Construction of RCC column in detail
RCC (Reinforced Cement Concrete) column belongs to a structural member that is associated with RCC frame structured building. This vertical member transmits loads from slab and beam directly to the soil underneath.
The entire building rests on columns. The collapsing of building occurs due to column failure. Besides, design errors, the substandard construction method is also responsible for collapsing of column. So, it is crucial to have clear & perfect conception about the construction method of the RCC column.
The following four phases of work are included in construction process of RCC (Reinforced Cement Concrete) Column :-
- Column layout work
- Column reinforcement work
- Column formwork
- Pouring concrete into column
Column layout work
Under this phase of works the position of the columns are settled practically in job site. It is performed by placing rope in accordance with grids demonstrated in the drawing and then marking the position of columns accompanying rope.
In drawing, column locations are demonstrated corresponding to grid-line with dimension. Practically, in the job site, ropes refers to the grid-line. Therefore, the columns are arranged incidental to rope-line by calculating dimension demonstrated in the drawing.
Also read : CANTILEVER SLAB REINFORCEMENT DETAILS
Column Reinforcement work
As soon as the positions of the column are marked, reinforcement is set according to the structural drawing.
It is usually provided in the drawing as follow :-
C1-12#16 mm dia and stirrup-10 mm dia @ 4″ c/c.
It signifies that column C1 contains 12 numbers of 16 mm diameter bar as vertical bar and 10 mm diameter steel should be arranged 4 inch center to center as stirrup.
C2-8#20 mm dia + 10#16 mm⌀ and stirrup-10 mm dia @ (4″+6“) c/c.
The reinforcement specification of C2 column signifies that it’ll contain 8 numbers of 20 mm diameter bar along with 10 numbers of 16 mm diameter bar as vertical reinforcement and (4″+6″) center to center of stirrups placement signifies that middle-half portion of clear height of column will contain 6″ center to center distance of stirrups and upper one-fourth together with bottom one-fourth height of column’s clear height will retain stirrups at 4″ center to center distance.
A sheet exists in structural drawing that comprises of structural notes from structural designer. The drawing sheet contains proposed lap length for column’s steel having diverse diameter bar and other vital notes. These should be followed prior to column reinforcement work.
In building, generally floor height is retained as 10 feet. If the slab contains the beam then, the concrete should be poured up to the bottom level of beam. Suppose, the beam height in drawing is provided as 1′-6″. So, the casting height of the column should be 8′-6″. The formwork height should be 8′-6″. But, it should be noted that dropping concrete from above 5′ height isn’t recommended at the time of pouring since it causes segregation of concrete. Therefore, one-side of column formwork should be constructed inside 5 feet height range. Once casting 5 feet of column is completed, just raise the short side up to full-casting height of column next day.
Another useful method to cast column devoid of segregation is to provide a small window at 5 feet level of full-height formwork. Once casting is completed up to that level, close the window and cast the rest of the column.
Pouring concrete into column
The process is simple for casting column. For small quantity of concrete volume, usually machine-mix concrete is suitable and for large concrete quantity, ready-mix concrete is best suited. When, moving pump is applied with ready-mix concrete and if it is required not to surpass 5 feet height range for dropping concrete, it becomes complicated.
If moving pump is not utilized, some problems may arise. Suppose, ready-mix concrete is utilized without pump. Under this circumstance, the concrete will be unloaded manually on the construction site from ready-mix concrete truck and poured into column manually. It will be very time consuming and the initial setting time of concrete will be surpassed. Consequently, the quality of concrete will be reduced significantly. Therefore, it is recommended to cast column with machine-mix concrete.