抄録
The method of structual design, so as to "Plastic Design", "Collapse Design", etc., is based on the ultimate strength of the structure. The calculation of ultimate strength requires the formation of plastic hinges with perfect rotation capacity after large plastic deformation. In this report, the stability criterion, as the limitation of width-thickness ratio, of flanges or webs of I-shape section, is discussed. First, the stability criterion of thin plate, which is already acted the yield stresses under various boundary conditions, is established, using the criterion of dynamic stability. Then, this criterion is rewrited by the Prandtl-Reuss' stress-strain relationship concerning elastic, perfectly plastic material. For example, the limitation numbers of the width-thickness ratio of the plate in the plastic region under four types of loading and boundary conditions, are calculated. Compared with the reported results of the experimental analyses, the results of calculations are rather high. One of the reasons of this difference is said to be the unavoidable imperfections of actual plates.
