The Plastic Theory and its Application to Design

In recent years considerable amount of investigational and research work has been carried out on the theory of Plasticity and its application to the design of structures. The "Physical" theory of Plasticity has been a matter of study for a long time. Thus a knowledge of the mechanism of plastic flow and the behaviour of materials under straining in the plastic region was in possession of the engineers when they grew an interest to build up a theory suitable for application in the design of structures. This interest has arisen since they realised that the failure of a highly redundant steel structure, such as a welded rigid frame, does not take place when yield of the material is developed at some individual point or points but there is only a redistribution of the Bending Moments so that the structure absorbs energy in its other less stressed parts. With the realization of this feature, engineers started investigating, both theoretically and experimentally, what happens if designs could be made with yield stress as the working stress instead of the usual design methods taking working stress at about half the yield stress.