Miami Beach, Champlain Towers South apartment building collapse, Part 16 24

[dik]

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

-Dik

 

[Sym P. le]

At this point, these units must be impossible to sell, but the land value is approx. $1 million per unit (Based on $120 million offer for south towers property and 111 units).

 

[Jeff Ostroff]

When they did core testing, I am pretty sure it was done in unit 612. I was able to get inside that building 6 months ago, checking interiors of several floors, and saw that 612 had signs on its doors for construction crews, and instructions, etc. I assumed this must have been the unit, as they showed it on the news when he first arrived last summer and took core samples.

 

[Optical98]

What I picked up on when Jeff posted the first photos of the shoring poles in the garage, is that most of them were under the Generator Room, which is right above the parking ramp. I was surprised there wasn't more discussion on that.

When this collapse occurred everyone said the building "pancaked", although it did collapse straight down for the most part...watching the video and rescue operations, it looked more like the floors just turned to sand, the balconies and columns were the only large chunks/slabs being retrieved by the cranes.
There has to be a problem with the concrete.

Yes, Sym I would be wanting out and selling at a loss to get out of that building.

 

[FJBnomics]

now they have added shoring poles on the patios of several units on the building here are some photographs I took on Saturday.

After watching Jeff Ostroff's video on shoring poles on the balconies, I noticed they did NOT shore all the way to the ground. This appears to imply that the shoring is just a safety factor while they work on repairing the area above the shoring. I counted 4 floors of shoring and it would appear that implies a balcony slab repair and not column repair.

 

[Jeff Ostroff]

Great observation on that 1st floor not having shoring poles as well there, Thermobaric. Others have commented the same on my video. If you remember, on the 2nd floor of this floorplan there are a ton of extra beams on the 2nd floor to support the large shear wall likely, and this along with 2" columns is why this part of the building on CTS survived the initial collapse. So they likely felt there was no need to go to the first floor, although I think it would be prudent to add them there as extra insurance and to put people's minds at ease.

 

[FJBnomics]

Great point on the beams under second floor, Jeff. Looking closer at the photo's posted above, I see the shoring aligns with a column line from the beam under the second floor to foundation. If that is a transfer beam, then it might appear they were supporting mid span deflection of floor slabs above transfer beam, at the exterior block wall that was not supposed to be load bearing?

 

[Jeff Ostroff]

I think their whole strategy here is preventing punching shear, and they are probably not so much worried about deflection. Well, one thing to keep in mind is that columns along the end of a building can only support half of a load of columns that are in the middle of the building because they have no other connection to a floor slab that continues onward, in other words, there are no tributaries outside the building only inside the building. likewise, columns on the corner of the building can only support about 1/4 of a load of a column that is in the middle of the building.

 

[FJBnomics]

Jeff, agree less axial load on exterior column than interior column, when both just supporting slab loads. However, exterior columns have to resist lateral detachment of slab at column/slab joint or asymmetrical loading of columns. In the collapse it appeared exterior columns lost lateral floor bracing, due to poor floor attachment to columns. Now if that is transfer beam, that would imply column line above second floor beam is not axially inline with first floor column? I have not looked at North floor plans to determine which.

 

[Jeff Ostroff]

On page 163 out of 336 of the 1979 floor plan, you will see how the Champlain Towers North floor plan is almost the same as the South floor plan. You will see the gigantic beams all over the place on the left side of the drawing and of course, there are 24-inch columns in the garage to support all of this, and then from the second floor up to the 6th floor, you have 16-inch columns.

So clearly this part of the building is much more robust than the part that collapsed, which has me questioning, even more, why did they need to put the shoring poles there.

So this points more in the direction of they think there are shearing forces along the outside of that wall even though the columns are 16 inches, and they are taking steps to prevent the shearing along that wall, where the patio slab meets the wall at the start of the cantilever.

It seems they suspect weakness at that connection, maybe from lack of adequate rebar there.

 

[FJBnomics]

Since you verified column line above beam is same as below, I would expect column or connection repair and they transferring slab load normally on column to lower floors then to column.

 

[Jeff Ostroff]

Just look at my 3rd picture of the photos I posted above, you can see the huge beam under the second floor, so no reason to add more shoring poles under the 2nd floor

 

[Sym P. le]

Thanks Jeff for keeping us appraised of what's going on down there. Sunlight is the best disinfectant.

 

[Ampaire]

Who is doing the work at CTN? Does anyone know if permits have been pulled?

 

[MaudSTL]

I’ve been monitoring the Miami Herald podcast on the CTS collapse Episode 5: Seven Minutes to Collapse is worth listening to because they interview Dr. Dawn Lehman, the structural engineer the MH hired. It kicks off with the WaPo interview with Chani Nir of 111, and features a very dramatic description of the collapse sequence by the MH reporter Sarah Blaskey plus a very colloquial translation of the Nicolas Vazquez statement. There’s a very good description by Adriana Sarmiento, who shot the TikTok video at 1:18 AM, of the wind that came out of the garage when the deck collapsed.

I still dispute the MH contraction of the timeline: Chani Nir’s contemporaneous interviews stated that she heard banging when she got home at 11 PM, but the Miami Herald doesn’t start the timeline until 12:50 PM. Also Sarah Nir’s original interviews stated that the loud bang (which Gabe called the first collapse) occurred at 1:10 AM instead of 1:14 AM, when she went to the lobby.

The MH now says that Sarah Nir was able to see the pool deck had collapsed all the way to the southern perimeter wall. Sarah never made this claim at the time of the collapse. I feel skeptical that Sarah was able to see through the dust and dark at that time, and would like to hear Sarah make that statement herself, rather than hear a reporter make that claim.

Next week, Episode 6 will be Ileana Monteagudo of 611 and the late Cassie Stratton of 410.

 

[Sym P. le]

Round 1 sold well in print so they're doubling down in podcast form. Again, the engineering model promoted by the Miami Hearld seems to assume the pool slab abutting the perimeter wall rather than resting upon it. I doubt the likelihood of this construction detail.

(from the second link below)

At the risk of being repetitive, here are the two Miami Herald article links:

1. Original story, headlined "The Herald built a computer model to explore how Surfside tower fell. Here’s what it showed" By Dawn E. Lehman and Sarah Blaskey Updated January 12, 2022 4:45 PM -- per Dawn Lehman, "... describes the timeline of the collapse that we used to support the modeling we did."

2. The follow up story, headlined "The last stand of Champlain Towers South. Computer model, witnesses reconstruct the tragedy" By Sarah Blaskey Updated January 21, 2022 2:31 PM -- per Dawn Lehman, "... the modeling approach and different scenarios that we evaluated."

 

[MaudSTL]

Agreed. The MH really wants that Pulitzer.

 

[Jeff Ostroff]

From what I remember seeing the drawings and the photos of the aftermath, the pool deck slab was sitting on top of the south pool wall

 

[Sym P. le]

From the first link above, it's difficult to reconcile the following statements:

Slab/Wall Connections

... 90-degree hooks were used, which adequately simulated 180-degree hooks called for in the plans

... Slab to perimeter wall connection - No. 5 bars at 12” on center, 90 degree hooks with 18” leg. ... the connector bars were placed at the middle of the slab.​

with the plans:

They've set up a sensationalized detachment scheme that allows a > 1" drop along the perimeter wall as a precollapse stress riser.

 

[spsalso]

The drawing seems to show a monolithic corner, between the deck and the wall. The deck does or does not sit upon the wall. The deck does or does not "hang" off of the wall.


spsalso

 

[Sym P. le]

The problem with having the deck abut the wall is that it sets up different shear scenarios for the slab. The slab rebar layout anticipates the wall supporting the slab (which a monolithic pour is consistent with). There are plenty of issues at play but MH's introduction of this nonstarter (my opinion) is not good for discussion or journalism.