ABSTRACT
The concept of strain energy is important in structural analysis, and it is useful to express the strain energy due to any type of stress in a general form amenable to matrix treatment. It is possible then to consider at the same time components of strain energy due to axial force, bending moment, shear, and torsion. The principle of virtual work relates a system of forces in equilibrium to a compatible system of displacements in any structure, linear or nonlinear. The chapter explores virtual forces or virtual displacements and use the equality of the complementary work of virtual external forces and the complementary energy of the virtual internal forces moving along the real displacements. Alternatively, it details the equality of external and internal virtual work of the real forces moving along the virtual displacements. Unit-load and unit-displacement theorems offer a convenient formulation. It should be noted that the latter theorem is applicable only to linear structures.
