Beam (structure)

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A beam is a structural element that carries load primarily in bending (flexure). Beams generally carry vertical gravitational forces but can also be used to carry horizontal loads (i.e. loads due to a gust of wind or an earthquake). The loads carried by a beam are transferred to columns, walls or girders, which in turn transfer the force to adjacent structural members.

Beams are characterized by their profile (the shape of their cross section), their length and their material. In contemporary construction, beams are typically made of steel, reinforced concrete, or wood. One of the most common types of steel beam is the I-beam or wide-flange beam, commonly used in steel-frame buildings and bridges.

Internally, beams experience both compressive and tensile stresses as a result of the loads applied to them. Under gravity loads, the top of the beam is under compression while the bottom of the beam is under tension, leaving the middle of the beam relatively stress-free. The I-beam is so common because it makes efficient use of material for carrying loads in bending: it maximizes material at the top and bottom of the beam where the bulk of the stress is carried.