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I use 2500 psi concrete for flagpole footing.

This is how I look at it. A residential continuous footing under short shear
walls with hold-downs due to small uplift causes bending on the continuous
footing. The minimum footing size and reinforcement works for this bending.
It is unreasonable na impractical to require 3000 psi concrete with
inspection on the whole continuous footing system where there are a lot of
these short shear walls with small uplift loads. I think this is more of a
footing than it is a grade beam subject to a lot of bending stress. 

As the lateral loads get bigger and the uplift loads get higher or where
steel columns are used to resist lateral loads and the moment at the bottom
of the column is resisted by a grade beam in bending, then, 3000 psi concrete
with special inspection may be required. I'll check the stresses in the grade
beams and if the concrete and reinforcing steel and if they are pretty close
to the allowable, it is more of a beam than a footing.If I want to avoid 3000
psi concrete with inspection, I increase the size of the grade beam and add
extra reinforcement such that stresses are very low, and then, I could say
that it is more of a footing than a beam. 

I use the same judgement for flagpole footings. If stresses on the concrete
and reinforcement is way below allowable, again, it is a footing more than it
is a beam. I increase footing size and add more reinforcement to a point that
I am satisfied with my judgement. For real heavy lateral loads where
increasing footing size is impractical, then I design it like a beam for
bending and use 3000 psi concrerte with inspection.

Ernie Natividad