News Florida Collapsed Condominium had been sinking since 1990s

[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?)

 

[artis]

That's right @Tom.G rust much like frozen water expands so in climate where there is also freezing this problem is twice as large because the rusted rebar opens up sub mm cracks and water then gets into them and freezes up and does an even better job at opening up concrete.

As for the rusted rebar well I would argue that in many projects the rebar arrives at site already brown colored , one would need to use stainless steel for rebar to avoid rusting completely or use some expensive painting of the rebar prior to insertion.

 

[Astronuc]

Sara Nir and her daughter Chani Nir, who escaped Champlain Towers moments before the condo collapsed last week, told CNN's John Berman on Tuesday night that they initially thought neighbors were doing construction.

Nir said she had just returned home to her two children around 12:30 a.m. ET when she started hearing “knocking sounds.”

As sounds became increasingly louder, Nir said she started to believe neighbors were doing “major construction,” and she went to speak to the building’s security guard about the early morning disturbance.

https://www.cnn.com/us/live-news/mi...e-06-30-21/h_b6d81cbe1f1752b2c1ec202b423e6320

I wonder if the knocking sounds were concrete cracking or rebar losing adhesion with the concrete or rebar fracturing.

I'm curious about the rebar still protruding/hanging from the standing structure. What can be learned?

If one column dropped or fractured, then its load would be transmitted to adjacent columns, and horizontal joints would likely fail. The rebar in the flooring and support beams would serve to pull adjacent columns from the vertical.

​

How can a building just collapse?​

https://www.cnn.com/2021/06/29/opin...-collapse-how-could-it-happen-kara/index.html

 

[Twigg]

There was some mention that there were roof repairs underway before the collapse. Do you think they might've tightened the PT rods as part of their maintenance? If the PT rods go all the way down to foundation, it might've been related. But OTOH I feel like when this scenario played out in the 2018 FIU pedestrian bridge collapse, the media immediately reported that workers had tensioned the PT rods shortly before collapse.

 

[Astronuc]

tightened the PT rods as part of their maintenance? If the PT rods go all the way down to foundation,

It's not clear that PT rebar was used, and certainly not in the vertical columns. I've only seen post-tension rebar in nuclear plant containment buildings, concrete pressure vessels and other special applications, long span structures, like the pedestrian bridge that collapsed.

Concerning PT tension systems -
https://www.structuraltechnologies.com/wp-content/uploads/2018/02/PT_Buildings.pdf
See - 3. Applications of Post-Tensioning in BuildingsAn interesting perspective on the 'horror of Surfside'.
https://slate.com/human-interest/2021/06/the-horror-of-the-surfside-building-collapse.html

 

[Astronuc]

Surfside building collapse latest: Death toll rises to 18 after 2 children found​

https://www.goodmorningamerica.com/...-collapse-latest-12-dead-149-missing-78574497

At least 18 people are dead and 145 others remain unaccounted for after a 12-story residential building partially collapsed in South Florida's Miami-Dade County last week, officials said.

The massive search and rescue operation marked its seventh day on Wednesday as crews continued to carefully comb through pancaked piles of debris in hopes of finding survivors. The partial collapse occurred around 1:15 a.m. local time Thursday at the Champlain Towers South condominium in the small, beachside town of Surfside, about 6 miles north of Miami Beach.

Edit/update:

Most of the board members of the Florida condo building that collapsed resigned in 2019 as debate raged over the cost of repairs, The Washington Post reported.

The board only voted in favour of the $15 million in repairs in April 2021, the Post reported, though dozens of residents had voiced complaints about how high that figure was.

https://www.msn.com/en-us/money/companies/most-of-the-collapsed-florida-condo-board-members-resigned-in-2019-amid-disputes-about-the-cost-of-repairs-that-never-went-ahead/ar-AALEYL8

Rescuers report hearing cracks in remaining structure​

The remaining structure was cleared by rescue crews last week, and all resources have since been shifted to focusing on the debris, according to Jadallah. Hundreds of first responders and volunteers have been working around the clock to locate any survivors or human remains in the wreckage. However, poor weather conditions and concerns about the stability of the still-standing building have periodically forced them to pause their efforts.

https://www.msn.com/en-us/news/us/surfside-building-collapse-latest-rescuers-hear-cracks-in-remaining-structure/ar-AALEihf

Figuring out what really happened in the Miami condo collapse could take more than a year, expert says​

https://www.insider.com/miami-condo-collapse-year-to-understand-expert-2021-6

 

[russ_watters]

Eyewitnesses (including one who died) reported a parking lot and pool deck collapsing before the building came down:

https://www.usatoday.com/in-depth/g...aused-building-to-fall-near-miami/7795023002/

 

[Vanadium 50]

I think there is an attempt to turn this into a morality play too soon.

The first attempt was to cast the rich, evil fat cats who owned the building as villains and the noble residents as heroes, or at least victims. The problem is, as pointed out upthread, that this is a condo, so our heroes and villains are the same people.

The second draft of the play could be titled "if only they had listened to the experts".

A few problems: one is that "the building is sinking" paper (which started this thread) does not suggest any urgent action, or even that this building is at particular risk, or even that this is the worst spot: it's #4 (or lower) in Miami Beach, and there are spots in Norfolk with 3x the rate.

A second is that the Morabito report did not say "this is an immediate safety hazard". It did say there was a "major error", but that was in regard to the pool and parking garage. Aha! You say - the pool and parking garage collapsed first and took the rest of the building with it! Thing is, the pool is still there:

Finally, the idea that the residents weren't repairing anything isn't true. They were in fact working on the roof at the time of collapse (which might or might not have had anything to do with it). At best one can say the residents were repairing things in the wrong order, but in our morality play that sounds like a pretty venial sin.

As an aside, I will believe an accident construction ahead of witness sequencing of events. One may notice Event A before Event B, but that does not mean Event A caused Event B, or even that Event A began before Event B.

 

[fresh_42]

The only issue with morality is in my opinion that I think everybody including the engineers underestimated the implications of ground, weather, water, and salt on the essential parts of the structure. Maybe herd effects added to the problem: "Wait until the neighbours take action and see how it goes. They must have the same issues." Sure, this is pure speculation but based on the knowledge of human behaviour.

That it is a beachside property and what that means could be addressed to the entire mankind. We tend to build cities in swamps (Mexico City, Berlin, New Orleans), at coastlines (NYC, HK), in deltas (Kolkata), deserts (Las Vegas), seismic active zones (Tokyo, San Francisco), etc. All those places are problematic.

 

[Vanadium 50]

swamps (Mexico City, Berlin, New Orleans),

Washington DC.

They can't all be Lincoln, Nebraska.

 

[russ_watters]

I think there is an attempt to turn this into a morality play too soon.

When something bad happens due to human factors, it is natural to try to assign blame, and speculate while learning. We're not the lawyers who filed the lawsuit the next day based on speculation here.

The second draft of the play could be titled "if only they had listened to the experts".

Yes we are seeing mixed messaging from the experts as well as some positive (if slow) motion from the powers that be.

While I do still see negligence, this does not appear as clear cut as the Pier 34 collapse, in which the owners basically opened the club after the engineer told them the collapse was in progress.

As an aside, I will believe an accident construction ahead of witness sequencing of events. One may notice Event A before Event B, but that does not mean Event A caused Event B, or even that Event A began before Event B.

Well...not to be too morbid, but some of these eyewitness accounts of the timeline basically have to be accurate because the collapse of the building was the last event they could witness. You can't witness the pool deck collapse after the building if you die when the building collapses. The one witness was literally on the phone with her husband, describing the scene until she died in the collapse.

On the positive side, watching part of the lower structure collapse before the tower led several people to evacuate and survive.

 

[russ_watters]

The only issue with morality is in my opinion that I think everybody including the engineers underestimated the implications of ground, weather, water, and salt on the essential parts of the structure. Maybe herd effects added to the problem: "Wait until the neighbours take action and see how it goes. They must have the same issues." Sure, this is pure speculation but based on the knowledge of human behaviour.

That it is a beachside property and what that means could be addressed to the entire mankind. We tend to build cities in swamps (Mexico City, Berlin, New Orleans), at coastlines (NYC, HK), in deltas (Kolkata), deserts (Las Vegas), seismic active zones (Tokyo, San Francisco), etc. All those places are problematic.

Sure, but building collapses like this are extraordinarily rare, at least in the West.

 

[Vanadium 50]

Well...not to be too morbid, but some of these eyewitness accounts basically have to be accurate because the collapse of the building was the last event they could witness.

My point is that what people report is not necessarily what happened. "Part A collapsed before Part B" is a statement of what happened "I saw Part A collapsing before I saw Part B" is a different statement. Things can happen out of view, and things can happen before they get your attention.

I may amend what I said - it looks like the pool deck remained in one piece, but has lost support on the side farthest from the building. Of course this makes it at least as hard to reconcile with "the pool took down the building" theory.

 

[Astronuc]

Structural failures are rare, but they do happen, and when they do engineers like myself want to know why. Afterall, we follow various strict design codes, e.g., ASME BPV code, which was established based on understanding failures in the distant past before such codes existed. Similarly, there are building codes that exist to ensure site characterization is appropriate, building design and materials are appropriate, construction methods are appropriate, and building maintenance (including periodic inspections) is appropriate, . . . . Maybe there are deficiency in one or more codes/regulations.

Residential buildings should not collapse, especially where there is not dramatic force like a tornado, hurricane or earthquake. If however, there is water, especially seawater, intrusion, or a ground is unstable, then that needs to be determined, and the matter addressed.

Something went majorly wrong under Chaplain Towers South. It could have been an initial design flaw/error, or materials, or environmental degradation, . . . . , or a combination. There were yellow/orange flags (alerts/warnings) and red flags (MC findings, and more recent observations), that went unheeded for too long, or otherwise, delays in addressing the problem because it cost too much.

We have to wait until the literally get to the bottom of the structure. If it si determined that a sinkhole developed, then we have to ask how and why, and also why such a structure was build on unstable ground. If seawater infiltrated the foundation, we need to know how and why, especially given the MC report indicating extensive damage that need immediate or near-term (months, not years) remediation. The MC report also flagged what appeared to be superficial damage to walls, concrete on balconies and exterior walls, but the more serious damage to the foundation (concrete cracking/spallation and rebar corrosion) was not addressed.

Daily News - The deadliest building collapses in U.S. history​

https://www.nydailynews.com/news/na...0210624-qb7erjrfnnctzfls2inqla22ye-story.html

July 17, 1981: The second- and fourth-story walkways inside the Hyatt Regency hotel in Kansas City, Mo., collapsed onto the lobby, killing 114 and injuring 200. Around 1,600 people were in the atrium of the building at the time for a Friday night dance party. The incident remains the deadliest non-deliberate structural failure in U.S. history and has become a common case study in engineering classes.

I remember the failure, and it was discussed in mechanical/civil engineering classes as a case study.

Some of the other, more recent, events I remember hearing about, including the pier collapse at a nightclub at Pier 34 in Philadelphia that Russ mentioned.

At CTS, perhaps more than 160 people were killed making it one of the worst building failures of its kind in recent history.

 

[Astronuc]

I may amend what I said - it looks like the pool deck remained in one piece, but has lost support on the side farthest from the building. Of course this makes it at least as hard to reconcile with "the pool took down the building" theory.

I don't believe failure of the pool deck would 'take down the building', but rather whatever caused that part of the structure to fail is probably related to whatever caused the building to fail. If there was a dramatic collapse, e.g., a sinkhole developing, under the structure, it might have been enough to undermine the pool deck/parking garage and the building foundation at the critical spot. The part that is still standing would seem to be on firmer (maybe drier, or less saturated) ground, and even the eastern most portion may have remained standing had the initial failure not pulled it off-balance.

Investigators will have to get down below the foundation to find out if subsidence or collapse of the geologic formation has occurred.

When I was at university, I took a part-time job working in the campus buildings and ground department. One of the jobs I did was service pumps, motors and generators, and I did this for one building that was built over spring! The building had a basement and sub-basement, and we had to make sure that the sump pump and backups worked, as well as the emergency generator worked, since if power was lost for too long, the sub-basement and possibly basement would flood and destroy all the equipment (hot water, air conditions, ventilation, . . . .) and offices in the basement area.

 

[artis]

See this demolition from CDI, also in Miami.
For those that don't want the whole deal start from 18:00
You will see there in action what I told here before , they detonated a single column on a structure that judging from the video seems like a on site cast reinforced concrete structure with vertical columns and floor slabs all being monolith.
And from what it seems the part where the column was cut isn't even at the top of the building where there would be much less gravity load on the column but rather at the lower part of it.
The building did not collapse afterwards , instead the vertical load of that column was distributed within the floor slabs that connect to it to adjacent columns.

I would argue that for a properly built reinforced concrete structure the loss of single column should not result in structural failure.Now in the Champlain towers case there were no explosives and no single column was detonated or cut, so I think that even more my argument holds , even a column in bad shape with rusted rebar etc, cannot lose it's vertical loading capability suddenly and abruptly and all at once.
The only way I see a column could lose it's loading capability completely and suddenly is if it lost ground beneath it.
Also I want to point out that the tower wasn't that big and I would argue that it's structure had the same level of wear throughout it with some part probably being worse and others better. Now if the tower itself , not the ground beneath it or other factors but if the tower itself was supposedly in such a critical condition then how would one explain the argument that half the structure survived the collapse of the other half?
For panel structures that would be easy because panels are welded together which is their weakest point and they usually separate at those points during a collapse. So in the many famous Russian gas explosions in panel concrete apartment structures one can see that only the portion above the weakened part collapses.

But the Champlain tower was a cast monolith reinforced concrete structure so each column was connected to every other one through the floor slabs. When half the building came down at that point the lateral pull on the other half through the rebar and floor slabs was probably immense not to mention the vibration from ground impact etc. Yet the structure is left standing and that seems like a clue to me that the structure itself was maybe not in such a critical condition and there could be other factors that led to it;s partial collapse.

Surely don't take any of this as truth I am just expressing a knowledge based guess here

 

[artis]

ps. as for the PT rebar discussion I think I saw drawings of the towers somewhere online recently at also from the live pictures it seems that all was regular rebar.
Also from what I know PT rebar is almost never used in vertical columns because columns are already under a compression type of load mostly. I think PT is more for longer lateral spans

 

[russ_watters]

Rest of the building likely to be demolished:
https://www.usatoday.com/story/news...resident-joe-biden-visit-surfside/7823596002/

 

[Vanadium 50]

Rest of the building likely to be demolished

I would have said "certain". How many years of studies would it take to convince you its safe?

 

[fresh_42]

Would be interested to know if there are insurances for complete structure failures.

 

[Astronuc]

Rest of the building likely to be demolished:
https://www.usatoday.com/story/news...resident-joe-biden-visit-surfside/7823596002/

From the article,

The National Institute of Standards and Technology established a National Construction Safety Team to investigate the building collapse, director James Olthoff said Wednesday evening in Miami.

Olthoff said it will be a "fact-finding, not a fault-finding technical investigation" that could take several years. It won't end until the team finds the "likely cause" of the collapse.

It'll be like the NTSB investigations of an airline crash or a bridge collapse.
https://www.ntsb.gov/investigations/AccidentReports/Pages/HWY18MH009-investigative-update2.aspx
https://www.ntsb.gov/investigations/AccidentReports/Pages/SPC2002.aspx
The main part of the investigation lasted more than 18 months, follow on actions took longer, and access to the accident site was relatively easy compared to the CTS collapse. CTS was 40 years old, while the pedestrian bridge was under construction.

 

[Twigg]

Rest of the building likely to be demolished:

If the lingering tower makes it through next week (tropical storm Elsa expected to make landfall early in the week)

 

[russ_watters]

I would have said "certain". How many years of studies would it take to convince you its safe?

Yeah, infinity. I'm not even sure I want anything to do with an adjacent property, much less the attached rest of the building.

The article's wording is a little off (so much of that...), but it implies an imminent demolition. Like, trying to demolish safely and without adding additional rubble on top of the recovery operation, within the next few weeks.

 

[russ_watters]

If the lingering tower makes it through next week (tropical storm Elsa expected to make landfall early in the week)

Yeah, so the article talks about expanding cracks on a day-to-day basis, but isn't specific about where they are. "expanding cracks" on that timescale equates to "collapse in progress". That's what preceded the Pier 34 collapse.

 

[Twigg]

Yeah, so the article talks about expanding cracks on a day-to-day basis, but isn't specific about where they are. "expanding cracks" on that timescale equates to "collapse in progress". That's what preceded the Pier 34 collapse.

Oh oops, disregard my comments

 

[Vanadium 50]

Would be interested to know if there are insurances for complete structure failures.

Yes, but whether the peril is covered or not depends on the cause. Fire, for example, is almost always covered. If the underlying cause was the "sinking" discussed in post #1, maybe not, because Earth motion is in the same category as earthquakes, which usually requires an addition to the policy (called a rider).

It is not impossible that the units destroyed in the initial collapse were not covered but rhe ones that will be destroyed in the upcoming demolition will be.

 

[russ_watters]

Oh oops, disregard my comments

Using my mentor supermediocrepowers for good, I read the post you deleted, and honestly it looked fine to me. Yeah, I don't know how easy it is going to be to bring down the rest of the building safely. If I were a structural engineer, I don't think I'd want to even be walking around in the rest of the building inspecting cracks that are growing as I look at them. And I definitely wouldn't feel good about climbing around on the rubble pile with a compromised structure looming over me.

 

[Astronuc]

Yeah, so the article talks about expanding cracks on a day-to-day basis, but isn't specific about where they are.

I noticed that as well, and that's annoying, since it's critical information. One cannot tell if it's columns of the failed section, or columns in the portion still standing. I read in a different article about cracking or noises from the northwest section, the part still standing but damage when the collapsed section pulled away. I notice floors on the exposed (eastern) face are sagging, so they have been compromised. The foundation or subsurface could be shifting, and I think it likely the structure would collapse onto the existing collapse pile.Edit/Update: Daily Mail, Miami condo collapse: Officials review work of suspended inspector
https://www.msn.com/en-us/news/us/miami-condo-collapse-officials-review-work-of-suspended-inspector/ar-AALFjEH

A Florida building inspector who assured residents of the collapsed tower that it was in good shape a month after being warned otherwise is having all of his previous work reviewed after being suspended from his new job.

Meanwhile, it has also been disclosed that the entire building department for the town of Surfside was under review at the time of the collapse.

Rosendo Prieto was chief building official of Surfside until November 2020. On Tuesday, he was placed on leave from his job as interim building official for C.A.P. Government Inc.

Now, city officials in Doral are planning on reviewing his previous work to make sure he didn't clear other buildings that may be dangerous.

 

[anorlunda]

With all this talk about sinking and salt water intrusion I see no mention of the tides. The former maintenance man mentioned "spring tides" and with tides we have currents. I don't mean swift water currents, but nonzero motion of water that can remove a small bit of material from the karst below the slabs with each tidal cycle. That makes analysis more difficult, and comparison with similar structures less relevant. Even the buildings across the street might have substantially different subsurface conditions.

It would be reasonable to expect all the other high rise buildings in the area to react with "an abundance of caution." A news report earlier this week said that a 6 story condo on the Miami River announced a $1 million per unit assessment to make repairs. Even rich people can find that $1 million here and another $1 million there starts adding up to big money. Couple that with beach erosion and alarmist predictions of sea level rise (my ridiculous neighbor believes 60 m rise this century instead of 60 cm) and what happens to the resale value of those condos? I expect that the owners may soon be financially underwater [inadvertent pun].

 

[Twigg]

I'm glad they're reviewing Prieto's other decisions. I hope for his sake that it was a case of not enough visible information for him to see the problem, and not gross negligence; however, given the 2018 reports that seems unlikely. Hope he remembers how to flip burgers.

It seems like rescue efforts have resumed according to NPR. Putting this all together, it seems that (1) there are expanding cracks somewhere in the structure, (2) either the cracks aren't in a critical location or the first responders are risking it anyways to try and find survivors before Elsa makes landfall, and (3) they are planning to take down the lingering building safely (?) assuming it doesn't collapse on its own in the next week or so.

Using my mentor supermediocrepowers for good, I read the post you deleted, and honestly it looked fine to me

Since my now-deleted comments seem relevant again, I'll repeat them here. Imagine you got the the job to demolish the remaining tower. Normally, you'd go to the city government office and grab the building plans, and spend a lot of time planning what features to manually cut and where to place explosives to bring down the building in a controlled manner. This time, the building is progressively collapsing, you don't know how much of the planned structure has failed, and you probably can't send anyone inside or underneath. You're also on an accelerated time table to bring the building down safely before it comes down whichever way it pleases. It will probably be wet, if the building survives the storm, and you still have all the usual hazards of working with explosives (imagine you push the detonator button and nothing happens. What do you do?). TL;DR version: YIKES!

The media seems to be repeatedly asking about the use of drones/robots for rescue work. I know no one has brought it up here, because I think the folks on this thread all know it's for the most part a ridiculous proposition. But since it's taken public interest, I just want to comment briefly. I'm under the impression that even the internet-famous dancing robots of Boston Dynamics don't have the agility to walk over a debris field, much less have the smarts to search for survivors (putting aside the not-killing-them during rescue aspect of things). I assume tread or wheel based machines don't stand a chance with this much physical obstruction. This doesn't even touch on the issue of on-the-spot problem solving capability that's necessary for unpredictable situations. What I can see being useful here are remote-controlled drones with IR cameras for looking for heat signatures (survivors, fires inside the debris pile, etc). Also drones with regular cameras for inspecting inaccessible parts of the remaining structure (even if it doesn't totally collapse from the ground up, it's just as bad if it starts raining cinderblocks from the top).

 

[artis]

@Twigg your assessment of media hype is well correct but I personally think that IR cameras are of little use here because I doubt a human body's heat signature can be captured if that body lies beneath several layers of reinforced concrete floor slabs. A building type like this when it collapses it doesn't turn into dust instead the vertical columns break and fall sideways while the large floor slabs just pancake one on top of the other they break apart but still they cover a large area much like sheets stacked on top one another.
I'd say regular cameras on long extensions work better here as they can be inserted into the maze of rubble.
As for the remaining structure my personal bet is that left as is it would collapse downwards just like the other part did and as most buildings do whether accidentally or in a controlled demolition the reason I think is because the vertical downforce due to gravity is much larger than any other lateral force that would sway the structure sideways , I mean you would need an extremely strong wind to blow a heavy 12 story concrete structure sideways but the weight of the building on the other hand is quite enough to make it fall vertically down even if the first weak spot or break happens asymmetrically.

In fact I think we all know of an infamous real life proof of this. Remember the 9/11 World Trade Center's south tower which got hit asymmetrically in one of it's corners where the most mechanical damage and heat load was located , when it started to collapse it's upper roughly 25 floors started to fall asymmetrically to one side , you can even see in the videos the whole upper part tilting visibly and strongly to one side at that point it even seemed it will topple over and fall on the adjacent buildings and streets but as it fell it rather soon "straightened" itself out and by the end of it the collapse was rather symmetrical and pretty much within the footprint of the building.
The reason I think is this, because for a heavy structure the downwards force due to gravity + inertia from movement (after collapse has initiated) is much much larger than any other lateral force like wind or asymmetrical breakage point within the structure.