I was surprised to learn that the codes and engineering requirements are specified strictly to avoid loss of life.
The buildings themselves are not required to survive in habitable fashion.
I was surprised to learn this and it disturbs me to consider that while a major earthquake in the SFBA might be (relatively) free of fatalities, an enormous portion of the built infrastructure would need to be demolished and rebuilt:
"The code also does not specify that a building be fit for occupancy after an earthquake. Many buildings might not collapse completely, but they could be damaged beyond repair. The interior walls, the plumbing, elevators — all could be wrecked or damaged."[1]
[1] https://www.nytimes.com/interactive/2018/04/17/us/san-franci...
This is the norm for the pacific rim. It's just not economically viable to build for longevity in the face of tectonic movement. Saving lives however? We know how and those cities and citizens at risk that don't invest pay terribly for it. Given what we know about quakes these days, it's inexcusable any civil infrastructure or building should lead to loss of life.
But if you think about the nature of earthquakes, it starts to make a little more sense. There is basically a probabilistic distribution of earthquake frequency and energy. The more powerful the quake, the less frequently it occurs, and there is a long tail to this distribution. So we need to draw a line in the sand somewhere and say “we will design for X, and detail the structure to avoid collapse if X is exceeded.” There is no such thing as an earthquake proof building, because there is always a bigger earthquake than the one considered for design. All we can do is play with probabilities.
In the US the life safety objective corresponds to earthquake hazard of 10% probability of exceedance in 50yrs. The industry has long accepted this as a good X point that balances construction cost and longevity. But more recently, with ballooning recovery costs in recent earthquakes, some are starting to see its not enough. For instance, in the Canterbury NZ earthquake many structures performed “well” and met their design intents, but around 70% of the downtown ended up being demolished. Insurance deemed them too costly and risky to repair.
Now industry is starting to use “performance based design” more often for seismic design of tall buildings (including the Millennium tower). It allows you to pick multiple hazards and set different objectives for them. For instance, we might say no damage allowed at 30% in 50yr hazard, cracking and light damage at 10%/50yr, and no collapse at 2%/50yr hazards. Then we do a bunch more sophisticated modelling to demonstrate the design meets the objectives. I wrote a little bit more about performance based design here :
https://kinson.io/post/what-is-performance-based-design/
Unfortunately it didn’t help the millennium tower with this geotechnical issue. Which I suppose says something about design being only as good as the input assumptions.
Imagine being tasked with identifying a famous painting, But you aren’t allowed to see the painting. You are provided with the five predominant colours in the painting, the type of paint used, and a 10mm x 10mm sample of the painting.
Now, please tell me the name of that painting?
Too many people think it's about "strongest" or "best" or "creative" or "durable" designs. Nope. Sometimes that's true, but it's always about controlling your failure modes.
Cars are designed to absorb energy during a major impact. They do this by folding in places that preserve the integrity of the passenger compartment. As a result, minor impacts result in the total loss of the vehicle.
If you read the building code (I have), sudden collapses are something that need to be avoided at all cost, think the recent sky scraper in Florida.
Restoring a structure instead of rebuilding after damage puts a lot of responsibility on the Civil Engineers because ultimately they are the ones who sign off on the plans that basically say this structure will not collapse at the blink of an eye. Older buildings get retrofitted all the time but those are also very expensive. Retrofitting is done to bring the building up to code and not fix a damaged building.
You run of the mill house gets bolted to the foundation and gets sheer walls.
https://www.sfgate.com/news/article/SFO-getting-the-latest-i...
https://en.m.wikipedia.org/wiki/Seismic_base_isolation
SFO International Terminal, several hospitals in the Bay Area, SF City Hall etc... all have these systems.
Construction is one of the last remaining sectors that is still able to employ low skilled workers and pay them good wages.
And yeah, it would really suck in the very short term. In the years following the quake, there would be a boom of work opportunities. Contrast to a situation where the buildings are spared at the cost of human life, you'd have ghost towns that would rapidly deteriorate to the point that the buildings would also fall to ruin
Part of what started this: a NYC architect and NYC construction contractor came to SF for the first time in their corporate and professional experiences and decided to build a building, cutting corners on standard local construction standards, regulations and laws because they found loopholes in all three and they thought it would save a lot of money.
So they did NOT do any of the standard "ground work" (sic) to prepare the foundation as every other skyscraper in SF and California normally does.
The normal process is to drive piles down to bedrock. They didn't do this. They put piles into sand. SF is primarily all sand sitting atop of deeper rocks but some of that rock is very deep below the surface. In that particular area, the rock is quite deep (all the hills you see like Nob Hill, Coit Tower, etc. are the rocky high spots surrounded by deep valleys covered with sand from ancient water inlets).
Local construction companies know all about this geophysical reality. Apparently these NYC companies did not and had zero engineering/professional intuition about the nature of earthquakes and construction in California.
Because of this the building started to both sink and tilt. And honestly, ANYTHING short of tearing the building down and starting again is at best a bandaid fix that may or may not work for long. This is a legendary FU.
And you are seeing these New Yorkers trying to lawyer their way out of the liability they will inevitably face by doing things on-the-cheap and half-assed. Here they got caught doing just that!
My late father was a big name in construction in the SF Bay Area. He was involved with most skyscrapers built in SF from 1970-1985 which includes the WF tower, Hyatt-Regency, Embarcadero Center building complex, etc. At that time I was a kid and he'd "take me to work" at these sites while under construction and I got to talk to construction workers, structural engineers, etc. about how it was done. It fascinated me enough to go into engineering professionally though the later PC and semiconductor revolution of the 1970s drove me to an EE degree instead of ME/CivE.
There was so much corruption here, and my personal belief is the city was paid off to facilitate the settlement.
Citation needed. Friction piles are quite normal too. I've lived in buildings in SoMa that used friction piles and none of them were tilting as much as this building. There's something more going on here (design or construction flaws), but it isn't as simple as "friction piles bad".
https://sf.curbed.com/2016/9/15/12930402/millennium-towner-s...
A selling point for my old condo building in SoMa is that it's one of the few buildings there that is built on bedrock.
[0] (PDF, pg. 2) https://sfdbi.org/sites/default/files/Millennium%20Tower%20S...
Of course Chicago doesn’t have earthquakes—but this building is leaning even without seismic activity.
They also said the shallow bedrock didn't force them to stay there. It isn't much of a problem to drill deeper and a number of early skyscrapers were built elsewhere... It's just that people wanted their skyscrapers to be in midtown and downtown.
One oddity is that the city’s inspectors and departments approved all of this - their surveys, geological analyses, foundation design, building design, and so on. That work spanned many contractors. SF is a city with many controls to prevent this kind of situations, so it is unclear as yet where all the faults lies.
- at least 6 units have sold within the past 6 months: https://www.sanfranciscocondomania.com/soldCondos/MILLENNIUM...
- at least 8 units are currently on the market: https://www.zillow.com/san-francisco-ca/millennium-tower_att...
I think at this point the building is way too heavy to ever fix and they should demolish it and cut the losses.
It happens all the time in China because of weak building codes.
Once a structure is compromised like this, there really is no sound way to salvage it in my experience, and it's a danger to the entire neighborhood, not only the occupants.
The bad part is that many of the occupants will suffer either way this goes... All insurance payouts should go to the unit buyers before any of the people involved in profiting get anything, but things never work that way. Attorneys will likely profit the most. The people responsible for the failed design and build should be blacklisted from future projects of this kind, that is where most injustice usually manifests in failures like this.
I don’t get this - the piers are 36 feet (engineers using feet?!) in diameter so should be 9 feet apart, but that’s not 3x 36.
What do they mean?
Architects for example almost exclusively work in feet in the US. The US construction field is almost entirely imperial.
The highest rates of metric use in the US are in cases where there is a possibility of international crossing/exchange, or if the field is distinctly metric-based. If you work for NASA, it makes sense to use global measurement standards. If you're building a house in Cincinnati, it largely does not matter.
If you're a German working in a store in Würzburg, you're far more likely to speak in German throughout your day. If you're a German working in programming with a bunch of US programmers, you're more likely to be using English when communicating with them. Why don't Germans speak English all the time? Because they don't want to and don't need to.
Cut yout losses. Demolish the whole thing.
It would appear the objections to the original plan were sound. The alternative proposal is to drill through the original foundation to set the piers from inside the building. My understanding is this would be more evenly distributed and attached to the original foundation evenly. Then jacks would be used to "climb" the piers to level the building - very slowly over time.
The original fix is cheaper because it relies on gravity to further sink the high corner of the building once the lower side is fixed in place by the piers, then once that has happened piers can be sunk on that side. It also spreads the cost out over a longer period of time.
The other objection to the original fix is seismic: if only one corner is resting on bedrock during an earthquake the building could be severely damaged.
I don't know anything about construction. But I do know that bureaucrats love to kick the can down the road, rather than deal with things directly. In this case, that would mean forcing some of San Francisco's wealthiest, and most-influential to demolish their luxury homes.
