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Re: Seismic Design Hypothetical

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Jordan,

This is where parking garages "screw" with things.  Parking garages are
typically concrete structures...lots of mass.  This can result in seismic
forces governing in the lateral load analysis even in very low seismic
areas and even assuming a full wind load (i.e. not trying to reduce wind
loads due to the open nature of the parking structure).  I once worked on
a parking garage in the Detroit area.  Seismic loading governed.  This was
back under BOCA 1993, where "bad" soils don't have the same effect in the
code that they do in the IBC (i.e. in terms of seismic loads).  SE
Michigan is a pretty low seismic area.

Regards,

Scott
Adrian, MI


On Mon, 29 Aug 2005, Jordan Truesdell, PE wrote:

> 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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