Types of column

[edit] Introduction

A column is a vertical structural member intended to transfer a compressive load. For example, a column might transfer loads from a ceiling, floor or roof slab or from a beam, to a floor or foundations.

Columns are typically constructed from materials such as stone, brick, block, concrete, timber, steel, and so on, which have good compressive strength.

[edit] Classical stone columns

In classical architecture, columns are often highly decorated, with standard designs including Ionic, Doric and Corinthian, and so on.

See Elements of classical columns for more information.

A colonnade is a row of columns spaced at regular intervals that can be used to support a horizontal entablature, an arcade or covered walkway, or as part of a porch or portico.

See: Colonnade for more information.

[edit] Steel columns

Steel columns have good compressive strength, but have a tendency to buckle or bend under extreme loading. This can be due to their:

Length.
Cross-sectional area.
Method of fixing.
Shape of the section.

The cross-sectional area and the section shape are incorporated into a geometric property of section, known as the radius of gyration. This refers to the distribution of an object's components around an axis. It can be calculated:

r = √I/A

Where, I = 2nd moment of area, A = cross-sectional area.

[edit] Slenderness ratio

The slenderness ratio is the effective length of a column in relation to the least radius of gyration of its cross-section. If this ratio is not sufficient then buckling can occur.

Column slenderness can be classified as:

Long or slender: The length of the column is greater than the critical buckling length. Mechanical failure would typically occur due to buckling. The behaviour of long columns is dominated by the modulus of elasticity, which measures a column's resistance to being deformed elastically (i.e. non-permanently) when a force is applied.
Short: The length of the column is less than the critical buckling length. Mechanical failure would typically occur due to shearing.
Intermediate: In between the long and short columns, and its behaviour is dominated by the strength limit of the material.

Classification will depend on the column's geometry (i.e. its slenderness ratio) and its material properties (i.e. Young's modulus and yield strength).

[edit] Shape

Columns can be classified according to their cross sectional shape. Common column shapes include:

Rectangular.
Square.
Circular.
Hexagonal
Octagonal.

In profile, they can be tapered, non-tapered, or 'barrel' shaped, their surface can be plain, fluted, twisted, panelled, and so on.

Columns may be of a simple uniform design, or they may consist of a central 'shaft' sitting on a column base, and topped by a 'capital'. See Elements of classical columns for more information.

[edit] Reinforced concrete columns

Reinforced concrete columns have an embedded steel mesh (known as rebar) to provide reinforcement.

The design of reinforcement can be either spiral or tied.

Spiral columns are cylindrical with a continuous helical bar wrapped around the column. This spiral provides support in the transverse direction.
Tied columns have closed lateral ties spaced approximately uniformly across the column. The spacing of the ties is limited in that they must be close enough to prevent failure between them, and far enough apart that they do not interfere with the setting of the concrete.

[edit] Other types of column

[edit] Stone column

Stone columns (or vibro stone columns) are formed by granular aggregate that is inserted into column shaped excavations and then compacted to improve the load bearing capacity of soil and fill material.

[edit] Pilotis

Pilotis are supports that lift a building above the ground or a body of water. In timber form, they were traditionally used in the vernacular architecture of Asia and Scandinavia, or wherever indigenous peoples lived at a water’s edge. They may also be used in hurricane or flood-prone areas, to raise the structure above storm surge levels.

The pioneer of modern pilotis was the architect Le Corbusier, who used them both functionally as ground-level supporting columns, and philosophically as a tool for freeing the rigidity of traditional plan layouts, enabling efficient, buildings as 'machines for living'.

See Pilotis for more information.

[edit] Piers

the term ‘pier’ can be used interchangeably for several different building elements. In general, it is an upright support for a structure or superstructure, but it can also refer to the sections of load-bearing structural walls between openings and different types of column.

See: Piers for more information.

[edit] Posts

The word 'post' is interchangeable with the word column, although is is typically used in relation to smaller structural members that may in some cases be independent, rather than part of a wider structure.

[edit] Knotted

A knotted column is a stone support that is carved in the shape of two or four columns joined by a knot. The knot in the columns is meant to represent various spiritual messages associated with humanity and its relationship to the Holy Trinity.

See: Knotted column for more information.