[HN Gopher] The Miami condo collapse is a devastating reminder o...
___________________________________________________________________
The Miami condo collapse is a devastating reminder of America's
landfill problem
Author : fortran77
Score : 55 points
Date : 2021-06-25 19:13 UTC (3 hours ago)
(HTM) web link (theweek.com)
(TXT) w3m dump (theweek.com)
| doggodaddo78 wrote:
| I haven't heard of any major collapses in Foster City. Plenty of
| fill there. The only collapse in recent memory was a section of
| SF that liquified in an earthquake.
|
| Maybe all buildings over 3 stories need more frequent and
| detailed periodic structural fatigue/engineering assessments, eh?
| rich_sasha wrote:
| Warsaw in Poland is built on sand. Everything moves, buildings
| subside, but don't collapse out of nowhere.
|
| Seems like building on unstable land is a bit of a solved
| problem.
|
| Of course very sorry for all the victims and their families, no
| matter what the root cause.
| throwawayboise wrote:
| Agree. Unstable land/foundation may be a contributing factor
| but my guess is that shoddy/cheap concrete work will be the
| root cause.
| genocidicbunny wrote:
| Shoddy concrete work seems to be a running gag in the south.
| I had a related experience when the NOLA Hard Rock Cafe
| collapsed onto the street seconds after I walked down said
| street. It wouldn't surprise me if the concrete work in the
| collapsed condo was of a similar (lacking) level of quality.
| gerdesj wrote:
| If you mean this: https://en.wikipedia.org/wiki/1031_Canal
| that is rather different - a non catastrophic, partial
| collapse of an unfinished structure. This was a
| catastrophic collapse of a well used structure. People died
| in both so please don't think I am trivialising the NOLA
| tragedy but it was different.
|
| When you use concrete in large amounts you take standard
| samples called cubes as you pour and these are subjected to
| standard tests. In the UK we use a 10x10x10 cm cube and
| then it's allowed to cure for a standard time in standard
| conditions and then crushed. There's a bit more to it than
| that but basically, it is quite easy to demonstrate
| "standard" concrete and there is not much money to be made
| with rubbish materials. There are exciting possibilities
| involving admixtures but that is down to workmanship.
| Shoddy concrete (whatever that is) is very unlikely but a
| popular meme.
|
| Conc. for a structure like that may be pre-stressed or at
| least reinforced. Pre stressed is where you put rods or
| creatively shaped steel through it and literally squeeze
| it. Conc is great in compression (pushed/squeezed) but
| rubbish in tension (pulled apart). Imagine a beam supported
| at both ends and think of pushing down on it in the middle.
| It will try to bend in a curve. The top surface will try to
| get smaller and hence is in compression and the bottom will
| try to stretch and is in tension. If you drill a hole along
| the length of your beam near the bottom and stick a steel
| rod through it and put some washers and nuts on and crank
| on some compression you now have a sort of model for pre
| stressed concrete. The steel rod is ace in tension and
| gives the concrete beam a lot more strength. Embedding
| steel mesh ("rebar" or reinforcement bars and the like)
| have a similar effect but ...
|
| The thing about pre stressing over adding mesh/rebar is
| that you are locking away a huge amount of energy into a
| static structure. There is a huge gain to be had in reduced
| thickness of conc and hence weight which means its a double
| win but you also need to ensure that the "rods" (in our
| model, not quite reality) never fail. If they do fail then
| it's normally rapid not just a gradual fail. The effect of
| prestressing can happen by accident in "normal" meshed
| conc. Most digger drivers that have used a pile driver
| attachment to break large chunks of conc. will have tales
| to tell of large lumps of conc suddenly exploding.
| Fishermen often tell tales of the one that got away ... 8)
| However it can happen.
|
| So I hope I've shown that shoddy concrete itself is
| unlikely. There are far more ways for a structure to fail
| than that. Workmanship is possible but for my money the
| ground basically dropped away from under the structure and
| it sort of exploded and imploded simultaneously. I can't
| put this any other way but it seemed to fail completely in
| every way possible, simultaneously.
|
| It is the most horrible thing to watch and will haunt us
| forever.
| gerdesj wrote:
| It would be quite hard to fake enough cube samples for that
| and unlikely to be worth the bother. The steelwork failing is
| more likely. Pre-stressed conc is basically an explosion
| waiting to happen, which makes demolitions interesting.
| Another possibility is concrete cancer but the map cracking
| is well known and easily recognised. That last is unlikely
| and easy to rule out with some simple chemistry. However,
| Miami is on the coast so the extra ingredients are there.
|
| There are loads of possibilities but at the moment I think
| foundation failure is most likely. Unless you pile down to
| bedrock or build a gigantic raft of conc. then you need very
| stable land for a building that size. Another other option is
| to build it flexible but that was obviously not the case. The
| geology there is likely to be a nightmare. Miami is a lot of
| reclaimed land, low lying and next door to the Atlantic.
|
| The sight of the collapse is something I won't forget in a
| hurry. The secondary collapse on the right in the security
| camera footage took about three seconds. That's insanely
| fast. The failure was absolutely catastrophic. It wasn't
| simply a cascade - the whole structure seemed to fail
| simultaneously from top to bottom and that is not normal.
| odiroot wrote:
| Sand on the upper layers. There's a lot of tough stone beneath,
| which made our underground system quite hard to build.
| gnicholas wrote:
| Fun fact: Sand Hill Road in Menlo Park has issues like this as
| well. I looked at a house that had been freshly-painted before
| being put on the market, and it was flawless in the pictures.
| But by the time I saw the home in-person several months later,
| there were huge cracks in the paint in many of the rooms.
|
| When I asked the realtor about it, she just said, "there's a
| reason it's called Sand Hill Road".
| 01100011 wrote:
| Depends on the degree of movement. My friend in Pasadena bought
| a house on an old stream bed. Now the house needs to be jacked
| up.
|
| Look at the land around Portuguese Bend in Los Angeles County.
| The water line is above ground because the pipes break if
| they're buried(that's a lot of movement though).
| saltedonion wrote:
| It's probably more likely that salt air corroded the steel
| rebars. This is a known issue.
| tomarr wrote:
| Is it? Spalling is usually noticed a lot more, you would
| probably see some yielding or signs of progressive collapse
| first.
|
| The pictures I have seen make foundational failure look more
| likely.
| saltedonion wrote:
| https://www.wsj.com/articles/what-we-know-about-the-miami-
| ar...
|
| Talks about it in this article
| [deleted]
| musicale wrote:
| Reminds me of San Francisco's massive liquefaction zone.
| grp000 wrote:
| Is that related to the Millennium Tower sinking?
| Scoundreller wrote:
| I'm going to wait for AvE's foul-mouthed explanation of what
| happened before listening to anyone else's.
|
| Here's his video on Miami's bridge collapse in 2018:
|
| https://youtu.be/KtiTm2dKLgU
|
| Written about here: https://www.miaminewtimes.com/news/fiu-
| bridge-collapse-myste...
| MattGaiser wrote:
| This seems highly speculative at this point.
| tolbish wrote:
| That was my initial reaction but the second paragraph makes the
| author's case.
| gumby wrote:
| I don't think so; the article correctly starts with the
| collapse but doesn't jump to a single-issue conclusion, then
| cites notable other examples including the Kansas Osaka airport
| and San Francisco
| dyingkneepad wrote:
| Let's start some conspiracy theory fake news right here right
| now: Big Condo took down this building down so the value of every
| property around it would plummet for a few years, giving them the
| opportunity to buy everything around it and sell years later when
| the value moves back to normal.
|
| Let's see how long it takes until my aunt shares this with me
| over Facebook :).
| ehw3 wrote:
| Frankly this is a pastime of mine. Whenever anything even
| vaguely mysterious comes up in the news I make up conspiracy
| theories to tell my wife and laugh about, always leaving it
| slightly vague how serious I might be, just to keep her on her
| toes. :)
| [deleted]
| sbierwagen wrote:
| Miami Beach is at sea level. It already floods during high
| tides. There aren't too many years of property value left.
| sokoloff wrote:
| Why does the HN headline say "landfill" while the original
| article says "artificial land"?
|
| To me "landfill" implies trash/refuse disposal and "artificial
| land" implies infill of formerly wet/low areas. Not nearly all of
| the latter is the former.
| fortran77 wrote:
| Title character limit. I posted the link and did my best.
| saltedonion wrote:
| Could have remove the "the" or subbing American with "us" lol
| ortusdux wrote:
| It seems to be a language issue. A 'landfill' is a trash dump,
| while 'land fill' is a form of reclamation.
|
| https://en.wikipedia.org/wiki/Land_reclamation
| antognini wrote:
| It's an unfortunate name collision, but landfill is frequently
| used to describe "artificial land" as well as a dump site.
| initplus wrote:
| Article says that some reclaimed land was filled with literal
| dumped trash in the past.
|
| "At worst, they are made by throwing some dirt over the top of
| a pile of garbage, and building more city on top of it"
| dragonwriter wrote:
| I suspect the HN headline, the URL slug, an (from those two, I
| assume) the original source headline befoe a correction all
| result from someone using "landfill" where just "fill" or "fill
| land" (which is the relevant kind of "artificial land") would
| have been accurate.
| [deleted]
| greyface- wrote:
| The URL slug says "landfill", too. The title was probably
| changed by the publication after it was published.
| fpoling wrote:
| The article implies it was sort-of landfill:
|
| This literal trash foundation is unfortunately how big parts of
| numerous American cities have been built.
| rsj_hn wrote:
| Not only American cities. If you talk to any archeologist,
| they will attest that building cities on trash is common all
| over the world.
| piinbinary wrote:
| Do building designs have to be certified in a way similar to how
| cars have to be crash-tested?
| Rapzid wrote:
| Yes
| cardiffspaceman wrote:
| I believe a Professional Engineer with correct certification
| has to sign off on if you go above two stories, before the
| authorities will allow it to be built.
| ska wrote:
| This is all jurisdictional of course, but typically something
| like that. More complex the project, the more levels of
| review.
| Shadonototro wrote:
| it's none of that
|
| it's people preferred to still profit as much as possible from
| this dying building instead of renovating/repairing it
|
| that is what you get for building a civilization where profit has
| higher priority than safety of your people
| sonicggg wrote:
| What's the point of reclaiming land in a country that has vast
| amounts of land to be used, like the US? I can understand why
| Singapore does it.
| ska wrote:
| All land is not of equal value.
|
| Coastal land near ports and rivers, is particularly rare.
| massysett wrote:
| The vast amounts of land are in boring locations, like Kansas
| prairie, not near the beach in Miami.
| cardiffspaceman wrote:
| Location. It's no different from Singapore. The people
| accomodated by any reclaimed land of Singapore could always go
| somewhere else.
| melling wrote:
| A landfill is where trash goes.
|
| https://en.wikipedia.org/wiki/Landfill
|
| Parts of Boston and Manhattan are built on reclaimed land.
|
| https://www.nationalgeographic.com/culture/article/Boston-la...
|
| https://gizmodo.com/watch-new-york-city-s-boundaries-expand-...
| ortusdux wrote:
| Per https://en.wikipedia.org/wiki/Land_reclamation, landfill !=
| land fill.
| ycom13__ wrote:
| Same is true in the Netherlands
| ajsnigrutin wrote:
| 2mm/year sounds like a very small number to me... compared to eg.
| thermal expansion during day/night and summer/winter cycles, that
| is practically zero, and even after 40 years of sinking, surely
| there'd be massive warning signs (eg. growing cracks) before such
| a collapse.
| tmh88j wrote:
| > surely there'd be massive warning signs (eg. growing cracks)
| before such a collapse.
|
| There were. I'm not a civil/structural engineer and I don't
| know how common this kind of thing is.
|
| > One condo owner sued the unit association for failing to fix
| the cracks in the outside wall of her unit in 2015, according
| to a lawsuit filed in Miami-Dade County. The condo owner, who
| could not be reached for comment, said the cracks led to water
| damage that cost $15,000. The court documents noted that
| because the cracks were a structural issue the building
| association was liable for the expense.
|
| > The condo owner had previously filed a lawsuit against the
| building association in 2001 due to a similar issue. The two
| sides settled outside of court, but that kind of cracking is
| described as "of interest" in the county's Structural
| Recertification Form.
|
| I read another article about a resident complaining about
| cracking near the pool deck.
|
| https://www.nbcnews.com/news/us-news/cause-miami-condo-colla...
| btilly wrote:
| The problem is that the 2mm is probably not even over the
| building. If one corner is subsiding significantly more than
| the other, eventually one corner of the building is being held
| up by shear forces from the rest of the building. But concrete
| isn't very good with handling shear stress. So then it breaks,
| drops, hits the ground and you have a building collapse.
| rmason wrote:
| The collapse may be as much a local government failure as
| anything else. The building was constructed in 1981. By the early
| nineties scientists found the building was sinking at what they
| called an 'alarming' rate.
|
| What was the problem? Local government rules stated that
| foundations were inspected every forty years. So the first
| inspection of this building was 2021 and had just begun when it
| collapsed.
|
| Why not inspect building foundations every twenty years (or
| sooner) if significant sinking was found?
| gerdesj wrote:
| "The building was constructed in 1981 ... building was sinking"
|
| Sinking isn't always a problem - look at Venice! I studied Civ
| Eng at Plymouth Poly (now a university, Devon not MA) back in
| 1989ish. Back then concrete cancer was all the rage ... and
| gabions (but I digress.)
|
| The failure of the building in Miami was catastrophic and not
| gradual. I don't think that monitoring would have worked but it
| is possible that stresses/strains built up over time - we'll
| have to wait and see. If it was gradual then there is a good
| argument in favour of fitting buildings like that with strain
| gauges as many bridges are. I do a lot of IoT stuff and I
| estimate that something like PS20,000 would get you strain
| gauges and a monitoring system for a structure like that. It
| might be PS10,000 or PS100,000 but a building that size in
| Miami is worth quite a lot. I'll bet rent on a flat was
| something like $2,000pm or more.
|
| Inspection of foundations is a tricky one. I am not a Civil
| Engineer but I trained for it but I don't have X ray eyes and
| nor do Miami's engineers. That's absolutely the wrong way to go
| about this sort of thing. I'm not even sure what an
| "inspection" even means.
|
| There was a fundamental error made at the initial design stage
| in my opinion. I don't know what but probably relating to the
| parameters of the ground that was built on. By that I mean that
| the architects/struct engrs. were promised certain properties
| of the geotechnics/geophysics - that basically means they were
| told how the ground would work in holding their structure up.
|
| When you design a structure, it needs to support itself and
| crucially, the thing it sits on needs to be able to support
| that structure. You also have to work to a timespan, so you use
| standard tables for wind strength, earthquake etc. You work to
| a 1 in n years events.
|
| This building collapsed catastrophically in seconds without
| warning. I think this will become a real lesson for Civ Eng and
| not a simple "I told you so" thing and certainly not "shit
| concrete".
| timbit42 wrote:
| Money.
___________________________________________________________________
(page generated 2021-06-25 23:02 UTC)