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Re: Snow load in combination with seismic.

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The Anchorage Amendments to the UBC/IBC requires a minimum of 25% of the
snow load to be included.  This particular provision of the code
actually started here and was introduced into the UBC at the insistance
of several Alaskan engineers. 

Since your building official has not set any limits, I would suggest
that if you do not want to use full snow load that you suggest a
percentage based on your experience and knowledge of the area.  Include
consideration of the frequency of maximum snow load vs required design
snow load, and frequency of earthquakes, potentential of the maximum
snow load remaining of the roof as a result of wind or melting which is
a function of heat lose insulation and weather.  The 25 percent that we
use is based on approximate statistics of maximum snow load and
earthquake at the same time.

> Bill Marczewski wrote:
> 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)

Forrest T. Braun, P.E.
BBFM Engineers, Inc.
Ph (907)274-2236
Fx (907)274-2520
Anchorage, Alaska

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