What is the purpose of a seismic building code? I always thought building codes were designed to protect the poor independent engineers from greedy owners. If the owner said 'Use wallpaper paste!", the engineer could say "That's against code.", and be backed up by professional associations, and inspections. The first codes sprang to life in 1933, since it was observed that buildings which were designed to resist 10%g lateral, did quite well in earthquakes. This was equivalent to tilting the building by about 6 degrees. All building codes eventually incorporate some lateral coefficient in a static sense. This has, unfortunately, tied the code to PGA (peak ground acceleration), which is the big mistake of the ages. Another problem is that the engineers now work under the direct lash of the owner.
When has a new building code failed? A building code is said to have failed when the modern buildings do worse than the old ones. A profound failure is when those buildings collapse in a killing manner.
What do we expect from codes? I expect that codes will produce a minimum ruggedness in terms of PGV. Thus, I demand (as a tech-purist) that there should be no damage up to 50 cm/s and no collapse up to 100 cm/s. That's standard. If you pour in more money in rich areas by major faults, then you can up it by 10 or 20 percent. Now, New Zealand was ridiculously fragile at 20 cm/s, but they soaked the Clueless Swiss. Bank towers are rugged, and condos are fragile, as we shall now see.
As a digression: Speaking of bank towers and condos, I was lucky to live and work in downtown Toronto for some number of years. I saw the bank towers go up, massive, huge foundations. The buildings were trimmed in real gold. I knew that they were earthquake-proof! Then I saw the condos - thin flimsy walls, with no shear resistance. I thought: Are you kidding me? Lately, I've seen everything go up like this, and I just wonder....
Back to Chile
I'm just concentrating on Santiago, since it was exposed to 40 cm/s and should not have experienced any damage. Yet the place is peppered with cheap condos, just like any you would see in Vancouver or Toronto. Know what did them in? Their insatiable demand for underground parking space! The whole foundation for these buildings was a stack of cards.
LEANING TOWER OF CONDO
There's a happy building. These towers are now tilted!
These condos are very trendy, I've seen them on Blue Clay in Boston!
I just extracted a small subset from the paper, which is somewhat Japanese-confused, but golden. It is fair to say that if a tower starts to lean at 40 cm/s, it's going over at 70 cm/s at ground zero, which is what happened.
Well, what does this mean? If you are a condo owner in Burlington or Vancouver, QUAKE IN YOUR BOOTS! Actually, I can't really say anything 'concrete' or I will be sued for diminished value. Luckily, we have the CLUELESS SWISS! Your condo value doesn't go to dirt if you scam them like New Zealand. Insure the whole market value of your asset, and double-insure the deductible. Hopefully, you'll walk out of it happy.