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Condo wreckage hints at less steel in columns than design drawings

nytimes.com

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Re: Condo wreckage hints at less steel in columns than design drawings

#41

Post by unavoidable »

secabeen wrote: post #24

The most important section though is buried in a late paragraph: >Engineers said it seemed unlikely that having less rebar would trigger a collapse in and of itself, even factoring in significant deterioration over many years. An inherent safety factor built into most projects would mean that a slight reduction in steel content would not necessarily lead to disaster. This certainly suggests that there may have been s…

Like aircraft disasters, most civil/structural engineering disasters have more than one "cause". There is not always a satisfying answer or a single "smoking gun". A bunch of things usually have to go wrong at the same time for a building to collapse catastrophically. Building codes and engineering designs have a lot of assumptions built in, including an assumption that construction does not follow the drawings exactly. But other assumptions include lack of corrosion to a degree, regular maintenance, proper materials specifications, no subsequent modifications, a particular load pattern, etc.

Even then, most buildings are not really designed for much more than 60 or 70 years. Of course, most buildings are also supposed to be designed in such a way that even if it fails, it does not result in a cascading failure. The fact that this particular kind of disaster (apparently spontaneous collapse) is so rare is what makes it newsworthy.

Re: Condo wreckage hints at less steel in columns than design drawings

#42

Post by aaron695 »

slipframe wrote: post #23
aaron695 wrote: post #21

> less steel reinforcement in certain areas than would have been expected from the 1979 design drawings They address this later, so it's a clickbait implication. Who cares if it's different to the design, is it not enough? How does it compare to normal. Given it's a cookie cutter design the workers would notice if it wasn't enough. 20 years of pumping concrete is enough to know if it's significantly wrong. If the imp…

> 20 years of pumping concrete is enough to know if it's significantly wrong. No, that doesn't make sense to me. Concrete buildings are expected to last longer than 20 years, though not expected to last forever. If the shortcuts they take were cutting the expected lifetime of the structure in half, 20 years of experience would not be enough time to see those failures start to happen.

Sorry, I mean a high school educated concrete pumper with 20 years experience will rote learn what the standards are. So the workers should see it's less than standard.

For something to be really off standard, it has to be complex or using illegal immigrant workers or something that is hard to see, like a bad concrete mix being brought in.

It also needs a reason. The cost benefit has to be more than risk. The builders won't risk a $xx million building by saving on re-bar. A contractor might, but they'd have to get away with it.

Re: Condo wreckage hints at less steel in columns than design drawings

#43

Post by Tarball10 »

ajsnigrutin wrote: post #36
brandon272 wrote: post #11

Saw a video today of a simulated collapse that suggests a possible failure mode given the likely parking garage collapse that occurred before primary collapse: https://www.youtube.com/watch?v=hynHiWE818c

This is an interesting theory... one would wonder, how come it collapsed at the place, where it only held one slab, and not somewhere under more weight... but i'm not a civil engineer, so yeah... time (and analysis) will tell.

That area, the pool deck, was exposed to the elements. Rainwater was allowed to pool on top and seep into the concrete because it was not constructed correctly. It should have been slanted to allow water to drain off. The slabs and pillars under the actual building may have been in better condition since they were mostly protected from the weather.

Re: Condo wreckage hints at less steel in columns than design drawings

#44

Post by secabeen »

brudgers wrote: post #40
secabeen wrote: post #27

Earlier quoted context omitted.

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 mi…

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. Likew…

> 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.

Re: Condo wreckage hints at less steel in columns than design drawings

#45

Post by daniellarusso »

Tarball10 wrote: post #43
ajsnigrutin wrote: post #36

Earlier quoted context omitted.

This is an interesting theory... one would wonder, how come it collapsed at the place, where it only held one slab, and not somewhere under more weight... but i'm not a civil engineer, so yeah... time (and analysis) will tell.

That area, the pool deck, was exposed to the elements. Rainwater was allowed to pool on top and seep into the concrete because it was not constructed correctly. It should have been slanted to allow water to drain off. The slabs and pillars under the actual building may have been in better condition since they were mostly protected from the weather.

Also, once the initial shift occurred, could that have caused enough plumbing to break to begin flooding and further cause solid ground to liquify?

Re: Condo wreckage hints at less steel in columns than design drawings

#46

Post by dehrmann »

8note wrote: post #26
secabeen wrote: post #24

The most important section though is buried in a late paragraph: >Engineers said it seemed unlikely that having less rebar would trigger a collapse in and of itself, even factoring in significant deterioration over many years. An inherent safety factor built into most projects would mean that a slight reduction in steel content would not necessarily lead to disaster. This certainly suggests that there may have been s…

I am partial to the climate change theory. Rising sea level means higher soil expanding/shrinking with the tides, leading to fatigue

But we're talking 4 inches over the life of the building. I'm not sure if buildings are positioned that precisely (if I had to guess, I'd guess it's right around there), the tidal range around Miami looks like it's around 16 inches, and hurricanes and tropical storms will do much more than sea level rise.

I could be wrong, it just seems like there are bigger factors at play, and I'd be surprised that it was build so close to safety margins.

Re: Condo wreckage hints at less steel in columns than design drawings

#48

Post by dehrmann »

LatteLazy wrote: post #12

One of the worst things about these disasters is that we will get months of daily reports of things being "hinted at". All the noise means that when the final cause is found, no one will care anymore or remember or they'll remember wrong and swear it was all to do with sinkholes or whatever. We need some quite and some rapid inspection of other buildings. Not hints and opinions.

I'm mostly ignoring all the theories until something definitive comes out. All this speculation is just so media outlets can sell ads.

Re: Condo wreckage hints at less steel in columns than design drawings

#49

Post by cratermoon »

Syonyk wrote: post #9

> Mr. Kilsheimer cautioned that it is common in construction for the final product to differ from drawn designs. Yes, and there's also a decent history of structural failure, or nearly so, from that particular habit. The Hyatt walkway collapse ( https://en.wikipedia.org/wiki/Hyatt_Regency_walkway_collapse... ) is one of the better known - designed one way, built another so it would be easier and cheaper to build, and…

Don't forget the Challenger SRB failure. Flown outside of design criteria with known flaws. But each time the shuttle flew with and SRBs had burn through, it was taken to mean not that there was a problem, but that the behavior was "safe".

Re: Condo wreckage hints at less steel in columns than design drawings

#50

Post by secabeen »

unavoidable wrote: post #41
secabeen wrote: post #24

The most important section though is buried in a late paragraph: >Engineers said it seemed unlikely that having less rebar would trigger a collapse in and of itself, even factoring in significant deterioration over many years. An inherent safety factor built into most projects would mean that a slight reduction in steel content would not necessarily lead to disaster. This certainly suggests that there may have been s…

Like aircraft disasters, most civil/structural engineering disasters have more than one "cause". There is not always a satisfying answer or a single "smoking gun". A bunch of things usually have to go wrong at the same time for a building to collapse catastrophically. Building codes and engineering designs have a lot of assumptions built in, including an assumption that construction does not follow the drawings exact…

Yeah, I've read _Normal Accidents_, and I follow AdmiralCloudberg's aircraft disasters. There isn't always a satisfying answer, but there often is, or at least one factor that's most damning.
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