Ahhhhh. Yes, that makes a lot more sense. So, I wonder who decided they could do without a temporary center support until the cable stays were complete: the designer or the contractor? ETA: Apparently that's the same group, since it was design-build. Oh boy.
Looking at all the video news footage from when that first span was put up, it's one big case of "premature celebration". Those quotes are going to haunt them for life.
Looking at the pictures from the collapse, the center section isn't missing. What we're seeing is the span from one end to the center section, the smaller span was never in place. Also there's this: "A Transportation Security Administration employee is suing Munilla Construction Management, one of the companies that built the pedestrian bridge at Florida International University, alleging a walkway it constructed collapsed under his weight and severely injured him. Jose Perez, filed his lawsuit on March 5, claims the “make-shift” bridge walkway for employees at Fort Lauderdale-Hollywood International Airport collapsed. The lawsuit states: "The Defendant failed to properly maintain and examine the make-shift bridge walkway to make sure they were safe and strong enough to support the weight of an adult, and improperly allowed it to deteriorate to the point of total failure."
The span that is there has to be held up with the cables that are not yet installed. We’re talking about a temporary support that would sit under the centre of that span until such time as the cables are installed and tensioned.
As a point of clarification, remember that this bridge was just beginning to be constructed, that what they had installed at the time of collapse was the first of several milestones that had to be reached until it could be opened to pedestrians (still they had to put in the other portion over the canal, ad in the middle support structure for both portions, build up and install the pedestrian platforms going up to the bridge etc). Here's a PDF with a lot of the details regarding the construction.
Obviously, as with anything else, there is a lot of detail here that is important before deciding who is the donkey that gets the tail pinned on them. Just as a general observation, this thing had quite a bit of post-tensioning that needed to occur to include a center cable stay that wasn't constructed (at least according to the rendering, it appeared to have one). I would think that this would require some additional false work to support the center of span against the bending moment prior to post-tensioning but, again, it's all just monday morning quarterbacking.
This was the part that had me confused initially... all the reports made it sound like it was a bridge that was done and operational, but it wasn't. It was still actively being built... and that span sat there for 5 days without having that central cable-stay installed. I get the sense that this bridge, just like the Tacoma Narrows, will be showing up in a few lectures moving forward. Totally agreed. I do have a weird fascination with trying to figure out things like this and then following up with the post-mortem. I learn so much in my line of work by seeing what others have done wrong, and there's so little public disclosure (for so many reasons, from pride to liability), that it's a rare treat to watch it unfold. While this isn't my line of work, I find it fascinating nonetheless. (No disrespect to those who died).
As a follow up on those school walk outs.... sorry, protests: The students who did it are now facing detention and in some cases several days of suspension. From reports it sounds like they weren’t very happy when the ACLU reminded them that the schools were well within their rights as long as the discipline was the same as what would be handed down for them cutting class for the day or for those hours in which they protested.
Apparently they were stress testing the bridge when it collapsed. If it stands, it passes. If it collapses, it fails. Given that those were the only two possible outcomes, why in the hell was traffic allowed to continue under the bridge?
How the hell did that thing sit in place for several days, without anybody saying, "Hey, this flat slab of concrete that is this thick is spanning a distance that is this long, without any mid support below or cabling above?" It can't support its own weight, much less the weight of the concrete trusses and roof structure. Any kid who has ever tried to lay a long plank of wood across a creek knows that.
They were too busy patting themselves on the back with press releases and photo ops and news stories. I have NEVER seen that kind of a celebration for just starting a bridge project... it's usually reserved for the finish line.
You have a source? It makes ZERO sense for them to be doing any kind of stress testing when the thing hasn't been put together yet. I heard rumblings of some tensioning equipment that was working, which would have been required to install the central cable support and cables, but stress testing? What kind of stress testing? On what? And how?
https://www.apnews.com/eecd6fdb2d80...'Stress-test'-preceded-collapse-that-killed-6 Apparently, that span had cables running through the span that were deemed strong enough to support the span without the cable stay tower. Testing had shown that the cables had loosened off, so they were tightening them back up when it broke. That was the tensioning equipment that was on-site and working. They were doing this without stopping traffic.
"As state and federal investigators worked Friday to determine how and why the five-day-old span failed, one factor may have been the stress test Miami-Dade Mayor Carlos Gimenez said crews were conducting on the span." http://www.foxnews.com/us/2018/03/1...pse-have-history-fines-failures-lawsuits.html
That part is what baffles me if the information is correct. I work for a construction company that builds these structures (freeway overpasses, similar span bridges etc..). When we are stressing the post tensioning strands everyone stays as far away as they can be because the forces used on the strands are pretty extreme (hundreds of thousands to millions of pounds per strand group). Generally for what we do there would be falsework supporting the deck from the street below until the strands are tensioned. Once that is complete they are encased in grout to prevent slippage (there are other methods but this is most common here). If they had started to slip they may have figured “Hey let’s just go tighten these up and no problem” which in theory should work, right up until something goes wrong. That’s a long way of saying tensioning a bridge with no faslework below and live traffic may be one of the dumbest things I’ve heard of doing. If that is what happened.