Shear Force is defined as the force acting on the beam in a perpendicular direction at given section to cause shear at that section. In Shear Force diagram general co-ordinate system is used. Here the downward direction will be treated as negative i.e. negative Y-axis and upward as positive. In Shear force diagram the section is considered one by one. The selection of section may be from left to right or right to left it depends. The signs shear force varies accordingly. For. if we consider the section from left to right then the upward Shear Force is assumed to be “+ive” and bending moment is considered negative in case of the clockwise moment.

Bending Moment

The internal couple which is trying to rotate the member is known as bending moment. The moment is a product of perpendicular distance and the force applied at a distance from the point. Bending moment is considered “+ive “ in case of the clockwise moment when considered from left to right. Below fig. can give a clear understanding of SFD diagram consideration.

TIPS to Solve SFD & BMD:

For cantilever beam consider the direction of section selection from its free end.

For Uniformly Distributed Load Load(UDL) the degree of curve is 1st(linear) in SFD and 2nd(parabola) in bending moment diagram(BMD). For Uniformly Varying Load Load(UVL) the degree of curve is 2nd (parabola) in SFD and 3rd(cubic parabola) in bending moment diagram(BMD).