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In architecture, “column” refers to such a structural element that also has certain proportional and decorative features. Egyptian architecture faceted cylinders were also common. 134 columns are lined up in 16 rows, with some columns reaching heights of 24 metres. The Minoans employed columns to create large open-plan spaces, light-wells and as a focal point for religious rituals. Being made of wood these early columns have not survived, but their stone bases have and through these we may see their use and arrangement in these palace buildings. Early columns were constructed of stone, some out of a single piece of stone.
Other stone columns are created out of multiple sections of stone, mortared or dry-fit together. In many classical sites, sectioned columns were carved with a centre hole or depression so that they could be pegged together, using stone or metal pins. This reduction mimics the parallax effects which the eye expects to see, and tends to make columns look taller and straighter than they are while entasis adds to that effect. More elaborate bases include two toruses, separated by a concave section or channel known as a scotia or trochilus.
Sometimes these sections were accompanied by still narrower convex sections, known as annulets or fillets. In the case of Doric columns, the capital usually consists of a round, tapering cushion, or echinus, supporting a square slab, known as an abax or abacus. Either type of capital could be accompanied by the same moldings as the base. Modern columns may be constructed out of steel, poured or precast concrete, or brick, left bare or clad in an architectural covering, or veneer. Used to support an arch, an impost, or pier, is the topmost member of a column. The bottom-most part of the arch, called the springing, rests on the impost.
As the axial load on a perfectly straight slender column with elastic material properties is increased in magnitude, this ideal column passes through three states: stable equilibrium, neutral equilibrium, and instability. The straight column under load is in stable equilibrium if a lateral force, applied between the two ends of the column, produces a small lateral deflection which disappears and the column returns to its straight form when the lateral force is removed. If the column load is gradually increased, a condition is reached in which the straight form of equilibrium becomes so-called neutral equilibrium, and a small lateral force will produce a deflection that does not disappear and the column remains in this slightly bent form when the lateral force is removed. The state of instability is reached when a slight increase of the column load causes uncontrollably growing lateral deflections leading to complete collapse. For an axially loaded straight column with any end support conditions, the equation of static equilibrium, in the form of a differential equation, can be solved for the deflected shape and critical load of the column. Manual of Steel Construction, 8th edition, American Institute of Steel Construction, Table C1.
The presence of the twisting deformations renders both theoretical analyses and practical designs rather complex. Eccentricity of the load, or imperfections such as initial crookedness, decreases column strength. If the axial load on the column is not concentric, that is, its line of action is not precisely coincident with the centroidal axis of the column, the column is characterized as eccentrically loaded. The eccentricity of the load, or an initial curvature, subjects the column to immediate bending.
The increased stresses due to the combined axial-plus-flexural stresses result in a reduced load-carrying ability. Column elements are considered to be massive if their smallest side dimension is equal to or more than 400 mm. When a column is too long to be built or transported in one piece, it has to be extended or spliced at the construction site. A steel column is extended by welding or bolting splice plates on the flanges and webs or walls of the columns to provide a few inches or feet of load transfer from the upper to the lower column section. A timber column is usually extended by the use of a steel tube or wrapped-around sheet-metal plate bolted onto the two connecting timber sections.