Last edited 21 Oct 2020


In structural engineering, the term 'stiffness' refers to the rigidity of a structural element. In general terms, this means the extent to which the element is able to resist deformation or deflection under the action of an applied force. In contrast, flexibility or pliability is a measure of how flexible a component is, i.e. the less stiff it is, the more flexible it is.

Young’s modulus (E - elastic modulus) is a measure of the stiffness of a material. This is a material constant, independent of the amount of material.

Increasing the stiffness or rigidity of a structural element reduces its deflection under load. This can be done by strengthening its section or increasing its size, but this will generally also increase its cost.

In a structure that is made up of many different structural elements, those elements will carry load proportionate to their relative stiffness. Therefore, the load an element will attract increases the stiffer it is.

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