| Primary value | 50 × bar diameter (≈ 800 mm for 16 mm bar (Fe500 / M25)) |
| Applies to | Fe500 deformed bars in tension · M25 grade concrete · Splices in slab and beam main reinforcement |
| Exceptions | Fe500 / M20 → 57 d |
| Fe500 / M30 → 41 d | |
| Fe415 / M25 → 41 d | |
| Compression lap (any grade) → Use Ld for compression — typically 30–40 d | |
| Splice in zone of high stress → Increase 25% (Cl. 26.2.5.1) | |
| Measured as | Lap length is measured from the end of one bar to the end of the lapping bar — the full overlap. For deformed bars in tension, lap length equals development length Ld unless lap zone is in high stress. |
| Source | IS 456 — Clause 26.2.5.1, 26.2.1.1 ✓ Verified |
68 related items across IS codes, knowledge articles, design rules, maps and tools
Lap splicing transfers force between two bars by bond — the bond strength of Fe500 in M25 works out to a bar-diameter multiplier of ~50 by the IS 456 formula Ld = φσs / (4τbd). Going shorter relies on the bar to slip without breaking, which the code explicitly forbids for tension splices.
Estimators and BBS engineers default to 50d for Fe500/M25 throughout the BBS without checking grade-by-grade — adequate for 95% of residential work. Lap zones are staggered so no more than 50% of bars are spliced at any cross-section, per Cl. 26.2.5.1.