Miami Bridge Failure- FIU Bridge Design
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- Опубликовано: 2 окт 2024
- One of the first things NTSB investigators will need to understand is how was this unique bridge designed.
Music:
"The Railroad"
Goodnight Texas
hiwearegoodnig...
Plans:
facilities.fiu...
This is first class journalism
times are changing, we now look to citizen journalist for real news
Good Job Juan, I am an engineer, and I was worried you would get too technical for a complex concept of post tensioning....you did a better job of it than my college professors.....dont tell them that! Keep up the good work.
But it was a professor who did the explaining..🤔
Why is it that I have to come to a RUclips page created and run by an airline pilot for Real News? Great report on the FIU bridge design and examples of how it all is supposed to work. You gave us real world examples of the same type of bridge but different designs then great explanations by a professional on how the design theory works and found animations of the actual bridge design and design features. Just straight up real news and a great presentation.
The MSM is propaganda. They haven't got the slightest interest in truth, information, or increasing understanding.
It's because large "news" channels are in the entertainment industry. It is in their financial interest to attract and serve the largest audience possible, and to do this they have to dumb down and hype up their stories for consumption by the least common denominators of the population they serve. They make complicated stories short and emotional. They find and focus on the human element. They emphasize what's controversial. If it bleeds it leads.
This is in fact the opposite of propaganda. Propaganda is designed to manipulate its audience. Main stream sources produce news that is shallow and uninformative because they've been manipulated BY their audience.
Main Stream Media is entertainment in the guise of news. There, the facts don't count, only the number of eye balls watching.
Arishia Nishi I'm a woman and I probably couldn't sit thru one hour of a real engineering class but Juan does such a good job of laying it out for me that I can get a good grasp on the subject. I wish more people actually tried to be thorough with their reporting I think more people could understand things better, and we might not have so many people freaking out all the time. 😀
Amanda Faulks that's why most real engineering classes are fifty minutes. We can't either!
Thank you, Juan! Great lesson in concrete and steel construction! Now some of the strange bridges I've seen make more sense!
A medieval rope bridge would have been safer than what FIU designed.
Yes, I agree with you. That bridge was a failure when it was built. Sad that people had to loose their life because of the arrogance of those thinking style was more important than function. A rope bridge would have been a lively experience to cross, good thought. Cheers!
One rope would of been safer.
You have the best videos on RUclips. You provide the best presentations and explanations on topics that reporters will never match. Stellar work Mr Brown!
Your videos are weirdly compelling. Good storytelling skills . It's the story reporters want to tell but they don't have the time or space. Thanks. I feel smarter!
Paige Winslow deadlines are the enemy of truth.
Or the intellect.
It's called real journalism.
The "Journalism" you see on TV takes a 5 second sound bite out of context, then has the "reporter" spew an ignorant opinion on what they think the 5 second clip means, scripted to support a specific narrative.
SlocketSeven - ...and they sometimes don't even do their own work, just copy what someone else said/wrote!
Once again Juan you've made something understandable that no one else has. Great explanations and looking forward to the follow-up video!
Juan, your channel is one of the very few sources for factual information. Mainstream media focuses on a tired theme-- What to be afraid of, and who to blame. You don't follow that theme, ever. You find, vet and report facts. I think you and your channel deserve a Pulitzer prize.
Juan, you continue to show the "News Media" why people don't watch them any more. Thank you for all you do!! Jim.
I have been interested in construction and how things are built since I was five. I enjoyed your presentation.
As a retired research professor, I wish I'd had lectures from you as an undergraduate and graduate student.
Thank you.
great video Juan...I spent about ten years in heavy construction...One of my projects was a coal mine, built on the side of a mountain, that was prone to slides...I was contracted to keep the side of a mountain from moving down hill...we drilled holes 175-200 feet into the side of the mountain, as far into solid rock we could find...we then dropped in two inch steel rods, anchored to the bottom of the hole...we then put the hydraulic puller at 12,000 lbs, and pulled...set the wedge, and grout it in...we installed about 300 with electronic monitoring on each wedge...we then covered it over with our form of RCC...I could then monitor the movement at home or office...there was some movement, but not much and it stopped quickly...since then the mountain side has been stable...over twenty five years...
Robert Soby: This reminds me of a presentation I saw on the Web some years ago-- to stabilize hillsides, etc. with steel rods about 18' long, shot into the hillside work site. Is your mine project a variant of that?
well, not really...I know about the technique of "pinning and fencing" steep or cliff faces lining a roadway...this was to stabilize the area around part of the coal processing plant, that was starting to move down hill...it was an "emergency" and we had to use extreme measures to stop the damage, and then we had to mitigate future movement...the basic physics are the same....we just had to upsize and figure out how to use existing technology quickly and effectively...this was not a fun project...
Juan, this was so interesting and informative. I swear, if you were a college professor, I would have taken any course you were teaching, because your explanations are so clear, well-thought-out and logical. I have enjoyed all of your videos starting with the very informative coverage of the Oroville dam. Give my warm regards to your family and please keep up your amazing work. Best wishes from an old sailor in Mobile, AL.
I don't have enough superlatives to throw out there for your amazing reporting/teaching, so I'll just say Thanks!
What a gift your videos are to us dummies! This was riveting information for me.
That British guy nailed it.Thanks Juan good show.
Thank-you so much for this video Juan, you made what could have been a really complicated explanation into something that I could follow......now that's not an easy thing to do
Great report. You obviously spent a lot of time compiling the material you presented.. Thank You.
Gosh, a slide rule. I can't remember when I last saw one of those! A nicely put together lecture.
Juan, another great job. I never knew I'd be interested in bridge design and construction, but you created a new interest in me!! Thank you...
Professor Juan, For devoted viewers could you award us an honorary degree in dam and bridge structural engineering? I've learned so much over the past year thanks to the blancolirio channel. Always looking forward to your next presentation. (from NY state)
Well said!
very very truthful statement DM.
I'm down for a honorary degree, just let me know where to send the paypal payment plz!
It's great to have such a patient, knowledgeable teacher, and with such great insight and even humor. We are truly blessed and honored to have this privilege of being his pupils! I don't need a degree - I already have my reward!
Agreed. I was being silly. Juan is a fine teacher blending facts, patience, and humor.
Juan, this was an excellent explanation of pre-stressing and post tensioning. It cleared up a couple of questions I’ve had for some time. I just retired from my company where we appraised commercial and industrial buildings. We always made a great effort to understand and accurately describe the structures we appraised. I spent countless hours examining plans, interviewing architects and structural engineers and reading the specifications in their project manuals. Did you study civil engineering before you became an airline pilot?
I studied Physics, and later worked for a PE and Architect .
Zero redundancy designs and single point of failure designs are the best!
with pedestrians crossing a major highway - yeah, not much to lose in case of failure, right? gee whiz.
Don't forget the engineering brilliance it took to put concrete in tension. The cracks that appear even before the bridge is put into service merely show just how strong the original design is. No reason to worry.
Hello JAUN,
Another very informative video! Thank you.
I have been very interested in the collapse of the FIU bridge as I spent much Miami time in the adjacent neighborhood many years ago, and also because accident analysis is so interesting.
I had earlier viewed several videos and read preliminary accident reports about the design principles used in the FIU bridge however only today did I understand the structure's construction design ....this after watching your presentation.
Best regards
Juan thank you your channel is the only place i can find this kind of information true honest reporting no matter what it is. Thanks for educating me on the design of the failed bridge I am really curious to see what the ntsb comes up with. Maybe you should go help them I'M you could help therm to do it faster and cheaper than they will do it. Safe flying give the family a hug and tell them hello. Have a great week God Bless!!!
Juan as always you give a great presentation. I have worked in the area and I can tell you, those people are not going to stand by and give you enough time to build the bridge in a safe way. When its all said and done we will find out some corners were cut To hurry things up.
Fantastic video Juan well done 👍🏻
I was wondering when you were going to get back to the failure of the Miami walking bridge. I'm glad that you've done your homework Juan and translating all that engineering mumbo jumbo for us not so engineers . What a tragedy to have to learn from an engineering disaster. Kind of like the same for the Oroville Dam ,which could have been a very big tragedy ,as well. We'll be looking forward to your next videos and put into terms ,so that we have a ore understanding. Thanks for your expertise ,Juan. God Bless and stay safe on your journeys.
Very much looking forward to the next video.
I don't know how to word it, but you're really interesting/keep things interesting. I stayed up last last night watching this. And with ADD, it's hard for someone to keep my attention lol
You used the plans I linked to very well. You also presented the information very well. I hope you will address the placement of the supports for the move from the casting location to the installed location with emphasis on how the tension in the cables changed with the relocation of the supports from design to actual. I realize my previous sentence is long but I believe it has everything to do with the failure. Most concrete beams are cambered for the typical load to be placed on them. If a load is not placed on the beam it will slowly over time creep into a greater camber from the tensioned strands and the concrete relaxing..
I believe this design was an experiment in esthetics that went awry. A much simpler steel or aluminum truss would have been less costly to build and erect to perform the same function. Heck, what do I know; I only pay taxes not build monuments.
Thanks Juan. I appreciate the education.
Thank you so much for explaining this! Great!!!
First class and informative, thank you Juan.
Coming from a post tension bridge carpenter.... You nailed it. Your awesome. Get it on
How risky is post-tensioning, in regards to catastrophic failures? It seems like even some homes are built with this now, and are having major problems. Seems to me like it is tricky to build because you need to make sure the concrete is set, otherwise it will fail to hold the required compressive forces. And this depends on a variety of factors that are hard to control/monitor.
Besides, concrete is semi permeable to water, so isn't it possible for corrosion to take place? Even worse, some form of electrolysis.
Benjamin Esposti Post tensioning is quite common and extremely safe. I wouldnt use this accident to come to any conclusions about the technique.
Stressing of concrete has many more variables than reinforcing it. Even the coating on the tension wires has to be taken into account. There are many failures of pre-stressed concrete beams (Minneapolis/St. Paul come to mind) in parking garages that are the result of poor adhesion between the concrete and the tendons due to the anti-rust coating applied and/or rusting of the tendon as it sat in a yard.
There are many factors that complicate concrete construction, including delayed ettringite formation, cure rate, moisture intrusion, mix errors, etc. Some critical factors are exposed early, other may be exposed years down the road and the force of gravity continues its relentless pull toward mother earth.
1st Hong Kong bridge looks like they might have use a Harbor Freight welder..Excellent explanation and use of graphics.
Fascinating!
Good to know that concrete is high in compression but low in tension .
..that bridge in Hong Kong looks mighty strong and "comfortable"...
when seeing the illustration of the Miami bridge, it doesn't inspire "stability" ( that asymetical beam structure?)...and doesn't have the forgiving EQ pads that are resilient to movement/vibration, ..
.
Thank you for this excellent report Juan ! (looking forward to more such comprehensive lessons on building/construction of major endeavor :)
Blessings
You wanted constructive criticism ? Well I for one can't find any for you. This is a fantastic report . ( as usual )
Nice Job Captain Blancolirio! I can't wait to see your Truss Design Review. You did a great job of reviewing a "build in place design." It should almost have a warning sign that says "Do Not Twist During Transportation" and don't build it in one location; pick it up in 2 different places; swing it around 90 degrees length wise; drive it down the road and set it in a different location. As you check the Truss design: Can you please zero in on the design details of the twisting tension of the platform to the truss perpendicular connections, and what probably happened during the relocation ABC process? Or where was the pivot point for the span during 90 degree swing around in the road? Thanks Juan.
Finally. I BEGIN to understand post-tensioned prestressed ETC concrete.
Thanks, me too.
Heck, at one time I worked at a place that made the huge box beams that go into bridges over multi-lane highways, and I learned more from watching the blancolirio channel than I did the entire time I worked there.
Thanks Juan.
Why not steel?
An ugly concrete slab made to look like it has no support and in fact, had no support.
A beautiful arched steel truss would have been perfect.
A concrete and steel slab suspended by towers.
I just don't understand a world where form matter more than function in a critical engineering project.
Even if that bridge had stood for a while, it seems like it would have failed eventually.
I agree, steel is so much more predictable than this flaky concrete stuff !
ME: That's my opinion. I think they were somewhat lucky that it didn't collapse when FIU held a celebration party with many students dancing on the bridge deck. The death toll could have been much higher.
I have to agree. They could have built a lovely, graceful steel structure, which would have been mechanically very simple, much lighter, and would have gone up more quickly. This sort of concrete design has the appearance of engineers trying to prove something, trying to push the envelope. Wrong design for the situation.
Matthew Edwards s
Thanks - really informative. Makes you realize why Roman engineers built their concrete walls and roofs so sturdy - no steel cables and no slide rules! The robust domes of the Pantheon and Hagia Sophia have stood for >1500 years.
In contrast, the poorly checked FIU bridge design, with its lack of redundancy and uselessly decorative tower and stays, was a lightweight fantasy. You wonder too how well the grouting would have stood up to Florida weather, long-term.
Excellent commentary; look forward to the next one. I see nothing definitive yet, but it is troubling to see that redundancy seems to have been sacrificed for aesthetics. We'll wait and see.
Thanks for some great info Juan. As an old mech engineer I'd never to be honest, have accepted that design - let alone the initial (temporary)placement and traffic permitted. Not a fan of the post tensioning system in this design... steel trusses would be way better IMO if a suitable method of incorporating those.
ChrisB257 Proof positive, in that the failure of a single component resulted in immediate and complete collapse. No redundancies. Unbelievable this was ever approved in the first place.
Prestressed concrete has been used for decades, and is an extremely reliable and economic method of constructing bridges.
You're correct about the redundancy in the design. Steel bridges have for a long time had requirements for "Fracture Critical Members" (FCM), which are defined as steel members in tension whose failure will result in collapse. A bridge with at least one FCM are designated fracture critical. Current design practice is to eliminate FCMs if possible. However, for some spans it's often not economic to eliminate them entirely; long-span truss bridges and tied-arch bridges are generally fracture-critical structures.
If a bridge is fracture critical, there are additional requirements for detailing (design of connections, basically), as well as more stringent inspection criteria. Fracture critical bridges require a "hands-on" inspection of the FCMs every 24 months, where "hands-on" meaning the inspector must be within arms reach of the tension component of the FCM. (NB: The National Bridge Inspection Standards don't apply to the bridge at FIU, since it's a pedestrian bridge, but many bridge owners will roll up all their bridges in one program that follow the NBIS.)
Note the wording in my definition of FCM: "...as steel members in tension whose failure will result in collapse." Concrete bridge members are explicitly excluded, because the standards were developed due to fatigue problems in steel bridges. Concrete doesn't suffer from fatigue, and typical concrete construction is generally highly redundant. A typical concrete bridge will have a number of parallel girders that provide redundancy; the economics of concrete construction generally just result in this outcome with no explicit code requirements.
It will be interesting to see if new standards are developed by AASHTO. Right now, you're typically not going to use the non-redundant structure found here for highway bridges, so changes there will probably have a very low benefit-to-cost ratio. The NTSB doesn't have to live with the costs of their recommendations, so it'll be interesting to see what comes out.
AASHTO *does* have a specification for pedestrian bridges (bookstore.transportation.org/Item_details.aspx?id=1552), which I'm not familiar with. However, the description on their website says, "Pedestrian bridges with cable supports or atypical structural systems are not specifically addressed." This bridge's structural system was weird in about 4 different directions at once, so I'm sure it's not covered. It probably will be after this, though.
I'd have to agree, I've worked on many Bridge decks and Parking structures for years there was nothing wrong with the old way
Raul R R Except to some people, they don't look fancy enough.
950 tons of concrete for a single span pedestrian bridge? Unreal.
Excellent lesson Professor Juan. Thanks!
Great report Capt. Juan. I liked that you showed another company's method of stressing. The Florida bridge had many mistakes built in. No redundancy seems to be a glaring issue. They could have used even some of the overhead " fake" cable stays to help reinforce just in case. Its seems engineering in some quaters today is sort of like just in time inventory in the logistics world. No redundancy just in case. Lets have a few items on hand in case the truck is late! Hey, lets put cribbing up under the bridge " just aa a precaution. No! It costs too much time and material. Besides, we can pay off families of the dead. Sorry, i had a family me ber killed , my only brother, due to industrial negligence. OSHEA was ignored, they gave a 165,000 dollar fine and we got the funeral paid for. My nephew grew up without a dad. Our state had a law against directly sueing a company. Arkansas, land of Bill and Hill!
Speaking of bridges, my favorite is the Sundial Bridge in Redding, California. Glass walkway. It's beautiful, does it's job and seems to have been stable for several years. (Since it was built, anyway.)
Well presented Juan. Really have to My head a good
scrach America must still be open for those who are prepared to work...:)
Phenomenal report. No criticism here. I think this is your best work to date. Now...It almost seems, providing the original engineering is correct, that if they supported the structure from underneath until all the post tensioning and grouting was complete, this bridge would not have collapsed. (They were obviously wrong about the ability of the bridge to support itself until the tensioning was complete). They should have used the center lane of the roadway to brace the bridge temporarily. It seems they were most concerned about obstructing traffic. Shoulda, woulda, coulda.
Guttebo....I am not an engineer, just an interested observer. But I have worked heavy construction for nearly forty years. And my hunch is that along with the team of expert engineers who will investigate this will be a team of lawyers. I assume that the need for this walkway was necessary and another will be built. It will be interesting to see what new design is used and what type of road closure procedure is used. I am also curious as to the weather conditions while the cement was poured in the building of the structure and if too hot, which would decrease setting times, were any catalysts used to normalize setting times. Though there are procedures for using the catalysts, sometimes the application can be haphazard. I have seen road surfaces poured when catalysts were used to speed up the setting of the concrete because of sub freezing temperatures, in the teens. And come the summertime, when the Road started to be used, those portions spawled badly. I realize Florida is the exact opposite temperature wise. Just thinking out loud.
Excellent video Juan. You have the ability to explain extremely technical matters in a manner that allows laymen's to understand.. thank you very much this was very informative,, keep up the great work.
guttebo on abridge with a large factor of safety built in, the tension being off would more likely result in a crack at the node, but not enough to bring down the bridge. That is why IMHO it has to be the concrete. The concrete is also an area where faults my not be visible. The mix in the trucks may be good, but that doesn't insure correct and timely placement. If they do their jobs right, they will find that the largest contributing factor was the placement of the concrete in an environment that couldn't be well controlled. I say this because the errors were too great not to be seen or measured if they were related to anything other than the concrete. Normally there are large areas where the web meets the upper and lower flanges/chords, but with this bridge, the full shear force had to be taken in comparatively small areas. All it takes is a small between pours and weakness between batches will be there even if they can be seen. This also won't show up in a core test. This is the only part of the build process that can't really be checked later. The part where the on site engineers would basically need to say- "sorry, the 27th of 40 trucks was late. We need to scrap this whole thing and start again" being an on site pour, there were probably only 2 people at most that could have made this call on site. Even if the engineer said "if any section of concrete in the entire bridge goes more than 1 hour before having new concrete poured on it " the more layman(in mind vs engineer) concrete worker may not have had the stones to go above someone else to point out one node that went 4 hours before having the next batch thrown on top.
Juan did some very good work on the Oroville spillway failure; but agree this is very nicely pulled together.
Thank you, Juan. As always, your videos are clear and full of information, well presented and put together. As an engineer myself, I really appreciate your no-nonsense approach. Best wishes to you and your family.
Good overview of the bridge components. Thanks for taking the time to show us the different components and amount of work that goes into building one of these structures. Safe flights.
Educated (or maybe just a wild) guess from another old mechanical engineer:
My bet is the deck, roof, and web members (i.e., the angled sections), taken individually, were all designed and built correctly. I suspect the problem will be found in the details of how the connections between these members were designed (or implements). Some examples of where this has happened: The primary cause of the collapse of the I-35W was the undersized gusset plates at the joints. The Hyatt Regency walkway collapse was also because of failed joints due to a poor redesign.
The forces in the straight sections away from the joints are easy to calculate. The forces in these areas are only slightly harder to calculate than it is to determine the force in a rope that has a 100lb weight hanging from it. At the joints, things get much more complicated. Computers have made it possible to calculate exactly what will happen in and around the joint. But the computer doesn't give you the right answer if what occurs in the real world doesn't exactly match what was put in the computer. For example, maybe there was a void in the concrete at a very bad location. Or maybe as they adjusted tension in the tendons, they developed highly unequal tension in different tendons that was not considered in the computer model. Or, in the pres-stress video, did you see the all the bits of reinforcing that are needed near the cable anchor? It's got to be even more complicated in the FIU bridge where tendons come into the same area from multiple angles. Maybe some of that reinforcing was not designed or placed quite right.
In short, I'm just saying the obvious -- mistakes are more likely happen where things are complicated than where they are simple. The joints are the complicated bits.
I agree. I have been pointing at the joints in many previous comments.
Great presentation
I get more than a little paronoid when it comes things like tensioned steel cables that are sealed and exempt from future testing due to bring grouted in.
You drive across them every day of your life. All bridges that utilize concrete beams have steel tensioned cables sealed within them and exempt from future testing. If you park in a modern parking garage there is a good chance it was built using prestressed precast concrete beams, the steal within completely sealed and exempt from inspection.
Aesthetics of no use are always suspect. For the same price, or not much more, they could serve the structure. Instead, they were a liability.
I realize the "Cable stay" feature didn't cause its undoing, but anytime you spend any time/effort thinking about aesthetics, and miss some thing important in planning and execution, then i say Tighten Up!!!
So far, your video is much better than another video I have seen on the FIU collapse. I look forward to see further videos. I have an undergrad in civil engineering, a masters in structural engineering, close to thirty years of experience, a P.Eng. and a Struct. Eng. designation and I can say that you just about got everything correct. The collapse is obvious interest to me so I have been looking at a lot of information on the subject. The only thing that I would say is the explanation of why we prestress is not exactly correct. Most people say we use prestressing because concrete is weak in tension. We reinforce concrete because it is weak in tension but we prestress primarily to reduce deflections (it also helps minimizes cracks). If you test a beam with tendons that just have the slack removed, it will have approximately the same bending strength as a beam with fully tensioned tendons.
Thank you, a sane comment. Yes, you are right - lots of concrete bridges, and building structures, in place that have only reinforcing bars, no prestress. Prestressed beams allow beams to be build off-site, lifted into place. The construction site time can be reduced. Concrete forms for the primary members does not need to be built on site. Other concrete, such as a deck, can be poured on site, but the primary prestressed beams provide a solid structure to hold forms for the poured deck.
So what you are saying is that the tension placed on the concrete helps hold it together but the tendons are actually what hold the weight? In other words if you could tension the concrete without having cables run through it then it wouldn't hold as much weight? Sorry if that was gibberish. I have no construction experience but have become interested in this particular story.
A typical simply supported beam (similar to how the truss in this case is being supported) goes into the compression on the top surface and tension on the bottom. The bottom concrete is too weak to take the tension stress by itself. We need to add reinforcing to take the tension. The reinforcing can be prestressed or not prestressed (it really doesn't matter in terms of strength). The reinforcing takes the tension load. However if the concrete is not prestressed it will crack under service loads (everyday type loading). The cracking on the tension side (bottom) makes the beam softer but the cracking actually does not make it weaker in bending. Prestressing will also camber up the beam. In other words, the prestressing pushes the beam upwards which counteracts the deflection from the dead weight (the camber and dead weight deflection hopefully cancel each other out). There are also long term effects from the concrete that are a little too complicated to get into with a RUclips response. I hope that makes sense. It is difficult to understand without pictures.
Thanks! I appreciate you taking the time to answer.
This is nothing new! pretension/post tension has been around for decades! It is early yet, it seemed they were loading at the wrong points.And changing the truss tension to compensate for just that. Really sad situation. very well done video!
Bingo for Tom Williams!
Hong Kong used steel, why was concrete used at FIU?
Thanks for adding the English Professor's simple explanation about "tensioning" of concrete. I have a much better understanding of the technique.
Excellent presentation on that complex design. As a civil engineering graduate (years ago) I found myself nodding in agreement! Found you doing the Oroville flyovers which I enjoyed very much. Also, you're a 777 pilot? I'm an engineer at P&W. Subscribed.
6:38 Professor Chris Burgoyne teaches a highly complex and sophisticated method in such a way that even passers-by and idiots can understand.
Sometimes the internet isn't that stupid silly shitty and becomes a valuable tool.
Thank you blancolirio for sharing and please keep posting.
Great job, and like most of your other videos a good in-depth discussion of the engineering issues at a level we non-engineers can understand. The only criticism I can give is you didn't link to the original videos you played clips from, that professor's video for example is one that I think would be worth watching in the entirety (at least for me) to garner a full understanding.
I do not know if you noticed in the animation for LMK the beam cables had a hold down in the middle. The hold down is there to pull the beam upward in the middle like a leaf spring. We did the same thing on large I-beams for bridge construction. For what I have seen about the FIU bridge there were only straight cables and I suspect the tension rods were to cause the bridge to spring upward. The black piece I do not think is a spacer, that piece likely presses on the collet wedges to keep them in the collet. The collet wedges have a rubber ring on outside to hold them together and teeth on inside to grab the cable. If you just pull the cable and not press them in, then they would come out with the cable. We never tensioned all cable at once, we tensioned each cable individually. Also nicks or chipped collet wedges were the #1 cause of cables breaking then tensioning. We did everything pre-stressed.
sc02.alicdn.com/kf/HTB1aMHAeRTH8KJjy0Fiq6ARsXXaq/Cable-collet.jpg
Excellent presentation Juan. Thank you.
The thing is though, that there was a lot of math involved here, and I didn't see the resident blancolirio mathematician anywhere around to help you through it. Strange.
Be honest Juan, Pete was off camera somewhere coaching you. Wasn't he? *;-)*
he was busy counting up all the cables.
Okay, that explains it. Totally understandable, that's a lot of cables. Thanks for the added info.
Somehow I just knew he wouldn't let you down, he is a first rate Co-Pilot.
Great video Juan.
Juan - You sound like a civil engineer. A very nicely put together video and, hey, I even saw you sneak in that slide rule when explaining the forces on a beam. There aren't very many slide rule engineers any more. Good job.
This type of construction seems to be very labor intensive. Which means to me... Error filled!
I've read through most comments here. Many include a comment, "Why didn't they just use tried and true designs?" or statements similar. In other words, the suggestion is to repeat what has been done before, because it is known to work. While pragmatism has merit, lots of merit, progress on new designs would never emerge. Many, many new designs for bridges, buildings, etc. have been tried, and proven to work just fine. Consider some of the unique high rise buildings in the Middle East - some really unique designs for very tall buildings, and they are just fine. Even in this case, many object to the ABC because it is "new." Sorry, it is not new. It has been employed for years and years. Likewise, many suggest that the design is bad because of use of concrete. Concrete has been widely used to build bridges and buildings for decades, with very long spans, weighing tons and tons. You, and I, drive across bridges like this every day.
@4:21 "How would i describe the main span of the FIU bridge?" *A CATASTROPHIC FAILURE!*
I did some product testing on a grout our company sells for sealing those tension rods. One of parameters you measure is water retention (?). The reason is, you don't want water separating out of the grout and forming a puddle, forever sealed inside the ducts and eventually rusting the tension rods.
Thanks Juan. It makes a lot of sense now. With Safety Factors I understand why they have so many cables in the lower portion. If one fails there is lots of redundant strength. That being said and the stress on the concrete it almost looks like the concrete was overstressed, probably in a local area. If the end plates deform as the wires are stressed then the concrete will over stress locally. That's why plates always have ribs on the back side.
Eastern Woods please stop, you don't know what you're talking about.
Good Evening Juan,
FROM MINNESNOWTA 15 inches of fresh spring SNOW !!!! ANY WAY , A BIG THANK YOU , FOR THE RESEARCH, and VIDEO, on that bridge failure.
What a FUN JOB you have, "GREAT RESPONSIBILITY" but (someone has to do it) !!!
Always ready and intrigued as to (WHAT) you will have to share, 'and"(WHERE) you will be !!!!
PS Do you folks need any more snow for the Sierras ?
FLY SAFE and GOOD LUCK .....
Appreciate your updates on this unfortunate disaster even while you're in H.K. Safe travels Juan!
Where's the REBARRRR?!?!! Haha Sorry. I had to.
Hunter Green - a reinforced concrete member/structure is not really a concrete member/structure. This FIU structure is really (mostly) a concrete structure!
Wish you were on Kauai to report on our 48" rain event over last weekend. We had 48" of rain in 72 hours which resulted in flooding the like I have never seen in the 25 years I've lived here.
I see that! wow.
Did you get your Pulitzer???
your videos are such high quality great going man
Enjoyed the Video,a clear concise report of the collapse of the Bridge,and what may of caused it.I read all of the comments and it sure generated quite a lot! Thanks for explaining this ,and sharing !
This same company has built or participated in building four seriously big bridges in Maine. I drive over two of them everyday for work and seriously think about the man power, engineering and hopefully the integrity of these awesome and beautiful structures. Yes, I cross my fingers everyday.
Now even I can understand how it works. Thanks for an excellent report (as always)
spot on again with great reporting information even a lame person could understand
Really appreciate your research, integrating in different information sources and walking many non-engineers thru the processes, language and concepts. I look forward to continuing updates.
Slide Rule! (no slide?) Very interesting examples of what works in other locations. In Florida, It may have been incorrect placement of reinforcing, and failure to understand how the changed bridge moving plan would interact with inherently non-ductile post tensioned truss members. That plan required additional adjustments to the truss member at the end that failed. You can see the failed PT rod sticking out of the duct from when it snapped during the failure in some photos. You can see how the side of the truss member beam out suggesting asymmetric compression on the member during adjustment. It was these adjustments post bridge movement combined with a risky re-tensioning procedure (why not block traffic?) and failure to analyze potential failure points correctly that are likely to play a prominent role in the failure mechanism. I hope that the inspection process during the construction of the failed part is also studied as small failures in the details can have big impacts when the structure is not redundant(as you pointed out). Too often the inspector is not viewed as a critical member of the construction team.
This Bridge type has no reserves left. The collapse of one beam cause a chain reaction and all other beams will fail, as seen in the collapse video. The Chinese construction is far more stable as done in steel. Its so well build that it's unlikely it will ever collapse in the next 50 years if proper maintained.
Excellent video. As Engineer with having a bachelor degree in CS, mechanic has never been a favorite of me. But this is so well explained its almost fun to learn all the details.
Great video Juan! Just wondering why they didn’t just build a cable stayed bridge. I am confused as to why they have the cables as a design element and not the actual structure. It seems to me that they could have pre-built the tower with the cables and also pre-built the span by the side of the road. Then move the span into place and attach the cables. Do you know why they didn’t just build a cable stayed bridge rather than the pretensioned concrete span?
They would have been unable to use ABC construction...in other words it would have blocked traffic for too long.
Extremely good job explaining the bridge construction for a lay man.
Awesome and informal video
In retrospect your explanation in this video is almost flawless. You could testify in court as an expert witness. Bottom line is concrete was a very poor choice to be used in this design, given its geometry was very poor.
MSM has failed. You have picked up their slack BIG time, Juan! THANK YOU! 👍
Thanks Juan very informative .
Very good explaination, as a structural engineer I feel the design of this bridge is very illogical. It oozes aesthetics over function, Concrete is not the first material I would think of as material to form the main truss. The PT-rods in the web section of the truss would require a lot of anti-splice reinforecement in the node points to prevent shear-punch failure in the relatively slender top and bottom flanges. There also exist PT-rod systems without grouting, these can have some durability problems if cement water leaks into the ducts they may corrode, it looks like those where used on this bridge.
dykodesigns2yt I guess they should have you over fiu instead of the others they had who preferred aesthetics
I have always thought that the ' shear connection ' between the upper roof member and the lower walkway member looks inadequate. The web section which is usually solid in a traditional I beam simply looks weak...the lack of symmetry of the so called ' web ' between the supports I think is a key indicator...well done video....
It is also worth noting that the work crew had already adjusted tension to the two tenons on the north side of the bridge and also one of the south end tenons. They were just starting to adjust the very last tenon when the bridge suddenly collapsed.
One hell of an event this morning in Philadelphia, video coming soon?
Very good information. Explanation at a level where I understand and learn much. I heard that Florida bridge was being tensioned after it was in place. How does it support its own weight if tensioning was incomplete?
Different parts of the design.
Hi Juan,
Great video. Here's a recent insight into what the workers on the bridge were doing at the time of collapse.
First, some background. The bridge design allowed for the PT rods to be tensioned from the bottom of the bridge prior to the move. As a result, once the bridge was in place, there was no way to make any further adjustments. The statement by a construction worker that they were going to de-tension the rods was wrong. Read on to understand why.
Once the bridge was lowered onto the piers, the load compression would have exceeded the pre-tension stress applied via the rods. There was therefore no reason to de-tension the rods. They were likely slack and effectively useless at this point.
Here's where it gets interesting. At the time of the collapse, workers on the bridge were attempting to add tension to the rods (in an apparent effort to solve an unknown problem). However, adjusting the tension after the fact was not allowed for in the design. The rods were embedded deep in the concrete below the top blisters and no access was provided.
So what did they do? Photos indicate that they jack-hammered holes into the blister in order to reach the rods (which would have been slack at this point). They managed to tighten one of them and were working on the second one when the bridge collapsed.
There's no way an engineer would have recommended this. Who knows what the effects of jackhammering would be on structural integrity - let alone the effect of removing concrete from the blister. What's more, a basic understanding of physics would tell you that the rods were not physically capable of applying anything close to the amount of stress that the member was already under due to loading. So whoever thought that tightening the rods would have any effect on anything was obviously clueless and was not in a position to devise or implement such a reckless plan.
So, there you have it. A weakness was suspected and the road was not closed. Then a crazy scheme was devised by an unqualified individual (not an engineer) without knowing that it would be pointless and potentially dangerous. Finally, it was undertaken - again with the road open!
Certainly the lack of redundancy, potential design flaws and/or damage during the move contributed to the integrity of the bridge once it was in place. And although this does not explain the exact mechanism of collapse, the work being done seems to have been the straw that broke the camel's back.
To see the evidence, check out this video from Construction Engineering & Photography: ruclips.net/video/JwYGmohun8ch/видео.htmlttps://ruclips.net/video/JwYGmohun8c/видео.html
Excellent video showing the critical points of detail for concrete constructed structures....your research and presentation is super high quality, well done.
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@ 3:18 visible on the right are the concrete counter weights that are needed to balance this bridge ~ which makes me think it is not per se such an ideal design, for it to be so asymmetrical after all. Architects, designing things like this, are really after the visual aspects, they want to harvest some feelings of awe, rather than this type of design necessarily being the safest, most intelligent, most functional. Something else, there now is a new type of super strength concrete that allows for very thin weight bearing parts (such as roadways) indeed, In the Netherlands a bridge meant to carry bicyclists over a river is completed a few years ago, that has roadways that are made of slabs of concrete not even an inch and a half in thickness. I do not believe the receipt has made it to America yet, as far as I know. Maybe it is a proprietory receipt, that I don't know.
My understanding is that the worker was adding tension to the diagonal tension threaded rods when it failed. I would think either the concrete failed in compression or the threaded rod failed.
WAAAAAY better report, Juan! This is much more like you normal calibre. Looking forward to your next. Thanks for your work on this - I’m happy to like & share it.
Have you considered a Update video for the Miami Bridge Failure? There's been two updates to the NTSB report (one in May and one in August), new photos of cracks on the deck before the collapse (taken 2 days before collapse, released in August I believe), two new time lapse CCTV footage released in August, OSHA fined 5 companies in Sept. NTSB still has not found or stated a direct cause of the collapse yet so the saga continues.
I should do that. Thanks Kevin.
Juan:
Very good and well thought out presentation. I am still saying the concrete was a factor. Why, I say this is the way it broke so smooth. Yes, I agree also something was wrong with all the steel. The re bars no Epoxy was used that close to salt water. In Virginia it's mandatory. I still not sure the contractor was capable of build this structure.
Enjoy your flying
Csbinet Maker 100% right, the broken rubble also didn't look as "sharp" as I would expect. I am all but certain the problem was in the pour. A delay in the pour is like taking away all the shear strength between those to layers. Once those chains start getting long, it's too late to put more on top. Going off his 187Mpa (13000psi) number at the start of the video, I can't imagine a continous(or close to it) pour of 60 trucks going off without a hitch.
Jimmy's Tractor how sharp should the concrete look? 😑
Ceasar Augustus lol, I know. It just looked like dough balls in some areas. I haven't seen much, but I remember when Tampa stadium was taken down and it looked more like chunks of granite
looks funny to me as well, almost looks like the aggregate sheared as well. Some of the photos look dead smooth.
Al S thought he was just giving me a hard time. You can leave that mixer running all day and you have a drum full of concrete balls. I just think it would be next to impossible to pour 600yds of concrete in a complex form like that without having a controlled environment.