From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
Date: Sat, 24 Jun 2000 15:03:51 -0400
Recent posts regarding snow loading have recommended contacting the building
official. While that may give you the snow load that the building official
may require, it may be nowhere near the actual snow load that may occur.
While the building official may give you a *minimum* snow load value, it may
not be anywhere near what you *should* use.
While many may think of Arizona as devoid of snow, we have a large variety of
conditions from warm desert to high, cold mountains. Pima County, in the
southeast part of Arizona has elevations that range from less than 2,000 feet
to over 8,000 feet. The Flagstaff area and the White Mountains in eastern
Arizona are in the 7,000 ft plus elevation range and are subject to
considerable snow loads. In the early 1970's, following the lead of Oregon,
the Structural Engineers Association of Arizona published an Arizona Snow
Load study that showed the snow loads that would be expected in a 30-year
return period. ASCE 7, in the Appendix, shows that for a 50-year return
period, the site-specific ground snow load for the Palisades Ranger Station
(35 miles from downtown Tucson but at an elevation of 8,000 feet in the
Catalina Mountains) of 125 psf, yet the County Building Official was
requiring only 20 psf for construction in the area. The Tucson Chapter,
Structural Engineers Association of Arizona, recommended that this be changed
and submitted recommendations based on the Arizona Snow Load study for snow
loads in various elevation ranges. It is unknown whether the recommendations
were adopted by the building official.
I have had a couple of recent projects in the White Mountains area where the
ground snow load was 50 psf. Drift snow loads, using the UBC appendix
procedures, had maximum drift loads of 130 psf.
A. Roger Turk, P.E.(Structural)