The Application of Plastic Theory to Bending: An Examination of the General Principles Involved in Applying ‘Limit Design’ to Structural Members

IN modern structural design the maximum carrying capacity of a member under non‐uniform static stress at normal temperatures is not necessarily the load which gives a maximum stress equal to that at the limit of proportionality. All experiments have shown the ultimate strength of beams to exceed the value predicted on the basis of the elastic theory. This applies to simply supported and redundant beams made of steel and wrought iron, as well as to beams constructed from other metals such as cast iron, aluminium, magnesium, etc. Investigators differ, however, in the interpretation of this increased strength and in their methods of a more advantageous use of the material. These are usually based on specific experiments and apply to certain conditions only, without embracing all materials and all possible load distributions and types of structures.