Column Construction Steps At Site
A column is a vertical member that transmits the load of the structure generating from slab, beams to underlying soil. The location of the columns should be provided in such a manner that no tensile stresses should be produced at the cross section of the columns. The location of the columns should be in such a manner that the columns can be hidden in the walls partly or completely.
Types of RCC Column are categorized as follow :-
Types of RCC Column depending on Shapes
- Circular for uncovered exterior for elegant architecture view.
- Conventionally Square or rectangular for any structure.
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Types of RCC Column depending on length
- Short column – if L/B<=12
- Long column – if L/B>12
Here, L means the height of the column, B is width
Normally, floor height should be roughly 3 m or 10 feet, L/B ratio should be lower than 12, so in most cases short column is provided. When the height of floor remains in excess of 3 m or 10 feet, it is necessary to verify L/B ratio so the result would be long or short column. Normally, on long column various forces are produced, so the design should be created cautiously.
Types of RCC Column depending on moments
- Biaxial column: It is specifically created for axial load and moment in 2 directions
- Uniaxial columns: It is specifically created for axial load and moment in 1 direction
Normally, in a building corner most columns belong to biaxial columns and side column belongs to uniaxial column and internal columns belong to any of these.
The construction process of RCC columns is divided into the following 4 phases :-
- Column layouts
- Column reinforcement work
- Column formwork
- Pouring of concrete
Layout of Columns
Column layouts are created by placing rope in the grid lines and label the position of columns.
The following points should be taken into consideration for column reinforcement works:
- Verify the numbers and diameter of vertical bars
- Span among vertical bars
- Verify development length that is based on the diameter of bar
- Lapping in alternate bars should remain at similar height
- Lapping should not be provided inside beam or slab.
- Lapping should be provided at l/3 or 2l/3 of column according to structural notes
- Spacing for stirrups should be provided according to the drawing
- Hook should be bent precisely at exact angles.
- Verify the stirrups corner. Vertical bar should be placed at right angle edge of stirrup perfectly tied with binding wire.
The columns bear the load of structure and that's why they are critical. It is recommended that the alignment of the columns should be in vertical direction in order that the load is transmitted perfectly. The column shuttering should adequately strong to sustain the pressure of fresh concrete and stand in position throughout concreting.
Concreting of RCC Column
Concreting of an RCC column is accomplished in the following ways :-
- With the aid of machine or pump
Following points should be considered during and after concreting:
- To deal with fewer quantities, machine mix concrete is suitable and for huge quantities ready mix concrete (RMC) is recommended.
- Get confirmation from the client, whether the concrete should be placed with pump or by hand.
- Concrete should be poured up to slab bottom; the concreting for left over column should be performed during pouring of slab & beam.
- Mechanical vibrator must be utilized in the column but too much vibration can lead to segregation. Each layer should be properly compacted.
- Target slump to be 160 mm.
- The concrete should be poured from a height not surpassing 1.5 m.
- There should be no construction joint in the column.
- Based on structural drawings, there should be proper cover.
- Temperature should be retained under 30 degree at the time of pouring concrete.
- Once the concrete is poured and vibrating of concrete through a vibrator is completed, the horizontality and verticality of column should be examined properly