Rules for cutting off (curtailing) tension reinforcement where it is no longer needed for moment resistance. Bars cannot simply be stopped at the theoretical cut-off point — they must continue beyond it for development length and special anchorage rules to prevent diagonal tension cracking.
Simplified Curtailment for Continuous Beams
Standard practice for beams designed with coefficients (no full BMD)
| Rule | Value | Extension | Note |
|---|
| Top steel — at supports | Length 0.30 × Ln | From face of support | For half of top steel |
| Top steel — full provision | Length 0.20 × Ln | From face of support | For other half |
| Bottom steel — full at midspan | Continuous through midspan | — | — |
| Bottom steel — at support | ≥ ¼ of midspan steel continued past support | Min Ld/4 | Or 50% per IS 13920 |
| Cantilever — top steel | Full length + Ld into supporting column | — | Anchorage critical |
Notes
• The 'd or 12 dia' extension beyond TCP is mandatory — never cut at the exact theoretical point
• If you cut bars in tension zone, you MUST EITHER provide excess stirrups OR double the continuing steel
• For continuous beams without full BMD, use the simplified 0.30/0.20/0.25 rules above
• Always check that ≥ ¼ of midspan bottom steel is anchored past internal supports
• At simple supports, anchorage check L1 ≥ Ld/3 (or Ld/2 if no transverse compression) is mandatory
• Hooks add anchorage value — a 90° hook = 8 dia, 135° hook = 12 dia, 180° hook = 16 dia equivalent straight
• For seismic detailing, ¼ rule becomes ½ — see IS 13920 Cl 6.2.4
• Commonly missed: top bars at internal supports must extend beyond the point of inflection, not just the support face