Miami Beach, Champlain Towers South apartment building collapse, Part 11 54

[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


SF Charlie
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[Sym P. le]

It would seem to be an exercise in futility to manage a structure constructed in an era of corruption at multiple levels. You would have no confidence in the substance of what you're overseeing.

 

[AusG]

From the building safety forum article:
"[The Surfside building] almost looked like a planned implosion, in the manner that the building collapsed. So, obviously, there was a lot of speculations initially," Ascunce said.

He means well but I don't believe anyone aiming for credibility in public should say stuff like that. There is idiot speculation and hot air on Reddit & YouTube in these terms and the merest mention just feeds it.

 

[SFCharlie]

From the building safety forum article:

I was left wishing I knew what was actually said at the meeting.


SF Charlie
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[AutisticBez]

So, here is a unique parking garage. It's South Lawn in Melbourne. And each column is shaped like this to support a tree above it. The tree's are perfectly positioned above each column and there is a lawn above the garage. It's very unique and I felt that it was a good example given other examples. It's constructed 10 years before CTS. It's old but still in good condition.

 

[CE3527]

AutisticBez - that looks like the building a structural engineer designed after reading an article on shear punch failure of column slab connections.

 

[IEGeezer]

AusG[/b] (Petroleum) 18 Aug 21 07:30 [The Surfside building] almost looked like a planned implosion, in the manner that the building collapsed.]...
He means well but I don't believe anyone aiming for credibility in public should say stuff like that.

Actually, I agree with how it looks. "Planned implosions" seek to weaken the structural elements at the ground level of a structure, which indicates to me that CTS collapsed because of the failure of ground level structural elements and probably not as a result of falling objects.

The video of the demolition of the part of the structure that remained standing is strikingly similar to the fuzzy security video of the initial collapse. If one were to use the planned demolition as a model of the initial collapse, I think one would have to prove that the initial collapse was NOT due to failure of ground level structural elements.

 

[StructuralMadness]

Hey, this is Jinal and I am new to this forum. But I am pretty sure everyone has seen Building Integrity's video on engineering failures. I have have few comments on it along with a part of incorrect information they may be sending to the user.
1. When he talks about high reinforcement of column, he mentions something about plastic yielding and all. Which doesn't make sense, because axial plastic yielding does not occur in columns even when they have high reinforcement ratio. The plastic yielding mainly occurs because of seismic loads. Rest of all the conditions, like wind and the daily gravity loads, the columns and all the building elements are essentially elastic. That too at ultimate loads.

2. When he talks about the pool deck and its capacity against the dead loads itself. He is not presenting any calculations. While when you do the calculations then the reinforcement works for just the 9.5" pool deck. But it does not work when we consider all the toping of sand, pavers and everything on top of it. So that is also an incorrect statement.

3. The temperature and shrinkage reinforcement splice. Again he is incorrect over here, and the splice and temperature and shrinkage reinforcement was correctly provided and detailed.

I do feel that he is mainly involved in concrete repairs through his career and would have limited understand on how buildings are actually designed, detailed and the actual capacities of members, in terms of reliability analysis. That is how the code equations derive the capacity with conservative equations while the actual capacities are much higher. He must be great at concrete repair and reinforcement repairs.

I am not being toxic here, but I just want everyone to understand the underlying assumptions that he is considering while presenting and a part, primarily related to load and resistance are little incorrect.

I did create a video 2 weeks prior to BI's video that flows along the same lines and talks about pool deck deficiencies but also go a bit deeper into actual analysis and repercussions of under designing a slab with some calculations. I think structural engineers may be interested in this so just thought of sharing.

https://youtu.be/fFQ7ey5CDLc

 

[SFCharlie]

Hey, this is Jinal and I am new to this forum.

Hi Jinal. Welcome. thanks for the link to your video.
...about 2. BuildingIntegrity is talking about the building as design before the sand and tiles were added. He also notes that the 50 ton+/- planters aren't on the prints.
...about 3. "...reinforcement was correctly provided and detailed."
I think someone pointed out that the specified rebar didn't fit in the specified column and still meet code.
There are two obvious solutions:
The structural engineer could have specified a wider column. OR
The construction crew could have left out some of the rebar.
Unfortunately, the debris seems to says the later happened.

I encourage you to reply with what is correct, better, or additional in your video!


SF Charlie
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[StructuralMadness]

Hi Charlie, so about point 2 again, he does mention in his video that the reinforcement was just barely enough to handle the slab's own weight, when someone mentions (in structural engineering community especially) just about the self weight of the member, we consider the member weight only. So, if I perform the calculations for the slab, then the steel that was provided was enough to handle its own weight plus the weight of pavers and sand and all except the planter boxes. Now the "direct design method" also has some inherent conservatism on how we calculate reinforcement as well as the way the slab typically engages the reinforcement in two directions. If we eliminate this conservatism, then the slab was just barely overstressed because of pavers and added sand and topping, note that I haven't included the weight of people on pool deck. This overstress isn't an issue in its own, the direct effects of this overstress is an issue. And what this overstress does is, it typically adds more demands to slab column connection. Again from engineering standpoint his concepts; the way he presented was incorrect. Based on building code equations if an element fails, then it is not the true failure of the element. Realistically the failure capacity is about 1.3 times higher than that plus there is inherent material over strength. Now for nonstructural engineers, it sounds like when someone mentions it fails, it should collapse immediately. But no that is not correct.

Coming on t point 3: The temperature and shrinkage reinforcement splice, where he shows the details call out for 6" overlap vs what should have been as 20" overlap is incorrect. Because the 6" overlap does meet the intent of the building code per ACI 318-77. The idea is, at the support, we add steel near the top face of the slab which is suppose to provide temperature and shrinkage crack resistance. Even in the current code the detail is still the same, except the requirement of integrity reinforcement. This integrity reinforcement prevents complete collapse of slab once punching failure has occurred and this requirement was added into the building code after Ronan point collapse in 1980s.

I mean the way videos are made on Youtube by a lot of non structural engineers. When I analyze the building, it was designed okay for the most part (95% of it). It was incorrectly designed for may be 5% of it. It is common that condos will have different finishes, heavier loading, added palm trees and planter boxes. There is inherent factor of safety that is considered from strength perspective and factored up loads from design load perspective so that people don't have to retrofit their home / apartment just to add marble on the floor. But again a lot of people miss it and people who don't actually design buildings miss it.

 

[SFCharlie]

From my perspective, BuildingIntegrity's point about the beams being removed when the valet parking was dropped to the level of the pool deck, was very telling.

SF Charlie
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[StructuralMadness]

Also, I think they structural engineer could have provided bigger column instead of 16x16 columns, but I doubt if the structural engineer even imagined anything like this remotely happening. The high % of reinforcement in the splice region that BI is talking about is definitely a "small" concern. I mean overall the column had reinforcement % of 9.2% compared to 8% limit specified by building code in 30" length of the column above pool deck. But I don't think that would have played a major role in the collapse. It is just another thing that structural engineer kind of waved his hands and thought that it is probably okay. Also based on the time of collapse, the building was no where near to it's full load carrying capacity. Far from it I would say, so the collapse should have been because of some instability of the column / step beam joint or deck pulling the column away (which again is a bit unlikely). Also, the consolidation of concrete is an issue with high rebar %, but still, based on the construction requirements of east coast which is a non seismic region, the overall congestion of steel there will be significantly less than the west coast and I have seen significantly high % of reinforcement in the columns without any consolidation issue. May be because of modern construction and concrete technology.

Also the contractor cannot reduce the rebar, because it is also essential in carrying the load of the building. Even if concrete column is in compression and concrete is good in compression, the column capacity comes from a combination of steel + concrete as both the elements compress together and support the building above. So contractor didn't have any choice.

 

[StructuralMadness]

On the point of pool deck last minute changes, here is something interesting. Even if that change wouldn't have been made, just 15' next to those beams that were removed, the deck was still under designed. So regardless of the change, the design of pool deck in general had some issues and would have required maintenance no matter what. But yes, that was a design change later on. And I think it was just important to check the pool deck after the design change. That is what forensic structural engineers do. They analyze the as built conditions and latest set of drawings. Because that is all matters.

 

[SFCharlie]

Also the contractor cannot reduce the rebar,

The debris says the rebar was reduced

SF Charlie
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[StructuralMadness]

Hey Charlie, are you talking about this image? BTW how do you guys quote someone else's response?

 

[Nukeman948]

Hey Jinal, Jason, of Building Integrity is not a member here and has no way of defending his analysis of the collapse on this forum. This is the second site I have seen you questioning his findings and conclusions. I think a better method would be for you to contact him through his Youtube account and discuss your concerns with him directly. Following him around the web and bad mouthing him behind his back just seems rather sleazy.

 

[StructuralMadness]

Hey Nukeman, hi! I did try reaching him out couple of times and couldn't do it successfully. I am not sure if I have questioned his findings anywhere else. Also, I am not bad mouthing him, so far what he had done was a really good job at explaining people. And again his latest video does have some credibility to it, and again I apologize to all of you if you feel I am coming out as negative. What I am implying is, to a nonstructural engineer it may seem like a lot of issues were present during construction, design and maintenance, but in reality the answer to this is rather very mundane and boring. Like Imagine NIST coming out and saying hey it was really just that pool deck collapse was because of some design issue and building collapse was unfortunate and coincidental, then this would lead to a lot of people blaming NIST for not doing their job appropriately. Just like what happened with WTC collapses. And again I am just drawing lines on things that actually wouldn't either contribute to building failure or are not as extreme as they are being represented.

I was also hoping some structural engineers will engage in this discussion and see if we do end up arriving at the same conclusion.

EDIT: Also I do agree with the conclusion that he has provided for the building failure in terms of slab being under designed. I have run the analysis both "Direct design method" as well as Finite element analysis and I did come up to the same conclusion that the pool deck was under reinforced and that started the collapse chain. So I am not even question his conclusion. But being a structural engineer, I was surprised that he added few incorrect information / details which were to an extent irrelevant. That is the reason I joined the forum to see what other structural engineers think about this.

 

[Nukeman948]

I am not sure if I have questioned his findings anywhere else.

Jinal Doshi,

https://www.facebook.com/groups/226...406251901&notif_t=group_name_change&ref=notif

 

[StructuralMadness]

Hey Nukeman, thanks for sending that link over, and yes I have joined that close group, interesting that we met here again. I have not discredited his findings, what I am trying to explain to everyone in that group is not to panic and question everything about buildings they are living in. Regarding planter boxes as well, like if you would ask any structural engineer you would get a similar response. I think what Josh did not influence enough is the level of concern these changes / adds contribute to the overall collapse. Nowhere will you see me calling him our as full of BS. Mainly because I have agreed with a lot of his conclusions. The things that I have not agreed upon which I do have a right to, if either the seriousness of the issue or the extrapolation of the design / details / changes towards the collapse. Because again, a lot of people freak out. While again that is not the case. Just because this building collapsed doesn't mean that you have to question all the buildings around you. I mean that is why I joined the group, is mainly to answer your questions so you guys can understand what a structural engineer would actually think.

Again, you will see videos created by very few engineers (including me) who are probably just not as versatile and experienced enough and who draws the conclusions very early on. Why do we think a lot of renowned researchers, forensic experts and structural engineers haven't said anything? Because they don't want to scare the public. Like adding marble to your floor does not lead to building collapse. That is all I am trying to do here.

 

[SFCharlie]

This is a tragedy, at least 98 people lost their lives. 100% lost the whole value of their structure. Many their life saving.

When I analyze the building, it was designed okay for the most part (95% of it). It was incorrectly designed for may be 5% of it.

To me, the lesson here is that the structural design has to be 100%. What scares me is you don't want to scare people but you say things like "it was designed okay for the most part (95% of it)"

SF Charlie
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[gonefishing2]

Ok, let’s talk from a structural point of view, about why in some condo units, did owners install thick set tile/marble floors, and not thin set, but not in all units? If the structural slab is reasonably level and flat in the condo, the cheapest and easiest solution is thin set tile laid directly on slab.

When I see thick set used on concrete slab floors, in some condo’s, but not all, it tells me the floor is out of level or has so much mid span deflection, that folks are willing to pay additional cost for thick set to re-level the floor.

This tells me we have a slab deflection issue or uneven changes in column elevations. So what has changed structurally with time to cause either one of these conditions. Either one it would seem would add stress and strain on structural members in the affected areas of building?

Raising floor height with thick set affects built in kitchen cabinets and all doors and base molding for example. Not a trivial go from vinyl or carpet flooring replacement.