Civil Detailing · Rebar Optimization
How to Prepare a Bar Bending Schedule (BBS): The Engineer's Guide
A Bar Bending Schedule (BBS) is an itemized list of all reinforcing steel bars in an RCC structural element, specifying bar mark, diameter, shape, cutting length, number of bars, and total weight. Accurate BBS preparation bridges structural drawings and physical steel procurement, eliminating steel cutting scrap and ensuring strict compliance with seismic hook standards.
Standard Bend Deduction & Cutting Length Formulas
When steel rebar is bent on site, the outer fibers stretch, increasing the overall measured length. To maintain exact concrete cover, bend deductions must be subtracted from the perimeter sum:
- 45° Bend Deduction: Subtract 1 × d (where d is the bar diameter).
- 90° Bend Deduction: Subtract 2 × d.
- 135° Seismic Hook Deduction: Subtract 3 × d.
- 180° Semi-Circular Hook: Subtract 4 × d.
- Unit Weight Formula (kg/m): Weight = (d² / 162.2) kg per linear meter (where d is diameter in millimeters).
Sample BBS Format for Continuous Beam
| Bar Mark | Location | Bar Dia (mm) | No. of Bars | Cutting Length (m) | Total Weight (kg) |
|---|---|---|---|---|---|
| B-01 | Bottom Straight | 20 mm (#6) | 4 | 6.85 m | 67.58 kg |
| B-02 | Top Support Hangers | 16 mm (#5) | 3 | 4.20 m | 19.91 kg |
| S-01 | 2-Legged Stirrups | 10 mm (#3) | 28 | 1.45 m | 25.03 kg |
Frequently Asked Questions
Why is 135° hook bending mandatory for column ties in Pakistan?
Under BCP Chapter 5 and ACI 318 seismic codes, standard 90° hooks straighten out and pop open when concrete spalls off during cyclic earthquake lateral movement. 135° hooks with 10d extensions anchor securely inside the confined concrete core, keeping columns intact under severe shaking.