Repairs of leaning San Francisco skyscraper on hold | Hacker News Reader

Repairs of leaning San Francisco skyscraper on hold

sanfrancisco.cbslocal.com

126 pointswoofyman89 comments

I find everything about this building hilarious in a dark, horrifying engineering and bureaucratic sense.

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.

> The normal process is to drive piles down to bedrock.

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 few years ago, one of the theories was construction of the transbay terminal caused this, but I have no idea if that was actually the case.

You can imagine why they floated that idea but the site is surrounded by other buildings which survived intact, including a 100-year-old unreinforced brick building.

Is it normal for the size of the building + use of concrete over steel (increased load)?

In other parts of the world, far taller buildings are constructed using friction piles[1].

Again, friction piles are not unusual at all. Drilling into bedrock happens in parts of Manhattan[2] , but that's because the bedrock is generally close to the surface.

Whatever's going on with Millennium Tower, it's not "friction piles bad".

1. https://youtu.be/N5i3UsiSoYY

2. https://buildingtheskyline.org/bedrock-and-midtown-i/

>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.

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.

The piles they used for the Millennium Tower were the same length—80 feet[0]—as those they'd use for a 22-story highrise on, say, 6th St. Millennium Tower is 58 stories and right on the water.

[0] (PDF, pg. 2) https://sfdbi.org/sites/default/files/Millennium%20Tower%20S...

Small nit on the location: I think it's landfill that was originally part of the bay...which is even worse for stability.

Below that is sand over bedrock

I'm honestly not sure. I assumed being marshland for millennia gave it significantly different soil than valleys in the area.

It's unlikely to come out in court, but my father worked on the investigation and it became clear both the engineer and architect had e-mail corresponding showing they planned to blame various 3rd parties for several secondary effects of the tower's sinking, including cracking caused by the tower pushing on the exterior wall of the underground garage causing water intrusion.

There was so much corruption here, and my personal belief is the city was paid off to facilitate the settlement.

From 1970 to 1985? That means he was part of the "Towering Inferno" debacle. Not pretty.

I am just a layman when it comes to this kind of thing, but I notice that many articles online claim that variable bedrock depth explains why Manhattan's skyscrapers come in two distinct clumps. If this is true, then it seems strange to me that NYC professionals would ignore bedrock depth in SF out of pure ignorance.

I just found a blog where the author explains that its actually a myth and mostly coincidental. The reason the skyscrapers are in midtown and downtown was due to historical and economic reasons. Those were the dense wealthy business areas where people wanted and needed to build taller buildings and it turned out they also had the shallowest bedrock.

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.

https://buildingtheskyline.org/bedrock-and-midtown-i/

Aren’t piles that don’t extend to bedrock common in many cities? They are ubiquitous in Dubai, and are even used in the Burj Khalifa. There’s a way to do it right. One confounding factor with this SF tower is the later construction of the Transbay Center nearby, which I read may have destabilized soils nearby through dewatering. Apparently their process reduced the water table by 20 feet (https://sf.curbed.com/2016/9/20/12991602/millennium-tower-si...), which would change the bearing capacity of soils and affect friction piles.

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.

You don’t necessarily need to drive piles into bedrock: https://informedinfrastructure.com/31619/building-skyscraper...

Of course Chicago doesn’t have earthquakes—but this building is leaning even without seismic activity.

Building (and seismic) codes in California are stringent, but not in the way many people think.

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...

>The buildings themselves are not required to survive in habitable fashion

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.

> It's just not economically viable

Is that code for "it costs too much"?

That’s literally what it says. It’s not code for anything

It’s interesting to see what some people consider to be big complicated words.

Yes, it costs too much to build it to last, it costs very little to rebuild it...

I may be mistaken, but I believe in Japan the standard is "build to remain habitable." as a result, skyscraper building techniques there are very different to the US.

“The Japanese Building Code (BSLJ) explicitly requires that buildings withstand moderate earthquakes with almost no damage, while collapse prevention and life-safety is required for severe earthquakes. It is expected that a typical building will be subjected to several moderate earthquakes during their service life, while the likelihood of occurrence of a severe earthquake during the same period is rare.”

(Comparison of the Seismic Code Provisions of the National Building Code of Canada and the Building Standard Law of Japan, https://www.caee.ca/12CCEEpdf/192-oZfU-119.pdf)

A similar approach is used in California and other places under the name Performance-Based Design.

If that is what it was optimized for, then building anything above 3 maybe 4 stories would be stopped. I disagree.

This is how some other professions operate. In a strict sense of what a profession is supposed to be and not counting the economic factor, doctors care more about loss of life than loss of a limb. If they have to save your life by cutting off your limb, they will.

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.

Engineering is about economically designing things that fail in a predictable manor.

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.

Modern car design.

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.

…while before, minor impacts often killed the occupants.

I don’t see a problem with that. We just need to factor in the costs appropriately eg via insurance premiums. Save lives and create the infrastructure for building back (eg via a quake recovery fund, contingency plans for rebuilding if a quake does wreck a building etc).

Construction is one of the last remaining sectors that is still able to employ low skilled workers and pay them good wages.

It's the same in NZ, without fundamental changes to engineering science it will continue, remember that a quake will stress a building's reinforcing / all materials beyond the elastic limit.

After watching the political quagmire of the housing crisis in California, this gives me some hope that The Big One might create a situation where it would be possible to reboot the architecture of major cities to prioritize humans over cars without significant loss of life.

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

This is a necessary trade off between the probability of extreme high intensity earthquake and economy of structural design. That is why we civil engineers call buildings “earthquake resistant” instead of “earthquake proof”.

It's also not possible to "proof test" a building against earthquakes.

This is something that the profession has done a terrible job in communicating with the public.

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.

It’s also worth noting that geotechnical engineering is a high risk and low tech field. Most of their design relations involve pounding a stick into the ground and counting how many hits it took to sink a unit depth (that’s a little bit jest, but also not far from the truth)

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?

Actually it depends on the type of structure. Newer or retrofitted hospitals, airports, bridges, and other essential facilities are designed to remain functional and hence habitable. That is why many of the newer versions of those structures have seismic isolation systems.

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.

The building was leaning 17" at the top when this work started. Within a year it is now leaning 22". That is a dramatic increase in such a short time.

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.

How do you drive piles once the building is completed? Do you go to the basement (probably a parking garage), open up space with the floor above it, and drive short segments that are welded together? I thing one of the earlier plans was to do this all outside the building on the perimeter, but if that's not enough, it sounds really complicated.

They should put a big hydraulic shaker in the bottom of the garage and just shake it until it hits solid ground. Then punch a new door in on whatever floor happens to be at grade.

They'd have to reinforce all the walls first.

The bedrock is over 100ft down, so that would be fun

On paper, people who bought those units, own multi million $$$ apartments, but what's their market value, zero? Who would ever buy an apartment in that building? Wouldn't be better to tear it down?

For the right price I am sure they would be bought, especially if someone (probably an investment group) is trying to profit long term assuming the building is "fixable" whatever that may mean.

You couldn't pay me to live in, visit, or even walk by that building, but apparently there is a market for the units:

- 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 wonder how the $/sq ft compares to similar but structurally sound condo buildings in the area.

I assume 1 Rincon Hill is very sound.

One of them actually sold AFTER the Miami collapse. I would think that after seeing the hubris fail elsewhere it would make people second guess a huge purchase like that. It was probably a long escrow and figured they should just close anyway - it won't happen to me, not in this leaning tower in a quake prone area.

> One of them actually sold AFTER the Miami collapse.

Why would the collapse of a different building, across the country, for unrelated reasons, affect their decision?

Hah, I'd buy one at a bargain basement price then insure it heavily if it wouldn't trigger a fraud alert...

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'm guessing insurance payouts would involve lots of lawyers and lots of time.

Those sales don't strike me as especially bargain basement either. 2BR, 1500 sq ft for about $1.5m. Maybe without the issues, as a premium property, it would be higher but those prices don't seem out of line with condos on the market.

> 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.

...no, they should be jailed, likely for life, because they knew exactly what they were doing.

Capitalism apologists prove they know no bounds, time and time again. Really exited to get to watch the incoming century of collapsing skyscrapers because of skirted regulations. Deaths will pile high and no consequences will be had.

I had two friends who were both skyscraper architects who rented there for several years. The average person just doesn’t have a good grasp on the actual risks, but they certainly did. They wouldn’t buy a unit there due to the uncertainty in cost for the repairs but it’s plenty safe.

Maybe they are opportunists hoping to collect insurance and/or lawsuit money.

Just wait until the HOA gives them a massive "Special Assessment" for the urgent repairs while the true liabilities get tied up in the courts for decades. No thanks!

It's actually a very low risk investment. The HOA is suing the city, blaming the construction of the Transbay terminal next door. They have access to some serious attorneys, so if the building falls down they'll still profit.

It's super high risk when there is any litigation. Most banks will stop mortgage loans when that's discovered.

Could be a fun exercise to look at the property records over time to see which financial institutions are publicly recording mortgages on these units to understand their risk tolerance.

So, is this thing going to fall over and kill everyone or what? Someone with engineering experience, please explain why this is hyperbolic and downvote me away.

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.

> “You never place piles or piers closer than three pier diameters apart. These are 36 feet so they should be nine feet apart and they’re, what? — five feet or something.

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?

It’s a typo. They’re 3 feet in diameter.

They meant 36 inches.

Wow. Maybe that’s why it’s falling down. Why aren’t engineers using metric?

America. I had to mentally switch to metric when I moved to Europe and now I have to switch back. Ugh.

Arithmetic continues to work even if you don't use metric units.

The arithmetic doesn’t work though - that was my point.

The arithmetic works, but the units were wrong, that can happen in the metric system too.

Almost impossible I'd say to confuse 1 m with 1 km or 1 mm, but easy to confuse feet with inches as they're much closer in value - the same order of magnitude even. As you can see - since it happened in this article.

I don't think an engineer would confuse inches with feet, and it's a stretch to assume that a newspaper reporter wouldn't confuse m with km.

And what about mm and cm? They are only a factor of 10 apart while inches and feet are 12X apart.

Simply put: i doubt the linked article was written by the engineers responsible.

Construction and civil engineering (in the USA) is still done in feet and inches. All construction materials are sold this way. It would just introduce error to try to plan a building in metric dimensions.

Even in the UK you end up with construction materials at those same sizes. Click the link and tell me how large the following sheet size in feet?

https://www.forestrallshop.co.uk/plywood-london/birch-plywoo...

Comically they apparently also imported our lumber price fiasco.

If the piers are sold in inches, then using metric to describe them is another level of indirection, so might make the chance of error worse. Would you feel safer if he said "The piers are 91.4cm"?

It's amusing to see newspaper stories where they report high precision numbers that are obviously metric conversions like "He drove 62.14 miles to work every day" when the original source said "100km".

The construction tradespeople only use imperial. The engineers could use metric, but then they would have to convert everything. It’s easier to just use imperial from beginning to end. Besides, all construction materials are in imperial. It is so much simpler for the engineers to use imperial. Plus, if they grew up in the USA, the engineers are as comfortable using imperial as you are using Metric.

"Eschew flamebait. Avoid unrelated controversies and generic tangents."

https://news.ycombinator.com/newsguidelines.html

> engineers using feet?!

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.

No way the piles are 36 feet in diameter. I don't think piles that big exist or are feasible, you're usually looking at a couple meters max.

In the USA the construction trade is all done using imperial measurements. If you go into any big box hardware store, the only thing you can find in metric is a few specialty bolts.

The Millenium Tower needs to be scrapped. It's a failed project. It will cost hundreds of millions of dollars to "fix", and no fix will work in the long term, because the problems are structural.

Cut yout losses. Demolish the whole thing.

What’s your expertise on this subject beyond armchair quarterbacking?

I'm guessing the Miami building as a lesson.

I personally wouldn’t consider someone’s awareness of another building’s collapse to be expertise, but hey it’s the internet

Your qualifications first.

What is anyone's expertise on a web forum? If he claimed any, what weight would that add when almost everyone here is anonymous?

I can assure you, as the world’s leading behavioral psychologist, a former Miss Universe, and the winner of last year’s Eurovision contest, that the poster is totally qualified to speak on the topic.

I think you are right. It was built to fail after all.

I hope this doesn’t chill demand for residential skyscrapers in SF. It seems like this building is (arguably justifiably) getting a lot of attention but there are multiple ongoing and completed projects that are a good solution to alleviate the housing crisis. Yes they’re all “luxury” condos but they’re satisfying some demand at least.

Towers are I guess the worst and least convenient way to alleviate housing crisis. Raising a few of the city’s hundreds of thousands of detached single-family houses to 2-to-7-story apartment houses would be a lot better, cheaper, faster, and easier.

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