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"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 uni

"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 £20,000 would get you strain gauges and a monitoring system for a structure like that. It might be £10,000 or £100,000 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".

magicalist 5y ago
> Sinking isn't always a problem - look at Venice! This seems like simultaneously survivorship bias (there have been plenty of buildings in Venice that have collapsed or have been irreparably damaged) and a good example of the dangers of sinking (how many billions on repairs and massive engineering projects to save the city?)
R0b0t1 5y ago
A civil engineer told me "settlement isn't a problem, differential settlement is a problem."
- Haga 5y ago
  If that were the case wouldn't a pressure monitor system injecting hardening material be used instead of pillars?
- jaclaz 5y ago
  Yes and no. Both statements are correct, but differential settlement is not an "instantaneous" problem, when a building, particularly a reinforced concrete one, is subject to differential settlement it deforms itself following the movements of the foundations or of the soil under the foundations, and this normally allows for several centimeters of deformation (in practice a building as seen from a side is made out of squares, when the foundations on one side lower, squares become a rhomb/diamond). All the rigid elements in the plane of the square (please read as walls, be them brick or other material) are forced "out of their natural shape" and start developing cracks. Nornally settlement is a process that is very, very slow, years, months or weeks, during which the cracks begin developing, long before the structure collapses. This must have been a form of failure of the soil that happened in a very short time, more similar to a landslide than to the kind of settlement common in soils (usually sands) near a waterfront.
  - R0b0t1 5y ago
    I never implied it was a fast problem, nor did I make two statements.
    - jaclaz 5y ago
      The engineer made two statements: 1) settlement isn't a problem, 2) differential settlement is a problem. Both are correct, but in this case neither settlement nor differential settlement appears to be involved in the collapsing of the building.
mc32 5y ago
The Millennium Tower in SF has been sinking[1] since it was erected. Tenants have sued and now there is a fix proposed. It all happened because the builder didn't want to go 200' to hit bedrock and instead cheapened out. [1]https://www.sfgate.com/news/editorspicks/article/SF-s-sinking-Millenium-Tower-to-finally-get-fixed-15439863.php https://www.sfgate.com/news/editorspicks/article/SF-s-sinkin...
- ericbarrett 5y ago
  I watched them build a 22-story high rise on landfill (mud/sand) in the SOMA district of San Francisco—it was right next to my building. After demolition of the old structure (a 3-story apartment) and excavation, they did the following: - Pump water out of the excavated ground. It was a slow drain, maybe 50 gallons per minute, but it ran for months. - Drive dozens of 90 foot steel pylons into the site with an enormous pile driver. - Pour the foundation over the pylons. The Millenium Tower is more than double the height of that, at 46 stories, and it’s right by the water. But they used the same length of pylon. Mind-boggling.
  - sjg007 5y ago
    Can you build a small replica of this with a bucket of mud, sand, etc…?
- ec109685 5y ago
  This is good point. If you are willing to go deep enough, can you build anywhere?
  - ocdtrekkie 5y ago
    Technically, probably yes, but the math could get ridiculous. Essentially you want to go into solid ground, and if you're in the ocean, solid ground might be miles below sea level. And reclaimed land doesn't change that. Also, if the material higher up shifts, your supports need to be able to survive the ground shifting around it, which means you need not just depth, but girth.
slipframe 5y ago
I'm no engineer either, but it seems logical to me that a building would not even notice mild to moderate uniform sinking, but that differential sinking could split the building in half. Also, I guess that differential sinking can be detected before catastrophic failure if the sink rate were measured on two or more points on the building. If the south side is sinking at 2mm/year while the north side is sinking at 0.2mm/year, that sounds like a recipe for disaster that you don't need xray eyes to see.
brudgers 5y ago
Most likely the brittle failure was due to corrosion of the steel reinforcing. The corrosion due to chloride ion intrusion. Chloride ion intrusion because it's on the ocean. Or socially, because fixing the problem was an economic non-starter for the condo association. Or a political non-starter depending on how you squint.
- ocdtrekkie 5y ago
  I'm learning that condo associations are essentially monetizing the structure as it was built how ever many years ago, and have just about no interest in long-term maintenance or value.

magicalist 5y ago

> Sinking isn't always a problem - look at Venice! This seems like simultaneously survivorship bias (there have been plenty of buildings in Venice that have collapsed or have been irreparably damaged) and a good example of the dangers of sinking (how many billions on repairs and massive engineering projects to save the city?)

R0b0t1 5y ago

A civil engineer told me "settlement isn't a problem, differential settlement is a problem."

Haga 5y ago
If that were the case wouldn't a pressure monitor system injecting hardening material be used instead of pillars?
jaclaz 5y ago
Yes and no. Both statements are correct, but differential settlement is not an "instantaneous" problem, when a building, particularly a reinforced concrete one, is subject to differential settlement it deforms itself following the movements of the foundations or of the soil under the foundations, and this normally allows for several centimeters of deformation (in practice a building as seen from a side is made out of squares, when the foundations on one side lower, squares become a rhomb/diamond). All the rigid elements in the plane of the square (please read as walls, be them brick or other material) are forced "out of their natural shape" and start developing cracks. Nornally settlement is a process that is very, very slow, years, months or weeks, during which the cracks begin developing, long before the structure collapses. This must have been a form of failure of the soil that happened in a very short time, more similar to a landslide than to the kind of settlement common in soils (usually sands) near a waterfront.
- R0b0t1 5y ago
  I never implied it was a fast problem, nor did I make two statements.
  - jaclaz 5y ago
    The engineer made two statements: 1) settlement isn't a problem, 2) differential settlement is a problem. Both are correct, but in this case neither settlement nor differential settlement appears to be involved in the collapsing of the building.

mc32 5y ago

The Millennium Tower in SF has been sinking[1] since it was erected. Tenants have sued and now there is a fix proposed. It all happened because the builder didn't want to go 200' to hit bedrock and instead cheapened out. [1]https://www.sfgate.com/news/editorspicks/article/SF-s-sinking-Millenium-Tower-to-finally-get-fixed-15439863.php https://www.sfgate.com/news/editorspicks/article/SF-s-sinkin...

ericbarrett 5y ago
I watched them build a 22-story high rise on landfill (mud/sand) in the SOMA district of San Francisco—it was right next to my building. After demolition of the old structure (a 3-story apartment) and excavation, they did the following: - Pump water out of the excavated ground. It was a slow drain, maybe 50 gallons per minute, but it ran for months. - Drive dozens of 90 foot steel pylons into the site with an enormous pile driver. - Pour the foundation over the pylons. The Millenium Tower is more than double the height of that, at 46 stories, and it’s right by the water. But they used the same length of pylon. Mind-boggling.
- sjg007 5y ago
  Can you build a small replica of this with a bucket of mud, sand, etc…?
ec109685 5y ago
This is good point. If you are willing to go deep enough, can you build anywhere?
- ocdtrekkie 5y ago
  Technically, probably yes, but the math could get ridiculous. Essentially you want to go into solid ground, and if you're in the ocean, solid ground might be miles below sea level. And reclaimed land doesn't change that. Also, if the material higher up shifts, your supports need to be able to survive the ground shifting around it, which means you need not just depth, but girth.

slipframe 5y ago

I'm no engineer either, but it seems logical to me that a building would not even notice mild to moderate uniform sinking, but that differential sinking could split the building in half. Also, I guess that differential sinking can be detected before catastrophic failure if the sink rate were measured on two or more points on the building. If the south side is sinking at 2mm/year while the north side is sinking at 0.2mm/year, that sounds like a recipe for disaster that you don't need xray eyes to see.

brudgers 5y ago

Most likely the brittle failure was due to corrosion of the steel reinforcing. The corrosion due to chloride ion intrusion. Chloride ion intrusion because it's on the ocean. Or socially, because fixing the problem was an economic non-starter for the condo association. Or a political non-starter depending on how you squint.

ocdtrekkie 5y ago
I'm learning that condo associations are essentially monetizing the structure as it was built how ever many years ago, and have just about no interest in long-term maintenance or value.