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RE: Drifting snow on small canopy

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Ken,
You are going to have to tell the engineer he is wrong. The drift loading criteria DOES apply. The research that led to this was conducted in the 1990's, was funded by the metal building people, and one of the leads was Dr. O'Rourke. He is correct in his article that Dave Evans referenced to an extent. One can show for very tall buildings that there is an upper limit to the drift. That upper limit provision was written into the ASCE 7 criteria in the '98 or '95 ASCE 7. Dr. O'Rourke wrote the provisions and the limitations that appear in the ASCE 7 today.

For more info:
http://www.hnd.usace.army.mil/techinfo/ti/809-52.pdf

Bring this to your engineer.
Snow load fear factor - 20 psf ground snow, 130 psf drift
Pay me now or pay the litigation later.

Regards,
Harold Sprague


From: Gale45man <gale45man(--nospam--at)yahoo.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Drifting snow on small canopy
Date: Fri, 13 May 2005 11:12:49 -0700 (PDT)

Paraphrasing ASCE J of Struc Engr 1990 Vol 116 No. 3
pg 650 (by O'Rourke):  "drift provisions are
applicable only for delta h up to 25' to 30', since
one does not see substantial drifts if delta h is more
than three stories."

d a v e e v a n s

__________________________________________________

From: "Ken Peoples" <kspeoples(--nospam--at)lvta.net>
Reply-To: <seaint(--nospam--at)seaint.org>
To: "Seaint" <seaint(--nospam--at)seaint.org>
Subject: Drifting snow on small canopy
Date: Fri, 13 May 2005 13:37:40 -0400

We are reviewing structural calculations for a small (5' perp. to bldg face and 8' parallel to bldg. face) flat canopy over a door for which the engineer has not included any snow drift. The distance from the high roof down to the canopy is 13'-6" and there is a 2'-6" high parapet. The main roof is flat and at least 140' wide. The engineer's position is that it is too short or too small to get any drift from the upper roof. I seem to recall someone telling me that if you had a roof projection less than 15' long, that you didn't have to consider show drift against it, but I don't know where this might be in the code - (might have been in BOCA, but is not in IBC?) If the canopy had not already been constructed, this probably would be a no brainer - just make it a little stronger to be able to handle the drift, but, unfortunately, it is already constructed. Anyone sure that we do or do not need to consider snow drift? The balance snow height is about 1'-3". Thanks for your help.


Best regards,


Ken

Kenneth S. Peoples, P. E.

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