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.
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]
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.
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.
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."
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?
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.
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/
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.
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.
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?
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.
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?
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.
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.
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
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.
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.
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.
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.