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
Eng-Tips.com Forum Policies

 

[waross]

StructuralMadness:

BTW how do you guys quote someone else's response?

Cut and paste the content that you wish to quote. Cntrl "C"
Click the cartoon speech icon.
You will see:

You may enter the source of the quote or leave this blank.
Click OK or Hit "Enter"
Paste your content. Cntrl "V"

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[IEGeezer]

I tried to recalculate the weight of the planters full of water as well as the walls. This time I tried to estimate the height of the planters a little better. I came up with an estimate of 42 in for the big square ones and 24 in for the lower and longer ones. I also missed some. In this calculation I am including ALL the planters, whereas before I had only included the weight of the planters in the collapsed section (although I missed some).

As before, I used the measurement feature in Acrobat. One can scale the pdf to the drawing. Unfortunately, the scaling does not seem to get saved with the file. It appears to be a per session feature. I used a drawing that had been submitted as part of the minutes of the Board of Directors of the CTS condo association on Oct 14, 2020. It is an 83 page document that was posted here, but I did not save the url. My apologies. The drawing I used was on page 43.

I extracted it and was able to remove the photos that had obscured what appear to be the drawings of the planters as of that date. The drawing was done by Morabito Consultants, bears a date of July 13, 2020, is titled First Floor (Lobby Level) Framing Plan and is identified as Sheet S2A-1.1. I have identified the planters with as #1, #2, etc. in blue. I scaled the drawing based on the 6 foot dimension for planter no. 1 (I hope this was a planter!), based on a dimension marked on some other blueprint. Building Integrity mentioned that he could not find a drawing of the planters, so I thought I would try to contribute this drawing to the mystery.

The dimensions of the planters are in red with the dimension itself in black. The scaling I used in the Acrobat session to make the dimension notations was 1 in to 13.73 ft. The original size of the drawing is 36 in by 24 in. I am (hopefully) attaching the cleaned up and annotated copy herewith with full resolution. I am also going to try to embed a lower resolution version.

I am also attaching and embedding (with luck) a pdf of my calculations so that somebody can check them. The planters appear to be much heavier than I previously thought. Based on Morabito's blueprint, the walls of the planters appear to be about 10 inches thick. That may or may not be accurate. I assumed the walls were constructed with CMUs. Maybe they weren't or maybe they were thinner, but this is a start anyway.

The total calculated weight of the planters completely empty is about 147 metric tons or almost 325,000 lbs. It was reported that it had been raining heavily. If the planters were full of water, then the weight would have increased by another 180 metric tons or close to 400,000 lbs for a total weight full of water calculated at close to 330 metric tons or over 700,000 lbs! Did I make a mistake somewhere? It's late and that may be. Hopefully somebody can point it out to me.

 

[IEGeezer]

I can only submit one file at a time, so here is the full resolutions pdf of the drawing.

I assumed that the height of the table was 32 in. I ignored errors caused by perspective.

 

[Demented]

The 4x8 planters as they were called were modified to 1.143m high around the same time the weep holes were plugged.
*shrugs*
Just more gravity.

 

[MaudSTL]

An editorial proposes sweeping changes in Miami-Dade.

A House of Cards: The Miami Condo Collapse Exposes a Dehumanized Mindset in the Built Environment calls for better oversight and less cost-cutting.

It’s like deja vu all over again! Another roof overhang collapses at Miami-Dade apartment evacuated in July

 

[arbitraria]

A House of Cards: The Miami Condo Collapse Exposes a Dehumanized Mindset in the Built Environment

Also brings up Grenfell Tower and other examples both large and small; good read for anyone in the AEC industry.

"While it may be tempting to dismiss these incidents as “cherry-picking” from an otherwise safe and pure building stock, the process of designing and constructing our built environment is fueled by an accepted norm of pushing health and safety regulations to their practical limits. Such fears were recently underlined in a major survey of construction professionals by the British Board of Agrément (BBA), a major UK body for issuing certificates for construction products. The survey asked respondents what factors they believed were “the most likely to cause an emerging or actual disaster in the next few years.” The top two results, ranking far higher than any other risks, were “poor workmanship / installation quality” and “uncontrolled value engineering.” The message from the industry is clear: our preoccupation with delivering projects for the cheapest price, with the fewest resources possible, is the single most likely factor to cause a future building disaster."

 

[arbitraria]

@IEGeezer - I need to look more closely at your plan and calcs, but I'm assuming you're going with a maximum possible water weight for the planters by volume? They appeared to be fairly filled-out with dirt and vegetation, and most likely pretty saturated with water. I'm curious whether planters full of dirt, dense shrubs, and water would actually weigh more than the volume of water alone?

I remember the discussion on the core samples and slab composition, but without going through the 10 previous threads, I don't recall if there was an idea of just how much water the slab components may have been holding?

It's going to be interesting to see what the verdict is down the line as far as just how overstressed the pool deck ended up. Original weight of materials plus additional layer of sand and pavers, planters full of vegetation, undernourished slab, lack of/failed waterproofing / trapped water, the occasional likely overweight vehicular intrusion, improper repairs (still wondering where that mystery partial slab replacement was)...am I missing anything?

 

[gonefishing2]

And don’t forget weight of large palm trees until 2017 and their root damage

 

[Phil1934]

article in new Pile Buck on p. 128 discussing repair procedures for similar bldgs. A nearby hi rise's concrete tested 1100 PSI!

https://links.constructionarchives....wYTgwMDAzNkBjb25zdHJ1Y3Rpb25hcmNoaXZlcy5jb20i

 

[Spartan5]

Regarding the planters… I’m a bit surprised by some of the musings.

Water alone is about 60 lb/ft3
Dry soil about 100-115 lb/ft3
Saturated soil 115-130 lb/ft3

I think they often use lightweight closed cell geofoams in the bottoms of planters to elevate the vegetation without adding weight.

 

[StructuralMadness]

I agree. It is not like water will add another 64.4 lb/ft3. A soil saturated with water just has air pockets filled with water and this depends on the void ratio of the soil. Good clarification there.

 

[StructuralMadness]

Charlie,
I completely agree, every structure is supposed to exceed the building code requirements, not just meet the requirements. But a lot of engineers have their hands tied because some developers / architects push the engineers to either reduce the member size or reinforcement tonnage. Again there are only a few. Fortunately through my career I have had a pleasure to work with good architects and developers and since I am mainly involved with designing buildings on west coast where seismic design governs a lot of things in the structure.

As a side note a lot of times there are owner driven / architect driven changes towards the end of the project and they are reluctant to shift the deadline. Now for them it may be just moving a column or eliminating a step, but for engineers it is redefining load path. Sometimes it is not a big deal, but a lot of times we face time crunch even after working 70 hour weeks to accommodate that change. And that's where a lot of mistake could happen. I think what arbitraria shared is a great post and talks a lot about reality that structural engineers face on day to day basis. It is not bad to push boundaries, but then at what cost? Because once the robustness and redundancy of the structural system is reduced, a system mainly just relies on a single load path which is a big issue. It is having just one road connecting your home to city center and if it breaks you can't travel kind of scenario.

Again, structural engineer's work is really important but it is always been shadowed by a lot of factors and that's where not everyone pays attention / listens to them. I think all the the structural engineers around the world feel the same way.

EDITS: "But a lot of engineers have their hands tied because some developers / architects push the engineers to either reduce the member size or reinforcement tonnage." A bit of explanation so that someone don't misunderstand the statement. What I meant by pushing to the limit is still satisfying the building code requirements, but then there is no more room for error from construction to material strength or any accidental event. A good example for Champlain towers condo collapse could be those skinny 16x16 columns that were heavily reinforced or the pool deck with marginal reinforcement in most of the region (Excluding that part that was under designed).

 

[Vance Wiley]

If that was structural concrete it is WAY past time to vacate.
Could this be an extreme case of chloride damage to concrete? Did they test for that?

 

[w-streng]

a lot of engineers[/b] have their hands tied because some developers / architects push the engineers to either reduce the member size or reinforcement tonnage]

Wow, this statement could really be seen in the wrong light. Yes, developers/architects push the limits to achieve their own agendas but I would seriously doubt that any engineer would knowingly ignore code requirements and compromise structural safety and serviceability to satisfy them. They would surely scoff at the suggestion that they have such powers.

Back to engineering:
Jinal, I'm curious to hear your thoughts on the wall noises that unit 111 heard in the lead up to the collapse. Yes, load re-distribution, but why exactly, what's happening in the structure, the planter area has evidently not yet collapsed. I am not a protagonist of top-down collapse btw, I don't have an agenda here.

 

[StructuralMadness]

I have thought about it for quite some time. Like why the creaking noises and why on the wall. Because the walls are just partition walls and these could very well be just dry walls since the building was built in 1980. I am not sure of cold formed steel existed back then. Again I have not grown up in US so can't say for sure. So when someone says low noises, could it be they were just trying to describe the type of noise, "Like someone banging on the wall" but it could have been a series of concrete failures? Like the deck failure itself could have progressed first from a single concentrated region through to the entire deck collapse prior to the building failure.

Like the failure of the pool deck should have started at one column point. And apartment 111 was the closest apartment to any failure points. And remember that it was just not her, but the security guard also head some series of loud noises. Which means it was not the wall banging for sure, the statement was just a metaphor. Even though there were multiple slab column joints that showed punching failures when doing the actual calculations, not that because of inherent material over-strength and factors of safety the actual capacity would be much higher. And the magnitude of rust, rebar delamination as well as cracks would have varied all across the deck. Also, as concrete breaks along a failure plane, it does typically create loud noise. Like we can hear it in structural test labs whenever they perform these tests. You can even hear such noises in steel buildings when bolt slip occurs. So once one of the section fails, it will again redistribute loads and other sections will see the stress and that's how it should ideally progress. This is what we know as series of brittle failures that are responsible for the deck collapse. I think when they head the loud bang, that's when the entire deck actually collapsed.

 

[arbitraria]

I think they often use lightweight closed cell geofoams in the bottoms of planters to elevate the vegetation without adding weight.

This is what I was getting at, and articulated very poorly, my apologies. Taking @IEGeezer's calculations for water volume, and comparing that weight to potential planter configurations (very heavy if the whole thing is full of dirt and plants, not so much if there's an internal platform to optimize space and weight, and how those would compare to his numbers).

Thanks for the numbers @Spartan5, I never did much in the way of "fun" landscape design, most of the projects I worked on in site civil were institutional and as such the landscaping components were mostly related to erosion control. I should really go back and look at the related details from the original plans. The Morabito details seemed to imply the new planters would be full-depth soil but I didn't really look very hard so I'm probably mistaken.

 

[IEGeezer]

That would be about 45 inches tall. Where did you get that the big planters were 4 ft by 8 ft. In this picture, they look roughly square as they do in the Morabito Consultants drawing I referenced.

 

[w-streng]

The walls were cement masonry units so could inadvertently end up carrying vertical load. Just throwing some ideas out there but think about slab deflections, gaps between top of wall and slab (if any), vertical lengths of wall from level 1 to roof on façade, vertical load transfer accumulating downward onto the stiffer beam element on pool deck level gridline 10 between column grids K/L and L/M.

Could the beam on gridline 10, at grid L (only 16.5" deep), have started to drop a little from shear failure initiation, loads then distributed to other columns and walls (creaking).....

Did the engineer intend the beam on grid 10 between K & M to be 27.5" and not 16.5"? So many possibilities and permutations.

 

[IEGeezer]

To make it easier to compare to my calculations:

60 lb/ft3 is about 0.96 kg/L
64.4 lb/ft3 is about 1.03 kg/L
100 lb/ft3 is about 1.60 kg/L
115 lb/ft3 is about 1.84 kg/L and
130 lb/ft3 is about 2.08 kg/L

 

[MaudSTL]

Jinal, I'm curious to hear your thoughts on the wall noises that unit 111 heard

Jinal, please review the data tab in the Timeline spreadsheet for a detailed compilation of collapse witness statements made in publicly available interviews.

Chani Nir heard knocking sounds when she got home at 11 PM. These continued until the first collapse. Her mother Sarah noticed the knocking sounds not long after she got home at 12:30, and has stated that they sounded like hanging pictures on the wall or construction going on in the apartment upstairs. These sounds gained in intensity over time. We do not know if Security Guard Shamoka Furman also heard the knocking sounds in the lobby. We also do not know what time these sounds actually started, if in fact they started before 11 PM.

The first collapse was at 1:10. All three Nirs perceived it as a wall collapsing from above, as if someone were doing demolition work in the middle of the night. Shamoka Furman also heard this loud sound in the lobby, and perceived it as something to do with the elevator. But since the elevator threw no alarms, she wasn’t concerned that anything was wrong.

The second collapse at ~1:15 was the deck, and the third collapse at ~1:22 was the building.