Post+and+Lintel



= The simplest illustration of load and support in construction is the post and lintel system, in which two upright members (posts, columns, piers) hold up a third member ( lintel, beam, girder, rafter) laid horizontally across their top surface. This is the basis for the evolution of all openings. But, in its pure form, the post and lintel is seen only in colonnades and in framed structures, since the posts of doors, windows, ceilings, and roofs are part of the wall. = = = = Lintel  = = The job of the lintel is to bear the loads that rest on it (and its own load) without deforming or breaking. Failure occurs only when the material is too weak or the lintel is too long. Lintels composed of materials that are weak in bending, such as stone, must be short, while lintels in materials that are strong in bending, such as steel, may span far greater openings. Masonry lintels are inefficient because they must depend on the cohesiveness of mortar, which is weaker than the blocks it bonds; so, in masonry construction, lintels of monolithic (single – slab) stone, wood, and stronger materials are employed. = = =



= Post  = = The job of the post is to support the lintel and its loads without crushing or buckling. Failure occurs, as in lintels, from excessive weakness or length, but the difference is that the material must be especially strong in compression. Stone, which has this property, is more versatile as a post than as a lintel; under heavy loads it is superior to wood but not to iron, steel, or reinforced concrete. Masonry post, including those of brick, may be highly efficient, since the loads compress the joints and add to their cohesiveness. Although monolithic stone columns are used, they are extravagant to produce for large structures, and columns are usually built up of a series of cylindrical blocks called drums. =