The equation for a quick estimate of the average shearing stress, (vavg), in the columns of concrete frames is as follows:
Ac = summation of the cross-sectional area of all columns in the story under consideration.
nc = total number of columns.
nf = total number of frames in the direction of loading.
Vj = story shear from Equation 2-11.
Equation 2-13 assumes that nearly all of the columns in the frame have similar stiffness. For other configurations of frames, compute the shear stress in the concrete columns from the principles of structural mechanics.