[brudgers]

The building collapsed because there was less steel due to corrosion than in the design drawings…less concrete too due to spalling.

But mainly it collapsed because the-building-is-falling-apart issues were not addressed despite being obvious even to lay people.

More steel might have delayed the collapse. It would not have avoided it altogether.

[secabeen]

Do you have a source for these claims? Concrete has great compressive strength, and that strength increases as it ages:

> https://www.hunker.com/12003167/tension-vs-compression-of-co...

I haven't seen any claims by qualified engineers that the spalling and corrosion described in the documents or personal reports were to a level that would risk building collapse. I've seen suggestions that the pool and parking deck might collapse, but not ones that would threaten the 40-year old columns holding up the building.

[brudgers]

Was in AEC in Florida for nearly twenty years. Started in a precast plant. During my MArch studied under one of the top forensic architects in Florida, Chuck Goldsmith, after grad school I worked as a Licensed Plans Examiner, got my Florida Architect License in 2007 - though it is currently inactive since I don’t practice there.

So yeah I do know someone with an informed opinion.

Concrete beams fail in tension. Likewise so do concrete moment connections where said beams join columns.

On the other hand columns fail by buckling when they become too slender…which is effectively what happens when a column loses steel and concrete due to corrosion and spalling.

From a personal standpoint I take the shit seriously because people might die if I get it wrong. I have been personally liable for buildings subject to salty conditions and dealt with the kind of people who would rather spend money on crown moldings than stainless steel structural components.

There is a lot of incentive to find rationales for saying the collapse is a one off.

The only unusual aspect is that it is the first. But Florida has buildings with similar issues down one side, up the other, and around the Big Bend all the way to Alabama.

I wasn’t surprised when I saw the building fell. I wasn’t surprised when I read that the first reports went back to the 1990’s. Wasn’t surprised to see the pictures from under the pool.

That’s what happens to concrete in salt air and how people ignore bad news about buildings falling apart.

The real price of fixing the problems with that building would have been comparable to building it new…hundreds of dollars per square foot not the few thousand per unit that the board was willing to spend.

No board is.

[secabeen]

> On the other hand columns fail by buckling when they become too slender…which is effectively what happens when a column loses steel and concrete due to corrosion and spalling.

Okay, great. So you're clearly more qualified than I. The above fits with my understanding too. I haven't seen reports that the columns in question were losing dangerous amounts of steel or concrete. Here is the picture from the 2018 report. Is this collapse-level amounts of spalling?

https://static01.nyt.com/images/2021/06/27/world/27miami-mys...

These are 2018 pictures, it could have certainly gotten worse. Enough to threaten the building in 3 years?

There were contractors and engineers bidding on the work for the upcoming 40-year maintenance. Would damage sufficient to threaten the building be obvious at a glance, or would that need testing and detailed analysis?

> The only unusual aspect is that it is the first. But Florida has buildings with similar issues down one side, up the other, and around the Big Bend all the way to Alabama.

This doesn't surprise me, unfortunately.

[brudgers]

See all that fairly fresh paint?

In the first picture they painted over failed concrete. The pictures are said to be “typical.”

The reasons it wasn’t evacuated at the time were business and politics not comprehensive structural investigation.

You see if the client isn’t paying to find problems below the surface, then they won’t be found. And it is common for clients to not want to find such problems. And for engineers to limit their analysis accordingly.

I know what my professional opinion would have been based on those pictures. It would not have been good for my business given the client profile.

Or to put it another way, those pictures show that what happened had a real chance of happening. That’s not hindsight. It would have caused me grave concerns.

[MertsA]

Yeah that's some pretty widespread spalling on the garage deck. Regardless of what went wrong, I'd be surprised if rust jacking or just plain section loss of the rebar wasn't a principle factor behind the collapse. All of that rebar has just been rusting for an additional 3 years since those photos were taken and it looks like the corrosion was already pretty spread out at the time and no one did anything to address it.

Tyler Ley has dozens of videos on the topic, I know I've seen a great overview of concrete deterioration but he's got so many videos I can't find it. Here's a intro to concrete corrosion though that explains some of it.

https://www.youtube.com/watch?v=mOCJFCaXN0s

[secabeen]

Thanks to both of you; this is better analysis than I've seen in other forums.

[mariuolo]

Could it be they thought they had more time to address the problem because the plans showed a different situation than it actually was?

[brudgers]

My educated guess is that there is a cadre of local engineers whose market includes similar buildings and that the deterioration was ordinary enough that the engineers could draw on years of experience to say "it is not likely to collapse because other buildings like it have not collapsed."

As I have said elsewhere, the only thing I suspect is unique is that this was the first building to spectacularly fail.

It failed with people in it because there are tremendous disincentives toward saying the sky is falling even when the sky is falling. It's bad for business and it's bad politics.

Or to put it another way, suppose it was bad design or bad soil. Do you think that the same engineers, owners, contractors, and government agents did everything right on every other building? Think of how hard it is to keep salt off of rebar during construction next to the ocean. Now do so when there is every incentive to save money and no incentive to predict catastrophe.