The necessity to save steel leads to a marked tendency towards thin-walled structures. Such structures are made of thin plating, the behaviour - and, of course, design - of which is very significantly affected by stability phemena. In fact, with up-to-date thin-walled steel plated structures, it is very frequently the point of view of stability that governs the design. So it is t astonishing that the attention of a great number of research teams in various parts of the world has been for a good many years directed to investigations into numerous aspects of the buckling behaviour of steel plated structures. However, the current problems of buckling research, which require to account for the effect of initial imperfections, post-buckled behaviour and plastic reserve of strength (this leading in theoretical research to the necessity to solve boundary value problems of geometrically and physically n-linear partial differential equations, and in experimental studies to conduct experiments on full-size test girders) are very complex and time-consuming. Then it is beyond the means of one investigator, or even of one research team, to deal successfully with such problems and, conse- quently, effective cooperation is indispensable. This was also the reason for the initiation of a fruitful collaboration between the first author of this book (Assoc. Prof. J. Djubek, D. Sc. ) and the third author (Assoc. Prof. M. Skaloud, D. Sc.