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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[tmwaits1]

It seems like a very realistic scenario for the collapse and one that has been well simulated in videos is that the pool deck slab failed in punching shear first and imparted a large lateral load to one of the main supporting columns (column M) of the building or if it didn't put a large lateral load on the column then it at least removed a key lateral support and doubled the unsupported length. I like this theory but there is one problem with it and that is the first column where failure occurred did not apparently fail in punching shear. The key to understanding this is the tic tok video which shows the column completely missing. I totally agree that this video is too blurry and low resolution to be certain of what the debris is but it does seem clear that the column is missing. If the initial failure was punching shear the column would almost certainly still be standing. Videos of the parking garage interior show the missing column painted white with a yellow band at the bottom just like the others and don't show any issues with this column that would indicate that it was over stressed.

the column

 

[MarkBoB2]

Thank you jbourne8 for your following comment:

It seems like all of the objects they believe have an importance are being sprayed painted with some sort of tag (usually in blue or black), and are nearly always removed on the day they tag them. I've yet to see anything that was clearly from the roof get tagged.

If you look at the photo below you can see that several shots of red spray paint can be found around one of the objects. I was wondering what this red coloring was, and now you have confirmed that objects of importance have been spray painted with some sort of tag before removal. This object must be considered to be one of importance. I believe that it is an air conditioning unit from the penthouse roof.

 

[1503-44]

It is not a "problem" for the failure theory at all, if the first column did not fail in punching shear. Columns do not fail in punching shear. Slabs and plates fail in punching shear. Columns usually fail by combination of axial load and buckling flexure, especially if they lose lateral restraint provided by a slab. With one column buckled out, the adjacent columns would get an instant 1.5 x design load. With the slab no longer providing lateral restraint to any of them, they're most certainly going to buckle instantly, probably faster than the first column. The next columns then have 2.5 times their design load and no lateral support and so on. Actually there is no need for a failing slab to pull on the columns at all, but that certainly would not help the situation if they did.


Without a known scale reference, its hard to say, but those look kinda chunky to be from the parapet. Surely the parapet wasn't more than 6-8-12" max thick, no? I mean if that's a fan, OK it is circular shaped, from an AC compressor, those blocks must be at least 18" cubes or more..

 

[Murph 9000]

Ok, here is a hypothesis which accounts for M11.1 being "missing". It can extend to include K11.1 and L11.1, if the evidence requires a similar failure mode for them. I'm not certain it is missing, in the blurry gloom of those video frames, but it's possible.

The pool deck fails in progressive punching shear somewhere south of 11.1, between the pool and surface parking, eventually forming a catenary between the southern boundary and the 11.1 columns. M11.1 stops the punching shear progression due to the additional beams there. Instead of breaking away from M11.1, the pull from the catenary breaks the beam and raised patio away from M9.1. M11.1 then fractures at the basement slab and is pulled over towards the deck collapse, assisted by the weight of the still-attached patio and beams as soon as it's off axis. This leaves M9.1 with catastrophic damage as the rebar for the beam is ripped away sideways, but not so much that it instantly collapses, and a 5 to 10 minute countdown is started for its failure.

Alternatively, the pool deck catenary pulls M11.1 away from the beam, folding the column over and leaving the beam unsupported at its south end. The beam hinges down on M9.1, doing catastrophic damage without instant collapse, before detaching and dropping to the basement slab with the patio.

The arrangement of beams there means you can broadly fit that hypothesis around any mix of KLM, 9.1, and 11.1; that you feel best fits the evidence. Add whatever corrosion theories you believe fit best, to weaken the joints as required.

 

[NOLAscience]

several shots of red spray paint can be found around one of the objects

I don't think that is red spray paint. It's too diffuse. Could it be Conduit Red in concrete, which is designed for coloring concrete used in utility work for proper identification, like this stuff:

https://conspecmaterials.com/shop/concrete-colors/utility-red-cement-mortar-color-copy/

?

 

[NOLAscience]

and a 5 to 10 minute countdown is started for its failure

I like your theory. That's been rattling around in my head for the past couple of days, too, but I didn't put it into words like that.

What is your explanation for the 5 to 10 minutes between the failure into the garage and the building collapse. Why does the load redistribution take that long?

Also, the "blurry gloom of those video frames" is easier to interpret when you watch the original videos. The slight movement of the camera allows the mind to develop a more 3D imagery of the objects.

 

[1503-44]

Exactly. Between loss of lateral support for columns, loads increasing on adjacents, possible lateral pull from failing slabs and ... corrosion, mayby excessive roof loads, there are more than enough bad actors there to fail any column. Nothing needs to fall from the roof or be hit by a car.

 

[Colostruct]

Hey. I'm new to this forum although I have read it for years and commented in the past under a user name I can't find...

I agree with the narrative that the terrace slab failed in punching shear and that initiated a progressive failure. I agree with posts above that the transfer beam at the slab elevation change may have failed in torsion, or may have released from the support columns due to the offset lateral loads from the catenary response of the failed terrace. Seems plausible. This beam failure may have provided a bit of time before total punching shear failure of other elements.

What continues to bother me is "why now?" What was the trigger event? It just seems too coincidental that work had begun just shortly before total collapse.

Did something impact the terrace slab from a partial failure of the upper roof cantilevers due to construction activity? Possible. Is it possible that the upper parking area supported a construction staging vehicle or heavily loaded truck the day before? Maybe this loading caused a failure that took some time or additional factor (thermal expansion water discharge ...)to manifest into a collapse? Perhaps the failure was hidden below the sand and pavers (I've witnessed this myself).

As a structural engineer I've worried many nights about potential for structural collapse and, especially, progressive collapses. I'm just a one man firm in a small resort area. But, in my limited experience, I have been involved in the shoring and redesign of a dozen structures that were nearing a collapse failure(column degredation, progressive joist failure, wall collapses due to excavation, deck pull out etc.) Each of these conditions was life threatening. In the case of the progressive joist failure, seventy five people may have been involved.

Sometimes s__t happens. Maybe the truck hauling the roofing material or the grout for a facade takes a wrong turn and ends up where it shouldn't. This happened on a project of mine where about to they use a residential elevated slab as a construction staging area. I caught it as they were backing a 20000 lb trailer onto the structure. I wouldn't expect a building official to catch that even though my plans did not allow staging on that structure. Had my slab broken, though, the remaining structure would have been fine because I designed the building to isolate failure areas.

We have some control over what happens within a building. But, open air, exterior terraces that load up structures supporting multiple floors maybe should be evaluated with additional care. I often separate the structure to reduce potential for water intrusion and thermal effects transferring to interior spaces. I wonder if this needs to be something the code addresses directly?

 

[1503-44]

Theoretically the steel should start stretching and take (allow) some small amount of time for deflections to form and secondary stresses to appear. Since the steel is designed to yield before the concrete reaches compressive failure levels, the concrete is actually failing from the added secondary stresses.

 

[MarkBoB2]

I don't think that is red spray paint. It's too diffuse. Could it be Conduit Red in concrete, which is designed for coloring concrete used in utility work for proper identification, like this stuff:

https://conspecmaterials.com/shop/concrete-colors/...

?

Then why is the rebar above it colored red as well?

 

[Spartan5]

If you look at the photo below you can see that several shots of red spray paint can be found around one of the objects. I was wondering what this red coloring was, and now you have confirmed that objects of importance have been spray painted with some sort of tag before removal. This object must be considered to be one of importance. I believe that it is an air conditioning unit from the penthouse roof.

A smudge of red on a pile of garbage.

No red on the “anchor”, “parapet blocks”, or “roof ventilation fan”.

No cones. No caution tape.

You’re doing more to undermine your “theory” than to support it.

I happen to think that that red smudge is the remains of someone’s oversized sock puppet.

 

[Santos81]

I was wondering what this red coloring was

Since it’s still a USR Triage site, red indicates HR location.

 

[Murph 9000]

What is your explanation for the 5 to 10 minutes between the failure into the garage and the building collapse. Why does the load redistribution take that long?

If the beams pull away from KLM9.1 just right, they potentially shatter the concrete inside the column's rebar cage over essentially anything up to the height of the beam. Hypothetically, the rebar for the beams ripping out both shatters them and empties out the rebar cage a little. That critically weakens the column, but it still has the heavy vertical rebar and some concrete remaining to provide some support and the building attempts to redistribute loads. The failure then radiates outwards from there, with neighboring stress points cracking and deforming under overload, until enough of the structure has lost margin that it goes into rapid collapse on the next big crack.

RC columns can survive a surprisingly long time under heavy overload before they finally give up. See the Hotel New World in Singapore, where the slow phase of failure took years.

 

[rodface]

I don't have time to do a full writeup at this point, hopefully later today. But I invite any of the video-pixel-peepers to revisit the CCTV from the condo to the south:

-SLOWLY scrub back and forth from 0:00 to 0:06 in the video, the beginning of the visible collapse.
-Note that the two arc flashes between the collapsed portion and the standing portion are the first frame of the clip.
-Note how the flashes don't correctly line up with the lights going out in the windows to the right.
-Note how the two windows right in the middle seem to stay lit up for a very long time after the flashes, once they seem to have moved more than 1-2 stories.
-Now I invite you to consider the following: those are not lights; they are reflections from lights across from the windows.
-Watch how tiny "lights" appear to turn on and off as the facade slides downwards. Notice that the sequence appears to match the movement of the building. Perhaps what looks like lights turned on is nothing but reflections.

What does this mean? Perhaps nothing. Just interesting.

For what it's worth, that mush doesn't look like it includes the penthouse parapet in the collapsed section :O

Edit: Well I don't know if it's there in its entirety or not, but the upper two parapets are clearly visible at the top of the falling facade:

 

[Seppe]

There is some creative photo "analysis" in these threads.

I mean, we're looking at a pile of mangled demolition debris, and we've got posters stating that the unidentifiables therein are, beyond a shadow of a doubt, proof of a roof-level failure as the source of the collapse.

Sprinkle in some "PROVE ME WRONG" vitriol, and it becomes clear that a couple folks are going to believe what they want to believe about this collapse, and their belief is limited to some sort of Rube Goldberg roof-level chain of events.

 

[John2025]

Re: Penagwin (Computer)14 Jul 21 04:49
New video of the balconies was just released showing more wear on the balconies.

I'm no SE, but it seems like there're an awful lot of pictures where the rebar is really close to the bottom. Did they design it that way to make the slab as thin as possible or is it a construction error, or a combination of both?

 

[rodface]

@john2025 one thing to keep in mind is that concrete spalling had been noted and was in the process of being addressed. There is one document (can't remember which) that describes the contractor actually having chipped away spalled concrete. I believe this explained the apparently terrible condition of the pool room ceiling; it had already been chipped away. Perhaps that is what we are seeing here, they were chipping away all damage all over the building before going in and patching. Not sure if this is standard or best practice for concrete repair.

 

[1503-44]

If I may offer a slight correction.

The slab bars may pull out some concrete from the columns with them at that connection point. That concrete fails from tension.

Column bars do not rip out. The column's concrete compressive failure is violent and blows the bars apart and away as the concrete explodes outward. That most likely occurs at the point of maximum flexure from the secondary bending moment, typically at column mid height, brought about by the buckling displacement x axial load, which in combination with the axial compressive stress exceeds the compressive strength of the concrete and it shatters.

 

[arbitraria]

I think that Cassondra Stratton lived in 412, not 410, based on an evaluation of her recent blog photos, which show her in a unit that she just redecorated at great expense.

If I'm not mistaken, the particular post you're citing is from 2017. Her blog design is irritating in its clumsy navigation, but if you're looking at one of her entries, you can hover on the main image and see white arrows to the sides, which is the only place there seems to be a date.

I've seen it mentioned elsewhere that her most recent posts (not on the blog, probably Instagram) show a different unit that corresponds with the layout of a x10 unit.

 

[1503-44]

It would be nice if we could take the non-engineering related subjects back to Twitter, or wherever they belong. It sure isn't here.

Thanks so much