The effects of local buckling and material yielding on the axial stiffness and failure of uniformly compressed I-section and box-section struts

The behaviour of thin-walled compression members is known to be significantly influenced by the effects of local buckling. Thin-walled sections lose axial compressive stiffness and the compressive carrying capability of the members can be considerably reduced as a result of the effects of local buckling. Finite element simulation is employed in this paper to examine the post-buckled response of thin-walled I-section and box-section struts, giving due consideration to the influence of geometric imperfections and to elasto-plastic material behaviour. A detailed account of the growth and redistribution of stresses after local buckling as well as the initiation of yielding and yield propagation throughout loading is given in the paper. The influence of different in-plane displacement boundary conditions imposed in the simulations at the section plate junctions is also detailed in the paper as well as the effect of yielding on the post-buckled stiffness and failure of the sections. It is shown that the effects of geometrical imperfections are most prominent for strut designs with near simultaneous buckling and yielding and that the ultimate failure and unloading of strut designs, in general, is synonymous with the development of yielding at the section junctions along the full length of the struts and through to the middle surface of the section walls.