Beam (structure)

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.

Related Topics:
Structural - Element - Load - Bending - Vertical - Gravitational - Force - Horizontal - Wind - Earthquake - Column - Wall - Girder

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Beams are characterized by their (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 (also known as a "universal beam" or, for stouter sections, a "universal column"). This is commonly used in steel-frame buildings and bridges. Other common beam profiles are the C-channel, the hollow structural section beam, the pipe, and the angle.

Related Topics:
Material - Construction - Steel - Reinforced concrete - Wood - I-beam - Flange - Bridge - C-channel - Hollow structural section - Pipe - Angle

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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. However, there are some reniforced concrete beams that are entirely in compression. These beams are known known as prestressed beams. High strength steel tendons are strecthed while the beam is cast over the them. Then, when the concrete has begun to cure, the tendons are released and the beam is immediately under eccentric axial loads. This eccentric loading creates an internal moment and in turn, increases the moment carrying cpapacity of the beam. They are commonly used on highway bridges.

Related Topics:
Compressive - Tensile - Stresses - Prestressed beams

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The I-beam is so common because it makes efficient use of material for carrying loads in bending—it material at the top and bottom of the beam where the bulk of the load is carried.

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The primary tool for structural analysis of beams is the Euler-Bernoulli beam equation. Other mathematical methods for determining the deflection of beams include "method of virtual work" and the "slope deflection method." Engineers are interested in determining deflections because the beam may be in direct contact with a brittle material such as glass. Beam deflections are also minimised for aesthetic reasons. A visibly sagging beam, though perhaps safe, is unsightly and to be avoided. A stiffer beam (high modulus of elasticity and high moment of inertia) produces less deflection. Mathematical methods for determining the beam forces (internal forces of the beam and the forces that are imposed on the beam support) include the "moment distribution method," the "force or flexibility method," and the "stiffness method."

Related Topics:
Euler-Bernoulli beam equation - Deflection - Virtual work - Brittle - Stiffer - Modulus of elasticity - Moment of inertia - Moment distribution

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