This document discusses analyzing statically indeterminate structures using the energy principle. It states that in beams and frames with rigid joints, both shear and bending stresses can occur at any section. The total strain energy stored depends on the magnitudes of direct forces, shear, and moments. When analyzing indeterminate structures, the work done by direct and shear forces is neglected compared to that done by bending. It also introduces Castiglione's first theorem relating the partial derivative of strain energy to displacements and forces/moments. It provides an example of using this method to determine the vertical deflection of a point on a rigid cantilever frame under a given load.