News Florida Collapsed Condominium had been sinking since 1990s

[Astronuc]

Cassie Stratton was on the phone with her out-of-town husband, looking down from her fourth-floor balcony in horror as part of the pool deck below apparently vanished into a sink hole.

She "told him that the pool was collapsing, that the ground was shaking and cracking," Stratton's sister, Ashley Dean, told CNN's John Berman. "It's my understanding that she let out a very loud scream and the phone went dead."

https://www.cnn.com/2021/07/03/us/surfside-condo-collapse-questions-unanswered-invs/index.html

from what is known to date, the tower's cave-in resembles less a cataclysmic event than a slow-motion catastrophe, made possible by years of missed warnings, mixed messaging and delayed action, according to public records, including emails and inspection reports, as well as experts who have spoken with CNN.

The true toll of the collapse, of course, remains buried in the rubble. Authorities have confirmed at least 22 deaths, along with 126 unaccounted for.

In recent years selling prices in the building have remained high. A week before the disaster, a three-bedroom condo there sold for $710,000, according to realty company Redfin. The price of most condos ranged from $295,000 (for a one-bedroom in March 2020) to $980,000 (for a three-bedroom a year later), real estate records indicate.

Morabito Consultants, the engineering firm hired to conduct the review, noted "abundant cracking and spalling" in concrete columns, beams and walls, "exposed, deteriorating rebar" and failing waterproofing beneath the pool deck and entrance that was causing "major structural damage."

Also, a photo taken that year by a mechanical engineering firm shows a crack around the edge of a beam running along the top of the room. Engineers and experts consulted by CNN said it appears the same crack is visible in a photograph of the pool equipment room taken just days before the collapse -- only the latter photo, first published by the Miami Herald, shows the crack in much worse condition.

Mounting repairs and sticker shock: 'This is where we are now'

About a month after the report was released by Morabito, a condo association member, Mara Chouela, forwarded a copy of it to Surfside's building official, Rosendo Prieto. Prieto came to the board's regular meeting a couple days later and shared his professional opinion, saying the building appears to be "in very good shape," according to minutes of the meeting.

 

[anorlunda]

There is more to question than just the engineering. If building management is the responsibility of the condo associations, and the boards of those associations are staffed by residents, then most will be amateur. Worse, board members are not only inexperienced, they are conflicted.

Perhaps building codes for multifamily dwellings need to be expanded to cover not only design and construction, but also ongoing management and finance.

 

[Twigg]

@Astronuc, knowing (assuming it's true) that Prieto saw the report ahead of time, I take back my previous statement. No one should trust this guy with flipping burgers even.

I'm sure you all saw, another condo building, Crestview Towers, was evacuated after the emergency review process on buildings older than 40 years showed structural damage that had been reported back in January 'of this year (haven't seen any media outlet elaborate on what variety of damage it was). At least some good may be coming out of all this.

 

[Vanadium 50]

Perhaps building codes for multifamily dwellings need to be expanded to cover not only design and construction, but also ongoing management and finance.

Why just multifamily?

 

[anorlunda]

Why just multifamily?

Fair question. Modern life is full of arbitrary distinctions like that. You need a license to drive a car, but not a bicycle.

 

[Astronuc]

@Astronuc, knowing (assuming it's true) that Prieto saw the report ahead of time, I take back my previous statement. No one should trust this guy with flipping burgers even.

I posted about the article that indicated that Prieto has been put on leave from his current job and all of his work is now being investigated.

Rosendo (Ross) Prieto has recently claimed he did not 'see' the report (hard to believe), but then went to a board meeting and told that the building was in 'very good condition'. If he had not seen the report, then he gave an uninformed, unsubstantiated opinion (that by itself would be gross negligence). On the other hand, there is evidence Prieto did review the report and discussed it with condo board members, and still told the condo folks that the building was in "very good condition". Again, that is "gross negligence" bordering on criminal negligence.

"Surfside records also show that a condo board member sent the report to Prieto before the 2018 meeting and the two met in his office to discuss the matter, according to the article," and he was subsequently invited to the condo board meeting." After the meeting at Prieto's office, a board member wrote, “Thank you so much for having us in your office. We appreciate your time a lot. We would like to invite you to our board meeting on [Thursday, Nov. 15, 2018] at 7:30 to explain the facts of the 40-year inspection,” Mara Chouela reportedly wrote. "

https://nypost.com/2021/06/29/ex-surfside-boss-on-leave-at-new-job-after-damning-report/

A review of the minutes of a condo association meeting by the newspaper found that Prieto told the board he had indeed reviewed the troubling report by engineer Frank Morabito.

WT*?!

 

[Twigg]

Yeah, I'm starting to think Mr Prieto would look reaaaaally good in orange.

 

[fresh_42]

Why just multifamily?

The number of floor levels is probably the better distinction.

However, people know for decades if not longer that Istanbul is built on shaky ground. They do have adequate directions for any buildings. Nevertheless, people did not stop building houses illegally and wildly.

I have to say more about the comparison, and why it is not completely off, but that will lead me on political ground, so I make only one comment about 'lessons learned': Did anybody else than I followed the current political debate about modernizing the country-wide infrastructure? I think the best that can be achieved are regulations for Miami and maybe some other cities will follow the example.

 

[Twigg]

knowing (assuming it's true) that Prieto saw the report ahead of time,

@Astronuc sorry, the "assuming it's true" wasn't aimed at you. I was just acknowledging the fact (I thought) that we only had Mara Chouela's claim that Ross Prieto had seen the report. Now that I see there is an email record that can be subpoena'd, it's a very different story.

 

[Astronuc]

@Astronuc sorry, the "assuming it's true" wasn't aimed at you. I was just acknowledging the fact (I thought) that we only had Mara Chouela's claim that Ross Prieto had seen the report. Now that I see there is an email record that can be subpoena'd, it's a very different story.

I didn't take it personally. Like you, I can only go by what is reported, which may or may not be valid, or perhaps, part of the story. As time goes by, more evidence becomes revealed, and it seems to be piling up with respect to Prieto's negligence, which is still only part of the story.

The investigation will have to look into the site characteristics (did a sinkhole open up, i.e., was the supporting ground unstable and why), the design (was the design appropriate), the construction (was the construction methods and materials appropriate), the maintenance (it appears the maintenance was deficient), the inspection process (seems to have been appropriate), the government oversight (clearly (in hindsight) there are those that feel the oversight was lacking).

 

[Lnewqban]

I posted about the article that indicated that Prieto has been put on leave from his current job and all of his work is now being investigated.

Rosendo (Ross) Prieto has recently claimed he did not 'see' the report (hard to believe), but then went to a board meeting and told that the building was in 'very good condition'. If he had not seen the report, then he gave an uninformed, unsubstantiated opinion (that by itself would be gross negligence). On the other hand, there is evidence Prieto did review the report and discussed it with condo board members, and still told the condo folks that the building was in "very good condition". Again, that is "gross negligence" bordering on criminal negligence.

"Surfside records also show that a condo board member sent the report to Prieto before the 2018 meeting and the two met in his office to discuss the matter, according to the article," and he was subsequently invited to the condo board meeting." After the meeting at Prieto's office, a board member wrote, “Thank you so much for having us in your office. We appreciate your time a lot. We would like to invite you to our board meeting on [Thursday, Nov. 15, 2018] at 7:30 to explain the facts of the 40-year inspection,” Mara Chouela reportedly wrote. "

https://nypost.com/2021/06/29/ex-surfside-boss-on-leave-at-new-job-after-damning-report/

WT*?!

After having worked with several Building Departments in South Florida, I wouldn't pay any attention to the technical opinion of any Building Official.
Even with the purest original intentions of protecting the public at the time of taking the job, most of these experienced Building Inspectors become political subjects within a jurisdiction administration power drama.

Their main priority becomes the pleasing of rich influencial citizens, as well as of town/city administrators who could terminate their employment.
If that means bending the Building Code a little and overlooking some violations, so be it.

Personally, I have not met one that could run a structural calculation or an accurate assesment.
Clearly and sadly, this condo association did not think the same way that I do, reason for which they seeked and trusted the opinion of Mr. Prieto.

Copied from
https://en.m.wikipedia.org/wiki/Building_officials

"Building officials of developed countries are generally the jurisdictional administrator of building and construction codes, engineering calculation supervision, permits, facilities management, and accepted construction procedures."

 

[russ_watters]

Why just multifamily?

Shared risks/responsibilities and conflicting interests are hard to manage.

 

[russ_watters]

Looks like the rest of the building is going to be demolished tomorrow:
https://www.usatoday.com/story/news...emolition-planned-within-36-hours/7851388002/

 

[Astronuc]

Looks like the rest of the building is going to be demolished tomorrow:
https://www.usatoday.com/story/news...emolition-planned-within-36-hours/7851388002/

I wonder if they will give the residents time to collect some of their irreplaceable valuables. Or do they consider it too dangerous.

 

[russ_watters]

I wonder if they will give the residents time to collect some of their irreplaceable valuables. Or do they consider it too dangerous.

Sounds like no, in the article.

 

[artis]

@Astronuc I think those who got out already collected their most irreplaceable valuable namely their own life. Going back one more time would risk loosing that single most precious valuable.

 

[artis]

This is a rather nicely made video echoing my own viewpoint , One thing I've noticed from both this video and other pictures is that for a rather large structure like this a 12 story building the main columns seem rather thin , also in the video he talks about the seemingly different thickness of columns where the ones that were located in the part that was left standing are much thicker.
Not saying this is the cause of anything but interesting nevertheless.

 

[anorlunda]

This is a rather nicely made video

Thanks for sharing that. The video is very detailed and instructive. I recommend it to everyone here who wants to discuss the collapse.

 

[Astronuc]

he talks about the seemingly different thickness of columns where the ones that were located in the part that was left standing are much thicker.

Thinner columns, which appear to be the case, would be more likely to buckle or shear, i.e., the loads at which they buckle/shear would be less. That the rest of the building is standing may be in part due to the larger columns. Questions remain as to the integrity of the columns at the base of the collapsed building and the foundation and subsurface ground underneath.

It's notable that the columns of the garage are still standing even after the pool deck/lower garage roof collapsed, which would imply that the rebar gave way and the deck structure sheared away from the columns. The garage didn't tall into a sinkhole, but the lady who mentioned it probably saw the garage deck drop into what she thought was a sink hole.

Early in the video, about 5:10, with the motor sitting on a slab and the pool pump sitting on a piece of wood on a cinder block. I agree about the criticism of the pool pump support, but the other motor seems to be on a concrete or cement slab (pad?), or a raised portion of the floor. I have seen that practice in many basements. It is design to let water run off if there is a pipe rupture and the idea is to prevent flooding of electrical equipment. One would not want to use aluminum RTU brackets (~5:39) because they would corrode in the dampness with chlorine or sea salt present.

The video mentions Architects Journal. I found one site -
https://www.architectsjournal.co.uk...apse-engineers-early-theories-as-to-the-cause
I haven't found the colored image of the building indicating the sections that collapsed by order.I have heard one report (I have not substantiated/verified) that the amount of rebar was insufficient. That will be revealed in an investigation.

I think the demolition will bring the building down on to its foundation and possibly onto the existing debris pile.

@Astronuc I think those who got out already collected their most irreplaceable valuable namely their own life. Going back one more time would risk loosing that single most precious valuable.

True, but for some it's all the mementos (e.g., pictures of family members) and personal gifts from family and friends, and possibly legal documents, that are just as important as their lives. But they have been told they will not be able to re-enter the building.

 

[Borg]

For those looking for the inspection reports, the city of Surfside has posted them all in one place on their website:
https://surfside.one/public-records-search/

 

[artis]

Well truth be told after the video I put in my post #117 it is now more clear on what could have happened there. The following surely without me being on site or being a licensed expert is speculation on my part but I would argue educated speculation not blind guessing.

It seems that a sinkhole is rather unlikely and that poor construction and maintenance of the building could be the cause. First of all I think there are plenty of (more like thousands and thousands) of similar reinforced concrete structures around USA and the world that are about 40 years of age and have rusted rebar. I mean there is rusted rebar in the panels in my garage and some spalling also.
Yet 99.9% of these old structures with rusted rebar don't collapse and are not expected to do so. Some lost weight carrying capability is to be expected with age and rusted rebar but not a complete progressive collapse.

So a quick guess would be either the rebar in this building rusted beyond belief and over anything commonly seen in other places or there were structural deficiencies from the very beginning which made the structure extra susceptible to any further loss of load bearing during it's lifetime.

What also got my attention was that it seems that the first part to fail structurally was not under or within the building itself but rather the floor slab which covers the yard and pool area , it seems from pictures the floor slab served no purpose on the building itself other than it was physically cast together with the columns and slabs that were also under the building.
Anyway this floor slab held mostly only it's own weight as we can see that after the collapse there were not much stuff atop it except for a few cars on it;'s side.
It's not a good sign that a floor slab that has to only bear it;s own weight collapses and much less that while it did so it seems to have completely taken out at least 3 or more of the very columns that held up the building. It can be seen in the CCTV footage that the inner wall facing the yard and pool falls first so it is very likely these columns that were taken out by the collapsed floor slab started the building collapse.All in all it seems weird that for a building that is the same dimensions and height part of it is built with thinner columns and the other part with thicker ones. It could explain why only half the building fell because as the first columns at the front were compromised due to the yard slab collapsing the rest of building collapsed because the collapsing floor slabs essentially pulled all the other columns sideways with a lateral force.

 

[Borg]

At 22:45 in the video, I was looking at the column sizes that he was talking about. I was curious whether the skinny columns in the collapsed section may have been designed that way because they were closer together. I put the video on full screen and my thumb took up the entire space between the thicker columns on the section that stayed up. However, when I did that in the other section, there was a sizable gap. If the floor plan is to scale, then it would appear that not only were the columns in the collapsed section smaller but they were also farther apart.

 

[Twigg]

True, but for some it's all the mementos (e.g., pictures of family members) and personal gifts from family and friends, and possibly legal documents, that are just as important as their lives. But they have been told they will not be able to re-enter the building.

Not to mention, I know some people who still keep their savings in cash in their home.

Thanks for sharing the video, @artis.

Can you elaborate on why a sinkhole seems unlikely? I would think that a localized sinkhole under the 5 columns that failed first would be consistent with the evidence presented in the video, no? Not trying to push a hypothesis, just feel like I'm missing something obvious.

I also don't understand what makes you say that the floor slab went out before the columns under it. Did I miss something in the video? Sorry, just checking I didn't miss anything important.So, I remember when I first read that there were drainage issues, I thought "it couldn't have been just a flat slab, that'd be just too silly". Now that I see the Murabito report states that the parking garage had a flat floor slab, I'm very confused. Personally, I'm a walking DIY calamity (slightly better than your local "Sawzall artiste"), and even I know that you need to grade a slab and have somewhere for runoff to go. How does such a rookie error happen in a major construction project like this? It would have to slip past the architects and structural engineers (both commercial and municipal) and the construction firm, right? I'm more interested in the failure of administrative controls than pointing fingers, here.

 

[Astronuc]

https://www.cnn.com/2021/07/04/us/miami-dade-building-collapse-sunday/index.html
(CNN)The remaining portion of the Champlain Towers South condo building in Surfside, Florida, was demolished just after 10:30 p.m. ET Sunday.

 

[mathwonk]

From what I have read,
1) there may well have been faulty construction.
2) The dangerous situation was known well in advance of the collapse.
3) The cost and politics of the repair caused a fatal delay.
4) There was a "trigger", which I am guessing (as a lay person with no engineering expertise) was possibly the construction of the next door high rise.

My perspective is as a member of a small community with some shared maintenance items that sometimes have issues in regard to paying for them. The difference is if our price tag for maintenance is $5,000 or $10,000, the agreeable members may be able to pay for it even without those of us who may be reluctant. But if the price tag is $9,000,000, then it is harder. So I have concluded it may be risky to join a condo group of 100 or more families and expect the common items will be well maintained.

 

[artis]

@Borg Well I think pictures might not be the best proof for size measurement because we don't know whether they are each to scale with the previous ones.
Here are the documents from Surfside about the building
https://www.townofsurfsidefl.gov/de...erk/champlain-towers-public-records-documents

Here is the column layout and structural plan for the condo for those that are interested
https://www.townofsurfsidefl.gov/do...s-ave---structural-plans.pdf?sfvrsn=b191194_3
@Twigg Well I base my conclusion same as the video author on the available evidence, if you watch the video one more time take notice of the pictures in there you will see also according to the eyewitness testimonies the slab that covered the yard/pool area fell first , the building came down afterwards.
We can see in the pictures the yard slab has broken in multiple places and fallen down into the underground parking garage but the very columns that held it up are still standing poking through the slab, this would indicate that the failure happened not in the vertical column load bearing but instead in the column to slab attachment part.
It seems like the building then fell because the slab that fell first pulled laterally on the outermost facade columns that it was also attached to, those columns apparently did not withstood the lateral pull force from the yard slab and they broke most likely sideways, this ofcourse robbed the structure and columns above off any vertical gravitational load bearing so that part of the structure started to fall, as it did so it apparently pulled similarly as the yard slab on each next row of columns deeper within the structure taking them down also, essentially like a domino effect.
You can see this in the CCTV footage from the next building that the outer wall falls first and then the inner parts follow with the ocean side part being the last falling few seconds afterwards but being visibly tilted from the neighboring collapse.

Now the method most of these reinforced concrete monolith structures are built is they first cast the vertical columns and then they leave some rebar sticking out from them and then they cast the floor slab all at once atop the columns.
Unlike a metal girder or truss which is much more elastic , concrete is not elastic at all so it's good in compression in vertical load and as we know if made thick enough vertical columns can even stand without rebar at all like in ancient Roman structures etc, but floor slabs made from concrete rely heavily on rebar because concrete is rather bad at lateral loads especially in thin slabs.
So the reason why the slab doesn't just punch through the vertical column is rebar and some added thickness which i have seen in designs where the part around the column right under the slab is much wider. See the picture

If you lose this the heavy yet thin floor slab become like a paper sheet sitting on top of a pencil, the pencil is very strong vertically but it's also sharp , has a low surface area and the sheet can be easily punched through the tip of the pencil and then the sheet slides down the pencil.
This is what happened to the slab in the yard. The columns are left standing but the slab has fallen down. There are advantages of floor slabs compared to girders or assembled panels and one of those advantages is increased overall strength but there is also a downside , each floor slab permeates the whole building and connects to each column, if a slab collapses it pulls on all adjacent columns simultaneously and if columns don't have enough strength in them they give way.
It's like sitting on a rug and the rug is then pulled sideways, it's very hard to resist that pull.
There might be multiple reasons why this happened, wear and age aka rusting rebar being one, maybe the concrete was inadequate and became soft with time and water accumulation , maybe the rebar count and thickness or slab thickness was inadequate really hard to tell not knowing much more.

 

[artis]

Just to add , I don't think concrete has to become brittle or soft due to water I mean we build hydro dams from concrete for hundred and more years and there the concrete is subjected to water 24/7 for decades yet it doesn't seep through or erode the structure, so with adequate chemistry and materials rainfall on a yard slab should not be a problem much less cause for structural failure.

As for building codes well I wouldn't bet my money on that because it's easy to inspect a column for it's diameter for example but it is much harder if not impossible to inspect the concrete quality within a column or multiple slabs that are covered with other materials.
In any way when building something a lot of rests on the honesty and morale of the builder/contractor and even individual workers laying out the rebar , tying it together, pouring concrete etc.

 

[Borg]

@Borg Well I think pictures might not be the best proof for size measurement because we don't know whether they are each to scale with the previous ones.

Agree 100%. I am still really curious about the column spacings though.

 

[Astronuc]

It seems like the building then fell because the slab that fell first pulled laterally on the outermost facade columns that it was also attached to, those columns apparently did not withstood the lateral pull force from the yard slab and they broke most likely sideways, this of course robbed the structure and columns above off any vertical gravitational load bearing so that part of the structure started to fall, as it did so it apparently pulled similarly as the yard slab on each next row of columns deeper within the structure taking them down also, essentially like a domino effect.

An interesting and perhaps plausible explanation. I don't know how much lateral movement there might have been, since the pool deck (or slab above the garage area seem to fall straight down off the columns.

Perhaps the collapse of that area either pulled on the support columns on the south face of the collapsed portion, or otherwise the bending pulled on the rebar and damage the support columns. Nevertheless, it seems the columns supporting the collapse section were undersized, especially when comparing to the main columns under the portion of the building that remained standing. We will not know until the base of the columns is uncovered by removal of the pile of building on top of the columns.

It also occurs to me that the standing water could degrade the concrete and rebar of the columns of the footing/foundation. One the footing(s) gave way, the rest of the building came down gradually, starting at the south face and expanding back into the building.

Just to add , I don't think concrete has to become brittle or soft due to water I mean we build hydro dams from concrete for hundred and more years and there the concrete is subjected to water 24/7 for decades yet it doesn't seep through or erode the structure, so with adequate chemistry and materials rainfall on a yard slab should not be a problem much less cause for structural failure.

Dams are designed with the purpose of holding water back in a lake or reservoir, and likely a different formulation of concrete/cement is used than that used in a building, in which it is probably assumed the concrete remains relatively dry, i.e., does not experience 'standing water', and certainly not chlorinated or standing water. Note the concern in the Morabito Consulting report about the "failed waterproofing" and according to the NY Times ""evidence of “major structural damage” to the concrete slab below the pool deck and “abundant” cracking and crumbling of the columns, beams and walls of the parking garage under the 13-story building.
https://www.nytimes.com/2021/06/26/us/miami-building-collapse-investigation.html

“Though some of this damage is minor, most of the concrete deterioration needs to be repaired in a timely fashion,” the consultant, Frank Morabito, wrote about damage near the base of the structure as part of his October 2018 report on the 40-year-old building in Surfside, Fla. He gave no indication that the structure was at risk of collapse, though he noted that the needed repairs would be aimed at “maintaining the structural integrity” of the building and its 136 units.

True that the building was not in danger of 'imminent collapse', but the point about “major structural damage” indicates a substantial risk. Also, the point about "most of the concrete deterioration needs to be repaired in a timely fashion," implies sooner, not later, or whenever we get around to it.

Mr. Morabito noted that previous attempts to patch the concrete with epoxy were failing, resulting in more cracking and spalling. In one such spot, he said, “new cracks were radiating from the originally repaired cracks.”

Clearly, a critical and serious condition. However, the engineer cannot say when the structure would fail, only the repairs need to be conducted in a time manner to prevent a condition leading to failure. Yet,

Donna DiMaggio Berger, a lawyer who represents the resident-led association that operates the building, said on Saturday that while the report outlined problems to fix, the condo board had no warning that there was a major safety risk.

“If there was anything in that report that really outlined that the building was in danger of collapse, or there was a hazardous condition, would the board and their families be living there?” she said. She noted that one board member, Nancy Kress Levin, was missing in the collapse, as were her adult children.

Clearly the board did not understand the gravity of the situation, and then the town building inspector (Rosendo Prieto) wrongly declared that the building was in "very good shape/condition," which certainly was not the case.
https://www.wsj.com/articles/surfsi...ndos-condition-is-placed-on-leave-11624999188

Edit/update: A good article in Engineering News Record

Engineer Probing Champlain Towers Debacle Eyes Possibility of Three Successive Collapses​

https://www.enr.com/articles/52015-...yes-possibility-of-three-successive-collapses

An area of interest is the surface parking zone near the lobby entry drive that goes partly under the remaining wing. That slab for the parking, which is next to the grade-level pool deck, is the roof of a one-level basement garage that fills the site's entire footprint.

According to Kilsheimer, it appears, from the position of the cars that dropped a level—one car’s nose ended up pointing to the pool area—that the lobby slab columns moved sideways toward the pool deck, causing the pool deck to drop, which then pulled on the tower columns, causing them to fail. “This will not prove where it started,” he says. "That is not something we can determine in a hurry."

 

[Lnewqban]

Continuation threads in the Florida Engineers forum:

https://www.eng-tips.com/viewthread.cfm?qid=484717

https://www.eng-tips.com/viewthread.cfm?qid=484915

 

[artis]

Well @Astronuc as for the column thickness I still hold my judgment on that one because I assume that it is a factor that is very hard to conceal and given that back when the towers were built the US was considered and still is considered a first world country I would find it hard to believe that one could pull off such a blatantly visible mistake in one of the country's most popular cities and tourist destinations. But who knows time will tell.

One thing is for sure the columns in the collapsed section indeed look thinner to the naked eye compared to the ones in the part that was left standing. Also the very fact that the building fell even though there was no direct structural damage directly underneath it most likely but instead it's few outer columns experienced a lateral force that exceeded their loading capability. Maybe the building was built to code but with very little reserve capacity so much so that a failure in one small par of it can result in a progressive collapse. As for the loud popping sounds herd by eyewitnesses hours before the collapse I would argue that it could have been snapping of rebar rods within the concrete, because concrete is a rather dull material sound wise has a very low resonant frequency and when it itself breaks or cracks it is mostly silent , metal on the other hand has a much higher natural resonant frequency and it's sound is sharp especially when under tension , so a metal rod inside concrete if it snaps or breaks can produce a sound that has nowhere to go so it travels through the concrete structure and reverberates throughout the building which apparently is what happened.
It could very well be that the yard slab was losing its rebar for hours before it fell, then it fell and soon followed the building itself.
Here I found a nice little "Slow Mo Guys" video of just that - rebar breaking under tension

 

[Astronuc]

even though there was no direct structural damage directly underneath it

We don't know that. The Morabito report did indicate structure damage to columns in the garage, but did not elaborate on which columns. I would prefer to read a report identifying which columns had corroded rebar and spalling concrete.

From the figure I posted in post #9, the thin columns, e.g., 42 and the one to the north, seem to have been sheared, or crumpled unlike the columns on the left side of the image, which remained supporting the building. Column 42 and its sibling either broke off below the deck, which could be that rebar was pulled out of the concrete, or perhaps they dropped about 0.5 to 1 meter, in addition to having been sheared across the top.
https://www.physicsforums.com/threa...been-sinking-since-1990s.1004491/post-6508032

 

[russ_watters]

Holy cow!

San Francisco's lavish Millennium Tower, with soaring panoramic views and world-class amenities, opened to great fanfare in 2009.

But, since it opened, the hulking blue-gray tower has sunk 18 inches into the soft downtown soil on which it was built -- and it's tilting, according to the Millennium's current engineer, Ronald Hamburger...

Now, amid reports suggesting the deadly collapse of the Champlain Towers South more than 3,000 miles away in Surfside, Florida, began in the building's lower reaches, questions are being raised about the Bay Area tower's structural integrity.

https://www.cnn.com/2021/07/05/us/san-francisco-millennium-tower-sinking/index.html

An examination in 2016 showed the building had sunk 16 inches (41 cm) with a two-inch (5.1 cm) tilt at the base and an approximate six-inch (15 cm) tilt at the top of the tower.[30] The building is leaning toward the northwest,[30][31][32] and has caused cracks in the building's basement and the pavement surrounding the tower.[33] As of 2018, the sinking has increased to 18 inches with a lean of 14 inches.[34]

https://en.wikipedia.org/wiki/Millennium_Tower_(San_Francisco)#Sinking_and_tilting_problem

 

[Keith_McClary]

Millennium Tower ... lean of 14 inches.

Do the elevators bump against the shafts yet?

 

[artis]

Please excuse my taste of humor but I can't resist.

@russ_watters quoted

But, since it opened, the hulking blue-gray tower has sunk 18 inches into the soft downtown soil on which it was built -- and it's tilting, according to the Millennium's current engineer, Ronald Hamburger...

Could Ronald Hamburger be the secret brother of Ronald McDonald?

Anyway McDonalds also needs to be checked because the structural integrity of my burgers are compromised regularly , I mean with just a little lateral pull force exerted by my teeth the whole burger structure collapses , the flat meat slab just goes sideways and the whole thing just pancakes.

 

[Astronuc]

Liability from Florida condo collapse: everyone will 'blame everybody else'
https://www.reuters.com/world/us/li...veryone-will-blame-everybody-else-2021-07-06/

Some good points on liability in Florida.

Morabito Consultants (MC) is being sued "for failing to warn residents of the danger of collapse."

The lawsuit blamed the Morabito engineering firm, which conducted the 2018 inspection, for allegedly failing to warn the condo association of the need to evacuate the building. The firm was retained again in 2020 and did not warn residents the damage it uncovered two years earlier had not been repaired, the lawsuit said.

I read the report and there was ample warning in item J,

"Abundant cracking and spalling of varying degrees was observed in the concrete columns,
beams, and walls. Several sizeable spalls were noted in both the topside of the entrance drive
ramp and underside of the pool/entrance drive/planter slabs, which included instances with
exposed, deteriorating rebar. Though some of this damage is minor, most of the concrete
deterioration needs to be repaired in a timely fashion. All cracking and spalling located in the
parking garage shall be repaired in accordance with the recommendations of ICRI."

Then under item K,

K. MC visual observations revealed that many of the previous garage concrete repairs are fail ing
resulting in additional concrete cracking, spalling and leaching of calcium carbonate deposits . At
the underside of Entrance/Pool deck where the slab had been epoxy-injected, new cracks were
radiating from the originally repaired cracks. The installed epoxy is not continuous as observed
from the bottom of the slab, which is evidence of poor workmanship performed by the
previous contractor. The injection ports were not removed, and the surfaces were not ground
smooth at the completion of the injection . Leaching of calcium carbonate deposits in numerous
areas has surely caused CTS to pay to repaint numerous cars. This leaching will continue to
increase until proper repairs are completed . MC is convinced that the previously installed epoxy
injection repairs were ineffective in properly repairing the existing cracked and spalled concrete slab.

MC could not predict that the building would collapse. It wasn't in imminent danger of collapse in 2018, and besides, MC warned, "The failed waterproofing is causing major structural damage to the concrete structural slab below these areas. Failure to replace the waterproofing in the near future will cause the extent of the concrete deterioration to expand exponentially." And that's exactly what happened since the condominium owners and board failed to take action in a timely fashion!

None of the owners contracted MC, but rather the CTS Condo Association contracted with MC, and a report was delivered. It was then the responsibility of the board to inform the owners, which they apparently did. But then the inspector for Surfside (Rosendo Prieto) apparently told an association/board meeting that the building was in "very good shape". The board should have followed up with MC regarding that representation, since it conflicted with the dire warning in the MC report.

It's not clear to me that MC was contracted for a structural integrity assessment, but MC certainly did point out potentially severe problems.

Incidentally, I recently read that Breiterman, Jurado & Associates, Consulting Engineers is a defunct corporation, i.e., it apparently ceased to exist.

June 26 - https://www.washingtonpost.com/nati...09519a-d5de-11eb-a53a-3b5450fdca7a_story.html

Last year, the U.S. Army Corps of Engineers did a full replenishment of Surfside’s beaches, Salzhauer said. Much of the sand for that project was initially stored directly in front of Champlain Towers, she added.

This tells me the ocean was much closer to the building before the built up the beaches. I have seen this situation in Wrightsville Beach, North Carolina, following one the hurricanes, where one building had the ocean right at the foundation, since the beach was completely washed away and new cut/channel through the barrier island had formed within meters of the building.

Edit/Update: Also from the Washington Post article,

Manuel Jurado said his side of Breiterman and Jurado handled the mechanical and electrical while Breiterman handled the structural side. (Sertio Breiterman died in the 1990s.) Jurado said he did not do anything with waterproofing or inspections. “To be honest with you, I don’t remember,” said Jurado, 92. “I don’t even remember this building in Surfside.”

Manuel Tapia-Ruano, a former vice president of the Friedman architectural firm, said the building’s design was handled by William Friedman, who died in 2018.

So this would confirm that Breiterman, Jurado & Associates dissolved after the death of Breiterman, especially if it was a partnership. I'm not aware of a successor. Similarly,
William M. Friedman & Associates Architects, Inc does not seem to exist either.

https://www.wsj.com/articles/miami-...ars-of-warnings-but-mixed-signals-11624994509 - also mentions Breiterman, Jurado & Associates as defunct.

https://www.enr.com/articles/52001-...r-champlain-towers-probable-collapse-sequence

There are at least three theories about the trigger of the progressive collapse, beyond the pool deck slab: column failure, slab failure due to punching shear or failure of the pile foundation system, perhaps under the pool deck. Kilsheimer, Bell and others speculate there may have been more than one contributing factor, as in a perfect storm.

Progressive failure is caused either by columns that fail axially due to axial over-stress or shear damage that progresses to axial failure or punching shear failure, says Moehle.

In punching shear, one or more of the building’s flat slabs develops a shear failure around the column and drops relative to the column.

If there is no continuous bottom reinforcement in the slab passing over the columns—a detail not required in 1981—then the slab can move downward relative to the column, redistributing load to adjacent slab-column connections, which in turn can fail. A slab that eventually lands on the floor below it overloads that floor system, and there is more punching shear, says Moehle, who has done extensive testing of concrete structures.

Also from the WP article of June 26

http://paduaresearch.cab.unipd.it/9896/1/Fiaschi_Simone_tesi.pdf - pages 65-66 in thesis (76-77 of 111 in pdf) - There is a figure that show subsidence rates on that barrier island, but not in Surfside. Nevertheless, the rates appear to be linear between 1993 and 2005, and possibly the continue to be linear even today, especially if water infiltrates the formation under Miami Beach and Surfside.

and

Kit Miyamoto, a veteran Los Angeles-based structural engineer who specializes in structural resilience, said that a pillar or column supporting the building appeared to have failed. Corrosion by the salty air or a “differential settlement,” meaning differences between how sides of the building were sitting on the land, could have caused a pillar to collapse, he said.

“This is truly a classic failure of a column,” said Miyamoto, chief executive of Miyamoto International, a global earthquake and structural engineering firm. “It was supporting many stories and that’s why it happened very suddenly.”

Miyamoto, who has studied building collapses around the world, added that it would be difficult to pinpoint the exact location of the degraded pillar because of the near-total destruction of the building. “It requires a forensic investigation, like peeling off the skin of an onion, one by one,” he said.

 

[artis]

By far the best video evidence is the CCTV footage from the building next door showing the initial collapse.
Anyway for a bunch of condo buildings where flats cost up to 7 figures in the year 2021 they seemingly had very few security cameras, more angles and videos would help to pinpoint the cause much better.

@Astronuc nice findings there but it seems that there could not have been multiple slab failures, because if we look at the building from bottom up, then the first slab is the underground garage floor , but that can't be normally considered a slab as it sits on soil/ground, then the first real slab that is connected to columns would be the one that separates the parking garage and the first floor. This slab as we know was continuous and permeated the whole building and the outside yard where in the yard it became the ground level. So from what I know the series of events went like this.

1) From eyewitness testimony we know that this slab in the yard part fell first.

2) At the other side of the building a tourist pair were in the neighboring hotel outside pool filming roughly 7 mins before collapse, the video shows concrete fallen to the parking garage ground and a broken water pipe with water gushing out. It seems this is after the yard slab had collapsed. This (at least to me) would indicate that the collapsed yard slab part as it fell did some damage in the rest of the slab that it was connected to. The garage damage most likely was not a separate incident but happened at the same time.

3) As can be then deduced from the CCTV footage, the outer wall columns facing the yard gave way first which would make use think they being directly attached to the fallen yard slab could have been compromised by the collapse of the yard slab and further compromised by the wear and rusting rebar over the 40 year life span. Given there seemed to be damage also at the other side of the garage prior to collapse as said before, it could very well be that the yard slab collapse impacted the integrity of the whole part that collapsed aka the middle section of the building at the basement level.

4) The last but as it might turn out most important factor here could be this, let the video speak for itself.


The video has two nice pictures and indeed it seems not only is the slab thin but rebar is thin as well and mostly absent.

 

[BillTre]

Here is a short simulation, nicely paired with photos of how the collapse might have happened.


This makes sense to me.
Matches with accounts I have read and seems to provide a feasible sequence.

 

[artis]

@BillTre nice video I think I saw it on youtube before. It makes me think of one more thing. When the yard slab fell it pulled laterally on the nearest columns it was attached to.

The question then is this, why did the slab managed to pull the columns in the collapsed portion but not the ones in the left standing portion?
the whole building was the same height and mass I would suspect, all of it's columns should have been similar to hold up a similar weight and structure.

 

[Astronuc]

then the first slab is the underground garage floor , but that can't be normally considered a slab as it sits on soil/ground, then the first real slab that is connected to columns would be the one that separates the parking garage and the first floor.

The first slab is the floor of the underground garage, and the slab should be attached by rebar to the columns. If the rebar in those joints failed, then the columns could drop into the ground underneath, which would compromise the structure above.

Looking at the video of the collapse, it seems there was simultaneous failure of multiple columns, which would suggest that the garage roof, or plaza (pool) deck failed, then pulled simultaneously on the several columns that failed by buckling or shearing. And it does appear from WPLG video with experts that the columns were poorly constructed (appear to violate the drawings with respect to rebar density) and they seem to be too thin. The columns supporting the uncollapsed building, i.e., those remaining intact, seem to be sized properly for the building.

If the rebar was insufficient, and there was corrosion of the concrete and rebar, it was probably a slow progression to failure over years.

the whole building was the same height and mass I would suspect, all of it's columns should have been similar to hold up a similar weight and structure.

From the drawings, it appears that the columns under the eastern portion of the building were undersized, and certainly smaller than the columns under the western (north-south) portion of the building.

Looking at the video at 1:22 - 1:30, the columns with 42 and 40 (numbers are presumably parking spaces) look like they had the rebar pulled out, and there appears to be a slight lean to those columns. Further east are columns for parking spaces 28 and 29. What do the images convey?

The investigation will have to look at each column, the slabs, the footings, the rebar, to see where the corrosion was most severe, and what might have failed first and direction of propagation.

 

[artis]

The first slab is the floor of the underground garage, and the slab should be attached by rebar to the columns. If the rebar in those joints failed, then the columns could drop into the ground underneath, which would compromise the structure above.

I would also tend to think that even the base slab that rests on ground is connected by rebar to the columns but in a building with 12 stories I would suspect that the columns themselves actually start well below the base slab (the floor of the parking garage) and are actually built on top of piles driven into ground or some anchoring. If the columns actually ended on the base slab then they would puncture right through the slab and drop to ground a soon as the building is finished being built. Or you would need an extremely thick slab , I'm thinking like a meter thick or more. So I think the slab is thin it just does the floor function and some lateral bracing of columns while the columns themselves have to rest on some deeper anchoring, especially in a soft ground like that next to ocean.So continuing our online investigation , here is a video that I found quite randomly, it seems to show a large part of the underground garage. In the end you can see the exit ramp for cars that was filmed in the tourist video with the leaking water pipe. You can observe plenty of pipes on the ceiling from fire water ones to some other ones. If that pipe burst because of the yard slab failure being at the other side of the slab it would indicate that the rest of the slab underneath the structure was heavily compromised. The most likely damage to the pipe could have resulted from large heavy portions of the concrete slab dropping freely and hitting the pipes in the process.
As for the column thickness well it seems that they were the same thickness throughout the structure , at least at the basement level because the part of the parking garage with the exit ramp seen in the video is the very part that collapsed.
Truth be told apart from a few cracks here and there the slab doesn't seem to be in such an extremely bad conditions like it is told on news. Lastly I hope this is the video of the building in question but it definitely seems so from the floor plan and exit ramp.

Lastly take a look at this video , a short clip by someone from the rescue team as they are working under the collapsed section in the parking garage. Take notice of the ceiling slab, the one that I think could be responsible for the compromising of columns. Notice how the rebar has separated from the slab and left deep trenches in the half fallen slab piece under which the people are working. It could very well be that similar damage happened under the building as the yard slab portion fell, rebar being metal has high tensions capabilities and it could have exerted a large pull on all the adjacent structure.
Also at the very beginning of the video take a close look of one of the columns and see how the slab has separated from the column and fallen down yet the column is left standing.


This is a picture under the half part that was left standing , notice how the failure of the yard slab has carried on through the rebar into the slab underneath the building.

I must say those people working in that hellish unsafe environment risking their lives should get all the respect they deserve.

 

[artis]

Here's a guy who has made a video with all the columns and the first floor slab which seems to be the place where failure started.

 

[artis]

One thing that hasn't been talked here as far as I see is about survivors.
Sadly I think there won't be any more survivors past the first ones that were found, there are mostly 2 reasons for that , first is time, living under rubble without water or food and with possible injuries can only last you a couple of days at best in most cases.

But the second reason is that I think most of the folks died upon collapse, in a structure like this the floor slabs being made from concrete they are heavy and as the building comes down those slabs literally fall one on top of the other. Being as heavy as they are ordinary apartment items cannot slow them down or stop them they annihilate everything from fridges to TV's and furniture , everything gets absolutely flattened under the weight and inertia so I would think anyone who was as the part of the collapsed building somewhere between the very top floor and basement got compressed to a coin.

See in the pictures how the balconies are sitting one atop the other with just inches of space between what was once a whole floor between.

 

[anorlunda]

Clearly the board did not understand the gravity of the situation

The board is comprised of residents with no particular qualifications. Can any condo board anywhere be expected to correctly interpret an engineering report? The condo board should be required to also hire an engineering firm to carry it a step further; to produce a detailed list of remedies that must be performed including schedule. The detail must be enough to present to possible bidders as an RFP.

In no case should we expect condo associations to competently decide engineering questions or even to understand them.

 

[Astronuc]

Can any condo board anywhere be expected to correctly interpret an engineering report? The condo board should be required to also hire an engineering firm to carry it a step further; to produce a detailed list of remedies that must be performed including schedule. The detail must be enough to present to possible bidders as an RFP.

A colleague owns an apartment in a condo in a major city. He was probably the only engineer on the board when he joined several years ago, and he made things happen, such as roof repair and proper ventilation that had been neglected to the point where apartments were suffering damage. And he had to deal with members who did not want to pay for repairs/improvements, much like the situation at CTS, but not as critical.

Going forward, there will probably be changes in the local and/or state laws, or mandates pushed by insurance companies, to impose more responsibility onto condo associations and/or owners of condos to ensure proper structural inspections. If there was less rebar in the columns and/or beams, especially in the joints, or if the columns were indeed undersized for the structure, then something went wrong in the construction and inspection/certification phase, so that will have to be addressed.

What agency/law would require a condo board to hire an engineering firm? Morabito Consultants (an engineering firm) was hired to do some kind of assessment in preparation for the 40-year review and recertification. MC warned of damage to the structure. The town inspector declared the building in "very good shape", so apparently the board concluded that the building was in very good shape despite MC's warnings. A 'timely fashion' for repairs would have been 2019 (@38 years), not starting 2021 at 40 years.

On the other hand, I'm troubled by the statement in the MC report (item J), "Though some of this damage is minor, most of the concrete deterioration needs to be repaired in a timely fashion. All cracking and spalling located in the parking garage shall be repaired in accordance with the recommendations of ICRI." The statement would be reasonable if the damage to the concrete was superficial (or minor), which in places it might have been. But the use of minor seems to undermine the severity of the situation. Even if it was minor, it was surely going to be major or critical at some point, because that is the nature of corrosion and environmental degradation.

Perhaps the requirements for a 40-year recertification don't go far enough, since MC didn't appear to do a full structural integrity inspection, and I'm sure MC did not expect apparent inadequacy in the rebar (if that proves to be the case). And look at the language in item K.

Does the 40-year recertification process require a full structural integrity assessment/inspection, i.e., would it require that the integrity of the rebar be inspected with GPR and/or X-ray?

MC offered to work with the CTS association board in the last paragraph, "MC trusts this initial report will assist the Champlain Towers South Condominium in understanding the required maintenance that is needed to properly maintain this existing residential property. MC is available to further discuss the recommended repair work and how it coincides with the owner's desires and constraints. We look forward to working with you in maintaining the structural integrity of the Champlain Towers South Condominium." Was that enough? How far does MC have to go to ensure the board 'understands'? In items J and K, MC states "All cracking and spalling located in the parking garage shall be repaired in accordance with the recommendations of ICRI."(J) and "All repaired concrete slabs located in the parking garage are to be
repaired in accordance with the recommendations of ICRI"(K). It's not clear on the followup.

I'm curious about the popping sounds in the apartment building/garage. Did they happen just before the collapse, or had they been happening for days before?

In no case should we expect condo associations to competently decide engineering questions or even to understand them.

But don't they have to be competent enough to hire an engineer to evaluate/assess a building's structural integrity? After all, aren't the owners responsible for ensure the structural integrity of their property? Sounds like there needs to be some law(s) or government regulation(s).

 

[Keith_McClary]

to impose more responsibility onto condo associations and/or owners of condos to ensure proper structural inspections.

If you put personal responsibility/liability on board members, nobody will want to serve on the board.

"MC trusts this initial report will assist the Champlain Towers South Condominium in understanding the required maintenance that is needed to properly maintain this existing residential property. MC is available to further discuss the recommended repair work and how it coincides with the owner's desires and constraints. We look forward to working with you in maintaining the structural integrity of the Champlain Towers South Condominium." Was that enough?

I would read that as a standard sales pitch that they tack onto every report.

 

[anorlunda]

Normally, I'm libertarian by nature. But this example sure seems to point to the need for new regulations/laws.

What would make sense in cases where there are thousands of similar condo owned buildings is to pool resources to hire a professional building management company to do most of the things that are today handled by the residents. The management company should have a legal fiduciary duty.

 

[artis]

Well I somewhat disagree with the assessment that owners need to be told like children what to do.
I am not a doctor or a surgeon but when I have legitimate concerns over my health I call one.
A building owner doesn't have to be a structural engineer but we all have eyes and if we see or hear or witness whatever we should simply call the "doctor".

I don't want to sound judgemental on people that have passed away horribly but eventually reality is reality and for every mistake there is a person or surname that is attached to it and in this case I do feel that the very people that died were somewhat responsible for this.
The same happens with folks and their health I know many folks who feel sick yet they disregard that as "no biggie" only to find months later that they are taken to intensive care and now the illness is vast and raging and often they die in the result from something that could have been treated easily.
Who is to blame in such a case? Should we now have laws that mandate everyone to sit right next to a doctor 24/7?

The problem is that even when people tend to worry about their own health very few would ever think that a building that they only partially own also needs some looking after. It's just how people are , we are essentially selfish and tend to disregard threats that are hard to understand or that are not visible. So I guess @anorlunda suggestion of tougher building evaluation and them being mandatory after certain intervals is the best option.

 

[artis]

@Astronuc as for the building evaluation in 2018, here I would say that if that building collapsed like it did only 3 years later I would say that a cosmetic repair or otherwise would not have made much of a difference, here is why I think that.
When you have reinforced concrete structure , when the rebar has rusted away and the concrete has cracked there is not much you can do further on, sure you can cover the cracks but concrete accumulates moisture through it's very self so there will still be further moisture and further rusting inside.
Also whenever pieces of concrete have fallen off , what is the remedy ? To patch new concrete in place? I'd say no, here is why I think that.
Whenever you cast concrete whether in factory pre-cast panels or on site you form it as a single monolith, when that concrete dries if it then later fractures or forms a void the new concrete or other material that will be put into this crack or void won't restore the same structural integrity that it originally had.

Like imagine taking a jack hammer and cracking out some pieces from a reinforced concrete panel or slab, then patch that hole with fresh cement made on spot say by hand or whatever , that new cement patch will never have the same adherence or load bearing capability the original uninterrupted slab/panel had, so it's structure will still be weakened.
This is much worse ofcourse when there is rusted rebar underneath.

I would say that beyond a certain point of rebar rust and concrete cracking and spalling there is no going back , patching up cracks is just making it seem pretty but structurally the load bearing is not and will not be there.
I would say that given how totally the structure failed and all the possible weak spots it had, even the year 2018 was too late to do anything useful in the long term , Id' say that building needed to be assessed professionally and then vacated peacefully and demolished. Or at least the yard slab needed to be demolished and rebuilt completely , although I'm not sure how one could do that and how that would have affected the structural integrity of the remaining tower.Anyway patching concrete is like heat soldering broken plastic, yes it can be done but the soldered part will never be as tough as the original.

 

[anorlunda]

It's just how people are , we are essentially selfish and tend to disregard threats that are hard to understand or that are not visible.

Yes. To make it worse, consider the case where the necessary repairs are more than the residents can afford. If unaffordable, the option is to abandon the building and their investment in the building and to shoulder the expenses of demolition. How many would vote to accept that conclusion? How many if most residents are retired and have most of their net worth tied up in that real estate investment?

@russ_watters said it best that shared responsibility and conflicted interests are hard to manage. Now compare how to manage that in the case of a commercial building compared to a condominium owned building. As a 76 year old senior myself, I would add a third case to compare -- a condo owned by residents all over 70 years old.

This incident shines the light on the basic business model of condominiums. This is an engineering forum, and it's natural that we are most interested in the engineering details, but preventing future repeats requires a hard look at the social side also.