A common type of statically indeterminate beam consists of a beam resting on three simple supports. The presence of a third support (i.e., a second roller support) means that there will be more unknowns than equilibrium equations. Consequently, one additional equation must be developed to solve this type of problem.

The priniciple of superposition provides a convenient means to obtain an additional equation based on the configuration of the beam and the fact that the beam deflection is known at the roller locations.