Miami Beach, Champlain Towers South apartment building collapse, Part 19 27

[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
Miami Beach, Champlain Towers South apartment building collapse, Part 13
Miami Beach, Champlain Towers South apartment building collapse, Part 14
Miami Beach, Champlain Towers South apartment building collapse, Part 15
Miami Beach, Champlain Towers South apartment building collapse, Part 16
Miami Beach, Champlain Towers South apartment building collapse, Part 17
Miami Beach, Champlain Towers South apartment building collapse, Part 18

 

[davefitz]

I am not sure if this was considered in earlier posts, but there are alternative concrete types that can ensure a much longer life of the rebar in salt spray conditions. It is my understanding that the florida DOT is applying a 3" thick stucco of geopolymer cement on concrete bridges near salt water sources to provide long life for the rebar, as the permeability fo clhoride ions in geopolymer cement is more than 1000 times lower than with ordinary portland cement.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[1503-44]

NIST says "FAILS Code By 50%! in pool area according to original ACI-77 and current ACI.

https://youtu.be/qgSitQ9iF_E

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[dik]

Additional news...

"More than two years after 98 people died in the collapse of a Florida condominium tower, federal investigators have released new details about the cause of the collapse. They're focusing on construction flaws on the building's pool deck.

Structural engineers with the National Institute of Standards and Technology say it's one of the most complex investigations ever undertaken. It began days after the 2021 collapse of the Champlain Towers South building in Surfside.

In a progress report, one of the team's leaders, Glenn Bell said the investigation continues to focus on the condo tower's pool deck. Investigators have previously said they found significant design and construction problems that left the deck weaker than required by building codes.

The team now has also found problems in how the concrete columns that supported the building were constructed. At a meeting at NIST headquarters in Maryland, Bell said, "These additional construction deviations further reduce the strength of the pool deck slab-to-column connections from the already compromised conditions that I reported in June.""

https://www.npr.org/2023/09/07/1198...pse-champlain-towers-south-investigation-nist

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Sym P. le]

The National Construction Safety Team (NCST) Advisory Committee, Sept. 7, 2023 Public Meeting videos

Direct link to Sept. 7, 2023 video

24:40 - Discussion of additional slab reinforcement at columns

At least 25% of all column strip reinforcement shall be centered over the column

Typically, that's four bars req'd over each column in each direction. Also, column strip reinforcement was spread over 20% to 40% greater area than called for on drawings.

33:20 - On average, concrete core tests reveal concrete to exceed compression strength requirements (though further analysis is still required as to broader findings and implications)

38:34 - Geotechnical studies - no evidence to date of voids/sinkholes beneath CTS. Potential for settlement is small, in order of 1/4". That magnitude would result in load redistributions from one column to the next of less than 5%.

 

[spsalso]

NIST can next investigate how the pool deck failure transferred to the adjacent building.

OR:

Why was the pool deck used to hold up the building? Because it did. While it was in place.

Yes, I know it's been discussed here, almost from the beginning. I just want to hear it from NIST.


spsalso

 

[Brian Malone]

spsalso - are the same/similar structural elements that caused the collapse of the south towers present in the still occupied north towers?

 

[Reverse_Bias]

I was interested in this part.

At the meeting, Bell showed stills of a video recovered from a motion activated camera that has provided investigators with intriguing information in the final moments as the building collapsed.

Investigation head Judith Mitrani-Reiser says the team has recovered 24 computer hard drives that may hold videos and is actively working to rebuild seven of them. She said, "if even one of those seven has a short amount of footage, that would be a huge impact to our investigation."

https://www.npr.org/2023/09/07/1198...pse-champlain-towers-south-investigation-nist

 

[stcbus]

^^ definitely interesting. I’d imagine it’s likely that the drives are in a RAID configuration, unfortunately, which makes recovery without all of the drives and knowledge of the controller very difficult.

 

[spsalso]

"spsalso - are the same/similar structural elements that caused the collapse of the south towers present in the still occupied north towers?"


Don't know. If I lived there (Champlain Towers North), I'd be curious.

There's "caused". And there's "allowed". They seem to work hand-in-hand.

Here's a brief video:

https://www.youtube.com/watch?v=T5qp4NE4uzs

Looks like the answer to your question is "maybe/maybe not".



spsalso

 

[stcbus]

They were shoring up that building for awhile but haven’t heard anything since or what, if any, findings.

 

[zebraso]

Why was the pool deck used to hold up the building? Because it did. While it was in place.

Is this some type of convoluted logic puzzle? Certainly if the deck could have been cleanly separated from the building in a timely manner the collapse would not have progressed to the tower. As stated in the question and answer period for the recent WJE webinar/report, Gary Klein answers that expansion joints in the pool deck would have most likely prevented the collapse of the main structure.

 

[spsalso]

I can see two interpretations of my statement:

"Because it did. While it was in place."

What I did NOT mean was that I approved or endorsed the idea of using the pool deck to hold up the building. Intentionally or unintentionally. I should have left those words out. Or perhaps put them in parentheses.

What I was getting at is that, so far, I'm hearing a lot about how the deck fell down. If ONLY the deck had fallen, this topic wouldn't have become 19 pages long. NIST still has to get to the second part of the collapse.

I first commented on the connection between the pool deck and the building on page 1 of this topic, on January 27, 2021.

How time flies when you're having fun!



spsalso

 

[dik]

tempis fuggit...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Mark R]

I just came across this but she had some more intrigue to the story.
A preliminary NIST report points to deviations from design in the Surfside, Florida, condo’s pool deck construction.

New details came to light Thursday regarding what caused the collapse of the Champlain Towers South building in Surfside, Florida, that killed 98 people in June 2021.

A report from the National Institute of Standards and Technology noted that the construction of the condominium’s pool deck deviated from design requirements and that the number of slab reinforcing bars centered over vertical columns was inadequate.

The NIST team also found that the reinforcing bars in the top of the slab in the vicinity of the columns were spaced farther apart than the design required. These deviations weakened the slab-column connections, the report said.

To me that sounds like a Surfside B&Z failure to properly inspect the rebar prior to allowing the pour to begin.

But then again this is Dade County which has the best inspectors money can buy.

Champlain Towers investigation yields more clues

 

[NOLAscience]

There was an important design change made in the months that the building was under construction. The change was sent to the EOR for approval. In effect the change removed a step-down of about 4"-6", as I recall. The architect or builder wanted to flatten this step down. When the design change was made, it essentially removed a beam which would have had 2 pieces of rebar, top and bottom. That area was revised into what became more of a "slab" than the beam it had been. This was in the exact area in the parking garage where sagging and water leaking had been observed (and patched and painted) for decades. There is no doubt in my mind that the deterioration in that slab was the location of the initiation of failure for this building. All other construction errors, like rebar spaced further than the design specified or fewer bars than shown on design drawings, might contribute 0.5% to the collapse; the removal of a beam such that a slab transfers load that it is not designed to support -- not by a long shot -- has to be at least 99.5% of the cause of collapse. This design change was probably sent to a junior engineer to review and approve. Not having designed the structure, the engineer may not have recognized the significance of the change. [I admit that the "junior engineer" idea is speculation. Paper records other than the designs on file with the county have undoubtably been trashed by now, and all people involved are likely dead (over age 75 or so), so we will never know what transpired in the design change process.]

Other factors discussed above and in other threads:

(1) Sea spray or salt did not materially contribute to the collapse. Corrosion may have allowed the building to collapse a few days, months, or years earlier than it would have if it were built 100 miles from the ocean, but the rebar and concrete would have eventually deteriorated due to rainwater just the same.

(2) Isolating the pool deck from the building structural support system would have prevented the pool deck failure progressing to a building failure. This is the difference between minor injuries and, at most, 1-5 deaths vs 98 deaths.

(3) Inadequate shear walls in building -- this is related to the severity of the collapse, and is secondary to the cause of collapse

Sorry that I don't have time to go back and find the screenshots of the original and revised design. As I recall, this was discussed earlier in one of these threads, although it may have been on another forum.

 

[zebraso]

In effect the change removed a step-down of about 4"-6", as I recall.

The step beam and beam type A deleted from plans stamped 1981 vs original (1980). This was noted a long time back in this topic. Are these beams present on the North Champlain Tower? Maybe this was mentioned somewhere in the past 18 pages. If so it's one less reason to be overly concerned about the other site. I think they are taking measures to improve the punching shear.

 

[Sym P. le]

Comparison of original design versus revised build copy with removed steps and BMA's highlighted.

Undoubtedly, the removed features would have reinforced the broad area of weak slab and offered some interruption between the pool deck and lobby parking. Is it wishing to much for NCST to study this aspect of the failure, that is how well are significant revisions evaluated prior to approval?

Note: The pool deck slab was raised one foot with implications towards garage clearance, building height, or excavation requirements.

 

[spsalso]

I believe this structure was "self-inspected".

Apparently, the building department thought it was over their head. I expect properly. I don't understand why the building department did not then hire an outside expert, rather than allow self-inspection.

I do wonder to what extent the city building inspector DID show up. It's not like they could keep him out. But, for whatever reason, he missed them errors.

The EOR has his name on it. If he had a junior apprentice woodchuck do the work, he clearly had every confidence in that 'chuck: his name is on it.


spsalso

 

[spsalso]

Jeff Ostroff has a new Youtube video on the building:

https://www.youtube.com/watch?v=jBzDtdZlXx0

He describes in the early parts that NIST discovered a severe lack of rebar crossing the columns in the pool deck area. He mentioned that the structural engineer would surely have been upset if he had known. As an illustration, he showed someone banging his (hard had protected) head on a wall.

Uh. The structural engineer SHOULD have known. He was also the inspector. He signed off on the rebar placement.

I am surprised Jeff didn't comment on that.

[Note: the "severe lack" mentioned above doesn't mean there was NO rebar there. There was half as much as called for in the plans.]

spsalso