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RE: Open Walled "Shed"

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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
 
-----Original Message-----
From: vicpeng [mailto:vicpeng(--nospam--at)vtcg.com]
Sent: Thursday, September 23, 1999 8:40 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Open Walled "Shed"

A peer has sought my opinion on the lateral wind loads to a structure that is essentially a non-walled structure.  I.e. just a roof on a braced post and beam assembly.
 
My opinion was that he should use the the exterior vector coefficients in the code for the roof using the internal pressure coefficients for a building that would have large openings open during high winds.  If the eave boards or beams are deep enough they could also contribute?
 
That analysis provides a resultant vector addition according to the roof slope (here 15 degrees) which would I believe be the main resultant lateral load to the roof structure (together with some serious uplift).
 
He felt that the load calculated that way was too small, even using corner/cladding coefficients.  I suggested using an elevated billboard of same projected dimensions as an upper limit, but that gave a much higher number, too high to be reasonable for what is essentially an aerofoil on stilts.
 
I think the simple vector addition of resultant roof pressures is sufficient.
 
What does the group think? 
 
James Cohen maybe has a good set of tables or references that I could access?

Thor A Tandy P.Eng, MCSCE
Victoria BC
Canada
e-mail: vicpeng(--nospam--at)vtcg.com