Techniques
The techniques of architecture in the sense that they will be considered here are simply the methods by which structures are formed from particular materials. These methods are influenced not only by the availability and character of materials but also by the total technological development of society, for architecture depends on an organized labour force and upon the existence of the tools and skills necessary to secure, manufacture, transport, and work durable materials.
The evolution of techniques is conditioned by two forces. One is economic—the search for a maximum of stability and durability in building with a minimum of materials and labour. The other is expressive—the desire to produce meaningful form. Techniques evolve rapidly when economic requirements suggest new expressive forms or when the conception of new forms demands new procedures. But they remain static when architects avoid the risk of pioneering with untried and possibly unsuccessful methods and depend instead on proved procedures or when the need for the observance of tradition, for the communication of ideas, or for elegance and display is best fulfilled by familiar forms.
The ultimate purpose of building techniques is to create a stable structure. In mechanical terms, structures are stable when all their parts are in a state of equilibrium, or rest. Walls and roofs can buckle, crack, or collapse if they are not properly designed. These movements are caused by forces that tend to push or pull bodies in a given direction. Forces acting on any member (part) of a building are, first, its own weight and, second, the loads it carries, principally from other members but also from persons, furnishings, wind, etc. Their action encounters a reaction in opposing forces that hold the member in place by resisting at its joints. These forces may be active in all directions, and they must be balanced for stability. They tend to crush, pull apart, and bend the member—in other words, to change its size and shape.
Within the member itself there are forces, too, that tend to resist any deformation. They are called stresses, and they vary according to the strength of materials and the form of the member. The kinds of stress under consideration are compression, which resists crushing; tension, which resists pulling apart; and bending, which occurs when one part of a member is in compression and the other is in tension. A column is put into compression by the loads it carries; in a trussed roof the piece that forms the base of the triangle is put into tension by the outward-pushing forces in the sides; and a lintel or beam (the member that spans a space) is put into bending by loads and forces that push down on its top and encounter a reacting force at its ends. Some materials are strong only in compression (e.g., stone, brick, cast iron, concrete) and others in tension as well (e.g., wood, steel, reinforced concrete), so the latter are more efficient in resisting bending forces.
Finally, the stability of the total structure whose single members are all in equilibrium is achieved by diverting the loads from all of them downward so that they may be resisted by the upward-supporting forces of the ground.
Techniques will be discussed in terms of the characteristics of building materials and the methods by which they are used in architecture (see building construction).
Materials
Stone
In most areas where stone is available, it has been favoured over other materials for the construction of monumental architecture. Its advantages are durability, adaptability to sculptural treatment, and the fact that it can be used in modest structures in its natural state. But it is difficult to quarry, transport, and cut, and its weakness in tension limits its use for beams, lintels, and floor supports.
The simplest and cheapest stonework is rubble; i.e., roughly broken stones of any shape bounded in mortar. The strongest and most suitable stonework for monumental architecture is ashlar masonry, which consists of regularly cut blocks (usually rectangular). Because of its weight and the precision with which it can be shaped, stone masonry (in contrast with brick) does not depend on strong bonding for stability where it supports only direct downward loads. The entablatures (the upper sections of a classical order that rest on the capital of a column) of an ancient Greek temple, for example, were bonded by small bronze dowels. But the weight creates problems of stability when loads push at an angle; stone vaults and arches require more support and buttressing than equivalent forms in other materials.
The best stone (and brick) bonding is that in which blocks are placed so that the vertical joints in one course are not above the joints in the courses above and below, since the stone resists deformation better than any bonding material. Many stones are strong enough to provide monolithic supports (columns and piers) and beams (lintels), and in some styles stone slabs are employed even for roofing (ancient Egyptian temples, early Christian basilicas in Syria), but this roofing requires so many columns that unvaulted masonry buildings are almost always combined with floors and covering in wood. Stone has been consistently used for building since the Stone Age, as exemplified by Stonehenge, in England. Although it has generally been replaced as a structural material by cheaper and more efficient manufactured products, it is still widely used as a surface veneer for its practical and expressive qualities.