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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

#81

Post by analog31 »

xrd wrote: post #61

There are lots of comments on HN over the years lamenting the cost of building infrastructure in the US, compared to China or elsewhere. I'm genuinely curious if this kind of corruption described in this article would be more or less common in China, or if this practice is rampant whenever you have construction projects anywhere in the world.

It doesn't seem to be all that uncommon to read about a building collapse, or fire, somewhere in the world. Invariably one learns about some kind of corruption in the process.

Fortunately the cases I know about haven't been life threatening, but there have been road construction projects in my town in the US, that had to be torn up and re-done at the contractor's expense because they missed some crucial specification such as the required thickness of the materials, and the roads started to crumble and buckle.

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

#82

Post by aaron695 »

Scoundreller wrote: post #60
aaron695 wrote: post #51

Earlier quoted context omitted.

I'm not a fan of the "Hyatt walkway collapse" as a teaching tool. The mathematics is extra interesting. Not sure it's good for the design failure which people reference. More people die from bad insulation design each year, it's the boring stuff that matters. The Hyatt walkway collapse was at a big dance party with a fair few people watching from above. Perhaps dancing? I-35 bridge collapse was rush hour. What's the…

> What's the peak here? Why 1am? I wondered this too. Maybe contraction or rate of contraction? Sun has gone down, outdoor temperature is dropping, max heat radiation out if the sky is clear, and everybody is home so A/C is on in all units.

The coldest is a bit after dawn. So the previous dawns should have stress tested it. It should fail when the stress is around maximum under this Hyatt peak theory.

Max rate of change of temperature is sunset and sunrise. Rate of contraction I'd expect similar?

I'm not sure AC would change the thermal mass of a building much. One cubic meter of air weights 1.2kg. Changing the concrete walls would be hard.

A drunk hitting a pole at speed in the carpark would fit perhaps. Drunkenness to an empty carpark would be high.

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

#83

Post by TheSpiceIsLife »

LeifCarrotson wrote: post #63
grogenaut wrote: post #52

Earlier quoted context omitted.

If the peak was actually a trigger, in a residential building 1am is about the start when the max people other than a party will be there (everyone back from clubs)

It's also approximately the time when the building will be coldest. If there were any thermal expansion/contraction issues, they would have been at a maximum near 1am. The thermal expansion and contraction of concrete and reinforcing steel are nearly identical, but the steel has much higher thermal conductivity and cools off far faster; perhaps something snapped under tension between concrete that was still holding h…

Wouldn’t the coldest part of the night typically be immediately before sunrise?

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

#84

Post by sjg007 »

sandworm101 wrote: post #66

Rip open any building short of a nuclear reactor complex and you will find such differences. Nothing, ever, gets built exactly as planned. We have only a few photos, blurry ones at that. Hold off on the conclusions until reasonable evidence emerges.

Are you suggesting it’s ok for the contractor to not follow the plans?

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

#85

Post by ggcdn »

politelemon wrote: post #4

The design drawings being referenced. Are they public documents, or I suppose I'm asking, how did those engineers get a hold of it? Can I, a public person get it? This isn't something I've thought about until now, are all buildings' drawings available at some... Central authority, an archive?

In this case the city proactively made all its files available for the building.

In general, that doesn’t happen (perhaps in Florida it does, I have no experience there). But most cities will only release their record drawings if you have permission of the owner.

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

#87

Post by sgc »

hellbannedguy wrote: post #62

As a former Contractor, and union electrician, who has worked on condos, pretty much just like this building in San Francisco for years; I can honestly say this is Very unusual. Personally, I have a feeling it might have been rusted rebar in the basement that caused the accident? Rebar can completely rust through, even encased in concrete if continually exposed to water. This happens only a very small percentage of t…

It's not that rare, I see it several times a year.

It is presumed that all foundation bolts are shot after about 50 years on any foundation in terms of their seismic performance. If you pull out an old foundation from say the 1950s, the bolts are almost invariably either totally corroded through or just a thread in the middle.

For a building basically sitting in saltwater, I would expect there to be widespread reinforcing steel failure at that age without proof to the contrary. Which is certainly one of the big reasons why they require recertification, although obviously the 40 year recertification schedule has proven to be woefully inadequate.

This will probably not wind up being more interesting than a failure to have rigorous enough inspection schedules and people dragging their feet to do what obviously had to happen. Those items appear far more important that the somewhat reduced amount of reinforcing steel compared to drawings at this point. It seems like relatively pedestrian negligence.

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

#88

Post by Scoundreller »

aaron695 wrote: post #82
Scoundreller wrote: post #60

Earlier quoted context omitted.

> What's the peak here? Why 1am? I wondered this too. Maybe contraction or rate of contraction? Sun has gone down, outdoor temperature is dropping, max heat radiation out if the sky is clear, and everybody is home so A/C is on in all units.

The coldest is a bit after dawn. So the previous dawns should have stress tested it. It should fail when the stress is around maximum under this Hyatt peak theory. Max rate of change of temperature is sunset and sunrise. Rate of contraction I'd expect similar? I'm not sure AC would change the thermal mass of a building much. One cubic meter of air weights 1.2kg. Changing the concrete walls would be hard. A drunk hitt…

> The coldest is a bit after dawn.

The building (and deck surface) will continue to radiate heat throughout the night on a clear night, especially with few obstructions like a waterfront building has. That's how crops can frost with airtemp > freezing, and why the guidance is to cover your plants. It's not to insulate them against convection.

Counterintuitively in this scenario, this effect is greatest when the wind is calm.

https://en.wikipedia.org/wiki/Radiative_cooling#Architecture

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

#89

Post by x0x0 »

xrd wrote: post #61

There are lots of comments on HN over the years lamenting the cost of building infrastructure in the US, compared to China or elsewhere. I'm genuinely curious if this kind of corruption described in this article would be more or less common in China, or if this practice is rampant whenever you have construction projects anywhere in the world.

Is there a reason to jump to this was corruption, rather than a fuckup? When you look at the price of rebar per linear foot, this doesn't seem like the first place I'd look to cut costs.

A fuckup aggravated by what seems like not particularly aggressive maintenance of the structure generally.

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

#90

Post by mariuolo »

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…

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