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FW: Tornadic Gust Wind Speeds vs Seismic

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> I would think it very impractical to "design" for tornado forces.  Many
> couldn't afford to buy their homes !  How could you design in an economic
> manner for a 250+ mph wind force?
> 
> ----------
> From: 	Ed Marshall[SMTP:elmarshall(--nospam--at)HASimons.com]
> Reply To: 	seaoc(--nospam--at)seaoc.org
> Sent: 	Friday, May 08, 1998 9:39 AM
> To: 	'seaoc(--nospam--at)seaoc.org'
> Subject: 	FW: Tornadic Gust Wind Speeds vs Seismic
> Importance: 	High
> 
> > Now that I've actually looked back at the 1970's paper that I
> > mentioned Thursday I'll quote from it correctly.  It's "Tornado Risks
> > and Design Wind Speed", by Yi-Kwei Wen and Shih-Lung Chu, December
> > 1973, ASCE Structural Division Journal.  The example they give is for
> > a Midwestern site.  For a 50 year return period (0.02 annual
> > probability of excedence) there is no significant increase in the
> > design wind speed of 80 mph when considering Tornado risk.  At 200
> > years the increase is from 90 mph for straight line wind to 95 mph.
> > At 500 years from 100 to 111 mph, and at 1000 years from about 110 to
> > about 165 mph.  Since wind pressure varies with the square of the wind
> > speed, the wind loading at 165 mph is approximately 4.25 times greater
> > than at 80 mph.  
> > 
> > For comparison, the ASCE 7-95 commentary states that the mean
> > recurrence interval for the values given in the seismic maps is 475
> > years (10% chance of being exceeded in 50 years) and I think it may be
> > greater than that in the East.  My thought is that the risk due to
> > Tornadoes in the Midwest and some parts of the East is similar to that
> > due to the earthquake, yet unlike earthquake it is ignored by the
> > codes.
> > 
> > Ed Marshall, PE
> > Simons-Engineering
> > Atlanta
> > 
> 
>