How is stirrup spacing determined in beam design?

Stirrup spacing is determined by shear requirements: (1) Calculate shear capacity of concrete Vc, (2) If Vu > Vc, provide stirrups such that Vs = Vu - Vc, (3) Spacing s = Av*fy*d/Vs where Av is stirrup area, (4) Maximum spacing is d/2 or 300mm for moderate shear, d/4 for high shear regions. Minimum shear reinforcement required even if Vu < Vc. Closer spacing near supports, can increase toward midspan where shear is lower. Stirrups also provide confinement and support longitudinal bars.