How to Calculate Quantity of Steel in One Way Slab

One-way slabs are used when the length-to-breadth ratio is two or more. They are supported on two sides and carry loads perpendicular to these supports.

Key Points

Main bars : In shorter span with crank for balancing bending moment.
Distribution bars : In longer span for load distribution and crack prevention.


Example Calculation

Slab dimensions:

  • Length: 6 meters
  • Width: 2 meters
  • Thickness: 150 mm
  • Clear Cover: 25 mm

Bar details:

  • Main Bar: 12 mm diameter, Spacing – 100 mm c/c
  • Distribution Bar: 10 mm, Spacing – 125 mm c/c
  • Extra Top Bar: 12 mm, Spacing – 250 mm c/c
  • Development Length (Ld) = 40 times diameter (d)

Step-wise Calculation

a) Number of Bars

  • Main bars: 61 numbers
  • Distribution bars: 17 numbers

b) Cutting Length

  • Main Bar: 2972 mm or 2.972 meters
  • Distribution Bar: 6800 mm or 6.8 meters

c) Top Distribution Bars

  • 10 numbers, Cutting Length: 6800 mm or 6.80 meters

d) Extra Top Bars

  • 24 numbers, Cutting Length: 980 mm or 0.98 meters

e) Steel Weight

  • Main Bar: 160.98 kg
  • Distribution Bar: 71.67 kg
  • Top Distribution Bar: 41.95 kg
  • Extra Top Bar: 20.88 kg

Bar Bending Schedule (BBS)

S.No. Bar Description Bar Shape Nos Length of Bar (m) Total Length of Bar (M) Bar Dia (mm) Unit Weight (kg) Total Weight (Kg)
1 Main Bar One Way Slab 61 2.972 181.292 12 0.888 160.98
2 Distribution Bar One way slab 17 6.8 115.6 10 0.617 71.32
3 Top Distribution Bar Longer span 10 6.8 68 10 0.617 41.95
4 Extra Top Bar Shorter span 24 0.98 23.52 12 0.888 20.88

Conclusion

  • 10 mm diameter Steel: 113.27 Kg
  • 12 mm diameter Steel: 181.86 Kg

This guide provides a simplified approach to estimating steel quantity for one-way slabs, ensuring structural integrity and safety.