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Elements Of Construction:

There are five basic structural principles, which have been of prime importance to the history of building, and in various forms, and variations account for almost all types of construction, as force and gravity fight it out. The five types are as follows.

  1. Post and lintel

  2. Corbel

  3. Arch and vault

  4. Truss

  5. Cantilever

Post and lintel describes basic vertical and horizontal construction elements. Two vertical members supporting a horizontal one - this is the simplest. The vertical is also known as a column, the horizontal as a beam. A major problem throughout history has been that if the span is great, the material used as the lintel or beam might fail from its own weight. You cannot stretch stone. Sometimes the horizontal member might split in the middle or shear at its points of support. In early construction, spans had to be small, resulting in spaces cluttered with columns. See the Hall of the Hundred Columns in Persepolis.

Corbels are overlapping arrangements of bricks or stones in which each course projects farther out than the course below. By corbeling towards the center from opposite sides of a planned space, a meeting of the corbels can be achieved, or they can be bridged by a horizontal element, creating an overhead enclosure of that space. The resulting appearance resembles an arch, but technically it is quite different. Corbels are self-supporting during construction and afterwards, while arches require support (centering) during construction.

Arches can be round (Classical or Moorish), or pointed (Gothic) as they leap upward into space, and descend down to the opposite side. Arches are composed of wedge-shaped or tapered masonry units with their narrow ends down and the wider ends on top of the curve. This acts in much the same way your dentist fills a cavity in a tooth - drilling out and widening the inside of the cavity, making it impossible for the filling to escape the narrower entrance hole. Each unit is known as a voussoir. The central or lynchpin of the assembly is called the keystone. It locks all the other members in place. Pennsylvania is called the "Keystone State" because it was centrally located in the thirteen original colonies, which became the United States.

In essence an arch has minimal depth, but a vault (such as a barrel vault) is theoretically composed of an infinite number of successive arches, which extend the curved plane of an arch in depth in order to cover or enclose a space.

Trussed construction grew from or with the pointed roof (gable or hip). It can be assumed that flat roofs leaked, and the wetter the climate the more leakage. So people began to slope their roofs to shed rain, using rafters to span two parallel walls (rafters are, in essence, angled beams). Someone eventually joined the rafters at their base with a horizontal beam, and the resultant triangular form was found very stable. This triangulation enabled greater spanning than mere rafters or beams placed independently. The truss is able to do so much more than the simple post and lintel.

Cantilevers are horizontal projections, sort of like sticking your arm straight out from your body. They can be thought of as brackets, projecting out in space while being supported at one end. In essence they exist through history, but not in a serious structural or supporting way. We mostly will see them as projecting cornices in roof overhangs. It was not until the development of steel and reinforced concrete that cantilevers took on a structural life of their own.

This course will see only the development of the first four of the above forms of construction, and indeed, trusses did not develop in a meaningful way, as we know them today, until the advent of steel. So we will see triangulation limited to pointed roofs made of wooden trusses. You might want to check out megaron development. We will get to that soon.

Now that we're armed with a smattering of architectural terms, we can begin to explore the man-made world, which we call architecture. And sometimes we might find that there has been architecture without architects.


Some time-framing here. The Stone Age is acknowledged to be the beginning of human use of tools - stone, supplemented or accompanied by wood, bone, antlers, and used for weapons. So much of human development stems from aggression or defense. Many natural implements were shaped, carved, or bent for purposes of warfare. Metals and their alloys advanced the causes of war first, and then were used for domestic, peaceful purposes. For this course, we will deal with the New Stone Age, the Neolithic Period of human growth and development; a time of the earliest settled communities, such as those at Jericho, mentioned above, dating from at least the 9th Millennium B.C.E. An addition at this time to man's repertoire of made materials was that of the use of clay to create pottery, enabling storage of all sorts of liquids and foods. Techniques of shaping stone improved, and we had heavy-duty stone construction built to last.

© Architecture Past Present & Future - Edward D. Levinson, 2009

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