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Re: Snow load in combination with seismic.

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100% of snow in combination with seismic?  Good Grief!!  The probability of having full snow load at the same time as a design seismic event is somewhere between slim and none.  Here in Utah, we use a percentage of the full snow load (when snow load is over 30 psf), which percentage increases with elevation.  The formula is 0.25+0.025*(h-5)  where h=elevation above sea level in 1000's of feet.  (h has to be at least 5 in order to comply with the 25% minimum rule.)  The theory is that at higher elevations, there is snow on the roof for a greater percentage of the year.
 
Hopefully this will give you a place to start.
 
Conrad Guymon, P.E.
----- Original Message -----
Sent: Wednesday, June 06, 2001 3:29 PM
Subject: Snow load in combination with seismic.

I have a multi-story building with high snow loads located in a very low seismic region (zone 1).  The building official is unable to provide information regarding the percentage of snow load in excess of 30psf that should be used in combination with the seismic load.  My preliminary calculations consisted of using 100% of the snow in the seismic dead load, and I feel this is a significant penalty.  I have previously been able to use only 25% of the snow load in seismic zone 3 in Jackson, Wyoming.  On the other hand, Steamboat Springs, Colorado (zone 1) has required 100% of the snow load to be used in combination with the seismic load.  The 1997 UBC states that snow loads beyond 30psf must be considered in seismic design, but may be reduced up to 75% when approved by the local building official.  What should I do, or does anyone have any recommendation on what percentage of snow to use when the building official cannot provide guidance on this issue?  I think the use of 100% snow load in combination with seismic is really to harsh.  Comments would be great.  Thank you.
 

Bill S. Marczewski
Martin Design, Inc.
1360 S. Clarkson St.
Denver, CO 80210
bmarczewski(--nospam--at)martind.com