ABSTRACT
The instability of elastic equilibrium occurs in general for slender or thin structural elements subjected to compressive loads, such as columns of buildings, machine shafts, struts of trusses, thin arches and shells, and cylindrical and spherical shells subjected to external pressure. But, also, other cases that are more complex as regards both their geometry and the loading conditions can equally be considered. It will suffice to think of the lateral torsional buckling of beams of thin rectangular cross section, where the disparity between the orders of magnitude of the two central moments of inertia can cause, in a deflected beam, a sudden torsional deformation. The instability of elastic equilibrium is, moreover, a critical phenomenon that may affect an entire beam system before it involves a particular element of the system. This occurs in the case of metal trussed or framed structures, which are frequently made up of extremely slender rods or beams.
