Florida Collapsed Condominium had been sinking since 1990s

[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.

 

[gmax137]

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!"

My understanding is this was a condo. The "responsible" people are therefore the individual unit owners. The reported $9 million cost to repair split among the (reported) 160 units would be a $415 per month assessment, for 15 years (at 3%). That looks like a bargain, but only with the benefit of hindsight. In any condo association I've been involved with, such a proposal would meet very strong pushback with little chance of it being passed. Just human nature, IMO.

 

[artis]

What I want to add is this. I personally don't think the building was in a critically bad structural condition. Bad yes most likely but not to the point where it can just go down like it did.
Here are my reasons for thinking this. When i watch the video I see the middle portion collapse first and the side portion left still standing for a couple of seconds in a tilted position and collapses only then. The other half of the building still left standing. Think of the lateral pull force created by the collapsing middle portion on the rest of the structure. One side of it survived this force till now, the other side survived it for a few seconds. For this I think the reason is that one side was much thicker (the left standing one) while the other side was much thinner (the one that stood up for a few seconds) The side that survived a few seconds based on the video was a thin outer portion which probably had no more than around 10 columns most likely in two rows.
Given such a structural arrangement and being pulled by a collapsing neighboring section I'd say it did rather well. If it was "that weak" it would have went smoothly down along the middle and you would not see a difference instead a smooth continual domino like collapse.
Also please see this video. (the action is more towards the end)


This building was "enjoying" a winter/summer climate left abandoned for some 25 years. At the moment of demolition it's total age was close to 40. It was a Soviet sanatorium built in the early 80's.
It has a very interesting reinforced concrete pillar/column type base that extends up to around the 3rd floor. On those columns sits the whole upper structure. Beneath them was built a smaller 2 story building.
https://www.google.com/search?q=sanatorija+liva&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiQqKf27LrxAhWqlYsKHX9-A9AQ_AUoAXoECAEQAw&biw=1366&bih=615

Now what I want to illustrate with this is that even after all the columns of this building were half cut to weaken them, not to mention they were out in the open rain and frost for decades , then even after breaking half of them just the structure directly beneath fell down while the rest was left standing. This structure was also assembled from reinforced concrete panels welded together, instead of floor slabs and columns cast as a monolith on site as the Florida building.
I highly doubt the Florida building was in a worse shape than this abandoned sanatorium.
Both were roughly the same size and height. It takes an awful lot of rusting and cracking where that alone can cause a collapse like this, in a reinforced concrete monolith structure.

In the FL case, since the structure seems like a monolith cast reinforced concrete , I'd say that in order to initiate a collapse multiple adjacent columns would need to completely lose vertical loading capability, one is not enough since if only one loses such capability it then "hangs" in the floor slabs connecting it to the adjacent columns. Surely it might be the case that the adjacent columns or floor slabs were so weak that having to bear the load of just one additional column was enough but again I doubt that. My bet is on multiple columns.
What can cause that is an open question in this case.

 

[Astronuc]

From the Miami Herald - https://www.miamiherald.com/news/state/florida/article252340108.html

Could it have been a sinkhole?​

Miami-Dade County Mayor Daniella Levine Cava told reporters Friday morning that there was no confirmed sinkhole beneath the condo building that crumbled.

But the sudden, unexpected nature of the building’s collapse left officials and experts wondering about the possibility.

Jason Borden, the Florida regional director at O&S Associates — which bid unsuccessfully last year to perform the 40-year inspection at Champlain South — said he did an hour-long site visit in January 2020 and “didn’t see anything alarming or out of the ordinary.” The property manager believed the roof should be repaired or replaced, Borden said, and there were some cracks in the ceiling of the parking garage below street-level, as well as in the stucco that coated the building’s concrete walls.

But he didn’t see anything that seemed to put the entire structure at risk.

“My suspicion is that there was something going on there that was not detectable,” Borden said. If a sinkhole were to open up beneath a building, he said, “you don’t know it’s going to happen until it happens.”

Borden said reviews of the underground structural integrity of buildings, including during the 40-year recertification process, are rare, in part because going underground is a “very pricey, very complicated” process. The bulk of a 40-year inspection is visual, he said, and excavations would likely only be done if there were visible evidence of shifting or movement in the foundation.

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

The 2018 report about cracked concrete and damage to the entrance/exit ramp from the lower portion of the garage gave 'red flags'. I don't think folks looked, for whatever reason. I have seen such behavior in the nuclear and aerospace industries, where folks don't look because they might find a problem, which will require costly remedial action. And sometimes, the result is catastrophic failure including loss of life in some cases.

Salzhauer said one resident of Champlain South told her that, while construction was being done over the past few years on the building next door — 8701 Collins Ave., known as Eighty Seven Park — the Champlain structure was “shaking” and there were “cracks” in the building as a result.

“The tenants in South were complaining a lot because their building was shaking and vibrating when they were digging and blasting at the construction site,” Arbide said.

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

It's a very good article looking at various aspects.

This building was "enjoying" a winter/summer climate left abandoned for some 25 years. At the moment of demolition it's total age was close to 40. It was a Soviet sanatorium built in the early 80's.

How close to the ocean or seawater? The Champlain tower is probably about 100 m from the ocean, and a former manager of maintenance indicated periodic flooding by seawater! Investigators will have to look to see if a void opened up under the building, or if the columns simply crumbled due to saltwater corrosion (chemical attack).

In the process industry, there have been stress corrosion cracking of stainless steel piping and vessels due to chlorine attack over 2 or more decades (I remember 25 years in one case), and there are similar failures due to polythionic acids or hydrogen sulfide, or a combination of these elements and compounds. Usually, the higher the temperature the shorter time to failure, depending on the stress level.

I personally have experience with degraded cement/concrete in the foundation of my house where persistent pooling of water due to failed gutters (previous owner failed to maintain) had caused cement and cinder blocks to disintegrate. The inside (basement) surface, which was painted and covered in gypsum board, showed minimal damage until I removed the gypsum board and found rotten wood. The cinder blocks looked intact, but mortar was cracked and powdery in some cases. It wasn't until I dug out the outside of the foundation that I found 2 and 3 courses of cinder block (concrete masonary unit) had disintegrated. I could pull the block apart with my hands. I replaced the damaged blocks, and properly sealed the foundation.

I subsequently found that the floor of the basement had been poured without rebar and improperly made concrete. Parts of the concrete were more sand than cement. In some cases, with pooling water, the cement may have dissolved leaving just the sand. It didn't take much effort to chisel into the floor, and in some cases, I could drag a cold chisel across the floor and scrape a channel into the cement/concrete. I eventually had to chisel out the crack and refill with proper concrete mix. Eventually, hired a company to place a trench drainage system to prevent flooding in the basement. So far, so good.

 

[Astronuc]

Surfside official was sent disturbing report. He told board condo was ‘in good shape’
Read more here: https://www.miamiherald.com/news/local/community/miami-dade/miami-beach/article252394393.html

A month after an engineer’s report flagged “major structural damage” at Champlain Towers South, the chief building official for the town of Surfside told residents the condominium was “in very good shape,” according to minutes from a November 2018 board meeting obtained by the Miami Herald.

Ross Prieto, who left the post last year, had reviewed the engineer’s report, the minutes say. Records show condo board member Mara Chouela forwarded a copy to him two days earlier.

But this past Saturday, Prieto told the Herald he didn’t remember getting the report.“I don’t know anything about it,” he said. “That’s 2018.”

Asked Sunday about the November 2018 board meeting, Prieto declined to comment, citing the advice of an attorney.

That was after details of the November 2018 meeting minutes were first reported Sunday by NPR.

The owners, or perhaps the board, should have asked for Frank Morabito of Morabito Consultants to provide a statement. Unless they were engineers, and particularly structural engineers, I imagine none of the board members understood the dire situation of the condo. It was not 'in good shape'!

 

[Astronuc]

Another "red flag" a day or two before the collapse?

From Miami Herald via Yahoo - https://news.yahoo.com/two-days-condo-collapse-pool-202849974.html

There was nothing unusual about the lobby and pool area at Champlain Towers South condo, which looked clean and well maintained to a commercial pool contractor who visited the building last Tuesday, just 36 hours before half of the building unexpectedly collapsed. Then, he saw the basement-level garage.

One has to wonder, if someone saw something alarming, then what is the responsibility to report it? Maybe it wasn't in his workscope, but geez . . . It seems the building has been deteriorating in front of everyone who went through the garage, but somehow no one thought to raise the alarm.

Mohammad Ehsani, an engineer and concrete restoration expert who invented QuakeWrap technology, a way to reinforce old concrete columns, reviewed the contractor’s photos from the pool equipment room.

“You can see extensive corrosion of the rebars at the bottom of the beam. That is very serious,” Ehsani said, commenting it was the worst damage he had seen documented in the building so far. The equipment room runs along the southern wall of the building — an area that did not collapse.

“If the condition of the beam in the pool guy’s photo is something that was also happening under the building, that is a really major concern,” Ehsani said. In that case, it “absolutely” could have contributed to the collapse.

However, he cautioned against rushing to conclude that all beams in the building showed similar levels of damage to those exposed to chemicals from the pool. The 2018 report that documented “severe” structural damage to concrete in the garage under the pool deck did not include photos of anything nearly as alarming as what the pool contractor documented, Ehsani said.

It seems that the corrosion observed recently was perhaps worse than three years ago. If that area was affected, then what other areas (columns) were affected?

 

[Tom.G]

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

https://www.google.com/search?&q=wastewater+plant+near:surfside,+fl

 

[Tom.G]

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.

Having been peripherally involved in the construction industry in the past, I decided to read the Engineering Report.

To me it read as 'This building is falling apart, you better fix it!'

Obviously he was right.

 

[artis]

@Astronuc the old Soviet sanatorium I was referring to was actually built in a local once famous small city which is basically located in the midst of a swamp. The area is very good for people's health having mineral water springs and lots of natural remedies that were used for health and disease treatment and rehabilitation.

But as for a reinforced concrete structure it is a bad environment , the sea was some 8 miles from the building so maybe the salt levels were not that high but the moisture from the surrounding swampy forests was all year round. I remember that once the building got abandoned after the dissolution of the USSR I went there to climb it as a kid because it was high and had a nice view. I mean it was sometimes so wet in there that you could see stalactite structures emerging from concrete walls not to mention the fact that whenever it rained i could see rivers of water flowing down from the upper floors through shafts and even through seems in the panels that formed the floor slabs.

Not to mention one other factor which is of big importance. Florida never has temperatures below zero or freezing from what I think. This sanatorium in my country is in a climate where we have hot summers and cold winters, so each year all that water froze up and you could see that it performed like a small explosive because as we all know here on PF water expands when freezing so if it's within a concrete column or panel or a brick it expands with great force and just tears the thing in half and makes cracks.

All of this happened for around 25 years year round.
See the links for pictures to see the base columns I am talking about
https://www.praeitieszvalgas.lt/sanatorija-liva-kemeri-latvija/
https://mapio.net/pic/p-9121735/When they took this thing down some 5 years ago they came up with a cheap and clever method because of the base columns were exposed they used a thick chain and two excavators to see-saw each column but before they could do that they needed to take about half the column out manually to ease the burden and time needed. A dangerous job as the guy in the cabin of the demolition excavator had to be very near the column as he was doing it.

Still after all columns were half cut and then they started to cut them one by one and yet still each time only the portion of the building fell that was directly above the completely cut columns. The rest stayed up.

Now it might be that the Soviets had used more concrete and rebar than necessary for this building as for many others because they had a planned economy and the builders did not care for the cost of material. The columns of that sanatorium were massive for it's 12 stories of height, from pictures it seems about twice the size of the Fl building ones , I remember it took about 3-4 people to join hands to completely surround a single column.
Still given what I described here I would doubt the Florida building being in a worse shape overall than this example.

 

[artis]

Now since we are talking about rusting rebar and salt effects on the structural integrity of reinforced concrete structures I want to show an interesting example.
I live in a country with winters and long autumns and springs so we have had all kinds of weather from -30 celsius in which no one can start a diesel to +35 in summer when asphalt becomes rubber like.
In winters we use a salt-sand mix for road safety so it's also sprayed on bridges where it mixes with water and seeps through every smallest crack and seem possible.
As you can imagine this is a nightmare for the bridges structural integrity, not only is it fully open to year round weather conditions without any heating (unlike a building) it has to endure concentrated salt-water mix being poured on it for months at a time.
Here we had a local bridge that is being renovated now after some 50 years of use without any major renovation. The reason they shut the bridge down because they realized that the concrete columns and particularly the rebar within them was so rusted that the concrete was becoming split open.
See the pictures to understand the condition better

https://www.lsm.lv/galerijas/31010/augusta-deglava-parvads-riga/?idx=6
See the link for additional pictures that might make you scared.

But given the extensive structural damage this bridge had and it's 50+ year history without any repairs it still did not collapse even though it had semi truck and bus traffic over it constantly.
There are many structures in similar climatic conditions like this in a shape even worse than this and a collapse is very rare for any of them.

As we know normally in the developed parts of the world whenever something is built it has some safety reserves put into it , rusting rebar is typically not enough and should not be enough to cause a complete structural collapse of a building/structure.As for the FL building , the floor slabs seem rather thin from the pictures , i'd say thinner than what I normally have seen in objects around here but then again it's a cast structure and an apartment blocks so the floor slabs are not meant to carry heavy loads and are probably enough for what they were made for.

Still I hold on to my own bet here that a collapse like this can only occur if multiple adjacent or otherwise structurally connected columns fail at the same time but for that to happen simply from rusting and degrading over time seems highly unlikely. I mean it surely impacted the structural integrity but not necessarily was the sole cause of the collapse.

If the rumors that residents heard cracking and popping sounds hours before the collapse are true then that would indicate that a major structural failure had happened hours before and overstressed the additional load bearing members or that a cause currently unknown was causing the whole structure or a large part of it to be overstressed beyond it's design limits. One such cause could be a sudden shift in the ground beneath part of the building whereby a number of columns lose their anchoring and are left hanging in their respective floor slabs dragging them to exert load beyond design limit to additional columns and slabs.

I remember a local case in my country where a big store collapsed. The store had a typical hangar like building with metal roof trusses atop which concrete panels were put. They wanted to create a garden on the roof so they put soil there but they somehow forgot to account for the additional weight of the soil during rain. So rain came and the soil got wet at one point in the day of the collapse residents heard cracking sounds and fire alarms went off (because of the pressure in fire water pipes was decreasing because the pipes were bending together with the roof)
The result was a sudden and abrupt roof collapse and 54 people killed.

The lesson here is simple. Even a intact structure without degradation can suddenly collapse due to large overpressure or exceeding of design parameters.
My bet is that structural deficiency is not enough to cause the FL building to collapse, it needed an additional catalyst to start the "reaction"

 

[Twigg]

If that reflects the average level of competence or diligence of local contractors, I wonder how many other buildings in Miami Beach are 'in good shape.' I highly doubt Champlain is the only building around with botched drainage or flooding problems.

 

[Astronuc]

If that reflects the average level of competence or diligence of local contractors, I wonder how many other buildings in Miami Beach are 'in good shape.' I highly doubt Champlain is the only building around with botched drainage or flooding problems.

Clearly there are a number of issues related to the abrupt and catastrophic failure of Champlain Towers South. Firstly, there is the site characteristics of ground on which it sits. Were the site characteristics properly determined? Then there is the design and contruction, including choice of materials. Was the design appropriate? Were the materials and contruction methods appropriate? Afterall, this is basically marine construction and one has to take into account exposure to the salt spray and occasional flooding from the ocean.

https://www.msn.com/en-us/news/us/this-is-a-moment-like-katrina-and-like-andrew-surfside-condo-collapse-raises-questions-beyond-south-florida/ar-AALyWb5

I have to wonder if the CTS would have been recertified. Imagine if it had been recertified and then collapsed. I'm wondering what happened during the last 2 to 3 years after the October 2018 report about concrete and rebar corrosion.

About the lack of drainage in the pool area and nearby 'flat slab', where water would stand until evaporated. Given the proximity to the ocean, the rain water probably has elevated levels of sea salt, and when that rain water evaporates, it leaves behind a concentrated salt residue. The next time it rains, some of that water runs off somewhere, but otherwise the salts continue to accumulated. This is the problem in the northern US from Minnesota through the Great Lakes region up into New England (Maine) where transportation departments spread salt on roadways. The salt eventually accumulates on roads and bridges/overpasses, and the asphalt and concrete deteriorate over time. I suspect that is what happened in the basement of the CTS, possibly in conjunction with a collapse of the ground underneath. However, we have to wait until the debris is removed and investigators can look into the buildings foundation and subsurface. Clearly, there is a potential for all high-rise building along the Atlantic and Gulf Coasts to be affected.

I read a comment yesterday that bascially indicated that flooding of the garage was a monthly routine! For 40 years?!
https://www.msn.com/en-us/money/realestate/collapsed-condos-ex-maintenance-manager-says-it-flooded-monthly/ar-AALyHcv

Edit/Update - https://www.insider.com/florida-con...ning-conditions-months-before-collapse-2021-6

The president of the association for the collapsed Florida condo warned months before the fatal disaster that conditions in the building's basement garage were worsening.

In an April 9 letter obtained by USA Today, Jean Wodnicki, president of the Champlain Towers South Condominium Association, said the damage had "gotten significantly worse" since an inspection around two and a half years before.

She also said that existing deterioration of the building's concrete was "accelerating" and detailed major repairs that were needed, USA Today reported.

She said that "the observable damage such as in the garage has gotten significantly worse."

Seriously?!

 

[Twigg]

How are people parking in a garage that gets 1-2ft of seawater once a month? I thought we got bad salt damage in the northeast...

 

[fresh_42]

How are people parking in a garage that gets 1-2ft of seawater once a month? I thought we got bad salt damage in the northeast...

I was very surprised, too, when I saw a former janitor (or so) on tv last night. He said that he saw cars swimming around in the garage and that the two pumps they installed weren't able to deal with the problem because it was too much water. You do not need to be an engineer to know that seawater within a concrete structure is a bad idea. There will be multiple reasons in the end, as it is always the case in major accidents, but I still think that rusty rebars plus the refusal to address this problem because it is an expensive, long-lasting, dirty, and very loud construction process were the main reasons.

 

[Astronuc]

How are people parking in a garage that gets 1-2ft of seawater once a month? I thought we got bad salt damage in the northeast...

I don't think it was 1-2 feet. The articles have not been specific, only that flooding occurred monthly. It could be a few inches to just puddles, but basically, it was chronically wet in a marine environment, and there was evidence of spalled concrete. It doesn't get better with time, rather it only gets worse.

It seems like some folks knew it was getting bad, but didn't understand how bad, and they didn't call an expert into ask questions. Maybe in future, people will be more proactive, but it's too late for the 11 confirmed dead and 150 missing or unaccounted for.

I keep thinking of a statement of an NTSB investigator (or maybe FAA), who said with every plane crash, we learn something and flying becomes safer. I'd prefer the learning in order to prevent plane crashes.

 

[gmax137]

Well, looks like I was wrong, the condo assoc did in fact impose an assessment to pay for the repairs

https://www.cnn.com/2021/06/28/us/surfside-condo-owners-assessments-invs/index.html

The Champlain Towers South condo association approved a $15 million assessment in April to complete repairs required under the county's 40-year recertification process, according to documents obtained by CNN.
The documents show that more than two years had passed after association members received a report about "major structural damage" in the building before they started the assessment process to pay for necessary repairs...

Owners would have to pay assessments ranging from $80,190 for one-bedroom units to $336,135 for the owner of the building's four-bedroom penthouse, a document sent to the building's residents said. The deadline to pay upfront or choose paying a monthly fee lasting 15 years was July 1...

The big assessment bill came as an unwelcome surprise to some owners of the building's 136 units.
"We struggled with it and everything," said Isabel Aguero, who owns an 11th-floor condo in the part of the building that stayed standing. ...

Aguero and her husband decided to go with the monthly payment, and sent in the paperwork on June 23 so the association would start adding $593 to their homeowner fees, they said. Early the next morning, the building collapsed...

 

[Twigg]

@Astronuc

'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.'

This from the retired maintenance manager's interview (https://www.msn.com/en-us/money/realestate/collapsed-condos-ex-maintenance-manager-says-it-flooded-monthly/ar-AALyHcv).

He could be exaggerating I suppose
On second thought, they must've had at least 6 inches if they were running pumps. It wouldn't make sense if there wasn't enough water to submerge the pump.

 

[Twigg]

I don't know anything about the socioeconomics of this area. How much money is $593/mo to these folks? Was it a life-changing amount?

 

[artis]

Well not sure how many of you read through my long previous posts but i would be cautious to blame the age and rebar rusting as the main cause. If a building is built with reserve in mind and according to code given the code itself is good and sufficient (which I hope US codes are) then overall rebar rusting should not cause a weakening sufficient to cause a collapse. It's an apartment building after all and even if it sits next to the ocean I still don't think it has went through anywhere near the salt and moisture and overall weather conditions an average reinforced concrete bridge deck goes through in a mixed climate.
I have been under bridge decks and columns on which full truck trailers with 40 tons of weight go over and the rebar is completely visible everywhere because the concrete outer part has completely fallen off , the rebar has lost on average about 1/3 it's diameter to rust etc. And yet these structures hold and don't just go down.

I saw a bunch of pictures where the pool repair guy claimed he saw the rusted rebar and I though to myself if this is/was the worst damage there was then well someone should drill and check the average concrete quality within those collapsed bits and pieces as well as the rebar itself.

Again I'm not an expert but it's a simple fact that concrete is exceptional in compression where it performs best. So rebar and it's condition is much more important in horizontal overlays like floor slabs , floor panels etc where concrete performs much worse and metal works best, on vertical compression type loads like columns where almost all the load is vertical and downwards concrete performs best.
Now I'm going to guess here so don't take my word for it but from what I have seen in real life with the building demolition that i saw , you can cut a reinforced concrete column down to half it;'s size (given it was originally good and to specification ) and it will still hold up the very weight it was supposed to.
The sanatorium in my previous posts , it's columns were cut to half size and even then they needed to cut them fully to initiate a collapse.
A bunch of rusted rebar in vertical columns (if they are made properly and thick enough) cannot cause a well made structure to collapse.
Keep in mind when i say rusted I am not talking about some extreme case where the whole rebar is just dust and no metal is left , I'm talking about your average case.

 

[russ_watters]

Again I'm not an expert but it's a simple fact that concrete is exceptional in compression where it performs best. So rebar and it's condition is much more important in horizontal overlays like floor slabs , floor panels etc where concrete performs much worse and metal works best, on vertical compression type loads like columns where almost all the load is vertical and downwards concrete performs best.

Vertical columns need rebar too, or they wouldn't have it. Vertical columns are indeed in tension tangentially.

 

[Tom.G]

The problem with re-bar rusting in concrete is that the rust has 13 times the volume of the original steel. That is why you see the concrete spalling off of reinforced concrete.

If I recall correctly, in a marine environment there is a chloride reaction between the concrete and the salt that then permeates the concrete. Eventually the chloride reaches the re-bar -- that's when the spalling starts. There are additives available for the concrete that inhibits this chloride reaction.

I ran across this about 15 years ago when a few steps on an outdoor stairway failed by breaking in two. The stair construction was I-beams run at an angle between two floors with precast reinforced concrete steps strung between them. Three years later those replacement steps, plus an original one, failed the same way.

It was an apartment building about 5 blocks from the Pacific Ocean. I was renting there so wasn't really upset about it, but was curious enough to research it. Those two replacement steps that lasted only a few years were low-cost imports that apparently didn't have the Chloride inhibitor added. The building owner (or contractor) learned their lesson, and the new steps were doing well after 6 years.

Cheers,
Tom

Rather irrelevant addendum:
That same 16-apartment, two-story, building sits on a concrete slab spanning underground parking. The slab has a crack running full length front-to-back, under the living room and bedroom of one apartment. A few years ago a chunk of concrete roughly 3 times the size of your head fell off the slab into the garage, exposing some rusty re-bar. Once a year, the second-generation owner, living out of state, arrives driving a Rolls Royce Silver Cloud to check up on his properties and the management company.
(Isn't free enterprise great?)