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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[Red Corona]

> All the while, you say something about being an engineer or just forget that your profile clearly identifies you as a Professional Engineer.

Good thing I'm not a professional engineer eh

I'm still interested in the unusual shape of the punching shear breaks and if I get around to it I will make a longer post with some (non professional, suck it Florida engineering board) opinions. Related to that, I think someone posted a document early saying how the pouring of the columns and the slab above worked. I'm interested as to whether the column was built first and the slab then poured around it (so there's a vertical joint around the column) or if column + slab above was all done at once.

 

[dik]

The board takes this very seriously, but they are strangely quiet... same for California, it seems.

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

-Dik

 

[MOJOJOHN]

Normal practice is to pour the Column first, stopping the pour an inch or so below the deck form. The column will shrink a little as the slab is prepared over the next few days.

If you pour the slab and column at the same time, you risk a crack at the top of the column when column shrinking occurs and downward movement of the slab is restrained by the shores.


Shear calculations consider the column support size and shape as well as the deck thickness and the cold joint does not play into it.

Normal failure will leave pieces of the slabs at the top. Failure straight down without leaving stubs from the slab sticking out is very unusual.

As to the Florida board, I doubt they would take offense to unofficial posts on a social media site for engineers. It is not a report for the Public.

Regards,

mojojohn

 

[dik]

Red... columns and slabs often have different concrete strengths and other properties.

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

-Dik

 

[AusG]

I'm surprised no-one in the color-glossy-infogram and sexy-3D-animation biz has picked up on the sub-spec rebar yet. Has anyone found a 60 grade rebar marking in any pic?

 

[Jeff Ostroff]

I uploaded my latest video last night which talks about how much water we've noticed pooling on the roof of both Champlain Towers South and North buildings a year ago shown on drone flyovers on dry days.

https://youtu.be/cNKMe4S0A2M

.
.

 

[SwinnyGG]

I'm surprised no-one in the color-glossy-infogram and sexy-3D-animation biz has picked up on the sub-spec rebar yet. Has anyone found a 60 grade rebar marking in any pic?

Is Gr 60 what was required/specified? Most of the bar in the images above appears to be grade 50. Although the pics aren't stellar.

 

[Red Corona]

> Normal failure will leave pieces of the slabs at the top. Failure straight down without leaving stubs from the slab sticking out is very unusual.

Yeah, that's why it's so interesting. It's not even straight down, the columns have been 'pinched' around the failure point. I feel like this has some interesting things to say about the material properties (rebar placement as well) there but I want to check I am not a total idiot before going into that

> Normal practice is to pour the Column first, stopping the pour an inch or so below the deck form. The column will shrink a little as the slab is prepared over the next few days.

The slab is then a complete, unbroken surface, right? There is no column of concrete going 'through' the slab (though there is rebar doing that if there will be another column above the slab - not true on the pool deck in this case)? That's my understanding from previous posts as well.

Something like this. Rebar in the slab optional if you're in Florida in the 1980s ...

 

[Jeff Ostroff]

The one thing I've always wondered about when they're pouring concrete for the columns if they stop at the end of their pour and I don't know how long they wait maybe a day or two? What do they do about cold joints forming? Are they required to use any kind of primer in between or bonding agent or anything like that? That's what I've always worried about is how do you continue that column all the way up as one homogeneous material?

 

[MOJOJOHN]

Red corona

Your understanding is correct.

Jeff

No primer or bonding agent.Does act monolithic due to steel passing through joint.

 

[SwinnyGG]

What do they do about cold joints forming?

There are cold joints for sure; typically the term 'construction joint' is used, as they are planned. 'Cold joint' implies a joint between pours that should be monolithic and only exists because someone screwed up.

All construction joints will have steel passing across them and will usually be chipped or roughened for mechanical engagement between poured sections.

 

[SwinnyGG]

Yeah, that's why it's so interesting. It's not even straight down, the columns have been 'pinched' around the failure point. I feel like this has some interesting things to say about the material properties (rebar placement as well) there but I want to check I am not a total idiot before going into that

I'm not so sure that it's a huge indicator.

A single punching shear failure in a big matrix of columns will have widespread effects- namely the doubling of the unsupported length of the slab between columns surrounding the failure. The slab may then fail in a few different modes, depending. If the slab cross section is strong enough to stay standing across the new unsupported length, you might see punching shear on surrounding columns, too. If it isn't strong enough to self-support across the new length, however, the slab at adjacent column/slab nodes might fail in bending, or in tension. It may only take one punching shear failure (ie punching shear failure at a single node in the matrix) to induce complete failure of the slab, but that doesn't mean every node is going to fail in shear. In order to really know, you'd need pictures of EVERY column/slab node to figure out how they each failed. We only have a few.

Not saying you're wrong.. just saying that IMHO we are short on information to support a big conclusion from the fact that a few nodes didn't fail in a fashion we normally associate with regular punching shear.

 

[Jeff Ostroff]

@Reverse_Bias I cannot find that NYT article for the life of me, tried searching on their site multiple was related to surfside but can't find an article from 9/22. Got a link to the article?

 

[rebardan]

from the CRSI:
Each Individual Reinforcing Bar is Manufactured with a Series of Individual Markings:

The first letter or symbol identifies the producing mill.
The next marking is the bar size.*
The third marking symbol designates the type of reinforcing steel — usually either "S" for carbon-steel (ASTM A615) or "W" for low-alloy steel (ASTM A706).
Finally, there will be a grade marking (60, 75, 80, 100, 120) or by the addition of one line (60) or two lines (75), three lines (80, 100), or four lines (120) that must be at least five deformations long.

 

[Demented]

Have we any indication as to why beams 33, 34, and 35 are still left on the slab?

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

 

[SwinnyGG]

from the CRSI

That's the current spec... but wasn't the spec in 1980.

 

[SFCharlie]

@Reverse_Bias I cannot find that NYT article for the life of me

Sept. 1 U.S.
The Surfside Condo Was Flawed and Failing. Here’s a Look Inside.
A Times investigation shows how faulty design and construction could have contributed to the collapse of the building in South Florida.
By Anjali Singhvi, Mike Baker, Weiyi Cai, Mika Gröndahl and Karthik Patanjali
PRINT EDITION: Here Are 11 Serious Flaws Discovered In the Surfside Tower
September 22, 2021, Page A12

SF Charlie
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[Jeff Ostroff]

Problem is Charlie they have a pay wall to read their stories, so I can't read it.

 

[MaudSTL]

Is “Here Are 11 Serious Flaws Discovered In the Surfside Tower” available online? It does not get returned in a search. And the image itself does not produce a hit in a reverse image search. Charlie indicates that it is page A12 from the print edition. The link he provided shows the interactive 3D model that we already saw about a month or so ago.

FWIW, like some other publications, the NYT counts number of views by IP address rather than by setting cookies. So clearing your cache will not reset the monthly count because it’s maintained server side. A typical way to avoid this limitation is to use a VPN, which can unfortunately slow your browsing by having narrowed your available bandwidth. To avoid cookies that other sites set, you can use Firefox to browse, and then erase your cache at the end of every session.

 

[Reverse_Bias]

Here's a higher quality readable version of the article for download. Eng forums mangled it when I inserted the image into the post.
The only internet record of the article I found was the tweet from the author. But link provided in the tweet is to the Sept 1st interactive article not to the image in the tweet. I assume the graphic was the print only version, with mostly the same information.

https://twitter.com/singhvianjali/status/1440724076117385231