Flexural rigidity: Definition, Formula, Unit, Significance

The term flexural rigidity is an important factor while the design of beams. Therefore in this article, we have tried to explain flexural rigidity along with its importance and numerical.

What is Flexural rigidity?

The flexural rigidity is the product of the modulus of elasticity (E) and moment of inertia (I) of the beam about the neutral axis. As we increase the value of flexural rigidity, the strength of the beam to resist bending also increases.

Flexural Rigidity equation = E x I

The flexural rigidity of components can be increased by raising the moment of inertia of the cross-section or by choosing the material with a higher modulus of elasticity.

Units of Flexural rigidity:

The SI unit of the modulus of elasticity is N/m² and the SI unit of moment of inertia is m4. Therefore the SI unit of flexural rigidity (FR) can be derived as,

FR = E x I
= (N/m2) x (m4)
= N.m2

Hence the SI unit is N.m2. While the FPS unit of flexural rigidity is lb.ft2, It is also denoted by the unit Pa.m4.

Significances of Flexural rigidity:

The significances are as follows:-

  1. The resistance of the beam for the bending depends on flexural rigidity.
  2. The beam with a higher value of flexural rigidity has less value of deflection.

Solved examples:

1] Find the flexural rigidity of the beam if the beam is made of timber with a modulus of elasticity of 13 GPa and a moment of inertia of 5.2 x 10-3 m4.


Modulus of elasticity, E = 13 GPa = 13 x 109 N/m2
Moment of inertia, I = 5.2 x 10-3 m4

The flexural rigidity of the beam is,

FR = E x I

= (13 x 109) x (5.2 x 10-3)

= 67.6 x 10⁶ Nm²

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Pratik is a Graduated Mechanical engineer. He enjoys sharing the engineering knowledge learned by him with people.

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