# Assumptions in theory of pure bending [with Pdf]

## What is pure bending?

For a certain length of the beam if the shear forces are zero and if it is subjected to the constant bending moment then this beam is said to be in the state of pure bending.

Therefore for the beam subjected to pure bending,

Shear force, (F) = 0 and Bending moment, (M) = constant

Therefore the beam under pure bending has zero shear stresses.

## Pure bending example:

As shown in the figure, there is no shear force is present in between portion BC and the bending moment is constant over the length BC. Hence we can say that the portion BC of the beam is subjected to pure bending.

## Assumptions in theory of pure bending:

Following are the assumptions used for the analysis of the beam under pure bending:-

A) Material of the beam is considered homogeneous and isotropic.

B) Each layer of the beam is free to expand or contract.

C) Young’s modulus is considered as same for the compression and the tension.

D) The radius of curvature of the beam is comparatively higher than the width or the depth of the beam.

E) The bam is loaded within the elastic limits.

F) The plane section remains plane after the deformation also. 