Miami Beach, Champlain Towers South apartment building collapse, Part 12 60

[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

SF Charlie
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[TheGreenLama]

Those cores went through previous repair work.

I went through the Oct 14 board minutes that Optical98 provided [

https://s3.documentcloud.org/documents/20985354/20201014bodminutesapproved.pdf

], where the images of the cores samples are shown, and I found no mention of the cores being made particularly to inspect previous repairs. Is this core location requirement coming from somewhere else, and if so do you remember where that may be found?

A couple of highlights from the board minutes (for those who haven't already read them):

 

[SFCharlie]

There is a separate thread for Millenium Towers, please keep any comments regarding that topic over there instead.

I second the motion!

SF Charlie
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[SFCharlie]

Are you sure you want all the "do-da's" and powerpoint guru's to invade a forum that has been lean, mean and focused?

I promise to leave them in peace and quiet.


SF Charlie
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[Demented]

@All About Money
I caught on day 1. Pretty sure others have known for a while.

@TheGreenLama
They weren't to inspect previous repairs. Some of the cores just happened to fall in the location of old repair work, especially those taken from the pool deck and lobby driveway. The concrete started to fail within a few years of building completion due to corrosion with rebar and spalling and failed or no waterproofing. 2 main restoration projects were undertaken, both of which were jobs that failed or were never completed. The Morabito work would be the 3rd main project going at some of these areas.

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

 

[SFCharlie]

Quote (Vance Wiley)
Now the question - about aggregates in Miami.
There is aggregate...

The google search was "Florida limestone aggregate concrete structural strength"

Effects of Coarse Aggregate on the Physical Properties of Florida Concrete Mixes

Also, please see the attachment: (everything you could want to know... ...I got as far as the "Mohr circles" and got lost...that was on the first diagram.

SF Charlie
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[TheGreenLama]

@Demented
Thanks. That's what I figured you meant, but just wanted to make sure.

 

[SFCharlie]

The attached paper goes with the slides attached above...

Also, please see the attachment: (everything you could want to know... ...I got as far as the "Mohr circles" and got lost...that was on the first diagram.

SF Charlie
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[SFCharlie]

Designed to fail: How Florida's lack of condo board oversight could mean another Surfside
(the title sounded like an old article, but much of the content is new and in perspective of the whole.)

SF Charlie
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[AutisticBez]

Okay, here is my question. The column has a coded 4% maximum rebar presence right? But in the splice its 8%. So, if 8% is okay during the splice, why is it 4% outside the splice? If it can take 8%, why the 4%?

Am I looking at this wrong? Shouldn't it be 4% or 8% maximum regardless of splice? Just because you double the rebar during a splice, does not mean the columns rebar percentage maximum should increase.

The two values should be the same right? Just the column thickness should be based around the splice percentage and reduced rebar elsewhere.

Is it possible the code is wrong with 4%, 8%? How is the code today?

 

[SFCharlie]

So, if 8% is okay during the splice, why is it 4% outside the splice? If it can take 8%, why the 4%?

Somewhere above I read that it was 4% so that at the splice it would not exceed 8%, but that the splice could be staggered to allow more...

Longitudinal reinforcement in columns should usually not exceed 4 percent if the column bars are required to be lap spliced, as the lap splice zone will have twice as much reinforcement if all lap splices occur at the same location.

SF Charlie
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[Vance Wiley]

++++
Charlie - I scanned well past the Mohr's circles and found only soil/rock(?) strata information for piles and foundations. Nothing addressing aggregates for concrete. I did find what I think is the source for concrete used at CTS - it looks just like many of the pics of crumbles and broken columns and slabs.
It is titled Figure 2-3. Newberry quarry excavation (Paul Bullock 2004; FDOT Public Report) and is found on pdf page 25 of your second reference -

https://files.engineering.com/getfile.aspx?folder=e9a9785b-a1c9-4b5f-9a38-e

 

[MaudSTL]

For those frustrated by the paywall, here’s an archived version of Designed to fail: How Florida's lack of condo board oversight could mean another Surfside. After reading this, it’s hard not to make acerbic remarks about condos.

 

[SFCharlie]

acerbic - "tasting sour or bitter."

SF Charlie
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[SFCharlie]

Nothing addressing aggregates for concrete.

Try the attached:

SF Charlie
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[MaudSTL]

acerbic

You could also just go with “sharp and forthright.”

 

[Vance Wiley]

Thanks, Charlie - that IS about aggregates.
Takeaway:
Florida uses oolite and Florida limestone for structural concrete.
Memo to self: NEVER get involved in concrete in Florida.

My concern remains about how these aggregates weather under fresh water conditions, acid rain, and coastal environments.
If you see anything about durability of Florida concrete, please let me know.
Thanks again,

 

[SFCharlie]

If you see anything about durability of Florida concrete,

Well, the first three articles were about "Fiber Reinforced Concrete"
Well...FDOT thinks it's a problem worthy of research...
See Attachment:
(more to come, only one attachment per post (as far as I can tell))
Actually no more to come, one article about using electrical resistance to measure durability, but that's all
Electrical Resistivity of Concrete for Durability Evaluation: A Review

SF Charlie
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[AutisticBez]

Yeah, but, if 8% max is fine at splice then 8% all the way up is the true max and 4% is merely less rebar?

 

[12345abc6ttyui67]

10.6.1.1 For nonprestressed columns and for prestressed
columns with average fpe < 225 psi, area of longitudinal
reinforcement shall be at least 0.01Ag but shall not exceed
0.08Ag.
Discussion/Comments
R10.6.1.1 Limits are provided for both the minimum and
maximum longitudinal reinforcement ratios.
Maximum reinforcement—The amount of longitudinal
reinforcement is limited to ensure that concrete can be
effectively consolidated around the bars and to ensure that
columns designed according to the Code are similar to the
test specimens by which the Code was calibrated. The 0.08
limit applies at all sections, including splice regions, and
can also be considered a practical maximum for longitudinal reinforcement in terms of economy and requirements
for placing. Longitudinal reinforcement in columns should
usually not exceed 4 percent if the column bars are required
to be lap spliced, as the lap splice zone will have twice as
much reinforcement if all lap splices occur at the same
location.

Yeah, but, if 8% max is fine at splice then 8% all the way up is the true max and 4% is merely less rebar?

That is what the code is saying. 8% is fine. But if you need to lap anything you are going to have to double up bars in the lap regions, so to remain below 8% total, you can only have 4% in the sections either side of the slices. In other words: if there are no splices 8% is fine, if there are splices, 4% max either side to remain below 8% at splice.

 

[MaudSTL]

A brief but apparently recent drone shot of the CTS slab with NIST at work. Is that L or M9.1/10 where they are drilling?