Apartment Building Collapsed Near Miami

dayhiker

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Of course, when I hear pool cave in, I have a certain mental image of what that means. What she called a cave in and what I would define as a cave in could be totally different. There are just so many things that could have caused it.

TexasBama, I assume you had Dr. Brown in school? He told us in the graduate concrete design course that in the first bombing of the World Trade Center that debris that had piled up around the column actually provided enough bracing to compensate for the change in unbraced length from the loss of a floor level and kept it from buckling.

I've seen lots of things in my career that I honestly have no explanation for how they hadn't already collapsed. I usually refer to it as air glue. I've also seen things that failed or behaved badly that took a whole lot of head scratching to figure out why it acted weird. Part of me thinks there will be some big smoking gun on this. Part of me thinks it'll be some subtle thing that leads to a change in ACI 318.


EDIT: One time I looked at a retaining wall that was leaning badly. It did not have a retaining wall type footing on it. I told them, this will fall. I can't tell you when, but it will fall. It could be tomorrow, it could be a year from now. I later got a call that it fell the next day.
 
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Bamaro

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By now they need to pull back the search and rescue and start the recovery and remove process if they haven't already. No sense in putting rescuers in harms way anymore.
I wonder if the north tower is still occupied. Seems to me it shouldn't be and they need to call in someone like CDI to remove it before it falls on its own. Nobody in their right mind would ever want to live there now.
 
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Go Bama

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By now they need to pull back the search and rescue and start the recovery and remove process if they haven't already. No sense in putting rescuers in harms way anymore.
I wonder if the north tower is still occupied. Seems to me it shouldn't be and they need to call in someone like CDI to remove it before it falls on its own. Nobody in their right mind would ever want to live there now.
After the Haiti earthquake, a 15 year old was pulled from the rubble fifteen days later.

They'll have to decide when it is hopeless before they call off search and rescue. There are so many missing and so many families distraught that it will be hard to face these people and tell them it's time to move on.
 

Bamaro

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After the Haiti earthquake, a 15 year old was pulled from the rubble fifteen days later.

They'll have to decide when it is hopeless before they call off search and rescue. There are so many missing and so many families distraught that it will be hard to face these people and tell them it's time to move on.
Unfortunately its extremely unlikely that's going to happen here. Much more likely that a rescuer will be severely injured or killed now.
 
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dayhiker

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So the pool deck collapses and the beams in the pool deck pull on the columns they're attached to on the main structure? But the pool is closer to the section of the building that came down second.
I realize you know most of this TexasBama, but adding detail for others.

I had previously just scanned the image of the building layout previously posted. In looking at it a little more and thinking back about that report makes me think more about just simply rusted out reinforcement on the beams could be it too. In concrete beams, you have 2 types of reinforcing. You have longitudinal steel that that takes the tension component due to bending. The bottom steel does the work between columns, the top steel over the top of the column. You also have stirrups. These are closed ties in a rectangular shape that are oriented vertically in the beam. Basically, they encase the long bars. They resist shear. Concrete takes part of the shear, the stirrups take the rest. You space them closer than half the depth of the beam. If you draw a 45 degree line on an edge view of the beam, you space these strirrups so that they always cross the 45 degree line. If not, a crack is not being crossed by steel, which is bad.

Stirrups are normally smaller bars, #3-#5. For #8 and below, you take the bar size and divide it by 8 for the diameter. A #4 bar is 0.5" in diameter. The longitudinal bars are typically bigger bars, #8 and above. They'd take longer to rust. So, if you're having all of those water issues and your stirrups have significantly deteriorated, you could have a sudden shear failure on a beam. When that happens, you likely still have a decent amount of longitudinal steel in good enough shape to do work/be intact. This means that the failing beam could yank on the rest of the assembly and then start a domino effect.

This leads to the question about it just suddenly and randomly happening. Concrete is heavy. A parking deck is only designed for 50 psf live load (future traffic). That plaza would have been designed for either 100psf, or, more likely, a firetruck. Firetrucks are darn heavy, but we'll ignore that for this example. Say those columns are on a 25' grid. This is just an example to illustrate the weight and is a gross oversimplification in many ways. 25*25*50psf = 31250# = 31.25k. Say you had a 6" slab, 14"x20" joists @ 8'-4" and then say a 48"x20" girder. The slab weighs 75psf. The joists about 25psf. The beam would be about 28psf. This estimate is a little high because there is some double counting on the beam and joist occupying the same space. Still, you're looking about 128psf - a little, but still 25*25*128 = 80k. Let's say the design live load was 100psf instead of 50, that means it's 62.5k. Your total would be 142.5k. 80/142.5 = .561, meaning over half the load is actually there. Adding weight for pavers, etc, puts you probably at 60% or more of the total design load actually in place. You're not allowed for the concrete to take over half the shear. If the shear steel had significantly rusted out, then you have over half the total design load in place and only concrete there to take the load, but you don't want the concrete to ever take over half the load. I'm not saying this is what happens, but it passes the initial smell test.
 
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dayhiker

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After the Haiti earthquake, a 15 year old was pulled from the rubble fifteen days later.

They'll have to decide when it is hopeless before they call off search and rescue. There are so many missing and so many families distraught that it will be hard to face these people and tell them it's time to move on.
I saw a press conference last night with some sort of official talking about how the families are having to come with terms that their family members are likely gone. She then added that they're having to come to terms that their family members are just body parts at this point. I thought, why in the world did you add that tidbit on the back end?
 

92tide

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I saw a press conference last night with some sort of official talking about how the families are having to come with terms that their family members are likely gone. She then added that they're having to come to terms that their family members are just body parts at this point. I thought, why in the world did you add that tidbit on the back end?
wow, that's cold.
 
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TexasBama

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I realize you know most of this TexasBama, but adding detail for others.

I had previously just scanned the image of the building layout previously posted. In looking at it a little more and thinking back about that report makes me think more about just simply rusted out reinforcement on the beams could be it too. In concrete beams, you have 2 types of reinforcing. You have longitudinal steel that that takes the tension component due to bending. The bottom steel does the work between columns, the top steel over the top of the column. You also have stirrups. These are closed ties in a rectangular shape that are oriented vertically in the beam. Basically, they encase the long bars. They resist shear. Concrete takes part of the shear, the stirrups take the rest. You space them closer than half the depth of the beam. If you draw a 45 degree line on an edge view of the beam, you space these strirrups so that they always cross the 45 degree line. If not, a crack is not being crossed by steel, which is bad.

Stirrups are normally smaller bars, #3-#5. For #8 and below, you take the bar size and divide it by 8 for the diameter. A #4 bar is 0.5" in diameter. The longitudinal bars are typically bigger bars, #8 and above. They'd take longer to rust. So, if you're having all of those water issues and your stirrups have significantly deteriorated, you could have a sudden shear failure on a beam. When that happens, you likely still have a decent amount of longitudinal steel in good enough shape to do work/be intact. This means that the failing beam could yank on the rest of the assembly and then start a domino effect.

This leads to the question about it just suddenly and randomly happening. Concrete is heavy. A parking deck is only designed for 50 psf live load (future traffic). That plaza would have been designed for either 100psf, or, more likely, a firetruck. Firetrucks are darn heavy, but we'll ignore that for this example. Say those columns are on a 25' grid. This is just an example to illustrate the weight and is a gross oversimplification in many ways. 25*25*50psf = 31250# = 31.25k. Say you had a 6" slab, 14"x20" joists @ 8'-4" and then say a 48"x20" girder. The slab weighs 75psf. The joists about 25psf. The beam would be about 28psf. This estimate is a little high because there is some double counting on the beam and joist occupying the same space. Still, you're looking about 128psf - a little, but still 25*25*128 = 80k. Let's say the design live load was 100psf instead of 50, that means it's 62.5k. Your total would be 142.5k. 80/142.5 = .561, meaning over half the load is actually there. Adding weight for pavers, etc, puts you probably at 60% or more of the total design load actually in place. You're not allowed for the concrete to take over half the shear. If the shear steel had significantly rusted out, then you have over half the total design load in place and only concrete there to take the load, but you don't want the concrete to ever take over half the load. I'm not saying this is what happens, but it passes the initial smell test.
I did some googling on Florida sinkholes and was a bit surprised there are some in south Florida. You'd expect it in central Florida where all the karst is (and there's a whole lot of them there).

I ran across this picture that shows the deck collapse. The pool area still looks level, but behind it is fallen (which is located out in front of the first buildling section that fell).

Capture.JPG
 

dayhiker

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I did some googling on Florida sinkholes and was a bit surprised there are some in south Florida. You'd expect it in central Florida where all the karst is (and there's a whole lot of them there).

I ran across this picture that shows the deck collapse. The pool area still looks level, but behind it is fallen (which is located out in front of the first buildling section that fell).

View attachment 17067
That shot plus a google street view image really help on the visualization. That is a really big area of collapsed plaza at the main floor level. Attached is a low resolution screen capture with snipping tool. Hopefully it'll have enough resolution to show. You can see how the plaza level is pretty close to that first elevated floor compared to what it looks like in your image.plaza1.JPG
 
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TIDE-HSV

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No, the pool deck collapses and is indictive that maybe a sinkhole caused this.
In her phone call to her husband, she actually said that the swimming pool "disappeared" into a sinkhole. I had to laugh about the retaining wall. I once owned a home over on Pine Island by Guntersville Lake. (Called "Pine Island," but really, it was on the mainland and the island was out even with it.) Behind it, the hillside went up very steeply for 600' or so. There was a patio between a single unreinforced cinder block wall.The first thing I did after buying it was to take a masonry bit and drill a bunch of bleeder holes. My intention was to built stepped block buttresses in front of it, but my FIL, who owned it with me passed and my MIL had no interest in it, so we decided to sell. The buyer was interesting. A guy from Grant had founded an insurance company in LA and retired to a house in Grant. His successor as CEO was a guy named "Rousseau." Some of you may remember both his name and the company from the news. Rousseau bought the house, in order to be near his still-boss (he'd retained chairman of the board). I gave him my bit, explained what I thought needed to be done to the wall and then, just to be safe, sent him a registered letter, signature required, explaining it all over again. My brother had a home in the area and, months later, we were over to visit and I stopped in to the neighborhood grocery store to say hello. They told me, starting with "Do you know what that crazy Cajun did?" that he had built back to within 3' of the wall without doing anything about the wall. Within six months, we had one of those 8" in an hour rain and the hillside ended up in the Cajun's master bedroom. A couple of weeks later, I got a call from him. He said he needed to discuss "your wall" with me. I just laughed at him and reminded him of our conversation and the registered letter. His conversation-ending remark? - "Well, it was worth a try." :) Later, I found out that he cut a lot of other (legal) corners also...
 

TexasBama

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That shot plus a google street view image really help on the visualization. That is a really big area of collapsed plaza at the main floor level. Attached is a low resolution screen capture with snipping tool. Hopefully it'll have enough resolution to show. You can see how the plaza level is pretty close to that first elevated floor compared to what it looks like in your image.View attachment 17068
There has to be a lot of collapsed deck you can't see that's under the rubble.
 
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dayhiker

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dayhiker

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This article makes me feel better about my own thought process as it sort of echoes the same things I suggested, discounted, then came back around to.
I read this from my phone on applenews and now when I go to the link, it wants me to subscribe. I wish I could find a clean link. This is the best article I've seen yet.

Basically, they jump on punching shear, talk about how the settlement isn't likely a cause, talk about low risk of sinkholes, talk about how they pool deck wasn't likely to pull the building down, then wait, maybe that could have been a bigger factor than they first thought. The difference compared to my ramblings was, on each item, they showed images explaining why they were thinking about it the way they were. One that was really telling is 3 columns, still vertical in the collapsed deck area. The columns were there, but the slab wasn't, meaning likely shear failure. One person interviewed said their initial thought was that even with the water damage, they still didn't see it failing like it did. I guess I'm saying all of this because I feel like I've been all over the place on this and have jumped around quite a bit. I was beginning to feel like it seemed like I was just throwing crap on the wall to see what stuck. I was glad to read an article that at least had people going through the same thought process as I was and that maybe I wasn't crazy after all.
 

92tide

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Best to be truthful rather than giving false hope by telling the truth.
saying the latter would not have given false hope, but would have been much more empathetic.

"they're having to come to terms that their family members are just body parts at this point"

"they're having to come to terms that their family members are deceased at this point"
 
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TIDE-HSV

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saying the latter would not have given false hope, but would have been much more empathetic.

"they're having to come to terms that their family members are just body parts at this point"

"they're having to come to terms that their family members are deceased at this point"
The official has an obvious sadistic streak. He/she must be a joy to work with...
 
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TIDE-HSV

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John, can you expound on this following paragraph? I understand the elevator shaft, but the beam differences seem awfully inconsistent to have been placed only for wind resistance...

The design may have been intended to help the building withstand powerful gales in an area that is frequently battered by hurricanes. “My guess is those columns on that left side [that] were shaped rectangularly and had those big beams going that way [were] probably designed that way for wind resistance,” said Bleakley of the Florida Institute of Technology.
 

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