Understanding the Factored Load
The factored load considers additional safety by increasing the actual load. This ensures stability and prevents failure.
Let’s assume:
Dead Load = 1200 kN
Live Load = 600 kN
Now, increase the total load by 50% for safety:
Pu = 1200 + 600 = 1800 kN
Alternatively, as per IS 456: Table 18,
Pu = 1.5 × 1200 = 1800 kN
This value will be used in further calculations.
Essential Design Parameters
According to IS 456 guidelines, the following parameters apply:
Concrete Grade (fck) = M30
Steel Grade (fy) = Fe 500
Factored Load (Pu) = 1800 kN
Use the IS 456 equation for axial load-bearing columns:
Pu = 0.4fckAc + 0.67fyAsc
Where:
Ac = Area of concrete
Asc = Area of steel
Ag = Gross area of column section
Assume:
Asc = 1% of Ag
Ac = 99% of Ag
This gives:
Asc = 0.01Ag,
Ac = 0.99Ag
Column Area Calculation
Now, apply the values to the equation:
1800 × 10³ = 0.4 × 30 × 0.99Ag + 0.67 × 500 × 0.01Ag
Simplify the equation:
1800000 = 11.88Ag + 3.35Ag
1800000 = 15.23Ag
Solve for Ag:
Ag = 1800000 / 15.23
Ag ≈ 118187.78 mm²
Now take the square root to find side length (assuming a square column):
√118187.78 ≈ 343.78 mm
For practicality and simplicity, round it:
Adopted Column Size = 350 mm × 350 mm
Final Recommended Column Size
Based on the above calculation:
Column Dimensions = 350 mm × 350 mm
This size ensures the column safely supports the applied load.
The design adheres to IS 456 provisions for safety and performance.
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