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The LA Times reports that Ls Angeles Mayor Eric Garcetti has proposed the most ambitious seismic safety regulations in California history that would require owners to retrofit thousands of buildings most at risk of collapse during a major earthquake. "The time for retrofit is now," says Garcetti, adding that the retrofits target buildings “that are known killers. Complacency risks lives. One thing we can’t afford to do is wait.” The mayor’s plan calls for thousands of wood buildings to be retrofitted within five years, and hundreds of concrete buildings to be strengthened within 30. The retrofitting requirements must be approved by the City Council, and would have to be paid for by the building owners, with the costs presumably passed on to tenants and renters. The costs could be significant: $5,000 per unit in vulnerable wooden buildings and $15 per square foot for office buildings, Business owners, who have expressed concern in the past that these kinds of programs may be unaffordable, said the cost of retrofitting some buildings could easily exceed $1 million each. “This will cost us billions of dollars in the private and public sector,” says Garcetti. “But we cannot afford not to do it.”
The last major earthquake in Los Angeles was the 6.7-magnitude Northridge quake, which killed close to 60 people in 1994. But it was not close to the catastrophe that seismologists predict if there is a major shift on the San Andreas fault, and the fact that it has not produced a major quake in recent years has fed a sense of complacency. Seismologists now say a 7.5-magnitude event on the Puente Hills would be "the quake from hell" because it runs right under downtown Los Angeles and have estimated that would kill up to 18,000 people, make several million homeless, and cause up to $250 billion in damage. “We want to keep the city up and running after the earthquake happens,” says Lucy Jones aka "The Earthquake Lady," a seismologist with the United States Geological Survey and something of a celebrity in a city that is very aware of the potential danger of its location. “If everything in this report is enacted, I believe that L.A. will not just survive the next earthquake, but will be able to recover quickly.”
(Score: 2) by Thexalon on Thursday December 11 2014, @04:51PM
I am not an engineer, but I could definitely imagine wood construction being less earthquake-resistant than concrete. Every time I've built wooden stud walls, we had to do a fair amount of work to keep them vertical and square, wooden structures tend to flex and bend a bit, all of which is a recipe for relatively small earthquake forces causing bigger structural problems with a building. By contrast, concrete will tend to resist until it cracks, and if it's reinforced concrete the steel will keep everything more-or-less in place.
An interesting fact though: Wooden homes built by mostly volunteers for groups like Habitat for Humanity have a better track record than those built by professionals. The two hypotheses on that: (1) the amateurs are less likely to cut corners and be generally more cautious than the pros, and (2) When an amateur makes a mistake, s/he'll likely leave extra nails and screws in place, which improves the structural integrity of the building.
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 2) by bob_super on Thursday December 11 2014, @07:57PM
You're both correct and wrong.
- Concrete is strong against compression but terrible against lateral loads (like earthquake ground acceleration). Pure concrete/bricks is why so many people get killed by their own house in earthquakes.
- Wood flexes, creaks and won't break nearly as easily. Above a certain threshold (depends on roof weight) it will collapse, but it's a higher threshold, and a slower failure mode, than pure concrete.
- Concrete with Rebar is the strongest, but also the most expensive/heaviest.
I went to the epicenter of the Taiwan 7.5 quake (1999). They left a school "as is", showing how in each pillar holding the upper floors, the concrete is completely gone over 20-30cm (8-12") right under the first floor ceiling (all walls and stairs too). The top two floors actually shifted by a few inches compared to the bottom, but they are intact as the rebar flexed under the strain, but held.
(Score: 2) by Thexalon on Thursday December 11 2014, @08:11PM
Ah, there's my mistake - I had assumed most concrete buildings had rebar in them.
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 0) by Anonymous Coward on Thursday December 11 2014, @11:54PM
Yeah, the ability to flex is the ticket in earthquake country.
The biggest problem with wooden structures was that they weren't tied to their masonry foundations worth a damn.
The lateral motion is what did the damage; the things would just shift sideways off their footings.
That was corrected in the code decades back.
It's also amazing how long houses in the hurricane belt didn't require parts of a house to be securely strapped to the other parts (with roofs detaching just when you need them most).
-- gewg_