Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

RE: canopy footing

[Subject Prev][Subject Next][Thread Prev][Thread Next]
If the restraining slab is not in contact with the cube I would tell them to use formula 6-1 or clarify how the slab is restraining the top of the foundation.  Formula 6-1 makes the footing deeper because it puts the whole overturning couple into the soil where formula 6-2 makes a couple between the slab and the soil. 
The pre-amble also says posts embedded in concrete footings.  If they are just bolting the canopy column to a cube and you wanted to nail them on semantics you could tell them to design it some other way, but if they are embedding the column then they are following the wording of the code.  If it looks scary I would make sure they did their numbers right - it would be deeper with formula 6-1 if there is not a slab restraining the top of the footing.

From: S. Gordin [mailto:mailbox(--nospam--at)]
Sent: Monday, February 13, 2006 12:02 PM
To: seaint(--nospam--at)
Subject: Re: canopy footing

Plain concrete is not allowed for structural applications in California. Anyway, the specified reinforcement of the "cube" was inadequate (as many other things in this design were).  For example, the restraining slab (as designed) is not even in contact with the "cube."
My main problem with the design is that - according to CBC/UBC Section 1806.8 preamble - the formulas 6-1 and 6-2 are both for distinctively column-like (3:1 aspect ratio) foundations.  Apparently, this is how it was tested back in the 1930s-1940s.  I am not sure that these formulas were intended for such use at all.
When drawn to scale, the canopy on such footing looks scary.
Steve Gordin SE
Irvine CA
----- Original Message -----
Sent: Monday, February 13, 2006 11:17 AM
Subject: RE: canopy footing

I have seen lots of canopy designers use pole sign formulas when I was a plan reviewer.  Formula 16-2 is the constrained formula.  If they are using that one they need to have an adequate portland cement concrete slab around the foundation to resist the thrust.  Up here they frequently put a small PCC slab around the pumps to resist spilled gas but have asphalt pavement close by.  If you do have an adequate slab I would tell them they need to use formula 16-1.
 You are not allowed to use plain concrete to resist seismic forces for other than houses/duplexes.  Are they reinforcing the "cube"?

From: S. Gordin [mailto:mailbox(--nospam--at)]
Sent: Monday, February 13, 2006 9:47 AM
To: Seaint@Seaint. Org
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.
Steve Gordin SE
Irvine CA