Miami Beach, Champlain Towers South apartment building collapse, Part 02 151

[dik]

thread815-484587


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

-Dik

 

[Damras]

Not sure if it's been clarified already, but there was some discussion about how Cassie Stratton, the resident who was on the phone with her husband when the building collapsed, was quoted as saying she saw the "pool" collapse.

According to this article, she referred to the "pool deck" collapsing.

Cassie told him that the building was shaking and the pool deck had collapsed.

There is no direct quote attributable to anyone, but I'd guess it's either based on an interview with the 911 dispatcher who spoke to the husband, or from the husband himself. I suppose it could also be editorial choice by the author.

 

[ChiefInspectorJ]

Rebar clearance ACI 318
I would double the allowable clearance without the tolerances. That is because the plans you draw are NEVER done exactly or sometimes close to the drawing. Lets call it a factor of safety that is calced in almost every other structural component.
And special cover required for special uses such as possible damage.
Also when you spec: 8" oc the field guys start at 8" not zero!!
Especially on nailing patterns.

In the field alot of these measurements are not taken from the outside of the bar.
Bars are not always straight. And neither is the structure.
CMU rebar clearances are also worrisome.
For standard C-90 plain vanilla CMU, let's see...

11.625" - face shell(1.5") - d(8.5") - 1/2 #6(0.375) - 530.1 tolerance(1") = 0.25" clear

or 11.625" - face shell(1.5") - d(8") - 1/2 #6(0.375) - 530.1 tolerance(0.5") = 1.25" clear

 

[saikee119]

DB27 (Structural),

On you marked up drawing of 1 Jul 21 21:43 post you indicated a column adjacent to and outside the un-collapsed building not visible and could have possibly collapsed.

There are evidence that this column had punched through the pool deck slab just like the rest of the other adjacent 6 columns nearby. In the Morabito drawing this column lies at the border fence of the bush area.

It is shown up in this shot. You can see its top just next to the parked car.

Another photo shows it is covered by the displaced fence but at 20' c/c distance with the other two columns you can make out it is there in this photo.

 

[warrenslo]

It's also interesting that many of the columns remain, but I don't see evidence that K/14.1 is still standing. If the beam at the slab drop (K/12.1 to K/16) failed at mid-span due to the missing beam, it would create a sudden eccentric load to column K/14.1, possibly causing it's collapse.

Column K-14.1 is still standing (visible between the fence and gray car):

All three of the following accounts depict initial debris coming from above:
1. Mr. Nir, Unit 111: Noises above her unit, knocking grew louder before she heard a "smash," as if a wall had collapsed in the unit above hers. She went to the lobby after hearing these noises. While with the building's security guard in the lobby, and as she complained about the noise, she said, they heard a boom. She ran toward the sound and witnessed the building's underground garage collapse. It was like something out of a movie, she said. Link
2. Ms. Monteagudo, Unit 611: She heard a strange noise and it felt like the building was moving, tried to close the sliding door to the balcony, and it wouldn't close. She then heard a crack, a line in the wall coming down from the ceiling "about two fingers wide" then it started getting wider and wider as she watched.
3. Rosie Santana’s camera, Unit 711: White, hail-like debris coming from above and heard pelting her living room, before the camera abruptly goes dark after 13 seconds. Link

Roof work was actively occurring, the building's new roof anchors were inspected by a city inspector, Jim McGuinness, on June 23, 2021.

Well look here... The roof anchor permit was issued by the city on June 23, 2021 to Concrete Protection and Restoration, LLC. Link The building collapsed on June 24, 2021, at approximately 1:30AM (less than 24 hours later.) It's possible the initial work was unpermitted, I doubt they could have installed all of these roof anchors in one day. The town has not posted any other roof anchor permits I can find.

Roof anchors visible on collapsed penthouse roof:

Work was not complete as rolls of roofing paper are visible on the roof of the remaining portion of building directly adjacent to the collapse (left circle below) and improperly installed roof anchor (right circle below further discussion below):

Close up of roofing paper from drone video - note the green plastic looks similar to that seen in the garage in the tiktok video:

The penthouse roof anchors are to be on or between the columns, not on the cantilever portion of the slab (the two anchors circled are the two columns which failed first in the surveillance video):

The roof anchors were improperly installed on the cantilever portion of the rooftop slab in the portion of the building that did not collapse:

Roof anchor drawings note required repairs of concrete and a slab thickness of 8" - to be verified (how exactly is a roofing contractor supposed to verify a slab thickness?):

Post roof anchor detail notes 6" slab, states anchors should not be installed on damaged concrete, slab to be xrayed, and notes 25% of anchors need to be proof load tested to 5,000 lbs.

I believe the roof anchors over the penthouse were installed incorrectly, the first bangs of construction Ms. Nir heard was pieces of the roof falling off onto the pool deck. This caused the pool deck to fail either by hitting a column in the parking area as the ENR article suggests or by overloading the slab.

Please poke holes in this...

-W

 

[Sym P. le]

Devils advocate here. Is this the pickup truck/vehicle that struck the column and knocked down the tower?

Motive, perhaps a disgruntled unit owner angry about the special assessments they are about to face?

All of the other deck area columns punched through the slab whereas this one appears to have snapped as though taking a lateral load.

Truck to same scale as plan

 

[Keith_1]

I totally apologize but I really don't see any "mechanical roof anchors". To me the term infers a mechanical connection between the base-ply and the underlying substrate, and not the connection for A/C stands, flashings or caps. The term mechanically fastened roof makes me think of anchors on a foam or thin lightweight concrete over a metal deck and not a pored a RC deck.

 

[saikee119]

MIStructE_IRE (Structural),

Your theory that the pool deck was the first one to fail that led to the collapse of the building may be hard to explain the following:-

(1) The external section of the pool deck, that has no building above, has dropped from ground level to the basement level. In so doing it shear-punched through at least 6 columns size of 16"x12". How could the pool deck punch through the 6 columns with such a huge vertical load when it had zero live load in the middle of the night when no one swam outside?

(2) The pool and its surrounding deck did not fall onto the basement floor. If leaking was to blame for weakening the pool deck then the leakage path would be very long for water to travel from the pool to the deck currently covered up with debris. I have assumed the entire +11'-0" level as the pool deck (in William M Friedman & Associates drawings) which is called Level 1 in Morabital drawings.

(3) The collapse was in two stages. First stage was by the inner section followed shortly by the outer section on the North end. The failure of the pool deck level had to be in a sequence or manner to reflect this two-stage movement.

 

[warrenslo]

I totally apologize but I really don't see any "mechanical roof anchors". To me the term infers a mechanical connection between the base-ply and the underlying substrate, and not the connection for A/C stands, flashings or caps. The term mechanically fastened roof makes me think of anchors on a foam or thin lightweight concrete over a metal deck and not a pored a RC deck.

The roof anchors I'm referring to are OSHA fall-protection roof anchors.

 

[SFCharlie]

The length of Part 02(in lines of text)is too long for me to scroll through with my browser.
Can someone start Part 3 Please.
Thanks

SF Charlie
Eng-Tips.com Forum Policies

 

[dik]

It just gets more interesting... It's a shame that lives were lost.

"A Florida building inspector who assured residents of the collapsed tower that it was in good shape a month after being warned otherwise is having all of his previous work reviewed after being suspended from his new job.

Meanwhile, it has also been disclosed that the entire building department for the town of Surfside was under review at the time of the collapse.

Rosendo Prieto was chief building official of Surfside until November 2020. On Tuesday, he was placed on leave from his job as interim building official for C.A.P. Government Inc.

Now, city officials in Doral are planning on reviewing his previous work to make sure he didn't clear other buildings that may be dangerous."

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

-Dik

 

[799931]

If the engineers performing the assessment weren't able to identify a need to urgently evacuate building clearly the building official wouldn't have been able to either.

His assessment of other buildings from a structural safety perspective is probably not relevant.

 

[NOLAscience]

For some reason I can't respond directly to the poster. Only to the thread. What am I doing wrong?

(1) Click in the Edit Post box that you have been using
(2) Copy the text you want to quote
(3) Click on the little icon with the cartoon speech bubble and blue shirt
(4) Enter the user's name
(5) Click paste and the quoted text will be pasted between the two sets of brackets
(6) Click below this block of characters to write your comments

 

[ldeem]

My experience is in industrial structures and mostly steel. I have seen a few failures due to corrosion but in all cases the corrosion was extensive. I keep thinking there must have been a triggering event.

What about a fire in a battery electric vehicle? Lithium Ion batteries burn at 2,000 C / 3,362 F, what if one was parked under a key transfer beam and caught fire? News reports from Saturday report a fire deep in the debris pile.

 

[Santos81]

Devils advocate here. Is this the pickup truck/vehicle that struck the column and knocked down the tower?

Residents of two units were in the basement garage within the 15min preceding the collapse of the plaza level.

Two were in the elevator which recalled to the lobby upon activation of the fire alarm due to the deck collapse. They exited the building with the Nir family. The other had been moving things to a hotel for over an hour and left via different transportation than the vehicle parked a short time earlier in the basement.

 

[DB27]

Many repairs, like resin injections on cracks and cosmetic repairs have been executed on this building according to Marabito report but many have failed or deteriorated.

I have not read if this was permitted or not, but this is a great example why it is critical that HOAs take structural repairs seriously. They should be inspected by engineers, repair work performed by licensed contractors, and respective permits pulled. Not only will there be better records for future reference, but liability can be determined if any problems do occur.

Had the HOA inquired an engineer to examine the original damages, maybe the building could have been salvaged or monitored better before things turned out the way they did.

 

[dold]

There are absolutely no OSHA deck anchors in this structure.

Scroll up to warrenslo's post at [2 Jul 21 00:27]. warrenslo is talking about the anchors that had just been/were being installed on the roof. I believe they are window washing anchors/davits, but the 5000lb ultimate load spec'd on the detail might lead one to believe it is a fall arrest anchor. I don't know the difference between the two though (load rating of a window washing davit vs fall arrest). Never designed one.

I believe the roof anchors over the penthouse were installed incorrectly, the first bangs of construction Ms. Nir heard was pieces of the roof falling off onto the pool deck. This caused the pool deck to fail either by hitting a column in the parking area as the ENR article suggests or by overloading the slab.

That is interesting. I still have a hard time believing that hammerdrilling 4 ~3/4" diameter holes in the roof slab would cause the balcony/roof slab to collapse. Which balcony's roof are you proposing fell first? Also, I doubt a falling chunk of slab would be able to bump sideways into a column hard enough to buckle it. If the piece was large enough, and it landed directly above one of the columns under the pool deck, perhaps it could cause some manner of crushing? I think it's far more likely (if a piece of the roof fell off and landed on the pool deck slab (+11'-10")) that it would have caused a punching failure as opposed to damaging the column somehow. Part of the slab collapses > triggers domino effect as the falling slab drags down the adjacent slab (slow or fast, who knows) > etc

 

[NOLAscience]

window washing anchors

I was wondering why there were so many "window washing anchors" when most windows can be accessed from balconies, then I went back to the original thread and followed the link to the anchor drawings and found out that they anchors will be used for window washing AND balcony repair. Made a little more sense after I saw that. The anchors will support a platform and some materials and tools, as well as the worker(s).

 

[Awestruc]

NOLAscience:
My comment regarding 3 layers of tile was tongue in cheek.
I do think that 40 psf is more than adequate for residential floors in most cases. But with that being said, how can a parking garage have the same design load? Try explaining that to a normal person.
The point that I was trying to make is that the design service loads are disproportionate in their difference to the real day to day loads, as evidenced by the pictures. For instance, the Lobby and pool deck would be designed for 100psf but empty most of the time, residences would be designed for 40psf but in reality just couches, TVs, beds and typical 5psf stuff, plus a few layers of tile .The Parking garage would be designed for 40psf and actually loaded to almost 40 psf daily for 40 years.
That’s almost 15000 load cycles on a part of the structure that is in distress from corrosion, flooding, lack of maintenance, and no waterproofing membrane.
I’m not saying the building or garage floors were overloaded. I honestly think corrosion of steel and deterioration of concrete combined with flat plate construction with little to no shear walls are some of the main reasons it fell apart the way it did. I do think that garages should be designed for corrosion in corrosive environments. I also think the columns should be designed for impact from a vehicle, especially when playing condo Jenga for 12 floors above. Seems like that could be achieved with better concrete and more cover at the least. It will be interesting to see what they discover at the bottom of the pile and foundations.

 

[warrenslo]

There are absolutely no OSHA deck anchors in this structure. I don't know what scares me the most is that you have absolutely no clue when such things are employed, or how they are employed.
This is a simple midrise, there are absolutely no geometric point that OSHA would require an anchor point for a complex geometry, nor is it tall enough to require a secondary anchorage.

I certainly do have a clue, I have designed many multifamily apartment/mixed use roofs with anchorage systems. They are required on buildings of approximately 5-stories or more in height now. CA is especially strict after Jerry Brown cracked down on the law not being enforced.

There weren't OSHA anchors on this structure until an unknown period shortly before collapse. They were in the process of being installed to facilitate the painting and repair of the decks and concrete walls. The permit pulled the day of the collapse was specifically for OSHA fall-protection anchors. Please see my post above for the permit info, etc.

[URL unfurl="true"]https://www.osha.gov/sites/default/files/publications/OSHA3146.pdf[/url]

 

[dik]

If the collapse were due to neglect over an extended period of time, that is where it gets really ugly.

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

-Dik