FUNDAMENTAL PROPOSITIONS IN THE PLASTIC THEORY OF STRUCTURES.

Synopsis According to the plastic theory, the collapse load of a ductile structure in the absence of instability due to axial stresses may be predicted by reference solely to the requirements of statical equilibrium. Since it is found unnecessary to consider the behaviour of the structure during the increase of the load to the collapse value, the assumption that the plastic theory will, in all cases, lead to a correct estimate of the collapse load and the mode of failure demands a rigorous proof. That assumption is vindicated in this Paper by reference to four formal propositions which are of fundamental importance in the plastic theory of structures.