I think it was insane that they were doing any sort of tensioning or structural adjustment without shutting down traffic as a matter of standard policy. Seems criminally negligent. Also I think it was a shame nobody stood up when I guarantee there were at least a few people on the construction site that knew exactly how bad the implications were to the cracking and damage they saw, but instead took a "cross my fingers and keep quiet" approach... likely because they knew the massive financial implications of what the truth was
We are well into the death of science/engineering, victims to political/social schemers who have hijacked most of the key processes. This could have been a relatively simple and inexpensive project but instead became a nightmare because the primary goals of its concept and execution were to meet sociopolitical aspirations, generate press-paganda, and to harvest the maximum amount of Federal $$$. As much as possible, the goal here was to avoid tried-and-true engineering truths and venture off into the fringes of fabrication and design expertise. "Ordinary" designs come with a wealth of well-proven data on the safe envelope of constraints to enjoy safety and acceptable serviceability. Once you strike out on your own, then you had better be good enough to anticipate every possible mode of failure and to understand everything going on with external loads. internal forces and reactions, and all the materials and methods in play. In this case, the concept, design, and construction was not very good at anything but capturing lots of taxpayer $$$. More than 40 years ago, another pedestrian bridge was built in Florida for school foot traffic. It was fabricated, mostly of steel, quickly at a reasonable cost and has served for more years than the number of days the FIU bridge stood, with minimal maintenance and maximum utility. This older bridge also dropped into place with less disruption to existing traffic than the FIU monster, and with additional cantilevered decking on each side and a more "organic" color scheme could have served the same "social" functions if desired. But FIU could not have looted the US taxpayer to such an extent with this steel design. www.google.com/maps/@30.3599954,-87.1676404,3a,37.5y,341.76h,91.81t/data=!3m7!1e1!3m5!1sZHlYz3AslRWyF0CXwKsxwg!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3DZHlYz3AslRWyF0CXwKsxwg%26cb_client%3Dmaps_sv.tactile.gps%26w%3D203%26h%3D100%26yaw%3D348.88428%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192?entry=ttu
just from the photos 4 days before no one should have been on the bridge or under it, especially 5 hours before it fell and messing with tension witch caused it to finally fail (lots of cracks and them some of them cracks turned into defection /rotation cracks)
In Chicago, an ENGINEER was on the L going to work. As his train came out of the subway to meet with an elevated line, he noticed structural defects in the elevated substructure. From the news reports I recall, the CTA was on top of it effectuating repairs immediately. Thanks to the engineers in our lives!
@sapienspace8814 Agreed. "Go fever" is also referred to as "get-there-itis" in aviation and has resulted in countless deaths. I know of a forensic engineer who's lied about their degrees and serves as an expert witness in court cases. I don't think their employer knows. It's scary :(
Facinating analysis unbelievable that the engineers seeing these cracks didn't suggest that this bridge get supported immediately to protect the traffic below and their Workers. Even worse when they decide to put the support structure in tension without shoring up the bridge is absolutely insane!
The construction company was trying to put the stressing cables under more tension to carry more load than to put the diagonal in tension. In prestress-concrete design, all tension load is carried by the reinforcing steel and NONE by the concrete. The concrete is there to hold the steel in the proper position. This design required the reinforcing to be post-tensioned or tensioned after casting instead of tensioned before casting in concrete.
I've been on the other side of this, engineering structures for public works, and there is a major status quo bias in these situations- "well, cracks have never been a big deal before". I've worked alongside plenty of engineers who I think would have done the same things FIGG did, sadly. It's the same kind of group think that led the Challenger disaster, everyone thinks that, if this was a big deal, then someone else at this table would really be freaking out about it . NTSB investigation of this disaster also found that everyone had been thinking, "if it's truly dangerous... then it's not my problem. FIGG stamped the plans. it's on them. If they're willing to take the risk, and say it's safe, I'm not going to inject myself in between them and the client. " in reality, safety is everyone's responsibility. Everyone at the table had the power to instantly stop work as result of a safety concern. They chose not to. If you're not serious about safety and quality, it's easy to ignore stuff, assume it's not a big deal, etc. You get wrapped up in keeping costs down, sticking to the schedule, soothing the client, managing construction issues, etc. These other concerns end up swamping the real mission: designing a safe structure.
Someone was seeing dollar signs. Closing the road and shoring would have put a lot of pressure and costs on them. They figured it was better to roll the dice. This time they shot craps and people died. If it wasn’t more dangerous, they should have moved it back to the side of the road. At least then it would have left the road open and still removed danger to the public. If I were an engineer associated with that, I would have been crapping bricks every minute cars were underneath it. I would have been a wreck by the time that last meeting started.
That should be a requirement for all bridge designers. There is a precedent. I've forgotten the exact details but I think it was a king who decreed that the first people to use a bridge would be the designers and builders.
@@Starchface the precedent I heard was that the builder/designer was required to stand underneath an arch as the support scaffolding was being removed. 🙂
Supposedly, in Roman times, the people who built a bridge were made to stand under it as soldiers passed over, to test that it's solid. Seems like a good idea...
When my dad retired from his engineering firm, their clients asked if he would be consulting as an independent contractor. He said he had considered that. His firms customers were already lining up to contract him to oversee their projects done 6 months to 2 years down the line because the engineers they hired to replace him and his firm didn't seem to know what they were doing and things were getting schetchy. He oversaw the projects and reported back to his customers what they already knew - the new engineers didn't know enough or had enough experience to be doing the jobs for which they were hired. He would improve their plans and oversee the construction for which his customers were delighted. He made a nice income that way until he decided to retire for good. That frightened me considerably for the future.
The universities provide basic theory. Exams for PE licenses test what the universities teach, and require a minimum of 5 yrs working under a PE. Applying the engineering theory to real world design requires a lot of years of experience which is acquired on the job working with more experienced engineers.
A lot of the designs on the bridge were from females that had been hired. There is always a nagging suspicion in my brain concerning female graduates with the "wokeism" so prevalent in today's world. Did they have the proper accreditation for the job or were they given the job because the were socially acceptable!? It seams today, the most qualified individual is not hired and instead an individual is hired based on social requirements which are deemed to be of greater importance, and these are the consequences!!!
The eternal struggle between Architects and Engineers. The Army taught me to Keep It Simple for Stupid. I learned Allowable Stress Design(ASD) in the early 1970s. In the 1980s I was told to use LFRD. When comparing bridge stringer designs, I found LFRD to be about 25% weaker than ASD. I stayed with ASD. In the 1990s foreign steel started coming into the US. I avoided it because a fellow Army Engineer Officer from Hawaii warned me about it when we were called up for Desert Storm. In 2005, I saw a case where chinesium was only 1/6 the tensile strength that it was supposed to be. Good video. Good Luck, Rick
Regarding chinesium steel. In the late 90's offshore, we were directed to return-to-shorebase, any lifting shackles that were not stamped, "USA" because of several failures. We were also directed that only USA made cables and shackles were to be purchased, henceforth. We sent a lot of metal back to the beach for disposal. Saving money by buying the cheap sh!t ended up costing a fortune. We should have stuck with the quality stuff from the beginning.
@@Quidisi Absolutely. I prefer cars, tractors, and trucks from the 1970s and 1980s because they are better built. I retired 13 years ago and am glad to be out of the bridge building business. Good Luck, Rick
@@richardross7219 But cars built today do have stronger steel in them, it's just thinner. Steel from cars is recycled into the steel that buildings are built from.
@@billj5645The thinner steel rots much faster than the older thicker steel. Many trucks' frames rot out in less than 8 years now. I never liked pushing the slenderness ratios either. Good Luck, Rick
This disaster just sickens me. All parties, owner, state, city, inspection, designer, contractor could have made a difference to protect the public and construction workers and they ALL failed completely. Superb video Jeff!
David Beck: “Anytime you want to mess something up in engineering, you get a whole bunch of people involved a little bit. This bridge is a prime example.”
Damn, that's brilliant! I'm just a programmer but that really summarizes my frustrations with the corporate style of software development instead of startup: far more people involved very minimally and no one actually responsible or fully aware of what's going on.
@@electrictroy2010 David Beck, a veteran New Hampshire engineer who independently analyzed FIGG’s bridge plans for the Miami Herald and reviewed the federal docket, said no one on the project team seemed to have a comprehensive overview of how the bridge was supposed to work. “No one designer had a full understanding and appreciation of the structure and mechanics of the main span,” Beck said. “No one from FIGG could see what was going wrong. And there was no follow-through on the quality control. No one was studying the cracks in a serious way. No one had the knowledge or took the initiative to understand the danger these cracks presented. “Anytime you want to mess something up in engineering, you get a whole bunch of people involved a little bit. This bridge is a prime example.” -- Miami Herald
Random dude on the internet, remember this like it was yesterday, got second degree PTSD hearing the interview at the time of the paramedics talking about their triage of the victims who survived the initial impact... On a positive note, channels like this one made me understand the complexity of modern bridge design and construction. Hindsight is 20/20 for all the comments saying xyz screwed up. We all need to learn from this.
I completely understand the tremendous amount of work doing these videos involves. Thank you for this work. I worked in construction, so it's a bit easier for me to follow. But if you save even one person from moving into living or working space that isn't sound, you have changed some lives for the better. Thank you for doing this.
Your opinion about the roughing is 100% correct. If that was the difference between a collapse or not, then the minimum factor of safety in the design was really a maximum factor of failure. - The fact that they went ahead with the re-tensioning job with all the crack and signs of structural failure shows that either deciders as to going forward with the job did not understand the physics of what they were doing or they did not give the signs of failure and it progression over time the importance it warranted likely due to their confidence in the design, which we know now was in error. Believe what you are seeing in the real world rather than what's on paper/computer model if they don't match.
On the federal jobs I was a contractor on, in addition to the usual "roughing" at cold joints, the on site inspectors required scrubbing away any latanence and flushing the surface clean before the next pour. The federal on site inspectors were always excellent. This bridge was designed for aesthetics, not function.
The fact that WJE, put their judgment forward that "Not Roughing" was the sole cause of the collapse is frightening in itself, that a major engineering firm could be so inept. I don't do civil but have done structural product development for 15 years. I do believe the shear at that node was miscalculated and that the column was trying to slide across the deck surface but being that the rebar was tied into the deck and the column meant that it couldn't slide. The cracks in the DECK are the smoking gun that the "Roughing" wasn't the issue and that the column was exerting forces on the deck, that the deck could not handle!!
I believe that the computer model they used for stress analysis was for steel construction where there is strength in tension and laterally... with concrete there is no strength in tension and the prestress steel load bearing characteristics are not the same as steel beams that offer lateral support as well. Reliance on computer models without a common sense overlay. also I notice that many if not most computer models tend not to include safety margins that also account for materials degradation with age... that is a complete unknowable in many situations I have been triple redundant in some cases where the cost of that was only a few thousand dollars compared to hundreds of millions of losses if it failed due to unforseen circumstances....
My grandfather used to say that there was book learning and there was real world learning. He also said that book learning need real world learning too which is why many industries have apprentices and journeymen.
After those cracks appeared, the project needed a crotchety, old contractor on the deck to say..."Cease work, round up all our shoring material." Shore it up first, then figure out those cracks. Signed, Crotchety, old, piling / foundation and general contractor.
this wasnt a lightweight aluminum wing they designed, with cutouts for wheel wells, fuel tanks, flaps, servomotors (etc) stressed to +/- 5Gs... it wasn't a ship stressed to deal with the possibility of huge waves... ...it wasnt even a highway bridge with dynamic loads or freezing/thawing contraction and expansion to control for... it was a mostly static _pedestrian_ bridge! 😅
The roughening should have been seen as a belt-and-suspenders feature. The safety factors used (not) were clearly inadequate. How this was overlooked during peer review in the design phase is one thing but the fact that this was still overlooked or minimized during forensic analysis is jaw dropping. Thanks for the detailed report. Very informative.
I’ve looked into this collapse in the past but never learned so much about it until this video. Thank you for such a detailed description of the failures.
Jeff - As a Structural Engineer I find your videos Excellent. You convey the technical for the non-technical quite well. Your conclusions are good, I can tell you were doing Engineering not requiring PE Licensing. If you were licensed you would be in the design office. Those web member to the deck connections were super full of steel, very hard to pour, it also changes the neutral axis, there is a factor 'n' that is the ratio of the steel E / concrete E. With 3 ksi concrete and Gr 60 bar n is 9, meaning you replace each square inch of steel wiht 9 square inch concrete. It adds lots of bending, raising the concrete's tension cracking.
Spider cracks are a tell-tale sign of lack of shear reinforcing. Great video. The connection was under designed. The roughening made zero difference. Its the inability of the end connections of member 11 to handle the load transfer.
those particular 'spider cracks' were one to two inches wide.... completely ludicrous. that music was a little too tough to face so even experienced engineers went into denial it seems....in this case it went to absolutely insane levels with jack hammering on top of the span with traffic allowed under it. I have seen the tendency in myself as well... pressing ahead when data is missing is always a mistake. and with one or two arrogant old timers (I am 83 myself) bellowing against anyone who 'nit picked' their project....pressure can blind a person. Over my own long career I have noticed that when I am absolutely and provably correct... I am calm.... . When I start getting jacked up or adamant there is always some aspect that I am missing ... a minor or major flaw in my thinking.
I tend to agree. If there are cracks everywhere, going in all directions and at both ends of the bridge, accompanied with serious spalling, it can't be just the lack of roughening on that one beam. Might have been a significant contributing factor but not the main cause.
My take about the failure in roughening is not that it caused the collapse, but it illustrates that multiple errors were occurring and nobody noticed or stood up to do something about it.
@@Phil_Scott Loved your response. Engineers are under a huge pressure to be right. You can have a career with 1 million critical design decisions, but just one mistake or omission can be deadly. Sometimes admitting to an omission is the right thing so it can be reviewed and fixed. We all need to check twice sometimes 3 times. These are complex structures. When you get a chance read about Engineer William LeMessurier's last minute redesign of the Citicorp Building structure in NY. Its an amazing story of recognizing an omission, admitting it, then making critical modifications at the last minute and accepting the wrath for the sake of safety.
Jeff, I listened to your comment that you reviewed thousands of pages of transcripts and hundreds of pages of engineering, designs and analysis. So you commented this was a very time intensive review and analysis. I agree. Good work.
Oddly this same company was hired to do a major road bridge in my town, large enough for ships to go under… fortunately they got canned, and another company took over and reengineered it, over a year delay but it’s almost done and safe
I love that you took a moment to explain certifications at around 4:30 in - and I also appreciate your explanation on how your certification(s) limit you but still provide you the experience and knowledge to explain these failures and collapses to us. I don't look forward to the disasters, but always look forward to your videos about them. Thank you again!
Great analysis of this issue! The guy that said there should be finger pointing, because everyone is partly to blame got it right! We have to change our system! The fact that the bridge was under designed to begin with, should have been picked up in the submittal process, not in a review after the fact, but in too many cases the AHJ will not check calculations to check the accuracy of submittals, they don't want to have liability! Then you have a company that was suppose to peer review, was deemed not qualified, but still allowed to do it! The system needs to be corrected!
This whole issue brings the reputation of FIU down as well for being a university where one goes to learn to build a bridge in the first place. Granted, they hired a firm to handle this. But the entire incident reflects on them, the bridge was being built to facilitate their students, the bridge had their name, the bridge was commissioned by them. I'm not saying they should carry some of the blame (that's already been decided in court) but it certainly will make people think twice about going there. Imagine having an engineering degree that says you know how to build bridges from a University that had it's OWN bridge collapse and killed 6 people.
It's all driven by marketing. There is an idea that the engineering is easy, anybody can do it, hire the company with the best marketing and don't worry if they have good engineers or not. But the engineering is not easy especially on an unconventional structure like this. Someone has to worry about how do the forces transfer, how do we build it, etc. For something of such importance as this it has to be double checked just as carefully by another company. And apparently someone has to sit down with the engineers actually doing the work and verify that they actually did the work. The marketing staff doesn't want to do this. The managers don't want to do this because they may not understand it either. If you build a more straightforward building that doesn't have these unconventional problems to overcome then maybe the system will work better. When you start building things out of the norm that's when you have higher chances of problems. Look at all of the buildings around the world being built now with angled columns. This is unconventional construction, it puts forces in places where we traditionally don't design for them. The first one of those that is designed by a company focused more on marketing than engineering will likely have serious problems. Jeff has a lot of experience with Champlain Towers. The evidence on the structural drawings of that building are that the engineer doing the work only understood reinforced concrete design about half way, the half that he didn't understand very well caused a collapse. His managers should have seen the problems and corrected them but they may have been more focused on marketing. But that is a relatively straightforward building and it took other factors beyond the engineering to compound the problem and cause a collapse. I knew a firm involved in designing schools. They got tired of paying engineering fees so they hired a few inexperienced engineers to work in their office. The next large project they built had serious problems and had to be shut down for a year for costly repairs. Don't ever think that the engineering doesn't matter.
@@Cowcow211 Wow. I suppose I could see a few people saying this, but I ultimately disagree with intense finger pointing towards FIU. FIU’s property faculty team is not going to consult with the teachers/students to give their opinions on such a project (especially if they are not be licensed or certified to do so), therefore that excludes that element. As you said, the work was performed by third party contracted firms that were not involved in usual FIU operations. Like when any other individual or business hires contractors to perform work, if the individual/business is not skilled or licensed to perform said work, then they have to put their trust in third party engineers/builders to follow through with it correctly and FIU did so here. You’re taking a shotgun approach with blame in this situation. If for some reason an engineering firm refuses to hire a graduate from FIU because of this collapse - then that graduate should be grateful they dodged a workplace management nightmare, as anyone worth their salt would know there was no relation between the students, their teachers, the third party contractors, and the construction/collapse of this bridge.
Jeff, thank you for your detailed report. This bridge doesn't look like such a big project, as bridges go. I'm surprised they had sooo many problems. At least they used good concrete and good rebar.
Huge respect to you for doing all those hours of tedious research to bring us this information! It's always a serious issue when blame gets shifted more than the failing structure itself.
Arrogance is absolutely the worst trait any engineering firm can possess. Like many building architects do this was designed to be totally different from any bridge built before. They claimed huge bragging rights even as the dust was rising from the collapse. Humility would have been a much better trait but then they would not have had this stunning bridge to brag about......until after it failed.
Allocation of contracts to minority companies (set asides) strictly for quota purposes and NOT "Best Practice" or "Most Qualified". Happens all the time.@@StarkRG
I love the extreme attention to detail you put in and you break down the terminology used in laymen's terms , the 50 mins flew by it was like i was getting a great lecture in class!
Jeff, all I can say is WOW. Superbly researched and narrated on your part. It makes one wish you had been part of the design team! I just found you and subscribed immediately. Well done! Looking forward to perusing your other videos. Thank you for what you do, and I hope you feel appreciated for all your efforts here. All good wishes!
Holy smoke, I'm surprised that thing made out of the yard without falling to pieces! Pity it didn't. Excellent work as ever Jeff, many thanks for posting.
Thanks for taking the time and effort to make this incredible video, I had no idea of the volume of material you had to go through to put it all together until you showed us at the end!
I'll admit I'm here because of the recent disaster in Baltimore. But I can't get enough of this Channel. Bridges are just fascinating and scary at the same time.
Never knew the warning signs were that bad. I don't think you need an engineering degree to see something wasn't right. The newly constructed flyover bridge in Downtown Orlando started showing signs of hairline cracks around the same time this bridge collapsed. They determined the cracks were nothing of concern, but this video makes me wonder if there was more than they were letting on to and I wonder if anyone has followed up over the years to see if the cracks have progressed since they were originally discovered.
You are 100% correct. Any layman seeing all those cracks days and weeks before the collapse would have said something. Did the City engineer EVER go on the bridge to view these cracks? Did ANYONE suggest a second opinion? I'm sorry Denny Pate does not know the seriousness of a crack from a hole in the ground.
I found you and your TH-cam channel after the apartment collapse -- and now I come to see what you have to say after any problem. Thank you for your professional expertise.
I see that YT made you remove all of the video of the bridge right after the collapse. I’m glad your original video is still to watch, it humanizes this whole situation.
Thanks! Yes, once I did that they removed the demonetization of my video. Very frustrating because there are hundreds of videos on this bridge collapse that had all those witness videos of the aftermath
‘Cracked like hell’ phrase in the email was very scary to read. Normal structural design has a factor of safety (redundancy). Having a non-redundant design removes this factor of safety.
VERY very good video!! Thanks for the information about the bridge - I had no idea about any of the behind-the-scenes info regarding the bridge what-so-ever, until now!
Thanks for taking all the time to make this video, Jeff. I love engineering, and sadly a lot of engineering learning is done through failed engineering. I am astonished that this failure was allowed. We all know that hindsight is 20-20 and it's easy to say what should've been done. It's way harder to be that person in the meeting to stand up and say "this is NOT right and we have to close the road immediately." Especially given the faulty numbers the company was using in the calculations to say "yeah, its fine...la la la no problem here..." So yeah, I guess the lesson in this one is to make sure you have all calculations reviewed by competent engineers. And use this lesson to bolster your position if you have to be the one to stand up in the meeting to say "STOP!!!"
It can be very costly to stop a contractor mid construction. The city and their inspectors should have made the call when the engineer failed to call a time out. A second opinion from the state structural engineers should have closed the highway and stopped tendon stressing over live traffic. Too many failed chances to stop this from being a deadly failure.
I lived in Sweetwater, about two blocks away from the bridge. I rode bike to get around at the time, and was literally stepping out the door to cross under the bridge when I got a bunch of frantic phone calls from friends asking if I was okay. That's how I found out the bridge had collapsed - had I left 2-3 minutes earlier, I'd of been under that bridge when it came down. I count my blessings every day. That was a horrible, horrible day. We all just stood around dumbfounded. There was no way to rescue anyone. Thank you for covering this @jeffostroff
Thanks Jeff for another outstanding video! I discovered you with your Ocean Titan disintegration series, and look forward to each of your engineering video releases. I agree with the comments about your voice -- so calming and soothing -- but, even more important than that, your analysis, explanations and analogies are top-notch. I appreciate the meticulous work you put into this and other videos. I'm sure you enjoy it or you wouldn't do it, but you also deserve recognition, as well as any revenue you glean from us viewing your high-quality output. Thanks again. Looking forward to the next one!
Great video. Of all the many and varied WTF moments in the design and construction of this bridge the part that most baffles me is that they looked at how this bridge was literally coming apart day by day and never realized that they had a major problem on their hands. It’s freaking obvious and should have been screaming at the guys that do this for a living that there was a major problem.
@@rwood1995 I do not keep track of the days it was up, as you know, I was under that bridge in traffic for the short time it was up. Something I want to forget.
Thank you Jeff. It was overconfidence and a lack of safety that resulted in a failure and loss of life. With the presence of structural cracks the project should’ve immediately been shut down and shoring installed. This would’ve resulted in a plan to remove the failing pedestrian bridge Again, thank you so very very much for your work.
totally agree with you - roughening a surface cannot be the key to success or failure... the factor of safety should have an order of magnitude greater impact the roughening (or lack of) for any particular connection surface
Thanks for the great work Jeff. Sadly these kinds of things happen too often. Much of it is due to complexity and the lack of appreciation of risk. But some of it is incentivized with $$$. I'm an electrical engineer by degree but have spent most of my career doing software engineering. When I was a student at the University of Michigan in Ann Arbor, the Engineering School was migrating from central campus to north campus. Two new buildings were erected while I was a student: the Dow Chemical building, and the EECS (Electrical Engineering and Computer Science) building. The Dow Chemical building housed the 'library' (at the time it was really just a computer lab). It also housed the civil engineering faculty offices, something to note for later... When the Dow building was opened, I had a materials science class and a mechanical engineering class in the building. I always used the stairs instead of the elevators. On my first walk up the west stairwell, I noticed a 1/8" crack from the ground floor slab all the way to the top floor ceiling. Concrete blocks. Some of the crack followed the mortar lines, some of it was through the concrete blocks. No idea what the rebar was inside. By the end of the second term, the crack was 1/4". I decided to ask one of the civil engineering professors about the crack. He blew me off. Of course it wasn't his job. But I come from a family of construction on my father's side, and here in Michigan we have a variety of soil types (thanks to the glaciers way back when). But much of it, including this spot, is mostly red clay. Which tends to hold water forever. The consequence is that we have fairly extreme frost heave in some areas. I've seen what it can do to residential structures (rip the deck off your house, sever your water and sewer lines from shear, crack up your foundation, etc.). This building was built into the side of a hill of red clay. This concerned me, but I was just a student without a real voice. Years after I graduated, part of the library in this building collapsed. Fortunately it happened during a break and no one was hurt. The irony: it housed the civil engineering faculty offices. What tends to bother me most about these types of issues is the willful ignorance. Lives lost in the name of pride and money. Shortsightedness. I am certain I wasn't the only one who noticed cracks growing from the footers to the top floor in a brand new building. Nor the only one who knew how university construction contracts were structured (finishing early or on time is incentivized with sigificant money); they're public. I'm assuming FIU had similar incentives? i.e. there were real $$$ consequences if the bridge was not completed on time or early? Not even accounting for the cost of proper remediation, I assuming any delay was going to cost all of the contractors a chunk of the money they were expecting? I hope all of the PEs involved lost their licenses. While they don't deserve all of the blame, we as engineers often wind up with it. If someone directs me to compromise safety in the name of their bottom line, I exit. We have to hold the line because those above us often will not. 🙁
I've spent the last 20 plus years of my working career as the guy who's job it is to operate the hydraulic equipment used to test and post tension all types of anchoring systems. If I was asked to post tension tendons on a structure that was obviously cracked and compromised I would just simply refuse. I call into question the knowledge / experience / judgment of the person responsible for that work on this bridge.
Excellent report and analysis. So many critical issues here. As a retired engineer from nuclear power plant civil and structural, I have seen many commercial contractors / engineering firms rejected for plant auxiliary structures such as office buildings and warehouses. Commercial construction is a completely different mindset.
This was simply a Superb Review and Diagnosis of the Bridge Collapse. The underlying drama that occured is also notable however I appreciate the Engineering Content the most. As a construction worker with an Engineering background it is very interesting to learn about these types of failures. I watch for issues such as these on Construction Projects and have spotted some minor design errors myself. Great Video :D
I'm a domestic plumber/gas engineer. The job in the photo at 23:20 was so bad I thought I was looking DOWN at the floor and the pipes were horizontal! OMG there are some clowns out there. Edit: and the fact that someone says scoring the concrete would have prevented the collapse! Total clown world.
Thanks for helping non engineers to understand. Very complex, you lost me a couple times but you brought me back. New love for structural engineering. I’ve watched all the Champlain Towers videos
If the concrete had been poured or cast continually to the tops of the vertical and diagonal members there would not have been a "cold" joint to worry about. It would not have prevented the ultimate failure in the end though. Designing without redundancy was the fatal flaw of this design. Have you looked at the I-40 bridge crack in the lower or bottom member of the bridge over the Mississippi River at Memphis, TN? This bridge, of 2 arched trusses, stayed up under traffic, despite one of the bottom members cracked enough apart to be able to insert a hand into the crack. I find it miraculous the span stayed up at all.
@@jeffostroff because that would have required a very elaborate or impossible forming setup.also NTSB said the joint had way too little rebar in the first place . it could not resist the shear . it needed more than double what they used
The I-40 would have gone into the river if that tie member had cracked all the way through. The tie member was still under a very significant load even though severely cracked more than 50% through. They got extremely lucky on that one; the only reason the member didn't fracture all the way across was because of how the top and side plates were all welded together; one of the weld lines turned the fracture crack to run along the length of the weld (for more than ten feet), rather than continue into and cut across the remaining inboard plate. So it turns out that sometimes the "weak points" like along this weld can turn into useful features!
It should have been slip formed for the vertical members. No cold joints. Of course it also is more expensive, and prep and planning is more intensive and far fewer companies are available to bid.
Great video Jeff. In my opinion, the most important image to explain the failure in detail is at 26:46 of the video. For stability, the design would require the floor deck reinforcement to balance the kick out force of diagonal member 11. But the crack pattern shown on the image indicates that the node 11 and 12 were not reinforced properly to transfer the force to the floor deck reinforcement. Roughening the surface would not have changed the situation. In my opinion, the engineer of record should have never allowed the recess for the drain pipe on the underside of the bridge in line with the truss. Instead, there should have been a highly concentrated amount of reinforcing steel (post tensioned and mild) to tie the bottom of the truss to the diagonals completing the load path in a more straight forward path.
Yes, the bottom web (deck) had post-tensioned tendons spaced across the entire deck width instead of converging at the base of the outer node diagonals. Totally puzzled me how they could rely on rebar alone to transfer all that shear to the center. Embedding a horizontal full-width steel truss in the lower web (at each end) would have made some sense, but not rebar alone.
Also, the upper web was in tension and had severe bending forces in the span above the outer diagonal #11. But the post tension was not yet applied. This tension and bending was excessive due to the failure in the lower web. A spontaneous crack in the ceiling next to the #11 column in the upper web could have acted like a blasting cap inside dynamite.
Thank you very much for your very impressive video from Germany! As an elderly, now retired civil engineer I very much appreciate this work. Well done!
I keep asking myself, when simple STEEL double truss bridges work for heavy trucks and trains, why we have to spend $11M on a funky concrete PEDESTRIAN bridge with "meaning." The meaning here is getting student across a busy highway safely. Take a steel double truss bridge, then add meaning with decorative touches affixed to the steel. Waste of money and lives.
The designers want to create a monument to themselves. Actually it was probably competition- if you have multiple companies trying for the contract then the company with the prettiest design has the best chance of getting votes from the board of directors. There is tremendous competition between engineering companies so companies will employ a lot of marketing people to get the edge. I once worked with a guy who asked if we were working for an engineering company or a secretarial company.
Thanks Jeff for another outstanding video!! I get involved in a number construction defects and failures so can appreciate all the work this took. I have one relatively simple job ($10 million size) with three parties to the litigation where there are over 100,000 pages of documents. On a job this complicated with that long list of depositions and documents it is a lot of work!! Cannot fathom why anyone seeing these FIU bridge cracks in photograph or in person thought this bridge was OK. That they just want to "seal up the cracks" and move forward is a hard-to-believe approach.
Thanks, LOL love your name too built Ford tough, did you see me? Mention and the previous video about the church collapse. How the two towers on either side of the steeple were built ford tough , and I even showed the ford logos on them
Many important legal cases have hinged on whether the word "shall", "should", "must", "may" are used. Years ago, there was a huge (kept very quiet) case where the wrong word was chosen in Medicare contracts. Kids, learn your grammar very very well for these words. I suggest looking in some law books first if you ever need these words in a verbal or written contract.
Next video?? A hangar collapse on Wednesday at Boise Airport in Idaho claimed the lives of three people and injured nine others. The 39,000-sq-ft hangar was under construction for Jackson Jet Center. The mishap is now under investigation by the Occupational Safety and Health Administration (OSHA).
Hi there 👋 I'm new to your channel & gotta tell you. ALL of your hard work, hundreds of hours (probably thousands), & absolute dedication to your craft was TOTALLY WORTH IT!! Thoroughly enjoyed this video! Love from Australia 💓
Extremely well done... An engineer's deep understanding of all issues AND very well explained and presented. THAT'S RARE. It shows that this video took weeks to to put together. Even I could understand most of it. And I am not engineer... lol... Watched from beginning to end with lots of j & l key hits. My only suggestion, and I might be wrong on this point, is to keep 11 on the right side of the screen at all times.
Don't know what aashto says, but aci says your resistance against sliding is 40% lower when you don't roughen the surface. that's a big difference. also, roughening concrete between pours is a standard construction practice. contractor should have done that. it might be that the design was still an issue but this could have definitely contributed. μ: Coefficient of friction as the following: 1.4 Concrete placed monolithically. 1.0 Concrete placed against hardened concrete with surface intentionally roughened. 0.6 Concrete placed against hardened concrete not intentionally roughened.
it wouldn't have prevented the bridge it self failing (roughened is not going to save a construction that is 92% below spec) it won't change the outcome no matter how much figg paid the 3rd party to make it look like the whole structure been reliant on roughening still gets an upvote because it's still valid information
I suspect there just wasn't enough focus on this required step while the concrete was fresh. A hand grinder or jack hammer might have solved the omission later on. However, if the construction workers couldn't roughen the deck surface due to obstructions, then the sloped cold joint should have been designed to be up inside the #11 column, but perpendicular to compression/thrust. Still, the deck itself was also failing badly in shear because the thrust / shear was not distributed by steel along the width of the deck. The deck needed an embedded post tensioned steel truss, and/or the deck tendons needed to converge on the #11-#12 node.
As I understood the NTSB report the primary cause was the structure design significantly lacked enough steel reinforcement to resist the sheer load where the member met the deck. I.E. more rebar coming out of the deck and into the supporting members. Of course roughening would have had some benefit. In the end, nobody had the fortitude to call the king naked...
@@steveo4749 That is correct but despite Jeff's discussion on steel bridges with 2 trusses it is difficult to build a large bridge that would resist loads with a major element removed. The Golden Gate Bridge for instance would completely fail if one of those cables broke.
@@billj5645 True. But those main cables are made up of many hundreds of smaller wires. After the original design, they knew corrosion inside the cable could still occur so they put a casing on the outside of the cable and then conditioned the air inside the cable to remove moisture. Structures that can fail in a controlled/observable way can be evacuated before a sudden collapse. Repair strategies can be identified before critical items are affected. This design was trash and had it been designed as a true cable stayed structure, it might have had a chance of survivability.
@@steveo4749 This FIU bridge did fail slowly, but nobody [in charge] panicked enough seeing the growing cracks. We need to empower even inspecting technicians to evacuate and close traffic.
Evidently, the "form follows function" concept was not in play on this project. Seemed more interested in the aesthetics' of the bridge than its' capacity/capability.
I'm engineering disabled and even I was able to keep up and understand. Well done presenting the facts and articulating them in such a way as to be understood. 👍
The fact that they allowed traffic to use the road while working on the bridge overhead just completely befuddled me. 🤯 Who thought THAT was a safe idea?? You not only have drivers going under the bridge, you also have construction workers on the bridge with traffic below. That's endangering two groups of people. 🙄 That's completely unacceptable!
Your comment reminded me of a tragic incident in Quebec. A concrete bridge was slowly disintegrating, dropping concrete chunks onto the road. One of the people driving under the bridge called 911, reported the bridge. A police officer arrived, looked at the bridge and asked for an structural engineer to show up to take a look. The officer in question didn't close the bridge, so when it finally gave out, it crushed a vehicle under it. Everyone was pointing at the cop as the final reason the people died. Although the engineers determined that the bridge was improperly built/designed (corner cutting by criminal organization which "owned" the construction firm)... but it did last for over 20 years before it experienced rapid disintegration.
31:54 tensioning means to add tension to the posttensioning rods which increases compression on the member. It's not a good idea but they were putting additional compression on the member not putting it in tension.
I believe that they had to de-tension the steel rod first to then re-tension it. Thus putting the concrete diagonal into tension? At least that is how I understand it.
@RBodge1234 I agree they released the tension after the bridge was set in place. The posttensioning was probably only needed when it was sitting on the transporters. Once it was on the pier that member would always be in compression regardless of how much tension was in the rods. Posttensioning is like a clamp. Retensioning would only add more compression internally to the concrete. That's partly why the decision to add tension should have set off alarm bells. The cracking had to be related to something else.
I am a structural Engineer and did a bunch of calculations on the bridge after the collapse. This video came across my desk and I just have a few comments. -Two trusses are generally not more redundant than one truss. The failure of the one member on one of the two trusses would cause a collapse. There is no alternate load path on the damaged truss. Concrete also tends to be more forgiving than steel. There are proportionally many more failed steel bridges than concrete bridges. -Contrary to the investigator's comments, there was significant redundancy in this design. The proof is in the pudding. The bridge failed slowly and this is a sign of redundancy and ductility. These were not brittle elements. Otherwise the design would not have shown such significant signs of failure before the collapse. It is really hard to define redundancy clearly in a code. Concrete structures (these are actually a combination of steel and concrete) generally have lots of redundancy with a few notable failure modes. The number and repeated members were not redundant but multiple rebar had to fail to cause a collapse. It is the large number of rebar that produces the redundancy. -The two pipes is a bit of red herring. It was the interface between the deck and the underside of member #11 that was the failure point. You would get the same result with or without the white pipes. You can include the pipes and justify the capacity to code. -At 21:53. This is really not a bending failure. There analysis showed it was not a bending failure since it was not a bending failure. The cracks were from the backside of #12 pushing Northward. Adding the extra pads really didn't required a peer review (IMO) since you are increasing the structural capacity. You are only adding to the safety even though the pads were irrelevant to the issue. However, retensioning the PT was definitely a change in design. -#11 was actually not buckling. The cracks were due to differential movement at the base. If you do the calculations on #11, it was strong enough but the shear friction at the joints was not strong enough. -#2 is bigger than #11 since #2 is at a lower angle, it has more load in it and it is longer. The longer and more heavily loaded a compression element is, the bigger it has to be to prevent buckling. -I suspect Figg understood that there was an issue before the collapse. In there presentation they went over the shear friction calculations (how the horizontal shear is transferred from the #11 member to the deck). They left out the load transfer from #11 to the deck at the pour joint between the deck and the member. This is the most obvious point of weakness. I can't remember the exact wording but Denny Pate indicated the real issue was connecting the #11/12 joint back to the #9/10 joint which is an indication he new what was happening. This was a very incriminating comment. He believed that was the way to fix the issue rather than adding vertical support at the #10/9 joint. They didn't want to block the road by adding shoring (it defeated the purpose ABC). -At 32:38 you got the PT order incorrect. The joint cracked worse after the PT was released. They were putting the PT back into the joint and not releasing it. The PT was suppose to be released after the move which was done. Adding the PT back into the member was the change in the design. Putting the PT back into the design increased the clamping force and shear resistance. However, putting the PT back on the member increased the shear force more than it increase the resistance. It was a pretty fundamental mistake. -FYI, putting PT into a concrete member does not put compression into the member as a whole. It adds compression to the concrete portion of the section. It is a really important concept to understand if you are working with PT. The member force is the tension (a negative force) in the rods added to the compression (a positive force) in the concrete. -Figg was not really confused about the factors or least there is no evidence for that. The project specification required them to use LRFD in intermediate stages of construction. In some projects, LFRD is only used at the final configuration of the project but if the public is at risk, you should use LFRD at all the stages. Figg did not use LFRD in the intermediate stages but they would have for the final configuration (or at least in the areas where there was no design errors). -Those 1/4" roughened surfaces are critical to the design and other building designs. It substantially increases the shear friction capacity. It is common practice to do this on buildings and bridges so it is a general specification rather than in bold. In general, you don't put thing in bold because most issues on a structural design are critical. I personally ask (specify) contractors to roughen the surface and then assume in the calculations that it was not roughened (I add more steel to make up the difference). There are some cases you can't make that assumption but then you just really have to make sure during the construction that they roughened the surface. This is done all the time for things like shear walls at floor slab connections or where one concrete beam interfaces another concrete beam. -The reason WJE and the investigating engineers don't agree on the significance of the roughening was because WJE used testing and the investigators used calculations. By calculation, it would not have made a difference even though you get a substantial boost in capacity with roughening. However, you often get substantially more capacity by testing than you do by calculation. Either way, that does not alleviate Figg from responsibility since Figg's only means of evaluation was through calculation and on top of that they should have use LFRD factors which they did not do. -Louis B. did not meet the requirement for the project to do the concept review. This is not the same as saying they were not qualified. -IMO, concept engineers should be engaged through the client and not the design engineer but this is still common practice. -I would not say from the pictures that the new design is conventional. There are only cables coming from one side of the pier. This is a complex design. However, the picture may not be the final appearance of the design. -The fundamental technical issue was there was way too little rebar crossing the deck into member #11 (and at all the joints). They failed to check the shear friction at these horizontal joints. -The cable stays actually would have provided significant redundancy and help reduce the feeling of bounce on the bridge. Figg noted the reduction of bounce in the design brief but not the redundancy. Many people have said they were just for appearance but that is not quite true. There are redundancy and factors that I put into design that I do not explicitly express. -There are actually good reasons to make the bridge out of concrete. Many people gave the choice of concrete a bad wrap but I tend to disagree. It was the design flaw in the end that was the problem and not the material choice.
Good points made in the detailed rebuttal, especially the point that the one engineering company may have lacked formal certification but that in no way automatically means they were incompetent. In point of fact, could the bridge not have been theoretically equally strong employing some design elements making a considerably lighter weight structure. That seems a heavy girder for the length and expected weight load. Were they figuring it would be packed with people at some point, with everyone stamping their feet in unison?
It seems to me that the CEI or Louis B should have been required to give an opinion (to the owner and/or FDOT) on the question of whether to close traffic because of the cracking. Figg was conflicted and should not have had the final say like they appear to have been given in that pre-collapse morning meeting.
@@davedoe6445 There needed to be an independent design review for the the tightening of the PT rods. Most contractors would have also gotten a second opinion given the extent of the cracks. The PT retightening was a change to the design on the drawings. Initially it seems like LB would have been the logical choice at the time but they missed the issue during the independent review. Since they missed the issue, it is actually better to bring in another engineer. The inspection engineer/firm is more responsible to point out the issue which they did do. The inspection engineers are not necessarily design engineers and not independent. The processes where I practice are different and actually less stringent. However, Fligg, the contractor, and LB skirted the rules. More importantly, Fligg likely knew the nature of the issue and put the project ahead of public safety. You can never do this as a professional engineer.
That was in 2018? Wow... I should've started having kids when I was much younger because one day they were born and now they're all in college and it happened in the blink of an eye. Not for them but for me.
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I think it was insane that they were doing any sort of tensioning or structural adjustment without shutting down traffic as a matter of standard policy. Seems criminally negligent. Also I think it was a shame nobody stood up when I guarantee there were at least a few people on the construction site that knew exactly how bad the implications were to the cracking and damage they saw, but instead took a "cross my fingers and keep quiet" approach... likely because they knew the massive financial implications of what the truth was
Yes, and it was even more on saying that they were even doing retentioning. 'cause that was the worst case possible thing you could do
We are well into the death of science/engineering, victims to political/social schemers who have hijacked most of the key processes. This could have been a relatively simple and inexpensive project but instead became a nightmare because the primary goals of its concept and execution were to meet sociopolitical aspirations, generate press-paganda, and to harvest the maximum amount of Federal $$$. As much as possible, the goal here was to avoid tried-and-true engineering truths and venture off into the fringes of fabrication and design expertise. "Ordinary" designs come with a wealth of well-proven data on the safe envelope of constraints to enjoy safety and acceptable serviceability. Once you strike out on your own, then you had better be good enough to anticipate every possible mode of failure and to understand everything going on with external loads. internal forces and reactions, and all the materials and methods in play. In this case, the concept, design, and construction was not very good at anything but capturing lots of taxpayer $$$.
More than 40 years ago, another pedestrian bridge was built in Florida for school foot traffic. It was fabricated, mostly of steel, quickly at a reasonable cost and has served for more years than the number of days the FIU bridge stood, with minimal maintenance and maximum utility. This older bridge also dropped into place with less disruption to existing traffic than the FIU monster, and with additional cantilevered decking on each side and a more "organic" color scheme could have served the same "social" functions if desired. But FIU could not have looted the US taxpayer to such an extent with this steel design.
www.google.com/maps/@30.3599954,-87.1676404,3a,37.5y,341.76h,91.81t/data=!3m7!1e1!3m5!1sZHlYz3AslRWyF0CXwKsxwg!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fpanoid%3DZHlYz3AslRWyF0CXwKsxwg%26cb_client%3Dmaps_sv.tactile.gps%26w%3D203%26h%3D100%26yaw%3D348.88428%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192?entry=ttu
just from the photos 4 days before no one should have been on the bridge or under it, especially 5 hours before it fell and messing with tension witch caused it to finally fail (lots of cracks and them some of them cracks turned into defection /rotation cracks)
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So this bridge failed because “wahmen”?
WTAF?
In Chicago, an ENGINEER was on the L going to work. As his train came out of the subway to meet with an elevated line, he noticed structural defects in the elevated substructure. From the news reports I recall, the CTA was on top of it effectuating repairs immediately. Thanks to the engineers in our lives!
@sapienspace8814 Agreed. "Go fever" is also referred to as "get-there-itis" in aviation and has resulted in countless deaths. I know of a forensic engineer who's lied about their degrees and serves as an expert witness in court cases. I don't think their employer knows. It's scary :(
@SapienSpaceit used to be the person driving the train.😅
Facinating analysis unbelievable that the engineers seeing these cracks didn't suggest that this bridge get supported immediately to protect the traffic below and their Workers. Even worse when they decide to put the support structure in tension without shoring up the bridge is absolutely insane!
The construction company was trying to put the stressing cables under more tension to carry more load than to put the diagonal in tension. In prestress-concrete design, all tension load is carried by the reinforcing steel and NONE by the concrete. The concrete is there to hold the steel in the proper position. This design required the reinforcing to be post-tensioned or tensioned after casting instead of tensioned before casting in concrete.
I've been on the other side of this, engineering structures for public works, and there is a major status quo bias in these situations- "well, cracks have never been a big deal before". I've worked alongside plenty of engineers who I think would have done the same things FIGG did, sadly. It's the same kind of group think that led the Challenger disaster, everyone thinks that, if this was a big deal, then someone else at this table would really be freaking out about it .
NTSB investigation of this disaster also found that everyone had been thinking, "if it's truly dangerous... then it's not my problem. FIGG stamped the plans. it's on them. If they're willing to take the risk, and say it's safe, I'm not going to inject myself in between them and the client. " in reality, safety is everyone's responsibility. Everyone at the table had the power to instantly stop work as result of a safety concern. They chose not to.
If you're not serious about safety and quality, it's easy to ignore stuff, assume it's not a big deal, etc. You get wrapped up in keeping costs down, sticking to the schedule, soothing the client, managing construction issues, etc. These other concerns end up swamping the real mission: designing a safe structure.
Someone was seeing dollar signs. Closing the road and shoring would have put a lot of pressure and costs on them. They figured it was better to roll the dice. This time they shot craps and people died.
If it wasn’t more dangerous, they should have moved it back to the side of the road. At least then it would have left the road open and still removed danger to the public. If I were an engineer associated with that, I would have been crapping bricks every minute cars were underneath it. I would have been a wreck by the time that last meeting started.
Must have been a Chinese contractor. They are used to their tofu dredg projects.
Maybe they should have held their meeting in a trailer under the bridge.
That should be a requirement for all bridge designers. There is a precedent. I've forgotten the exact details but I think it was a king who decreed that the first people to use a bridge would be the designers and builders.
Omg yes. Someone would have stood up and said “close the bridge now and adjourn this meeting!” 😬
@@Starchface the precedent I heard was that the builder/designer was required to stand underneath an arch as the support scaffolding was being removed. 🙂
Of course, sound idea, under the bridge, in the shade ya know.
Supposedly, in Roman times, the people who built a bridge were made to stand under it as soldiers passed over, to test that it's solid. Seems like a good idea...
When my dad retired from his engineering firm, their clients asked if he would be consulting as an independent contractor. He said he had considered that. His firms customers were already lining up to contract him to oversee their projects done 6 months to 2 years down the line because the engineers they hired to replace him and his firm didn't seem to know what they were doing and things were getting schetchy. He oversaw the projects and reported back to his customers what they already knew - the new engineers didn't know enough or had enough experience to be doing the jobs for which they were hired. He would improve their plans and oversee the construction for which his customers were delighted. He made a nice income that way until he decided to retire for good. That frightened me considerably for the future.
Something is amiss in our universities passing engineers who should not be passed .
The universities provide basic theory. Exams for PE licenses test what the universities teach, and require a minimum of 5 yrs working under a PE. Applying the engineering theory to real world design requires a lot of years of experience which is acquired on the job working with more experienced engineers.
A lot of the designs on the bridge were from females that had been hired. There is always a nagging suspicion in my brain concerning female graduates with the "wokeism" so prevalent in today's world. Did they have the proper accreditation for the job or were they given the job because the were socially acceptable!? It seams today, the most qualified individual is not hired and instead an individual is hired based on social requirements which are deemed to be of greater importance, and these are the consequences!!!
The eternal struggle between Architects and Engineers. The Army taught me to Keep It Simple for Stupid. I learned Allowable Stress Design(ASD) in the early 1970s. In the 1980s I was told to use LFRD. When comparing bridge stringer designs, I found LFRD to be about 25% weaker than ASD. I stayed with ASD. In the 1990s foreign steel started coming into the US. I avoided it because a fellow Army Engineer Officer from Hawaii warned me about it when we were called up for Desert Storm. In 2005, I saw a case where chinesium was only 1/6 the tensile strength that it was supposed to be. Good video. Good Luck, Rick
Regarding chinesium steel. In the late 90's offshore, we were directed to return-to-shorebase, any lifting shackles that were not stamped, "USA" because of several failures. We were also directed that only USA made cables and shackles were to be purchased, henceforth.
We sent a lot of metal back to the beach for disposal.
Saving money by buying the cheap sh!t ended up costing a fortune. We should have stuck with the quality stuff from the beginning.
@@Quidisi Absolutely. I prefer cars, tractors, and trucks from the 1970s and 1980s because they are better built. I retired 13 years ago and am glad to be out of the bridge building business. Good Luck, Rick
@@richardross7219 But cars built today do have stronger steel in them, it's just thinner. Steel from cars is recycled into the steel that buildings are built from.
@@billj5645The thinner steel rots much faster than the older thicker steel. Many trucks' frames rot out in less than 8 years now. I never liked pushing the slenderness ratios either. Good Luck, Rick
This disaster just sickens me. All parties, owner, state, city, inspection, designer, contractor could have made a difference to protect the public and construction workers and they ALL failed completely. Superb video Jeff!
David Beck: “Anytime you want to mess something up in engineering, you get a whole bunch of people involved a little bit. This bridge is a prime example.”
Damn, that's brilliant! I'm just a programmer but that really summarizes my frustrations with the corporate style of software development instead of startup: far more people involved very minimally and no one actually responsible or fully aware of what's going on.
Too many cooks spoil the broth. It’s not just an engineering principle.
Who knew a soccer player knew so much about structural engineering
David Beck is who? Somebody we should listen to?
@@electrictroy2010 David Beck, a veteran New Hampshire engineer who independently analyzed FIGG’s bridge plans for the Miami Herald and reviewed the federal docket, said no one on the project team seemed to have a comprehensive overview of how the bridge was supposed to work. “No one designer had a full understanding and appreciation of the structure and mechanics of the main span,” Beck said. “No one from FIGG could see what was going wrong. And there was no follow-through on the quality control. No one was studying the cracks in a serious way. No one had the knowledge or took the initiative to understand the danger these cracks presented. “Anytime you want to mess something up in engineering, you get a whole bunch of people involved a little bit. This bridge is a prime example.” -- Miami Herald
Random dude on the internet, remember this like it was yesterday, got second degree PTSD hearing the interview at the time of the paramedics talking about their triage of the victims who survived the initial impact...
On a positive note, channels like this one made me understand the complexity of modern bridge design and construction.
Hindsight is 20/20 for all the comments saying xyz screwed up. We all need to learn from this.
Safest bridges are the ones built just after tragedy.
Hindsight 20/20? You are making excuses for lazy, incompetent, unsafe, greedy people who got six people killed with their negligence.
@dannybryant6873 Yup. Safety regulations are written in blood.
I don’t need to learn from it. I don’t build bridges.
@Heyu7her3 THE design was obviously flawed on paper. You didn’t need to build a bridge to see it would collapse
.
I completely understand the tremendous amount of work doing these videos involves. Thank you for this work. I worked in construction, so it's a bit easier for me to follow. But if you save even one person from moving into living or working space that isn't sound, you have changed some lives for the better. Thank you for doing this.
I work as a structural analyst in Aerospace. Every engineering project is a Bureaucratic Cluster Fk. Great work on this video, thanks.
boeing!
Your opinion about the roughing is 100% correct. If that was the difference between a collapse or not, then the minimum factor of safety in the design was really a maximum factor of failure. - The fact that they went ahead with the re-tensioning job with all the crack and signs of structural failure shows that either deciders as to going forward with the job did not understand the physics of what they were doing or they did not give the signs of failure and it progression over time the importance it warranted likely due to their confidence in the design, which we know now was in error. Believe what you are seeing in the real world rather than what's on paper/computer model if they don't match.
On the federal jobs I was a contractor on, in addition to the usual "roughing" at cold joints, the on site inspectors required scrubbing away any latanence and flushing the surface clean before the next pour. The federal on site inspectors were always excellent.
This bridge was designed for aesthetics, not function.
The fact that WJE, put their judgment forward that "Not Roughing" was the sole cause of the collapse is frightening in itself, that a major engineering firm could be so inept. I don't do civil but have done structural product development for 15 years. I do believe the shear at that node was miscalculated and that the column was trying to slide across the deck surface but being that the rebar was tied into the deck and the column meant that it couldn't slide. The cracks in the DECK are the smoking gun that the "Roughing" wasn't the issue and that the column was exerting forces on the deck, that the deck could not handle!!
I believe that the computer model they used for stress analysis was for steel construction where there is strength in tension and laterally... with concrete there is no strength in tension and the prestress steel load bearing characteristics are not the same as steel beams that offer lateral support as well. Reliance on computer models without a common sense overlay.
also I notice that many if not most computer models tend not to include safety margins that also account for materials degradation with age... that is a complete unknowable in many situations
I have been triple redundant in some cases where the cost of that was only a few thousand dollars compared to hundreds of millions of losses if it failed due to unforseen circumstances....
My grandfather used to say that there was book learning and there was real world learning. He also said that book learning need real world learning too which is why many industries have apprentices and journeymen.
After those cracks appeared, the project needed a crotchety, old contractor on the deck to say..."Cease work, round up all our shoring material."
Shore it up first, then figure out those cracks.
Signed,
Crotchety, old, piling / foundation and general contractor.
this wasnt a lightweight aluminum wing they designed, with cutouts for wheel wells, fuel tanks, flaps, servomotors (etc) stressed to +/- 5Gs...
it wasn't a ship stressed to deal with the possibility of huge waves...
...it wasnt even a highway bridge with dynamic loads or freezing/thawing contraction and expansion to control for... it was a mostly static _pedestrian_ bridge! 😅
That was not about to happen with the Florida Bimbo bridge!
The roughening should have been seen as a belt-and-suspenders feature. The safety factors used (not) were clearly inadequate. How this was overlooked during peer review in the design phase is one thing but the fact that this was still overlooked or minimized during forensic analysis is jaw dropping. Thanks for the detailed report. Very informative.
I love when you include the doom sound bite when you make a scary point, really stresses the blunder
They worried too much about looks, rather than using age old designs that are proven
I’ve looked into this collapse in the past but never learned so much about it until this video. Thank you for such a detailed description of the failures.
All the work was worth it, this was the gold standard for this bridge story.
Jeff - As a Structural Engineer I find your videos Excellent. You convey the technical for the non-technical quite well. Your conclusions are good, I can tell you were doing Engineering not requiring PE Licensing. If you were licensed you would be in the design office.
Those web member to the deck connections were super full of steel, very hard to pour, it also changes the neutral axis, there is a factor 'n' that is the ratio of the steel E / concrete E. With 3 ksi concrete and Gr 60 bar n is 9, meaning you replace each square inch of steel wiht 9 square inch concrete. It adds lots of bending, raising the concrete's tension cracking.
Spider cracks are a tell-tale sign of lack of shear reinforcing. Great video. The connection was under designed. The roughening made zero difference. Its the inability of the end connections of member 11 to handle the load transfer.
those particular 'spider cracks' were one to two inches wide.... completely ludicrous. that music was a little too tough to face so even experienced engineers went into denial it seems....in this case it went to absolutely insane levels with jack hammering on top of the span with traffic allowed under it.
I have seen the tendency in myself as well... pressing ahead when data is missing is always a mistake. and with one or two arrogant old timers (I am 83 myself) bellowing against anyone who 'nit picked' their project....pressure can blind a person.
Over my own long career I have noticed that when I am absolutely and provably correct... I am calm....
.
When I start getting jacked up or adamant there is always some aspect that I am missing ... a minor or major flaw in my thinking.
I tend to agree. If there are cracks everywhere, going in all directions and at both ends of the bridge, accompanied with serious spalling, it can't be just the lack of roughening on that one beam. Might have been a significant contributing factor but not the main cause.
My take about the failure in roughening is not that it caused the collapse, but it illustrates that multiple errors were occurring and nobody noticed or stood up to do something about it.
@@Phil_Scott Loved your response. Engineers are under a huge pressure to be right. You can have a career with 1 million critical design decisions, but just one mistake or omission can be deadly. Sometimes admitting to an omission is the right thing so it can be reviewed and fixed. We all need to check twice sometimes 3 times. These are complex structures.
When you get a chance read about Engineer William LeMessurier's last minute redesign of the Citicorp Building structure in NY. Its an amazing story of recognizing an omission, admitting it, then making critical modifications at the last minute and accepting the wrath for the sake of safety.
Jeff, I listened to your comment that you reviewed thousands of pages of transcripts and hundreds of pages of engineering, designs and analysis. So you commented this was a very time intensive review and analysis. I agree. Good work.
Oddly this same company was hired to do a major road bridge in my town, large enough for ships to go under… fortunately they got canned, and another company took over and reengineered it, over a year delay but it’s almost done and safe
> safe
Or so you think
I’ve learned more about compression and tension in your videos than I did in statics…
I love that you took a moment to explain certifications at around 4:30 in - and I also appreciate your explanation on how your certification(s) limit you but still provide you the experience and knowledge to explain these failures and collapses to us. I don't look forward to the disasters, but always look forward to your videos about them. Thank you again!
Great analysis of this issue! The guy that said there should be finger pointing, because everyone is partly to blame got it right! We have to change our system! The fact that the bridge was under designed to begin with, should have been picked up in the submittal process, not in a review after the fact, but in too many cases the AHJ will not check calculations to check the accuracy of submittals, they don't want to have liability! Then you have a company that was suppose to peer review, was deemed not qualified, but still allowed to do it! The system needs to be corrected!
Yes, it proves that even the people using the simulation sometimes don't know what they are doing. If you put garbage in you'll get garbage out
This whole issue brings the reputation of FIU down as well for being a university where one goes to learn to build a bridge in the first place. Granted, they hired a firm to handle this. But the entire incident reflects on them, the bridge was being built to facilitate their students, the bridge had their name, the bridge was commissioned by them. I'm not saying they should carry some of the blame (that's already been decided in court) but it certainly will make people think twice about going there. Imagine having an engineering degree that says you know how to build bridges from a University that had it's OWN bridge collapse and killed 6 people.
It's all driven by marketing. There is an idea that the engineering is easy, anybody can do it, hire the company with the best marketing and don't worry if they have good engineers or not. But the engineering is not easy especially on an unconventional structure like this. Someone has to worry about how do the forces transfer, how do we build it, etc. For something of such importance as this it has to be double checked just as carefully by another company. And apparently someone has to sit down with the engineers actually doing the work and verify that they actually did the work. The marketing staff doesn't want to do this. The managers don't want to do this because they may not understand it either. If you build a more straightforward building that doesn't have these unconventional problems to overcome then maybe the system will work better. When you start building things out of the norm that's when you have higher chances of problems. Look at all of the buildings around the world being built now with angled columns. This is unconventional construction, it puts forces in places where we traditionally don't design for them. The first one of those that is designed by a company focused more on marketing than engineering will likely have serious problems. Jeff has a lot of experience with Champlain Towers. The evidence on the structural drawings of that building are that the engineer doing the work only understood reinforced concrete design about half way, the half that he didn't understand very well caused a collapse. His managers should have seen the problems and corrected them but they may have been more focused on marketing. But that is a relatively straightforward building and it took other factors beyond the engineering to compound the problem and cause a collapse. I knew a firm involved in designing schools. They got tired of paying engineering fees so they hired a few inexperienced engineers to work in their office. The next large project they built had serious problems and had to be shut down for a year for costly repairs. Don't ever think that the engineering doesn't matter.
They'll change the courses to "This is how NOT to design or build a bridge".@@Cowcow211
@@Cowcow211 Wow. I suppose I could see a few people saying this, but I ultimately disagree with intense finger pointing towards FIU. FIU’s property faculty team is not going to consult with the teachers/students to give their opinions on such a project (especially if they are not be licensed or certified to do so), therefore that excludes that element. As you said, the work was performed by third party contracted firms that were not involved in usual FIU operations.
Like when any other individual or business hires contractors to perform work, if the individual/business is not skilled or licensed to perform said work, then they have to put their trust in third party engineers/builders to follow through with it correctly and FIU did so here. You’re taking a shotgun approach with blame in this situation. If for some reason an engineering firm refuses to hire a graduate from FIU because of this collapse - then that graduate should be grateful they dodged a workplace management nightmare, as anyone worth their salt would know there was no relation between the students, their teachers, the third party contractors, and the construction/collapse of this bridge.
Jeff, thank you for your detailed report.
This bridge doesn't look like such a big project, as bridges go.
I'm surprised they had sooo many problems.
At least they used good concrete and good rebar.
Huge respect to you for doing all those hours of tedious research to bring us this information! It's always a serious issue when blame gets shifted more than the failing structure itself.
"Figg did not think there was a issue"
I think Figg were so busy basking in their smug self satisfaction that they didn't think at all, period.
Arrogance is absolutely the worst trait any engineering firm can possess. Like many building architects do this was designed to be totally different from any bridge built before. They claimed huge bragging rights even as the dust was rising from the collapse. Humility would have been a much better trait but then they would not have had this stunning bridge to brag about......until after it failed.
All they wanted was a walkway across a motorway, how in this day do you mess that up?
By unnecessarily trying to reinvent the wheel, apparently.
@@inwiththenew Thag: "Look Grok! Me invent wheel!" Grok: "Wheel need more corners."
Affirmative action messes up a lot of things.
@@tippyc2 You wanna explain how affirmative action is related to this bridge failure?
Allocation of contracts to minority companies (set asides) strictly for quota purposes and NOT "Best Practice" or "Most Qualified". Happens all the time.@@StarkRG
I love the extreme attention to detail you put in and you break down the terminology used in laymen's terms , the 50 mins flew by it was like i was getting a great lecture in class!
Jeff, please do more voiceover work. I could listen to you read the phone book.
His voice is amazing
@@elizabethsahu7822 haha… I oddly agree
Thanks , I have a lot of people tell me , I sound like charlie sheen only I don't have the porn star girlfriend
Jeff. You could get one if only for your image 😆
whats stopping you?? @@jeffostroff
Jeff, all I can say is WOW. Superbly researched and narrated on your part. It makes one wish you had been part of the design team! I just found you and subscribed immediately. Well done! Looking forward to perusing your other videos. Thank you for what you do, and I hope you feel appreciated for all your efforts here. All good wishes!
Thank you so much for your kind words and for subscribing! I really appreciate your support.
Holy smoke, I'm surprised that thing made out of the yard without falling to pieces! Pity it didn't. Excellent work as ever Jeff, many thanks for posting.
Thanks for taking the time and effort to make this incredible video, I had no idea of the volume of material you had to go through to put it all together until you showed us at the end!
Glad it was helpful! Yes it was literally thousands of pages, and hundreds of pages of photos
After this disaster TxDOT removed FIGG from $800M Corpus Christi, Texas Harbor Bridge design
I'll admit I'm here because of the recent disaster in Baltimore. But I can't get enough of this Channel. Bridges are just fascinating and scary at the same time.
Never knew the warning signs were that bad. I don't think you need an engineering degree to see something wasn't right. The newly constructed flyover bridge in Downtown Orlando started showing signs of hairline cracks around the same time this bridge collapsed. They determined the cracks were nothing of concern, but this video makes me wonder if there was more than they were letting on to and I wonder if anyone has followed up over the years to see if the cracks have progressed since they were originally discovered.
You are 100% correct. Any layman seeing all those cracks days and weeks before the collapse would have said something. Did the City engineer EVER go on the bridge to view these cracks? Did ANYONE suggest a second opinion? I'm sorry Denny Pate does not know the seriousness of a crack from a hole in the ground.
I found you and your TH-cam channel after the apartment collapse -- and now I come to see what you have to say after any problem. Thank you for your professional expertise.
more, more, more. must have more data like this.
thanks Jeff, your videos rock!
Wow thanks dave glad you like them
Excellent video. Perhaps your extensive research into this failure will save lives.
I see that YT made you remove all of the video of the bridge right after the collapse. I’m glad your original video is still to watch, it humanizes this whole situation.
Thanks! Yes, once I did that they removed the demonetization of my video. Very frustrating because there are hundreds of videos on this bridge collapse that had all those witness videos of the aftermath
@@jeffostroffThat's what's most important here definitely
@@randombutler Are you being sarcastic?
I got a short attention span and watched the whole thing!Great Job!
‘Cracked like hell’ phrase in the email was very scary to read. Normal structural design has a factor of safety (redundancy). Having a non-redundant design removes this factor of safety.
Redundancy and safety factor are not the same thing....at all. You can have one without the other, neither, or both.
VERY very good video!! Thanks for the information about the bridge - I had no idea about any of the behind-the-scenes info regarding the bridge what-so-ever, until now!
Thanks for taking all the time to make this video, Jeff. I love engineering, and sadly a lot of engineering learning is done through failed engineering. I am astonished that this failure was allowed. We all know that hindsight is 20-20 and it's easy to say what should've been done. It's way harder to be that person in the meeting to stand up and say "this is NOT right and we have to close the road immediately." Especially given the faulty numbers the company was using in the calculations to say "yeah, its fine...la la la no problem here..." So yeah, I guess the lesson in this one is to make sure you have all calculations reviewed by competent engineers. And use this lesson to bolster your position if you have to be the one to stand up in the meeting to say "STOP!!!"
It can be very costly to stop a contractor mid construction. The city and their inspectors should have made the call when the engineer failed to call a time out. A second opinion from the state structural engineers should have closed the highway and stopped tendon stressing over live traffic. Too many failed chances to stop this from being a deadly failure.
they surrounded by YES man
Your videos are very well done! Well organized and thorough. They’re always a pleasure to watch.
Jeff, you are the best in the biz when it comes to these breakdowns. Well done sir!
Thank you for the breakdown. It's sad and outrageous that other people had to pay dearly for others to learn a hard lesson.
Excellent video and simple explanations for the layman. Thanks for the effort you put into this video Jeff.
Shoot, don’t know anything about engineering, but your explanation makes me feel like an expert. Good job
Congrats, you are now a certified PE engineer!
Damn, this guy is good! I watched a lot of TH-cam videos on this bridge collapse, and this is the best by far. Good work, Jeff!
You make this so easy for the layman to understand. Thank you.
I lived in Sweetwater, about two blocks away from the bridge. I rode bike to get around at the time, and was literally stepping out the door to cross under the bridge when I got a bunch of frantic phone calls from friends asking if I was okay. That's how I found out the bridge had collapsed - had I left 2-3 minutes earlier, I'd of been under that bridge when it came down. I count my blessings every day. That was a horrible, horrible day. We all just stood around dumbfounded. There was no way to rescue anyone. Thank you for covering this @jeffostroff
Thanks Jeff for another outstanding video! I discovered you with your Ocean Titan disintegration series, and look forward to each of your engineering video releases.
I agree with the comments about your voice -- so calming and soothing -- but, even more important than that, your analysis, explanations and analogies are top-notch.
I appreciate the meticulous work you put into this and other videos. I'm sure you enjoy it or you wouldn't do it, but you also deserve recognition, as well as any revenue you glean from us viewing your high-quality output.
Thanks again. Looking forward to the next one!
Great video.
Of all the many and varied WTF moments in the design and construction of this bridge the part that most baffles me is that they looked at how this bridge was literally coming apart day by day and never realized that they had a major problem on their hands. It’s freaking obvious and should have been screaming at the guys that do this for a living that there was a major problem.
To think I got stuck in traffic under that exact bridge a week before the collapse. Could’ve been me.
Yakes sounds like you dodged a bullet
Would have been less than a week because the bridge was not there a week before the collapse.
@@rwood1995 I do not keep track of the days it was up, as you know, I was under that bridge in traffic for the short time it was up. Something I want to forget.
Thank you Jeff.
It was overconfidence and a lack of safety that resulted in a failure and loss of life.
With the presence of structural cracks the project should’ve immediately been shut down and shoring installed. This would’ve resulted in a plan to remove the failing pedestrian bridge
Again, thank you so very very much for your work.
totally agree with you - roughening a surface cannot be the key to success or failure... the factor of safety should have an order of magnitude greater impact the roughening (or lack of) for any particular connection surface
They could have poured the base of all the pillars along with the deck, and just made perpendicular cold joints a -couple feet- foot or two higher.
Thanks for the great work Jeff.
Sadly these kinds of things happen too often. Much of it is due to complexity and the lack of appreciation of risk. But some of it is incentivized with $$$.
I'm an electrical engineer by degree but have spent most of my career doing software engineering. When I was a student at the University of Michigan in Ann Arbor, the Engineering School was migrating from central campus to north campus. Two new buildings were erected while I was a student: the Dow Chemical building, and the EECS (Electrical Engineering and Computer Science) building. The Dow Chemical building housed the 'library' (at the time it was really just a computer lab). It also housed the civil engineering faculty offices, something to note for later...
When the Dow building was opened, I had a materials science class and a mechanical engineering class in the building. I always used the stairs instead of the elevators. On my first walk up the west stairwell, I noticed a 1/8" crack from the ground floor slab all the way to the top floor ceiling. Concrete blocks. Some of the crack followed the mortar lines, some of it was through the concrete blocks. No idea what the rebar was inside. By the end of the second term, the crack was 1/4".
I decided to ask one of the civil engineering professors about the crack. He blew me off. Of course it wasn't his job. But I come from a family of construction on my father's side, and here in Michigan we have a variety of soil types (thanks to the glaciers way back when). But much of it, including this spot, is mostly red clay. Which tends to hold water forever. The consequence is that we have fairly extreme frost heave in some areas. I've seen what it can do to residential structures (rip the deck off your house, sever your water and sewer lines from shear, crack up your foundation, etc.). This building was built into the side of a hill of red clay. This concerned me, but I was just a student without a real voice.
Years after I graduated, part of the library in this building collapsed. Fortunately it happened during a break and no one was hurt. The irony: it housed the civil engineering faculty offices.
What tends to bother me most about these types of issues is the willful ignorance. Lives lost in the name of pride and money. Shortsightedness. I am certain I wasn't the only one who noticed cracks growing from the footers to the top floor in a brand new building. Nor the only one who knew how university construction contracts were structured (finishing early or on time is incentivized with sigificant money); they're public. I'm assuming FIU had similar incentives? i.e. there were real $$$ consequences if the bridge was not completed on time or early? Not even accounting for the cost of proper remediation, I assuming any delay was going to cost all of the contractors a chunk of the money they were expecting?
I hope all of the PEs involved lost their licenses. While they don't deserve all of the blame, we as engineers often wind up with it. If someone directs me to compromise safety in the name of their bottom line, I exit. We have to hold the line because those above us often will not. 🙁
I've spent the last 20 plus years of my working career as the guy who's job it is to operate the hydraulic equipment used to test and post tension all types of anchoring systems. If I was asked to post tension tendons on a structure that was obviously cracked and compromised I would just simply refuse. I call into question the knowledge / experience / judgment of the person responsible for that work on this bridge.
He died.
@@imconsequetau5275 sadly, the tensioner tech had skin in the game - unlike the "engineers" who were "not concerned" about the cracks
Excellent report and analysis. So many critical issues here. As a retired engineer from nuclear power plant civil and structural, I have seen many commercial contractors / engineering firms rejected for plant auxiliary structures such as office buildings and warehouses. Commercial construction is a completely different mindset.
Should have built massive supports ASAP , egos and poor engineering caused this!
Yes , too much arrogance and engineering sometimes , and if it's in the wrong spot can cause a lot of damage
I am patiently waiting on your take on the Baltimore bridge collapse 😊
This was an amazing piece of work. Well done and thank you for this.
This was simply a Superb Review and Diagnosis of the Bridge Collapse.
The underlying drama that occured is also notable however I appreciate the Engineering Content the most.
As a construction worker with an Engineering background it is very interesting to learn about these types of failures.
I watch for issues such as these on Construction Projects and have spotted some minor design errors myself. Great Video :D
Thanks sean!
I'm a domestic plumber/gas engineer. The job in the photo at 23:20 was so bad I thought I was looking DOWN at the floor and the pipes were horizontal! OMG there are some clowns out there.
Edit: and the fact that someone says scoring the concrete would have prevented the collapse! Total clown world.
Thanks for helping non engineers to understand. Very complex, you lost me a couple times but you brought me back. New love for structural engineering. I’ve watched all the Champlain Towers videos
Glad to help
A well put together presentation! Good on Ya, Jeff!!!
I know nothing about engineering, however I was thoroughly engaged in your discussion. Thank you for the clarity.
If the concrete had been poured or cast continually to the tops of the vertical and diagonal members there would not have been a "cold" joint to worry about. It would not have prevented the ultimate failure in the end though. Designing without redundancy was the fatal flaw of this design.
Have you looked at the I-40 bridge crack in the lower or bottom member of the bridge over the Mississippi River at Memphis, TN? This bridge, of 2 arched trusses, stayed up under traffic, despite one of the bottom members cracked enough apart to be able to insert a hand into the crack. I find it miraculous the span stayed up at all.
@@jeffostroff because that would have required a very elaborate or impossible forming setup.also NTSB said the joint had way too little rebar in the first place . it could not resist the shear . it needed more than double what they used
The I-40 would have gone into the river if that tie member had cracked all the way through. The tie member was still under a very significant load even though severely cracked more than 50% through. They got extremely lucky on that one; the only reason the member didn't fracture all the way across was because of how the top and side plates were all welded together; one of the weld lines turned the fracture crack to run along the length of the weld (for more than ten feet), rather than continue into and cut across the remaining inboard plate. So it turns out that sometimes the "weak points" like along this weld can turn into useful features!
It should have been slip formed for the vertical members. No cold joints. Of course it also is more expensive, and prep and planning is more intensive and far fewer companies are available to bid.
This content is so interesting! I can appreciate how much work has to go in to making these videos, thank you!
I'm glad you find the content interesting! Thank you for recognizing the effort.
Great video Jeff. In my opinion, the most important image to explain the failure in detail is at 26:46 of the video. For stability, the design would require the floor deck reinforcement to balance the kick out force of diagonal member 11. But the crack pattern shown on the image indicates that the node 11 and 12 were not reinforced properly to transfer the force to the floor deck reinforcement. Roughening the surface would not have changed the situation. In my opinion, the engineer of record should have never allowed the recess for the drain pipe on the underside of the bridge in line with the truss. Instead, there should have been a highly concentrated amount of reinforcing steel (post tensioned and mild) to tie the bottom of the truss to the diagonals completing the load path in a more straight forward path.
Yes, the bottom web (deck) had post-tensioned tendons spaced across the entire deck width instead of converging at the base of the outer node diagonals. Totally puzzled me how they could rely on rebar alone to transfer all that shear to the center.
Embedding a horizontal full-width steel truss in the lower web (at each end) would have made some sense, but not rebar alone.
Also, the upper web was in tension and had severe bending forces in the span above the outer diagonal #11. But the post tension was not yet applied. This tension and bending was excessive due to the failure in the lower web. A spontaneous crack in the ceiling next to the #11 column in the upper web could have acted like a blasting cap inside dynamite.
Thank you very much for your very impressive video from Germany! As an elderly, now retired civil engineer I very much appreciate this work. Well done!
I keep asking myself, when simple STEEL double truss bridges work for heavy trucks and trains, why we have to spend $11M on a funky concrete PEDESTRIAN bridge with "meaning." The meaning here is getting student across a busy highway safely. Take a steel double truss bridge, then add meaning with decorative touches affixed to the steel. Waste of money and lives.
It is the dangers of a Daring new design to boldly. Go where no one else has gone before
The designers want to create a monument to themselves. Actually it was probably competition- if you have multiple companies trying for the contract then the company with the prettiest design has the best chance of getting votes from the board of directors. There is tremendous competition between engineering companies so companies will employ a lot of marketing people to get the edge. I once worked with a guy who asked if we were working for an engineering company or a secretarial company.
It was a "place to gather" (right over a noisy, busy road. Great place to gather.)
Cost?
Thanks Jeff for another outstanding video!! I get involved in a number construction defects and failures so can appreciate all the work this took. I have one relatively simple job ($10 million size) with three parties to the litigation where there are over 100,000 pages of documents. On a job this complicated with that long list of depositions and documents it is a lot of work!! Cannot fathom why anyone seeing these FIU bridge cracks in photograph or in person thought this bridge was OK. That they just want to "seal up the cracks" and move forward is a hard-to-believe approach.
I enjoy your tool sale videos, but figured I would give this a shot. Not fascinated with engineering, but still a good video. Thanks man!
Thanks, LOL love your name too built Ford tough, did you see me? Mention and the previous video about the church collapse. How the two towers on either side of the steeple were built ford tough , and I even showed the ford logos on them
Great video, fantastic amount of information & detail into the failure.
Why if the non-redundant criterion was so important did they say “should” instead of the more prescriptive “must”?
Many important legal cases have hinged on whether the word "shall", "should", "must", "may" are used. Years ago, there was a huge (kept very quiet) case where the wrong word was chosen in Medicare contracts.
Kids, learn your grammar very very well for these words. I suggest looking in some law books first if you ever need these words in a verbal or written contract.
I don’t think it would have mattered. FIGG somehow thought their design WAS redundant. (Per the NTSB report.)
"Should" is a suggestion. "Shall" is a requirement.
You make civil engineering easy to understand (as easy as possible) and fascinating.
Next video?? A hangar collapse on Wednesday at Boise Airport in Idaho claimed the lives of three people and injured nine others. The 39,000-sq-ft hangar was under construction for Jackson Jet Center. The mishap is now under investigation by the Occupational Safety and Health Administration (OSHA).
That was so sad.
Osha is a joke. I doubt they stopped many work place fatalities.
Hi there 👋
I'm new to your channel & gotta tell you. ALL of your hard work, hundreds of hours (probably thousands), & absolute dedication to your craft was TOTALLY WORTH IT!! Thoroughly enjoyed this video!
Love from Australia 💓
Extremely well done... An engineer's deep understanding of all issues AND very well explained and presented. THAT'S RARE. It shows that this video took weeks to to put together. Even I could understand most of it. And I am not engineer... lol... Watched from beginning to end with lots of j & l key hits. My only suggestion, and I might be wrong on this point, is to keep 11 on the right side of the screen at all times.
Love how detailed and informational your videos are! This is the 2nd video I've watched, and I'm learning so many fascinating things!
Don't know what aashto says, but aci says your resistance against sliding is 40% lower when you don't roughen the surface. that's a big difference. also, roughening concrete between pours is a standard construction practice. contractor should have done that. it might be that the design was still an issue but this could have definitely contributed.
μ: Coefficient of friction as the following:
1.4 Concrete placed monolithically.
1.0 Concrete placed against hardened concrete with surface intentionally roughened.
0.6 Concrete placed against hardened concrete not intentionally roughened.
it wouldn't have prevented the bridge it self failing (roughened is not going to save a construction that is 92% below spec) it won't change the outcome no matter how much figg paid the 3rd party to make it look like the whole structure been reliant on roughening
still gets an upvote because it's still valid information
I suspect there just wasn't enough focus on this required step while the concrete was fresh. A hand grinder or jack hammer might have solved the omission later on.
However, if the construction workers couldn't roughen the deck surface due to obstructions, then the sloped cold joint should have been designed to be up inside the #11 column, but perpendicular to compression/thrust.
Still, the deck itself was also failing badly in shear because the thrust / shear was not distributed by steel along the width of the deck. The deck needed an embedded post tensioned steel truss, and/or the deck tendons needed to converge on the #11-#12 node.
Such an interesting channel, thank you so much for your hard work.
Your explanations make complicated subjects really easy to understand and enjoy
As I understood the NTSB report the primary cause was the structure design significantly lacked enough steel reinforcement to resist the sheer load where the member met the deck. I.E. more rebar coming out of the deck and into the supporting members. Of course roughening would have had some benefit. In the end, nobody had the fortitude to call the king naked...
Simply roughening the surface on a joint like this makes more difference than you would think.
@@steveo4749 That is correct but despite Jeff's discussion on steel bridges with 2 trusses it is difficult to build a large bridge that would resist loads with a major element removed. The Golden Gate Bridge for instance would completely fail if one of those cables broke.
@@billj5645 True. But those main cables are made up of many hundreds of smaller wires. After the original design, they knew corrosion inside the cable could still occur so they put a casing on the outside of the cable and then conditioned the air inside the cable to remove moisture. Structures that can fail in a controlled/observable way can be evacuated before a sudden collapse. Repair strategies can be identified before critical items are affected. This design was trash and had it been designed as a true cable stayed structure, it might have had a chance of survivability.
@@steveo4749
This FIU bridge did fail slowly, but nobody [in charge] panicked enough seeing the growing cracks. We need to empower even inspecting technicians to evacuate and close traffic.
This video is the 2nd I've watched on your channel... I'm hooked so I subscribed instantly... Very informative and educational... Great job sir...
They really should have stopped and questioned what they were doing when they made a simple pedestrian bridge weigh almost 1000 tons.
@@busterbiloxi3833Evidently common sense isn't....
Part of the problem i reckon, it was so ludicrously heavy it couldn’t even support its OWN weight, let alone any live loading.
Evidently, the "form follows function" concept was not in play on this project. Seemed more interested in the aesthetics' of the bridge than its' capacity/capability.
Appreciate the hard research you put into this analysis. Very interesting. Thanks!
Its mind boggling how many people dropped the ball on this. It was so obvious that something was seriously wrong
Extremely thorough in his analysis and thank you.for taking the time to go through it all.for us.
This video was phenomenal. So much work went into this by a very competant engineer.
I'm engineering disabled and even I was able to keep up and understand. Well done presenting the facts and articulating them in such a way as to be understood. 👍
The fact that they allowed traffic to use the road while working on the bridge overhead just completely befuddled me. 🤯 Who thought THAT was a safe idea?? You not only have drivers going under the bridge, you also have construction workers on the bridge with traffic below. That's endangering two groups of people. 🙄
That's completely unacceptable!
Your comment reminded me of a tragic incident in Quebec. A concrete bridge was slowly disintegrating, dropping concrete chunks onto the road. One of the people driving under the bridge called 911, reported the bridge. A police officer arrived, looked at the bridge and asked for an structural engineer to show up to take a look. The officer in question didn't close the bridge, so when it finally gave out, it crushed a vehicle under it.
Everyone was pointing at the cop as the final reason the people died. Although the engineers determined that the bridge was improperly built/designed (corner cutting by criminal organization which "owned" the construction firm)... but it did last for over 20 years before it experienced rapid disintegration.
Excellent coverage of a massive engineering design screwup. You explained it very well, with great graphics!
31:54 tensioning means to add tension to the posttensioning rods which increases compression on the member. It's not a good idea but they were putting additional compression on the member not putting it in tension.
That’s what I thought too.
I believe that they had to de-tension the steel rod first to then re-tension it. Thus putting the concrete diagonal into tension? At least that is how I understand it.
@RBodge1234 I agree they released the tension after the bridge was set in place. The posttensioning was probably only needed when it was sitting on the transporters. Once it was on the pier that member would always be in compression regardless of how much tension was in the rods. Posttensioning is like a clamp. Retensioning would only add more compression internally to the concrete. That's partly why the decision to add tension should have set off alarm bells. The cracking had to be related to something else.
we appreciate all the work Mr. Ostroff!
I am a structural Engineer and did a bunch of calculations on the bridge after the collapse. This video came across my desk and I just have a few comments.
-Two trusses are generally not more redundant than one truss. The failure of the one member on one of the two trusses would cause a collapse. There is no alternate load path on the damaged truss. Concrete also tends to be more forgiving than steel. There are proportionally many more failed steel bridges than concrete bridges.
-Contrary to the investigator's comments, there was significant redundancy in this design. The proof is in the pudding. The bridge failed slowly and this is a sign of redundancy and ductility. These were not brittle elements. Otherwise the design would not have shown such significant signs of failure before the collapse. It is really hard to define redundancy clearly in a code. Concrete structures (these are actually a combination of steel and concrete) generally have lots of redundancy with a few notable failure modes. The number and repeated members were not redundant but multiple rebar had to fail to cause a collapse. It is the large number of rebar that produces the redundancy.
-The two pipes is a bit of red herring. It was the interface between the deck and the underside of member #11 that was the failure point. You would get the same result with or without the white pipes. You can include the pipes and justify the capacity to code.
-At 21:53. This is really not a bending failure. There analysis showed it was not a bending failure since it was not a bending failure. The cracks were from the backside of #12 pushing Northward. Adding the extra pads really didn't required a peer review (IMO) since you are increasing the structural capacity. You are only adding to the safety even though the pads were irrelevant to the issue. However, retensioning the PT was definitely a change in design.
-#11 was actually not buckling. The cracks were due to differential movement at the base. If you do the calculations on #11, it was strong enough but the shear friction at the joints was not strong enough.
-#2 is bigger than #11 since #2 is at a lower angle, it has more load in it and it is longer. The longer and more heavily loaded a compression element is, the bigger it has to be to prevent buckling.
-I suspect Figg understood that there was an issue before the collapse. In there presentation they went over the shear friction calculations (how the horizontal shear is transferred from the #11 member to the deck). They left out the load transfer from #11 to the deck at the pour joint between the deck and the member. This is the most obvious point of weakness. I can't remember the exact wording but Denny Pate indicated the real issue was connecting the #11/12 joint back to the #9/10 joint which is an indication he new what was happening. This was a very incriminating comment. He believed that was the way to fix the issue rather than adding vertical support at the #10/9 joint. They didn't want to block the road by adding shoring (it defeated the purpose ABC).
-At 32:38 you got the PT order incorrect. The joint cracked worse after the PT was released. They were putting the PT back into the joint and not releasing it. The PT was suppose to be released after the move which was done. Adding the PT back into the member was the change in the design. Putting the PT back into the design increased the clamping force and shear resistance. However, putting the PT back on the member increased the shear force more than it increase the resistance. It was a pretty fundamental mistake.
-FYI, putting PT into a concrete member does not put compression into the member as a whole. It adds compression to the concrete portion of the section. It is a really important concept to understand if you are working with PT. The member force is the tension (a negative force) in the rods added to the compression (a positive force) in the concrete.
-Figg was not really confused about the factors or least there is no evidence for that. The project specification required them to use LRFD in intermediate stages of construction. In some projects, LFRD is only used at the final configuration of the project but if the public is at risk, you should use LFRD at all the stages. Figg did not use LFRD in the intermediate stages but they would have for the final configuration (or at least in the areas where there was no design errors).
-Those 1/4" roughened surfaces are critical to the design and other building designs. It substantially increases the shear friction capacity. It is common practice to do this on buildings and bridges so it is a general specification rather than in bold. In general, you don't put thing in bold because most issues on a structural design are critical. I personally ask (specify) contractors to roughen the surface and then assume in the calculations that it was not roughened (I add more steel to make up the difference). There are some cases you can't make that assumption but then you just really have to make sure during the construction that they roughened the surface. This is done all the time for things like shear walls at floor slab connections or where one concrete beam interfaces another concrete beam.
-The reason WJE and the investigating engineers don't agree on the significance of the roughening was because WJE used testing and the investigators used calculations. By calculation, it would not have made a difference even though you get a substantial boost in capacity with roughening. However, you often get substantially more capacity by testing than you do by calculation. Either way, that does not alleviate Figg from responsibility since Figg's only means of evaluation was through calculation and on top of that they should have use LFRD factors which they did not do.
-Louis B. did not meet the requirement for the project to do the concept review. This is not the same as saying they were not qualified.
-IMO, concept engineers should be engaged through the client and not the design engineer but this is still common practice.
-I would not say from the pictures that the new design is conventional. There are only cables coming from one side of the pier. This is a complex design. However, the picture may not be the final appearance of the design.
-The fundamental technical issue was there was way too little rebar crossing the deck into member #11 (and at all the joints). They failed to check the shear friction at these horizontal joints.
-The cable stays actually would have provided significant redundancy and help reduce the feeling of bounce on the bridge. Figg noted the reduction of bounce in the design brief but not the redundancy. Many people have said they were just for appearance but that is not quite true. There are redundancy and factors that I put into design that I do not explicitly express.
-There are actually good reasons to make the bridge out of concrete. Many people gave the choice of concrete a bad wrap but I tend to disagree. It was the design flaw in the end that was the problem and not the material choice.
Good points made in the detailed rebuttal, especially the point that the one engineering company may have lacked formal certification but that in no way automatically means they were incompetent. In point of fact, could the bridge not have been theoretically equally strong employing some design elements making a considerably lighter weight structure. That seems a heavy girder for the length and expected weight load. Were they figuring it would be packed with people at some point, with everyone stamping their feet in unison?
It seems to me that the CEI or Louis B should have been required to give an opinion (to the owner and/or FDOT) on the question of whether to close traffic because of the cracking. Figg was conflicted and should not have had the final say like they appear to have been given in that pre-collapse morning meeting.
@@davedoe6445 There needed to be an independent design review for the the tightening of the PT rods. Most contractors would have also gotten a second opinion given the extent of the cracks. The PT retightening was a change to the design on the drawings. Initially it seems like LB would have been the logical choice at the time but they missed the issue during the independent review. Since they missed the issue, it is actually better to bring in another engineer. The inspection engineer/firm is more responsible to point out the issue which they did do. The inspection engineers are not necessarily design engineers and not independent.
The processes where I practice are different and actually less stringent. However, Fligg, the contractor, and LB skirted the rules. More importantly, Fligg likely knew the nature of the issue and put the project ahead of public safety. You can never do this as a professional engineer.
Brilliant forensic report. Great job, Jeff and staff.👍👍
That was in 2018? Wow... I should've started having kids when I was much younger because one day they were born and now they're all in college and it happened in the blink of an eye. Not for them but for me.
I have seen quite a few videos on this subject and by far, your presentation makes the most sense to me, and very agreeable. Thank you.