RCC column construction methods
The entire building is rested on RCC columns. Column failure is the prime factor for collapsing most of the buildings. Besides, design errors, inferior construction practice is also responsible for column failure.
Therefore, sufficient & exact knowledge should be gathered on the construction process of the RCC column.
Given below, the detail construction process of RCC column :-
1. Column Layout Work: Initially, the positions of the columns are set practically in the construction site by placing rope as per grids demonstrated in the drawing and then marking the location of columns accompanying the rope.
In the drawing, the positions of the column are demonstrated with reference to the grid-line with dimension. In the construction site, ropes are provided as grid-line. Therefore, the columns should be arranged with reference to rope-line by working out the dimension provided in the drawing.
2. Column Reinforcement work: Once the marking of the locations of the column is done, then the reinforcement should be placed as per instruction in the structural drawing.
It is generally stated in the drawing as follow :- C1-12#16 mm⌀ and stirrup-10 mm⌀ @ 4″ c/c.
It signifies that column C1 will contain 12 numbers of 16 mm diameter bar as vertical bar and 10 mm diameter steel should be arranged 4-inch center to center as stirrups.
or C2-8#20 mm⌀ + 10#16 mm⌀ and stirrup-10 mm⌀ @ (4″+6″) c/c.
This C2 column’s reinforcement specification signifies that there are 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 spacing 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 spacing.
There is a sheet in the structural drawing with structural notes provided by the structural designer. In that drawing sheet, recommended lap length for column’s steel for several diameter bars and other important notes are provided. These should be properly studied prior to column reinforcement work.
3. Column Formwork: In buildings, floor height is generally maintained as 10 feet. If there are beams in the slab, then the concrete should be poured up to the bottom level of beam.
As for example, if the height of beam indicated in the drawing is 1′-6″. Therefore, the casting height of the column should be 8′-6″. The formwork height should be 8′-6″.
But keep in mind that dropping concrete from over 5′ height during pouring isn’t recommended since it results in segregating the concrete. Therefore, one-side of column formwork should be created inside 5 feet height range. After casting 5 feet of a column, just upraise the short side up to the full-casting height of column next day.
Another useful process 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 remaining part of the column.
4. Pouring Concrete into The Column: Casting process for column is simple. For a small quantity of concrete volume, generally machine-mix concrete is ideal and for the large concrete quantity, ready-mix concrete should be used.
It is recommended to use machine-mix concrete as if it is required to use a moving pump with ready-mix concrete and if it is not required to go beyond 5 feet height range for dropping concrete that would be complicated.
If the moving pump is not applied, yet problems may occur. If it is required to employ ready-mix concrete devoid of a pump. Under such situation, the concrete should be unloaded manually on job site from the ready-mix concrete truck and should be manually poured into the column. The process is time consuming and the initial setting time of concrete will be crossed. Consequently, the quality of concrete will be reduced. Therefore, it is recommended to cast column with machine-mix concrete.