The another structure under consideration is a four-span continuous beam as shown in Figure 5.9. The degree of static indeterminacy of the beam is 3. Two basic determinate structures are illustrated. On the left-hand side of the figure, the basic determinate structure is formed by releasing moment in the beam at the three interior supports. On the right-hand side of the figure, the basic determinate structure is formed by releasing the vertical reaction at the three interior supports.

For each basic determinate structure, bending moments (bending moment in the basic determinate structure due to applied loading) (due to ), (due to ), and (due to ) are plotted. For the basic determinate structure on the left-hand side of the diagram, all integrations required for calculating the deflections can be easily performed using integration tables. In addition, for the left-hand side of the diagram, several deflection coefficients are zero. On the right-hand side, however, all coefficients are nonzero. The choice of basic determinate structure on the left allowed the influence of a given redundant force to be restricted to a relatively small portion of the structure (two spans in this particular case). For the structure on the right-hand side, the influence of a given redundant force R j is felt throughout the structure. It can be concluded that the basic determinate structure on the left-hand side is preferable because it reduces the computational effort.