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.

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**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. 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.

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

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**Reference:**

Strength of material, By R. K. Bansal

Image Courtesy: Google