The bending stiffness is equal to the product of the elastic modulus and the area moment of inertia of the beam cross-section about the axis of interest. In other words, the bending stiffness is . According to elementary beam theory, the relationship between the applied bending moment and the resulting curvature of the beam is
where is the deflection of the beam and the coordinate. In literature the above definition is sometimes used with a minus sign depending on convention.
Bending stiffness in beams is also known as Flexural rigidity.