The ultimate shear strength provided by the concrete, 'fVc', is calculated as follows:
For shear and flexure only (no axial load):
fVc = 2*f*(f'c*1000)^(1/2)*b*d
For shear with axial compression:
fVc = 2*f*(1+Pu/(2*Ag)*(f'c*1000)^(1/2)*b*d
For shear with axial tension:
fVc = 2*f*(1+Pu/(0.5*Ag)*(f'c*1000)^(1/2)*b*d
where: f = 0.75
Ag = b*h
Note: for members such as one-way slabs,
footings, and walls, where minimum shear
reinforcing is not required, if fVc >= Vu
then the section is considered adequate.
For beams, when Vu > fVc/2 , then a
minimum area of shear reinforcement is
required.

The ultimate shear strength provided by the shear reinforcing in beams, 'fVs', is calculated as follows:
fVs = f*fy*d*Av/s2
where: f = 0.75

The required amount of shear strength to be provided by the shear reinforcing in beams is:
fVs(req'd) = Vu-fVc >= 0.
The required amount of shear strength to be provided must be <= fVs(max).

The maximum allowable ultimate shear strength to be provided by the shear reinforcing in beams, 'fVs(max)', is calculated as follows:
fVs(max) <= 8*f*(f'c*1000)^(1/2)*b*d/1000
where:
f = 0.75

The required area of shear reinforcing, 'Av', perpendicular to axis of the beam is calculated as follows:
Av = fVs*s/(f*fy*d) >= Av(min)
where:
f = 0.75
fVs = max. of: (Vu - fVc) or 0
Note: Av = area of both legs of a closed stirrup.

The minimum area of shear reinforcing, 'Av(min)', to be provided for beams is calculated as follows:
Av(min) = 75*SQRT(f'c*1000)*b*s/fy
but not less than: 50*b*s/(fy*1000)
Note: Av(min) = area of both legs of a closed stirrup.

The maximum allowable shear reinforcing (closed stirrup) spacing, 's', shall not exceed d/2, nor 24". However, when fVs > 4*f*(f'c*1000)^(1/2)*b*d, then the maximum spacing given above shall be reduced by one-half. (Note: f = 0.75)