ABSTRACT
The energy principles are based on the law of conservation of energy which requires that the work done by external forces on an elastic structure be stored in the form of strain energy which is completely recovered when the load is removed. Betti's law derived from this law, applied to linear structures, serves a useful purpose in transformation of information given in one form into another. The chapter consider Maxwell's theorem, which is a special case of the more general Betti's theorem. The energy theorems presents in the chapter lead, in the case of linear structures, to equations which were derived in a different manner. For example, Castigliano's and the principle of stationary potential energy, are the same as the equilibrium equations used in the displacement method. It is therefore apparent that the energy principles are not merely methods of calculation of displacements but they can form the basis for derivation of equations satisfying the requirements of equilibrium and compatibility.
