In building construction, a system in which two upright members, the posts, hold up a third member, the beam, laid horizontally across their top surfaces. In Britain it is called post-and-lintel system, but in the U.S. “lintel” is usually reserved for a short beam that spans a window or door opening. The post and beam formed the basis of architecture from prehistoric to Roman times, and is illustrated by such ancient structures as Stonehenge. All structural openings evolved from this system, which is seen in pure form only in colonnades and in framed structures, the posts of doors, windows, ceilings, and roofs usually being hidden in walls. The beam must bear loads that rest on it as well as its own load without deforming or breaking. Post-and-beam construction has largely been supplanted by the modern steel frame.
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In building construction, a horizontal member spanning an opening and carrying a load. The load may be a wall above the opening (see post-and-beam system) or it may be a floor or roof. Beams may be of wood, steel or other metals, reinforced or prestressed concrete, plastic, or even brick with steel reinforcement. For weight reduction, metal beams are I-shaped, having a thin vertical web and thicker horizontal flanges where greater stress occurs. A joist is any of a series of small parallel beams supporting a floor or roof. Seealso girder, spandrel.
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