In San Francisco, a Sinking Skyscraper and a Deepening Dispute | Hacker News Reader

In San Francisco, a Sinking Skyscraper and a Deepening Dispute

nytimes.com

130 pointsBinaryIdiot52 comments

It's leaning 6 inches so I'm assuming it's going to continue to lean further and further each year unless they make modifications to the building (so lopping off the top 20 floors or whatever else that could fix or mitigate it). At which point does it lean far enough that they have to demolish the building? At which point does the entire building become a safety issue should an earthquake (or even "the big one") ever hit?

Working in the city these tall buildings going up kinda worry me with the area being prone to earthquakes. I'm not a structural engineer so maybe my worries are misguided but they're there.

My thoughts as well. Does anyone here have any insight on if it's misguided to worry here? Second, what exactly, if anything, can be done to fix the lean, or prevent it from leaning any further?

Depends on what your worry is. It can lose value. There are many options to keep it straight but they all come with some disadvantages. Worst case you build something next to it and tether them together.

You can't really build anything next to that building. It's surrounded on three sides by major thoroughfares and a brand new terminal on the fourth.

Tall buildings built to seismic code are some of the safest structures to be in in an earthquake. Though you'll probably need a change of underwear afterwards: https://www.youtube.com/watch?v=NisWbAXfyWI

Holy crap you're not kidding! That's incredibly cool and terrifying at the same time! I wonder how this tower in SF compares and if it did meet seismic code, will the sinking and leaning eventually take it out of code?

A building can have a tuned mass damper[1] to help counteract the swaying. You can even turn that into a tourist attraction of sorts.[2]

[1] https://en.wikipedia.org/wiki/Tuned_mass_damper [2] https://www.youtube.com/watch?v=ohKqE_mwMmo

Taipei 101 even turned it into a mascot of sorts, the Damper Baby

http://www.alamy.com/stock-photo-damper-baby-and-tuned-mass-...

http://josellesoh.deviantart.com/art/damper-baby-292759048

I was asleep on about the 20th floor of a hotel in LA in 1992 when the 7.3 Landers and 6.5 Big Bear earthquakes hit [0]. The building (which I believe was on rollers) was rocking quite noticeably.

I wasn't afraid for myself, though by the large, low-frequency motion I could tell it was a very large earthquake whose epicenter was a good distance away. I hoped it hadn't just taken out San Diego.

Though I'll admit, to go back to sleep and then be wakened by a second large quake (Big Bear hit about 3 hours later; it is considered a separate quake rather than an aftershock) was starting to get a bit freaky.

[0] https://en.wikipedia.org/wiki/1992_Landers_earthquake

[1] https://en.wikipedia.org/wiki/1992_Big_Bear_earthquake

I can't even imagine.

My daughter was born the day a 4.0 quake hit Piedmont, CA. I was in the fourth floor of a hospital in SF. The hospital beds were rolling around and I could feel the building moving. Very humbling for a guy from Minnesota who had only experienced minor quakes that didn't do much more than make it feel like a semi-truck was passing by outside. I don't know how I looked, but the mother of my child looked over at me and was like, "that was nothing."

I was in the shower on the second floor of a house in Orange County during the second quake. That was a wild ride.

> It's leaning 6 inches so I'm assuming it's going to continue to lean further and further each year

Why? Maybe it's settling into a new spot and the leaning will taper off. I think we need to wait and see what the experts say on this.

Oh fair enough. That thought never crossed my mind. I kinda assumed if it starts leaning then gravity is only going to make it lean further. At least that's what it sounds like each time I read about it. But I don't know anything about structural engineering ¯\_(ツ)_/¯

No one really knows; it's built on landfill that used to be part of the bay and it isn't anchored to bedrock. However the rate of movement will most likely continue to slow over time and the foundation that is present will keep it from falling over anytime soon. Think Leaning Tower of Pisa, which sank and tilted slowly over many years... long enough for corrective measure to be take.

Fixing it will probably require cutting holes and driving down to bedrock, then pouring new concrete. It will have to be carefully done to avoid weakening the foundation and to make sure the new Piles don't poke through the concrete like a bed of nails.

The developer cheaped out... using reinforced concrete is less expensive than steel but it makes the building a lot heavier. Why the city let them skip out on anchoring to bedrock for such a tall building in an earthquake zone I have no idea. I do find it hilarious that all the other big towers going up are happily advertising their bedrock pillar work.

> built on landfill

Silly question, but does this mean "built on reclaimed land" in the US? Where I'm from it would mean "built on top of literal garbage."

In the US, "reclaimed land" and "on top of literal garbage" are essentially the same thing. Discussion of that very thing is in this really interesting episode of 99% Invisible from last week: http://99percentinvisible.org/episode/making-up-ground/

A lot of the "landfill" in that part of SF is rubble from the 1906 quake, which there was a lot of. They disposed of it by making the city bigger!

Expert here! We need to wait and see if the angular velocity accelerates exponentially. Until then, we can't be certain that there is any hazard. You may all go back to work now.

We'll measure its angle regularly and bill your insurance monthly until something or nothing happens.

You might be interested in the story of the Citicorp Center, a building in NYC that was dangerously susceptible to being literally blown over.

>...LeMessurier calculated that a storm powerful enough to take out the building hits New York every 16 years. In other words, for every year Citicorp Center was standing, there was about a 1-in-16 chance that it would collapse.[0]

[0] http://www.slate.com/blogs/the_eye/2014/04/17/the_citicorp_t...

They didn't even give the student recognition, sleazy basterds. Should have given her a job right away!

During hurricane Sandy I lived directly across from the Chase building in the financial district. The motion of the Chase building made me sea sick looking at how much it swayed in the wind. You could see the window shades flying back and forth, some office chairs moving around. The displacement was obvious with the naked eye, it reminded me of palm trees at the beach during high winds.

I worked in that building in 2012, and when we got back into the office later that week there were huge cracks running down the drywall from ceiling to floor.

Swaying is not necessarily indicative of a problem. The Sears Tower has a fair bit of sway as well. The general idea is "bend, don't break" and allow some give in high winds.

A lot more details in this new article:

http://www.sfchronicle.com/bayarea/article/Sinking-Millenniu...

Including comparisons to neighboring buildings with a very well done chart. And this frightening statistic:

On Friday the transbay authority released a report by the engineering firm ARUP, showing that the Millennium Tower is four to five times heavier than any other building in the area with a similar foundation, including 100 First St., 199 Fremont St. and 555 Mission St. Building weights are measured in kips — 1,000 pounds — per square inch of pressure on the soil below. The tower at 555 Mission, for example, is 487 feet tall compared with 645 for the Millennium, but it exerts 2.4 kips per square inch while the Millennium exerts 11.4 kips.

25 years ago working summer construction projects doing foundations in Siberia we were explained what depth to reach and why (permafrost etc.), and in particular we were taken on a short sightseeing tour of couple of buildings for which it wasn't done properly - the screwed geometry of those buildings one could see with naked eye from distance. I guess that tower in SF will be serving similar educational purpose for decades to come :)

In my hometown there is a building that was built in 1529 and leans more than the tower of pisa. It was intended to be taller than our rival cities tower, but it already started sagging during construction. To counteract the sagging the builders actually made kinks in the construction so next layers would be level again, but obviously this didn't help. They never got further than the base of the tower, which still stands and is a fun place to visit.

https://en.wikipedia.org/wiki/Oldehove_(tower)

Because the building sank 8 inches, did the builder subsequently need to fix they entrance to the building? Does one step down into it from street level?

So I was wondering this as well. Walking by the building I never noticed. Checking Google Maps Street View I also couldn't tell. So I'm curious how this works. It's sank a total of 16 inches; 8 of which happened after it was completed. So why does it not look funny? Am I thinking about this wrong?

No. Besides some cracks in the sidewalk you can't tell that it has sunk. (I work across the street from the Millennium Tower).

Thanks. It must have pulled down the adjacent sidewalk with it, creating a more gradual slope then.

That was the conclusion the last time this story came up a month or so ago. They've also been continually re-pouring the sidewalk concrete so you can't see the cracks.

How does this not snap the pipes going in and out of the building?

Pipes have special joints for thermal expansion compensation.

It's about to, says the article.

The city has stated that water and sewage connections to the building might soon fail depending on how much more sinking there is.

The area just outside the building should have sunk down with it.

It's kind of mind blowing that a building of this magnitude would go in a location that is bay fill in a region renowned for earthquakes, yet not have pilings going down to bedrock.

The real aftershocks are going to be the lawsuits over this.

Unless I am losing my memory, I remember learning in geology class that seismic waves travel the least in clay and most in rock.

Soil liquefaction is the real risk during earthquakes. Clay absorbs the energy and shakes a great deal more, and the soil can potentially destabilize further and allow structures to sink in.

For anyone not familiar, this is an effect where if you load wet soil just right it will break the structure of the soil grains and turn into a fluid. Demo here, you can skip the first minute if you're short on time: https://www.youtube.com/watch?v=-X9-4tWpMCo

Wikipedia has more information and some good photos: https://en.wikipedia.org/wiki/Soil_liquefaction

It's a really cool and equally terrifying phenomenon if you're used to thinking of the ground as a solid object. Plenty of videos on YouTube as well.

EDIT- Here's a car that sunk into the ground, which then resolidified around it: https://youtu.be/2WoKu5VxKgs?t=50

http://izismile.com/2012/08/31/christchurch_liquefaction_26_...

Pile foundations are impractical for much of San Francisco founded on bay mud (bedrock hundreds of feet below surface). There're other practical solutions - including soil improvement, micropiles and/or raft foundation - that have been proved capable of supporting highrises.

On a different note, a settlement (even differential) in excess of one foot is expected for a significant fraction of building stock in SF in the event of a "design-level" earthquake.

The tower is reportedly 6" out of plumb. Over its 600ft height, that's 0.08%. For perspective, it is generally accepted that construction tolerances will result in a building 1/500, or 0.2%, out of plumb at the time of erection.

Many San Francisco buildings are placed in a zone called the liquefaction zone. There are maps that show which areas will suffer liquefaction in the event of an earthquake.

Map for reference: https://www.google.com/maps/d/u/0/viewer?mid=19TDkFjIeO9wD5s...

For those curious, this is a (crappier) map of the whole bay: https://commons.wikimedia.org/wiki/File:SFBALiqufactionMap.j...

Hi-res PDF of that bay map: http://pubs.usgs.gov/of/2000/of00-444/of00-444_8b.pdf

Conveniently, the Millennium Tower is in the middle of it.

This exact same thing is happening in Oslo.

All of the new skyscrapers downtown around the opera house are sinking into the ground, and new construction is making the situation worse.

Curiously I can't find any articles about this in English, but here is one in Norwegian.

http://www.tu.no/artikler/bjorvika-synker/231007

Last time this was mentioned on HN, someone asked me to go take pictures of the building. I did:

https://www.flickr.com/photos/vonguard/albums/72157672701771...

You can see the bowing of rht sidewalk outside, and where the foundation is breaking away from the ground.

I find it amazing that an earthquake prone city had no requirements for building a skyscraper in a reclaimed soil area needing outside verification of the engineering plan.

Anyone wish to comment on whether "lopping off the top 20 floors" is an even remotely plausible plan? It sounds completely implausible to me, but then I'm not a civil engineer.

Sounds indeed implausible but it has been done before: https://youtu.be/8_4G_8gEjng

Okay that is the coolest thing I've seen in a while. I never really thought about how you'd dismantle a building without a single demolition event. I wonder how practical / cost effectice this is in comparison.

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