News Florida Collapsed Condominium had been sinking since 1990s

[Astronuc]

I imagine there is a potential for 'negligent homicide'. Even a study in 2020 indicated the building was unstable.

MSN - Land around the Florida condo that collapsed was showing signs of sinking, according to a 2020 study
https://www.msn.com/en-us/money/realestate/land-around-the-florida-condo-that-collapsed-was-showing-signs-of-sinking-according-to-a-2020-study/ar-AALp3eT

Why weren't the residents warned? Why wasn't the building condemned? And it was undergoing a review for recertification?!

https://www.msn.com/en-us/news/us/collapsed-miami-condo-had-been-sinking-into-earth-as-early-as-the-1990s-researchers-say/ar-AALoUP0

There reason that licensed professional engineers are licensed is so this s*** doesn't happen! Same reason for building inspections and certification.

This didn't just happen. It was a slow, and apparently detectable, condition, a disaster waiting to happen. Someone neglected the evidence, and neglected to warn the residents.

 

[russ_watters]

Probably. We'll see, but at first glance it definitely looks like it was predictable if not predicted. But even then it may be tough to unpack where the fault lies (design, construction, owner/maintenance?), and even more difficult to obtain a conviction/prove willful negligence:

https://en.m.wikipedia.org/wiki/Philadelphia_Pier_34_collapse

 

[Vanadium 50]

I don't think we know if

• The standards were followed but inadequate
• The standards were adequate but not followed

 

[jack action]

This didn't just happen. It was a slow, and apparently detectable, condition, a disaster waiting to happen. Someone neglected the evidence, and neglected to warn the residents.

These are not just residents, they are owners (condominiums). They are responsible for the maintenance of their building. From your link:

In 2015, a lawsuit alleged building management failed to maintain an outside wall, resulting in water damage and cracks. The owner who filed that suit had previously sued over the same issue, according to a court filing. The management company paid for damages in the earlier case, according to records.

Cracked walls or shifting foundations can be clues that sinking has affected the stability of a structure, according to Matthys Levy, a consulting engineer, professor at Columbia University and author of “Why Buildings Fall Down: How Structures Fail.”

Residents of the building might have noticed changes, he said.

“Had there been changes in the building? Cracks in the walls, in the floor? Floors not being level, things rolling off tables?” he said. That would indicate the building was shifting.

It was their responsibility to hire the right people to investigate the condition of their building, just like you are responsible for your house. The residents were most likely the ones who neglected the evidence. At the very least, they were responsible for staying there if the rest of the group chose to ignore the potential danger. You don't need someone to condemn your building to move from a potentially dangerous place.

 

[Twigg]

https://www.msn.com/en-us/news/us/collapsed-miami-condo-had-been-sinking-into-earth-as-early-as-the-1990s-researchers-say/ar-AALoUP0

A Florida high-rise that collapsed early Thursday was determined to be unstable a year ago, according to a researcher at Florida International University.

Exhibit A: Florida International University living in a glass house and throwing stones (see bridge collapse 3 years back)

(Not the same engineers I know, but I couldn't resist.)

 

[Astronuc]

Exhibit A: Florida International University living in a glass house and throwing stones (see bridge collapse 3 years back)

Yeah, I was thinking about that just now.

I'm curious to see who signed the 'Certificate of Occupancy'.

 

[Twigg]

Does anyone have access to Wdowinski's report in the journal Ocean and Coastal Management? I'm very curious what the signs of subsidence are, and how confident they were in their evidence. It sounds like satellite images were used. Do they measure relative position to nearby landmarks or something? I'm curious how they singled out a single condo building. Maybe they canvased every building in a set of images and this one stood out? Is data like Wdowski's 2mm/yr subsidence rate normally part of the prevention process, or is it considered speculative? (In other words, do you think anyone relevant to condemning decisions read Wdowinski's paper?)

 

[Astronuc]

These are not just residents, they are owners (condominiums). They are responsible for the maintenance of their building. From your link:

It was their responsibility to hire the right people to investigate the condition of their building, just like you are responsible for your house. The residents were most likely the ones who neglected the evidence. At the very least, they were responsible for staying there if the rest of the group chose to ignore the potential danger. You don't need someone to condemn your building to move from a potentially dangerous place.

On the other hand, someone 'certified' the building, and it was apparently supposed to undergo a recertification process this year. Last year's study should have been a RED flag. Was the study made available to residents? If so, it's on them. If not, then we'll see.

 

[Twigg]

Was the study made available to residents?

https://www.sciencedirect.com/science/article/abs/pii/S0964569119309470
I hit a paywall, but then found I could get in with my school's access. Do you think elsevier gave special access to affected parties (residents)?

 

[Twigg]

The study doesn't single out individual structures. They claim they have taken vertical displacement data over time on >20 satellite image scenes. Think heat map, not direct measurement of a structure's position. These data were collected in the years 1993-1999. They measure subsidence rates between 1 and 3mm/yr throughout Miami Beach, with standard deviation between 0.2 and 0.7mm/yr.

Attached:
(1) Image from the publicly available graphical abstract

(2) Google maps of the collapsed building

Bottom line: If you wanted to not certify a building based on this data, you'd have to de-certify all of Miami Beach. (Am I reading this wrong?)

Edit: Added strike-through to false claims based on a misunderstanding of the heat map's y-axis. My bad

 

[Astronuc]

https://www.sciencedirect.com/science/article/abs/pii/S0964569119309470
I hit a paywall, but then found I could get in with my school's access. Do you think elsevier gave special access to affected parties (residents)?

That would be a general study, and it applies along the Atlantic and Gulf coasts.

The folks in the condo would need a site specific study.

 

[Twigg]

Yeah, I read this one because it is the article cited in the news releases you shared. Was there another one I missed?

 

[Astronuc]

Yeah, I read this one because it is the article cited in the news releases you shared. Was there another one I missed?

I'm sure there are numerous studies.

I'm sure there will be a lot of inspections on buildings in Miami Beach.

High-rise structures (the taller, i.e., the heavier) are particularly vulnerable. Pilings have to go deep, ideally to bedrock, with depth based on the mass of the building and compressibility of the subsurface. I've worked with a couple of civil engineers, one of who designed the pilings under his house, which sits on a hillside (basically sandstone) overlooking the Pacific Ocean.

Think of the leaning Millennium Tower in San Francisco.
https://en.wikipedia.org/wiki/Millennium_Tower_(San_Francisco)

Four dead, up to 159 missing, which may include those confirmed dead.
https://news.yahoo.com/surfside-miami-condo-collapse-death-toll-unaccounted-for-141756029.html

Numbers have changed over the last 12 hours.

 

[Twigg]

I stand corrected. There was specific mention of the structure in the article, and I completely mis-understood the y-axis of that heat map (for some reason, I read green as being "2mm/yr" when it is actually 0mm/yr whoops)

So yes, the article does single out the collapsed structure as a place that was sinking 2mm/yr when most (93% per the article) of Miami Beach was stable.

From the journal article:

In some locations, as in the eastern part of the city, the detected subsidence is of a 12-story high condominium building (northernmost black circle in Fig. 3A).

(I don't think I can reproduce their figures here :/ but yes, they singled out the condo building in one of their heat maps.)I'd also point out an additional quote from https://www.msn.com/en-us/news/us/collapsed-miami-condo-had-been-sinking-into-earth-as-early-as-the-1990s-researchers-say/ar-AALoUP0 @Astronuc linked:

Wdownski said he doesn’t believe anybody in the city or state government would have had a reason to be aware of the findings of the study. The bulk of it focused on potential flooding hazards, not engineering concerns.

 

[Twigg]

(Copied from https://www.msn.com/en-us/news/us/collapsed-miami-condo-had-been-sinking-into-earth-as-early-as-the-1990s-researchers-say/ar-AALoUP0)

For context, the high rises are the minority in this part of Miami Beach. The other problematic subsidence spots seen in the study were under much smaller loads.

 

[Astronuc]

I looked on GoogleMaps and found the overhead before shot.
About half the building collapsed!

 

[rsk]

Similar but different
The Grenfell fire in the UK in 2017 exposed the widespread use in tower blocks of cladding which poses a serious fire risk.
Many other tower blocks using unsafe cladding have been identified and the owners are now liable for paying for this to be corrected. The costs run into millions. The tower blocks aren't in general luxury, expensive ones for the very wealthy - they are full of flats which have been bought by ordinary working people on mortgages. They are now facing huge debts to make their buildings safe and are, of course, unable to sell.

I wonder whether the costs of making other towers in Florida safe will also fall to their residents. I know there are mega rich people in Florida but I'm guessing the people who have bought in these blocks are just ordinary people with ordinary incomes.

 

[Vanadium 50]

The "sinking" article is paywalled. the data was taken at some time between 1992-1999, so it covers no more than 7 years.

The reason I bring this up is the building is 40 years old. 2mm/year x 40 years is 8 cm. That's a lot to go unnoticed.

 

[Astronuc]

Condo Owners Are Suing The Collapsed Building's Association
https://www.npr.org/sections/live-u...o-owners-lawsuit-suit-building-surfside-miami

What We Know About The Condition Of The Florida Building Before It Collapsed
https://www.npr.org/sections/live-u...ion-of-the-florida-building-before-it-collaps

Kenneth Direktor, an attorney for Becker, a law firm that has worked for the condo association for about five years, told the Herald the complex had already hired an engineer for the recertification process.


"They were well into the review with the engineer about the project," Direktor said.

A possible weakening of concrete​

Greg Batista, an engineer who specializes in concrete repair projects, told the Herald he suspects concrete spalling, a process whereby saltwater seeps into concrete and ultimately causes support beams to rust, expand and weaken, to be a factor in the building's collapse.

Did seawater penetrate the concrete, which would degrade the concrete AND corrode the rebar?

Wdowinski and Fiaschi found that in the 1990s, Miami Beach experienced subsidence at the rate of 1 to 3 millimeters per year, which the former said could add up to a few inches of over the course of a decade.

Well, 25.4 mm to an inch. 10 mm < 0.5 inches and 30 mm ~ 1.2 inches. Did it continue to subside for 4 decades?

I have to wonder how far the inspecting engineer got into the current examination for recertification. Did he even know about the history of subsidence?

I've read that the collapse was caught on video, but I have not seen such a video, or any evidence of such a video. Found it. https://www.yahoo.com/news/video-captures-moment-high-rise-140614000.html


Edit/update: https://www.wsj.com/articles/miami-...ve-emergency-response-11624532492?mod=itp_wsj

I attached part of a picture from the WSJ article. The two columns to the left side look like they are damaged. It seems like rebar is splayed and protruding from the columns. The upper brown-colored portions looks like it shifted with respect to the lower white-colored portion. I think the floor of the parking garage has collapsed having separated from the columns. The rebar protruding from the columns seems to have been part of the garage floor.

 

[mcastillo356]

A pray for hope, I have no words.

 

[Borg]

Here's a short before and after video from this CNN article - Mystery of what caused Florida collapse deepens

https://dynaimage.cdn.cnn.com/cnn/animations/w_307/210625103334-desktop-floridabuildingcollapse.mp4

 

[Astronuc]

Miami Herald reports,

In a 2018 report about the Champlain Towers South condo in Surfside, an engineer flagged a “major error” dating back to the building’s origin where lack of proper drainage on the pool deck had caused “major structural damage,” according to records released late Friday night by town officials in the wake of the tower’s disastrous collapse on Thursday.

Read more here: https://www.miamiherald.com/news/local/community/miami-dade/miami-beach/article252385083.html

The concern was laid out in an October 2018, “Structural Field Survey Report,” produced for the condo association by engineer Frank Morabito of Morabito Consultants. Morabito wrote that the “main issue” at Champlain Towers was that the pool deck and outdoor planters “laid on a flat structure” preventing water from draining. The lack of waterproofing was “a systemic issue” that traced back to a flaw “in the development of the original contract documents” 40 years ago, the report said.

From two days ago,

But while a critical, county-mandated process designed to catch any serious structural damage was underway at the Champlain Towers South, it was not yet complete. The 12-story, 136-unit building was erected in 1981 and was still early in its recertification process, which is required for most non-single-family structures countywide once they turn 40 years old.

Read more here: https://www.miamiherald.com/news/state/florida/article252340108.html

“While the Champlain Towers had begun the 40-year recertification process, the 40-year inspection report had not yet been generated or submitted to the Town,” McCready said in an email.

The engineer retained by the Champlain towers as part of the recertification process was Frank Morabito, according to an attorney for the building’s condo association. Morabito could not be reached for comment Thursday.

Morabito is the same engineer that warned of structural issues in 2018.

 

[Vanadium 50]

It's not clear to me that engineering problems with the swimming pool and parking garage did (or for that matter, didn't) have anything to do with the collapse. It will, however, serve to muddy the waters: "It couldn't be that my concrete was poor quality - look at the report on the swimming pool design!"

This will take time. The Kansas City Hyatt walkway collapse had a clear cause (obvious even to a physicist) and the report came out almost a year after the collapse. It's only been two days.

 

[Lnewqban]

Please, see:
https://www.eng-tips.com/viewthread.cfm?qid=484587

 

[anorlunda]

If the sinking land theory is proven, it will have huge consequences for all the other beachfront properties from Fort Lauderdale to Miami Beach.

If you have a big enough budget, single buildings can be saved (the leaning tower of Pisa for example). But hundreds or thousands of buildings seems out of reach even the very rich. Predictions of sea level rise make it worse, because new investments today may have benefit for only a limited number of years.Historically, the North American East Coast Barrier islands have rapidly moved far east and west. It is only since humans began building structures there that it becomes a problem.

From
https://pubs.usgs.gov/pp/pp1827/pp1827.pdf

 

[Lnewqban]

View attachment 285031
(Copied from https://www.msn.com/en-us/news/us/collapsed-miami-condo-had-been-sinking-into-earth-as-early-as-the-1990s-researchers-say/ar-AALoUP0)

For context, the high rises are the minority in this part of Miami Beach. The other problematic subsidence spots seen in the study were under much smaller loads.

That is a very good picture.
Most I have seen are way too close to provide an accurate perspective.
We can see the twin building, erected following similar drawings and about the same time frame.
It is the third building farther North from the disaster point.
Also, the size of the next building on the South side can give us an idea of the amount of vibration (mainly due to pile driving) that its construction transferred to the decaying structure of the old building.

 

[Twigg]

If the sinking land theory is proven, it will have huge consequences for all the other beachfront properties from Fort Lauderdale to Miami Beach.

I've been wondering about this. How would the investigative team prove/disprove this? Can you just measure how much of the foundation is sticking above ground on the remaining structure and compare it with the plans? (Ho boy, am I glad I'm not the guy with tape measure for that job )

I think @Vanadium 50 has it right. The cause isn't immediately obvious to the public eye like other famous disasters, and we will need to wait for a thorough and exhaustive investigation.

Out of curiosity, does anyone know if poor drainage could cause subsidence? Every time I've heard of bad drainage causing settling issues, it was because of high clay content in the soil. But that shows up as a seasonal cycle (wet/dry seasons causing swelling/sinking), not as a linear trend like was shown in Wdowinski's study. Not trying to speculate here, just trying to learn. One day, I'd like to take a class in dirt science...

 

[Greg Bernhardt]

This is terrifying and sad. Infuriating the building managers didn't act on the recommendation. This hits me a little personally because I lived in a condo building several years ago where similar things were happening where waterproofing was failing and water was destroying not only the underground concrete pillars but each condo's bump-outs (wood support beams). In fact, while they were being repaired one of the engineers commented to me that they were so bad he thinks they would have failed within a year and the bump-outs would have started shearing off. It appears the critical difference between my situation and this is that my building managers acted on the engineering recommendation and got it fixed in time. We also sued the condo builder to cover much of the cost and won.

 

[anorlunda]

Every time I've heard of bad drainage causing settling issues, it was because of high clay content in the soil.

But clay content in beach sand is zero. I live 100 miles inland in Florida, it's still all sand.

 

[Twigg]

Again, I don't know much here. But my understanding is that sand is relatively course-grained for a soil type, and so it's not very compressive/expansive (compared to clay which is super fine grained). Should I interpret the subsidence as sand being washed away by all the undrained water from the parking garage/pool deck?

Guestimating the area of the plot as 100ft x 100ft, and taking the density of loose sand as 1442 kg/m^3, 2mm/yr makes 6 short tons of sand washed away per year. Am I thinking about this correctly? It seems like a lot!

 

[Vanadium 50]

I am looking at the paper of Fiaschi and Wdowinski. To be honest, I can't tell if the point in question is Champlain Towers South or immediately north.

• Figure 3 is low resolution and blowing it up 800% proved unhelpful.
• The data points obscure the geography
• The most obvious landmark, the building to the immediate south, wasn't built until 2018, so it's harder to align the data and a map than I first thought.

 

[Vanadium 50]

I reread the paper in the clear light of day. The authors identify the point in question as a 12-story condominium, which suggests it is the collapsed building. However, immediately north is Champlain Towers East Condo. Figure 3 shows it northeast of a park, which suggests East, but the park seems not to be shaped as it is today, which opens the question up again.

I think the paper isn't really intended to pick out a single building.

Was this paper a warning? Not explicitly. It's more about flooding, and is more focused on the opposite end of the island, where historical flooding has happened. Larger subsidences are observed elsewhere on Miami Beach and much larger ones still near Norfolk.

I don't even think it's actionable. "Excuse me ma'am, but you have to evacuate right now, because we were just made aware of a re-analysis of 20-25 year old data that shows that this building has a subsidence rate of 5 microns per day, which causes it to rank #4 out of all spots on this island, and is almost one-third the rate of parts of Norfolk. No ma'am, no problems seen at Norfolk. No ma'am, we don't think you'll ever be able to return home - can't` be too careful."

Three other points I'd like to make. One is that there is actually no problem if the building sinks 8 cm (which seems to me kind of hard to miss, but...). The problem is if the building sinks non-uniformly: 8 cm here, but only 1 cm there. It shifts the loads, and worse, forces that were purely horizontal develop vertical components and vice versa. The 2mm/year number tells only a part of the story and not a very big part at that.

The second is that the swimming pool sits over a parking garage, and is not terribly close to the building.

Finally, concrete is about the most complex inorganic building material there is (and reinforced concrete just makes it worse). People use supercomputers to try and model its properties. It's also not as chemically inert as you might think. Even if inferior concrete was poured 40 years ago, it might be hard to prove that today.

Nothing has changed my viewpoint: I don't think we know if

• The standards were followed but inadequate
• The standards were adequate but not followed

and are unlikely to know on the timescale of days or weeks.

 

[fresh_42]

Salty winds and water aren't rebars' friends. It could have been simple rust.

Repairing concrete is not only expensive, it is also rather dirty, takes months and most of all it is very, very loud. I don't know whether these points were an issue at the owners' regular meetings, but I do know people.

 

[Vanadium 50]

A building next to my office has a metal post sunk into a concrete slab. After only a decade, the concrete looks like a chromatography experiment - browns, and yellows and greens...

I'm not sure if rust is simple. The concrete shouldn't be under tension, which is where the rust might cause the rebar to yield. However, in combination with other factors, such as forces in an unanticipated direction, absolutely.

 

[Astronuc]

The report described failed waterproofing that caused "major structural damage" to the concrete below the pool deck and entrance drive, as well as "abundant cracking" in the concrete columns, beams, and walls of the parking garage.

It's unclear if any of those issues flagged in the 2018 report contributed to Thursday's collapse. Officials told reporters in a press conference Saturday that the cause of the collapse will be investigated after the search-and-rescue efforts finish.

Morabito Consultants' statement noted that the 2018 report had "detailed significant cracks and breaks in the concrete, which required repairs to ensure the safety of the residents and the public."

https://www.yahoo.com/news/engineering-firm-found-structural-damage-031857075.html

Remedial work was necessary and identified in 2018. Three years later it hadn't been addressed.

From the video of the collapse, the central portion of the north wing collapsed and then the eastern portion collapsed (somewhat being pulled sideways and down). There was an entry point to the garage under the center section of the building. (See figure)

Concrete should be in compression and the rebar would take some tensile or bending load, and shear if present. Concrete is porous (unless specially designed and treated) meaning water can infiltrate, and salt water is particularly damaging to concrete and the rebar (corrosion). Even without saltwater, standing water can cause concrete to deteriorate.

It will take time to get to the foundation and collect forensic evidence as to the condition of the subsurface and concrete used in the foundation.

Some article on concrete and seawater.
https://theconstructor.org/concrete/concrete-seawater-effects-preventions/843/

https://www.concreteconstruction.net/_view-object?id=00000153-8bb0-dbf3-a177-9fb9d6200000 (link to pdf, save or open pdf)

http://onlinepubs.trb.org/Onlinepubs/hrr/1966/113/113-002.pdf

An interesting Nature article - Rare mineral is the key to long-lasting ancient concrete
https://www.nature.com/articles/nature.2017.22231

 

[Borg]

The Washington Post had a story on the front page this morning which described a man whose wife was talking on the phone from her balcony when the collapse occurred. He said that she saw the pool collapse into the garage. After that, the building collapsed and her line went dead.

 

[Astronuc]

The Washington Post had a story on the front page this morning which described a man whose wife was talking on the phone from her balcony when the collapse occurred. He said that she saw the pool collapse into the garage. After that, the building collapsed and her line went dead.

I heard a similar story. The area near the pool should be one of the least stressed/loaded areas. Also the garage floor to the west of the pool area collapsed, but it's not clear if it collapsed first or got hit by the building as it collapsed.

Furthermore, the section of the tower structure to the west of the pool is still standing, whereas the part that collapse was further away and diagonally opposite the corner with the pool. The central portion of the wing north of the pool collapsed, then the part at the eastern end, directly north of the pool collapsed (it seemed to get pulled down by the collapsed section). It may mean the ground became unstable, as in a sinkhole situation, or perhaps liquefaction. If that is the case, then all the high rise buildings are at risk, regardless of the concrete and reinforcement.

Someone listed an apartment next door for $1.375 M. It was purchased in October last year for just over $1M. The listing has since been pulled after negative comments. I should clarify that the apartment was in one of the other sister towers, not the Champlain Tower South that collapsed. I was expecting that the apartments in the CTS are probably on the order of $1M each, although the apartments on the lower floors are probably less.

 

[Vanadium 50]

The engineer's report is available. The issues that have been brought up are there. What isn't there is a sense of threat or urgency.

 

[Astronuc]

I think that Items I, J and K on pages 7, 8 and 9 look pretty threatening, and urgent, especially at the top of page 7, where MC indicates the failed waterproofing is causing major structural damage to the concrete structural slab below these areas, after indicating the waterproofing is beyond its useful life. Then it states, "failure to replace the waterproofing in the near future will cause the extent of the concrete deterioration to expand exponentially." That is a fairly dire warning. It should have been repaired during 2019!

Of course, MC only looked at the building, not under the building. I'm sure insurance companies will force highrise building owners to look under the buildings for unstable areas.

 

[Vanadium 50]

failure to replace the waterproofing in the near future will cause the extent of the concrete deterioration to expand exponentially

And you might lose a parking garage.

 

[Astronuc]

And you might lose a parking garage.

I recall seeing a number like $9 million for repair, but I don't know the scope of that.

The town/city or whatever responsible entity will now have to check the stability of the ground on which that building and nearby high-rises sit. If indeed, there was some kind of sinking or subsidence, then all such structures are at risk. It will depend on the loading of the foot print.

Some of the other information indicates the garage was subgrade, or subsurface, to see if it was unstable. Also, in figures J1 and J2, it's not clear which entrance; there are two, one of 88th Street on the north side of the building and one near the southwest corner, which may be to the upper garage deck. I'm guessing from the slope, J2 is looking north up the ramp to 88th St.

Could street runoff travel down that ramp and pool in the garage? Could the water/rain and upper garage deck pool and drain to the lower garage level? If the waterproofing failed, the water could seep into the foundation and subsurface, where drainage may be poor, given that it is near sea level. Then if water pooled in the subsurface, the ground could become soft (and more easily flow), AND if there is saltwater intrusion into that formation, then the pooled freshwater would allow migration of the sea water into the formation, which might explain the corrosion of the rebar and concrete floor.

Inspections will have to look at the subsurface to see if there is seawater intrusion under the concrete flooring and footings of the building. Then they will probably have to rewrite the code to prohibit similar construction on the island. They should probably look for corrosion in Surfside's sewer/storm drain system.

I was looking for the wastewater treatment plant, but I cannot readily find it.

 

[Vanadium 50]

One thing that's not mentioned is geology. The whole thing sits on karst. Lots can happen with karst.

 

[Astronuc]

One thing that's not mentioned is geology. The whole thing sits on karst. Lots can happen with karst.

https://en.wikipedia.org/wiki/Karst

Maybe also Coquina, which is also porous, or perhaps a combination.
https://www.nps.gov/casa/learn/historyculture/coquina-the-rock-that-saved-st-augustine.htm

They did not have long to wait before the coquina walls were tested. In 1702, Governor James Moore of Charleston led his English forces against St. Augustine and the Castillo. He captured the town and set his cannon up amongst the houses to bombard the fortress. But a strange thing happened. Instead of shattering, the coquina stone merely compressed and absorbed the shock of the hit. The cannon balls just bounced off or sunk in a few inches. The shell rock worked!

I don't know the details of the geology in the Miami area, but I do know that local governments have expressed concern about infrastructure due to rising sea level and heavy flooding with high tides. There is a lot of infrastructure at risk, and the collapse of CTS in Surfside may the a warning to all the cities along the Atlantic and Gulf Coast, especially for older structures built during the early 80s and before.

https://news.yahoo.com/beach-residents-wondering-whether-building-150945957.html

 

[Twigg]

If the building sat on karst, that (speculatively) explains a lot.

I took a look at this report on karst geology in Florida. In Fig 10 (page 22), you can see that Dade county is marked as "thinly covered karst". With the poor drainage, there was probably standing water that seeped deep into the ground and corroded the karst. That speculative hypothesis could explain the 2mm/yr subsidence rate that was seen in Wdowinski et al's data from 1992-1999.

Not suggesting that this subsidence was the cause of the collapse. It's just a complicating factor, and it's unclear to me how it might've fit in. The failed waterproofing and corroded foundation smells fishier to me.

Another question that bugs me is why the building pancaked. I saw in the engineering thread @Lnewqban linked that the walls are CMU. Is this kind of failure mechanism typical for that construction?

Still need to read the engineer's report.

 

[Astronuc]

Another question that bugs me is why the building pancaked. I saw in the engineering thread @Lnewqban linked that the walls are CMU. Is this kind of failure mechanism typical for that construction?

There is some focus on the base of the building and the underground garage.

https://www.msn.com/en-us/news/us/possible-failure-point-emerges-in-miami-building-collapse/ar-AALvJr3

While no definitive conclusions could be drawn from the surveillance video, which was shot from a distance and reveals only one perspective of the disaster, some of the engineers reviewing it last week said it seemed to suggest that the failure began at a specific point near the bottom of the structure — perhaps as far down as the parking garage beneath the building, or on the first few floors.

From what can be seen in the video, part of the structure first slumped, seemingly falling vertically in one giant piece, as if the columns had failed beneath the southern edge of the center of the building, not far from the pool. Like a nightmarish avalanche, the failure quickly spread and brought down the entire center of the building. Seconds later, a large section to the east also toppled.

In the video of the collapse, there is some lateral motion of the building, and columns and their joints don't do well with lateral motion. Once the columns sheared or buckled at the first floor and below, then the upper mass drops with a jolt, the lowest intact floor collapses/pancakes, and there is a progression up the remaining structure until all the floor collapse.

Edit/update from the cited article:

Gregg Schlesinger, a contractor and lawyer in Florida, said that cracks and a kind of crumbling in the concrete known as “spalling,” also identified in the 2018 report, should have been a “red flag” if it seemed serious at the time. If that were the case, he said, engineers should have dug deeper to find out what was causing the deterioration.

 

[Astronuc]

The Washington Post had a story on the front page this morning which described a man whose wife was talking on the phone from her balcony when the collapse occurred.

I heard another story of some guy who spoke with his mother who was awakened from noise in the building and she couldn't go back to sleep. She described popping and creaking sounds. I don't know if she was a survivor or one of those missing.

Edit/update:

The night before the Champlain Towers South building collapsed, Pablo Rodriguez recalls his mom telling him she heard a loud creaking noise.
She’s among the 150 people still missing, along with Rodriguez’s grandmother.

https://www.wbur.org/hereandnow/2021/06/29/surfside-condo-missing-family

 

[Astronuc]

Apparently, the garage under the Champlain Tower South building had a chronic flooding problem with seawater, especially with high tides, and presumably hurricanes.

https://www.msn.com/en-us/news/world/ex-maintenance-manager-for-surfside-condo-that-collapsed-recalls-saltwater-intrusion/ar-AALvrfH

William Espinosa, who oversaw maintenance of the Champlain Towers South condo building from 1995 to 2000, recalled the building's garage experiencing a concerning amount of seawater during high ocean tides.

"Any time that we had high tides away from the ordinary, any King Tide or anything like that, we would have a lot of saltwater come in through the bottom of the of the foundation," he told CBS 4 Miami, adding they had to use two large pumps to try and remove the rising water.

"But it was so much water, all the time, that the pumps never could keep up with it."

Furthermore, building managers discovered a large hole under the condo after the collapse that may have been caused by saltwater intrusion. Saltwater intrusion can be particularly corrosive to older concrete, as it attacks the pillars and foundation and can slowly erode concrete and cause damage to steel, CBS 4 Miami reported.

"The water would just basically sit there and then it would just seep downward," Espinosa told the news outlet. "It would just go away after a while. And I would think, where does that water go? Because it had to go in through somewhere. I'm talking about a foot, sometimes two feet of water in the bottom of the parking lot, the whole parking lot."

I don't understand the statement, "building managers discovered a large hole under the condo after the collapse". I would imagine that first responders discovered a large hole and reported it, but was that the garage, or there is actually a large void under the foundation/garage. The could imply flooding or saltwater intrusion, and based on the observations of the former maintenance manager, they should have investigated 20+ years ago. Did the flooding continue, and was it simply ignored?

 

[Twigg]

I'm starting to see a coherent story here. The poor drainage made this building a high maintenance property. It likely caused both the subsidence and the damage to the foundation that was seen in 2018. (The failure of the waterproofing sounds like it was an expected event after that much time.) Whoever was responsible repeatedly ignored these action items / costs, preferring stop-gap measures (like pumps) to actually fixing anything. "My other properties don't need all this maintenance, it'll be fine!"

How does the investigative team determine what caused the hole in the foundation? Anyone have experience with this kind of thing?

 

[Astronuc]

How does the investigative team determine what caused the hole in the foundation? Anyone have experience with this kind of thing?

The investigation will have to characterize (topographical mapping) the surface and subsurface. Besides taking core samples of the surrounding formation (i.e., that which did not collapse), they will have to take chemical samples around the void and into surrounding formation. There are also other methods, such as ground-penetrating radar (GPR), which could have been employed on the concrete columns, and a relatively new method, electrical resistivity tomography (ERT), or ground conductivity measurements. And one could use methods employed by mining and petroleum industries to investigate formations, e.g., well-logging techniques.

https://en.wikipedia.org/wiki/Electrical_resistivity_tomography
https://en.wikipedia.org/wiki/Well_logging

 

[artis]

Don't want to sound like a "wise guy" but judging from the pictures seems like the building had a structural system made from reinforced concrete cast on site which unlike reinforced concrete elements welded together on site is more structurally stable. A single reinforced concrete column can easily hold its own full height given weight plus the added weight of whatever is attached given it has lateral anchors or stability.
Normally when a building sinks it happens to either the full building or some portion of it.
Still I personally think sinking of few mm a year can't cause a collapse like this, unless it manages to single out many individual columns such that the cracks form around them and they are not laterally anchored anymore which is very unlikely.
What does seem more probable is that the structural elements like columns were weakened over time , also some lateral stability was lost but even this I believe could not case the collapse if not acted by some third force which I might speculate was a sinkhole or some ground fault.
Based on the CCTV video it seems like the collapse started from the middle of the building then went through to the other side and then one of the side which survived the initial collapse but was visibly tilted also went down.

As I said before even with cracks in the concrete rebar being still in place serves some lateral anchoring so I don't think concrete columns could just buckle under their own weight given they have the building structure still around them, also given concrete is best at compression so unless broken otherwise typically doesn't yield.So what I think happened was this. The cracks and rebar rusting over time created structural weakness, in itself not being enough to cause collapse, then some other factor caused a few of the columns in the middle of the building to collapse, this weight was still attached to the rest of the building by rebar so it created a pull force. This I believe is the reason why the portion of the building in the video collapsed a few seconds later than the first portion, you can see that it has visibly tilted.
I have heard that experts in controlled demolition often use this to take down buildings with less explosives. They break a crucial portion of the building and then they let the collapsing inertia to pull on the adjacent building via the rebar laid into the structure, or for steel structures the girders and trusses.
In this way one can blow out the middle of a tower for example and make that the outer portions fall inwards because of the pull and lost lateral stability.
If anything this Florida case seemed almost like a perfect controlled demolition case where the middle went straight down and the side fell inwards on top of the already collapsed middle portion.