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RCC column design as per IS 456-2000 code | building design | civil engineering | structural design |
RCC Column design is one of the most important concept in structural design. The reinforcement values of the column sections are depends upon the total amount of the vertical load acting on that particular column section. Basically loads which are related to combination of dead load and live load is initially transfer to slab section through that slab section it will distributed to beams and then to columns and to foundation. So if we design the column section with safety then entire building will be stable.
In my previous blogs I was explained how to design beam and slab section by using IS 456 code provisions so please read complete calculations with the following links
Beam design as per IS 456 code click here to read
One way slab as per IS 456 code click here to read
Two way slab as per IS 456 code click here to read
Design of columns as per IS 456 code basic formulas
The complete column design process as per IS code is determined by using below 3 basic formulas
- The minimum eccentricity values as per IS 456 code provision is calculated by using below formula in the column design we need to consider minimum or greater than 20 mm value as eccentricity value.
emin = (L/500) + (D/30) ≥ 20 mm
2. The calculation of main steel is determined by using the below formulae which is shown below
Pu=0.45fckAc+0.67fyAsc
3. The gross area, steel area required for the column section is determined by using below formulae
Ag=Asc + Ac
Basic key points taken in design
The following four key points are used in complete RCC column design
- Percentage of steel in RCC column is taken as 0.8% to 6% of the gross area.
- Minimum of 4 Bars are used in Rectangular column and 6 Bars in circular column
- Transverse reinforcement (pitch not greater than)
Least lateral dimensions
16d (d is small longitudinal bar diameter)
300 mm
- Diameter of the bar not less than
0.25 d
5 mm
Steps followed in column design by using IS456-2000
The following 4 steps are followed in RCC column design
- Calculation of Ac by assuming Asc
- Calculation of dimensions of the column by using Ag
- Calculation of reinforcement values of main steel Ac
- Calculation of transverse reinforcement
Example of column design by using IS456-2000 code
Design RCC column which carries 1200kN load with 3.5 m length. Assume M20 grade concrete and Fe415 grade steel
Since given load is 1200kN we need to make that to factored load
Factored load = 1.5X1200 =1800 KN
Step 1: Calculation of Ac by assuming Asc
By assuming the percentage of steel as 1% of the gross area
Asc =(1/100)Ag
So Asc = 0.01Ag
And also we have Ag = Ac + Asc
By substituting the Asc value we can easily get Asc
So Ac = Ag-0.01Ag
So finally Ac = 0.99Ag
Step 2: Calculation of dimensions of the column by using Ag
Since we have
Pu=0.45fckAc+0.67fyAsc
By substituting the values
1800X103=0.45X20X0.99Ag+0.67X415X0.01Ag
By calculation we can get Ag = 153971.173 mm2
By taking column as square section which is having a side area of the rectangle is a2.
So a2 = 153971.173 mm2
And Finally a = 392.39 mm
So, Take a as 400 mm.
Now the next step is checking for the emin
Since
emin = (L/500) + (D/30)
= (3500/500) + (400/30)
= 7+13.333
= 20.33 mm
Hence it is safe as per emin
Since the emin value is less than 20 mm so we can proceed to the design section of 400 mm X 400 mm column
Step 3: Calculation of reinforcement values of main steel Ac
Again we will use same Pu formulae for calculating the reinforcement values
Since
Pu=0.45fckAc+0.67fyAsc
By substituting the values
1800X103=0.45X20X(153971.173-Asc)+0.67X415XAsc
By calculating we can get Asc = 1539.711 mm2
So let us consider 1540 mm2 area
By assuming the 16mm diameter bars
The area of 1 single bar is (Π/4)162 = 201 mm2
Number of bars required is given by is given by (Asc/Area of 16mm bar)
N = 1540/201 = 7.661 no’s
Take approximately 8 no’s
So take 8 no’s of 16mm diameter bars as main reinforcement
Step 4: Calculation of transverse reinforcement
In transverse reinforcement initially we need to determine the pitch
Pitch is the least for following 3 values
- 16d =16X16 = 256mm
- Minimum lateral dimensions =400mm
- 300mm
The least of above three values is 256mm so we will take 256mm is the pitch for the column section design.
Diameter of bars calculation
The diameter of the transverse reinforcement is calculated by using two expressions shown below
- 0.25d = 0.25 X 16 = 4 mm
- 5 mm
So the final reinforcement use of 8 no’s of 16mm diameter main reinforcement and 6mm diameter bars of 256 mm center to center distance is used in the 400mmX400mm size with 1200kN point load.
The complete reinforcement details are shown in the below figure
The full details of column design as per IS456 code is explained in my YouTube channel Civil engineering by shravan see below
Conclusions of RCC column design by using IS456 code
Well now the above explained concepts are related to the complete RCC column design as per IS 456-2000 code. The reinforcement details are calculated as per 4 steps Calculation of Ac by assuming Asc, Calculation of dimensions of the column by using Ag, Calculation of reinforcement values of main steel Ac and Calculation of transverse reinforcement
As per the calculation the reinforcement values obtained as use of 8 no’s of 16mm diameter main reinforcement and 6mm diameter bars of 256 mm center to center distance is used in the 400mmX400mm size with 1200kN point load.
Please follow our previous posts here
Cost estimation of marbles and tiles for 1000sft and1500sft slab area click here to read
Volume of concrete per cubic meter click here to read
What is slab? Types of slabs? Difference between one way slab and two way slab ? click here to read
What is minimum and maximum center to center distance between RCC columns click here to read
What is cost estimation of 3BHK building click here to read
Please watch interesting concepts in my YouTube channel Civil engineering by shravan. Please feel free to text us at contact us page for any quarries.
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Your Shravan
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