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

[Seppe]

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Previous thread (Part 06)
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[hochhaul]

So the roof anchor permit is dated June 23, 2021 and the condo collapsed at approximately 1:20am +/- on June 24, 2021, less than 24 hours after the permit was issued. My experience with permits is generally the contractor doesn't schedule the work until they have the permit in hand, because sometimes there are unknowns on when you'll actually get it once you apply. Is there evidence that the contractor mobilized to the project and installed these anchors before the collapse?

So you're saying that they managed to cut down to the slab and mount a couple dozens of roof anchors all on the same day they got the permit?

 

[12345abc6ttyui67]

JAKLED:

I'm not sure what your latest screenshot is supposed to be highlighting. Are you trying to suggest a roof anchor has fallen through the top right of the ceiling? That's clearly some HVAC ducting in my opinion and not at all related to the roof anchor. Presumably ripped through the ceiling as the remainder of the building collapsed taking the HVAC continuation with it.

 

[1503-44]

The numerous posts about x" of tile added being somehow relevant to the building collapse seems to be a complete red herring. Even if the design dead load was exceeded, the total design load would have to be reached to get anywhere near collapsing a beam or floor. It would take 6" of normal weight concrete=75psf on the entire floor to roughly equal a minimum 40psf live load X the 1.7 live load factor. It would seem that at least 50% of the units above would have to had 6" of concrete added to their floors in order to collapse a properly designed column. To presume that remodeling one, two, 3, or even all 13 units had any (substantial) impact on building performance seems just a bit ... illogical.

 

[Murph 9000]

I'm not sure what your latest screenshot is supposed to be highlighting. Are you trying to suggest a roof anchor has fallen through the top right of the ceiling? That's clearly some HVAC ducting in my opinion and not at all related to the roof anchor. Presumably ripped through the ceiling as the remainder of the building collapsed taking the HVAC continuation with it.

I agree. There's nothing that looks like a roof anchor there. That section of corridor (NW corner) has HVAC ducts above a dropped ceiling. It's associated with the large common areas HVAC plant on the roof, with vertical supply and return ducts adjacent to the elevators. The fall of the north wing included part of the same ducts, so they are sheared off at the ragged edge with everything else.

It would be a billion-to-one magic bullet scenario for a roof anchor to end up in the middle of that corridor, in my opinion. There's a considerable volume of solid material between the roof anchors and the central corridor. Also the general momentum of debris would have been away from the remaining building at the 8th floor; it's well above the top of the pile that deflected some material back to the west.

 

[Demented]

In an ideal world, yeah, but how does it all affect a building with obvious signs of concrete deterioration and a lack of steel reinforcement?
Just adding more weight to the overall picture.
Normally a few inches of rain pooling up in Florida wont be an issue either, but that likely was a contributing factor in the days leading up as well.
Possible data showing the building, and not adjacent properties, has been sinking into the earth since the 1990's.
This is reclaimed wetland.
Multiple copies of drawings floating around, some with revisions to the piles done months before construction, some without those revisions, some with revisions but construction notes specifically stating to ignore the revisions and make the piles 14"x14" precast. *shrugs*
As drawn and as built as it seems has been quite different


While not the reason of why a floor, or the building, collapsed, in my honest opinion, it's pretty illogical to discount a few hundred extra tons of load on an entire, but highly concentrated area.


Edit: @hochhaul
Those images turned out to be irrelevant it seems. It appears it can be inferred from the emails over the smell and the location of the maintenance parking spot that these items were likely on ground level before and at the time of the collapse. I was also looking at the image thinking I was at an incorrect point. I failed to notice the ramp was sloping down and away from image point, not up and away from image point.

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

 

[Murph 9000]

To presume that remodeling one, two, 3, or even all 13 units had any (substantial) impact on building performance seems just a bit ... illogical.

I'm inclined to agree with that, but I don't think it can be discounted from a more holistic analysis. If we combine the reduced margin from that extra weight with everything else, it could be a contributing factor. Perhaps the column damage in the middle of the 9.1 row would have taken longer to hit total failure, or even survived, if there wasn't so much extra weight bearing down on the damaged columns.

Two of the most important questions are why the pool deck brought the tower down, and why it progressed so quickly from first major sign to full collapse. That weight could possibly be a quite significant part of the equation, along with the general structural deterioration.

 

[12345abc6ttyui67]

Thinking out loud more than anything here (this is not my industry) and just testing my thought process.

If we assume one of the lower columns failed first, how would the remaining building react to load redistribution?

My assumption is that the upper floors/beams/columns will not be as highly utilised as the lower floors/beams/columns. This should mean they will have more capacity to accept load redistribution as the building reacts to the loss of the column and tries to find equilibrium. Seen as the upper elements are now being loaded to say 100% capacity (from say only 25% previously [notional numbers here just to illustrate the point]), whereas any lower elements also experiencing redistribution are being loaded to say 100% capacity (from say 90% previously), it would stand to reason more distress may be noticed at the higher levels due to the much greater change in utilisation from 'as is' to 'redistributed' loads.

Does this perhaps go some way to helping explain why many of the witness accounts felt like the noises were coming from above? There was simply more capacity, and a higher change in utilisation (therefore cracking etc.), occurring in the upper floors first?

 

[Demented]

Speaking of roof anchors, could this be a roof anchor attached on the PH-A balcony? I have not a clue as to what else it could possibly be, why it's still there, and what is was doing there in the first place.

Original since potato cam upload.

https://pbs.twimg.com/media/E40BC6BX0AM_jnu?format=jpg&name=medium

Not the newest of images. This unit was just sold 05/11/21.

Edit: Core drill for railing with odd rusting stains being blurred and sharpened by cell phone camera? It appears to be protruding up rather than going down in.

 

[1503-44]

Murphy9000, My 6" concrete is way over the top. I did reduce it by 50% for multiple floor considerations. I'm saying in effect realistically that additional dead loading of an inch or two of marble in two units or so is a red herring. Of course one pound might have been the straw that broke the camel, but in general excess floor loads is not likely to lead to building collapse.

Random, If the basement column failed, I feel that you don't have to consider how the entire building reacted to load redistribution. You probably don't have to consider any more possible redistribution of load in more than the local floor above and the immediately adjacent columns to reach eminent total collapse. One column failure basically causes adjacent columns to experience a 50% load increase, so they are within a hair of ultimate factored load right there, not considering the rapidity of such a load increase, which must be near impact conditions. If just one adjacent column failed in a full design load scenario, game over. Loss of lateral bracing to prevent column buckling even more serious.

It is also unlikely that a residential building ever gets fully loaded. Nobody I know puts 6" of concrete on their floors, nor makes a guest list based on 4 people per square meter and fills the room, nor would you expect that to happen for 50% of the units all at the same time.

That points the finger away from building dead and live loads causing failue.
Construction loads, poor workmanship, material defects become more suspect, but even generating high loads from remodeling work is not all that easy. Even considering maintenance anchors. Another red herring.

 

[pellucidar]

So the roof anchor permit is dated June 23, 2021 and the condo collapsed at approximately 1:20am +/- on June 24, 2021, less than 24 hours after the permit was issued. My experience with permits is generally the contractor doesn't schedule the work until they have the permit in hand, because sometimes there are unknowns on when you'll actually get it once you apply. Is there evidence that the contractor mobilized to the project and installed these anchors before the collapse?

Evidence beyond the presence of new roof anchors on the roof? I dimly recall some discussion of the after-the-fact permitting on an earlier page of this thread, but I may have seen it elsewhere instead.

 

[LionelHutz]

it's pretty illogical to discount a few hundred extra tons of load on an entire, but highly concentrated area.

Lets not over-exaggerate how much extra weight the change in flooring would actually add to a unit.

 

[LionelHutz]

How'd those anchors on the roof get installed before the permit posted by JAKLED was issued? I'd tend to believe the permit was for some other anchors yet to be installed and has no relevance.

I'd also tend to agree that the ones on the roof are for tie off when working on the roof and not for use as tie off when working on the sides of the building.

 

[gonefishing2]

The point of my posts is to generate out of box thinking, as I feel that is what it takes to solve this riddle. IMO it is a system of many parameters that led to the structure giving way to gravity.

As a child I built many things with erector sets, and this may not be a Spartan5 level analogy, but I think the tight original design wing-nuts will see this more from a by the book perspective, where as the loose wing-nuts will look outside the box at the warning signs that may have been overlooked because our Special Inspector Training is NOT GOOD ENOUGH yet to solve this unfolding new riddle.

This was a system of failures from original design to lack of well baby care that led to this collapse. Why did they not start working on ground level first, it was because Association would not allow pool out of service nor possibly loss of parking spots, so they started on roof of a time bomb.

I know when my wing-nuts were loose at the joints of my erector set vs tight joints, the load capacity and stability of the structure varied greatly. Now this was a young child figuring this out.

Loose joints probably were one of the biggest issues in this building, leading to racking of structure, thus shifting load paths over time and shifting stresses. Think about removing masonry in fill non load bearing partitions that may have been proving some racking support.

It appears column cold joints between floors were not well tied together. Slab deflections will put lateral stresses on the column to slab joints and could put the columns in towards the middle of some units, while pulling them away from slab to column joints in adjacent units.

Why can't some folks see this concept???

I would argue it takes a far different skill set to design a structure from scratch, with the Architect dictating a lot of problems for the structural engineer to figure out solutions too, that go against anything the EOR wants to do, but hey what happens if Architect and customer unhappy with EOR..... They find another EOR that will do what they want.....

Folks are ignoring the loose joints of this building, and the effects of vibrations of varying degrees on those loose joints, yet the joints are the most critical part of the design process.

Look at Hard Rock Collapse in NOLA. Did not the steel erectors leave out bolts at connections and leave the joints loose as they added floors above, coupled with design issues.

Loose joints whether steel or concrete can become a big issue.

So if you read this to this point, you realize I am a loose wing-nut.... I did the opposite of Demented and went from Structural start to Aerospace. Think about it, Aerospace engineers design stuff to blow up or exploit what Structural Engineers Design......

And AeroSpace Engineers do all this without a PE Stamp and the liability that comes from doing Public Structures....

The shaking of Champlain Towers appears to have started being noticed when the stimulus of pile driving started next door. Does that mean the pile driving caused the collapse. NO. But it may have been a key contributing factor to a exponentially decaying defective structure. And this construction happened after the 2018 Morabito Report.

What I really don't understand is why so many tight ass wind-nuts are taking such a hard stance that only a simple solution and only their theory could be possible.

You can not pick and choose which pieces of evidence you consider. It is all important, and must be considered and factored into the algorithm....... And that algorithm may not be a simple linear equation......

PS I typed this on the fly, and did not proof read, so there may be typos....

Think about it. I, K, L, M 9.1 Column line had cantilevered slabs to transport moisture into the exterior column line to slab joints at each floor column joint. Was the cantilever slabs well maintained to prevent moisture intrusion in this area? I think no, these were neglected just like the garage slab at wall interface. We can see the water soaking into the building in the garage tour. Water intrusion is not stopping at the exterior wall...

Edit for Spartan5. Dirac Live does a great job eliminating those room modes you are referring.

 

[dik]

In the country you can see numerous old collapsed timber framed barns... the reason... lack of maintenance. In the case of this condo... it was occupied at the time.

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

-Dik

 

[spsalso]

I discovered with my Erector Set that if I installed diagonal bracing, I could leave the bolted connections loose, and it wouldn't fall down.

I also discovered no wing nuts. Mine came with square nuts and some crappy flat wrenches. Old school, I guess.



spsalso

 

[Demented]

@lionelhutz
To each floor, I agree minimal. To the columns and and piles with an unstable subsurface. Weight matters.

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

 

[SFCharlie]

I was about to ask why the hallway sheer walls didn't halt the collapse, and then I realized that, viewing the security cam footage, they did, momentarily. First between the pool side and the street side of the center section and again between the center and the ocean (east) side. I think if this open design continues to be used, a way to limit the collapse needs to be designed. What are the thoughts on how the collapse propagated across the sheer wall central core of the building, and how it could be limited at that core?

SF Charlie
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[Colostruct]

One thing that continues to haunt me on this building is that lack of evidence...at least from the photos...of SIGNIFICANT and dangerous degradation of the reinforcing within the columns. Sure, there is some spalling paint and a few locations of damaged columns and spalled concrete. But, it just seems to me that the apparent, observable, signs of continuing widespread rusting of reinforcing does not appear to be evident. I have done some repair designs on seriously damaged (by de-icing agents) columns and slabs. The amount of rust staining I encountered was way beyond anything that I have seen in the photos so far.

Was this building so tightly designed, or missing enough of the reinforcing at strategic locations, that poor maintenance was the secondary cause and not the primary?

I continue to wonder if the beam spanning between cols m9.1 and m11.1 was NOT bearing on the columns and, instead, was constructed hanging from the columns? If this is the case, and the stability relied on the horizontal bars supporting the loads in shear it would take very little reinforcing damage to release this beam from the support. This beam could then collapse at M11.1 and push against col M9.1. This could cause the collapse of the pool deck prior to collapse of the main structure as the structure tries to re-distribute the loads from the lost or displaced column. Many of us have theorized that this is the area of initial collapse.

I also continue to wonder why the collapse occurred so shortly after construction commenced? IF this area was subject to additional loading as a result of the construction activity could this beam support been jeopardized? Could slab rotation have tweaked the (maybe) poorly supported beam and been the trigger?

I also have my doubts that the overall lateral stability of the structure was up to the job. Rigidity attracts load. We have a, relatively, flexible east wing of the building (lateral load transferred by slab to column connections) bringing loads onto the first level framing system where those loads are distributed to the perimeter walls and lower columns. When I design a building, I design the systems to experience deflections at similar rates...ie the stiffness is compatible for the anticipated loads. IF locations of rigidity exist with poor connections, those connections may well fail and the loads will seek another path.

IMO, the biggest issue here is how we take the lessons from the collapse of this building and apply it to our designs going forward. IF this structure would have been constructed with additional shear walls would that have bought occupants some additional time to evacuate? I know many of us do design with consideration to preventing progressive collapse...these days. But, do we need to consider retrofitting existing buildings to limit the collapse potential? Maybe once we cross a threshold on occupancy?

 

[bones206]

The point of my posts is to generate out of box thinking, as I feel that is what it takes to solve this riddle.

As long as we learn the lessons that this collapse shows us and implement improved processes going forward, to me that is more important than necessarily pinpointing the exact cause of the collapse. The more avenues of potential causation that we examine, the more we can reflect on the way things were done and hopefully improve them going forward. I'm a structural engineer, so I hope to eventually learn the cause of this collapse for the sake of closure. But in the meantime, there have already been plenty of design, construction/inspection and maintenance/renovation/durability issues identified to ruminate on. The least I can do for the victims and their families is to learn all I can from this to make my future designs more durable and resilient. For me it's more about the process than the final result. I think everyone on this forum has done a great job investigating the limited public info and employing the scientific method to imagine plausible hypotheses and vet them out.

 

[Teguci]

Has anyone observed rusted through rebar from the plaza slab demolition? For all the talk about deterioration, I haven't seen much spalling and rusting from the top layer of rebar.

As for the deterioration caused trigger theory, my thinking is that the slow failure of the stepped slab added moment to the building column(s) which caused the creaking noises of the structure that were observed. I don't have a big enough margin to do that calculation, but a frame analysis could certainly serve to discredit my theory (there would have to be a bit of rotation in those columns to cause audible distress in the floors above). I take it as a given that people heard the noises that allowed them to flee the building before the collapse of the plaza slab followed by the building collapse.