RCC column is a vertical structural member which transfers loads from beam and slab directly to the underneath soil. That means an entire building stands on columns. Most of the building failure occurs not only for design fault but also for poor construction practices. Therefore it is essential to know the construction procedure of RCC column appropriately. In this article, I will discuss the basic construction process of RCC column.
RCC columns are mainly constructed in four different stages, which are
1. Column Layout Work.
2. Column Reinforcement Work.
3. Column Formwork and
4. Pouring Concrete,
1. Column Layout Work:
This is the first step of column construction. In this step, the location of columns is decided practically in the field. It is done by laying rope as per the grids are shown in the drawing and afterward, the location of columns are marked.
2. Column Reinforcement Work:
When marking of column location is done, the reinforcement of columns are placed according to the structural drawing.
For example, C1-12#16 mmØ and stirrup-10 mmØ@4″c/c.
This means, the column C1 will have 12 numbers of 16 mm diameter bars as the vertical bar and 10 mm diameter steel should be placed 4 inch center to center spacing as the stirrup.
Lets look for another example, C2-8#20 mmØ +10#16 mmØ and stirrup – 10 mmØ @(4″+6″)c/c
So the column will have 8 numbers of 20 mm dia bar and 10 numbers of 16 mm dia bar for vertical reinforcement and (4″+6″) c/c means the middle half portion of clear height of column will have 6″ center to center spacing of stirrups and the upper one-fourth as well as bottom one-fourth height of the columns clear height will hold stirrups at 4″ center to center spacing.
Additional notes such as lap length for column steel of different diameter etc will be given in the sheet of structural drawing.
3. Column Formwork:
The floor height is normally kept at 10 feet. If the slab contains beam, then concrete has to be poured upto the beam bottom level. For example, if the beam height is given in the drawing is 1′-6″, the casting height of column and formwork will be 8′-6″. But as we know that dropping concrete more than 5 feet height is not allowed because it will cause segregation, we should create formwork within 5 feet height. When the first part will be cast completely, the rest part should be started.
4. Pouring Concrete Into Column:
Concreting of column is done in two different methods
2. Using machine or pump.
Points To Be Followed During And After Concreting:
1. Use machine mix concrete for less amount of concrete, and ready-mix concrete for larger amount of concrete.
2. Approval of placing concrete whether by manually or by pump should be taken from the client.
3. Concrete should be poured upto slab bottom and the remaining column should be concreted during beam and slab concreting.
4. Mechanical vibratior must be used for full compaction of the column, but remember excess vibration can create segregation of the concrete. So each layer should be compacted properly.
5. The target slump is 160 mm.
6. Concrete should not be poured from more than 1.5 m height.
7. Always avoid construction joints in the column.
8. Covers should be given properly as per the structural drawing.
9. During concreting pouring, the temperature should be below 30º.
10. Check verticality and horizontally of the column after pouring and vibrating the concrete.