Beams Subjected To Couples:

A beam might be subjected to a clockwise (called as positive couple) or anticlockwise couple (called as negative couple) at a section. To determine the reactions at the support, the magnitude & the direction of the couple is considered. The bending moment at the section of the couple alter suddenly in its magnitude. Whereas drawing the bending moment diagram, the bending moment, just left of section of the couple & only right of the section of the couple, should be calculated, along the help of the reactions at both the ends. As the couple does not involve any load, the shear force does not alter at the section of the couple.

Some instance of equivalent couples has been specified in Figure.