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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.
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.
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.
From prehistoric times to the Roman Empire, the post – and – lintel system was the root of architectural design. The interiors of Egyptian temples and the exteriors of Greek temples are delineated by columns covered by stone lintels. The Greeks opened their interior spaces by substituting wooden beams for stone, since the wood required fewer supports. The development of the arch and vault challenged the system but could not diminish its importance either in masonry construction or in
wood framing, by its nature dependent on posts and beams.
Ancient uses of the post – and – lintel were refined but not fundamentally altered until the production of cast – iron columns, which, offering greater strength and smaller circumference, greatly reduced the mass and weight of buildings. Much construction in modern materials is based on the post – and – lintel system of the post. Steel and concrete skeletons restore to modern architecture the formal simplicity of the oldest structures known. But, because they are rigid frames, they abandon the fundamental concept of the duality of post – and – lintel by fusing them into a unit through which stresses are
