We were discussing some basic concepts of strength of materials in our recent posts. Today we will see here the basic principle of shear force and bending moment with the help of this post.

First we will understand here the meaning and importance of shear force and bending moment and after that we will discuss further the method to draw the diagram of shear force and bending moment.

### Shear force

Shear force is basically defined as the algebraic sum of all the vertical forces at any section of the beam either left hand side or right hand side of the section. Shear force is also a type of force and hence its unit will be Newton.

Shear force will be represented by S.F and therefore we will use S.F for indicating shear force during the determination or drawing of shear force diagram.

### Bending moment

Bending moment is basically defined as the algebraic sum of the moments of all the forces acting at any section of the beam either left hand side or right hand side of the section. Unit of bending moment will be Newton-meter or N-m.

Bending moment will be represented by B.M and therefore we will use B.M for indicating bending moment during the determination or drawing of shear force diagram.

Let us consider the following figure, we can see here one simply supported beam of length L and loaded with load W at the midpoint of the beam.
Now we will understand here the basic concept of shear force and bending moment with the help of the above figure.

As we can see from above figure that, there are two forces acting at the ends of beam and one load is applied over the beam in opposite direction at mid point and hence there will be possibilities of splitting of beam in two parts. Â Splitting of beam under this situation will be termed as shearing action and force, which will be responsible for shearing of the beam, will be termed as shear force.

If we consider one section at the midpoint of beam, we can easily say that shear force will be determined by taking the algebraic sum of all the forces acting either left hand side or right hand side of the section.

We can also see from above figure that, beam might be bending under the action of above loading and we have also shown the bending of beam in above figure. If we consider similar section i.e. at the midpoint of beam, we can easily say that bending moment will be determined by taking the algebraic sum of moments of all the forces acting either left hand side or right hand side of the section.Â

We will discuss shear force diagram and bending moment diagram in our upcoming post, but first we will discuss the various types of beams in our next post i.e. Types of beams.

Do you have any suggestions? Please write in comment box

### Reference:

Strength of material, By R. K. Bansal