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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[SFCharlie]

Please somebody put on your best Florida country club outfit. (you know white polo shirt or blouse, golf slacks or skirt, white socks, cross trainers) and call a real estate agent to show you a unit overlooking the CTS. tell them you want to see the view from the balcony. Have them take you over and while your there, take a couple of photos of the tower and the blue thing.
We will all thank you very much!


SF Charlie
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[AutisticBez]

What I guess I am trying to say, is that a columns maximum rebar percent should be uniform down the entire length. That if its 8% at the lap, then technically it can take 8% down the entire length.

Or its 4% down the length and the splice is a weak point at 8%.

Someone mentioned staggering the splice, sure, its possible, you have the start and end of the rebar at different points, such that you reduce congestion of rebar at any one point. Its a little complicated, but still possible.

The problem to me, is the splice occurring just above the slabs, and someone deciding they can't fit as much rebar from the slabs through the column due to congestion?

 

[Nukeman948]

take a couple of photos of the tower and the blue thing.

There is a live cam but it only shows about 1/3 of what we want to see. When the vid was posted it was already gone. I'm way too busy to keep a close eye on that and there is not much to see most of the time.

Link

 

[Optical98]

SFCharlie

"the blue thing."

I think those are counterweights or stabilizers for the crane.

 

[Nukeman948]

Just something I found, looks similar.
They may have been assembling or disassembling the apparatus when the video was made. We may never know its final form.

Dynamic Load Testing (DLT)

Dynamic Load Testing is a method to assess pile load capacity by applying a dynamic load to the pile head (usually drop weight in frame) while recording acceleration and strain at the pile head. DLT is a high strain dynamic test which can be undertaken on cast in situ piles when the pile concrete is strong enough to withstand the stresses generated during impact. For preformed piles (eg. steel, timber or precast concrete), testing can be done either during or after installation.

 

[SFCharlie]

Just something I found, looks similar.

I think you may have nailed it.


SF Charlie
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[Nukeman948]

I think you may have nailed it.

The definition and the picture came from two different web-sites but from the same search. Couldn't tell you how it works or if it works on an old slab but I'm not getting paid enough for that. At least we have more pixels.

 

[Vance Wiley]

You are right on track. And it is the duty of the design engineer to determine that the calculated and specified reinforcing can be installed with the proper separations and developments. That is particularly difficult for structures in seismic zones, where joints may have 4 beams intersecting and a column above and below.
In the case of splices in column bars, with bars in compression, the bar above the splice has some load - and it passes that load to the lap bar. So at the top of the splice the upper bar has 100% of whatever load, and the bar from below has no load. Half way down the lap the bars would have 50% each, and at the bottom the lower bar has 100% of the load from the above bar and the above bar has none. So, theoretically, the load being carried by reinforcing is the same throughout the splice length. Another 4% (lets say) of concrete area is lost but it seems the code does not address that. Other things are going on also, with the upper bar having 90% load (10% from top of splice) with a corresponding strain of 90% while the bar from below has only 10% load and strain - and there is some discontinuity in the relative strains in bars which are in contact. But the code does not seem to be concerned here. So, paraphrasing Brad Pitt in Moneyball, "when you get the answer you want, shut up". (Keep it simple.)
Compression bars at a splice could develop end bearing of maybe 5 to 10 kips - which is disregarded unless one is trying to save his butt.

It would seem to be proper to disregard calculating the column capacity by using the doubled reinforcing (eg. 8%) in a lap splice zone. After all, just above the lap splice the reinforcing drops to half (eg. 4%) and the column loses the stability provided by the slab or beams. This would seem to be a more critical place to check the column, if no frame action has induced moments in the column.

 

[KingBobo]

Yep; I can imagine that Tardis-like thing being lowered down into that rig as depicted in Nukeman's photo. Good work!

Here's a slightly-less potato-ey grab from that drone footage...

 

[Vance Wiley]

Charlie - you are the go-to guy when it comes to sources and references.
I cannot locate an on-line source for an ACI 318-77 code. Can you find one? I have looked for more than 4 hours.
Does anyone on this thread have one and could copy the Column Design section, which is Chapter 10 in the -14 version, and post it here, please?
I would like to verify the 4%/8% issue. If the maximum allowed reinforcing was 8% for splice zones in the ACI 318-77 version several columns are/were not code compliant at the splice zones.
If that is the case, special measures were necessary to ensure dense and well conslolidated concrete at those zones, and it seems the concrete for this project had little special attention.
The possible consequence would be low density or incomplete consolidation of the concrete, and possibly leaving voids and rock pockets at some locations. Most serious locations would possibly be at the top of the pile caps and locations where salt water could collect from whatever source - winds off the ocean, wet tires, or underground water.
Thanks,
EDIT ADD: Drawing sheet S-11 references ACI 318-72..ACI 318-77 should have been in effect when the design was performed.

 

[AusG]

The gadget is certainty not ground penetrating radar, and is way too big for a seismic testing device. The dynamic tester idea looks good to me. The van on the near side of the site in badged Cone Tec or Conc tec, if that rings bells with anybody.

 

[AutisticBez]

Yes, thanks for that explanation. To me, also, it feels like a bad idea to attempt to design columns as small as possible. I mean, you have a set percentage for the rebar to concrete ratio. As your column shrinks, as does the content of rebar.

When I was referring the vehicle impact data, it was obvious that only a little bit more thickness of the columns was enough to completely prevent the issue. If an extra inch of concrete column thickness was enough to save nearly a hundred people from dying, isn't that worth it?

If we added up the total cost of an extra inch calculated into every dimension of the building, and that cost spread over 40 years. What amount are we talking about? Is the lowest common denominator acceptable here?

The code says this, so we won't do anymore then the code? Like I am sure that the code isn't there to put the bare minimum into your building. How safe do people feel living in a condo where only the bare minimum was put in to satisfy the "code"? Maybe the code should be set at a 4x amount that makes it super impossible for buildings to ever fall over ever again?

 

[TheGreenLama]

Dynamic Load Testing (DLT)

I believe you are correct. Lying in bed last night that was another option that came to mind. I've never seen this done, but this would be something entirely plausible. Below is video of an operation. I can't vouch for all the info presented.

https://www.youtube.com/watch?v=ZWN5dO1U1ms

Obviously they need to set up above an existing pile cap. Another pile test option is a static test.

 

[dik]

You do, within reason; columns are non useable floor space. You keep the same column size for several floors changing the amount of reinforcing and you can change the concrete strength, too. You want to keep the same concrete strength for all columns on a given level. I haven't designed a multi-storey concrete building for a couple of decades, but that's the way it was done; I assume it's still done the same for economy.

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

-Dik

 

[Nukeman948]

I believe you are correct.

And yet I am not 100% convinced on my own theory. From your video it says the minimum pile exposure is 2 times the diameter. They may have found a way to get usable data even with a slab that would distribute the the impact over multiple piles or maybe they are using DLT equipment in a different manner or for a different purpose. I check the live cam at least once on most days if I have time, and never saw them while they were there. I'm pretty sure they only tested one or two locations if that means anything.

Edit: Live cam is missing in action right now, maybe they know I'm watching!

 

[SFCharlie]

I cannot locate an on-line source for an ACI 318-77 code. Can you find one?

my google search was "ACI 318-77"

ACI 318-77 Topic - American Concrete Institute

https://www.concrete.org

› topicsinconcrete › topicdetail
JOURNAL Articles ON ACI 318-77. Behavior and Design of Multistory Building Frames of Unbonded Post-Tensioned Concrete. Publication: Journal Proceedings
People also search for
aci 318-77 pdf
aci 318-89
aci 318 history
aci 318 versions
reinforced concrete
aci
People also ask
What is the current version of ACI 318?

I clicked on:
INFORMATIONAL RESOURCES ON ACI 318-77
on that page, I clicked on:

Standards & Documents (1)

on that page I found:
I clicked on:
318 Historical ACI Building Code Requirements (1908-2005)
on this page I found all the revisions of ACI 318-77



SF Charlie
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[SFCharlie]

Edit: Live cam is missing in action right now, maybe they know I'm watching!

Maybe they don't know we are watching?
Please like and comment
Let YouTube and Them know you care! Thanks


SF Charlie
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[KingBobo]

Related to the drone video showing test rig and blue drop mass, here's an interesting description of the information gathered from Dynamic Load Testing (DLT):

[URL unfurl="true"]https://www.youtube.com/watch?v=bTK-Im3FQ3M[/url]

The narrator speaks of "drilled shafts" (a terminology not much used in this thread).

Drilled Shafts: Elements formed by creating a drilled hole into which structural steel and concrete is cast or placed.

Driven Piles: Foundation support typically using steel or precast concrete elements driven into soil with impact or vibratory methods.

I think that the Franki piles in use at CTS are sort of a hybrid, since their installation involves both wet concrete placement and driving.

Regarding ConeTec (as spotted by AusG), I found no specific mention of DLT on their website, but they are clearly specialists in doing geotechnical site investigations.

 

[12345abc6ttyui67]

Vance, just to confirm I agree completely with what you are saying re: reinforcement %'s. Not sure if you thought I didn't, or it just came across like that on the interwebs. I was merely trying to elaborate on the practicalities for AutisticBez's sake.

I don't do concrete design, but I suspect if I was, and I knew that a) I had to lap bars and b) the maximum reinforcement % was 8%; then I would design everything I knew had to be lapped with 4% reinforcement so it wasn't an issue / didn't matter where the splices ended up being.

 

[dik]

you almost never design columns for the max 4% reinforcing... generally 2-1/2% and then go up to about 4% and then you change column size.

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

-Dik