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RE: canopy wind uplift

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Concur on the complexity of the provisions for everyday use...
Uplift is still generated (maybe someone else can chime-in but I have vague recollections of this being how airplane wings generate lift)
Unfortunately the only values provided in ASCE are for mono-slope open structures (the load acts perpendicular to the surface so at low roof angles it is primarily uplift) so it takes some extrapolation. One of the old military TM's (5-809-1) used to contain info for arched and gabled open canopies- I have the 86 printing in front of me but not sure if the info was updated or dropped in the newer manuals.  It shows a Cf of .8 for 30deg and higher and a Cf of .6 for under 30 deg for a gable.

Michelle Motchos, PE

Columbia, SC


From: Joe Grill [mailto:jgrill(--nospam--at)]
Sent: Thursday, June 01, 2006 11:13 AM
To: seaint
Subject: canopy wind uplift


ASCE wind load provisions still confuse me at times.  Well, actually most of the time.  They are way too complicated for the small structures that we do around here.


Anyway, I?ve been ask to look at a small bus stop canopy.  It is to be made of timber (got to have that wild west feeling) and the roof is a gable. The ?designer? has shown some really shaky connections.  In my mind it is an ?open structure?.  Am I correct in that in an open structure there is no uplift forces and it would fall into section 6.5.13 ?Design Wind Loads on Open Buildings and Other Structures??






Joseph R. Grill, P.E. (Structural)

Shephard - Wesnitzer, Inc.

Civil Engineering and Surveying