One of 3 piers, actually, the center one. That's correct but the tower (not the pier) that sits on that same, center pier after the 2 sections of bridges are placed and that holds the cables needs to be erected after the two sections of bridges are in place, as in the picture you posted. The center pier (or a portion of it that the bridge was to rest on) was already there and that part of the bridge swung into place and sat on a section of that pier.
You can see that both ends of the bridge were still sitting on their piers after the collapse. So the problem was obviously somewhere in the integrity of the span of that section and why it didn't sustain it's own weight until the smaller section of bridge was installed, the tower erected and the cables installed is the unknown. It was supposed to withstand at least its own load without any cables until they're installed like most of these bridges do, but it didn't.
Yep that wasn't even in the picture at the time because that center pier didn't look like it was completely poured yet. If you notice, just the portion of the pier where the first bridge sat on was complete. The rest of the pier where the tower's weight and the smaller section was to sit on looks like it was still formed and rebarred but not poured yet. They were going to do that after that first section of the bridge was installed. And the tower was going to be erected probably after both sections of bridge were installed or at least after this first section. So there was a long way to go before any of the suspension cables were going to take effect which means that first section of bridge was supposed to sustain its weight on its own for quite some time and it barely did.
Yeah, I actually agree with you because that is the safest way to build something like this. That's the way we build houses or decks or any type of structures that have critical bearing elements to them. You erect the vertical support structure first, then you install the horizontal structures to sit on those supports and if you're missing any of the vertical bearing supports at the time for any reason (like if they're in the way or whatever,) you put up temporary supports. It's the conventional way so I'm with you. But this method for this quick bridge is not like that, and they've never failed before, they've actually always worked.
One thing you can easily notice is where the failure occurred. In the picture you can see the bridge broke into several sections. That first section that is leaning up against the pier was the first section to give way in the video. You can even see the A-frame for the cable connection came right through the top layer. You can see that section fall first in slomo in the video.
In Florida, most of these bridges are built using poured concrete instead of steel because of hurricanes and damaging wind forces etc. They don't build them with just steel and planking etc. because concrete is much stronger. But if you look at the amount of concrete and rebar they used on this, it's really incredible. 950 tons for that section. There are also long, curing periods when you use so much concrete before any pressure is applied to it.
You also can't pour all the concrete in even a small bridge like this at one time. It's physically and practically impossible. Therefore all the concrete in this bridge isn't all joined together by one pour. In other words it's not one single slab of concrete that is molded together at once. That means there are sections and those sections are joined together in a dry/wet process. Naturally those joints are pretty important and depending on the design, they're made to blend in and not look like joints. That's where the rebar work is extremely critical.
There's also another major factor for when you pour concrete into heavily rebared slabs or sections where you're supposed to use vibrating probes to ensure the concrete funnels into all the voids between the rebars. There have been cases where the engineers called for way too much rebar that there was hardly enough space between them for the concrete to fully flow, creating voids. Voids are like cracks. They use those vibrating probes to stimulate the movement of the concrete into those tight ares but that's a very tricky thing to do because there's also a negative to that vibration method. If you do too much of it, it separates the aggregate from the cement in the poured concrete itself which then weakens it. Any or a combination of all these things could have contributed to the failing of this bridge.
who graduated from the university FIU.
