Lateraletorsionele

Lateraletorsionele, in English known as lateral-torsional buckling, is a form of instability that can occur in beams or other flexural members when they are loaded in bending. It describes a combined lateral displacement and twist of the cross-section around its centroid, typically on the side of the beam’s compressive flange. This buckling mode reduces the member’s effective bending capacity and can lead to sudden failure if not properly restrained.

The phenomenon is most common in slender steel beams, such as wide-flange I-beams or hollow sections, that are subjected to bending about their major axis with insufficient lateral support along the unbraced length. It can occur under both uniform and point loads, and is influenced by load position, support conditions, and the beam’s cross-sectional properties. If a beam is only laterally restrained at its ends, the tendency to twist increases as the unbraced length grows.

Key factors affecting lateral-torsional buckling include the unbraced length, the torsional rigidity and warping stiffness of the section, and the distance between lateral restraints or bracing points. Increased torsional stiffness, a more compact cross-section, and shorter unbraced spans all raise the critical moment at which buckling occurs. Load type and placement relative to the beam’s shear center also play a role.

Prevention strategies focus on increasing lateral restraint and torsional stiffness. This can be achieved with end or intermediate bracing, diaphragms or bolted/stiffened connections, restraints along the span, or by selecting cross-sections with higher torsional rigidity. Proper detailing and adherence to relevant design codes help ensure safe performance under bending.