In this post, we will discuss the rules for designing a Column layout. we will discuss the essential thumb rules to be followed for giving a column layout. Of course, columns have to be designed in accordance to the total forces acting on the structure, but apart from that, it is essential Civil engineers and Architects to remember a few thumb rules so that they are prevented from making mistakes.
Three thumb rules to be followed are following:
- Size of the Columns
- The distance between two Columns
- Alignment of columns
Size of the Columns
The size of a column depends on the total load on the column. The minimum size of an RCC column should not be less than 9”(inches)x 9”(inches) [(225mm x 225mm)] with 4 bars of 12 MM Fe500 Steel.
9”(inches)x9”(inches) columns are to be used for a single story structure with M15 (1:2:4) (cement: sand: aggregate ) grade of concrete. These days the minimum used in the projects is 9″ (inches)x 12″(inches) (225 mm x 300mm) with 6 bars of 12 MM Fe500 steel. one can never go wrong with strong columns. It is also recommended to use of M20 grade concrete for the structure (ratio 1 part Cement: 1.5 parts sand : 3 parts Aggregate with 0.5 parts water by volume). It is recommended the use of 8 MM stirrups at a distance of 150 MM center to center throughout the length of the column.
In case, 9”(inches) x9” (inches) column size is to be used for 1 and a half story structure, then it is advised to use M20 grade concrete. A safe and structurally sound column size for a 1 and a half story structure should not be less than 12”x9” using M15 grade concrete.
The distance between two Columns
It is recommended to try to maintain equal distance between the centers of two columns. Always plan a column layout on a grid.
The distance between two columns of size 9”(inches)x9”(inches) should not be more than the 4 meters center to center of the column.
The size of the columns increase because of two factors:
Increase in the distance between two columns (This increases the dimensions of the columns as well as the depth of the beam).
The height of the building (Increase in the number of floors) is directly proportional to the dimensions of the columns. It is always recommended to use structural design software like ETabs or Staad pro for design.
There are other considerations like secondary and tertiary spans, wall loads and point loads which have to be considered.
Alignment of Columns
For placing the columns a rectangular grid is to be made. This helps in avoiding mistakes and placing in columns can be done in the right way.
The columns can preferably be arranged in two different fashions
- In a circular fashion for circular buildings.
- In a straight line with the help of a grid.
The zigzag arrangement of columns is an absolutely wrong way of working out Structural design. It is recommended that when columns are erected, beams are laid connecting the columns.
The Zigzag column placement causes three major issues.
Problems in wall construction
Problems in laying beams
Unbalanced load transfer
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