Redundant beam systems, i.e. ones that contain a surplus number of constraints, are statically indeterminate. As we have seen in Chapter 3, this means that they can be balanced by ∞v−g different sets of reactive forces, v − g being the degree of redundancy. We therefore need to identify the particular single set of reactive forces which, in addition to equilibrium, also implies congruence, or rather the respect of the internal and external constraints, notwithstanding the deformations induced in the structural elements.