I recall you have to check the allowable bending moment based on allowable concrete stress, also:
M = 0.5 * f'c * j * k * b * d^2
Correct me if I'm wrong. It's been a long, long time.
You could also get a masonry design book. Masonry WSD is just like Concrete WSD.
Bob Garner, S.E.
R. Garner
Moffatt & Nichol
Tel.: (619) 220-6050
Fax.: (619) 220-6055
e-mail: rgarner@moffattnichol.com