It was the first time they ever tried to do a bridge like this. Built off site, then moved in place. So, that seems problematic...
This reminds me of the bridge collapses in the early 2000s. If I remember correctly there was a big one somewhere in MN. The media went into a big frenzy about it, and it came out that a high percentage of the bridges in the US were deemed in disrepair by engineers. Hopefully someone smarter than me can find the exact numbers. The closest thing I was able to find to what I remember is a report that says 56,000 bridges are structurally deficient.
The problems in those findings were that the bridges had exceeded their lifespan/improper maintenance. This bridge was put in place on Saturday. So unless it's projected lifespan was 5 days, some one fucked up big time.
That's an understatement. I'm sure the NTSB is already looking at the numbers and figuring out which engineer they're gonna hang first.
I know nothing about this project and just heard about the accident. I can tell you right now what happened just looking at this picture: This was tweeted celebrating the bridge's placement. There is no way that concrete deck can span that far with those loads of its own weight and the roof weight above. There is no web below the slab, and there can't possibly be enough steel, even if the concrete was cast off-site and prestressed. I am NOT a structural engineer, but that looks horribly underdesigned. ETA: Maybe there was supposed to be another temporary support there in the middle? But, that's just all kinds of wrong.
How? I don't get it. It looks like that deck cross section looks just like this top sketch, when it should have looked like one of the bottom two.
The Professional Engineering Association will probably be first on scene to help... they take this kind of thing very, very seriously.
It'll be very interesting to see if construction crews installed it following the signed-off plans... if the right concrete was mixed and prepared the right way... if the right reebar/steel schedule was followed... I can't imagine this going up without the signing engineer being on-site... yeah, this will be interesting to follow.
Five DAYS?!?!?! “Fucked Up” to say the least. And people thought the Kansas Hyatt Regency skywalk massacre was bad construction, holy crap.
I also wonder if they took into account any kind of resonance created by traffic passing under the bridge? Get some heavy loads going under it, the road flexes, sets up a standing wave, and all of a sudden your bridge stresses are well outside the initial values it was designed to handle... do that for a few days, and you get the "bend the aluminum can enough and it breaks" thing going on.
After seeing the Tacoma Narrows bridge video, I'll believe anything about resonant frequencies. But, either the deck design is just totally inadequate, or the stressed the concrete as it was moved into place. It may have twisted around the center of the bridge deck as they pivoted simply rolling over the crown of the road. I don't know, but as stated earlier, it's a major fuck up.
Interesting thread over on Reddit: https://www.reddit.com/r/engineering/comments/84osxn/west_miamidade_fiu_pedestrian_bridge_collapses/ The engineering company who built it have gone fully dark... web site down, no phones, etc. Gotta feel for them... I imagine someone just made a mistake, and it wasn't intentional.
Good BBC article with lots of video of the installation and the recovery immediately after the collapse. http://www.bbc.com/news/world-us-canada-43418898
And I'm really thinking this will be the key: The FIU-Sweetwater UniversityCity Bridge is the largest pedestrian bridge moved via Self-Propelled Modular Transportation in U.S. history. It is also the first in the world to be constructed entirely of self-cleaning concrete. When exposed to sunlight, the titanium dioxide in the concrete captures pollutants and turns it bright white, reducing maintenance costs. I wonder how close the material strengths are between normal concrete and this "magical self-cleaning" concrete. I'm betting it's weaker than traditional concrete, and they could have used numbers for "normal" concrete in their calculations. Interesting paper describing self-cleaning concrete. http://civilenggseminar.blogspot.ca/2016/06/self-cleaning-concrete.html
Interesting (to me, anyway) paper talking about the mechanical performance of self-cleaning concrete: https://www.matec-conferences.org/articles/matecconf/pdf/2017/11/matecconf_etic2017_01022.pdf
It could turn out to be one of those perfect storm things, like problem A was marginal, but on its own wouldn't cause failure; problem B, C, etc. But, then all 4 or 5 things together couldn't overcome the factor of safety limitations. And, that concrete was the final problem. However, it still appears to me that any kind of concrete wouldn't work on that design / implementation. It still looks like there is at least a temporary center span missing that was supposed to be there until the end treatments were connected.
Totally agree. It's like, "yay! we get to do something nobody else has done before!" "Shit... we have to do something nobody else has done before."
I wonder how much the concrete factored into the structural integrity of the span? It would seem to me that it was more of a failure in the steel at one of the ends due to the loading of a straight line span as opposed to using even a slight grade arch.
Sounds like it was a cable-stay bridge without the central cable support installed yet. That would explain why it looks so off... because it's not complete. Initial, unconfirmed reports also talk of the construction crew doing something with a crane and tensioning equipment. Which seems really fucking strange to do while traffic is still going under it.