Miami Beach, Champlain Towers South apartment building collapse, Part 07 90

[Seppe]

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Previous thread (Part 06)
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https://www.eng-tips.com/viewthread.cfm?qid=485223

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[Demented]

Well pointing on reclaimed ocean land would have been tricky. On the beach it's far easier to just build the temporary cribbing walls as you already have the pile driver there, and pump the water out. Plus it helps hold the sand together.


Precision guess work based on information provided by those of questionable knowledge

 

[spsalso]

Thanks, all, for explaining things to me about the slab and the water, etc.

Always good to learn new things.


spsalso

 

[Red Corona]

Hello, I've been following this for a few days and it's been very informative.

Now we're in the demolition phase, I wonder if anyone saw the point where they dug down to the garage deck? By the time I saw it, they had already removed all the columns, so there was no way to tell if M11 (which is the one 'missing' in the TikTok video, right?) was on its side rather than standing in punch-through like all the others. We may be making a bit much of the column being 'missing' - after all you can't see M12 in that video either and we know that was still standing.

One thing that the demolition videos showed to me is that the lower rebar all looked in pretty good condition, where they'd ripped the columns out. It doesn't look like the water intrusion from the bottom had damaged the column-basement joints.

Teguci posted a very plausible natural deterioration scenario back on page 5. That slab step is not a shape that concrete enjoys, and it ran right behind a constantly wet planter in the L-M area. We all want there to be an inciting event because it's quite disturbing to think buildings like this could degrade naturally to a collapsing state - how many other buildings, then, might also be dangerous? What about CT North? (Although interestingly it seems that slab step doesn't exist there - maybe someone twigged it was a bad idea?)

The 'car rams a column' and 'roof parapet drops onto pool deck to start the collapse' don't work for me. The reports of noises well before the final collapse indicates that the building was already redistributing load, and if the parapet had fallen down to start the collapse at 12.30 then lots of people would have reported that.

I've enjoyed the analysis of the 711 video as well which tells us more about the final failure. One interesting thing with that, and the exterior security video, is it shows the collapse starting with the floors still spaced normally, i.e. floor slabs have not detached from columns yet (at least as far down as 7). But when you look at the rubble pile in the immediate aftermath photos, there are large sections of continuous column; the columns didn't get crushed between the floors, so in the final pancaking, they must have detached? Or are those near-complete columns from the eastern section, not the first collapse?

There's a few loose ends that don't make sense to me yet.

- The timing of those Argentinians coming back versus the TikTok video, the 'loud crash' from the Sirs, and the pool deck collapse. They got back so late that you'd think that crash, which people have suggested is the slab step or M9-M10 beam letting go, would have already happened, but they didn't see anything on entering the garage. Can you get into that garage from the Collins St side? It doesn't look like it. So what was that crash if it wasn't something falling within view of the garage ramp?
- What was the 'creaking' above 1211 the day before? It certainly sounds like the roof work had done some damage up at the top levels of the building. It's hard to see how that could contribute to a bottom-level failure though, and the columns at roof level (even if seriously weakened) are nowhere near their load capacity. Maybe it's just a coincidence that the roof and ground floor had problems at the same time.
- So many of the reports of noises were from 'above'. Does this just mean that concrete and/or rebar was under severe strain throughout the building already, making noises throughout the x10/11 stack?

 

[Spartan5]

So many of the reports of noises were from 'above'. Does this just mean that concrete and/or rebar was under severe strain throughout the building already, making noises throughout the x10/11 stack?

Aside from the creaking, which could have been anything, all there was was 111.

The woman who escaped (from 611?) reported noises that caused her to go towards the balcony to investigate. I don’t recall her saying anything about noises from above.

What other reports were there?

Edit:

Monteagudo, who is in her 50s, woke up from a restless sleep and heard strange noises. She initially believed they came from the open sliding door to the oceanfront balcony.

“I ran and tried to close it but I couldn’t, I imagine because it was unlevel already because of all the movement,” she recounted. “I heard a crack and when I looked, I saw a crack traveling in the wall two fingers thick. Something told me, you need to run.”

 

[Murph 9000]

This feels like a fairly big stretch, but here's a hypothetical scenario for creaking in 1211 the night before. Keep in mind that the failure from severe overload progressed over years in Singapore's Hotel New World, so 24 hours isn't totally crazy.

The failure started in or around the M9.1–M11.1 beam the previous night. M9.1 cracked a little and dropped just a little. Let's say less than an inch, and it just looked like more miscellaneous spalling that they are used to ignoring. This wakes the lady in 1211 when there's a small bang and jolt, and she hears creaking as the structure around her complains about the new load distribution. A day and another thermal cycle passes, then the complex beam arrangement fails and brings the pool deck down, followed by the towers.

It seems odd that nobody else, particularly in the x11 stack, reported anything. Did they sleep through it? Was it small enough to be ignorable on lower floors, but something about the penthouse and roof structure amplified the stress up there?

Unfortunately, most of the people who could tell us about the small stuff they routinely ignored or accepted in that section of the structure perished in the collapse.

 

[Demented]

Could a lack of insulation explain it? In my building maintenance noises from the ground floor behind on other side sounded like they were coming from above me today. Just how the noise travels through the structure.

More potato cam. January 2019.

Precision guess work based on information provided by those of questionable knowledge

 

[SFCharlie]

I wonder if anyone saw the point where they dug down to the garage deck?

The BecauseSurfside channel has broadcast that on YouTube live, but I can't seem to find the video in their archive. I beleive it happened about July 14th...
Please see my post in part 6

Right Now, and since at least 6:40 PDT (9:40 EST) the search team has been ripping up the pavers midway between the pool and guest parking. They are sawing holes in the pool deck and removing the slab with an excavator.

 

[gonefishing2]

Below is a picture of Unit 1010 posted on part 2 of this thread noting what appears to be deflection in the slab at the end of counter top (red circle). Not sure how long before collapse this picture was taken.

What has troubled me about this picture, and I don't think it has been mentioned, is the green area around Column K. It appears the slab had dropped in relation to it's attachment to the column, but somehow the slab is being supported by load transfer to other elements of the structure. Of course I am ass_u_ming that the baseboard in this area was actually flush with finish floor when the flooring was installed.

 

[Demented]

Shadows. Other angles of the same room show no deflection.

Precision guess work based on information provided by those of questionable knowledge

 

[Demented]

As I have not seen them posted anywhere after scrolling back through.

Precision guess work based on information provided by those of questionable knowledge

 

[gonefishing2]

Thanks Demented. I was having a hard time explaining that one in my 'Vintage Brain'. I see something interesting in your pictures. It appears the sliding glass door frame is sandwiched on both sides by finish floor heights that are noticeably higher than original finish floor height.

 

[Demented]

4" spacing between those railing bars for the record. 3-7/8" if the shop that made them was as good as they claim they were back in the day. That's not a 2" spacing beneath the channel. I'm not having any luck finding any work permits for 1010.

Precision guess work based on information provided by those of questionable knowledge

 

[Demented]

That unit definitely has flooring that is substantially higher.
There was never any calculations figured in for all of these units being fitted with marble flooring, bathroom, kitchen counter-tops, or all of the added weight of hurricane windows either?

Precision guess work based on information provided by those of questionable knowledge

 

[Demented]

Finally. Original an condo unit.

Unit 212

Precision guess work based on information provided by those of questionable knowledge

 

[Demented]

*shrugs*
I'm still inclined to believe the pool deck failed first. There is definitely signs of settlement along that area.

Source of original.

https://images.condoblackbook.com/mls-units/357780193/30.jpg

Precision guess work based on information provided by those of questionable knowledge

 

[Santos81]

Was there a sea wall in the plans? Was the East facing wall in the parking garage what was intended to be the barricade between the ocean tides and the interior of the building? Water does flow 2-3ft below sea level here.

Permanent Site Bulkhead (orange) along the eastern lot line, 120’ west of the hardpack bulkhead (yellow). Retaining wall along the other boundaries. The bulkhead now visible visible along the south wall (green) was added in 2019 during construction of 87 Park. Blue is Tatum bulkhead, northern red is the assumed location of the old Biscay Island bulkhead, southern reds are the Normandy Beach bulkhead.

The west side of Collins Ave there was the eastern shore of biscayne bay with “The Quarry” located between Collins and the ocean at what is today 87th terrace and 88th St.

A sub-basement level exists below the garage slab.

 

[Paul Austin]

Thank you

officer put a cone where there was a tripping hazard hidden below the water's surface

I agree, the question is why there is no remnant of that column/s. The rest of the columns were affected by the collapse of the building but despite that they have big rebars left.

These are the totally non-existent columns.
Maybe it's nothing but I just bring it up.

 

[Demented]

Unit 511, images from March 2021

https://www.condoblackbook.com/surfside/champlain-tower-south/unit-511-for-Sale

611 above it for comparison. 611 was the resident who noticed the cracks at the start of the collapse.

https://www.condoblackbook.com/surfside/champlain-tower-south/unit-611-for-Sale

This unit appears it does have evidence of failure. That floor aint right. Door gaps are not even horizontally but are vertically. Cracking evident along single rows of tile. Sliding glass door is sunken in.

Maybe noises did come from above 111.

Precision guess work based on information provided by those of questionable knowledge

 

[GPR_Tech]

Throughout the TOWN OF SURFSIDE memo (ref Date: July 7, 2021) it REPEATABLY STATES:
"after GPR to AVOID reinforcing steel" when taking concrete core samples...

The M.C. Oct. 2020 report shows core samples that were taken of the C.T.S. pool deck concrete slab cutting completely through multiple reinforcing bars...
.

.

https://uc199e99c9a0c47ae8a72fd96a9...LM33s8t8H4XjYbmcOeSfx2JEAlx6Hdqls_yhUqw/file#

 

[Murph 9000]

This unit appears it does have evidence of failure. That floor aint right. Door gaps are not even horizontally but are vertically. Cracking evident along single rows of tile. Sliding glass door is sunken in.

The front doorframe to the building's corridor certainly looks twisted. It appears that the M column line has dropped a fair bit relative to the L line. Mentally extrapolating the gap at the top of the M-side door to the width of the L–M span, it could have dropped by more than an inch, assuming a uniform deformation across the span. That feels like a rather bad thing and sign of significant distress.

Maybe we are looking at some sort of compressive failure in overload scenario? If it hit the M line worse, maybe that could have failed the beam attached to M9.1 ahead of total failure, to collapse the pool deck ahead of the tower?