Application of surfaces of ultimate strength for thin-walled beams

This paper deals with the problem of ultimate load-carrying capacity of thin-walled sections subject to combined load. That has direct implementation in sizing and design of thin-walled structures. It is solved using the ultimate strength method based on the theory of plastic analysis of structures. It is assumed that the elastic strains are negligible in comparison to the plastic strains and that justifies the application of a fully plastic model. The following problems have to be analyzed before the sizing and design is completed: ectors and load components ons of the plastic neutral axes rface of ultimate strength st important achievement presented in this paper is an improvement for the location of the plastic neutral axis. Until now, the position of the plastic neutral axis has been localized by iterations, starting with the position from the elastic model. That led, in some cases, to a statically inadmissible model and lack of equilibrium in case of asymmetric sections or asymmetric loads. essful solution to the problem consists in covering the whole section with a mesh of plastic neutral axes and a cluster of corresponding points on the surface of ultimate strength. the points on the surface has load components in proportion with the load vector. The corresponding location of the plastic neutral axis is precisely the one we are seeking. ad vector may be extended to pierce one of the triangles that the surface is made of. The coordinates of the point where the load vector is piercing the triangle is a weighted-average of the coordinates of three vertices of the triangle. The same weight is used to localize the plastic neutral axis corresponding to the piercing point of the surface.