NTSB is a national gem. This meeting is a model of thorough and objective root cause analysis. As a citizen and taxpayer I want to thank NTSB and its professional staff for an excellent job. For those who cannot afford the time to see the whole report, I recommend the animation around 8:00 and the first three presentations (Accetta, Lamm, Prouty) up to 38:00.
that’s how long formal meetings required by law and adherence to standards last. If you stayed the course you may have noticed that the screen was blank for 15 minutes at the break. I think this video record is a legal document and that unedited record was left in to prove that the transcript was complete, as you sometimes see blank pages in a standard with the note, “ this page intentionally left blank.”
@@johnerickson2673 Yes 3 hours 18 minutes to solidify many months of investigation. This was a very serious accident and one that should not be repeated. Taxpayers money was spent well here, unlike those who designed and managed the accident bridge.
I watched it all in two sessions. It was very informative. It was fortuitous that so many cameras captured the exact moment of collapse or this investigation may have taken longer and been less conclusive. Those videos are available elsewhere. Sadly, in addition to the motorists, one of the deceased was the young engineer tasked with operating the tensioner. He was just doing his job as instructed by Figg engineering. I am impressed at the diligence of this NTSB panel.
Engineer said it was not a concern. (5 times) How many workers on site were engineers? It’s easy to point the finger at the workers but we all know how these things happen because after all this is a chain of events to bring us to a disaster. Money is the reason this happened. FDOT is to blame, the college is to blame and the engineer is to blame. The contractor truly has little to do with the disaster. The contractor used all the products and processes needed to build, tension and prep the bridge as laid out by the engineer.
@@jaybrooks1098 The fictitious quote was more pointed towards a site manager. With that being said Stanislav Petrov prevented WW3, every person has agency and should act when they know it is right.
@@jaybrooks1098 I would argue that is not an engineer, but a person acting as if they are an engineer without the qualifications of abilities (versus fake certificates proclaiming abilities) to do the job.
I have worked on post-tensioned concrete structures for 30 years and have observed minor cracking in all of them, those cracks were terrifying. Any competent structural engineer would have seen those and closed the structure.
As an SE myself, I fully agree. It is negligence at its worst to see those cracks and do nothing. To expect that they will close up due to retensioning of the tensions in the diagonal is sheer idiocy. You cannot un-yield a yielded reinforcing bar.
The concept to shim with the caliber of cracking is angering. I actually had to replay what PE (Dan) stated as the dimensions of some of the cracks. It's far worse than hacks screaming Can't see it from my house. Truly horrific ignorance jeeze
This report shows the bridge as 90% under designed at node 10/11 and 43% at node 11/12 - the bridge was doomed from the beginning. Plus independent engineering firm failed to find those errors.
The number 375% when inverted implies that the bridge, as constructed, had 26% of rebar area required to withstand shear, but at 50:50 we see that nodal region #10-#11 (canopy) had only 9% of capacity to withstand load.
That seems to be the modelling only, not how it was actually constructed. For example, some areas were found to have more strength than was required. ie: While the modelling they used vastly understated what was needed, not everything was constructed as weakly as the modelling showed was required. Presumably this was practically of construction more than anything.
I’m bit flustered with the remarks that FIGG wanted a delay in the November update, completely shows they knew they messed up and wanted help with damage control. Completely inappropriate. Thank You NTSB for making this public. 2:44:00 My thoughts and prayers for those who lost loved ones in this incident. Should have never happened, too many missteps.
Really shocking. As if the negligence and incompetence weren't disturbing enough. Attempting to delay findings so they can do settlements with victims means they were trying to understate their responsibility in the tragedy and, likely, short change the victims. These parties are allowed to work on public interest projects. If these parties work on anything again, you can guarantee the project is not in the public's interest.
Even with the miscalculations and non-accredited peer certification - structures don't just collapse. They always have warning signs and these signs are almost always obvious. The biggest crime here, to me, is that no engineers on the project felt the cracking of this magnitude served as a tell-tale structural integrity compromise/failure. Every man and his dog knows new structures will display a level of cracking due to movement or settlement. But an engineer should know when cracking goes from normal structural settlement to structural compromise. The recommendations made by the NTSB here are extensive and will close some of the gaps in the process regarding review of planning and structural assurance. However, I can only hope the penalties for such negligence and incompetence on the part of the design team, construction team, and those employed to oversee the project mean that we do not have this group of parties handling public infrastructure works for the foreseeable future. I must also agree with @randomsanwhich regarding the Member making public the request of FIU, FIGG, MCM, and Bolton Perez and Associates Consulting Engineers to delay, essentially, the findings of the investigation undertaken by the NTSB so as not to expose them to the full rights of those affected to pursue legal compensation to a fair level. Basically - they wanted to short-change the victims before the findings came out. This, alone, should have an investigation (non-NTSB, obviously). It's absolutely shocking and disgusting practice. It also shows that these parties knew their negligence and incompetence was fully encompassing them, and them alone. They knew that these was no act of God in this tragedy, yet presented that as a side-possibility in weight of blame to victims with regards to settlement money. These parties should never be licenced to work on projects that have the public as the main beneficiary. They have proven themselves to have no interest in the value of people, but rather in the power of money.
planchetflaw I suspect that a lot of design engineers may not have first-hand experience of failure in structures. There seems to have been a collective sense of disbelief at the unfolding reality.
This was at the height of #metoo and the design team were consisting mainly of women and POC, if anyone brought anything up you would simply be accused of being an intolerant bigot or a woman hater.
I believe there was a mention of an actual loud bang as well at some point, so many things was done wrong I can imagine fig going to be taking most of the punishment here, for failing to even do basic bridge design correctly and not having it reviewed by independent company from start and paying someone on the cheap to inspect it towards the end (other issue was everyone on site been so incompetent on concrete structural failure been ignored when massive progressive cracks was happening)
lee x very true. The lack of rebar thru the critical nodes on the ends were astonishing,and those lightening pipes(???)-yep, cutting a lot of corners here! Maybe if it didnt have that walkway covering atop it and had a dual support (rails) we probably wouldnt be talking about this! Steel is a good choice-sheesh!
@@joetexas1546 at some point they mention that end part that failed was 300% less then what was required (I been listening to this on my Bluetooth headset while I've been doing deliverys so I missed most of the pictures) the key safety net that fig loss was not having the required independent company reviewing each steps they was doing
Joseph Troyer - The canopy was supposed to help support the structure, because it makes the entire structure a large I-beam. Or it would have, if not for the weak cold joints.
@@othername1000thanks but it's 2 am. I just watched a short recreation vid and this played after. I don't have 3 hours of meeting in me. I do hope there is some resolve in this though. Damn shame
NTSB is one of those organizations that is anonymously heroic. These folks could make three times as much money with ten times less headache but choose public service.
@@othername1000 wrong! I know our ground is soggy here in FL. and drinking straw tunnel was on the drawboard and approved by All Parties except Figg, because it would not make good publicity interest and photos for their portfolio, (stole this from Mike Perry's comment and Figg website) "Bridges designed by FIGG are purposeful works of art, functional sculptures...."
It has to be noted that identity politics were a factor at all levels. The selection of designer, constructor and the university and government agencies selecting the design and build works were all working with biases. How this impacted quality can only be guessed as the alternatives cannot be provided. It might also reflect in the softening of blame (no criminal sanctions).
@@francoistombe - I think the “good old boy network” has more to do with it. There were several firms involved and they all knew each other and worked for each other frequently. That’s how “groupthink” takes over. No one was willing to challenge the Engineer of Record on the safety, and the EoR was unwilling to admit his firm made a huge mistake.
10:00 "The design of the bridge was non-redundant meaning that failure of an individual truss member would cause collapse of the bridge." They should have put a "FRAGILE" sticker on the side.
This board is fantastic! All the members demonstrate a deep compassion to helping the public by doing amazingly detailed analysis to get to the root cause. I am so proud of them. What a treasure. Thank you, thank you for your service!
Excellent and informative review. Frightening to learn how the system failed at all levels and no one called to stop the project and close the road/bridge.
This bridge seems to have been intended as a bit of a "showoff " with the design showing the pylon and cable-stay arrangement and an additional column underneath that were not to be structural members! So the REAL effective structure was simply a single I-BEAM spanned across the road. Now an I-beam has basically three components, the upper flange( canopy in this case), the web ( vertical in this case), and the lower flange ( the deck) in this case. This I-beam was made of individual components, unlike conventional steel I-beam where flanges and web are continuously distributed AND CONNECTED along the whole length of the I-beam. Within the shape of an I- beam, one can always find an ARCH and if one looks at 12:56 and dismiss the two canopy ends, the ARCH effect can be easily seen. Any low ARCH needs heavy side-thrust to support it on the pivoted anchor points and so in this case, there being no " side mountains" to generate the side thrust, the designer achieved this through the lower flange or deck, being in tension. With member 11 being at 32 degrees with the deck, and the total bridge weighing well over 960 tons, hence 480 tones on each end, then if we assume 30 degrees then the demanded side- thrust would be about 960 tons at each end With the manner in which the 12 bundles of rebars were distributed in the lower flange or deck and the cold joint acting in shear between members 11 and deck, one can easily appreciate that that north tip end structure at deck level was not adequate to hold that amount of side-thrust. That tip end " side thrust" or shear, in this case, would only have held if the base of the triangle between elements11/12 and 9/10 anchored element 11 to the deck with a much longer reinforced gusset towards the south to elements of the 9/10. node with suitable lateral linkages to the 12 bundles in the deck. Note at 13:09, the canopies at the two ends of the bridge were redundant including member 12 and did not contribute to the strength of the structure, while at 12:59 the lower end tip of member 11 sheared horizontally the tip extreme end part of the lower flange (deck) over the main support column underneath gave way, outwards see 39:06 ( the canopy offering no contribution to holding) and while the main support column held the deck temporarily over it, the deck broke at the junction of elements 9-10. as it lost the contribution of element 11 working in a torque action in conjunction with the height of the canopy (18 feet) above the deck. If one looks carefully at the diagram shown at 38:47, it is clear that all the reinforcements at the base of elements 11 and 12 are useless unless there is a lateral arrangement of rebars linking the longitudinal bundles. It would have been better to use continuous L-shaped rebars where the upper part entered element 11 while the horizontal part entered the deck and went as far back even further than node 9/10. It was no use having the node linking 11 and 12 as strong as required unless that node was tied laterally not only to the tips of the inner two bundles near their northern extreme ends but also to the other bundles starting much further south in the deck. The NTSB mentioned that 18 square inches of rebars in sheer were necessary, but even if this was provided, it would have been useless if it was simply inserted between the two inner existing bundles and no lateral longer ties were existing at that northern tip in the deck to link effectively the outer bundles in the deck. That drain pipe did not help much to strengthen the truss! The L-shaped continuous very long rebars linking the deck with element 11 would have been a better choice. Tensioning and de-tensioning of element 11 before and after the move was absolutely not necessary and futile and probably did more harm to the brittle concrete. What would have helped was to somehow tie in tension mode, as fast as one possibly could, the junction 9/10 to the junction 11/12. I feel that the engineer who designed this I-BEAM bridge should have known much better and SHOULD HAVE USED THE CABLE STAY ARRANGEMENT with a much lighter deck or walkway. It would have been cheaper and more artistic Life is what it is and there must be more " human and financial characteristics" planned and used in the construction of this bridge. addenda:- Here is the detail of the downfall. 1. The bridge was pivoted and rested on the two ends each taking about 480 tons. ( static load) When it started to fall it pivoted and rotated on one end, the south side. Because the canopy was 18 to 20 feet much much higher than the rotation point at the south anchor point, this caused the other end at the north canopy tip to move out, to bend the vertical column outwards causing it to fail. 2. So, the shear joint between the last diagonal 11 and deck surface ( first node) on the north side failed, ( causing the first downwards failure slow speed failure see 38:47), as it could not take 960 tons static side thrust with the anchorage being so close to the northern tip ends between two inner bundles of the tensioned longitudinal bars. ( this joint should have had plenty of L shaped rebars going into the member 11 and back south in the deck as far as the node 9/10). Node 11/12 failed in sheer at the surface of the deck where the cracks began to show and then as the concrete could not take the compression, the rebars in the lower end of diagonal11 bent and hit the vertical column 12 holding the canopy above it. As the North end of the bridge dropped, and gained momentum, it rotated about the south side pivot, were due to the height of the canopy (20 feet above) this caused the north canopy to move out and bending out its supporting column 12, which in turn caused the lower end of the north diagonal 11 to move out further and faster. The lower deck lost the torquing height of the canopy and without it, all those post tensile bundles of (12 multiplied by 19=228) high tensile cables acting in the thin deck could not hold the bridge. ( second downwards dynamic failure as the bridge had some downward momentum) If the bridge was 2 feet thick and the cables were at the middle of its thickness, and the length of the base of the triangle to the next diagonal was 32 feet then what the concrete at the deck was subjected to was (480* 32) = load *1 hence, load = 15,360 tons of compression on the upper edge of the deck. Considering the downward momentum I would double this to 30,000 tons compression load on the thin upper edge of the deck. The deck acting alone ( without the geometry and the torquing effect of the canopy, 20 feet above it) with its numerous post tensile cables in it, just could not hold this high loading stress, hence the second failure at the next diagonal node 9/10 to the south. The node 11/12 was too near the northern tip and was not suitably anchored laterally to those existing 12 bundles but only the inner couple with just concrete in shear. See 38:47. Continuous L-shaped rebars angled to join element 11 to the deck where the part in the deck would go back south even further than node 9/10 would have been a better choice. The outer bundles on the twelve inserted did not provide any appreciable contribution to anchor in shear node 11/12. and this is so clear at 38:47 It is suggested that outer bundles in the flat deck were absolutely useless. and the two inner ones were not adequately connected to node 11/12. All those steel bundles in the deck should have been centralized under the truss with only lateral rebars holding the deck. Basically the I -beam had a too slender lower flange to hold the end side thrust/buttress requirements.
This analysis seems correct, but the customer specifically wanted a bridge that could be lifted into place (the ABC method). Their objective could not have been met with a cable-stayed design. The engineers should have just refused to try to make a truss look like a cable-stayed span, or, for that matter, to make a concrete truss of this size.
Wouldn't a steel truss or girder structure (like the ones used on nearly every other pedestrian bridge) have been a much better option in terms of safety/cost?
Yes. A concrete truss is highly unusual. Trusses are typically constructed from steel. The advantage with steel is that it yields significantly before it fails, where as concrete goes ‘bang’. So with steel you get a bit more warning of failure
@@justjackman There is a famous engineer in italia who made a lot of concrete trusses and concrete encassed cable bridge. Most of the bridges have failed now...
I recall that during the moving process they ran into a clearance problem on the north side of the span with traffic berms in the way of the moving device. Instead of moving the traffic berm, they relocated the moving device in towards the center of the span causing an increase in cantilever force to the north side of the span causing the stress on the internal metal rebar and the beginning of the cracks. They mention nothing about this and attribute the initial faulty stress on the span to the different type of support used when they began the process of transferring the weight at the casting site onto the moving device only using four shim points for support.
DrHarryT Yeah there’s so many stupid things that happened with this whole process. I’m amazed more engineers we’re not shooting up flares and saying we must stop now. How were they are blinded what were they drinking.
There was discussion that the process of moving did not worsen the cracks that had already started when the false works were removed after the pour had cured and before moving.
Retensioning a highly compressed member 11 was a big mistake. There does not seem to be any anti bursting links at the junction 11 12 and the bottom deck. Being the top chord of a simple supported structure, the top canopy is in also in compression. To prestressed it is also a poor decision. Lack of redundancy was also a no no in such a high risk consequence structure.
Prestressing compresses concrete to a small fraction of its capacity and, here, was essential in the canopy span between 11-12 where there was no compressive force, but much rotational and shear force.
However, I find it astonishing that the primary concentrated region of tension, directly under the truss, was completely lacking in post-tension tendons. In fact, the deck had post tension everywhere *except* under the truss. Totally Backwards. When I first viewed the bridge photos, I saw the drain outlets and _assumed_ that the strongest post tension member was located in there. Well, it certainly _should_ have been located there, and would have counteracted the thrust from truss members 2 and 11.
The immediate cause of the collapse was due to an order made by FIGG’s top engineer on the project, W. Denney Pat who instructed workers to jackhammer the 10-11 blister to gain access to the internal steel support bars in 11 and using hydraulic ram retention it in an attempt to close the bridge’s existing cracks.
So you want to transfer 2 million pounds of force going outward and have it held by the deck, right? And the idea is to do that with no steel, but through the shear in concrete. By definition, that makes me nervous. It's kind of the definition of unreinforced masonry, the worst building material for earthquakes. And this bridge was going to be moved and jostled around and see reverse loadings similar to an earthquake. I would imagine 11 to deck should have been a massive jungle of rebar, and a larger interface area for more relish on the joint. Looking at the Saarinen's TWA terminal, or Dulles airport, there does seem to be high level knowledge on structural concrete to do extremely complicated projects.
It seems like a steel truss bridge would have been a much lighter & safer design. They continued to erect a concrete truss bridge that was crumbling in front of their face. Irresponsible and unprofessional. Somebody should have said, "Stop!"
A first of type design and installation! There was plenty of warning, with the cracks and the rupture, to say “Stop”. Is this another example of cost and schedule overriding safety?
A number of people in the lay community assumed it had to be some sort of unpredictable failure of the tensioning system because ... Well who would assume the sort of apparent incompetence/negligence that seems to be the end cause.
Robert Szasz - A “number of people” are prone to speculating about complex structural problems so as to prove how smart they are. If they churn out enough YT videos on the subject, they will probably guess right once in awhile, so can point to that success as proof. They hope everyone will forget about their pronouncements which were wrong.
I smell behind the scene shenanigans going on during initial design then during subsequent build for what was an obvious dubious design, a stay cable bridge design without the cables.
@@fahembree - If they had designed a cable-stayed bridge, it would have been considerably different. Just adding cables to this one wouldn’t have made sense.
Do you know why FIGG blundered so badly? Go to their own website and weep. The company's slogan is "Creating Bridges as Art." Under FIGG Philosophy, the company says: "Bridges designed by FIGG are purposeful works of art, functional sculptures within the landscape, that are created through a careful analysis of the site, contextual and environmental sensitivity, and a regional approach that encompasses a community's particular needs, as well as the realities of funding and maintenance. FIGG's exclusive focus on bridge design and construction engineering inspection enables us to provide state of the art technology, innovative aesthetics and materials, and a unique capacity to partner for research. By capturing the powers of imagination, function, and technology, we build bridges that improve the nation's infrastructure, while enhancing the appearance of communities across America and the quality of life for the people who live in them." www.figgbridge.com/philosophy.html Notice that there's no mention of their bridges being strong and safe, a core engineering principle. And if you want to be absolutely terrified, look at all the bridges they have designed, every one one of which needs its design safety reviewed. There are a lot of them. Note again that there's no mention of their structural strength. "Our dedicated team of engineers and technicians is recognized as a leader in the design, engineering and inspection of prestressed concrete segmental bridges and comprises the largest and most experienced concrete segmental bridge team in the United States. The FIGG team has studied, designed or built bridges in 39 states and six nations with construction values over $10 billion. FIGG bridges are each custom-developed to be in harmony with the site, sensitive to the environment and capture the community’s sense of place." www.figgbridge.com/focus_on_bridges.html You can find pictures of their bridges here. I hope you don't have to use any of them regularly. www.figgbridge.com/portfolio.html I'm left hoping that the lawsuits flowing out of this collapse will send this 'award-winning' company into a well-earned oblivion.
The joint that failed was designed with less than 25% of the strength ultimately required, fudging the calculations to enable an architechts bridge instead of a engineers bridge.
Now what I keep bringing up in design discussions (I just go, I’m not by any means an engineer), why go through astounding effort and materials to make something that ordinarily would be structural, and that’s about all it does, like a beam, or a cable stayed tower cable structure, but don’t make it structural, just for aesthetic appeal. For god sakes, you had to built it anyways, just make the thing support weight, may not need to support ALL the weight, but at least make it somehow useful.
@@jaysmith1408 I wondered that as well and if it was due to the ABC requirement that it was difficult to construct the two sections off site in a cable stayed design.
@@jaysmith1408 And maybe thats what they did... and thought that in it's final form with would be fairly safe. Therefore fast tracked the analysis of the truss to a point where very important details are ignored... and here we are.
The whole concept was ridiculous: the same bridge with a similar span would have cost a fourth of the 14 million US$ if made in structural steel, a technology that is well proven and is a lot lighter!
I wonder why the workers would be okay with the condition of the bridge and continuing to work on it. The bridge was screaming shouting and squealing. Did any contact FDOT, the University, the City, OSHA, or if nobody else would listen, the press?
Temporary work during construction is often left to the main contractor. However, temporary condition of the partially constructed permanent work can often be more onerous. The load path and changes of load from tension to compression in the last two diagonal members 2 and 11 was not investigated properly. It was a pity that the cracking in the members and at the junction 11/12 was not taken seriously.
What about ground moment over time at each end of the span?. Would it not have eventually failed as those anchoring buttresses move apart under the pressure?
1) Why does the NTSB amend the current procedures and standards? The root cause is that the current procedures are not adhered to, COMPLIANCE is what needs to be addressed. Adding more steps will just make people more complacent about the whole process. 2) Louis Berger. Shouldn't Louis Berger know if they are qualified to do the peer review ? Even if they were "mistakenly" put on the website by some "odd miracle" that did not involve bribery. Once FIGG requests them to do the work, shouldn't Berger know if they are qualified to do the work and refuse to do it ? I find it so sad that workers that were probably worried about the cracking and their safety had to go on the bridge and carry an action that lead to the failure (i.e. tensionning adding to the stress to node 11/12). They should have taken the engineer that made that call with them during the procedure, he might have thought it through a bit more then. Martin Politick Nov. 2019
The north end of the main span is an extremely complicated set of forces during both construction and installation. Therefore let us under specify, install lots of pipes and remove supports before installing span two. With span two in place the shear stress would have been relieved.
It is totally astonishing to me that the deck had post tension members everywhere *except under the truss web.* When I first viewed the bridge span photos, I saw the drain outlets and confidently _assumed_ that the strongest post tension member was located in there. Well, it certainly _could_ have been located there, and would have counteracted the thrust from truss members 2 and 11. This has to be the reason that so many cracks appear in the deck below the cold joint. The deck was transferring the concentrated truss loads _entirely in shear_ to the remote post tension members. Concrete doesn't like that.
A post tension member that crossed the cold joint at a shallow angle could have accepted the truss web forces from members 2 and 11, transferring loads to the opposite ends of the deck and *eliminating shear across the cold joint.*
Hey David, thank you for the insightful comments. Out of curiosity, what do you do for a living? You seem very knowledgeable in structural mechanics and I noticed you also watch Scott Manley, I couldn't help asking.
@@chris-hayes LOL, I follow over 99, including Tyler Ley, Engineer Guy, AvE, etc. [You really should watch every episode of Tyler Ley. Fantastic insights into concrete!]
@@avid0g I haven't heard of him, I'll absolutely check him out. UA-cam sometimes recommends interesting videos, but most of the time it comes down to seeking out the channels that are quietly making high quality educational content. I do follow Engineer Guy, I believe he's the one that made a really great video on water hammer. Fascinating stuff.
I was hoping to learn how this cockamamie design came about, but I suppose it doesn’t fall within the purview of the board. Did FIU create the concept or FIGG? Did FIU create the concept and FIGG make substantial changes to it? If the latter, what was state of the design concept when it was passed to FIGG?
GH1618 FIU tried to project an image of technical excellence, and wanted a flagship structure. The architectural competition came up with this FIGG concept.
My understanding is the the Architecture Dept at FIU came up with the design (maybe thru a competition). They wanted the bridge to be an advertisement for the Arch. Dept and for the School. When they took their design to FIGG and said “can you build this” FIGG said “yep, but it’s going to cost you” Obviously cost wasn’t an issue because they were using other people’s money (taxpayer money) - so why wouldn’t FIGG build it to the design? Then it becomes FIGG’s job to produce the specs to make it a safe construction.
D C FDOT was one of the parties involved in this screw up. The recommendations apply nationally, and I’m sure all other state DOTs are closely watching this and making sure they dont have similar designs.
You know what is evidence that people were worried about the cracks in the node region? The fact that a tonne of photo's were taken, and that FIGG had to actively inform all parties that it was not a safety concern. I'm prepared to believe that workers falsely didn't understand the risks associated with the cracking. But, it would have been constantly on their minds. Another thing is, the problem with this bridge design is it's backwards. They get an artist to put something that looks nice on paper, and then they shoot it off to the engineers to make their dream come true. All the members that point at an angle towards the pylon, and the members are placed at intervals which correspond not with any structural design in mind, but, does this look good. And then the members that run in the opposite direction, are just crudely placed to counter that, and if you take a look at the forces as mapped out on a computer, the forces aren't equal. The shear force at 11-12 deck node is absolutely massive compared to the rest, and the ones in the middle of the span are practically sleeping. Yet most of the members are a near identical thickness, meaning additional weight is added to the span just to make it look good. And you can clearly see that the completed span has a higher load, which means the stupid pylon in the middle and it's pipes are actually increasing the load. The design is dumb, because it attempts to start off looking good, and then work it's way back. A bridge design should start off by being minimalist, what is the bear minimum we need to make this bridge span happen, and then after that, once you have something which works, then maybe you get artistic and start moving things about. But, when you do this, you are making the thing heavier as a result. And that is a real problem for me. To give you my opinion, there is a bridge in Melbourne called the Bolte Bridge, and the bridge is boring, it's just a simple bridge, but they decide to erect these two upright beams that don't even connect to the bridge, so you see, their artistic merit is completely unconnected to the structure. See what they did there? And there are plenty of examples of this in Melbourne, where the artistic elements are mostly unconnected and thus don't effect the structural integrity of the construction. Learn this. FIU should go out of their way to put the most boring replacement to this bridge. It should be pure steel truss, and it should be an absolute stark reminder of how putting artistic impression ahead of structural intergrity is a bad idea.
Great point, form follows function. Architects should stick to faux walls and art. Leave the engineering alone. Just make a trust bridge and throw a bunch cool lights on it. Add some abstract fiberglass poles up and make it look great.
There were repeated NTSB comparisons between members #2 and #11 in terms of horizontal and vertical thickness (which are quite different). When considering that #2 is both longer and has a steeper slope than #11, I expect #2 to be more robust. However, from other sources, I know that #2 and nodes were revised to be stronger, but #11 was left unchanged. 2:06:30 If #11 had been revised similarly, the deck node strength would have also been _revisited,_ and the bridge would likely have not cracked and failed so soon.
I really don't know how much blame FIU has here. They were the client, and had a meeting with 11 other people from FIGG, FDOT, MCM, and Bolton Perez who all said it was fine to not close the bridge on the day of the collapse. If I am a client and 11 engineers tell me something is safe I will believe them, as I hired them specifically to build and understand that structure. Also, I don't know how anyone in construction can see those cracks and not know that some is very wrong. If Bolton Perez requested shoring be done and FIGG said no, why then allow FIGG to make a change like tensioning without having the shoring in place. If you want something shored up, it is for a reason, you should then not allow a change to occur that you just found about, without other proper safey precautions in place like shutting down the street.
I blame FIU for wanting this concept in the first place. They wanted to showcase high-concept design and Accelerated Bridge Construction. They produced (or accepted) a concept which was unique, therefore inherently high-risk. There first objective should have been to build a safe pedestrian crossing.
Very impressive! But when this Board makes recommendations to the FAA about plane crashes, the FAA rarely adopts them. Let's hope the agencies involved here are more responsive.
@@bchadaway7469The economic impacts of major accident investigation and cleanup, to say nothing of the human costs (immediate and loss of future potential) are far larger than costs to prevent accidents. Corporations are just greedy and shortsighted, always.
Engineer of record "failed to identify the significance of cracks" prior to collapse. I wonder if any of the blue collar construction guys who saw those cracks grow to 3/4" in a couple days recognized their significance?
Conclusion is this is a poorly design concrete truss bridge that looks like a cable stayed bridge for artistic value. It don't have qualify peer review of the under design bridge, which cannot handle it's own weight. The guilty parties send letter to threaten NTSB to delay the inquiry or else they will not pay the victims the settlement that they deserve.
The bridge are cracking, and it's getting worse: Then Shut The Road! And Do Not Reopen until extensive research and modeling of the structural integrity has been done and confirmed by unbiased people.
How about that Millenium Tower in San Francisco? It has sunk 18" and tilted 14". Lots of concrete construction. Was it designed to take those loads? What assumptions on loadpaths were made? Are those assumptions still valid? Usually in a grid of posts there is an assumption of uniform load. If there is differential settling, there is the possibility of some posts loaded three to four times design load while other posts carry no load. Loud sounds, windows cracking? Definitely some cause for concern. Not to say that the structure is not salvageable, but to understand the intricacies of what is going on structurally and for an engineer to guarantee a fix with their license and insurance seems pretty sporty.
I wonder why no analysis has been done with full fixity of the nodes showing bending moments across the diagonals in the deck and the canopy. I would expect to see bending moment causing tension at the bottom of member 11 at node 11/12 that would open the the joint and counteract clamping force at the front causing ever more severe under-design.
There were so many major failures involved in this tragedy that it is surprising that buildings and bridges aren't collapsing all over south Florida. The travesty followed right into the legal settlement were jerking the victims families around continues to this day.
Did they miss that figg thought the bridge was redundant so by expanding the inspections to only include none-redundant bridges they will mis the next one like this.
Thomas Bonse Tell that to the families. Lets face it, it was a stupid design that was doomed from the start and as the money was spent they could not turn back
@@shopart1488 I agree that due to poor engineering and the general ambivalence towards public safety, the bridge was doomed to fail. This doesn't mean that artistic design can't or shouldn't be considered, it just cannot supercede sound engineering.
Thomas Bonse, Agree, but public safety always comes first. it’s kind of like what do you call an architect or an engineer that graduated last in their class. The sad thing is it’s architect and engineer!!!!
I have seen a number of concrete truss bridges in Northern Oregon, and on the coast highway in Calif and Oregon. They were mostly built before the 1920's.
@@gordonrichardson2972 Only because it was never loaded in torsion. A closed structure, such as a box beam, tube, conventional truss bridge with bracing each side, top and bottom, is very rigid for torsional loading. The subject bridge was H shaped, on the horizontal, and has very little torsional rigidity. The first thing that jumped out at me was the #7 stirrups (shown in green). It appeared that they stopped at the lower cold joint, they should have been fully closed or inverted U shaped, extending from near the top of the diagonal member to near the bottom of the deck slab. From the animation, it appears that there is not enough embedment to develop the tensile capacity of the bars, thus they serve almost no purpose. In addition, there should have been 3 or 4 times as many as installed.
They may have their own rules for adopting motions that have nothing to do with Robert's Rules of Order (Revised). Robert's Rules are simply a guide, not the law, and don't matter if the entity in question has their own methods of operating. But, thanks for the sanctimonious exercise in trivia...
Is anyone aware whether there is a particular reason that MCM is never referenced to as Munilla Construction Management, at least in the written accident report?
Which accident report? In the OSHA report, they are first referred to as “Munilla Construction Management, Inc. (MCM), the design-build contractor,” and thereafter “MCM” for convenience.
I t is offensive and incomprehensible as to why the five entities responsible for the collapse of the bridge didn’t want the findings to be released before the completion of the litigation. And the reason was purely for money or the risk of losing more money in awards to family members who lost love ones and those injured by the collapse of the bridge.
2:13:01 so can I also guess, that if there was a 300% deficit in rebar, was the concrete also not enough for the loads on it (AKA the members needed to be larger in diameter)? I'm guessing probably, as the strength was overestimated and the loads underestimated.
Zarcondeegrissom What I heard in the discussion is that there would have needed to be more concrete to accommodate more rebar, but since the trusses are under both compressive and tensional forces, and concrete is not really a good material for handling tension or shear forces well, the strength of the concrete is only one factor.
"shear forces" is a good point. been thinking about that 'slip' thing, that is sheer, and longitudinal rebar would only do part of the load-bearing of shier, the rest taken up by the concrete's tensile weakness holding the column together laterally (the rebar would just peel the back off the column and exit the column akin to peeling a potato with a peeler). And agreed about the "not really a good material for".
FDOT did not hire competent engineers for oversite of work by it seems incompetent bridge builder. This was a ClusterFkkk waiting to happen. Not closing the work site when HUGE cracks appeared...any competent construction worker would know, something is very wrong...foremen, superintendent, on site engineer, what were you doing at that work site???
12 isn't a truss member, it's a stick holding up the roof. To call it such, is just a sign of ignorance in concise structural explanation and understanding, IMO.
@dothemathright 1111 Take away the deck and the canopy, and there won't be much of a truss left. 12 does not have any structural value in carrying the load of the span through truss action. If there was a diagonal going to the top of 12, then yes.
All of this talk about shear resistance brings to question, why rely solely on rebar shear resistance across cold joints _in any design?_ There are more direct methods to counteract loads. For example cold joints can be formed as *protruding sloped structures* that are directly at right angles to each truss web members axis. Roughened/textured cold joints will be far more efficacious with that matching slope. Why solely rely on rebar situated at right angle to the shear? For example, a pair of rectangular formed rebar criss-crossing the cold joint at a shallow angle to the shear. It will take up shear mostly in tension which results in less concrete strain (cracking), _especially if it is _*_basalt._* Post tension members can be situated to _remove large shear forces_ and replace them with _directed compression forces._ In this case, a post-tensioned tendon bundle rises above the bridge deck into the outside web member node (#11-#12). It would cross through the existing cold joint at a shallow angle in the FIU design (but as I suggested above, the concrete deck pour could have filled the lower web member node).
@@gordonrichardson2972 I updated my comment to offer generalized suggestions to eliminate shear in concrete, especially at cold joints. I'm really more interested in avoiding it in the future.
This kind of construction, imo, is an abomination, done without forethought. What it IS done with? "PROFIT MARGINS". For myself? I am NOT one of those, who thinks all business is bad, nor growth, nor construction, having spent my life IN such. Although I was a Plumber, I, too, ran into something extremely similar to this, many years ago. A fairly new technique, where floors are pre-made for high-rises, (say 7 stories-up), with cut-in & reinforced "Plumbing cut-outs" are created, to help speed up the building processes, all-around. This are massive floors, for "Live-in" units, that have kitchens, and are very much like an apartment, but are really just for "Extended Stays', hence the name of one of those companies. The problem? The job I was working on, the plumbing wall was created in the WRONG part of this pre-made floor. Instead of ordering a new floor be created, they "fixed it", by cutting in a NEW plumbing chase-way, "fashioning" some braces which were installed, and CALLING IT GOOD. Now, people have to understand, this job? Was in the Bay Area, of CA. Earthquake country. They have stringent polices, (some moronic, imo- others logical), for all aspects of construction in CA, and for good reason, in most cases. What they did, imo, was circumvent safety, for PROFIT, and to "Keep the project on time". I was NOT ok with this. And began trying to make people aware of this, and the dangers I foresaw, even though I was just a lowly plumber. Needless to say, it was NOT received well, and the more I pushed, the worse it became for myself. But that kind of crap doesn't deter me. I kept going, even, eventually, speaking to the Building Inspector- who also, basically, ignored me. This later? Got me removed from my job site. I'll bet you there was at least ONE person, who tried to warn on this overpass, as well. And who was also, IGNORED. That floor? Far as I know, is still in that building. Right in the MIDDLE of it. I wonder how many cracks may have developed, as I told them I believed would happen, even with OUT any Earthquakes helping out, these.. what? 25-26 years later? Maybe I'm completely wrong. It's possible. But these "cut-outs" are reinforced the way they are, for a REASON. And to cut through REBAR, that's part of the integral construction of the floors when pre-fabbed? And the SIZE of this cut-out, to allow 4" Cast Iron and all the rest to rise up through? To go along with the Original cut-out, already there? IMO, posses a grave danger of collapse over time, but ESPECIALLY in the instance of an Earthquake. Now, I've not heard of any Earthquakes in that area, of any size, since that time. But what will happen, when, not IF, once DOES? I don't remember how many people can fit, in that section, of what is a pretty large complex, but it could rise into the hundreds- just from the collapse. If there are any gas-lines or maybe vehicles that end up in a possible collapse? Who knows. The worst part? People see, from this video, that this is NOT an uncommon thing. How many people must have seen these cracks? When are cracks EVER A GOOD THING, but especially when dealing with Concrete? Ever seen your Driveway's cracks travel? Yeah. So there you go. We can only do so much, to try and warn people of dangers we believe exist. And for some of us, we pay a price. Some are willing. Some are not. In fact, the "Are Not's"? I've no doubt, out-weight the "Willing", and by quite a lot. So how many other, similar situations do you think are out there, ready to FAIL? People never think it can happen to them. Until it does. And many times, somewhere, there is someone, who tried to warn, in order to save lives. The problem lies, in finding those, who will not only listen, but ACT.
When ever they come up with a clever design the basic's seem to be over looked Concrete is great in compression but useless in tension unless rebar is heavily used They tried being to clever Ive worked on bridge construction for 35 years and ive never seen a concrete bridge design look like this
@@gordonrichardson2972 ua-cam.com/video/9X-gmagrMjs/v-deo.html is an example of an NTSB investigative hearing. Here's another one from the official NTSB UA-cam channel ua-cam.com/video/YEXTJDhGOSQ/v-deo.html
I want to point out tho. In the video I see the load transfer from the canopy to deck. Millisecond before sheer effect on base of 11-12. Its more capacity vs load, pulling bridge. Breaks at node and back. I don't see anywhere it is mentioned. Simple sequence of events. Feb 24 the first crack heard is the capacity vs load and removal of shoring on ends.🇨🇦 we stop. Review Next 2 weeks ,cracks in important nodes and cold joints grow. Good idea guys let's move it. Then 2 over tolerances during move...But then you set all that 950 tons on improper shim stacks to transfer the bad design load paths. Releasing tension on the member allows the capacity to eat at the bridge for 5 more days.... last ditch you get the poor guy up there to over tighten basically what amounts to string holding this thing up. Soon as the string pops the load transfers backwards in bridge and you see capacity pull the bridge at the hinge point. Is it not more hinge and capacity, then sheer and force on lower node. In end bad design and building with inadequate oversight. You get this. Ottawa built a " UNIQUE PEDESTRIAN BRIDGE " almost exactly same thing happened. Only never made world wide news because we shord it up. Bridges don't fall on highways. We put safety over money. Try it. How about building normal regular Pedestrian bridges and save money to put elsewhere because what is a bridge...You walk over.it. . That shouldn't cost lives.
NTSB is a national gem. This meeting is a model of thorough and objective root cause analysis. As a citizen and taxpayer I want to thank NTSB and its professional staff for an excellent job. For those who cannot afford the time to see the whole report, I recommend the animation around 8:00 and the first three presentations (Accetta, Lamm, Prouty) up to 38:00.
As a citizen and a taxpayer... really.. 3 hours and 18 minutes
that’s how long formal meetings required by law and adherence to standards last. If you stayed the course you may have noticed that the screen was blank for 15 minutes at the break. I think this video record is a legal document and that unedited record was left in to prove that the transcript was complete, as you sometimes see blank pages in a standard with the note, “ this page intentionally left blank.”
@@johnerickson2673 Yes 3 hours 18 minutes to solidify many months of investigation. This was a very serious accident and one that should not be repeated. Taxpayers money was spent well here, unlike those who designed and managed the accident bridge.
I watched it all in two sessions. It was very informative. It was fortuitous that so many cameras captured the exact moment of collapse or this investigation may have taken longer and been less conclusive. Those videos are available elsewhere. Sadly, in addition to the motorists, one of the deceased was the young engineer tasked with operating the tensioner. He was just doing his job as instructed by Figg engineering. I am impressed at the diligence of this NTSB panel.
They screw up a lot when it comes to plane crashes, but they are excellent at a lot of other things.
"Hey our bridge is falling apart, should we tell people not to go under it?"
"No, lets just screw around with its tensioning instead."
Well when the EOR says to do it, what are you supposed to do?
@@andrewmalone8709 contact OSHA emergency hotiline
Engineer said it was not a concern. (5 times) How many workers on site were engineers? It’s easy to point the finger at the workers but we all know how these things happen because after all this is a chain of events to bring us to a disaster. Money is the reason this happened. FDOT is to blame, the college is to blame and the engineer is to blame.
The contractor truly has little to do with the disaster. The contractor used all the products and processes needed to build, tension and prep the bridge as laid out by the engineer.
@@jaybrooks1098 The fictitious quote was more pointed towards a site manager. With that being said Stanislav Petrov prevented WW3, every person has agency and should act when they know it is right.
@@jaybrooks1098 I would argue that is not an engineer, but a person acting as if they are an engineer without the qualifications of abilities (versus fake certificates proclaiming abilities) to do the job.
Fascinating, superbly articulated, expert diagnosis - excellent work from the NTSB - thank you all
I have worked on post-tensioned concrete structures for 30 years and have observed minor cracking in all of them, those cracks were terrifying. Any competent structural engineer would have seen those and closed the structure.
I'm a layman, and the 5 day progression was terrifying. It was very clearly coming apart at the seams.
As an SE myself, I fully agree. It is negligence at its worst to see those cracks and do nothing. To expect that they will close up due to retensioning of the tensions in the diagonal is sheer idiocy. You cannot un-yield a yielded reinforcing bar.
A concrete truss... the dumbest idea I’ve heard in a while
The concept to shim with the caliber of cracking is angering. I actually had to replay what PE (Dan) stated as the dimensions of some of the cracks. It's far worse than hacks screaming Can't see it from my house. Truly horrific ignorance jeeze
Competent ? Hard to find in the U.S. See the FBI DOJ and on and on !!!!!
This report shows the bridge as 90% under designed at node 10/11 and 43% at node 11/12 - the bridge was doomed from the beginning. Plus independent engineering firm failed to find those errors.
failed , or' ignored 'the fact .
The number 375% when inverted implies that the bridge, as constructed, had 26% of rebar area required to withstand shear, but at 50:50 we see that nodal region #10-#11 (canopy) had only 9% of capacity to withstand load.
That seems to be the modelling only, not how it was actually constructed. For example, some areas were found to have more strength than was required.
ie: While the modelling they used vastly understated what was needed, not everything was constructed as weakly as the modelling showed was required. Presumably this was practically of construction more than anything.
I’m bit flustered with the remarks that FIGG wanted a delay in the November update, completely shows they knew they messed up and wanted help with damage control. Completely inappropriate. Thank You NTSB for making this public. 2:44:00
My thoughts and prayers for those who lost loved ones in this incident. Should have never happened, too many missteps.
Really shocking. As if the negligence and incompetence weren't disturbing enough. Attempting to delay findings so they can do settlements with victims means they were trying to understate their responsibility in the tragedy and, likely, short change the victims. These parties are allowed to work on public interest projects. If these parties work on anything again, you can guarantee the project is not in the public's interest.
randomsanwhich Question starts at 2:42:40.
Not only that, a veiled threat that the victims families would get a smaller payout.
Even with the miscalculations and non-accredited peer certification - structures don't just collapse. They always have warning signs and these signs are almost always obvious. The biggest crime here, to me, is that no engineers on the project felt the cracking of this magnitude served as a tell-tale structural integrity compromise/failure. Every man and his dog knows new structures will display a level of cracking due to movement or settlement. But an engineer should know when cracking goes from normal structural settlement to structural compromise.
The recommendations made by the NTSB here are extensive and will close some of the gaps in the process regarding review of planning and structural assurance. However, I can only hope the penalties for such negligence and incompetence on the part of the design team, construction team, and those employed to oversee the project mean that we do not have this group of parties handling public infrastructure works for the foreseeable future.
I must also agree with @randomsanwhich regarding the Member making public the request of FIU, FIGG, MCM, and Bolton Perez and Associates Consulting Engineers to delay, essentially, the findings of the investigation undertaken by the NTSB so as not to expose them to the full rights of those affected to pursue legal compensation to a fair level. Basically - they wanted to short-change the victims before the findings came out. This, alone, should have an investigation (non-NTSB, obviously). It's absolutely shocking and disgusting practice. It also shows that these parties knew their negligence and incompetence was fully encompassing them, and them alone. They knew that these was no act of God in this tragedy, yet presented that as a side-possibility in weight of blame to victims with regards to settlement money. These parties should never be licenced to work on projects that have the public as the main beneficiary. They have proven themselves to have no interest in the value of people, but rather in the power of money.
planchetflaw I suspect that a lot of design engineers may not have first-hand experience of failure in structures. There seems to have been a collective sense of disbelief at the unfolding reality.
This was at the height of #metoo and the design team were consisting mainly of women and POC, if anyone brought anything up you would simply be accused of being an intolerant bigot or a woman hater.
Certainly a PE should recognize structural failure. Mr Pate, the engineer of record, is a PE. He declared the cracking structure safe more than once.
The road should have been shut down-period! Those visible cracks were quite alarming and so any further work should have been ‘Closed’!
Absolutely, a deadly sequence of more than a few very bad decisions.
I believe there was a mention of an actual loud bang as well at some point, so many things was done wrong
I can imagine fig going to be taking most of the punishment here, for failing to even do basic bridge design correctly and not having it reviewed by independent company from start and paying someone on the cheap to inspect it towards the end (other issue was everyone on site been so incompetent on concrete structural failure been ignored when massive progressive cracks was happening)
lee x very true. The lack of rebar thru the critical nodes on the ends were astonishing,and those lightening pipes(???)-yep, cutting a lot of corners here! Maybe if it didnt have that walkway covering atop it and had a dual support (rails) we probably wouldnt be talking about this! Steel is a good choice-sheesh!
@@joetexas1546 at some point they mention that end part that failed was 300% less then what was required (I been listening to this on my Bluetooth headset while I've been doing deliverys so I missed most of the pictures) the key safety net that fig loss was not having the required independent company reviewing each steps they was doing
Joseph Troyer - The canopy was supposed to help support the structure, because it makes the entire structure a large I-beam. Or it would have, if not for the weak cold joints.
1:19:25 break ends, meeting resumes
What the H, I'm watching a 3 hours long video....was watching atleast. I noticed this comment during the intro
@@ballsdeep2520 it's a short break about 15 minutes. it starts at 1:03:10. So you still good a good 3 hours of meeting
@@othername1000thanks but it's 2 am. I just watched a short recreation vid and this played after. I don't have 3 hours of meeting in me. I do hope there is some resolve in this though. Damn shame
Thanks for the bookmark.
@@MichaelOnines
Timestamp.
Cracks before collapse were massive. How did engineers, designers, regulators, FIU, construction crews all ignore the obvious failure?!?
$$$$$$$
@Dead Horse To cover the eyes, it only takes two quarters.
This was a political wank-fest. Nobody could criticize the design
@Alistair Muir Great story. Miami would be elated to have NZ quality engineering and workmanship.
NTSB is one of those organizations that is anonymously heroic. These folks could make three times as much money with ten times less headache but choose public service.
Why on Earth a pedestrian bridge weights over 900 tons? It was a terrible design.
The "artistic" nature at FIGG, emphasizing looks over safety
Pride
FIU wanted this bridge to change people's outlook on life as they crossed it... Stupid Design Requirements from the Get Go.
They found out the ground was too soggy for a tunnel reinforced by recycled drinking straws. This was the next logical idea, apparently.
@@othername1000 wrong! I know our ground is soggy here in FL. and drinking straw tunnel was on the drawboard and approved by All Parties except Figg, because it would not make good publicity interest
and photos for their portfolio, (stole this from Mike Perry's comment and Figg website) "Bridges designed by FIGG are purposeful works of art, functional sculptures...."
I really hope people go to jail for this. They should not be allowed to design a toothpick in the future.
When was the last time anyone went to jail for catastrophically failing their government job resulting in the death of the public?
@@garymcfarlan4840 They usually get a promotion, made an ambassador or head of the DHS.
The haphazard way this project was run and the fact no one went to prison for this is ludicrous.
It has to be noted that identity politics were a factor at all levels. The selection of designer, constructor and the university and government agencies selecting the design and build works were all working with biases. How this impacted quality can only be guessed as the alternatives cannot be provided. It might also reflect in the softening of blame (no criminal sanctions).
@@francoistombe - I think the “good old boy network” has more to do with it. There were several firms involved and they all knew each other and worked for each other frequently. That’s how “groupthink” takes over. No one was willing to challenge the Engineer of Record on the safety, and the EoR was unwilling to admit his firm made a huge mistake.
10:00 "The design of the bridge was non-redundant meaning that failure of an individual truss member would cause collapse of the bridge." They should have put a "FRAGILE" sticker on the side.
Correct. Plus a sign stating “ENTER AT YOUR OWN RISK”.
This board is fantastic! All the members demonstrate a deep compassion to helping the public by doing amazingly detailed analysis to get to the root cause. I am so proud of them. What a treasure. Thank you, thank you for your service!
Excellent and informative review. Frightening to learn how the system failed at all levels and no one called to stop the project and close the road/bridge.
This bridge seems to have been intended as a bit of a "showoff " with the design showing the pylon and cable-stay arrangement and an additional column underneath that were not to be structural members! So the REAL effective structure was simply a single I-BEAM spanned across the road.
Now an I-beam has basically three components, the upper flange( canopy in this case), the web ( vertical in this case), and the lower flange ( the deck) in this case. This I-beam was made of individual components, unlike conventional steel I-beam where flanges and web are continuously distributed AND CONNECTED along the whole length of the I-beam.
Within the shape of an I- beam, one can always find an ARCH and if one looks at 12:56 and dismiss the two canopy ends, the ARCH effect can be easily seen. Any low ARCH needs heavy side-thrust to support it on the pivoted anchor points and so in this case, there being no " side mountains" to generate the side thrust, the designer achieved this through the lower flange or deck, being in tension.
With member 11 being at 32 degrees with the deck, and the total bridge weighing well over 960 tons, hence 480 tones on each end, then if we assume 30 degrees then the demanded side- thrust would be about 960 tons at each end With the manner in which the 12 bundles of rebars were distributed in the lower flange or deck and the cold joint acting in shear between members 11 and deck, one can easily appreciate that that north tip end structure at deck level was not adequate to hold that amount of side-thrust. That tip end " side thrust" or shear, in this case, would only have held if the base of the triangle between elements11/12 and 9/10 anchored element 11 to the deck with a much longer reinforced gusset towards the south to elements of the 9/10. node with suitable lateral linkages to the 12 bundles in the deck.
Note at 13:09, the canopies at the two ends of the bridge were redundant including member 12 and did not contribute to the strength of the structure, while at 12:59 the lower end tip of member 11 sheared horizontally the tip extreme end part of the lower flange (deck) over the main support column underneath gave way, outwards see 39:06 ( the canopy offering no contribution to holding) and while the main support column held the deck temporarily over it, the deck broke at the junction of elements 9-10. as it lost the contribution of element 11 working in a torque action in conjunction with the height of the canopy (18 feet) above the deck. If one looks carefully at the diagram shown at 38:47, it is clear that all the reinforcements at the base of elements 11 and 12 are useless unless there is a lateral arrangement of rebars linking the longitudinal bundles. It would have been better to use continuous L-shaped rebars where the upper part entered element 11 while the horizontal part entered the deck and went as far back even further than node 9/10. It was no use having the node linking 11 and 12 as strong as required unless that node was tied laterally not only to the tips of the inner two bundles near their northern extreme ends but also to the other bundles starting much further south in the deck. The NTSB mentioned that 18 square inches of rebars in sheer were necessary, but even if this was provided, it would have been useless if it was simply inserted between the two inner existing bundles and no lateral longer ties were existing at that northern tip in the deck to link effectively the outer bundles in the deck. That drain pipe did not help much to strengthen the truss! The L-shaped continuous very long rebars linking the deck with element 11 would have been a better choice.
Tensioning and de-tensioning of element 11 before and after the move was absolutely not necessary and futile and probably did more harm to the brittle concrete. What would have helped was to somehow tie in tension mode, as fast as one possibly could, the junction 9/10 to the junction 11/12.
I feel that the engineer who designed this I-BEAM bridge should have known much better and SHOULD HAVE USED THE CABLE STAY ARRANGEMENT with a much lighter deck or walkway. It would have been cheaper and more artistic Life is what it is and there must be more " human and financial characteristics" planned and used in the construction of this bridge.
addenda:- Here is the detail of the downfall.
1. The bridge was pivoted and rested on the two ends each taking about 480 tons. ( static load) When it started to fall it pivoted and rotated on one end, the south side. Because the canopy was 18 to 20 feet much much higher than the rotation point at the south anchor point, this caused the other end at the north canopy tip to move out, to bend the vertical column outwards causing it to fail.
2. So, the shear joint between the last diagonal 11 and deck surface ( first node) on the north side failed, ( causing the first downwards failure slow speed failure see 38:47), as it could not take 960 tons static side thrust with the anchorage being so close to the northern tip ends between two inner bundles of the tensioned longitudinal bars. ( this joint should have had plenty of L shaped rebars going into the member 11 and back south in the deck as far as the node 9/10). Node 11/12 failed in sheer at the surface of the deck where the cracks began to show and then as the concrete could not take the compression, the rebars in the lower end of diagonal11 bent and hit the vertical column 12 holding the canopy above it. As the North end of the bridge dropped, and gained momentum, it rotated about the south side pivot, were due to the height of the canopy (20 feet above) this caused the north canopy to move out and bending out its supporting column 12, which in turn caused the lower end of the north diagonal 11 to move out further and faster. The lower deck lost the torquing height of the canopy and without it, all those post tensile bundles of (12 multiplied by 19=228) high tensile cables acting in the thin deck could not hold the bridge. ( second downwards dynamic failure as the bridge had some downward momentum) If the bridge was 2 feet thick and the cables were at the middle of its thickness, and the length of the base of the triangle to the next diagonal was 32 feet then what the concrete at the deck was subjected to was (480* 32) = load *1 hence, load = 15,360 tons of compression on the upper edge of the deck. Considering the downward momentum I would double this to 30,000 tons compression load on the thin upper edge of the deck. The deck acting alone ( without the geometry and the torquing effect of the canopy, 20 feet above it) with its numerous post tensile cables in it, just could not hold this high loading stress, hence the second failure at the next diagonal node 9/10 to the south. The node 11/12 was too near the northern tip and was not suitably anchored laterally to those existing 12 bundles but only the inner couple with just concrete in shear. See 38:47. Continuous L-shaped rebars angled to join element 11 to the deck where the part in the deck would go back south even further than node 9/10 would have been a better choice. The outer bundles on the twelve inserted did not provide any appreciable contribution to anchor in shear node 11/12. and this is so clear at 38:47 It is suggested that outer bundles in the flat deck were absolutely useless. and the two inner ones were not adequately connected to node 11/12. All those steel bundles in the deck should have been centralized under the truss with only lateral rebars holding the deck. Basically the I -beam had a too slender lower flange to hold the end side thrust/buttress requirements.
This analysis seems correct, but the customer specifically wanted a bridge that could be lifted into place (the ABC method). Their objective could not have been met with a cable-stayed design. The engineers should have just refused to try to make a truss look like a cable-stayed span, or, for that matter, to make a concrete truss of this size.
Wouldn't a steel truss or girder structure (like the ones used on nearly every other pedestrian bridge) have been a much better option in terms of safety/cost?
Not if the bridge was under designed by 90% like this one...
Yes. A concrete truss is highly unusual.
Trusses are typically constructed from steel.
The advantage with steel is that it yields significantly before it fails, where as concrete goes ‘bang’. So with steel you get a bit more warning of failure
@@justjackman
There is a famous engineer in italia who made a lot of concrete trusses and concrete encassed cable bridge. Most of the bridges have failed now...
@@justjackman And I would be easier to repair the steel bridge
Seems that a steel structure could have been fitted with some sort of concrete looking facade if that element of design was important.
engineers and foreman who allowed road not to be closed when cracks progressed should be put in 25 years behind bars
I recall that during the moving process they ran into a clearance problem on the north side of the span with traffic berms in the way of the moving device. Instead of moving the traffic berm, they relocated the moving device in towards the center of the span causing an increase in cantilever force to the north side of the span causing the stress on the internal metal rebar and the beginning of the cracks.
They mention nothing about this and attribute the initial faulty stress on the span to the different type of support used when they began the process of transferring the weight at the casting site onto the moving device only using four shim points for support.
DrHarryT Yeah there’s so many stupid things that happened with this whole process. I’m amazed more engineers we’re not shooting up flares and saying we must stop now. How were they are blinded what were they drinking.
DrHarryT The main bridge deck was more than strong enough to handle the faulty transportation process, so it was not a cause of the collapse.
There was discussion that the process of moving did not worsen the cracks that had already started when the false works were removed after the pour had cured and before moving.
They stated the bridge was in the same state before and after the bridge move. This is based on a direct data captured before and after the move.
Retensioning a highly compressed member 11 was a big mistake.
There does not seem to be any anti bursting links at the junction 11 12 and the bottom deck.
Being the top chord of a simple supported structure, the top canopy is in also in compression. To prestressed it is also a poor decision.
Lack of redundancy was also a no no in such a high risk consequence structure.
Prestressing compresses concrete to a small fraction of its capacity and, here, was essential in the canopy span between 11-12 where there was no compressive force, but much rotational and shear force.
However, I find it astonishing that the primary concentrated region of tension, directly under the truss, was completely lacking in post-tension tendons. In fact, the deck had post tension everywhere *except* under the truss. Totally Backwards.
When I first viewed the bridge photos, I saw the drain outlets and _assumed_ that the strongest post tension member was located in there. Well, it certainly _should_ have been located there, and would have counteracted the thrust from truss members 2 and 11.
The immediate cause of the collapse was due to an order made by FIGG’s top engineer on the project, W. Denney Pat who instructed workers to jackhammer the 10-11 blister to gain access to the internal steel support bars in 11 and using hydraulic ram retention it in an attempt to close the bridge’s existing cracks.
So you want to transfer 2 million pounds of force going outward and have it held by the deck, right? And the idea is to do that with no steel, but through the shear in concrete. By definition, that makes me nervous. It's kind of the definition of unreinforced masonry, the worst building material for earthquakes. And this bridge was going to be moved and jostled around and see reverse loadings similar to an earthquake.
I would imagine 11 to deck should have been a massive jungle of rebar, and a larger interface area for more relish on the joint.
Looking at the Saarinen's TWA terminal, or Dulles airport, there does seem to be high level knowledge on structural concrete to do extremely complicated projects.
It seems like a steel truss bridge would have been a much lighter & safer design. They continued to erect a concrete truss bridge that was crumbling in front of their face. Irresponsible and unprofessional. Somebody should have said, "Stop!"
But the design looked good! Modern. Not like an old fashioned railroad bridge. So it must be good...
A first of type design and installation! There was plenty of warning, with the cracks and the rupture, to say “Stop”. Is this another example of cost and schedule overriding safety?
A number of people in the lay community assumed it had to be some sort of unpredictable failure of the tensioning system because ... Well who would assume the sort of apparent incompetence/negligence that seems to be the end cause.
Robert Szasz - A “number of people” are prone to speculating about complex structural problems so as to prove how smart they are. If they churn out enough YT videos on the subject, they will probably guess right once in awhile, so can point to that success as proof. They hope everyone will forget about their pronouncements which were wrong.
Robert Szasz The unique model always looked weird, and it was hard to develop a proper physical understanding of the design.
What I cannot understand is why concrete? at 150 pcf in a non-redundant design with the many potential QC/QA issues.
I smell behind the scene shenanigans going on during initial design then during subsequent build for what was an obvious dubious design, a stay cable bridge design without the cables.
The concrete guy paid off a politician for no bid contracts.
I worked in a concrete testing lab long time ago (mostly compressing concrete) . I tell you.... if you see those types of cracks... you better run
@@fahembree - If they had designed a cable-stayed bridge, it would have been considerably different. Just adding cables to this one wouldn’t have made sense.
Do you know why FIGG blundered so badly? Go to their own website and weep. The company's slogan is "Creating Bridges as Art." Under FIGG Philosophy, the company says:
"Bridges designed by FIGG are purposeful works of art, functional sculptures within the landscape, that are created through a careful analysis of the site, contextual and environmental sensitivity, and a regional approach that encompasses a community's particular needs, as well as the realities of funding and maintenance. FIGG's exclusive focus on bridge design and construction engineering inspection enables us to provide state of the art technology, innovative aesthetics and materials, and a unique capacity to partner for research.
By capturing the powers of imagination, function, and technology, we build bridges that improve the nation's infrastructure, while enhancing the appearance of communities across America and the quality of life for the people who live in them."
www.figgbridge.com/philosophy.html
Notice that there's no mention of their bridges being strong and safe, a core engineering principle. And if you want to be absolutely terrified, look at all the bridges they have designed, every one one of which needs its design safety reviewed. There are a lot of them. Note again that there's no mention of their structural strength.
"Our dedicated team of engineers and technicians is recognized as a leader in the design, engineering and inspection of prestressed concrete segmental bridges and comprises the largest and most experienced concrete segmental bridge team in the United States. The FIGG team has studied, designed or built bridges in 39 states and six nations with construction values over $10 billion. FIGG bridges are each custom-developed to be in harmony with the site, sensitive to the environment and capture the community’s sense of place."
www.figgbridge.com/focus_on_bridges.html
You can find pictures of their bridges here. I hope you don't have to use any of them regularly.
www.figgbridge.com/portfolio.html
I'm left hoping that the lawsuits flowing out of this collapse will send this 'award-winning' company into a well-earned oblivion.
The joint that failed was designed with less than 25% of the strength ultimately required, fudging the calculations to enable an architechts bridge instead of a engineers bridge.
Now what I keep bringing up in design discussions (I just go, I’m not by any means an engineer), why go through astounding effort and materials to make something that ordinarily would be structural, and that’s about all it does, like a beam, or a cable stayed tower cable structure, but don’t make it structural, just for aesthetic appeal. For god sakes, you had to built it anyways, just make the thing support weight, may not need to support ALL the weight, but at least make it somehow useful.
@@jaysmith1408 I wondered that as well and if it was due to the ABC requirement that it was difficult to construct the two sections off site in a cable stayed design.
@@jaysmith1408
And maybe thats what they did... and thought that in it's final form with would be fairly safe. Therefore fast tracked the analysis of the truss to a point where very important details are ignored... and here we are.
FIGG is still around in 2021. But this bridge is conspicuously missing from their portfolio 🤔
Sooo who's being held accountable? Does anyone know if charges have been filed or law any suits...?
FIGG and Pate have been barred from federal contracts for ten years.
@@GH-oi2jf They will be designing parking garages and condo tower's I would expect.
How you can retension a cracked up destroyed support structure is a mystery, even I know it, and I'm a dumb medic.
The whole concept was ridiculous: the same bridge with a similar span would have cost a fourth of the 14 million US$ if made in structural steel, a technology that is well proven and is a lot lighter!
I wonder why the workers would be okay with the condition of the bridge and continuing to work on it. The bridge was screaming shouting and squealing. Did any contact FDOT, the University, the City, OSHA, or if nobody else would listen, the press?
othername1000 All cowards, as usual. Hope they will be remembered of being cowards every day.
Temporary work during construction is often left to the main contractor. However, temporary condition of the partially constructed permanent work can often be more onerous. The load path and changes of load from tension to compression in the last two diagonal members 2 and 11 was not investigated properly.
It was a pity that the cracking in the members and at the junction 11/12 was not taken seriously.
Contracts and payments is where you start any investigation of this type.
"we are not pointing fingers". Well they were and if done fairly, nothing wrong with that.,
At 37:00 there is speculation that the backspan may have helped. Well, that might work, if both far ends were fixed connections against thrust.
What about ground moment over time at each end of the span?. Would it not have eventually failed as those anchoring buttresses move apart under the pressure?
1) Why does the NTSB amend the current procedures and standards? The root cause is that the current procedures are not adhered to, COMPLIANCE is what needs to be addressed. Adding more steps will just make people more complacent about the whole process.
2) Louis Berger. Shouldn't Louis Berger know if they are qualified to do the peer review ? Even if they were "mistakenly" put on the website by some "odd miracle" that did not involve bribery. Once FIGG requests them to do the work, shouldn't Berger know if they are qualified to do the work and refuse to do it ?
I find it so sad that workers that were probably worried about the cracking and their safety had to go on the bridge and carry an action that lead to the failure (i.e. tensionning adding to the stress to node 11/12). They should have taken the engineer that made that call with them during the procedure, he might have thought it through a bit more then. Martin Politick Nov. 2019
Roman engineers where made to stand under their bridge as the falsework was removed
@@tommypetraglia4688 That would definitely improve the QC process.
@@tommypetraglia4688 Really is it true? 🤣 🤣
The north end of the main span is an extremely complicated set of forces during both construction and installation. Therefore let us under specify, install lots of pipes and remove supports before installing span two. With span two in place the shear stress would have been relieved.
It is totally astonishing to me that the deck had post tension members everywhere *except under the truss web.*
When I first viewed the bridge span photos, I saw the drain outlets and confidently _assumed_ that the strongest post tension member was located in there. Well, it certainly _could_ have been located there, and would have counteracted the thrust from truss members 2 and 11.
This has to be the reason that so many cracks appear in the deck below the cold joint. The deck was transferring the concentrated truss loads _entirely in shear_ to the remote post tension members. Concrete doesn't like that.
A post tension member that crossed the cold joint at a shallow angle could have accepted the truss web forces from members 2 and 11, transferring loads to the opposite ends of the deck and *eliminating shear across the cold joint.*
Hey David, thank you for the insightful comments. Out of curiosity, what do you do for a living? You seem very knowledgeable in structural mechanics and I noticed you also watch Scott Manley, I couldn't help asking.
@@chris-hayes
LOL, I follow over 99, including Tyler Ley, Engineer Guy, AvE, etc. [You really should watch every episode of Tyler Ley. Fantastic insights into concrete!]
@@avid0g I haven't heard of him, I'll absolutely check him out. UA-cam sometimes recommends interesting videos, but most of the time it comes down to seeking out the channels that are quietly making high quality educational content. I do follow Engineer Guy, I believe he's the one that made a really great video on water hammer. Fascinating stuff.
@@chris-hayes
Dirk Bondy, prestressed concrete design: ua-cam.com/video/1_SVVbhKY9I/v-deo.html
The main problem is they can make all the recommendations they want but if there isn’t any power behind them, they can be ignored.
What about the structural issues that mde this collective failure of all involved parties possible?
I was hoping to learn how this cockamamie design came about, but I suppose it doesn’t fall within the purview of the board. Did FIU create the concept or FIGG? Did FIU create the concept and FIGG make substantial changes to it? If the latter, what was state of the design concept when it was passed to FIGG?
"talent" lol. should have lifetime ban from construction industry.
www.figgbridge.com/bridges_as_art.html
GH1618 FIU tried to project an image of technical excellence, and wanted a flagship structure. The architectural competition came up with this FIGG concept.
My understanding is the the Architecture Dept at FIU came up with the design (maybe thru a competition). They wanted the bridge to be an advertisement for the Arch. Dept and for the School.
When they took their design to FIGG and said “can you build this” FIGG said “yep, but it’s going to cost you”
Obviously cost wasn’t an issue because they were using other people’s money (taxpayer money) - so why wouldn’t FIGG build it to the design?
Then it becomes FIGG’s job to produce the specs to make it a safe construction.
Good grief. I thought she was going to pass out helmets at 4:00.
Kind of surprised some of the recommendations are targeted at just Florida and not at all the States. Not sure why they would limit it?
D C FDOT was one of the parties involved in this screw up. The recommendations apply nationally, and I’m sure all other state DOTs are closely watching this and making sure they dont have similar designs.
The level of details in this investigation is astounding.
You know what is evidence that people were worried about the cracks in the node region? The fact that a tonne of photo's were taken, and that FIGG had to actively inform all parties that it was not a safety concern.
I'm prepared to believe that workers falsely didn't understand the risks associated with the cracking. But, it would have been constantly on their minds.
Another thing is, the problem with this bridge design is it's backwards. They get an artist to put something that looks nice on paper, and then they shoot it off to the engineers to make their dream come true. All the members that point at an angle towards the pylon, and the members are placed at intervals which correspond not with any structural design in mind, but, does this look good. And then the members that run in the opposite direction, are just crudely placed to counter that, and if you take a look at the forces as mapped out on a computer, the forces aren't equal.
The shear force at 11-12 deck node is absolutely massive compared to the rest, and the ones in the middle of the span are practically sleeping. Yet most of the members are a near identical thickness, meaning additional weight is added to the span just to make it look good. And you can clearly see that the completed span has a higher load, which means the stupid pylon in the middle and it's pipes are actually increasing the load.
The design is dumb, because it attempts to start off looking good, and then work it's way back.
A bridge design should start off by being minimalist, what is the bear minimum we need to make this bridge span happen, and then after that, once you have something which works, then maybe you get artistic and start moving things about. But, when you do this, you are making the thing heavier as a result. And that is a real problem for me.
To give you my opinion, there is a bridge in Melbourne called the Bolte Bridge, and the bridge is boring, it's just a simple bridge, but they decide to erect these two upright beams that don't even connect to the bridge, so you see, their artistic merit is completely unconnected to the structure. See what they did there? And there are plenty of examples of this in Melbourne, where the artistic elements are mostly unconnected and thus don't effect the structural integrity of the construction. Learn this. FIU should go out of their way to put the most boring replacement to this bridge. It should be pure steel truss, and it should be an absolute stark reminder of how putting artistic impression ahead of structural intergrity is a bad idea.
Great point, form follows function. Architects should stick to faux walls and art. Leave the engineering alone. Just make a trust bridge and throw a bunch cool lights on it. Add some abstract fiberglass poles up and make it look great.
Man they could have used steel and achieve the same design and just cover it up with masonry and achieve the same look!
Nope - steel would have failed too since the bridge was under designed by 90%
Well done NTSB. So, who is going to jail for slapping together "this preventable accident.”?
By their charter, criminal charges are not an NTSB function. Criminal charges have to be brought by a law enforcement agency, either federal or local.
@@buckhorncortez Thanks. I was aware of that investigation vs. prosecution function. But, the questions still remains.
Some girls. This bridge was so wonderful in the beginning, planned and designed by girls !!! Glory be.
dks13827 Here's to fine art and shitty bridges.
There were repeated NTSB comparisons between members #2 and #11 in terms of horizontal and vertical thickness (which are quite different).
When considering that #2 is both longer and has a steeper slope than #11, I expect #2 to be more robust. However, from other sources, I know that #2 and nodes were revised to be stronger, but #11 was left unchanged. 2:06:30
If #11 had been revised similarly, the deck node strength would have also been _revisited,_ and the bridge would likely have not cracked and failed so soon.
I really don't know how much blame FIU has here. They were the client, and had a meeting with 11 other people from FIGG, FDOT, MCM, and Bolton Perez who all said it was fine to not close the bridge on the day of the collapse. If I am a client and 11 engineers tell me something is safe I will believe them, as I hired them specifically to build and understand that structure. Also, I don't know how anyone in construction can see those cracks and not know that some is very wrong. If Bolton Perez requested shoring be done and FIGG said no, why then allow FIGG to make a change like tensioning without having the shoring in place. If you want something shored up, it is for a reason, you should then not allow a change to occur that you just found about, without other proper safey precautions in place like shutting down the street.
I blame FIU for wanting this concept in the first place. They wanted to showcase high-concept design and Accelerated Bridge Construction. They produced (or accepted) a concept which was unique, therefore inherently high-risk. There first objective should have been to build a safe pedestrian crossing.
Very impressive! But when this Board makes recommendations to the FAA about plane crashes, the FAA rarely adopts them. Let's hope the agencies involved here are more responsive.
The FAA has competing mandates and has to take the economic impact of any given measure into consideration.
@@bchadaway7469The economic impacts of major accident investigation and cleanup, to say nothing of the human costs (immediate and loss of future potential) are far larger than costs to prevent accidents. Corporations are just greedy and shortsighted, always.
Poured in place concrete is the way not a pre cast type. How long was the concrete cured for? Probably not enough time.
Engineer of record "failed to identify the significance of cracks" prior to collapse. I wonder if any of the blue collar construction guys who saw those cracks grow to 3/4" in a couple days recognized their significance?
Even if, there's not much they can do when every agency involved is aware of those cracks already. Who should they call? Ghostbusters? ;)
it basically becomes a hot potatoe, "it is not MY fault, i already told everyone else about it"
Bitterrootbackroads The NTSB don't name the FIGG Engineer of Record, but his name was in all the news reports.
@@gordonrichardson2972
Oh you mean the engineer of record who couldn't turn over his assigned work phone loaded with pictures and texts and a phone log discussing the cracks because some how his wife washed his pants with the phone in a pocket? His name is... Denny Pate.
That's...
Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate. Denny Pate.
Got it? Denny Pate, who incidently immediately lawyered up and hasn't said Word One to a single investigator.
That Denny Pate
@@tommypetraglia4688 That was indeed shocking. I am surprised his name was not brought up. Hopefully some criminal charges will follow.
Conclusion is this is a poorly design concrete truss bridge that looks like a cable stayed bridge for artistic value. It don't have qualify peer review of the under design bridge, which cannot handle it's own weight. The guilty parties send letter to threaten NTSB to delay the inquiry or else they will not pay the victims the settlement that they deserve.
Why was there no redundancy designed into this bridge?
The bridge are cracking, and it's getting worse: Then Shut The Road! And Do Not Reopen until extensive research and modeling of the structural integrity has been done and confirmed by unbiased people.
How about that Millenium Tower in San Francisco? It has sunk 18" and tilted 14". Lots of concrete construction. Was it designed to take those loads? What assumptions on loadpaths were made? Are those assumptions still valid?
Usually in a grid of posts there is an assumption of uniform load. If there is differential settling, there is the possibility of some posts loaded three to four times design load while other posts carry no load.
Loud sounds, windows cracking? Definitely some cause for concern. Not to say that the structure is not salvageable, but to understand the intricacies of what is going on structurally and for an engineer to guarantee a fix with their license and insurance seems pretty sporty.
That problem is due to an inadequate foundation, not the structure.
@@GH-oi2jf There are cracking structural columns in the basement of the Millenium Tower , so the foundation imbalance is being transferred to columns.
I really wish software engineering postmortems were a patch on this. Incredible work -- thank you to everyone involved.
I wonder why no analysis has been done with full fixity of the nodes showing bending moments across the diagonals in the deck and the canopy. I would expect to see bending moment causing tension at the bottom of member 11 at node 11/12 that would open the the joint and counteract clamping force at the front causing ever more severe under-design.
Gotta say I want Jennifer Homedey on my team... Whatever that is. She is pretty awesome at speaking honestly with some badass mixed in.
NTSB is my favorite federal agency/board. I love them and hope they get increased budget year over year
There were so many major failures involved in this tragedy that it is surprising that buildings and bridges aren't collapsing all over south Florida. The travesty followed right into the legal settlement were jerking the victims families around continues to this day.
Did they miss that figg thought the bridge was redundant so by expanding the inspections to only include none-redundant bridges they will mis the next one like this.
One look at the number of boxes on the "org chart" tells you what the problem is. If everybody is responsible, no one is responsible.
After all the layers of "oversight" in these projects there is little budget to actually build something.
''but it would have cost money to close this street and put in a detour!''
so, how many jail terms for the principals? and how many decades?
Why allow uncommon designs. Bridges do not need to be pretty, they ONLY need to function safely.
Simply because it's no longer the 70's.
Thomas Bonse Tell that to the families. Lets face it, it was a stupid design that was doomed from the start and as the money was spent they could not turn back
@@shopart1488 I agree that due to poor engineering and the general ambivalence towards public safety, the bridge was doomed to fail. This doesn't mean that artistic design can't or shouldn't be considered, it just cannot supercede sound engineering.
Thomas Bonse,
Agree, but public safety always comes first. it’s kind of like what do you call an architect or an engineer that graduated last in their class. The sad thing is it’s architect and engineer!!!!
If designed and constructed properly why can't something be aesthetically pleasing?
2:00:50 summary by the chairman.
I have seen a number of concrete truss bridges in Northern Oregon, and on the coast highway in Calif and Oregon. They were mostly built before the 1920's.
Jeffrey Nelson True, but nobody has ever tried to build a single beam concrete truss before.
@@gordonrichardson2972 As far as I know, you are right. The subject bridge appears to have little torsional rigidity.
Jeffrey Nelson The main deck span is quite well reinforced, and torsional rigidity was the least of the design faults.
@@gordonrichardson2972 Only because it was never loaded in torsion. A closed structure, such as a box beam, tube, conventional truss bridge with bracing each side, top and bottom, is very rigid for torsional loading. The subject bridge was H shaped, on the horizontal, and has very little torsional rigidity. The first thing that jumped out at me was the #7 stirrups (shown in green). It appeared that they stopped at the lower cold joint, they should have been fully closed or inverted U shaped, extending from near the top of the diagonal member to near the bottom of the deck slab. From the animation, it appears that there is not enough embedment to develop the tensile capacity of the bars, thus they serve almost no purpose. In addition, there should have been 3 or 4 times as many as installed.
Jeffrey Nelson The report does mention the insufficient rebar at the #11/12 joint (along with other design errors). I'm still digesting the video.
I wouldn’t want to be in the shoes of those engineers. We’re always told how vital it is to do things right.
What did it ultimately cost (aside from lives)?
Nobody cares, it's public money
The bridge was protesting for 5 days. Cracking more and more amd more.
Sadly, no one was listening. Incompetence galore.
A three-member board does not need a second for motions, according to Robert’s Rules of Order (Revised).
They may have their own rules for adopting motions that have nothing to do with Robert's Rules of Order (Revised). Robert's Rules are simply a guide, not the law, and don't matter if the entity in question has their own methods of operating. But, thanks for the sanctimonious exercise in trivia...
The NTSB has historically been a 5 member board (notice the five seats). Maintaining that practice is good form.
44:50, regulatory capture, just like the 737 MAX
Ted Cook Florida regulations...
Is anyone aware whether there is a particular reason that MCM is never referenced to as Munilla Construction Management, at least in the written accident report?
Which accident report? In the OSHA report, they are first referred to as “Munilla Construction Management, Inc. (MCM), the design-build contractor,” and thereafter “MCM” for convenience.
I t is offensive and incomprehensible as to why the five entities responsible for the collapse of the bridge didn’t want the findings to be released before the completion of the litigation. And the reason was purely for money or the risk of losing more money in awards to family members who lost love ones and those injured by the collapse of the bridge.
2:13:01 so can I also guess, that if there was a 300% deficit in rebar, was the concrete also not enough for the loads on it (AKA the members needed to be larger in diameter)? I'm guessing probably, as the strength was overestimated and the loads underestimated.
Zarcondeegrissom What I heard in the discussion is that there would have needed to be more concrete to accommodate more rebar, but since the trusses are under both compressive and tensional forces, and concrete is not really a good material for handling tension or shear forces well, the strength of the concrete is only one factor.
"shear forces" is a good point. been thinking about that 'slip' thing, that is sheer, and longitudinal rebar would only do part of the load-bearing of shier, the rest taken up by the concrete's tensile weakness holding the column together laterally (the rebar would just peel the back off the column and exit the column akin to peeling a potato with a peeler). And agreed about the "not really a good material for".
@@Zarcondeegrissom
It did exactly that at the underside of member 11. The PT rods ripped out like a zipper
I can't imagine the amount of litigation as a result of this disaster.
So, Figg was grossly , criminally negligent in every aspect of this design, build and tragedy.
FDOT did not hire competent engineers for oversite of work by it seems incompetent bridge builder.
This was a ClusterFkkk waiting to happen. Not closing the work site when HUGE cracks appeared...any competent construction worker would know, something is very wrong...foremen, superintendent, on site engineer, what were you doing at that work site???
T B The engineers kept telling them it was okay
The design was crap. It failed.
Stop with the goofy designs.
Or, put a focused effort on anything "new". Without structural engineers pushing the limits, we would still be building pyramids.
@@bradwilson6601 pyramids are 5000 years old & the walkway didn't last one.
1:03 offer wishes? What about financial support?
It seems that a number of people are going to have an uncomfortable day or two in court.
It would not feel confident if an engineer said to post tension at 50 kip intervals and “see what happens”. Yikes!
I really feel for the technician who was tasked to run the tensioner. He was killed. Probably just accepting the knowledge of the engineer.
12 isn't a truss member, it's a stick holding up the roof. To call it such, is just a sign of ignorance in concise structural explanation and understanding, IMO.
@dothemathright 1111 Take away the deck and the canopy, and there won't be much of a truss left. 12 does not have any structural value in carrying the load of the span through truss action. If there was a diagonal going to the top of 12, then yes.
What a major screw up...
All of this talk about shear resistance brings to question, why rely solely on rebar shear resistance across cold joints _in any design?_ There are more direct methods to counteract loads.
For example cold joints can be formed as *protruding sloped structures* that are directly at right angles to each truss web members axis. Roughened/textured cold joints will be far more efficacious with that matching slope.
Why solely rely on rebar situated at right angle to the shear? For example, a pair of rectangular formed rebar criss-crossing the cold joint at a shallow angle to the shear. It will take up shear mostly in tension which results in less concrete strain (cracking), _especially if it is _*_basalt._*
Post tension members can be situated to _remove large shear forces_ and replace them with _directed compression forces._ In this case, a post-tensioned tendon bundle rises above the bridge deck into the outside web member node (#11-#12). It would cross through the existing cold joint at a shallow angle in the FIU design (but as I suggested above, the concrete deck pour could have filled the lower web member node).
David Ogawa Multiple questions that may never be answered.
@@gordonrichardson2972
I updated my comment to offer generalized suggestions to eliminate shear in concrete, especially at cold joints. I'm really more interested in avoiding it in the future.
This kind of construction, imo, is an abomination, done without forethought. What it IS done with? "PROFIT MARGINS". For myself? I am NOT one of those, who thinks all business is bad, nor growth, nor construction, having spent my life IN such.
Although I was a Plumber, I, too, ran into something extremely similar to this, many years ago. A fairly new technique, where floors are pre-made for high-rises, (say 7 stories-up), with cut-in & reinforced "Plumbing cut-outs" are created, to help speed up the building processes, all-around. This are massive floors, for "Live-in" units, that have kitchens, and are very much like an apartment, but are really just for "Extended Stays', hence the name of one of those companies.
The problem? The job I was working on, the plumbing wall was created in the WRONG part of this pre-made floor. Instead of ordering a new floor be created, they "fixed it", by cutting in a NEW plumbing chase-way, "fashioning" some braces which were installed, and CALLING IT GOOD.
Now, people have to understand, this job? Was in the Bay Area, of CA. Earthquake country. They have stringent polices, (some moronic, imo- others logical), for all aspects of construction in CA, and for good reason, in most cases. What they did, imo, was circumvent safety, for PROFIT, and to "Keep the project on time".
I was NOT ok with this. And began trying to make people aware of this, and the dangers I foresaw, even though I was just a lowly plumber.
Needless to say, it was NOT received well, and the more I pushed, the worse it became for myself. But that kind of crap doesn't deter me. I kept going, even, eventually, speaking to the Building Inspector- who also, basically, ignored me. This later? Got me removed from my job site.
I'll bet you there was at least ONE person, who tried to warn on this overpass, as well. And who was also, IGNORED.
That floor? Far as I know, is still in that building. Right in the MIDDLE of it. I wonder how many cracks may have developed, as I told them I believed would happen, even with OUT any Earthquakes helping out, these.. what? 25-26 years later?
Maybe I'm completely wrong. It's possible. But these "cut-outs" are reinforced the way they are, for a REASON. And to cut through REBAR, that's part of the integral construction of the floors when pre-fabbed? And the SIZE of this cut-out, to allow 4" Cast Iron and all the rest to rise up through? To go along with the Original cut-out, already there? IMO, posses a grave danger of collapse over time, but ESPECIALLY in the instance of an Earthquake.
Now, I've not heard of any Earthquakes in that area, of any size, since that time. But what will happen, when, not IF, once DOES? I don't remember how many people can fit, in that section, of what is a pretty large complex, but it could rise into the hundreds- just from the collapse. If there are any gas-lines or maybe vehicles that end up in a possible collapse? Who knows.
The worst part? People see, from this video, that this is NOT an uncommon thing. How many people must have seen these cracks? When are cracks EVER A GOOD THING, but especially when dealing with Concrete? Ever seen your Driveway's cracks travel? Yeah.
So there you go. We can only do so much, to try and warn people of dangers we believe exist. And for some of us, we pay a price. Some are willing. Some are not. In fact, the "Are Not's"? I've no doubt, out-weight the "Willing", and by quite a lot.
So how many other, similar situations do you think are out there, ready to FAIL?
People never think it can happen to them. Until it does.
And many times, somewhere, there is someone, who tried to warn, in order to save lives.
The problem lies, in finding those, who will not only listen, but ACT.
Sad, but excellent content, thank you!
Were any charges pressed? Civil lawsuits? These dangerous people need to get their licenses revoked.
*_How could this terrible project get approval?_*
Complacency
Great job NTSB!
After this 3 hour meeting, the results certainly could be summarized in 10-15 minutes.
There should be an executive summary in the final report.
How does FDOT not know the peer reviewer was not certified to PEER REVIEW.
When ever they come up with a clever design the basic's seem to be over looked
Concrete is great in compression but useless in tension unless rebar is heavily used
They tried being to clever
Ive worked on bridge construction for 35 years and ive never seen a concrete bridge design look like this
It was unique.
Anybody know if there were any investigative hearings for this, and if there are any videos somewhere?
othername1000 Its Florida, don't expect too much digging at state level...
@@gordonrichardson2972 gotcha. Was wondering about NTSB investigative hearings
@@othername1000 AFAIK the NTSB investigations are held behind closed doors. Only the results are made public. This video is dramatic enough.
@@gordonrichardson2972 ua-cam.com/video/9X-gmagrMjs/v-deo.html is an example of an NTSB investigative hearing. Here's another one from the official NTSB UA-cam channel ua-cam.com/video/YEXTJDhGOSQ/v-deo.html
I'm no engineer ,but the rebar that I see are too small and too few.
I want to point out tho.
In the video I see the load transfer from the canopy to deck. Millisecond before sheer effect on base of 11-12. Its more capacity vs load, pulling bridge. Breaks at node and back. I don't see anywhere it is mentioned.
Simple sequence of events.
Feb 24 the first crack heard is the capacity vs load and removal of shoring on ends.🇨🇦 we stop. Review
Next 2 weeks ,cracks in important nodes and cold joints grow. Good idea guys let's move it.
Then 2 over tolerances during move...But then you set all that 950 tons on improper shim stacks to transfer the bad design load paths.
Releasing tension on the member allows the capacity to eat at the bridge for 5 more days.... last ditch you get the poor guy up there to over tighten basically what amounts to string holding this thing up. Soon as the string pops the load transfers backwards in bridge and you see capacity pull the bridge at the hinge point. Is it not more hinge and capacity, then sheer and force on lower node. In end bad design and building with inadequate oversight. You get this. Ottawa built a " UNIQUE PEDESTRIAN BRIDGE " almost exactly same thing happened. Only never made world wide news because we shord it up. Bridges don't fall on highways. We put safety over money. Try it. How about building normal regular Pedestrian bridges and save money to put elsewhere because what is a bridge...You walk over.it. . That shouldn't cost lives.