Florida condo collapse

[Dleg]

Alright, I'm just a lowly enviro so I have nothing to offer in the forensic discussion, but I wanted to start a thread so I could hear what all the structural types have to say about this situation.

Any preliminary guesses as to what happened?

I am posting this article only because it has a really excellent, interactive before - after visual:
https://www.nbcnews.com/news/us-new...otos-florida-condo-building-collapse-n1272299

 

[pbrme]

Wow, that's horrible. Looks like there was a major tower going in right next to it. I wonder if there is some connection with either recent site activity or if investors didn't like the view.

 

[bwin12]

Alright, I'm just a lowly enviro so I have nothing to offer in the forensic discussion, but I wanted to start a thread so I could hear what all the structural types have to say about this situation.

Any preliminary guesses as to what happened?

I am posting this article only because it has a really excellent, interactive before - after visual:
https://www.nbcnews.com/news/us-new...otos-florida-condo-building-collapse-n1272299

1. I think this is a geotechnical issue as much as a structural
2. I didn't read the article in the link but I read elsewhere:
a. there was roofing work going on
b. the building was going through a recertification process because it was 40 years old
c. In the 90's an analysis was done and it was determined the building was sinking ~2 millimeters per year at the time

This is a horrible situation. I can't understand how a portion of a building would just collapse like this one did. I assume there was too much weight on the roof or the foundation just moved too much. It seems like the part of the building still standing did nothing to support the portion that collapsed. I am interested to hear from the structurals as well.

 

[Dleg]

If you look at that before/after, it almost looks like the part that collapsed could have been an addition to an original L-shaped structure in the front.

 

[Reverse Polish]

1. I think this is a geotechnical issue as much as a structural
2. I didn't read the article in the link but I read elsewhere:
a. there was roofing work going on
b. the building was going through a recertification process because it was 40 years old
c. In the 90's an analysis was done and it was determined the building was sinking ~2 millimeters per year at the time

This is a horrible situation. I can't understand how a portion of a building would just collapse like this one did. I assume there was too much weight on the roof or the foundation just moved too much. It seems like the part of the building still standing did nothing to support the portion that collapsed. I am interested to hear from the structurals as well.

In my experience investigating damage to structures, there are usually at least three contributory factors. Structures have sufficient redundancy and factors of safety to withstand one (or maybe two) adverse conditions, but there is usually a third that tips the scales, so to speak. This is especially true in a completed structure that was presumed adequate for nearly 40 years. Again, that's just a rule of thumb based on my experience.

I think it's rash to speculate at this point. What we do know is that there was a progressive collapse "pancake" failure, similar to what happened at the World Trade Center. To me, this suggests that a column-to-beam connection disengaged, or a column buckled, triggering overstressed conditions elsewhere as the loads redistributed. What triggered this mechanism remains to be seen.

The engineers investigating this collapse will be looking to identify these candidate causes based on the physical evidence and review of the original design, determine who made a mistake, and who should have known about the problem(s). Like all catastrophic failures, I expect there will be lessons learned that will improve engineering, construction, and maintenance practices in the future.

 

[jeb6294]

An article popped up on my feed this morning that had a guy whose mother lived in the condo and is now missing. The day before, she told him that she’d been woken up the night before by “creaking noises” in the middle of the night. It also talks about it having structural issues for years, but it looks like that is in reference to the building sinking.

 

[jeb6294]

https://www.fox19.com/2021/06/24/ca...Wdxq5gRIxL71nurYI1aM5ImRd4tDscNnSyd8XHWhE10Sg

 

[kevo_55]

HFS!

This whole thing is sad.

 

[snickerd3]

hopefully it was a lot of snow birds that are elsewhere right now. 150+ people unaccounted for is just too sad.

 

[Deep_Freeze26]

I think it's rash to speculate at this point. What we do know is that there was a progressive collapse "pancake" failure, similar to what happened at the World Trade Center. To me, this suggests that a column-to-beam connection disengaged, or a column buckled, triggering overstressed conditions elsewhere as the loads redistributed. What triggered this mechanism remains to be seen.

I don't think it's rash to speculate as engineers outside of an active forensic investigation. I think it's important to use our own intuitions about structural behavior and monitor outcomes of such investigations. Our ultimate duty is to protect the general public and tragedies like this with significant loss of life are sickening for any engineer. Case in point, the FIU bridge collapse. I remember seeing the dash cam video and immediately said out loud, "That's a prestressing failure." You could see the loss of the PT rod and subsequent buckle as the top chord crushed. Turns out, that's exactly what the GC was doing on that member trying to add additional prestressing to close the distress shear cracking at the bearing seat.

In this case, this building looks like a RC two way slab system with CIP cores for lateral stability to me. I don't think there is beam framing in this structure. The collapse to me suggests significant vertical movement of the internal columns and subsequent punching shear failure through the slab due to the dynamic displacements. There is a remaining CIP core still standing that probably prevented the other side of the building from collapsing in the same manner. I think it's a combination of triggers that will ultimately be found.

hopefully it was a lot of snow birds that are elsewhere right now. 150+ people unaccounted for is just too sad.

Let's pray this is true. This is gut wrenching.

 

[letsseeaction]

I don't think it's rash to speculate as engineers outside of an active forensic investigation.

I tend to agree here.

I'll be the first to admit I don't know everything and can't fully speculate when I'm not familiar with the details of the design or the circumstances surrounding this awful tragedy... however, there are so many lawyers and wannabe-engineers running their mouths that it's important to have trained, professional voices in public discourse. When there's a lack of knowledge, insight, instinct, or intuition among the general public surrounding significant events like this, I do believe it's not rash to fill the space with facts and correct wrong info or half-truths.

Case in point: the lawyer for the condo association was quoted as saying that hairline cracks don't lead to this kind of failure, and that really struck a nerve with me.

 

[Deep_Freeze26]

Case in point: the lawyer for the condo association was quoted as saying that hairline cracks don't lead to this kind of failure, and that really struck a nerve with me.

Everybody's an engineer until someone needs to accept liability for something, then it becomes "Well, I'm no engineer."

 

[1973Olds98]

I am no structural engineer but is it possible a large sinkhole formed under the building, leading to such a collapse? I know Florida is prone to sinkholes and have seen who houses swallowed by them in Florida. As I know some talk about the oxidation of rebar due to the salty environment, but there are literally thousands of structures like this along the beach and none have collapsed in this fashion, plus the rebar is embedded in concrete. It seems like something was going on in the sandy soil beneath the tower leading to settlement, etc. But perhaps a large sinkhole formed which, I would think, could lead to a catastrophic collapse like happened. A terribly sad event and we all need to learn what happened to make sure it never happens again. Prayers to those who were unfortunately killed in this event.

 

[jeb6294]

Just read an article saying the building was due for $9+ million worth of repairs. A million of that was for “structural issues”. Maybe I’ve been in the Gov’t too long, but $1M doesn’t sound like a lot given the scale of the building/property. Keep in mind, a lot of the info was based on a proposal from an Engineering consultant getting paid for the repairs, so the worse they can make the building look, the more money they make.

The roofing work was the first of the $9M repairs, but the property owners had gotten kudos from the city because the repairs were for the building’s 40-year recertification, and they were a few years ahead of schedule.

There was reference to another email from the property owners tot he city raising concerns about construction going on next door and them digging to close.

I would not be surprised if it comes down to a combination of non-critical issues…structural issues that wouldn’t normally be fatal compounded by vibration/undermining from the construction next door.

 

[Platypus Engineer]

I am no structural engineer but is it possible a large sinkhole formed under the building, leading to such a collapse? I know Florida is prone to sinkholes and have seen who houses swallowed by them in Florida. As I know some talk about the oxidation of rebar due to the salty environment, but there are literally thousands of structures like this along the beach and none have collapsed in this fashion, plus the rebar is embedded in concrete. It seems like something was going on in the sandy soil beneath the tower leading to settlement, etc. But perhaps a large sinkhole formed which, I would think, could lead to a catastrophic collapse like happened. A terribly sad event and we all need to learn what happened to make sure it never happens again. Prayers to those who were unfortunately killed in this event.

There are reports of noticeable cracks in the parking garage before collapse.

I remember seeing in one of the articles about this that the waterproofing on the concrete needs to re applied periodically. Given the salt air the waterproofing is critical to prevent chlorides from reaching the rebar, which will lead to corrosion. Rebar expands as it corrodes causing cracks in concrete and eventually causing pieces of it to fall off. Corrosion weakens the metal reducing its strength. There are pictures from this showing exposed rebar.

There was also a case at the auto racing track outside of Charlotte. The parking lots are on the opposite side of the road from the track. Elevated walkways were installed using precast slabs. The grout used to plug the holes where the lifting rings were had chlorides in it . The chlorides got to the rebar causing one of the walkways to collapse.

 

[Reverse Polish]

There are reports of noticeable cracks in the parking garage before collapse.

I remember seeing in one of the articles about this that the waterproofing on the concrete needs to re applied periodically. Given the salt air the waterproofing is critical to prevent chlorides from reaching the rebar, which will lead to corrosion. Rebar expands as it corrodes causing cracks in concrete and eventually causing pieces of it to fall off. Corrosion weakens the metal reducing its strength. There are pictures from this showing exposed rebar.

There was also a case at the auto racing track outside of Charlotte. The parking lots are on the opposite side of the road from the track. Elevated walkways were installed using precast slabs. The grout used to plug the holes where the lifting rings were had chlorides in it . The chlorides got to the rebar causing one of the walkways to collapse.

This is exactly why I don't want to speculate at this point. The news media, which reports to the ignorant general public, has speculation all over the place, which may or may not make sense. Not that the media or lay people care about drawing accurate conclusions. I think that having engineers contribute their own speculations to the white noise of Amateur Hour only muddies the engineering message of careful and deliberate study, and does a disservice to those who have lost their lives and homes.

Cracks in concrete. Spalling. Work on the roof. Pool deck waterproofing. If any of these factors could single-handedly explain a collapse, we wouldn't have any reinforced concrete buildings standing anywhere in the world. It's incumbent upon us engineers to not contribute to what is already an emotionally-charged situation, and stick to facts vis-a-vis hearsay.

 

[bwin12]

The news media, which reports to the ignorant general public, has speculation all over the place, which may or may not make sense. Not that the media or lay people care about drawing accurate conclusions. I think that having engineers contribute their own speculations to the white noise of Amateur Hour only muddies the engineering message of careful and deliberate study, and does a disservice to those who have lost their lives and homes.

This thread is over a week old, but it seems a lot of the media I have read (I generally read articles, not watch Fox/CBS/NBC) seem to recently be focusing on the lack of repairs and how expensive those repairs were going to be. I agree that engineers drawing inaccurate conclusions isn't helpful and feeds a narrative, but it also captures an emotional situation and gets the message out that these buildings (and infrastructure in general) needs to be maintained.

I am interested in the legal proceedings that will happen. Who is going to be found at fault and be financially responsible? I unfortunately keep circling back to the residents/board. Obviously we don't have all the facts, but what is being reported makes sense.

 

[Reverse Polish]

This thread is over a week old, but it seems a lot of the media I have read (I generally read articles, not watch Fox/CBS/NBC) seem to recently be focusing on the lack of repairs and how expensive those repairs were going to be. I agree that engineers drawing inaccurate conclusions isn't helpful and feeds a narrative, but it also captures an emotional situation and gets the message out that these buildings (and infrastructure in general) needs to be maintained.

I am interested in the legal proceedings that will happen. Who is going to be found at fault and be financially responsible? I unfortunately keep circling back to the residents/board. Obviously we don't have all the facts, but what is being reported makes sense.

Right. And that's not necessarily a bad thing. Most lay people (esp. condominium associations, in my experience) don't want to recognize that a building is an organism that needs to be maintained, and that this maintenance costs money. I think current media reports unecessarily feed fear to the public, though, implying that concrete buildings with cracks or spalls are susceptible to collapse.

 

[jeb6294]

I am interested in the legal proceedings that will happen. Who is going to be found at fault and be financially responsible? I unfortunately keep circling back to the residents/board. Obviously we don't have all the facts, but what is being reported makes sense.

It certainly sounds like the residents/board were dragging their feet on costly repairs, but I'm sure the circling vultures are going to ask if any structural issues that required such extensive repairs fall at the feet of the city/Engineer/Architect. Even if there wasn't necessarily anything that can be ties back to the initial design, those three would have much deeper pockets.

 

[Platypus Engineer]

Accordng to link, there were penthouses added that were not part of original design, concrete not thick enough, no shear caps on columns.

https://www.constructiondive.com/ne...ctices-likely-contributed-to-surfside/607517/