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Re: canopy footing

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Daryl,
 
Luckily, it is just being designed, and was sent to me for review.  
two things bother me: 1) based on the responses, it apparently "have been done in the past"; and 2) it is supposed to be a "standard" (repetitive) design.
 
Thanks for sharing your thoughts.
 
Steve Gordin SE
Irvine CA
 
----- Original Message -----
Sent: Monday, February 13, 2006 4:01 PM
Subject: Re: canopy footing

Steve,
 
        Our last posts seem to have crossed in the mail.
 
        If this overturns there is obviously much more overturning moment than I assumed in my quickie assessment.
 
        You weren't clear in your previous correspondence whether this is already built or just proposed.  If just proposed there are, of course much more efficient foundation shapes than a cube.  6' by 6' by 4' deep or 8, by 4, by 4' deep are a couple of suggestions, as if you needed any.  You can simply change the design.
 
        If it's already built that's a different mater.  The cheap solution would seem to be to replace the lateral backfill with concrete.  This should supply positive resistance to overturning rotation; and, with the overturning resistance provided by the new concrete the soil pressure below the cube should be fine for resisting vertical load only.  If there are too many other problems such as inadequate reinforcing per code, you probably have to get rid of the thing and start fresh anyway.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
From: S. Gordin
Sent: Monday, February 13, 2006 2:14 PM
Subject: Re: canopy footing

Daryl,
 
If allowed to work as a real footing, it overturns, and the soil pressures are through the roof.  If it is a "caisson" - it may work, but the "cube" does not meet the code definition of that type foundation.
 
Steve Gordin SE
Irvine CA     
----- Original Message -----
Sent: Monday, February 13, 2006 12:47 PM
Subject: Re: canopy footing

Steve,
 
        It looks reasonable to me.
 
        The structure you describe would have quite a large of overturning moment,  It would, therefore, require quite a large weight to resist overturning.  Most of the concrete in the cube would seem to be dedicated to that end.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
From: S. Gordin
Sent: Monday, February 13, 2006 11:46 AM
Subject: canopy footing

Good morning,
 
I am reviewing a "standard" design of a canopy - a steel-framed structure with two cantilevering columns 14' tall supporting a light "low-pitched V" roof measuring 16'x24' with 12' cantilever. 
 
The engineer used UBC formula 6-2 (Section 1806.8) to justify the adequacy of the footings for the columns - 5'x5'x5' "cubes."  According to the UBC Commentary p. 297, the formulas of UBC 1806.8 are historically applicable to "pole-" or "column-" type footings. 
 
To me, these "cube" footings do not even look right for the subject application.  Any comments on the situation will be highly appreciated.
 
TIA,
 
Steve Gordin SE
Irvine CA