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Re: Seismic Design Hypothetical

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I can see how it would rarely - if ever - come up in D.C.  I live just 30 miles from the largest earthquake to hit Virginia in (recorded) history. It was a 6.0-6.3 (only sporadic, anecdotal evidence was available) back in the mid-late 1800s.  My S1.0 is about 150% of that around DC, and it only rarely controls when the site soils are poor.  If the configuration or site is questionable, I check base shear, and have only had a couple of instances where EQ ruled in one direction.  There are some on the east coast that will never check earthquake forces - it's a waste of time, especially as your wind loads increase near the east coast (and you're not near Charleston).

Eli Grassley wrote:

Gail (and some others) –


How can you “not do” seismic design??  I have heard that before from others on this list.  Granted I do most of my work on the West coast, but there are pockets of seismically active areas all around the country.  I know there are some in WY and MT.  And especially if you are working on a critical facility that has an Ie = 1.5.


I guess my real question is what you mean when you say, “I don’t have a good feeling for it.”  Do you mean lateral force design in general?  Because EQ design is really not very different than W design…the code allows you to treat them both as *equivalent STATIC lateral forces*.  It’s pretty rare to do a dynamic (modal analysis or wind tunnel modeling) design.


Just curious.


~~ Eli Grassley, PE

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