16, No.

3.) [Illustration: FIG.

16 .-- Three common forms of beams.1.

Simple.
2.Cantilever.3.

Continuous.] _Stiffness of Beams_ The two main requirements of a beam are stiffness and strength.
The formulae for the _modulus of elasticity (E)_ or measure of stiffness of a rectangular prismatic simple beam loaded at the centre and resting freely on supports at either end is:[10] [Footnote 10: Only this form of beam is considered since it is the simplest.