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RE: canopy footing

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Steve,

 

It seems to me that the proportions of the cube should not prevent its use for this application.  Suppose that, by a trial-and-error solution, you found that an 18” wide by 5-ft deep footing did not have adequate capacity by the formulas of 1806.2.  You would have a couple of options for improving the capacity: try deepening the footing or try widening it; either seems to be a reasonable option.  At what width does the increase in width become unreasonable?  What if it took a width of 5 feet to develop the capacity?  That seems O.K. to me.  What if it took 6-ft?  Seem O.K. to me too, but I would probably try to figure out how to take advantage of the gravity-moment-of-stability provided by the weight of the massive footing.  It would take more concrete than a deeper footing, but I think it would comply with the Code.

 

However, if for some reason, the footing needed to be dug by hand, widening is may be a better option than deepening it; for example, if the OSHA rule is in effect that requires that an excavation that a worker enters must be shored if its depth exceeds 5-ft.

 

Nels Roselund, SE

South San Gabriel, CA

njineer(--nospam--at)att.net


From: S. Gordin [mailto:mailbox(--nospam--at)sgeconsulting.com]
Sent: Monday, February 13, 2006 10:47 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.

 

TIA,

 

Steve Gordin SE
Irvine CA