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.
Condo wreckage hints at less steel in columns than design drawings
61–70 of 114 posts
Re: Condo wreckage hints at less steel in columns than design drawings
#62As 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 the time though. It takes more years than this building was up though?
I know of ferro cement boats that have hollow spaces where the rebar used to be because the owner didn't know about electrolytic, and galvanic action.
(I would love to hear from an engineer, or a trades person on this. Have you ever seen rusted rebar in such a young building?)
I would not have ever thought rebar could rust that quick over pool water, or rain water though in those columns. I originally though the standing water in the basement was salt water, which might make the rusting process easier.
I am no expert. I'm not an engineer. I just know rebar can rust through in concrete. It is very rare though. I have seen one column where rust got to the rebar, and the rust went through the concrete. It was like a rust highway, and the rebar was the road. Rusted right into all the rebar encased in the concrete.
I do want to stress I have never seen a collapse like this, even when building codes were not as strict as they are now. Building codes have been very strict for probally 70 years.
I hope they don't revise building codes again unless they find the exact reason this building failed. The building codes in high rises/apartments/homes you guys live in are in many cases overkill.
Re: Condo wreckage hints at less steel in columns than design drawings
#63Earlier 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…
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 heat from the setting sun and steel that had shrunk in the chill of the night.
Incidentally, that chill is also why the 'low battery' alarms on smoke detectors tend to vexingly wake you up in the middle of the night, rather than conveniently running out in the 16 hours a day you're awake, which you might expect to happen twice as often. No, it's not just a bias that causes you to remember waking up to smoke alarm low battery chirps but not hearing them in the daytime, the electrochemical reaction in the batteries happens more readily at higher temperatures. It's a different chemistry, but the same reason a lead acid car battery has a hard time turning a starter in the dead of winter. The sensors in the smoke alarm always draw the same few microamps of current, but when it's coldest in the middle of the night, the battery is less able to meet the demand, and wakes you from your sleep.
Re: Condo wreckage hints at less steel in columns than design drawings
#64> 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…
The Hyatt Walkway collapse was a failure of communications, the problems actually building it as designed, and the importance of building as it was designed, weren't properly communicated. If anyone had the whole picture, and realized what had happened, it would have been fixed at construction time.
Re: Condo wreckage hints at less steel in columns than design drawings
#65> 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…
If the Hyatt walkway had been built as it was designed, I'm sure it would have worked fine. But was it realistic to build it as designed? The design called for something like 12 meters (12m is my estimate from it needing to span the 2nd to 4th floor) of continuously threaded rod. Is cutting 12 meters of continuous thread on one rod a realistic design? This is a real question, I don't know the answer but this seems su…
It is possible to cut a single thread 12 meters long, but it would be hard to position on the construction site.
I worked in a gear shop for 5 years, yes, threads that long can be done. I suspect it might have been cheaper to get a rolled thread in that length, rather than a cut thread. Rolled thread is likely to be stronger, as it is formed, and not cut.
Re: Condo wreckage hints at less steel in columns than design drawings
#66Rip 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.
Re: Condo wreckage hints at less steel in columns than design drawings
#67> 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…
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?
Re: Condo wreckage hints at less steel in columns than design drawings
#68Would it help to have a higher rust/concrete ratio?
Classic HN response: "Should have built it in Rust."
Re: Condo wreckage hints at less steel in columns than design drawings
#69Where 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 type of plumbing application necessary.
No one knew how it happened, how inspections could have signed off on the discrepancy. Everyone from that time was gone, and the construction company was a ghost. It's unclear if it was incompetent oversight that allowed the contracter to cut corners or something more "inside job" in nature.
Re: Condo wreckage hints at less steel in columns than design drawings
#70> 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…
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…
The 1978 Citigroup Center engineering crisis is a good teaching tool. The chair of my Uni's Mechanical Engineering department has gotten a good amount of engineering colleges (mainly Mechanical and Civil) to use it as an example/study for students first semester.