Beam: structural member and directed flow of waves, light or particles

Structural beams

Structural beams appear in buildings, bridges, machinery and vehicles. Typical elements include joists, lintels, girders and purlins; common cross-sections are rectangular, I-section, T-section, box and channel. Materials range from timber, steel and reinforced concrete to engineered composites. Choice of section, depth and material balances stiffness, strength, weight and economy for a given span and loading.

Beam theory and analysis

Engineers evaluate beams for bending moment, shear force and deflection. Classical models such as the Euler–Bernoulli beam theory assume plane sections remain plane and are adequate for slender beams; more refined models (for short, deep or shear-sensitive members) account for shear deformation and rotary inertia. Analysis considers load types (point loads, uniformly distributed loads), boundary conditions (simply supported, cantilever, fixed) and limit states including yielding, buckling and fatigue. Design follows building codes and uses factors of safety, serviceability limits and connection detailing.

Beams in optics, electronics and particle physics

In optics a light beam is a directed propagation of photons; common examples are laser beams and collimated lamp beams. Radio systems form electromagnetic beams with antennas and phased arrays to improve range and directivity. Particle beams—streams of electrons, protons or ions—are produced and controlled in accelerators and used in materials processing, imaging and medical therapies such as radiotherapy. Beam control techniques include focusing, collimation, steering and beamforming.

Applications, testing and history

• Applications: building floors and bridges, crane booms, vehicle frames, laser cutting, radar, communications and radiation therapy.
• Testing and inspection: load testing, strain measurement, non-destructive testing and fatigue assessment ensure performance and safety.
• History and terminology: timber beams are among the oldest structural elements; metal rolled sections and formal beam theory matured with industrialization and developments in mechanics. Distinctions: a column primarily resists axial loads, a truss shares loads through members, and a girder is a principal beam carrying other beams.