3D Beam‐Column Element with Generalized Plastic Hinges

Beam‐column elements in which plastic hinges may form are commonly used for elastic‐plastic analysis of frames. The concept of a zero‐length plastic hinge (lumped plasticity) is a mathematical abstraction, because it implies infinite strains. Nevertheless, the concept is convenient computationally, and can be sufficiently accurate for many practical applications. For simple beams, plastic hinges can be introduced easily into a mathematical model. For 3D beam‐columns, however, the concept of a “generalized” hinge is needed, accounting for interaction among axial, torsional and biaxial bending effects. A theory and computational procedure based on plasticity concepts are presented. Numerical examples indicate how the element might be used, and show that results in agreement with more elaborate models can be obtained. Because the lumped plasticity assumption is not necessarily accurate, caution is advised in use of the element.