Post and Lintel

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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.


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 lenght, 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, 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 monolitic 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.


Lintel

A lintel (or header) is a horizontal beam used in the construction of buildings, and is a major architectural contribution of ancient Greece. It usually supports the masonry above a window or door opening. Lintels may be made of wood, stone, steel or reinforced or pretensioned concrete. For example, at Stonehenge, stone lintels top off some of the megaliths. In typical homes today, lintels are commonly used in fireplaces where one will span the opening of the firebox. In this use they are most often steel, either straight for a square opening or arched for a more decorative effect. 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.


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Trabeated

In architecture, a trabeated system or order (from Latin trabs, beam; influenced by trabeatus, clothed in the trabea, a ritual garment) refers to the use of horizontal beams or lintels which are borne up by columns or posts. It is the opposite of the arcuated system, which involves the use of arches. The trabeated system is a fundamental principle of Neolithic architecture, Ancient Greek architecture and Ancient Egyptian architecture. Other trabeated styles are the Persian, Lycian, nearly all the Indian styles, the Chinese, Japanese and South American styles. A noteworthy example of a trabeated system is in Volubilis, from the Roman era, where one side of the Decumanus Maximus is lined with trabeated elements, while the opposite side of the roadway is designed in arched style. In India the style was used originally for wooden constructions, but later the technique was adopted for stone structures for decorative rather than load-bearing purposes.


Disadvantages

The biggest disadvantage to a post and lintel construction is the limited weight that can be held up, and the small distances required between the posts. Roman developments of the arch allowed for much larger structures to be constructed. There are two main force vectors acting upon the post and lintel system: weight carrying compression at the joint between lintel and post, and tension induced by deformation of self-weight and the load above between the posts. The two posts are under compression from the weight of the lintel (or beam) above. The lintel will deform by sagging in the middle because the underside is under tension and the topside is under compression.

Post and Lintel in the history

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 distributed . The “mushroom” column is a further departure, since the unit can be extended into a covering slab and becomes a ceiling as well as a support.

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