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Millennium Tower is tilting, sinking

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Re: Millennium Tower is tilting, sinking

#71

Post by vacri »

was_boring wrote: post #37
Finnucane wrote: post #31

Earlier quoted context omitted.

Most of our big coastal cities are like that. Boston is about twice as big as it was in colonial times; all of the Back Bay is landfill. A lot of Cambridge is landfill. And yes, most of the taller buildings cluster around the more solid bedrock areas closer to downtown. But the engineering principles needed here aren't unknown--cities like Las Vegas and New Orleans have modern buildings that are much taller than were…

To add on, Chicago and New Orleans are both built on swamps, and the outer edges of New York are filled in -- making land for cities isn't the issue with the tower.

As an aside, the land in New Orleans is so flat that the zoo has a 28' hill donated by a benefactor, "so that the children of New Orleans can know what a hill is like" according to the plaque next to it. And when I visited, the kids were going nuts over this little hillock, running up and careening down it, giggling.

Re: Millennium Tower is tilting, sinking

#72

Post by zubat »

djsumdog wrote: post #17

The article doesn't talk about the how this practically affects the entrances to the building. Do the doors have to be adjusted for such a drastic sinkage, or are buildings somehow designed so this isn't noticeable to the public?

I don't know what skyscrapers do but throughout SF one can find smaller houses that have subsided. They dealt with the problem by adjusting the sidewalk and adding ramps, some of which are absurdly steep now.

Re: Millennium Tower is tilting, sinking

#74

Post by spectre »

RGamma wrote: post #65

This brings me back to a question I have frequently asked myself: What do you do with unsafe or old skyscrapers? How would you raze such a thing? What if it falls over, breaks apart or breaks in on itself (9/11 gives an idea)? To a layman (with slight acrophobia) skyscrapers seem pretty fragile, and I'd much rather have them built into the ground than towards the sky, but obviously they're holding up in general and I…

I did a bit of work on a 28 story building that developed a 1.5m lean during an Earthquake. The story of the demolition http://www.ward-demolition.co.nz/grand-chancellor/

Re: Millennium Tower is tilting, sinking

#75

Post by aetherson »

CPLX wrote: post #55
Someone1234 wrote: post #20

Earlier quoted context omitted.

Loving your attitude. I often feel like with a lot of building (big and small) there is insufficient evaluation of site factors. For example: Is there a hill above the site? THAT needs to be evaluated (sometimes they do, sometimes they don't). Is the site on a traditional floodplain? If so what actions have been taken to redirect the water flow? Does the system have the capacity to move the water away? Is the site it…

Or one could just live in a place geologically suited for human habitation, such as the northeastern United States.

Yeah, but then you'd have to live in the northeast.

Re: Millennium Tower is tilting, sinking

#76

Post by Animats »

shepting wrote: post #33
Animats wrote: post #19

From the article: "To cut costs, Millennium did not drill piles to bedrock." I'm amazed that a building of that height would be built on a slab with friction piles in the mudflat fill zone of the SF bay. How did they get a building permit for that? 16 inches of sinkage in 8 years is huge. Building sinkage isn't all that unusual, but not for skyscrapers. There was a time when skyscrapers were only built on competent r…

There's another building that was built on friction piles: http://www.aboutcivil.org/burj-khalifa-design-construction-s...

They write that the chance of ground liquefaction there is zero, since they're not in an earthquake zone. Does not apply to SF.

Re: Millennium Tower is tilting, sinking

#77

Post by wahern »

JosephHatfield wrote: post #61
wahern wrote: post #29

Earlier quoted context omitted.

I live in the Outer Richmond district of San Francisco, which was built on sand dunes. Most houses in my neighborhood were built in the 1920s and 1930s, +/- a decade. I was told by a contractor that it's extremely common for houses to have shifted considerably, sometimes by several feet. Mine certainly has, though not nearly that bad. Most of the houses are built on concrete foundation walls that go about 3 feet into…

The city is currently requiring many owners of soft story buildings in the Outer Richmond district to pay for seismic refitting.

Only those buildings with 5 or more units, which is only a tiny fraction of the structures. Ideally it should be every building, but it's ridiculously expensive to install moment frames, which is pretty much what every house needs given the typical layout of the houses. Each installation costs between $30k to $50k, and as well-off as you need to be to afford to purchase in San Francisco, that's still an expense few can justify even if they could afford it.

We had structural plywood sheathing installed in our garage, and the typical job is around $10k. The pre-existing sheathing was installed by [presumably] a fly-by-night contractor shortly after the 1989 earthquake. Fortunately I noticed that it wasn't installed correctly and used the wrong materials, and so it was basically useless. But given that the garage door, garage side entrance, and entryway make up greater than 80% of the front wall of our first story, that we have a big window and door on the back wall, there's not much room for sheathing (properly installed or not) to control movement along that axis. The house is now very unlikely to collapse into the street, but we're still lucky to be sandwiched between two other houses. Fortunately, our neighbor on the corner had his foundation rebuilt and a third structural wall installed. I should probably be remunerating him somehow.

Re: Millennium Tower is tilting, sinking

#78

Post by nostromo »

dpark wrote: post #57
Nuffinatall wrote: post #40

Pretty sure they need to safely dismantle this building and try again. In non-earthquake prone areas, it might make sense to jack it up and what not, but not in SF.

There is no scenario in which a 350 million dollar skyscraper deemed "not a safety issue for residents" will be torn down so they can "try again". They'll find a way to stabilize it and that will be that. No one is going to tear down nearly half a billion dollars worth of skyscraper if there's any chance of salvaging it.

It's not without precedent.

In Seattle a cost-cutting method was used to build a 25-story downtown apartment building in 2001.

In 2010 it was found to be flawed and unfixable, and so it was dismantled.

And now there's a new building being built on the site.

http://www.seattletimes.com/seattle-news/9-year-old-belltown...

Re: Millennium Tower is tilting, sinking

#79

Post by jondiggsit »

WalterBright wrote: post #7

My house is on a steep hill, and Seattle has a reputation for hills sliding away under heavy rain. Before building it, I hired 3 separate geologists to evaluate the site. After digging holes, they said the site was sitting on "glacial till", which is clay that was compacted by about a mile of ice, and said there was nothing to worry about. Paying them was worth it for the peace of mind. (Turns out the till was so har…

I, for one, would rather be building on sand rather than clay. Clay is an absolutely terrible substrate for construction. Not to mention it does not drain. Hills don't become saturated with water... the water tends to flow to ze bottom of ze hill, where it will saturate things. I'd be curious to know what exactly you are draining into... drywells and clay are not friends.

- High-end residential builder here

Re: Millennium Tower is tilting, sinking

#80

Post by JonRB »

RGamma wrote: post #65

This brings me back to a question I have frequently asked myself: What do you do with unsafe or old skyscrapers? How would you raze such a thing? What if it falls over, breaks apart or breaks in on itself (9/11 gives an idea)? To a layman (with slight acrophobia) skyscrapers seem pretty fragile, and I'd much rather have them built into the ground than towards the sky, but obviously they're holding up in general and I…

As a fellow layman I imagine that's where incredibly skilled demolition work comes in. There are some wonderful videos of very precise building demolitions out there.
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