Miami Beach, Champlain Towers South apartment building collapse, Part 13 44

[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
Miami Beach, Champlain Towers South apartment building collapse, Part 06
Miami Beach, Champlain Towers South apartment building collapse, Part 07
Miami Beach, Champlain Towers South apartment building collapse, Part 08
Miami Beach, Champlain Towers South apartment building collapse, Part 09
Miami Beach, Champlain Towers South apartment building collapse, Part 10
Miami Beach, Champlain Towers South apartment building collapse, Part 11
Miami Beach, Champlain Towers South apartment building collapse, Part 12


SF Charlie
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[SFCharlie]

My Theory:
The pool deck delaminated. The concrete corroded to the point that it got so weak that it could no longer hold onto the columns. It was not traditional punching-shear*. There was no, let me call it a "top hat", of slab on top of the column.
Enough of the pool deck structural slab failed that it's "catenary action" (pull) rotated the slab drop under the south face of the north wing. (1979 plans 31 of 336)
The slab drop failed from "M" to at least "K" or "I" so that it was possible for the entire center of the south face to fall intact.
This tilted the floors and roof, which in turn though "catenary action" pulled the rest of the north wing down on top of itself.

*punching-shear-punching-shear-flat-slabs

What is Punching Shear? Punching Shear in Flat Slabs
July 17, 2014 by Anand Paul
What is Punching Shear?
Punching shear is a type of failure of reinforced concrete slabs subjected to high localized forces. In flat slab structures this occurs at column support points. The failure is due to shear. This type of failure is catastrophic because no visible signs are shown prior to failure. Punching shear failure disasters have occurred several times in this past decade. An example of punching shear failure can be see in image.

SF Charlie
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[SFCharlie]

The Trigger:
The Trigger is building a condo on the beach next to the Atlantic Ocean.
Not because of the sand, but because the Atlantic Ocean is full of water so bitter that when I got some of it in my mouth, I threw up; because the Atlantic Ocean is so huge and soaks up the Sun's energy, and creates hurricanes that suck up salt water into the sky where the salt has no place to go, but to come back down as the bitter rain.

Trigger #2:
Trigger number 2 is that some of us humans are unwilling to spend money to keep us humans safe;
Unwilling to spend the money to build it safe, unwilling to spend the money to keep it safe.

SF Charlie
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[Jeff Ostroff]

My former condo 7 miles inland has all sorts of rebar rusting and spalling and it is nowhere near the coast. So while salt intrusion might be present I think the far bigger threat is the freshwater rains of any water type that soak into the concrete. Any pool deck that is over a garage and not built on the ground is not seeing salt water intrusion from the water table, because it is elevated off the foundation below it. Plain and simple this pool deck had water pooling for some time, we even saw numerous MLS photos I have shown where water was sitting there on sunny days with nowhere to go. Everyone wants to keep blaming it solely on the ocean, but think of it as only a contributing factor. Note these photos below showing standing water or stains, and pooling water on concrete is worse than anything else because concrete is a sponge to water.

.

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[SFCharlie]

My former condo 7 miles inland has all sorts of rebar rusting and spalling and it is nowhere near the coast. So while salt intrusion might be present I think the far bigger threat is the freshwater rains of any water type that soak into the concrete.

I'm not saying that Florida rain doesn't rot concrete. It does!
I'm just saying that hurricanes carry salt way inland. I know condos are your business. Concrete in Florida and I don't know where else is going to rot if it is not waterproofed, and I think that's what you're saying also?

pooling water on concrete is worse than anything else because concrete is a sponge to water.

Yes! Drainage around any structure anywhere is of primary importance. ... and checking the slope of anything exposed to the weather also, decks, walks, patios...

 

[Vance Wiley]

Charlie - notice the size of the remaining slab atop the column - particularly relative to the column ? It appears the Piper's Row Car Park slab had drop panels at the columns.
Note that image having what looks like a 4 foot square section of slab remaining and compare that to any of the columns at CTS pool deck area after the slab dropped.
There was likely the delamination and rusty reinforcing as you suggest, and ( I suspect ) VERY weak concrete likely due to the effects of chloride damage to the slab.
I await compression test results of core samples and a chemical analysis to show the chloride content. I am not sure the concrete I have seen in the pics can be effectively analysed using petrographic examination.
Thanks,

 

[miningman]

Theres a number of parking parkades here in Calgary showing seriously exposed badly corroded rebar. Calgary is 1000 kilometres from the ocean. I dont think anyone has suggested salt in the air is the cause. Might want to revaluate how critical / relevant this salty discussion is.v

 

[Jeff Ostroff]

Piper's Row Car Park did not have drop [panels, they had the typical punching shear perimeter at each column, which Champlain for example had 16 #5 rebars in a line across each column if I remember correctly. Piper's Row Car Park used a lift slab method and anchored to the column with wedges.

 

[Red Corona]

Regarding saltiness of the water - yes, the sea will spray in that far sometimes, but rain isn't generally salty, even on the coast.

But do you guys use salt over there in winter to keep snow and ice off exposed surfaces? Because if you do, that would result in saltwater being put into exposed slabs like a pool deck for sure.

 

[Vance Wiley]

Do they never use salt on the streets in the winter?
So it was not the concrete thickness that defined the quite regular rectangular failure perimeter. Too much reinforcing terminated at one location?
Thanks,

 

[SFCharlie]

I am not sure the concrete I have seen in the pics can be effectively analyzed using petrographic examination.

Yep! You're right


SF Charlie
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[SFCharlie]

But do you guys use salt over there in winter

In Florida? ...not sure they know what that is. (Winter is what they call it when the snowbirds arrive from Canada
I was driving home from Huntsville Alabama and it snowed. They were (resourcefully) spreading gravel on the roads...


SF Charlie
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[Demented]

Winter is what we call those 2 weeks of 50*F before it's hot again. Other than beach sand, there's no salt on our streets.

@Jeff Ostroff
What makes that standing water situation worse is the fact that the drains on the deck were known to be inop damn near all the time, especially when the building next door was being built. Water pooling for days on the deck, especially in shades areas closest to the building, was a constant resident complaint.

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

 

[AutisticBez]

I mean, I wouldn't call a broken core sample a reason to evac the building. I would call it further investigation. Like maybe perform further inspection to see the full extent?

To me, a failing pool deck might be the trigger, but it shouldn't have pulled the building down. Thats a design flaw. The pool deck should be designed to shear away from building. The beams at edge of building acted to prevent the isolated collapse of pool deck which might have taken no lifes, had it just sheared off.

This to me reminds me of my failing outdoor patio roof. Its a semi water proof covering. The wooden structure is rotten and failing. Its future collapse wouldn't be a problem except for the strong connections to the roof of the house.

Landlord says they will remove structure after it fails, but if part of the roof comes away, the property itself might be condemned due to old age.

 

[SFCharlie]

To me, a failing pool deck might be the trigger, but it shouldn't have pulled the building down.

Yes.


SF Charlie
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[ChiefInspectorJ]

A main reason for the slab failure and then the building was months of vibrations from the new Condo being built next door. Basically continuous seismic loads microscopically cause loss on rebar bond strength.
If someone here can do the calc on the patio detaching from the step beam that may solve part of the puzzle.
The step beam was damaged by the ripping apart of the BM A planter supports.
Along with an elevation change at the step beam which took 12" depth away. All this is enough.

 

[SFCharlie]

Catenary Action
To me, a Catenary is a curve, but I first heard it applied to the overhead power wire used on the Pennsylvania Railroad. The support wire hangs in, yes, a Catenary.
To the best of my knowledge, the curve was discovered by an architect and a scientist trying to build the world's largest dome. They found that if they piled rocks in the shape of a Catenary, the thrust of the weight of the rocks was down through the legs of the Catenary. The biggest example I know of is the Saint Louis Arch.
With chain the pull/thrust is in the opposite direction. Pulling sideways on the ends of the chain pulls the center up. Imagine a chain of chunks of concrete sand and pavers strung on rebar. The chain pulls sideways on whatever it is anchored in. In this case that's the bottom of the south slab drop (step beam) of the north wing. The pull on the bottom tends to rotate the drop (step beam).
Another potentially counter action is that if beams anchored to the drop (step beam) at the north end and a column at their south end, lose the support of the column, they twist the drop (step beam) in the opposite rotation. Twisting concrete is a great way to break it.

SF Charlie
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[Nukeman948]

A main reason for the slab failure and then the building was months of vibrations from the new Condo being built next door. Basically continuous seismic loads microscopically cause loss on rebar bond strength.

I guess that explains why they have never successfully built buildings close together in New York City.

 

[AusG]

The unusual pencil-sharpening of the columns is to me a critical feature. Poor concrete, poor rebar placement or something else. It stands out and has to get a mention in any logical assessment of the collapse.

Re the core drilling. Morabitos specs for core drilling stated (somewhere) that structural reinforcing should be avoided. This below was posted by Lizard7709 back in thread 4 but the exact source was not stated

 

[SFCharlie]

Re the core drilling. Morabitos specs for core drilling stated (somewhere) that structural reinforcing should avoided.

This is from:
8777-collins-avenue---preliminary-review-plans-for-40-year-re-certification.pdf (sheet 2)
Which can be downloaded from the City of Surfside Champlain Towers Public Records & Media Information
Use the Sherlock Homes looking glass to search for "40 year" for example.


SF Charlie
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[spsalso]

"...requesting approval prior to cutting any bars."


Bars appear to have been cut. Was there approval?

I ask not because I think it contributed to the fall, but because I would really like to hear about someone involved who did a Really Good Job. I like people who do Really Good Jobs. Warms my little heart, it does.


spsalso