San Francisco high-rise sinking, tilting

[Poolio]

But not completely unprecedented:

Ocean Tower - Wikipedia

en.wikipedia.org

The Harmon in Las Vegas is another interesting story. "Completed" in 2009 but never occupied. It was originally intended to be 49 stories but cut back to 28 when construction defects were found. It was deemed unsafe anyway though, and they ended up demolishing it just a few years later.

 

[theSil]

Excellent video trending on YouTube explaining the construction of Millenium Tower and how they're trying (and failing) to right it now. Probably nothing eye-opening if you've been following closely or are in the construction trades, but extremely interesting as a layperson.

One thing I still don't understand is that at 5:32 the video states that the building has settled 17 inches, more than 3 times than what was expected over the building's lifespan, and is out-of-plumb by over a foot. Yet, the narrator says that one probably wouldn't notice this with their naked eye. How can a building settle about a foot more than expected, unevenly, and it not be noticeable to someone on the sidewalk? Is there not a step-down created? I must be misunderstanding something.

 

[393b40]

I must be misunderstanding something.

Geometry. Think about a right angle, now think if you make it an acute or obtuse angle... the top of the line will be much much further out than the bottom depending on the height of the line.

 

[theSil]

Geometry. Think about a right angle, now think if you make it an acute or obtuse angle... the top of the line will be much much further out than the bottom depending on the height of the line.

You're describing the building being out-of-plumb by a foot. I understand how that would be imperceptible from the sidewalk because for a 600-foot tower like this one, that means it's now making an 89.9-degree angle with the ground.

What I don't understand is how a building settling 17 inches into the ground , about a foot more than expected, is imperceptible. Wouldn't there be 12-inch step down when entering the building now? Do engineers design buildings of this size with the expected amount of settlement "built-in", such that it will be level with its surroundings once finished?

 

[bigpicture7]

You're describing the building being out-of-plumb by a foot. I understand how that would be imperceptible from the sidewalk because for a 600-foot tower like this one, that means it's now making an 89.9-degree angle with the ground.

What I don't understand is how a building settling 17 inches into the ground , about a foot more than expected, is imperceptible. Wouldn't there be 12-inch step down when entering the building now? Do engineers design buildings of this size with the expected amount of settlement "built-in", such that it will be level with its surroundings once finished?

Presumably because the surrounding ground was impacted by the sinking as well. You'd have to look at the true horizontal level of the sidewalks/roads before and after. I would bet that their localized slope is different now.

 

[nomc]

Presumably because the surrounding ground was impacted by the sinking as well. You'd have to look at the true horizontal level of the sidewalks/roads before and after. I would bet that their localized slope is different now.

How would that not cause visible cracking, at least in some locations?

 

[bigpicture7]

How would that not cause visible cracking, at least in some locations?

You mean like this?

https://www.theguardian.com/us-news/2021/aug/26/san-francisco-millennium-tower-sinking

 

[nomc]

You mean like this?

https://www.theguardian.com/us-news/2021/aug/26/san-francisco-millennium-tower-sinking

I do mean like that

 

[stick n move]

SF Millennium Tower Tilts Quarter Inch in Four Days



https://www.nbcbayarea.com/investig...-tilts-quarter-inch-in-four-days/2750189/?amp

 

[stellarfun]

MT continues to tilt at a rate of three inches per year, and sink at a rate of half an inch a year. Five more years of the three inch annual tilt rate would increase the tilt to 40 inches and the building becomes non-functional.

https://www.architecturaldigest.com/story/millennium-tower-san-francisco-leaning

 

[stick n move]

I bet theyre going to have to de-construct the tower. It feels inevitable at this point. After the few examples so far in nyc and other cities its not as crazy as it once was. Theyre now saying that the sewer/water lines are going to fail and the added piles are actually making it worse so theyre adding much less. Theres really no other option but to declare it a total loss and take it down. Of course theyre going to keep bandaging it up in the mean time, but its coming.

 

[Johnnyrocket891]

I bet theyre going to have to de-construct the tower. It feels inevitable at this point. After the few examples so far in nyc and other cities its not as crazy as it once was. Theyre now saying that the sewer/water lines are going to fail and the added piles are actually making it worse so theyre adding much less. Theres really no other option but to declare it a total loss and take it down. Of course theyre going to keep bandaging it up in the mean time, but its coming.

Wonder who takes the hit on this?