Based on the American Institute of Steel Construction (AISC) specifications for load-and-resistance factor design (LRFD) for buildings, the shear capacity V _u , kip (kN = 4.448 X kip), of flexural members may be computed from the following:

Stifferners are required when the shear exceeds V _u . In unstiffened girders, h/t _w may not exceed 260. In girders with stiffeners, maximum h/t _w permitted is 2,000/( F _yf ) ^½ for a/h £ 1.5 or 14,000/( F _yf (F _yf + 16.5) ) ^½ for a/h > 1.5, where F _yf is the specified minimum yield stress of the flange.
For shear capacity with tension – field action, see the AISC specification for LRFD.