beamcolumn

A beam-column is a structural member designed to resist both bending moments and axial forces. It is common in frames where members carry significant vertical loads along with lateral loads, such as building frames, bridge approaches, and tower structures. Unlike a pure beam or a pure column, a beam-column combines bending stiffness with axial load carrying capacity, and its behavior reflects the interaction between these actions.

The response of a beam-column is governed by the interaction between axial force (N) and bending moment (M). For slender members, geometric nonlinearity and P-Delta effects can be important, and strength is often represented by interaction curves or capacity surfaces rather than separate capacity limits for N and M. In linear analyses, an effective moment of inertia approach or frame interaction can approximate the reduction in stiffness and strength with increasing axial load. Failure modes include Euler buckling of columns, lateral-torsional buckling of beams, and local buckling of flanges, depending on member configuration, end conditions, and bracing.

Design considerations focus on preventing excessive interaction between N and M, providing adequate lateral support to avoid lateral-torsional buckling, and accounting for P-Delta effects. Slenderness, end fixity, bracing, and reinforcement detailing (in steel or concrete) are important. Design codes provide interaction equations or capacity surfaces to ensure safe combinations of axial load and moment.

Applications include many steel and concrete frame structures, such as multi-story buildings, bridges, and towers. Materials commonly used are structural steel, reinforced concrete, or composite sections. Analysis often employs beam-column elements in structural models, incorporating geometric and material nonlinearities to capture realistic behavior under combined axial and bending actions.