TYPES OF COLUMNS
The column is a very important structural element that is used in different segments of a structure. It is a vertical member that transfers the load from one structural member to another. The load that the column carries in compression is transferred from a beam, slab (roof/ floor) to a floor or foundation. Columns can be used as a decorative element, such columns are non-structural and thus do not carry any load. Failure of columns that are used to transfer loads and are the chief structural members concludes in the collapse of the structure. Over the decades’ many types of columns have been developed and are classified into different categories.
Classification of Columns
There are various types of columns, depending on the design, requirement, or aesthetics a specific type of column is built. Subject to various conditions columns can be broadly classified into five categories:
- Based on the type of reinforcement
- Based on the materials used
- Based on the shape
- Based on loading
- Based on the slenderness ratio
For further understanding, the types of columns are further elaborated in brief with illustrations of the same
1. Types of columns based on the type of reinforcement
- Tied Column: Tied columns are constructed from reinforced concrete. The longitudinal reinforcement is tied laterally, using independent transverse bars or ties that are of smaller diameter. These ties are approximately and uniformly spaced along with the height of the column. The spacing of these ties is critical as excessive spacing can result in shear failure and barreling in between ties. Thus to prevent this the ties should be placed close enough but not so close that they hinder the mounting of the concrete. It is observed that 95% of columns constructed are tied columns due to the lower construction cost.
- Spiral Column: Spiral columns too are constructed from reinforced concrete. Alike the tied columns spiral columns have longitudinal reinforcement bars that are squeezed within closely spaced ceaselessly wound spiral bars also as helical reinforcement or spiral reinforcement. These spirals support the column in the transverse direction that refrains the column from barreling. Spiral columns are cylindrical in shape and mostly are reinforced with 6 bars for longitudinal support. Column ductility and toughness are much more than the tied column and indicate its failure to take the necessary measures before it collapses.
- Composite Columns: In composite columns, structural steel sections or pip are used for reinforcement instead of the bars. A composite column is a blend of two conventional structural forms, namely the structural steel concrete. As these columns were developed much later the design approach varied on either of the column design methods of steel or concrete. The cross-section is fairly small and thus maximize the available floor space. Mostly used in high rise buildings, because of the high strength and properties of fire and corrosion resistance that increase the durability. Composite due to the property of corrosion resistance are also preferred to be used in truss structures.
2. Types of columns based on the materials used
- Reinforced Concrete Column
- Steel
- Timber
- Stone
- Brick
A
B
C
D
E
3. Types of column based on the shape
- Square or Rectangular Column: Square or rectangular columns are mostly used in the construction of a building. If compared to a circular column square/ rectangular columns are easy to construct and cast as the shuttering is easier. The construction cost is comparatively less that makes the construction of square and rectangular columns economical and preferable.
- Circular Column: Circular columns are specially designed that are used in piling and as an elevation element of buildings. Minimum 6 steel bars are used for reinforcement and thus the bending resistance is generally higher compared to a square or rectangular column. As the circular columns have good deflection resistance they are majorly used as bridge pillars also because they are aesthetically appealing.
- L Type Column: L type column is generally constructed to support boundary walls. These columns are also used on a turn of a metro rail and to support a flyover. These columns are designed with primary and secondary reinforcement that are interconnected with links called stirrups.
- T Type Column: The columns that are extensively used in the construction of bridges are T type columns. Their attributes are no different than a square or a rectangular column. Based on the design requirement this type of column is also provided in a boundary wall or along with a retaining wall.
- V Type Column: V type columns are used in the corners of a trapezoidal room. This type of column requires more concrete if compared to the other types. The framework is a tapered pile shuttering with a flitch tie. There is a difficulty in the execution as the framework of the scaffolding is complicated and thus requires skilled workmanship.
- Y Type Column: For the support of the bridges and flyovers, Y type columns are constructed. The Y shape of the column sustains the bridge’s dead load and the vehicle motion’s live load. Two symmetrical inclined members are designed on either side of the column.
- Y Type Column with Arch: These columns are similar to the Y type of column with the difference of curved edges or sides. These columns with an arch sustain heavy loads and thus are constructed under bridges and flyover to avoid the congestion of building multiple columns.
- Hexagon Column: Hexagon columns are mostly shaped columns that have six sides. These columns are aesthetically appealing and generally designed for elevations. Hexagon columns are planned in verandahs, cinema halls, auditorium, and many such spaces.
- Arch Type Column: If the room has an arch shape these arch type columns are constructed. When there is no possibility of building a square or rectangular or circular column arch columns are constructed. The scaffolding and casting of arch columns are difficult and thus are used very rarely.
4. Types of columns based on loading
- Axially Loaded Column: When all the load on the column passes through the central axis that is that it coincides with the center of gravity, that column is axially loaded. These types of columns are infrequently constructed. The load that it carries is either compression or tensile.
- Eccentrically Loaded Column: When the line of force that is transferred does not coincide with the line of gravity but is shifted is called an eccentrically loaded column.
- When the load is transferred eccentrically either on the X or Y axis then the column is eccentrically loaded column (uniaxial)
- When the load is not transferred eccentrically on either of the axis then the column is eccentrically loaded column (biaxial)
5. Types of columns based on the slenderness ratio
Slenderness ratio is the value of the length of the column divided by its radius of gyration. The slenderness ratio helps in perceiving the buckling stress of the column, based on this value columns can be classified into short columns and long columns.
- Short Column: If the effective length of the column to the minimum lateral dimension ratio that is the slenderness ratio is smaller than 12, the column is a short column. The chief reason for the failure of a short column is crushing i.e. by the compression stress.
- Long Column: On the other hand if the effective length of the column to the minimum lateral dimension ratio i.e. the slenderness ratio is greater than 12, the column is a long column. Long columns are comparatively weaker than the short columns and thus are not prioritized more, these columns fail due to buckling or bending.
References:
- https://theconstructor.org/tips/types-columns-building-construction/24764/
- https://civilread.com/different-types-columns/
- https://dailycivil.com/types-of-columns-used-in-construction/
- https://concretecivil.com/what-is-column-and-its-types/
