Bending About the Z Axis

The equations relating to the moment generated in a beam type spring element and the beam's displacement, (Figure 1) is given by:

Where,

${\theta }_z={\theta }_{z2}-{\theta }_{z1}$ is the relative rotation of node 1 and 2.

$f_{zz}\left({\theta }_z\right)$ is the function defining the force-displacement relationship.