Editing Column (section)

==Structure==
{{further|Fluting (architecture)}}
{{More citations needed|section|date=July 2021}}

Early columns were constructed of stone, some out of a single piece of stone.  Monolithic columns are among the heaviest stones used in architecture.  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.  The design of most classical columns incorporates [[entasis]] (the inclusion of a slight outward curve in the sides) plus a reduction in diameter along the height of the column, so that the top is as little as 83% of the bottom diameter.  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.

There are flutes and fillets that run up the shaft of columns. The flute is the part of the column that is indented in with a semi circular shape. The fillet of the column is the part between each of the flutes on the Ionic order columns. The flute width changes on all tapered columns as it goes up the shaft and stays the same on all non tapered columns. This was done to the columns to add visual interest to them. The Ionic and the Corinthian are the only orders that have fillets and flutes. The Doric style has flutes but not fillets. Doric flutes are connected at a sharp point where the fillets are located on Ionic and Corinthian order columns.

===Nomenclature===
Most classical columns arise from a basis, or base, that rests on the [[stylobate]], or [[Foundation (engineering)|foundation]], except for those of the [[Doric order]], which usually rest directly on the stylobate.  The basis may consist of several elements, beginning with a wide, square slab known as a [[plinth]].  The simplest bases consist of the plinth alone, sometimes separated from the column by a convex circular cushion known as a [[molding (decorative)#types|torus]].  More elaborate bases include two toruses, separated by a concave section or channel known as a scotia or trochilus.  Scotiae could also occur in pairs, separated by a convex section called an [[astragal]], or bead, narrower than a torus.  Sometimes these sections were accompanied by still narrower convex sections, known as [[Annulet (architecture)|annulet]]s or fillets.<ref name="Clarke">[[Hewson Clarke]] and [[John Dougall (writer)|John Dougall]], ''The Cabinet of Arts'', T. Kinnersley, London (1817), pp. 271, 272.</ref><ref name="Architectural Glossary">"Architectural Glossary", in ''The Universal Decorator'', Francis Benjamin Thompson, Ed., vol. III (1859).</ref>

At the top of the shaft is a [[capital (architecture)|capital]], upon which the roof or other architectural elements rest.  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 (architecture)|abacus]]. [[Ionic order|Ionic capitals]] feature a pair of [[volute]]s, or scrolls, while [[Corinthian order|Corinthian capitals]] are decorated with reliefs in the form of acanthus leaves.  Either type of capital could be accompanied by the same moldings as the base.<ref name="Clarke"/><ref name="Architectural Glossary"/>  In the case of free-standing columns, the decorative elements atop the shaft are known as a [[finial]].

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 (architecture)|impost]], or pier, is the topmost member of a column. The bottom-most part of the arch, called the springing, rests on the impost.

===Equilibrium, instability, and loads===
{{Main|Buckling#columns}}
{{Mechanical_failure_modes}}
[[File:ColumnEffectiveLength.png|thumb|220px|Table showing values of K for structural columns of various end conditions (adapted from Manual of Steel Construction, 8th&nbsp;edition, American Institute of Steel Construction, Table C1.8.1)]]
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 load at which neutral equilibrium of a column is reached is called the critical or [[buckling]] load. 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. With hinged, fixed or free end support conditions the deflected shape in neutral equilibrium of an initially straight column with uniform cross section throughout its length always follows a partial or composite sinusoidal curve shape, and the critical load is given by

<math>f_{cr}\equiv\frac{\pi^2\textit{E}I_{min}}{{L}^2}\qquad (1)</math>

where ''E'' = [[elastic modulus]] of the material, ''I<sub>min</sub>'' = the minimal moment of inertia of the cross section, and ''L'' = actual length of the column between its two end supports. A variant of (1) is given by

<math>f_{cr}\equiv\frac{\pi^{2}E_T}{(\frac{KL}{r})^{2}}\qquad (2)</math>

where ''r'' = [[radius]] of gyration of column cross-section which is equal to the square root of (I/A), ''K'' = ratio of the longest half [[sine]] wave to the actual column length, ''E''<sub>''t''</sub> = tangent modulus at the stress ''F''<sub>cr</sub>, and ''KL'' = effective length (length of an equivalent hinged-hinged column). From Equation&nbsp;(2) it can be noted that the buckling strength of a column is inversely proportional to the square of its length.

When the critical stress, ''F''<sub>cr</sub> (''F''<sub>cr</sub> =''P''<sub>cr</sub>/''A'', where ''A''&nbsp;= cross-sectional area of the column), is greater than the proportional limit of the material, the column is experiencing inelastic buckling. Since at this stress the slope of the material's stress-strain curve, ''E''<sub>''t''</sub> (called the [[tangent modulus]]), is smaller than that below the proportional limit, the critical load at inelastic buckling is reduced. More complex formulas and procedures apply for such cases, but in its simplest form the critical buckling load formula is given as Equation&nbsp;(3),

<math>f_{cr}\equiv{F_y}-\frac{F^{2}_{y}}{4\pi^{2}E}\left(\frac{KL}{r^2}\right)\qquad (3)</math>

A column with a cross section that lacks symmetry may suffer torsional buckling (sudden twisting) before, or in combination with, lateral buckling. 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&nbsp;mm. Massive columns have the ability to increase in carrying strength over long time periods (even during periods of heavy load). Taking into account the fact, that possible structural loads may increase over time as well (and also the threat of progressive failure), massive columns have an advantage compared to non-massive ones.

===Extensions===
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 [[reinforced concrete column]] is extended by having the steel reinforcing bars protrude a few inches or feet above the top of the concrete, then placing the next level of reinforcing bars to overlap, and pouring the concrete of the next level. 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.

===Foundations===
A column that carries the load down to a foundation must have means to transfer the load without overstressing the foundation material. Reinforced concrete and masonry columns are generally built directly on top of concrete foundations. When seated on a concrete foundation, a steel column must have a base plate to spread the load over a larger area, and thereby reduce the bearing pressure. The base plate is a thick, rectangular steel plate usually welded to the bottom end of the column.