Bending is usually accompanied by shear. The combination of shear and bending stresses produces the principle stress which causes diagonal tension in the beam section. The diagonal tensile stress caused by the shear and combination of shear and bending is likely to cause failure of the section by producing cracks as shown in the Fig. This should be resisted by providing shear reinforcement in the form of vertical stirrups or bent up bars along with stirrups. Find the Vertical Stirrups and Bent up Bars.

Crack Pattern in Beams (Simply Supported Beam)