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Re: Open Walled "Shed"

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That's true.  The uplift is as you described.  The lateral loads are the one under discussion.  If the amount of "parapet" is very small then the only loads that I can see are, in the limit, the horizontal vectors calculated from the "perpendicular to member" coefficients acting on the roof planes.  Different slopes give different resultants.  These may be larger than the exposed "parapet" and column loads.  I concur with your assessment but my associate still thinks that calculation is too small and I'm trying to convince him that his fear is not justified. 

Thor A Tandy P.Eng, MCSCE
Victoria BC
e-mail: vicpeng(--nospam--at)
-----Original Message-----
From: Jim Persing <jpersing(--nospam--at)>
To: seaint(--nospam--at) <seaint(--nospam--at)>
Date: Friday, September 24, 1999 1:41 AM
Subject: RE: Open Walled "Shed"

Thor A Tandy,
When we design structures similar to the one you described, we use the projected area method in the 97 UBC.  The structures we design are generally flat-roofed service station canopies.  The fascias are treated as parapets with both sides receiving wind loads in the same direction and any protruding beams are also included for wind pressures unless they are closely shielded by the fascias.  And of course the contribution of the columns is also included. The additional 0.5 value for uplift found in footnote 1 is not used since the structures are classified as "UNENCLOSED STRUCTURE OR STORY", Section 1616.  It is my understanding that the "serious" uplift you described is actually caused by suction on the roof from unbalanced pressure due to partial openings, not full openings, as described under "PARTIALLY ENCLOSED STRUCTURE OR STORY".
Jim Persing