Miami Beach, Champlain Towers South apartment building collapse, Part 06 131

[SFCharlie]

A continuation of our discussion of this failure. Best to read the other threads first to avoid rehashing things already discussed.
Miami Beach, Champlain Towers South apartment building collapse
Miami Beach, Champlain Towers South apartment building collapse, Part 02
Miami Beach, Champlain Towers South apartment building collapse, Part 03
Miami Beach, Champlain Towers South apartment building collapse, Part 04
Miami Beach, Champlain Towers South apartment building collapse, Part 05

SF Charlie
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[SFCharlie]

parts of the Local10 news video

Thanks for calling our attention to this.
Please, can you give us a link to the Local10 video?
Thanks

(Found it)
Structural expert studying still-standing Champlain Towers North looking for clues

 

[dik]

I have a bit more experience than the security guard... If I would have been there, I would never have guessed the outcome... a recent collapse in China where about a dozen people were killed... almost expect that sort of problem in other countries... and the perps, real or imagined, will see swift justice... I would have never expected this in the US.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Jedidad]

The "Building Integrity" YouTube channel has posted a video analyzing the garage tour footage:

https://youtu.be/ZAIJsaSo4Sw

 

[SFCharlie]

definitely resting on crushed cars at some height and there is a good amount of water down there.

Yep
I like to scroll the video back to earlier, to see what I've missed...

SF Charlie
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[SFCharlie]

The "Building Integrity" YouTube channel has posted a video analyzing the garage tour footage:

Thanks for the link!

SF Charlie
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[Sym P. le]

Watch: Yes, several, they have been being craned away.

Slavaging portions of deck, maybe columns next. Approx 10:30 a.m. edt

Note: L and M grid lines on perimeter wall.

 

[Sym P. le]

Local10 video

“The police department has made the site a criminal investigation site and they have not yet given the right to do any of that sampling,” Kilsheimer explained.

So they are taking samples from the north complex for comparative purposes.

 

[Sym P. le]

Collecting column samples. Approx 12:30 a.m. edt

 

[SwinnyGG]

If the rebar was wrong this building would have fallen during construction or shortly thereafter.

Strongly disagree with this. It is entirely possible for rebar to be insufficient such that primary loads are supported without any problems, but reduced excess capacity in the initial construction creates an issue later after loading conditions change due to occupancy changes, corrosion, reduction of concrete sections, and other aging affects take place which can take years or decades to make themselves evident.

 

[rodface]

Just wanted to say: flipping through the plan set for the 40 year restoration... it's quite heartbreaking. So much work was going to be done, involving all manner of disciplines: structural, electrical, gas, fire, landscaping, architecture. It is silly to mourn the time lost in preparing those plans, an untold amount (most??) of design work never amounts to any real product or finished outcome, but there is just something about how this particular project came to an end, so unexpectedly, and so suddenly, with the deaths of so many, that makes reading these plans a moving experience.

 

[Sym P. le]

from Youtube, also a local10 video

Salvaging vehicles from parkade. Entrance ramp wall visible behind.

 

[NOLAscience]

So much work was going to be done, involving all manner of disciplines: structural, electrical, gas, fire, landscaping, architecture.

Was any work to be done on the 'beam' at the 11" stepdown near Col Row 11.1? If not, and if the planter up against that change in elevation was to remain. then the building could have collapsed the day after the renovations were completed.

 

[CE3527]

NOLAscience - the 40 year plans called for removal of the existing pavers and topping slab so the original concrete slab could be inspected for damage. The plans include several different types of repairs depending on the specific damage conditions uncovered and observed. From my experience, that's a pretty typical approach to concrete restoration since it's difficult to pinpoint every single crack that needs to be repaired especially in this case, before the topping is removed. Usually the contractor will get paid by an established unit rate for actual quantities of work, like $/linear foot or $/square foot for the repair type.

 

[Sym P. le]

Could you upload a copy of the USA Today video? Thanks.

 

[dik]

...but they can drop another building down on top; are they concerned about damaging a crime scene? Go figgure...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Awestruc]

There seems to be something missing in test core A. If you add up the depths of different materials in test core A, the result is 14-1/4". The picture taken by MC shows a test core that is 13" in depth. MC defines the top layer as 1-1/4" pavers on sand. I assume the pavers and sand were removed before coring and therefor would not be included in the picture of the core sample. So, if you add back the 1-1/4" pavers to the 13" core, you get 14-1/4". This leaves no room for the sand and makes me wonder how much sand does one need to lay out in order to install pavers over existing tile? According to the internet, you need 1 to 1-1/2" of sand to form a nice smooth bedding for pavers. Therefor there could be a layer of sand that is unaccounted for.

In addition, if the waterproofing had failed and there was 2-3" of rain in the days proceeding the collapse, the materials could have been saturated with water, adding to there dead load. Below I have calculated the approximate dead load for the stack of materials on top of the pool deck structural slab and have also included the weight of water absorbed by each material with rough estimates of absorption by weight.

WORST CASE: Pool deck loading according to test core A with additional 1.5" sand layer needed for paver installation and saturated materials.

1-1/4" pavers = (11psf/sf/in)x(1.25in/sf) x 1.06 (6% absorption) = 14.6 psf
1.5" sand layer = (120pcf) x (1.5/12ft/sf) x 1.06 (6% absorption) = 15.9 psf
1-3/8 tile and mortar = ((10psf) / (3/4in)) x 1.375in x 1.03 (6% absorption for mortar layer only) = 19.4 psf
2-1/8" concrete topping slab = (150 pcf) x (2.125/12) x 1.1 (10% absorption for ordinary concrete) = 29.2 psf
9-1/2" structural slab = (150 pcf) x (9.5/12) x .06 (6% absorption for commercial concrete) = 7.13 psf
TOTAL = 86.2 psf

From my experience it is reasonable to assume that the engineer designed the structural slab for 100 psf LL + self weight of the 9-1/2" slab and ignored the weight of the floor covering assuming it would just be 1 layer of tile or pavers like CTN. ASCE allows you to ignore the 15 psf load for partitions when designing for 100 psf LL, so ignoring 15-20
psf for the 1-3/8" layer of tile wouldn't be surprising.

The 2-1/8" layer of concrete topping is kind of a mystery also. The contractor could have built the 9-1/2" structural slab level, then poured a topping slab to build in the slopes required by the original 1979 architectural plans. The engineer might never have know about this extra 25-30 psf layer.

Therefor, the slab could have been permanently loaded to 80-90% of its allowable design load and could have been in this condition just prior to the collapse. If you add in deterioration due to chlorides, soft concrete, questionable design of connections used in this time period, and poor installation of required rebar over the column, then there doesn't necessarily need to be another event to start the collapse other than the slab to column connections finally gave out progressively undermining the stability of the exterior columns.

 

[MechinNC]

Hi all, long time reader and this is my first post here.

Mech engr, not structural, but have a good bit of experience with failure analysis, but mostly machinery.

Been reading as much as I can on this, and have come up with some tidbits:

1. The collapse video from neighbor building of course is a vid of a vid, and lacks very important earlier frames.
But one thing I think I see is a red-ish dust cloud hovering over the patio deck between the collapsing structure and the camera.
This may further corroborate the witness statements that the patio deck collapsed minutes in advance of the main structure. This seems to be supported by debris in the tik-tok garage ramp vid, but so hard to make out details in that dark area.

2. The architect (in the spanish language vid, well done by the way) seems to favor the theory that the collapsing patio deck put a lateral load on a few columns, especially near the heavy planter, possibly causing their buckling toward the failed patio deck.

3. The analysis of the ring cam vid from 711 is very well done and eye opening. It does seem to show the dimensional distortion of the room, as well as it rotating as a whole. Fits a column collapse from below.

4. The engr hired by the town (can't remember his name) has put out a request through the town to examine soil conditions supporting columns in similar structures. I doubt he would go in that direction this early without having a good reason. They may have enough rubble cleared to view the remnants of the first failed columns and whether they moved downward prior to or during the collapse.

So in my mind, seems two plausible theories at the fore: Patio deck failed first and put lateral load on columns, causing buckling.

Or column subsidence due to soil failure below. But why would this cause the patio deck failure minutes prior. Could, I suppose, if subsidence was a slow process.

Either could be compounded by construction or design errors.

Fortunately, the debris removal will soon (??) allow inspection of the critical bits and critical areas. How soon, figure in a matter of days/week.

And I think speculating on causes and piecing random bits is a healthy mental exercise for engrs, even if not in our field. It's how we learn how to parse through mountains of clues and pick out the important bits.

I can imagine the remaining video evidence, and there should be a good bit out there, has been gathered up by "powers that be" and will likely be kept out of public view for a good while. So that certainly frustrates us speculators.

They should already be doing inspections of failed slabs, columns and their attachments to look for design problems, missing reinforcement and can also do chemical and strength tests on the concrete. We probably won't hear much about that as with the hordes of lawyers involved, the engrs involved probably will not feel free to post things on sites like this or youtube.

I bet when the final debris removal exposes the first failed columns, you will see a tent set up over it to prevent vids taken by drones or the neighbor buildings. Under the guise of "weather protection". Wait for it!!

 

[spsalso]

Being on the west coast, I'm just visiting now.

The third "video"(above), from way at the beginning of 6, has me puzzled.

The bar chairs in the background never move. The floor tips, in the video, up to 40% (21 degrees), and they don't slide or tip.

The floor reflects the bar chairs, so thus it is a smooth surface.

They are not fixed in place, as no one would do that and have an uneven spacing--this ain't Soho.


The stack of three boxes in the foreground: no movement there, either. And that's with a formerly vertical box adding its horizontal force.



Curious.


spsalso

 

[rodface]

For those who have not seen it, I wanted to bump this link to the full reserve study which was uploaded in the part 04 thread:

boo1 (Mechanical)10 Jul 21 12:53
Document with work to be preformed. Where is the major structural work?

https://files.engineering.com/getfi...hamplaintowerssouthcareservestudy03202020.pdf

There are photographs of every conceivable major component, the original generator, the security system monitor (could help identify what sort of system was in use).

 

[1503-44]

They are just there to observe the entrance and call 911 if a problem develops, such as intruders.

Dude, you're admitting yourself its not relevant, so...
Thank You.

The missing parapet is far more interesting.