Last edited 17 Oct 2016

#  Introduction

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

Columns are typically constructed from materials such as stone, brick, block, concrete, timber, steel and so on.

In classical architecture, columns are often highly decorated, with standard designs including Ionic, Doric and Corinthian. See Elements of classical columns for more information. Other stylistic types include; composite, Tuscan, Egyptian and so on.

###  Steel columns

Steel columns have a tendency to buckle or bend under extreme loading. This can be due to:

• Length.
• Cross-sectional area.
• Method of end 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.

Columns can be categorised in several different ways:

#  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 (ie its slenderness ratio) and its material properties (ie Young's modulus and yield strength).

#  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'.

#  Lateral reinforcement

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.