bending moment, internal resistance to rotation, moment determining methods, types of bending moment at a section

# Bending Moment - Definition & Calculation at Any Section

## Definition

It is the internal resistance to rotation.

OR

Bending moment at a point or at a section is the algebraic sum of Moments caused by forces action to the left or right of that point or section. Mathematically it can be written as

`'''Moment = Σ ML = Σ MR'''`

Moment can not be find out directly however it can be find out by using many practical and theoretical methods such as:

1. Double integration method
2. Conjugate beam method
3. Area moment method

## Bending Moment at any section

Bending moment at any section is the sum of all moments to the left or right of that section.

### Positive bending moment

Bending which produces compression in upper (outer) fibers and tension in lower fibers.

### Negative bending moment

Bending which produces compression in lower (inner) fibers and tension in upper fibers.