News Florida Collapsed Condominium had been sinking since 1990s

[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.