Shear reinforcement in SAP2000 is given in the units of 'length^2/unit length'. For example, if the displayed unit of length is in inches, shear reinforcement is in 'in^2/in.' units.
To convert shear reinforcement value ( given by SAP2000 in 'inch' units) into stirrup spacing, multiply the given value by 12 to convert it in into normally used units of 'in^2/ft.' Now, divide the product of 'cross-sectional area of one stirrup & 12' by the required area of shear reinforcement, calculated earlier. The result of division will be the stirrup spacing in inches.
For example, if the shear reinforcement value (given by SAP2000 in 'inch' units) is 0.025, required As =0.025x12=0.3 in^2/ft.
Cross-sectional area of one #3, 2-legged stirrup is 0.11 x 2 = 0.22 in^2.
Then, required spacing of #3 stirrup will be = 0.22 x 12 / 0.3 = 8.8 in.
Alternately, you may get the same result by dividing the 'cross-sectional area of stirrup' with the 'required shear reinforcement
value, given by SAP2000 in inch units, directly. [ 0.22 / .025 = 8.8 in.]
Regards.