We would certainly put a safety factor on whatever the blowout load was determined to be, and perhaps that wouldn't end up changing the design that much. There's a very good chance that the conservatism also lies within the equations for calculating the footing soil pressure and the allowable...
I have been designing foundations and cantilever columns for gas station pricing signs for a client for some time. Many of these signs go up to 40' in the air and have a fairly large surface area and wind loading governs the design. Typical design is to provide a pole footing that is 4' in...
