>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.

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.

> 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...

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?

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.

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.

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.

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.

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.

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

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