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RE: Tornadic Gust Wind Speeds vs Seismic

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I agree with much that you say but not with the comment that "It is hard
to compare risk factors for tornados with risk factors for earthquake,
because earthquakes affect all structures within a given area, whereas
tornados affect a relatively narrow path."  While this is true for a
single incident, the probability that any individual building in a
tornado prone area being hit but by at least a small or moderate tornado
is similar to the risk for it experiencing an earthquake of the
magnitude specified in the code.  Or in other words, over a period of
500 to 1000 years, at least 50 percent of locations in such an area can
be expected to have been in the path of a tornado.  Over that same
period of time the risk of the "design" level ground motion occurring at
a given location due to earthquake is similar.

Ed Marshall, PE
Simons Engineering
Atlanta


> -----Original Message-----
> From:	Bill Sherman [SMTP:SHERMANWC(--nospam--at)cdm.com]
> Sent:	Friday, May 08, 1998 2:35 PM
> To:	seaoc(--nospam--at)seaoc.org
> Subject:	Re: Tornadic Gust Wind Speeds vs Seismic
> 
> I think the idea of requiring a tornado resistant shelter makes sense
> in
> some areas but I don't think it makes as much sense even to try to
> design normal 
> homes and commercial buildings to withstand tornado forces, other than
> 
> requiring certain details such as "hurricane anchors".  It is hard to
> compare risk factors for tornados with risk factors for earthquakes,
> because 
> earthquakes affect all structures within a given area, whereas
> tornados
> affect a relatively narrow path.  Thus a given city or county may have
> a
> significant risk of being hit by tornados but the risk for a single
> building would be
> much less.   
>  
>