TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
The stresses in the reinforcing steel will not exceed the values shown in table 5-8.
The allowable axial stress, Fa, can be determined as follows:
Fa = 0.20f'mR
R = The stress reduction factor for the wall based on the height to thickness ratio as follows:
h = The clear height of the wall, feet.
tn = The nominal thickness of the wall, inches.
The stress reduction factor limits the axial stress on the wall so that buckling will not occur. When analyzing
the top or bottom of a wall, where buckling is not a concern, the stress reduction factor should not be used.