of bridge installation, so as to minimise traffic disturbance. Decision to ignore cracks in the newly installed bridge. Decision to carry out post tensioning/ fault finding and rectifiication with public exposed to risk. I personally believe that concrete has no place being used in a structural truss- it's strength is in compression.Trusses are all about tension. Using boxed steel for the truss web would not have changed the appearance of the bridge and would've had many times the failure resistance and safety factor of what was there. Likewise, a couple of simple steel I beams in the lower span would've provided a huge margin of redundancy for the structure.
This is an excellent analysis and suggested redundancy features. I noticed that the post tensioning on the truss member that failed was *internal* to the member... not external to the member. So that only the center section of the truss was under tension, leaving each end, one in the blister on top and one in the pier area under *tension, the concrete in both of these areas is seen to be exploded or shattered after the failure... concrete was under tension in those two critical areas. Just one of the major engineering and management errors... ignoring those massive cracks in the failed area and not stopping the project on that basis alone was inexcusable imo, likewise cutting into the blister on top of the canopy with cement saws and jack hammers was insane on the face of it, even if there was no traffic under the bridge..with traffic one has to wonder what they were smoking.
Hi Juan -- listening to your description and seeing the picture the end of the beam, it looks like it blew out during tensioning operations, this is a not uncommon occurrence -- but typically you still have the scaffold in place and it costs a little money and time but is not usually a tragedy. This is caused by 1) poor design and /or poor execution, ( the concrete does not consolidate adequately around the " Bugle head" a thick plate structure that applies the tension from the rods / or cables depending on which system you use and or it does not reach adequate strength due to design, batching, or placement issues. But the biggest issue is it was designed without redundancy by someone who thinks looking good and attaining some architects vision is more important than safety and durability.
Tension adjustment failures happen, I have witnessed three in my 30 years of engineering. An anchor failure, cable failure, and concrete failure. It happens, so to think you can pull off a tension adjustment with zero probability of failure violates Murphy's Law.
Dude. The cables are for compressing the concrete so that elements can perform in tension. They aren't for adjusting the camber because they can't significantly affect the length of the concrete elements. The 'canopy' is the compression element of the beam, the deck is the tension element, but hugely preloaded with the tendons run through the deck.
Nice review Juan. You have a way of making information like this understandable, without injecting a lot of fear and hysteria into it. As you point out, without having two sets of truss web members, there is no load path redundancy in the bridge. The earlier reports of cracking may or may not have anything to do with the failure. I'm thinking it is probable that the crew adjusting the post-tensioning stressing on the dywidag bar in the web had a significant role in the failure. The NTSB final report will be very comprehensive, with everything related to that structure undergoing scrutiny. As with many structure failures, it probably wasn't just one thing contributing to it, but a cascade of events leading to the failure.
The movement of the structure via transporter will be of interest to investigators since the support for the bridge section during transport may have caused some flutter of the north section. The engineers noticed cracks, and that rod was being tensioned so there was a stress concentration near where it hinged and pulled the lower slab down from the support. From another angle you can see the north end of the rod waving free where the joint failed at the base.. Your point about the value of a temporary support and blocking traffic during such activity is solid. Temporary supports would have been expensive, but hubris more so. Appreciate your comments on structural redundancy as an important safety factor in civil construction.
That is what I was thinking. The design was good. Some unforeseen stress was placed upon the structure during the move. The ABC technique has been used successfully before - but usually a 'simple' parallel shift. The rotation was novel.
The concrete was pulled in tension. If you are pulling on something, that is tension. If you are pushing on something, that is compression. Ignore for a moment that concrete was used and just look at the system as someone was pulling tension on a truss rod. This situation is so sad. Usually multiple design engineers are involved on a project like this. Now steel has high elastic properties (like a rubber band)...not quite that elastic...but steel can take a beating in tension. I bet if those truss webs had been made of steel, the bridge may not have collapsed. I have one simple question for the Engineer...Why are you excessively pulling concrete under massive tension?
Best comment. Hits the nail. Who can EVER come up with the idea of a truss bridge (in COCRETE!), decorated by a Pylon and cables? Who is responsible for this gross professional incompetence?
You Sir are amazing. Only three days after this horrific accident you have nailed it. Your "No Drama" analysis based on only the facts and your amazing technical vision is truly inspiring. You exhibited this through the entire evolution of the Orrville spillway near disaster. You clearly can apply that same clear vision to other disasters. My hat is off to you. It will be months or years before your insights are proven to be spot on. But your clear vision will be proven to be absolutely spot on. Congratulations to you.
I think the biggest failure, regardless of design or construction, inspections or any procedural move pertaining to post tension cables is the fact that there was no sub structure to support bridge or just the fact that they were allowing traffic under bridge at all while they were doing any tweaking via post tension cables or anything else.
*When do engineers ever use a just single truss? trusses are usually employed in pairs or in parallel sets... as I recall a major disadvantage in truss design is they are prone to twist or deflection to the sides.*
+Sideslip *It still does not give you any redundancy protection if one of the struts fails... which appears to be exactly what happened in this accident. Especially considering this bridge collapsed with pedestrian no load either... its takes several "weak links in the chain" to result in a total failure of this type, I will bet that although the design was not the primary cause of the failure, it was at least a contributing failure.*
I like you said spring time and with snow in the background, not so much spring. Thank you for sharing your amazing video. God bless you and your family
Through my life, I was a nurse and a horse person, I have had NO engineering training, just day to day observations of people building things. And, because I do have a love for science and how things are put together, I may have paid more attention than some people. After the collapse, when I saw the design of the bridge, my FIRST thought was why do they only have one line of trusses!? Then when I learned that EVERYTHING was concrete, I wondered why they wouldn't use some lighter materials where possible... at least for the trusses. Who cares what it looks like!!! Its main purpose was to be a bridge not a work of art. Either they should have either made the suspension part of the engineering, or left the tower and cables off and put more money into design and stronger more sensible materials for it. There is a pedestrian bridge over a freeway here that is not fancy, but functional. And knowing the folks here they probably closed the freeway, in sections, until it was completed AND tested. It was built before I got here in 1976... Still working well!
Nice report. Here in Utah they have been using the ABC for quite some time and as I understand it many of our bridges were built that way. Your report set my mind at ease as it does seem the design is the problem. None of our bridges are designed or look like that. A lot of ours are overpasses that see heavy traffic.
added redundancy, I suspect, not strength. this concrete wannabe I-beam is such an unsafe design. and having to use supports in the wrong locations for the installation of the section. wow.
They're not suspension cables in any case. That's a cable-stayed design not a suspension design. So if they are aesthetic it's an aesthetic cabled-stayed bridge, not an aesthetic suspension bridge.
David Newton I read somewhere that they weren't even supposed to be cables, but just hollow steel tubes. If so, then it wasn't even partially cable-stayed. In an NTSB briefing, one of the investigators stated that it was his understanding that the part above was purely cosmetic.
So many mistakes made from the design table to the disaster that lead to this, i can't wrap my head around that this is possible in our western world 2018. Very nice analysis Juan
Well not completely cosmetic as they were needed to support the pedestrian loads from what I read here. facilities.fiu.edu/projects/BT_904/MCM_FIGG_Proposal_for_FIU_Pedestrian_Bridge_9-30-2015.pdf Also they would have offered some level of redundancy to the system. I thought the failure of the Silver Bridge at Point Pleasant had taught engineers abut the necessity of redundancy in bridge design but obviously that was not the case if the failure of one tensioning member can collapse the entire structure in a catastrophic manner. The factor of safety of this design in its as installed condition had to have been less than 2 , and that is poor practice. It also seems we are doomed to repeat the mistakes of using high strength materials to save costs and reduce material use. That too has proven problematic in the past as imperfections in the materials result in a flawed and unsafe structure. Low stress = long life. Still hard to get engineers to accept that.
bcbloc02 As an engineering student going through uni, it’s only incidents like this that serve to remind us of the importance of getting it right. It’s important to realise that with so many successful bridges and engineering projects, complacency creeps in, redundancy and fail mechanisms don’t seem relevant because, well, the bridge isn’t going to fail! That being said, to design a bridge unsafely on the whim that it won’t fail is utterly reckless and I’m sure this collapse will be used as an example in many lecture halls globally about why we have redundancy in designs.
bcbloc02 yes that's also what I heard on a news report. That the majority of the support comes from within the main truss system. But the cable tower was designed to provide support especially while the bridge is in use by absorbing vibration.
The “cable” stay component is definitely mostly aesthetic, they weren’t even high strength cables but tubular pipes. The details provided in the drawing show a relatively light duty anchor bolt ties which would only provide some restraint.
A 16" diameter steel pipe even with only 1/8" wall thickness still adds 225,000lbs of tension loading to help support the structure. With 4 per span that is almost 1,000,000 pounds of force! It wouldn't support the whole bridges weight but it would take about 1/3 of it and that is a significant reduction in the forces on the bridge itself. Of course without the other side of the bridge installed to counter the stay forces it would have likely failed the tower and brought it down too. If it was quarter wall pipe instead it could have reduced the loading on the bridge by in half. The design details of the construction are unknown though so it is impossible to calculate the actual values. The bridge builders did call it a cable stayed bridge in their project description so they must have thought they were doing some supporting work. ruclips.net/video/5Y_71L35CvM/видео.html They don't call it an innovative truss bridge with a towering pylon decoration.
"Low stress = long life. Still hard to get engineers to accept that."...Not competent engineers. I would never have sealed a bridge design without a significant safety factor AND redundancy built in - Bill Gillette PE
Anyone here remember the I-5 Skagit River bridge collapse May 23 2013? The bridge was a subdivided warren truss which was struck by an oversized load causing a single-point failure and total collapse of a span. Security video of the Skagit collapse is disturbingly similar to FIU. Non-redundant truss technology was already considered obsolete in 2013 - why FIU adopted an obsolete bridge design raises serious doubts as to the competence of their engineering department.
From what is obvious to me is that the tensioner supporting the end of the bridge that wasn't supported during application of the bridge was weakened by the hundreds of tons of NON compressed concrete overhang, therefor stretching the tensioner supporting that particular end. It's obvious to me that once that end of the bridge is placed on it;s correct supporting pillar at that end, they "the engineers" would have found that the tensioner that had been supporting the unsupported weight was now loose and so begun to rectify the problem of the loose tensioner by retensioning it but the damage had already been done. A tensioner can only support so many hundreds of tons and with hundreds of tons of uncompressed concrete that had already weakened that tensioner then this disaster was inevitable. Just saying.
That was basically the point of AvE's 2nd video and i think in the end it will probably be a large part of the investigations focus and conclusions. Who decided to sign off on moving the falseworks away from the original load points and placing them mid span without the required spanner plates even between the hydraulic lifts? The rest was them just chasing their tail trying to fix a problem (loose tensioner) without realizing the real problem or cause was a previously over loaded and over stressed tensioner that would never come to spec without failing first. One of the big take aways is that bridges fail far more often in construction because the many fail safes and over engineering of a completed design are not in place to check one another, thus allowing for a much simpler chain of events to cause a failure. Sometimes its stupid simple, right in front of you, and everyone (with clout anyway) misses it because of intense focus on other concerns. No way traffic should of been going under it in hind sight, and its probably true that the FIU was pushing things and bulldozing concerns because it was their flagship demonstration for their faster building method and they probably focused on speed of the project more than they should have. Sometimes people get to close to their designs too and they try to blame issues on outside factors instead of admitting weakness. Wouldn't be the first time.
when i was looking at it being moved ( they have time lapse and reg ) it looked like the bottom piece is curved...like concave...smiley face smile, but slight...and when it was first put on the two side supports it looked like one end was higher than the other...it still looked like that to me after it was in place...is that what you are talking about...and i cant figure out why the bottom part looked like it was slightly curved, not like a v, but like a smiley face...and yet when it was put in place, one of the ends, on one side end, was up like a tupperware container ( top ) not closed right...or a piece of fabric stretched on part of one end so it wouldn't lay flat...did anyone else see that or was it supposed to look like that...can't do math at all so definitely not engineering material... just curious...all these comments are interesting
You have to wonder, did anyone measure the tensioning rods to see if they had stretched. That is one thing that a mechanic uses to get proper bolt tightening in some cases. Or were they just going on " well it is loose so we will retorque it to the proper torque"? And never consider the fact that the rod was stretched? A mechanic knows that if you don't get the right torque reading and the bolt/stud has reached the correct stretched length, that the bolt/stud has to be replaced. Because it has reached its design service life limit.
This is quite strange... why were they tensioning truss members that were in compression? I would have thought that the main post tensioning would have been in the bridge deck on the tensile side. Also once the bridge is hung from the tower support elements of this bridge would swap from being compressive to tensile. It is normal procedure to "half-span" a bridge during testing and completion and that could have been easily achieved with a trestle placed where the road has chevrons and at either end next to both piers to prevent rotation in the event of a failure.. A "belt and braces" approach to engineering is the preferred route especially where public safety is in question.
This story was posted late Saturday afternoon, www.nytimes.com/2018/03/17/us/florida-international-university-bridge.html It discussed FIU's connection to the ABC style of bridge construction. ABC is not new, rather something that has worked, and continues in refinement. The irony is the center of the world's braintrust on the ABC method is the engineering department at FIU. This bridge was to be a showpiece for the expertise and innovation of the ABC method of bridge construction. As somebody who had an engineering career, some of it in bridge work, their idea is a great one - build on-site, but not in place, then move to intended location. I've advocated for something similar for a long time. With the huge need of infrastructure improvements in the US, especially in bridges, we need to find a better way than what has been done for decades,... sorry, I digress. There is an inherent facade in this design. In the Warren design, the top strut is in compression, the bottom one in tension, and the diagonal struts in alternating compression and tension. In this case, the designers wanted the appearance of the struts to be the same, whether in compression or in tension. This idea is fine for steel design, where both compression and tension are possible. Steel does well with tension. Steel does well in compression, to a point, when buckling consideration becomes important. However, concrete, by its very nature, is very capable in compression, and not in tension. Therefore, in order to deal with the struts that are in tension (by the design of the Warren), the design included post-tensioning cables (could be rods, bars - does not matter, but will call them cables for the same of simplicity here). These cables are internal to the concrete strut, and then can be tensioned after the structure is in place. It is entirely possible, these same cables were tensioned before the move on Mar 10. But, now the need to refine the load on the cables is needed to bring to spec, and to adjust for the camber. The tension in the cables, not only carries the load of the bridge (through the Warren trust design), but has an overage of force, so that the concrete can be put into compression (remember, concrete does not hold tensile forces). The cables would be in a sheath, well lubed, so that their only load bearing capacity would be developed at the end - far end may be varied load, but the pulled end would be against an end plate. After final positioning, they may be grouted into position. Post-tensioned concrete bridge beams, albeit a different design, have been used for decades. They have also been used widely in building applications. To be sure, the deign is a bit unusual, but not impossible (IMO). Proper tensioning, with the proper sequence of events, can fulfill the intended purpose, that is, having a tension member be in compression at the end. I know some ask "Why was the road open?" This task could have been started last Saturday, immediately after the placement, started on Monday, started at the other end, and maybe even some work on the failed strut. My point is that the failure may have happened after much similar work had already been accomplished on this structure.
I'll bet by the time the investigation is concluded, a "Roger Boisjoly" will come out of the shadows. Who was Roger, he was one of two engineers protesting the launch of the Challenger. I'm far from being able to say I have an education related to the design of the bridge, but if you have the skill set to build a house or garage you have a good "feeling" how weight reacts. One look a this, no support in the center, a solid slab, no steel beams, who in the hell signed off on this? One thing I do know. The codes used by the railroads for a structure that crosses over their rails are pretty tight, and I'll stick my neck out and say there isn't a railroad in this country that would permit that bridge to cross over the rails. It's a real shame that just because you came to work you got killed or because you caught a red light you got killed.
From observing comments this is not a Juan VS. AvE issue. In fact they compliment each other. Just like some folks don't like Jalapenos some don't like AvE's channel because it's to spicy and that's alright. Just don't try to value signal by condemning AvE's content as well as his language.
I had heard that eye witnesses saw the hook on the crane that was used to maintain tension on the steel cables while they were being re-tensioned either straightened out or broke just prior to the bridge collapse. That should be easy enough to verify or disprove assuming that crane remained on site. blancolirio as I've grown to expect provides the best coverage if you want the facts as they are known with some intelligent speculation that is presented as just that. The link to the design plan was particularly welcome.
I would like to see an analysis using classic truss analysis. looking at the picture I have a suspicion as others have said that the bottom connection to the angled concrete beam that they were tightening the cables on failed. the lower beam especially at the ends is in tension and the connection from the angle compression memeber to the lower horizontal beam seems totally destroyed in the pictures. In any even good information and pictures. thanks for the explanation. you collected lots of good information.
I saw this on the wikipedia page last week. It was only there for a couple of hours. Looks like they don't want to criticize the design. 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.{{fact|date=March 2018}} Except for this one tragically.
The lack of redundancy unbelievable - with a threat to not only pedestrians on the bridge, but traffic below. Especially with such a "unique" design, the owner should have had independent peer review of the design and oversight of construction - even if they had their own "experts' in-house. .
The designers should have benefitted from the hindsight of studying past bridge failures. This design will go down in history and will be studied as precisely what not to do. The first mistake was designing a new type of modified I-beam truss bridge with a single row of vertical struts. It is a single point failure with ZERO redundancy. See Silver Bridge collapse about the need for redundancy and the dangers in a new design: "It is that its legacy should be to remind engineers to proceed always with the utmost caution, ever mindful of the possible existence of unknown unknowns and the potential consequences of even the smallest design decisions" The Silver bridge was criticized for low redundancy. In light of this, how was a bridge with no redundancy ever approved? I would like to know what the published safety factor for this bridge was. The initial proposal called it a cable stayed bridge. It evolved into a truss design that mimicked a cable stayed design. It probably would have worked if it was a true cable stayed design with the cables tied into and supporting the deck. When they decided to make the truss with post tensioned concrete they could not have the cables support the deck so they made them decorative. The second mistake was designing a post tensioned concrete truss. There are complex sheer and bending forces between the intersecting adjacent post tensioned bars within the concrete that the concrete can't handle. The truss should have been two or more rows of steel girders and connecting plates that can transfer the changing loads effectively. The designer should be prosecuted. The lack of robustness of the design is evident by the fact that a single worker was able to bring it down.
Call me an armchair engineer , but this truss design is upside down !!! The first truss member should go from top to bottom !! If you look at the rendering at 2:31 , from the main column you see the two truss members go from the bottom up, now imagine yourself holding two buckets of water in the air in that position....that would be a challenge to keep them up....same with this design.....
Juan thanks for your insight into this tragedy learned more from your video than all the news i have watched about it. Curious to see what they find in the investigation. I'M sure you will keep us to date. Take care have a great weekend and God Bless
Thanks for your illuminating information about the FIU bridge being a "fake" cable stayed suspension bridge at 1:30. I could not understand why they were stress testing a cable stayed bridge before the center post or the cables were in place. In a cable stayed suspension bridge, the strength of the bridge comes from the vertical posts and the suspension cables. I do not understand FIU going to all the expense to put up a fake center post and fake cables simply for aesthetics.......but then it is a college!! A steel bridge could have been built on site and swung into place, but it probably would have looked ugly to the college administrators.
Wow! When you consider how many people were involved in the design, approvals, legal contracts, construction, etc. . . . well, it makes you wonder who if anyone will be held accountable for this disaster. Throughout the video, I kept wondering, "WHAT were they thinking?"
The contractor was thinking " Hmm, I bet i can save money by offering the folks at Building and Safety to look the other way rather than calculate loads, second guess the engineering firm. We can pay them to approve the ABC method and that way it will their fault if it falls down". The folks at the Building and Safety Department were thinking about how to spend extra cash.
likely no one or company will be held responsible. Years of legal b.s, bribes to lawmakers, and.the victims families will be left in the dark. seen it before.
Given the nature of the grant program, 2 things are certain: A) Errors were made in WHO the contracts were assigned to (no problem with set-asides or "women in engineering" preferences, but they won't go with the DESERVING women or PoCs) and B) whoever made those costly decisions will NOT be held accountable. Oh, they'll find some taxpayer money to pay off the victims but the people responsible are too well-connected to have to pay. I make this prediction with as much confidence as saying a dropped rock will fall downward.
Engineers trying to be Architects=folly. This structure is almost a hybrid I beam since the chords(flanges) cantilever over the webs. Appears eccentrically unstable.
I've done a lot of post tension cabling during my years of concrete reinforcement..... Never never never once (and I can't stress this enough) have we ever started putting the reinforcement cables under stress without it being supported and or braced. Samples of the concrete used had to be sent to a lab independent from the concrete company to be pressure tested and the reinforcements in the concrete itself had to be inspected by a qualified inspector before you can even pour the concrete itself. I've had anchor points for our post tension cabling set in concrete that have been poured and let cure for 3 days still malfunction and blow out entire 20 x 20 foot corners of a slab on a high rise building. But the entire floor stayed in place because it was brace from underneath..... So I can't figure out why they were applying the the tension on those cables without there being support from underneath. If it is determined that the post tension cabling had a malfunction and this was the cause of the collapse there should be criminal charges pending on whoever decided that no support was needed during the process.
This is like the Hyatt Hotel sky walk collapse in the 80's. That was in the end put on the engineer that approved a change to the connecting rods who thought the company that made the beams understood the need for the extra sleeves if they went to dual rod system. They didn't do it and it was the largest loss of life due to collapse until 9-11. It was a very traumatic event for the Kansas City area for many years following. Kansas City was also home to another engineering failure, the Kemper roof failure which luckily came after a concert or it would have been another huge loss of life. It showed that ponding of water on the roof can quickly overcome the weight the roof was ever rated to hold.
Not an engineer here, but I believe that steel can flex more than concrete. I tend to agree that the design may likely be the primary culprit, also contributing to the deaths was no plan to close the road to traffic during testing. Initial reports said they were stress testing. Also Juan has an excellent point, that the single set of angled beams meant that a single failure guaranteed bridge collapse. I bet aesthetics won out for design choice (concrete instead of steel) but a steel bridge could have still been made to be fairly attractive, and with the tower and supporting cables. Very sad for those killed or injured by the collapse. RIP.
I find the argument that damage occurred to the joint where the two diagonals met the upper canopy, possibly when the tension rod in the outer member was supporting the overhanging end of the truss with the transporter lift points being too far from the outer end of the truss. Either the cable was too loose during transport, allowing tension forces to separate the joint area, which then gave way when put under compression when the span was placed on the end supports or the tension was adjusted too high in an effort to support the overhanging end during transport, causing failure of the tension rod and damage to the joint area under tension forces. Either way, that joint appears to have failed after the span was in position for several days. Trying to tension the damaged joint structure after the diagonal member itself was already in compression rather than tension could have been the straw that broke the camel's back.
Should a truss design (symmetry) be altered to accommodate an "ornamental" tower/cable support structure? Of course, as you mentioned, it should have been a dual truss design for redundancy.
I dont know all the facts. As a retired QC for the Corps of Engineers It appears that safety was overlooked in the testing process. Was there some sort of load testing before allowing vehicles to pass? Our job was to ensure that everything meets the specs, to code and our standards, and drawings, the job gets done on time, on budget and NOBODY gets hurt.
Hard to imagine a shallow solid concrete truss being capable of holding its own weight. For the members in tension, the entire bridge depends on on one single threaded rod?
Vaughan, a well-presented objective presentational view specific to the collapse. A point to consider is that the cabling itself in its being incorporated in the design being the 'necessary adjustment component 'may have been the critical error in the design of such a huge and heavy bridge. (My overview of the above video and your appraisal has facilitated my observation and resultant opinion.) I am still okay if my opinion is proven wrong.
The newscasts I watched stated that a stress test had just been completed, and that the cables were being re-tensioned,.indicating to me that the tensioning had been relaxed for the test. I really don't know how much of a factor that could have been, as my only exposure to that technology are the post-tension slabs used as foundations for homes in north central Texas. In that application, the cables are used to stiffen the slab, so that it floats as a single unit on top of a layer of sand. The results of the NTSB investigation will be interesting, as they will look at everything from the design itself, to the grade of steel used in the cables. Update: Photographic evidence has now surfaced, that a tension rod failed, resulting in the failure of the truss, and the collapse of the bridge. (The tension rod actually shot out several feet.) There's also evidence that the span was mishandled when it was placed on the piers. The lifts on the end that failed were out of position. One was supposed to be right under the end of the span, where the deck met the truss. There were also supposed to be spreader bars between the bridge deck and the lifts, but photos show they were not used. The engineers on reddit believe that the tension rod was damaged/weakened when the span was moved, and that tensioning that rod AFTER placement led to it's complete failure.
this reminds me of the Kansas City Hyatt Regency walkway collapse. Only that the Hyatt Regency in Kansas City had the walkway inside. The reason that the Kansas City structure collapsed was because of a design error as well. However, the original design of the walkways were sound. What happened was that the design was changed during construction: modified 'as builts' were the culprit. The changes to the structure were approved by phone, if you can believe it, and they altered the way that the walkways were supported. A specific design for box girders was altered and left out a crucial 'collar' that would go inside the girder to support the weight of the walkways suspended from the connections. The reason I know all of this so well is because, as a civil engineering student, we were required to study that disaster as a way to know 'how not to let the construction of your structure, that you seal, get out of your control at any time during the construction of the project.' This may be something similar where adequate precautions were not taken. Kansas City had horrible injuries and close to 120 people died. What will be interesting, is to see if they conduct a full scale forensic investigation into the exact reason for the collapse. Engineering licenses will be lost and hefty lawsuits filed, that can be sure. What will be interesting is to see the level of scrutiny this collapse gets versus the very hasty investigation and clean up of ground zero in NYC after 9/11. Those collapses, supposedly due to fire weakening of the steel, received a comparatively cursory investigation compared to Kansas City and the commission was delay for over a year. One of the buildings, which, for eight seconds, fell at free fall speed during the day of 9/11 (WTC7) was hardly mentioned in the final commission report. Let's see the attention the local government officials give to this disaster that was not deemed a "war zone" and thus under military control. Let's see how much care they put into the investigation when there is no bearded man in a cave half way around the world, next to his dialysis machine, with his satellite phone and laptop, who was supposedly able to defeat the most powerful military defense system in the world with 19 fellow Muslims armed with plastic box cutters.
Do we know the depth of the rebar in the walkway and roof? The Pictures of the bridge looked like the structure folded. Like the rebar in the walkway was to shallow.
Is the design comes from the university? Do the people know that "safety first" is the number priority in all construction sites? Launching this across the road with traffic moving under is definitely a breach of engineering practice. The design is obviously wrong. How is it possible to post tension such a thin concrete section without causing it to warp and hence internal cracks. The triangular concrete trusses above are overloading the bottom. Post tensioning any one of the truss member produces a force in the direction along the adjacent member ( bending moment) to the bottom tending to overstress the point and breaking the bottom section at that point. This is my view. Please correct me if I am wrong.
I'm not an engineer but just looking at the bridge I notice no center piece for support too and given that the other parts are simply for looks why didn't they use something similar to the Golden Gate and the many pedesrian bridges that are similar in design. Lastly, why use concrete and have traffic underneath while testing ?
Last collapse in fiu & Miami Dade county booth had fatalites within the last few years soon after construction. my dad works for the architect company for both garages ( same company) after further review it was found the prefab concrete work was very poor and was found to be the reason : perhaps its the Reason for this bridge the Miami /Hialeah company making the prefab is still making crappy work
Clicked on this without even noticing it was Juan until the video started. Happy to see other engineering journalism by you, Juan. Your reporting is top notch.
The thing I find striking about the image of the collapsed bridge is that the concrete trusses on the one side look like they're absolutely pulverized.
I'd like to see the source of the claim that the cables were ornamental. We know the budget was a big deal with this project (as it usually is); does it make any sense that the client would pay big money for a large complicated ornamental feature?
I agree that the design of the bridge should be closely examined. The reliance on too much perfection ... And the lack of failure amelioration as would be present in plastic hinges on steel bridges is very worrying. Things always go wrong during construction. But we have few fatal disasters because of "graceful" failure modes.
Is it really true that it’s made to look like a cable stayed bridge rather than actually being one? Seems crazy. Concrete only works in compression, the design is bizarre.
Not all trusses are under tension. Trusses are either under tension or compression. The one at the end which you claim was being adjusted for tension is a truss that's under compression. The best way to know if it's under compression or tension is to pretend that the truss doesn't exist. Will the nodes move toward or away from each other? If they would've moved away, then it was under tension. If the nodes would've gone toward each other, then the truss was under compression. And BTW, trusses under compression can't be simple cables.
I'm no civil engineer (studying mechanical), but anyone and their brother can tell that truss design is trash. Stuff like this happens with you have too many architects and not enough engineers.
Great. South Florida cannot depend on their sheriff department, or local FBI and now south Florida cannot depend on construction on anything. Florida. The new California.
Thanks for trying to explain but I am just confused as ever. Why would they let traffic go under during a stress test? Makes no sense. I pray for the loved ones who have to deal with the aftermath. So sad.
Looking at the image at 9:59, it sure looks like it bowed enough for the bottom to slide off of the support column. The "truss" configuration only works if the triangle points remain attached. In this image, it sure looks like the vertical and horizontal points of the end triangle separated.
Juan, you may of have missed today's news about a report of cracks appearing two days or so ago by inspectors who rightly did not sign off on the bridge and raised red flags. I wonder about vibrations caused by the traffic, heat from the sun and the weight of the concrete in this design. Here's a link to the news on the cracks www.nbcnews.com/news/us-news/engineers-saw-cracks-miami-bridge-days-collapse-n857481
"From a safety perspective we don't see that there's any issue there, so we're not concerned about it from that perspective," the engineer said according to the transcript, "although obviously the cracking is not good and something's going to have to be, ya know, done to repair that." Cracks in concrete is not unusual and not necessarily a sign of a structural issue.
There was an engineer who claimed that because cracks were found in the MetroRail structure spans, they would collapse. Well guess what we are still waiting for that to happen. Cracking of concrete is just something that is common. No matter what you build with it. The cracks may not be big, but I have never seen a single concrete item that did not crack somewhere. But that is what the cables, and steel in the structure are supposed to make up for. Concrete is good in compression, but poor in tension and a failure of any of the cables, rods, rebar, should have been figured into the design. But it appears that it was not for this part of the construction process.
Thanks for your customary clarity and insight. For further info about shortcuts and screwups, you might want to go back a few decades and check out the near-collapse of the Zilwaukee Bridge in Michigan. For us non-experts, an excellent read is "WHY BUILDINGS COLLAPSE" by Matthys Levy and Mario Salvadori.
It broke because the freaking main support post and leads were not installed. Why not have the center column built to grade ready for bridge to sit on?
Thanks for another great video, Juan. I'm no engineer, but common sense tells me that making a bridge like this from concrete, then adding the steel reinforcements is just plain dumb. There must be other safer designs to satisfy this pedestrian bridge's purpose.
Juan, Yes - I have a much better understanding of the bridge fail THANKS to your straightforward, clear explanation. Now, John Roebling, builder of the Brooklyn Bridge (late 1800s), would be horrified by this design and/or construction fail. The Brooklyn Bridge to this day requires less maintenance than others built afterwards in NYC. Love your snowy yard! Greetings from the Catskill Mountains, NY State.
Thank you... So this was a Mock Suspension Bridge with top part of no value. To the people who use and died under this thing.... Why? It shocking! Maybe all of people... most people are good people and try to do the right thing... may have got mix up.. maybe with the Plans... printed out wrong? One for Suspension Bridge.. one with out! And why have a 200 feet span bridge with a 100 feet roadway? And 950ton is the weight of a Battleship! I just hope that any question that were ask by anyone down the line.. from start to... were listen to. I am very very.. afraid there were Alarm Bells. Will we listen to dead people now?
Watching one of the videos from just after the bridge was placed, a superintendent or engineer said that now that the bridge was in place some tension would be released. It will be interesting to learn what, if anything, that had to do with the collapse.
I can’t for the life of me grasp the lack of falsework to keep such as massive span of concrete in place, at least until the entire span is complete. It’s almost arrogant.
Mark Phillips but FIU was trying to prove the feasibility of the Accelerated Bridge Construction techniques. Too bad they didn't stick to the design for placement of the hydraulic movers.
damn...I'm an uneducated person...and I see the flaws...well, at least since you pointed out the materials used.......it appears to me, they were far more worried about aesthetics and "time spent".............How n the hell did they expect THAT much concrete to stay up without something n the center of the length.........blows my mind!!!!
Design & Construction executions that was not positively consider to prevention from incident (I mean the Site Geological Condition and Soil Investigation results, Soil & Rock Bedding formation and Strata, Construction materials, Load Bearing Capacity for the High Way Roads environment, Strengthening of Structure) after the disaster if you see in the Pictures showing that concrete and Steel combination not OK both look like separate scenario that why it must be consult with Geological and Civil Structural expert’s opinions before implementation, to avoiding such kind of happened will not be come out in the future, I think hope So ???
![OsamaSon - ik what you did last summer [Official Music Video]](http://i.ytimg.com/vi/4DIQDnu3mr4/mqdefault.jpg)
The original design plan from FIU LINK-facilities.fiu.edu/projects/BT_904/MCM_FIGG_Proposal_for_FIU_Pedestrian_Bridge_9-30-2015.pdf
After reading the proposal it states that the cable stays will provide added stiffness and pedestrian load... so they were not only an aesthetic feature.. the cable stays were actually intended to provide some support. After watching the video and looking at pictures what I see is the lower deck became disconnected from the last column / diagonal support.. when that happened the lower deck fell causing the total collapse. The lower deck likely had ether pre or post tensioned cables. If they are post tensioned there are wedge sockets that secure the cables and it's possible that the wedges failed or the strength of the connection at that point was inadequately designed / engineered. If that's the case review of the design / calculations should have caught it, but maybe not... I've suggested this book before... not sure if you or any of your followers have read it but it's a really good read for folks who are interested in this sort of thing. www.goodreads.com/book/show/271495.To_Engineer_Is_Human
Thank you for this website. Obviously the cable column towers and cables were not 'ornamental'
Could be a failure in the design of the testing plan rather than the design of the structure.
they are...stby for an update...
Interesting that the drawing of the deck shows that member 11 (the end diagonal) did not have post-tensioning bars. Maybe these were added to accommodate the temporary support position which was in from the span end during the installation?
Damn, in 10 min you gave a more insightful presentation than all the cable channels combined. No interviews of people about what they thought, how sorry they were. I'm sure a lot what you presented is in the hours of blather, you distilled it down perfectly. As Joe Friday would have said "Just the facts Ma'am"
Tensioning that bridge while allowing traffic underneath was incompetent and criminal. The people responsible should never work in the field again.
Jayyy Zeee Dont you mean THE design team should never work again. The Erectors were construction guys, they didn't design it.
Jayyy Zeee I was thinking the same.
Samual Whittemore, while the designers could be found to be at fault also, someone in charge ordered those people to adjust the tensioning without closing traffic. I don't fault the construction guys who were following orders. I blame the people responsible as I said.
So the FIU bridge was a truss design made to look like a cable-stayed bridge - resulting in one of the most moronic truss layouts I've ever seen. Juan describes it as a Warren truss but it actually morphs from half-ass Warren on the north failure end to half-ass Howe on the south end, with absolutely ZERO redundancy! Were this span designed in steel it could have been done at one-third the weight, half the cost, a redundancy factor of at least three, and WITH NO LOSS OF LIFE!!! Did FIU engineering dept go through any what-if worst case analysis? If not it should be shut down permanently.
I'm guessing that FIU has an "engineering" department which provided the original concept as a class project. I"ve seen it before in other colleges. Modifying the truss design to appear to be part of a suspension system was the first serious mistake. Using friable concrete throughout was the second big mistake. Erecting an untensioned truss was the third mistake. All in the name of "Accelerated Bridge Construction" so they could brag about closing the street for only one weekend. Heads need to roll.
eccentric moments induced by cantilevered top chords,
Inspector Jeff
if an engineering company can't build a walkway then no sidewalk is safe from those guys...the students have little to fear until the next project is started
This was an "all-female no men allowed feel-good safe-space" project. She said "it just felt right" the design just felt right. That is proper engineering, just feelings....
The question of why traffic was allowed while they were allegedly tightening cables was one of my first questions.
Thanks for the report Juan. Look forward to next report...if there will be one. 😎
Waiting to see if you can match AvE's analysis, Edit: ruclips.net/video/KtiTm2dKLgU/видео.html
who's that?
Juan, I understand that you are being cautious and reporting only the facts, but others have made a much more in depth analysis, and come to preliminary (but unproven) conclusions that mainstream media haven't touched, and the NTSB will take months to release.
FIU 3D bridge visualisation video: ruclips.net/video/5Y_71L35CvM/видео.html
Slow-motion zoomed-in dash-cam video, showing exact point and sequence of collapse: ruclips.net/video/Ucflj-MsJBI/видео.html
Excellent analysis as always! Minor correction: in your credits at the end, you state that it happened in March 2017. It’s 2018. I am not an engineer, but the whole design concept and the way it was executed seems like a disaster waiting to happen.
I appreciate you making complex technical situations more understandable.
I discovered your RUclips channel a couple few days after the spillway failure at the Oroville Dam and have been watching your excellent videos since them. Your new videos are one of the small handful that I genuinely anticipate. Thank you for the informative service that you are providing the public. The mainstream media is a complete failure when it comes to most MAST related subjects.
You are becoming the “goto guy” that the public turns to for better information on Civil Engineering disasters - you are becoming the Neil deGrasse Tyson of Civil Engineering. As proof of what I observe, you are now attracting professional engineers such as Barry Gerbracht, Bob Crosby and bcbloc02. (Ok, Brian - bcbloc02 - is not a Civil Engineer, he’s a MSME. But unfortunately, he can tell you all about catastrophic structural failure.)
The reason that I mention this, is that whether or not you chose this ‘profession spokesman role’ or it just fell into your lap (which is what I suspect happened), you now occupy this spot by simple RUclips viewership. If you want to further explore this path (which I sincerely hope you do), then someone should probably point out who some of your viewers are.
Again thanks for all of the exceptional videos, and I eagerly look forward to seeing many more.
Great analysis, and yes pre and post stress was a significant factor. Cribbing and traffic control could have saved lives!!!
All the holes in the cheese lined up that day. Several key decisions led to this chain of events, any one of which could've been changed.
Decision to transport and support bridge in a different position than engineered (mid span between truss hard points).
Decision to not install or leave falsework/cribbing in place after initial bridge placement during critical post tensioning/ final inspection works.
Decision to rush the initial process of bridge installation, so as to minimise traffic disturbance.
Decision to ignore cracks in the newly installed bridge.
Decision to carry out post tensioning/ fault finding and rectifiication with public exposed to risk.
I personally believe that concrete has no place being used in a structural truss- it's strength is in compression.Trusses are all about tension. Using boxed steel for the truss web would not have changed the appearance of the bridge and would've had many times the failure resistance and safety factor of what was there. Likewise, a couple of simple steel I beams in the lower span would've provided a huge margin of redundancy for the structure.
This is an excellent analysis and suggested redundancy features. I noticed that the post tensioning on the truss member that failed was *internal* to the member... not external to the member. So that only the center section of the truss was under tension, leaving each end, one in the blister on top and one in the pier area under *tension, the concrete in both of these areas is seen to be exploded or shattered after the failure... concrete was under tension in those two critical areas. Just one of the major engineering and management errors... ignoring those massive cracks in the failed area and not stopping the project on that basis alone was inexcusable imo, likewise cutting into the blister on top of the canopy with cement saws and jack hammers was insane on the face of it, even if there was no traffic under the bridge..with traffic one has to wonder what they were smoking.
Hi Juan -- listening to your description and seeing the picture the end of the beam, it looks like it blew out during tensioning operations, this is a not uncommon occurrence -- but typically you still have the scaffold in place and it costs a little money and time but is not usually a tragedy. This is caused by 1) poor design and /or poor execution, ( the concrete does not consolidate adequately around the " Bugle head" a thick plate structure that applies the tension from the rods / or cables depending on which system you use and or it does not reach adequate strength due to design, batching, or placement issues.
But the biggest issue is it was designed without redundancy by someone who thinks looking good and attaining some architects vision is more important than safety and durability.
Patrick Curtis best description of the Design Failures. that ABC isn't looking so pretty now.
Tension adjustment failures happen, I have witnessed three in my 30 years of engineering. An anchor failure, cable failure, and concrete failure. It happens, so to think you can pull off a tension adjustment with zero probability of failure violates Murphy's Law.
AVE did a good job explaining the Rod failure.
Dude. The cables are for compressing the concrete so that elements can perform in tension. They aren't for adjusting the camber because they can't significantly affect the length of the concrete elements. The 'canopy' is the compression element of the beam, the deck is the tension element, but hugely preloaded with the tendons run through the deck.
Nice review Juan. You have a way of making information like this understandable, without injecting a lot of fear and hysteria into it. As you point out, without having two sets of truss web members, there is no load path redundancy in the bridge. The earlier reports of cracking may or may not have anything to do with the failure. I'm thinking it is probable that the crew adjusting the post-tensioning stressing on the dywidag bar in the web had a significant role in the failure. The NTSB final report will be very comprehensive, with everything related to that structure undergoing scrutiny. As with many structure failures, it probably wasn't just one thing contributing to it, but a cascade of events leading to the failure.
Thank you for the clearest, best-presented explanation i've seen!
The movement of the structure via transporter will be of interest to investigators since the support for the bridge section during transport may have caused some flutter of the north section. The engineers noticed cracks, and that rod was being tensioned so there was a stress concentration near where it hinged and pulled the lower slab down from the support. From another angle you can see the north end of the rod waving free where the joint failed at the base.. Your point about the value of a temporary support and blocking traffic during such activity is solid. Temporary supports would have been expensive, but hubris more so. Appreciate your comments on structural redundancy as an important safety factor in civil construction.
bruce bagnoli I
That is what I was thinking. The design was good. Some unforeseen stress was placed upon the structure during the move. The ABC technique has been used successfully before - but usually a 'simple' parallel shift. The rotation was novel.
Once again you come through with a clear description of the event...thanks.
Great update !
..had no idea , should have put money from the fake tower & span wires, into the actual bridge. Imo
1BigBen I'm glad someone knows the true function of the tower and suspension wires.
So sorry for the people lost and relatives of them !
Yet another excellent video and a fascinating subject Juan THANKYOU
The concrete was pulled in tension. If you are pulling on something, that is tension. If you are pushing on something, that is compression. Ignore for a moment that concrete was used and just look at the system as someone was pulling tension on a truss rod. This situation is so sad. Usually multiple design engineers are involved on a project like this.
Now steel has high elastic properties (like a rubber band)...not quite that elastic...but steel can take a beating in tension. I bet if those truss webs had been made of steel, the bridge may not have collapsed. I have one simple question for the Engineer...Why are you excessively pulling concrete under massive tension?
Have you ever seen how a pre-stressed bridge beam is constructed?
No I haven't.
Great. Best info I’ve seen. Yes I want more on this subject
"Let's build a suspension look-alike bridge" smh
Best comment. Hits the nail.
Who can EVER come up with the idea of a truss bridge (in COCRETE!), decorated by a Pylon and cables?
Who is responsible for this gross professional incompetence?
You Sir are amazing. Only three days after this horrific accident you have nailed it. Your "No Drama" analysis based on only the facts and your amazing technical vision is truly inspiring. You exhibited this through the entire evolution of the Orrville spillway near disaster. You clearly can apply that same clear vision to other disasters. My hat is off to you. It will be months or years before your insights are proven to be spot on. But your clear vision will be proven to be absolutely spot on. Congratulations to you.
THANKS JUAN FOR MAKING IT MORE CLEAR.... THUMBS UP.....
Love the way you go after the 'facts' and inform us all :)
I think the biggest failure, regardless of design or construction, inspections or any procedural move pertaining to post tension cables is the fact that there was no sub structure to support bridge or just the fact that they were allowing traffic under bridge at all while they were doing any tweaking via post tension cables or anything else.
*When do engineers ever use a just single truss? trusses are usually employed in pairs or in parallel sets... as I recall a major disadvantage in truss design is they are prone to twist or deflection to the sides.*
Precisely, although the super wide lower deck would help mitigate that.
+Sideslip *It still does not give you any redundancy protection if one of the struts fails... which appears to be exactly what happened in this accident. Especially considering this bridge collapsed with pedestrian no load either... its takes several "weak links in the chain" to result in a total failure of this type, I will bet that although the design was not the primary cause of the failure, it was at least a contributing failure.*
I like you said spring time and with snow in the background, not so much spring. Thank you for sharing your amazing video. God bless you and your family
Through my life, I was a nurse and a horse person, I have had NO engineering training, just day to day observations of people building things. And, because I do have a love for science and how things are put together, I may have paid more attention than some people. After the collapse, when I saw the design of the bridge, my FIRST thought was why do they only have one line of trusses!? Then when I learned that EVERYTHING was concrete, I wondered why they wouldn't use some lighter materials where possible... at least for the trusses. Who cares what it looks like!!! Its main purpose was to be a bridge not a work of art. Either they should have either made the suspension part of the engineering, or left the tower and cables off and put more money into design and stronger more sensible materials for it. There is a pedestrian bridge over a freeway here that is not fancy, but functional. And knowing the folks here they probably closed the freeway, in sections, until it was completed AND tested. It was built before I got here in 1976... Still working well!
The tension rods are NOT to adjust the camber of the bridge. They are meant to keep the concrete in compression.
They can do both if designed properly.
Nice report. Here in Utah they have been using the ABC for quite some time and as I understand it many of our bridges were built that way. Your report set my mind at ease as it does seem the design is the problem. None of our bridges are designed or look like that. A lot of ours are overpasses that see heavy traffic.
The suspension mast and cables were ornamental? I hadn't heard that before in other reports...
I find that to be a way to shift any stupidity for not having something under JIC.
Jeff Bangle I thought that part of the structure was more for added strength during high forced winds and hurricanes. but it was also for aesthetics.
added redundancy, I suspect, not strength. this concrete wannabe I-beam is such an unsafe design. and having to use supports in the wrong locations for the installation of the section. wow.
They're not suspension cables in any case. That's a cable-stayed design not a suspension design. So if they are aesthetic it's an aesthetic cabled-stayed bridge, not an aesthetic suspension bridge.
David Newton I read somewhere that they weren't even supposed to be cables, but just hollow steel tubes. If so, then it wasn't even partially cable-stayed. In an NTSB briefing, one of the investigators stated that it was his understanding that the part above was purely cosmetic.
So many mistakes made from the design table to the disaster that lead to this, i can't wrap my head around that this is possible in our western world 2018. Very nice analysis Juan
Well not completely cosmetic as they were needed to support the pedestrian loads from what I read here. facilities.fiu.edu/projects/BT_904/MCM_FIGG_Proposal_for_FIU_Pedestrian_Bridge_9-30-2015.pdf Also they would have offered some level of redundancy to the system. I thought the failure of the Silver Bridge at Point Pleasant had taught engineers abut the necessity of redundancy in bridge design but obviously that was not the case if the failure of one tensioning member can collapse the entire structure in a catastrophic manner. The factor of safety of this design in its as installed condition had to have been less than 2 , and that is poor practice. It also seems we are doomed to repeat the mistakes of using high strength materials to save costs and reduce material use. That too has proven problematic in the past as imperfections in the materials result in a flawed and unsafe structure. Low stress = long life. Still hard to get engineers to accept that.
bcbloc02 As an engineering student going through uni, it’s only incidents like this that serve to remind us of the importance of getting it right. It’s important to realise that with so many successful bridges and engineering projects, complacency creeps in, redundancy and fail mechanisms don’t seem relevant because, well, the bridge isn’t going to fail! That being said, to design a bridge unsafely on the whim that it won’t fail is utterly reckless and I’m sure this collapse will be used as an example in many lecture halls globally about why we have redundancy in designs.
bcbloc02 yes that's also what I heard on a news report. That the majority of the support comes from within the main truss system. But the cable tower was designed to provide support especially while the bridge is in use by absorbing vibration.
The “cable” stay component is definitely mostly aesthetic, they weren’t even high strength cables but tubular pipes. The details provided in the drawing show a relatively light duty anchor bolt ties which would only provide some restraint.
A 16" diameter steel pipe even with only 1/8" wall thickness still adds 225,000lbs of tension loading to help support the structure. With 4 per span that is almost 1,000,000 pounds of force! It wouldn't support the whole bridges weight but it would take about 1/3 of it and that is a significant reduction in the forces on the bridge itself. Of course without the other side of the bridge installed to counter the stay forces it would have likely failed the tower and brought it down too. If it was quarter wall pipe instead it could have reduced the loading on the bridge by in half. The design details of the construction are unknown though so it is impossible to calculate the actual values. The bridge builders did call it a cable stayed bridge in their project description so they must have thought they were doing some supporting work. ruclips.net/video/5Y_71L35CvM/видео.html They don't call it an innovative truss bridge with a towering pylon decoration.
"Low stress = long life. Still hard to get engineers to accept that."...Not competent engineers. I would never have sealed a bridge design without a significant safety factor AND redundancy built in - Bill Gillette PE
Anyone here remember the I-5 Skagit River bridge collapse May 23 2013? The bridge was a subdivided warren truss which was struck by an oversized load causing a single-point failure and total collapse of a span. Security video of the Skagit collapse is disturbingly similar to FIU. Non-redundant truss technology was already considered obsolete in 2013 - why FIU adopted an obsolete bridge design raises serious doubts as to the competence of their engineering department.
From what is obvious to me is that the tensioner supporting the end of the bridge that wasn't supported during application of the bridge was weakened by the hundreds of tons of NON compressed concrete overhang, therefor stretching the tensioner supporting that particular end. It's obvious to me that once that end of the bridge is placed on it;s correct supporting pillar at that end, they "the engineers" would have found that the tensioner that had been supporting the unsupported weight was now loose and so begun to rectify the problem of the loose tensioner by retensioning it but the damage had already been done. A tensioner can only support so many hundreds of tons and with hundreds of tons of uncompressed concrete that had already weakened that tensioner then this disaster was inevitable. Just saying.
great point!
That was basically the point of AvE's 2nd video and i think in the end it will probably be a large part of the investigations focus and conclusions. Who decided to sign off on moving the falseworks away from the original load points and placing them mid span without the required spanner plates even between the hydraulic lifts? The rest was them just chasing their tail trying to fix a problem (loose tensioner) without realizing the real problem or cause was a previously over loaded and over stressed tensioner that would never come to spec without failing first. One of the big take aways is that bridges fail far more often in construction because the many fail safes and over engineering of a completed design are not in place to check one another, thus allowing for a much simpler chain of events to cause a failure. Sometimes its stupid simple, right in front of you, and everyone (with clout anyway) misses it because of intense focus on other concerns. No way traffic should of been going under it in hind sight, and its probably true that the FIU was pushing things and bulldozing concerns because it was their flagship demonstration for their faster building method and they probably focused on speed of the project more than they should have. Sometimes people get to close to their designs too and they try to blame issues on outside factors instead of admitting weakness. Wouldn't be the first time.
when i was looking at it being moved ( they have time lapse and reg ) it looked like the bottom piece is curved...like concave...smiley face smile, but slight...and when it was first put on the two side supports it looked like one end was higher than the other...it still looked like that to me after it was in place...is that what you are talking about...and i cant figure out why the bottom part looked like it was slightly curved, not like a v, but like a smiley face...and yet when it was put in place, one of the ends, on one side end, was up like a tupperware container ( top ) not closed right...or a piece of fabric stretched on part of one end so it wouldn't lay flat...did anyone else see that or was it supposed to look like that...can't do math at all so definitely not engineering material... just curious...all these comments are interesting
You have to wonder, did anyone measure the tensioning rods to see if they had stretched. That is one thing that a mechanic uses to get proper bolt tightening in some cases. Or were they just going on " well it is loose so we will retorque it to the proper torque"? And never consider the fact that the rod was stretched? A mechanic knows that if you don't get the right torque reading and the bolt/stud has reached the correct stretched length, that the bolt/stud has to be replaced. Because it has reached its design service life limit.
This is quite strange... why were they tensioning truss members that were in compression? I would have thought that the main post tensioning would have been in the bridge deck on the tensile side. Also once the bridge is hung from the tower support elements of this bridge would swap from being compressive to tensile.
It is normal procedure to "half-span" a bridge during testing and completion and that could have been easily achieved with a trestle placed where the road has chevrons and at either end next to both piers to prevent rotation in the event of a failure..
A "belt and braces" approach to engineering is the preferred route especially where public safety is in question.
This story was posted late Saturday afternoon, www.nytimes.com/2018/03/17/us/florida-international-university-bridge.html It discussed FIU's connection to the ABC style of bridge construction. ABC is not new, rather something that has worked, and continues in refinement. The irony is the center of the world's braintrust on the ABC method is the engineering department at FIU. This bridge was to be a showpiece for the expertise and innovation of the ABC method of bridge construction. As somebody who had an engineering career, some of it in bridge work, their idea is a great one - build on-site, but not in place, then move to intended location. I've advocated for something similar for a long time. With the huge need of infrastructure improvements in the US, especially in bridges, we need to find a better way than what has been done for decades,... sorry, I digress.
There is an inherent facade in this design. In the Warren design, the top strut is in compression, the bottom one in tension, and the diagonal struts in alternating compression and tension. In this case, the designers wanted the appearance of the struts to be the same, whether in compression or in tension. This idea is fine for steel design, where both compression and tension are possible. Steel does well with tension. Steel does well in compression, to a point, when buckling consideration becomes important. However, concrete, by its very nature, is very capable in compression, and not in tension. Therefore, in order to deal with the struts that are in tension (by the design of the Warren), the design included post-tensioning cables (could be rods, bars - does not matter, but will call them cables for the same of simplicity here). These cables are internal to the concrete strut, and then can be tensioned after the structure is in place. It is entirely possible, these same cables were tensioned before the move on Mar 10. But, now the need to refine the load on the cables is needed to bring to spec, and to adjust for the camber. The tension in the cables, not only carries the load of the bridge (through the Warren trust design), but has an overage of force, so that the concrete can be put into compression (remember, concrete does not hold tensile forces). The cables would be in a sheath, well lubed, so that their only load bearing capacity would be developed at the end - far end may be varied load, but the pulled end would be against an end plate. After final positioning, they may be grouted into position. Post-tensioned concrete bridge beams, albeit a different design, have been used for decades. They have also been used widely in building applications.
To be sure, the deign is a bit unusual, but not impossible (IMO). Proper tensioning, with the proper sequence of events, can fulfill the intended purpose, that is, having a tension member be in compression at the end. I know some ask "Why was the road open?" This task could have been started last Saturday, immediately after the placement, started on Monday, started at the other end, and maybe even some work on the failed strut. My point is that the failure may have happened after much similar work had already been accomplished on this structure.
I'll bet by the time the investigation is concluded, a "Roger Boisjoly" will come out of the shadows. Who was Roger, he was one of two engineers protesting the launch of the Challenger. I'm far from being able to say I have an education related to the design of the bridge, but if you have the skill set to build a house or garage you have a good "feeling" how weight reacts. One look a this, no support in the center, a solid slab, no steel beams, who in the hell signed off on this?
One thing I do know. The codes used by the railroads for a structure that crosses over their rails are pretty tight, and I'll stick my neck out and say there isn't a railroad in this country that would permit that bridge to cross over the rails. It's a real shame that just because you came to work you got killed or because you caught a red light you got killed.
From observing comments this is not a Juan VS. AvE issue. In fact they compliment each other. Just like some folks don't like Jalapenos some don't like AvE's channel because it's to spicy and that's alright. Just don't try to value signal by condemning AvE's content as well as his language.
Liked video before watching...I can't help it, It's Blancolirio.
I don't think that bragging about coming to a conclusion before you have seen any evidence is in the spirit of this channel.
I hope after its all cleaned up they just put up an old railroad type of box beam bridge.
Why not a tunnel?
I had heard that eye witnesses saw the hook on the crane that was used to maintain tension on the steel cables while they were being re-tensioned either straightened out or broke just prior to the bridge collapse. That should be easy enough to verify or disprove assuming that crane remained on site.
blancolirio as I've grown to expect provides the best coverage if you want the facts as they are known with some intelligent speculation that is presented as just that. The link to the design plan was particularly welcome.
Appreciate your perspective on this particular engineering failure.
I would like to see an analysis using classic truss analysis. looking at the picture I have a suspicion as others have said that the bottom connection to the angled concrete beam that they were tightening the cables on failed. the lower beam especially at the ends is in tension and the connection from the angle compression memeber to the lower horizontal beam seems totally destroyed in the pictures. In any even good information and pictures. thanks for the explanation. you collected lots of good information.
I saw this on the wikipedia page last week. It was only there for a couple of hours. Looks like they don't want to criticize the design.
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.{{fact|date=March 2018}}
Except for this one tragically.
The lack of redundancy unbelievable - with a threat to not only pedestrians on the bridge, but traffic below. Especially with such a "unique" design, the owner should have had independent peer review of the design and oversight of construction - even if they had their own "experts' in-house. .
The designers should have benefitted from the hindsight of studying past bridge failures.
This design will go down in history and will be studied as precisely what not to do.
The first mistake was designing a new type of modified I-beam truss bridge with a single row of vertical struts. It is a single point failure with ZERO redundancy. See Silver Bridge collapse about the need for redundancy and the dangers in a new design: "It is that its legacy should be to remind engineers to proceed always with the utmost caution, ever mindful of the possible existence of unknown unknowns and the potential consequences of even the smallest design decisions" The Silver bridge was criticized for low redundancy. In light of this, how was a bridge with no redundancy ever approved? I would like to know what the published safety factor for this bridge was.
The initial proposal called it a cable stayed bridge. It evolved into a truss design that mimicked a cable stayed design. It probably would have worked if it was a true cable stayed design with the cables tied into and supporting the deck. When they decided to make the truss with post tensioned concrete they could not have the cables support the deck so they made them decorative.
The second mistake was designing a post tensioned concrete truss. There are complex sheer and bending forces between the intersecting adjacent post tensioned bars within the concrete that the concrete can't handle. The truss should have been two or more rows of steel girders and connecting plates that can transfer the changing loads effectively. The designer should be prosecuted.
The lack of robustness of the design is evident by the fact that a single worker was able to bring it down.
Thanks!
that's exacty my thougths
but is very difficult for me to translate these thought in english while use the propper technical terminology
Call me an armchair engineer , but this truss design is upside down !!! The first truss member should go from top to bottom !!
If you look at the rendering at 2:31 , from the main column you see the two truss members go from the bottom up, now imagine yourself holding two buckets of water in the air in that position....that would be a challenge to keep them up....same with this design.....
Juan thanks for your insight into this tragedy learned more from your video than all the news i have watched about it. Curious to see what they find in the investigation. I'M sure you will keep us to date. Take care have a great weekend and God Bless
Thanks Juan. there's a reason why engineers in Ontario Canada wear iron rings. More important to me than my wedding ring.
Well, if you watch the Ave equivalent you'll learn a lot more that's actually right. Some of this is between simply wrong and flat out foolish.
Thanks for your illuminating information about the FIU bridge being a "fake" cable stayed suspension bridge at 1:30. I could not understand why they were stress testing a cable stayed bridge before the center post or the cables were in place. In a cable stayed suspension bridge, the strength of the bridge comes from the vertical posts and the suspension cables.
I do not understand FIU going to all the expense to put up a fake center post and fake cables simply for aesthetics.......but then it is a college!!
A steel bridge could have been built on site and swung into place, but it probably would have looked ugly to the college administrators.
Wow! When you consider how many people were involved in the design, approvals, legal contracts, construction, etc. . . . well, it makes you wonder who if anyone will be held accountable for this disaster. Throughout the video, I kept wondering, "WHAT were they thinking?"
The contractor was thinking " Hmm, I bet i can save money by offering the folks at Building and Safety to look the other way rather than calculate loads, second guess the engineering firm. We can pay them to approve the ABC method and that way it will their fault if it falls down". The folks at the Building and Safety Department were thinking about how to spend extra cash.
newbeequilter everyone involved has their press release ready to go..."We looked into it and we found out that we didn't do anything wrong ".
The bridge designer was thinking "how can I sex this up so it'll win the bid from those rubes at FIU?"
likely no one or company will be held responsible. Years of legal b.s, bribes to lawmakers, and.the victims families will be left in the dark. seen it before.
Given the nature of the grant program, 2 things are certain: A) Errors were made in WHO the contracts were assigned to (no problem with set-asides or "women in engineering" preferences, but they won't go with the DESERVING women or PoCs) and B) whoever made those costly decisions will NOT be held accountable. Oh, they'll find some taxpayer money to pay off the victims but the people responsible are too well-connected to have to pay.
I make this prediction with as much confidence as saying a dropped rock will fall downward.
Engineers trying to be Architects=folly. This structure is almost a hybrid I beam since the chords(flanges) cantilever over the webs. Appears eccentrically unstable.
I've done a lot of post tension cabling during my years of concrete reinforcement..... Never never never once (and I can't stress this enough) have we ever started putting the reinforcement cables under stress without it being supported and or braced. Samples of the concrete used had to be sent to a lab independent from the concrete company to be pressure tested and the reinforcements in the concrete itself had to be inspected by a qualified inspector before you can even pour the concrete itself.
I've had anchor points for our post tension cabling set in concrete that have been poured and let cure for 3 days still malfunction and blow out entire 20 x 20 foot corners of a slab on a high rise building. But the entire floor stayed in place because it was brace from underneath..... So I can't figure out why they were applying the the tension on those cables without there being support from underneath. If it is determined that the post tension cabling had a malfunction and this was the cause of the collapse there should be criminal charges pending on whoever decided that no support was needed during the process.
This is like the Hyatt Hotel sky walk collapse in the 80's. That was in the end put on the engineer that approved a change to the connecting rods who thought the company that made the beams understood the need for the extra sleeves if they went to dual rod system. They didn't do it and it was the largest loss of life due to collapse until 9-11. It was a very traumatic event for the Kansas City area for many years following. Kansas City was also home to another engineering failure, the Kemper roof failure which luckily came after a concert or it would have been another huge loss of life. It showed that ponding of water on the roof can quickly overcome the weight the roof was ever rated to hold.
Sad sad tragedy. Why WAS traffic being allowed to flow during this work?
Not an engineer here, but I believe that steel can flex more than concrete. I tend to agree that the design may likely be the primary culprit, also contributing to the deaths was no plan to close the road to traffic during testing. Initial reports said they were stress testing. Also Juan has an excellent point, that the single set of angled beams meant that a single failure guaranteed bridge collapse. I bet aesthetics won out for design choice (concrete instead of steel) but a steel bridge could have still been made to be fairly attractive, and with the tower and supporting cables. Very sad for those killed or injured by the collapse. RIP.
I find the argument that damage occurred to the joint where the two diagonals met the upper canopy, possibly when the tension rod in the outer member was supporting the overhanging end of the truss with the transporter lift points being too far from the outer end of the truss. Either the cable was too loose during transport, allowing tension forces to separate the joint area, which then gave way when put under compression when the span was placed on the end supports or the tension was adjusted too high in an effort to support the overhanging end during transport, causing failure of the tension rod and damage to the joint area under tension forces.
Either way, that joint appears to have failed after the span was in position for several days. Trying to tension the damaged joint structure after the diagonal member itself was already in compression rather than tension could have been the straw that broke the camel's back.
Thanks, that's the best description of the bridge and its collapse that I've seen so far.
so fare, even I can understand what happened,,, because you explain things so well!!! thank you!
THANK YOU JUAN ... GREAT JOB !!!
Thank you. I did not realize that the “suspensions” portion was not part of the structural design.
Should a truss design (symmetry) be altered to accommodate an "ornamental" tower/cable support structure? Of course, as you mentioned, it should have been a dual truss design for redundancy.
I dont know all the facts. As a retired QC for the Corps of Engineers It appears that safety was overlooked in the testing process. Was there some sort of load testing before allowing vehicles to pass? Our job was to ensure that everything meets the specs, to code and our standards, and drawings, the job gets done on time, on budget and NOBODY gets hurt.
Hard to imagine a shallow solid concrete truss being capable of holding its own weight. For the members in tension, the entire bridge depends on on one single threaded rod?
Vaughan, a well-presented objective presentational view specific to the collapse.
A point to consider is that the cabling itself in its being incorporated in the design being the 'necessary adjustment component 'may have been the critical error in the design of such a huge and heavy bridge. (My overview of the above video and your appraisal has facilitated my observation and resultant opinion.) I am still okay if my opinion is proven wrong.
The newscasts I watched stated that a stress test had just been completed, and that the cables were being re-tensioned,.indicating to me that the tensioning had been relaxed for the test. I really don't know how much of a factor that could have been, as my only exposure to that technology are the post-tension slabs used as foundations for homes in north central Texas. In that application, the cables are used to stiffen the slab, so that it floats as a single unit on top of a layer of sand. The results of the NTSB investigation will be interesting, as they will look at everything from the design itself, to the grade of steel used in the cables.
Update: Photographic evidence has now surfaced, that a tension rod failed, resulting in the failure of the truss, and the collapse of the bridge. (The tension rod actually shot out several feet.) There's also evidence that the span was mishandled when it was placed on the piers. The lifts on the end that failed were out of position. One was supposed to be right under the end of the span, where the deck met the truss. There were also supposed to be spreader bars between the bridge deck and the lifts, but photos show they were not used. The engineers on reddit believe that the tension rod was damaged/weakened when the span was moved, and that tensioning that rod AFTER placement led to it's complete failure.
this reminds me of the Kansas City Hyatt Regency walkway collapse. Only that the Hyatt Regency in Kansas City had the walkway inside. The reason that the Kansas City structure collapsed was because of a design error as well. However, the original design of the walkways were sound. What happened was that the design was changed during construction: modified 'as builts' were the culprit. The changes to the structure were approved by phone, if you can believe it, and they altered the way that the walkways were supported. A specific design for box girders was altered and left out a crucial 'collar' that would go inside the girder to support the weight of the walkways suspended from the connections. The reason I know all of this so well is because, as a civil engineering student, we were required to study that disaster as a way to know 'how not to let the construction of your structure, that you seal, get out of your control at any time during the construction of the project.' This may be something similar where adequate precautions were not taken. Kansas City had horrible injuries and close to 120 people died. What will be interesting, is to see if they conduct a full scale forensic investigation into the exact reason for the collapse. Engineering licenses will be lost and hefty lawsuits filed, that can be sure. What will be interesting is to see the level of scrutiny this collapse gets versus the very hasty investigation and clean up of ground zero in NYC after 9/11. Those collapses, supposedly due to fire weakening of the steel, received a comparatively cursory investigation compared to Kansas City and the commission was delay for over a year. One of the buildings, which, for eight seconds, fell at free fall speed during the day of 9/11 (WTC7) was hardly mentioned in the final commission report. Let's see the attention the local government officials give to this disaster that was not deemed a "war zone" and thus under military control. Let's see how much care they put into the investigation when there is no bearded man in a cave half way around the world, next to his dialysis machine, with his satellite phone and laptop, who was supposedly able to defeat the most powerful military defense system in the world with 19 fellow Muslims armed with plastic box cutters.
Do we know the depth of the rebar in the walkway and roof? The Pictures of the bridge looked like the structure folded. Like the rebar in the walkway was to shallow.
Is the design comes from the university? Do the people know that "safety first" is the number priority in all construction sites? Launching this across the road with traffic moving under is definitely a breach of engineering practice. The design is obviously wrong. How is it possible to post tension such a thin concrete section without causing it to warp and hence internal cracks. The triangular concrete trusses above are overloading the bottom. Post tensioning any one of the truss member produces a force in the direction along the adjacent member
( bending moment) to the bottom tending to overstress the point and breaking the bottom section at that point. This is my view. Please correct me if I am wrong.
I'm not an engineer but just looking at the bridge I notice no center piece for support too and given that the other parts are simply for looks why didn't they use something similar to the Golden Gate and the many pedesrian bridges that are similar in design. Lastly, why use concrete and have traffic underneath while testing ?
Last collapse in fiu & Miami Dade county booth had fatalites within the last few years soon after construction. my dad works for the architect company for both garages ( same company) after further review it was found the prefab concrete work was very poor and was found to be the reason : perhaps its the Reason for this bridge the Miami /Hialeah company making the prefab is still making crappy work
The surprise is that the suspension system was only ornamental considering the weight and that concrete is not generally good in bending
As ALWAYS! You have the important questions and insight!
Clicked on this without even noticing it was Juan until the video started. Happy to see other engineering journalism by you, Juan. Your reporting is top notch.
The thing I find striking about the image of the collapsed bridge is that the concrete trusses on the one side look like they're absolutely pulverized.
I'd like to see the source of the claim that the cables were ornamental. We know the budget was a big deal with this project (as it usually is); does it make any sense that the client would pay big money for a large complicated ornamental feature?
The source is from FIU and their deign plans.
It only makes sense when using "other peoples" money....ie 'TIGER' funds.
Crazy stuff. Please do updates as things progress. The likelihood of getting any meaningful info from the mainstream media seems small :(
I agree that the design of the bridge should be closely examined. The reliance on too much perfection ... And the lack of failure amelioration as would be present in plastic hinges on steel bridges is very worrying. Things always go wrong during construction. But we have few fatal disasters because of "graceful" failure modes.
Is it really true that it’s made to look like a cable stayed bridge rather than actually being one? Seems crazy. Concrete only works in compression, the design is bizarre.
Not all trusses are under tension. Trusses are either under tension or compression. The one at the end which you claim was being adjusted for tension is a truss that's under compression. The best way to know if it's under compression or tension is to pretend that the truss doesn't exist. Will the nodes move toward or away from each other? If they would've moved away, then it was under tension. If the nodes would've gone toward each other, then the truss was under compression. And BTW, trusses under compression can't be simple cables.
"Blancolirio World HQ's" - love it! Pretty background of 'spring' snow too. Thx for update on this unfortunate situation; prayers for all affected 🙏
I'm no civil engineer (studying mechanical), but anyone and their brother can tell that truss design is trash. Stuff like this happens with you have too many architects and not enough engineers.
Great. South Florida cannot depend on their sheriff department, or local FBI and now south Florida cannot depend on construction on anything. Florida. The new California.
Thanks for trying to explain but I am just confused as ever. Why would they let traffic go under during a stress test? Makes no sense. I pray for the loved ones who have to deal with the aftermath. So sad.
3:19 *CONFIRMED:* Juan Browne's magic wand is a paint brush.
EVA_Unit_4A true that! Lol.
Total *NEGLIGENCE* on the part of the designers! Absurd! I hope the courts put them *UNDERNEATH* the jail.
Looking at the image at 9:59, it sure looks like it bowed enough for the bottom to slide off of the support column. The "truss" configuration only works if the triangle points remain attached. In this image, it sure looks like the vertical and horizontal points of the end triangle separated.
Juan, you may of have missed today's news about a report of cracks appearing two days or so ago by inspectors who rightly did not sign off on the bridge and raised red flags. I wonder about vibrations caused by the traffic, heat from the sun and the weight of the concrete in this design. Here's a link to the news on the cracks
www.nbcnews.com/news/us-news/engineers-saw-cracks-miami-bridge-days-collapse-n857481
"From a safety perspective we don't see that there's any issue there, so we're not concerned about it from that perspective," the engineer said according to the transcript, "although obviously the cracking is not good and something's going to have to be, ya know, done to repair that."
Cracks in concrete is not unusual and not necessarily a sign of a structural issue.
There was an engineer who claimed that because cracks were found in the MetroRail structure spans, they would collapse. Well guess what we are still waiting for that to happen. Cracking of concrete is just something that is common. No matter what you build with it. The cracks may not be big, but I have never seen a single concrete item that did not crack somewhere. But that is what the cables, and steel in the structure are supposed to make up for. Concrete is good in compression, but poor in tension and a failure of any of the cables, rods, rebar, should have been figured into the design. But it appears that it was not for this part of the construction process.
Thanks for your customary clarity and insight. For further info about shortcuts and screwups, you might want to go back a few decades and check out the near-collapse of the Zilwaukee Bridge in Michigan. For us non-experts, an excellent read is "WHY BUILDINGS COLLAPSE" by Matthys Levy and Mario Salvadori.
It broke because the freaking main support post and leads were not installed. Why not have the center column built to grade ready for bridge to sit on?
Thanks for another great video, Juan. I'm no engineer, but common sense tells me that making a bridge like this from concrete, then adding the steel reinforcements is just plain dumb. There must be other safer designs to satisfy this pedestrian bridge's purpose.
Juan, Yes - I have a much better understanding of the bridge fail THANKS to your straightforward, clear explanation. Now, John Roebling, builder of the Brooklyn Bridge (late 1800s), would be horrified by this design and/or construction fail. The Brooklyn Bridge to this day requires less maintenance than others built afterwards in NYC. Love your snowy yard! Greetings from the Catskill Mountains, NY State.
Thank you... So this was a Mock Suspension Bridge with top part of no value. To the people who use and died under this thing.... Why? It shocking! Maybe all of people... most people are good people and try to do the right thing... may have got mix up.. maybe with the Plans... printed out wrong? One for Suspension Bridge.. one with out! And why have a 200 feet span bridge with a 100 feet roadway? And 950ton is the weight of a Battleship! I just hope that any question that were ask by anyone down the line.. from start to... were listen to. I am very very.. afraid there were Alarm Bells. Will we listen to dead people now?
Watching one of the videos from just after the bridge was placed, a superintendent or engineer said that now that the bridge was in place some tension would be released. It will be interesting to learn what, if anything, that had to do with the collapse.
I can’t for the life of me grasp the lack of falsework to keep such as massive span of concrete in place, at least until the entire span is complete. It’s almost arrogant.
Mark Phillips but FIU was trying to prove the feasibility of the Accelerated Bridge Construction techniques. Too bad they didn't stick to the design for placement of the hydraulic movers.
Great info update. I like how you took Petes paint brush for a pointer, worked great.
damn...I'm an uneducated person...and I see the flaws...well, at least since you pointed out the materials used.......it appears to me, they were far more worried about aesthetics and "time spent".............How n the hell did they expect THAT much concrete to stay up without something n the center of the length.........blows my mind!!!!
Design & Construction executions that was not positively consider to prevention from incident (I mean the Site Geological Condition and Soil Investigation results, Soil & Rock Bedding formation and Strata, Construction materials, Load Bearing Capacity for the High Way Roads environment, Strengthening of Structure) after the disaster if you see in the Pictures showing that concrete and Steel combination not OK both look like separate scenario that why it must be consult with Geological and Civil Structural expert’s opinions before implementation, to avoiding such kind of happened will not be come out in the future, I think hope So ???