Title: CRITICAL SURVEY OF THE THEORY OF PLASTICITY
Abstract: The Author was the first to publish in 1914, in a Hungarian review, the idea that the determination of the true load capacity of hyperstatic structures had to reckon the residual steel strains. This true load capacity exceeding that according to the theory of elasticity, the residual strain might be reckoned with in the practical design of structures. In the meantime this problem had been discussed, expounded from several aspects, and experimentally tested. Let us have now a critical survey of the domain as a whole. There are different denominations for the new design method. Theory of plasticity means a design method taking also residual deformations into consideration, as against the theory of elasticity relying on elastic deformations alone. It is also called ultimate load method (theory of plastic equilibrium), a term other than unambiguous, namely some authors e.g. STUSSI mean by ultimate load the maximum load carried by the structure, ,,,-hile others such as F. BLEICH, lVlAIER-LEIBNITZ and the Author himself in an earlier publication, have meant the maximum load allowed in practice. The approach to this problem depends on certain fundamental principles. What is the goal of designing our structures? That is the serviceability in use. Taking uncertainties of manufacture, material characteristics and load into consideration, the structures have to be designed ,.,ith a certain to failure. As stated at the Vienna Congress, the safety degree is a question of economy. On one hand, construction is expected to be inexpensive, on the other hand, the possible damage must not exceed the economy resulting from reduced cross sections. Thus, the higher the possible damage, the higher safety is required. These considerations make it clear why to be satisfied with a safety factor of 1.6 or 1.8 in cases where failure is unlikely else thanin an excessive deflection, as against about 3 in cases where an excessive strcss in the member would entrain instantaneous collapse without warning (e.g. buckling). :Members likely to become unserviceable if excessively deformed are attempted to be given a satisfactory safety to excessive deformation rather than to failure. As a rule on the value of the allowable deflection, the load where the deflection is accelerated under monotonically increasing load could be considered as limit load (critical load or practical ultimate load). In tests by F. STUSSI and C. F. KOLLBRUNNER [3] (Fig. 1) 1.71 t rather than 2.35 t should be taken as limit load of simple beams. Looked at from this aspect, also the conclusions drawll from these tests are slightly different, namely that the limit load (hence not the true load carry-
Publication Year: 1984
Publication Date: 1984-01-01
Language: en
Type: article
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