There are several types of columns used in construction structures. Column is vertical member which transfer loads of structure from beam and slab to the foundation. carry loads distrubuted to slab, and trasfered loads from ceiling, floor slab, roof slab or from beam to floor or foundation. Column is vertical member effective length is greater than 3times. Columns are typically constructed from materials such as stone, brick, block, concrete, timber, steel, and so on, which have good compressive strength.
The column is the most important structural member of the building; without the column, you cannot construct RCC building or structure. build up a small size structure by RRC masonry at a certain height but the multi-story building cannot be constructed by RR masonry because the structure can able to transmit the heavy load to the ground level. column designed to distribute the compressive axial load & additional forces to foundation. Additional loads natural loads from the snow, wind and other horizontal forces can cause the column to bend. Columns can also carry primary axial loads and designed for compression.
Types of Columns
Basically columns are many types, choosing type of column depends upon structure plan, load bearing capacity and ultimate load bearing point. There are many several types of columns used in structures. The types of columns can be classified depending upon various conditions.
Columns are classified based on the several conditions which include:
- Based on Types of Reinforcement
- Based on Types of Loading
- Based on Slenderness Ratio
- Based on Shape
- Based on Construction Material
Based upon Shape
Shape Columns can be classified according to their cross sectional shape. Common column shapes include:
- Rectangular or Square.
Square Or Rectangular Shape Columns
Rectangular shape columns we mostly used in many building constructions. For Normal residential plans everyone suggest Square or rectangular column for better conditions. These traditional Rectangular shape columns are budget-friendly and easy to construct. Its easy to shuttering and reinforcement placement. these type of columns covered under Tied columns positionings. These Tried columns are commonly used in reinforced concrete building structures. Longitudinal reinforcement are confined within closely spaced tie reinforcement. This is primarily for the ease of working with the shuttering and to support it from it collapsing due to pressure while the concrete is still in flowable form. According to ACI 7.10.5: The ties vertical spacing must be in between 16D of the longitudinal bar (D is the diameter of the bar) and 48D from the ties diameter.
Circular columns are mostly used in industrial and commercial building types. we can see many columns elevations and piling positing. In the circular column, more than 4 steel bars are used as reinforcement and its bending resistance is usually higher than the square or rectangular column. These types of columns under considering as spiral columns. Column and longitudinal bars are confined within closely spaced and continuously wond spiral reinforcement. Spiral type circular columns are also used as bridge pillars due to good deflection resistance. Spiral columns are cylindrical with a continuous helical bar wrapped around the column. its provides support in the transverse direction.
Mainly these types of columns used at heavy turning, sudden breakdown places. L type columns are used in boundary wall construction and in the turning of metro rail in flyover construction. these type of columns utilized in the corners of the boundary wall and has similar characteristics of rectangular square tie shaped columns. These kind of columns are very less used.
T – Shape Column
These type of columns mostly used in Bridges. These types of columns having the same characteristics and properties like the Square/Rectangular type column. it provided along with retaining wall or boundary wall based on design requirement. boundary wall constructed by masonry than square or rectangular column placed in every 6 m at the same time if it is an RCC type wall than the column was designed as T shape.
These Types of columns are mostly used in flyover constructions. The design of bridges to sustain the dead load of the structure & live load of the vehicle motion, the load was eventually distributed to the column. Hexagonal columns and octagonal columns also work like same.
Based on Types of Loading are classified into three different types.
- Axially Loaded Column
- Column with Uniaxial Eccentric Loading
- Column with Biaxial Eccentric Loading
If vertical axial loads act on the center of gravity of the cross-section of the column, then it is termed as axially loaded column.
When vertical loads do not coincide with center of gravity of column cross section, but rather act eccentrically either on X or Y axis of the column cross section, then it is called uniaxially eccentric loading column.
When vertical on the column is not coincide with center of gravity of column cross section and does not act on either axis (X and Y axis), then the column is called biaxially eccentric loaded column.
Based on Slenderness Ratio:-
Depending upon the Slenderness ratio (ratio of effective length to least lateral dimension of the column), the columns are classified as (most important)
It is used extensively for finding out the design load as well as in classifying various columns in short/intermediate/long. 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.
If the ratio effective length of the column to the least lateral dimension is less than 12, the column is called as the short column. A short column fails by crushing (pure compression failure).
If the ratio effective length of the column to the least lateral dimension exceeds 12, it is called as long column. A long column fails by bending or buckling.
Design Requirements for Columns
Columns must be designed or all bending moments associated with loading conditions. Minimum number of longitudinal bars in the compression member shall be 4 for bars within rectangular or circular ties, three for minimum triangular ties, and 6 for bars within spiral type of columns.
The clear distance between the longitudinal bars must not be less than the 1.5 times the nominal bar diameter nor 1 ½ inch.
The ratio of the volume of spiral reinforcement to volume of concrete within the spiral should be at least
40mm concrete cover should be provided then column to avoid the rusting of steel.
The center to center spacing of the ties or rings must not exceed the smaller of 16 longitudinal bar diameter, 48 tie bar diameter.