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Comment by BinaryIdiot | Hacker News Reader

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.

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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...

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.

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

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

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.

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

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?

> 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.

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.

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!

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.

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