The number of steel bars in a column is determined by the design specifications, and it involves considering factors such as the column dimensions, type of reinforcement, and the spacing of the bars.
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Dia and number Iron rod/steel bars used in a RCC column depending on size of column ,percentage of Steel used in RCC structure. Column size decided on the basis of load acting on column, Lateral forces, number of floor, alignment of column, span between two column and size of column.
IS 456:2000 recommendation for designing of column
1) minimum clear cover for column 40mm is provided, if size of column is less than 200mm then clear cover is 25mm is provided.
2) minimum diameter of bar 4 nos of 12mm should be taken
3) minimum area of Steel =0.8%of Ag
Maximum area of Steel=6%of Ag ( Steel should not overlap) 4%of Ag if steel is overlap
4) maximum spacing between two longitudes renforcement shall not greater than 300mm
5) minimum dia of Stirrup 1/4×16 greater
6) maximum spacing of stirrup 16D, B and 300mm whichever is minimum.
When we go through the column design we should mention following point: 1) the possible distance or span and depth it all depend on load to which the beam is subjected, 2) column size depend on amount of load on the column acting on it by beam and RCC slab, 3) many axial and Lateral load acting on column, 4) large span greatly influence the bending moment not only on beam, but it also affect the column due to stress acting on it, 5) Thumb Rule for column design are appropriate for very small project like G+1,G+2 & G+3 Building and 6) column design for building construction it depend on many factors like topography, whether and size of building. How to calculate number of steel bars in column
How to calculate number of steel bars in column
In this article, we will go through the essential thumb rules to be followed for giving a column layou and how to calculate number of steel bars in column. Ofcourse columns have to be designed in accordance to the total forces acting on the structure, but apart from that, it is essential for every Civil engineer and Architect to remember a few thumb rules so that they are prevented from making mistakes.
Minimum size of RCC column:-for residential building minimum size of an RCC column should not be less than 9”x 9” (225mm x 225mm) with 4 bars of 12mm Fe500 Steel with m20 grade of concrete and stirrups of T8@6″C/C.
How to calculate number of steel bars in column? we assume a percentage of steel as per IS456:2000 in following steps:
1)Put that percentage of steel and Gross area of column in Load formula.
2)Determine the permissible stress in steel in compression.
3)Calculate Area of Steel required.
4)Calculate No. Of bars = (area of steel÷area of a single bar).
Generally, we provide steel reinforcement 1 to 2% of gross area of concrete inside RCC column for 1,2 and 3 storey residential building.
Formula we used for calculate number of steel bars in column,1) Ag = Ac +Asc, this formula is used to find out gross area of concrete, if size of column is given.
2)Asc=Ag-Ac, this formula is used to find out area of Steel used in RCC column, if their gross area and concrete area is given.
3) n = Asc/πD2/4, this formula is used to calculate number of steel bar in a RCC column if their area of Steel diameter of bar is given.
4) Asc = n×πD2/4, this formula is used to calculate area of Steel in RCC column if their size and number of steel is given.
5) D = √4Asc/nπ, this formula is used to find out diameter of Steel bar in RCC column if their area of Steel and their number is given.
How many Steel bars in a column
● Given:- we have given Gross area of concrete Ag=100%, suppose minimum 1% of steel is provided in a 9″×12″ rcc column for ground floor residential building, so steel area Asc=1%of Ag =0.01Ag, and concrete area Ac = 99% of Ag=0.99Ag.
● Calculating gross area of 9″×12″ size column:- Total Gross area Ag =230mm×300mm=69000mm2, suppose we are using 12mm dia of rebar in 9″×12″ size rectangular column, then how many 12mm dia of rebar required in a 9″×12″ size rectangular column?.
● Area of Steel calculation:- Formula we used, Ag = Ac +Asc, Asc=Ag-Ac, Asc = 69000 – 0.99×69000, Asc = 69000 – 68310, Area of steel Asc =690mm2,
● How many Steel bars in a column:- To find out number of 12mm dia of iron rod in a 9″×12″ rcc column, we used the formula, Area of steel Asc = n×πD2/4, Where n= number of iron rod, D = dia of rebar, π =3.14, putting all value in above mentioned formula, we get,
690mm2 = n ×πD2/4, 690mm2 = n ×3.14×12×12/4, 690mm2 = n ×113.04, Number of required iron rod n = 690/113.04 =6.10, taking in round figure 6nos of T12 rebar, so minimum 6nos of 12mm dia of rebar/iron rod is used in a 9″×12″ rcc column.
How many Steel bars in a 9″×12″ (230mm×300mm) column:- providing Steel 1% of gross area of concrete in 9″ x 12″ (230mm×300mm) size rcc column, the minimum iron rod/ steel bars is 6 bars of 12mm with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm. If we use 16mm dia of iron rod/steel bar inplace of 12mm in 9″×12″ size column, then 4nos of 16mm is required.
How many Steel bars in a 9″×9″ (230mm×230mm) column:– providing Steel 0.8% of gross area of concrete in 9″ x 9″ (230mm×230mm) size rcc column, the minimum iron rod/ steel bars is 4 bars of 12mm with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
How many Steel bars in a 12″×12″ (300mm×300mm) column:- providing Steel 1% of gross area of concrete in 12″ x 12″ (300mm×300mm) size rcc column, the minimum iron rod/ steel bars, it could be 8 nos of 12mm or either combination of 4nos of 16mm & 2nos of 12mm dia of steel bar used, provided with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
How many Steel bars in a 12″×15″ (300mm×380mm) column:- providing Steel 1% of gross area of concrete in 12″ x 15″ (300mm×380mm) size rcc column, the minimum iron rod/ steel bars, it could be 10 nos of 12mm, or 8nos (combination of 4nos of 16mm & 4nos of 12mm) of steel bar used, provided with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
How many Steel bars in a 12″×18″ (300mm×450mm) column:- providing Steel 1% of gross area of concrete in 12″ x 18″ (300mm×450mm) size rcc column, the minimum iron rod/ steel bars, it could be 12 nos of 12mm, or 10nos (combination of 4nos of 16mm & 6nos of 12mm) of steel bar used, provided with stirrups of 10mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
How many Steel bars in a 15″×18″ (380mm×450mm) column:- providing Steel 1% of gross area of concrete in 15″ x 18″ (380mm×450mm) size rcc column, the minimum iron rod/ steel bars, it could be 12 nos (combination of 8nos of 12mm & 4nos of 16mm), or 10nos (combination of 6nos of 16mm & 4nos of 12mm), or 8nos (combination of 4nos of 16mm & 4nos of 20mm) of steel bar used, provided with stirrups of 10mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
How many Steel bars in a 18″×21″ (450mm×530mm) column:- providing Steel 1% of gross area of concrete in 18″ x 21″ (450mm×530mm) size rcc column, the minimum iron rod/ steel bars, it could be 12 nos (combination of 4nos of 12mm,4nos of 16mm & 4nos of 20mm), or 10nos (combination of 6nos of 16mm & 4nos of 20mm) of steel bar used, provided with stirrups of 10mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
How many Steel bars in a 18″×24″ (450mm×600mm) column:– providing Steel 1% of gross area of concrete in 18″ x 24″ (450mm×600mm) size rcc column, the minimum iron rod/ steel bars, it could be 12 nos (combination of 2nos of 12mm,6nos of 16mm & 4nos of 20mm), or 14nos (combination of 4nos of 16mm, 4nos of 20mm & 6nos of 12mm) of steel bar used, provided with stirrups of 10mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
How many Steel bars in a 24″×24″ (600mm×600mm) column:- providing Steel 1% of gross area of concrete in 24″ x 24″ (600mm×600mm) size rcc column, the minimum iron rod/ steel bars, it could be 12 nos (combination of 6nos of 16mm & 6nos of 20mm), or 16nos (combination of 4nos of 16mm, 8nos of 20mm & 4nos of 12mm) of steel bar used, provided with stirrups of 10mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
How to calculate diameter of steel bar used in a column
We use the formula, D = √4Asc/nπ, this formula is used to find out diameter of Steel bar in RCC column, if their area of Steel and their number is given.
To calculate diameter of 4nos of iron rod in a 9″×9″ rcc column, Area of steel Asc = n×πD2/4, where Asc= 423.2mm2, number of rebar =4nos and π=3.14, putting all value we get, Asc = n×πD2/4, 423.2 = 4 ×3.14×D2/4, D^2 = 423.2/3.14, Diameter of rebar D =√134.78mm2, Diameter of rebar D =11.60mm, taking in round figure as 12mm, so 12mm dia of 4nos of rebar/iron rod is used in a 9″×9″ rcc column.
Which diameter of Steel bar used in a 9″×9″(230mm×230mm) size rcc column:-providing steel bar 0.8% of gross area of concrete in 9″ x 9″ (230mm×230mm) size rcc column, the minimum diameter of iron rod/ steel bar used is 12mm, providing 4 bars of 12mm with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
Which diameter of Steel bar used in a 9″×12″(230mm×300mm) size rcc column:-providing steel bar 1% of gross area of concrete in 9″ x 12″ (230mm×300mm) size rcc column, the minimum diameter of iron rod/ steel bar used is combinatiom of 12mm & 16mm dia, providing 6 bars of 12mm or 4nos of 16mm with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
Which diameter of Steel bar used in a 12″×12″(300mm×300mm) size rcc column:-providing steel bar 1% of gross area of concrete in 12″ x 12″ (300mm×300mm) size rcc column, the minimum diameter of iron rod/ steel bar used is combinatiom of 12mm & 16mm dia, providing 4 bars of 16mm and 2nos of 12mm with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
Which diameter of Steel bar used in a 12″×15″(300mm×380mm) size rcc column:-providing steel bar 1% of gross area of concrete in 12″ x 15″ (300mm×380mm) size rcc column, the minimum diameter of iron rod/ steel bar used is combinatiom of 12mm & 16mm dia, providing 4 bars of 16mm and 4nos of 12mm with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
Which diameter of Steel bar used in a 12″×18″(300mm×450mm) size rcc column:-providing steel bar 1% of gross area of concrete in 12″ x 18″ (300mm×450mm) size rcc column, the minimum diameter of iron rod/ steel bar used is combinatiom of 12mm & 16mm dia, providing 4 bars of 16mm and 6nos of 12mm with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
Which diameter of Steel bar used in a 15″×18″(380mm×450mm) size rcc column:-providing steel bar 1% of gross area of concrete in 15″ x 18″ (380mm×450mm) size rcc column, the minimum diameter of iron rod/ steel bar used is combinatiom of 12mm & 16mm dia, providing 4 bars of 16mm and 8nos of 12mm with stirrups of 8mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
Which diameter of Steel bar used in a 18″×21″(450mm×530mm) size rcc column:-providing steel bar 1% of gross area of concrete in 18″ x 21″ (450mm×530mm) size rcc column, the minimum diameter of iron rod/ steel bar used is combinatiom of 12mm,16mm dia & 20mm, providing 4 bars of 16mm,4 bars of 20mm and 4nos of 12mm with stirrups of 10mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
Which diameter of Steel bar used in a 18″×24″(450mm×600mm) size rcc column:-providing steel bar 1% of gross area of concrete in 18″ x 24″ (450mm×600mm) size rcc column, the minimum diameter of iron rod/ steel bar used is combinatiom of 12mm,16mm & 20mm dia, providing 6 bars of 16mm,4 bars of 20mm and 2nos of 12mm with stirrups of 10mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.
Which diameter of Steel bar used in a 24″×24″(600mm×600mm) size rcc column:-providing steel bar 1% of gross area of concrete in 24″ x 24″ (600mm×600mm) size rcc column, the minimum diameter of iron rod/ steel bar used is combinatiom of 12mm,16mm & 20mm dia, providing 4 bars of 16mm,8 bars of 20mm and 4nos of 12mm with stirrups of 10mm steel rings at a distance of 150mm (6″) centre to centre of Fe500 grade of Steel and M20 grade of concrete ratio 1:1.5:3 and providing clear cover of 40mm.