Introduction
In Overhead Transmission Line (OHTL) projects, pier foundations are commonly used in river crossings, steep terrain, or rocky soil conditions. Accurate Bar Bending Schedule (BBS) and Concrete Volume Calculations ensure the foundations are structurally sound, cost-effective, and executed with precision.
This guide provides:
- Step-by-step BBS calculations
- Concrete volume estimation
- Formulas, site-based examples, and best practices for civil engineers
BBS (Bar Bending Schedule) for Pier Foundation
Why Prepare BBS?
- To estimate exact steel quantity
- Guide cutting, bending, and placing of rebar on site
- Minimize material wastage
- Support budgeting and planning
Step-by-Step BBS Calculation
We’ll use a typical circular pier as an example.
Assumptions:
- Pier Diameter (D) = 1.0 m
- Pier Height (H) = 5.0 m
- Concrete cover = 50 mm
- Main bars = 16 Nos of 20 mm dia
- Stirrups (ties) = 8 mm dia @ 150 mm spacing
Main Reinforcement Bars
➤ Length of One Main Bar:
=H−2×cover=5.0−0.1=4.9 m= H – 2 × \text{cover} = 5.0 – 0.1 = 4.9\ m=H−2×cover=5.0−0.1=4.9 m
Add extra for hook/lap: =4.9+0.5=5.4 m= 4.9 + 0.5 = 5.4\ m=4.9+0.5=5.4 m
➤ Total Length:
=5.4 m×16=86.4 m= 5.4\ m × 16 = 86.4\ m=5.4 m×16=86.4 m
Weight of Steel:
Weight=(d2162)×Length=(202162)×86.4=2.47×86.4≈213.4 kg\text{Weight} = \left(\frac{d^2}{162}\right) × \text{Length} = \left(\frac{20^2}{162}\right) × 86.4 = 2.47 × 86.4 ≈ 213.4\ kgWeight=(162d2)×Length=(162202)×86.4=2.47×86.4≈213.4 kg
✅ 2. Stirrups (Lateral Ties)
➤ Diameter for Stirrup:
Clear dia=D−2×cover=1000−100=900 mm=0.9 m\text{Clear dia} = D – 2 × \text{cover} = 1000 – 100 = 900\ mm = 0.9\ mClear dia=D−2×cover=1000−100=900 mm=0.9 m
➤ Length of One Stirrup (Perimeter):
= π × D = 3.14 × 0.9 = 2.83\ m \text{Add bend allowance (10%)} = 2.83 + 0.28 ≈ 3.11\ m
➤Number of Stirrups:
Spacing=150 mm=0.15 mNumber=H/spacing=5.0/0.15≈34\text{Spacing} = 150\ mm = 0.15\ m \text{Number} = H / spacing = 5.0 / 0.15 ≈ 34Spacing=150 mm=0.15 mNumber=H/spacing=5.0/0.15≈34
➤ Total Length:
=3.11×34=105.74 m= 3.11 × 34 = 105.74\ m=3.11×34=105.74 m
➤ Weight:
=(82162)×105.74=0.395×105.74≈41.75 kg= \left(\frac{8^2}{162}\right) × 105.74 = 0.395 × 105.74 ≈ 41.75\ kg=(16282)×105.74=0.395×105.74≈41.75 kg
BBS Summary Table:
| Component | Dia (mm) | No. of Bars | Length/Bar (m) | Total Length (m) | Weight (kg) |
|---|---|---|---|---|---|
| Main Bars | 20 | 16 | 5.4 | 86.4 | 213.4 |
| Stirrups | 8 | 34 | 3.11 | 105.74 | 41.75 |
| Total Steel | — | — | — | — | 255.15 kg |
Concrete Volume Calculation for Pier Foundation
Shape: Circular Vertical Pier
➤ Formula:
Volume=π×(D2)2×H\text{Volume} = π × \left(\frac{D}{2}\right)^2 × HVolume=π×(2D)2×H
➤ Calculation:
=3.1416×(0.5)2×5=3.1416×0.25×5=3.927 m3= 3.1416 × (0.5)^2 × 5 = 3.1416 × 0.25 × 5 = 3.927\ m³=3.1416×(0.5)2×5=3.1416×0.25×5=3.927 m3
➤ Add 3% for Wastage:
Final Volume=3.927×1.03≈4.045 m3\text{Final Volume} = 3.927 × 1.03 ≈ 4.045\ m³Final Volume=3.927×1.03≈4.045 m3
On-Site Checklist
| Material | Quantity (Estimated) |
|---|---|
| OPC Cement (43/53) | 12–14 bags |
| Sand | 2.5 m³ |
| Aggregates (20 mm) | 4.5 m³ |
| Steel Bars | ~255 kg |
| Binding Wire | 2–3 kg |
| Shuttering Ply | As per pier size |
Practical Tips for Civil Engineers
- Use IS 2502 for bar bending detailing
- Maintain proper cover blocks and alignment before concreting
- Ensure overlaps or couplers are according to design
- Use vibrators to prevent honeycombing
- Record BBS in digital spreadsheets for easy updates
Conclusion
Accurate BBS and concrete volume calculation for pier foundations in OHTL projects ensures structural integrity, efficient budgeting, and smooth execution. By following standardized formulas and real-world practices, civil engineers can make better decisions on-site.
