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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

#71

Post by s5300 »

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…

>"why now, after 40 years?"

Huh? Cyclic fatigue yo. Incredibly simple and well known killer.

Less whatever type of supports than spec'd to distribute the fatigue across, earlier things fall apart or break from it.

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

#72

Post by throwawayboise »

aaron695 wrote: post #42
slipframe wrote: post #23

Earlier quoted context omitted.

> 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 builder…

It was 1979. The height of Mafia control over large building projects especially anything using cement. I would be totally unsurprised if corners were cut to reduce costs and pad the pockets of some capo who was running the union on that job.

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

#73

Post by XorNot »

secabeen wrote: post #35
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

That's an interesting theory that I hadn't seen before. It would require the horizontal rebar in the pool deck to be strong enough that it could pull over the columns, which contrasts with that rebar also being weak enough to collapse. Likewise, in this scenario, would there still be punch-through columns in the parking deck area, instead of those columns falling over too? The other question that obviously follows fr…

Steel is strongest in extension, and a horizontal pulling moment is going through the cross section of the rebar rather then perpendicular to it.

The rebar would have different load bearing capacities in different directions, particularly if it was rusting (i.e. most likely the corrosion was principally on the top face).

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

#74

Post by mikewarot »

Looking at the photo of the column, I see 3 of the 4 rods in one direction (the side labeled 72) 2 sticking out of the column, can't see the 3rd one presumably sheared off, and the 4th obviously slid down the column, and is the loop sticking up, and 4 of 4 in the other, labeled 73.

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

#75

Post by brudgers »

ineedasername wrote: post #69

Where I work an old building had massive plumbing problems for years-- flooded floors. After it happened a few times someone went back to the original plans to see if it might reveal the cause. They were shocked to discover it specified & contracted to have copper pipes. The building had PVC instead. And engineering firm was brought in to make an assessment and determined that the PVC used wasn't even rated for the t…

My William of Occam hat says most likely the Owner approved the change. Shaving money from the materials budget saved money.

So yes an inside job as inside as inside can be.

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

#76

Post by brudgers »

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.

In salty environments, exposure to the weather tends to allow rain to wash away salt. Semi- exposed areas tend to fair worse for corrosion due to the absence of scouring by rain.

A bit counter intuitive.

But that’s building by the sea. Salt can be deposited by mist and chloride ions are the nemesis of reinforced concrete.

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

#78

Post by icegreentea2 »

ianai wrote: post #67
icegreentea2 wrote: post #32

Earlier quoted context omitted.

The Hyatt walkway collapse could be interpreted as you said, but I think the specific phrasing ("built another so it would be easier and cheaper to build") shifts the blame onto suppliers and manufacturers a bit too much. The wiki article states that the architectural/engineering firm signed off on the suggestion of their supplier/manufacturer. While yes, it's easy to point the finger at cost cutting, we should also…

Can you come up with some examples that you’d grade well?

Not really off the top of my head, especially in North America.

I suspect you if you really go through (https://www.osha.gov/construction/engineering) you'll find some good examples of construction time problems. By it's nature, the vast majority of these are going to be "during construction time", so it'll be biased. They're also typically smaller scale operations... but that's also reflective of reality. Most construction is not the scale of 100+ unit condo buildings.

From my skimming through it there's a pretty even mix of:

a) Designer dominant (note there are a significant number of so called "design-build" entities present as well).

b) Construction/contractor supervisor/company dominant

c) Construction/contractor crew on the ground dominant

The NTSB also has a set of building related investigations to read through. Unfortunately, I seem to be having problems figuring out their search.

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

#80

Post by shados »

ineedasername wrote: post #69

Where I work an old building had massive plumbing problems for years-- flooded floors. After it happened a few times someone went back to the original plans to see if it might reveal the cause. They were shocked to discover it specified & contracted to have copper pipes. The building had PVC instead. And engineering firm was brought in to make an assessment and determined that the PVC used wasn't even rated for the t…

This is unfortunately very common. The building I live in is not that old (about 15 years. I moved in 10 years ago).

We have the original plans, which were somehow never registered with the city (which has been part of the permitting process for buildings of this size since long before it was built). The codes to the fire alarms were never registered with the fire department (also a requirement). A lot of extremely visible features, like stairways, are not up to code. Every time we fix, rebuild or renovate anything, we find the builders didn't just ignore the plans here and there: they may as well be plans for a different buildings. Nothing matches except the floor plan and the amount of units/stories.

Yet the permits are on file and were all signed on. Somehow when we try to get permits for anything, the processes are INCREDIBLY strict, stricter than in any other city I've lived by an order of magnitude. But somehow, for this building, there's very nearly more violations than there are things done kosher.

It's not an isolated incident either...that shit happens everywhere. Inspectors get paid, turn a blind eye, profit.

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