Beam
A beam is an abstract model where only the extension in the axial direction is modeled explicitly on an edge. The cross section is specified in terms of properties such as area and moments of inertia.
The exact stress distribution in the beam is not explicitly modeled. It is actually not even fully determined by the cross-sectional properties. Instead, six (in 3D) resultant section forces are used: axial force, shear forces in two perpendicular directions, two bending moments, and one twisting moment.
Two formulations are available in the Beam interface: