- Classification of Columns or strut is defined as a compression member whose effective length exceeds three times the least lateral dimension.
- A structural element that is predominantly subjected to axial compressive forces is termed a compression member.
- When a compression member is vertical, it is called a
**column**, and when it is horizontal or inclined, it is called a**strut**.

#### Classification of Columns based on Cross Section

1.Rectangular

2.Square

3.Circular

5. T, L, or + shapes

#### Classification of Columns based on Type of Reinforcement

1.**Tied columns**: Columns reinforced with longitudinal reinforcement and lateral (transverse) ties. Tied columns are applicable to all cross-sectional Shapes.

2.**Spiral columns**: Columns with longitudinal reinforcement tied by continuous spiral reinforcement. Spiral reinforcement is used mainly in columns Of circular cross section, though they can have hexagonal, octagonal, or even square shapes.

3.**Composite columns**: Columns reinforced longitudinally with structural steel sections, such as hollow tubes and I-sections, with or without additional longitudinal reinforcement or transverse reinforcement.

#### Classification of Columns based on Types of Loading

Cross section of column with different types of loading (a) Concentric axial loading (b) Loading with one axis eccentricity (c) Loading with biaxial eccentricities

1.**Columns with concentrically applied loads: **Such columns with zero bending moment are rare. In multi-storey frames, interior columns will be subjected to axial compression and shear, under gravity loads.

2.**Columns with ****uniaxial**** eccentricity—***e*_{x}** = 0, ***e*_{y}** ≠ 0 or ***e*_{x}** ≠ 0, ***e*_{y}** = 0: **Edge columns such as B and D in Fig. 13.3 are subjected to uniaxial bending moments.

3.**Columns with biaxial eccentricity—***e*_{x}** ≠ 0 and ***e*_{y}** ≠ 0: **Corner columns like C in multi-storey buildings are subjected to biaxial bending moments in addition to the compressive force. When subjected to lateral loads, most of the columns will be subjected to uniaxial or biaxial bending moments.

#### Classification of Columns based on Slenderness Ratio

Columns, struts, beams, and ties are often slender members.

The slenderness ratio** of a member is defined as the ratio of the effective length to the radius of gyration of the section.**Based on the slenderness factor, columns can be classified as follows:

1.

**Short columns:**These types of columns generally fail after reaching the ultimate load carrying capacity of columns.

2.

**Slender columns:**These types of columns generally fail suddenly at relatively low compressive loads due to

**buckling**