How the Lap & Development Length works
Find the development length (Ld) and lap length for beams, slabs, ties and columns as per IS 456:2000. Choose the bar diameter, steel grade, concrete grade and where the lap is; the tool shows the result with every step of the working and the clause it comes from.
Frequently asked questions
What is the lap length as per IS 456?
For bars in flexural tension the lap length is Ld or 30φ, whichever is greater; in direct tension 2Ld or 30φ; in compression it equals the development length in compression but not less than 24φ (cl. 26.2.5.1). The straight length of the lap must be at least 15φ or 200 mm.
What is the development length formula?
Ld = φ σs / (4 τbd), where σs = 0.87 fy and τbd is the design bond stress (cl. 26.2.1). τbd for plain bars in tension is 1.2, 1.4, 1.5, 1.7 and 1.9 N/mm² for M20, M25, M30, M35 and M40+; it is increased by 60% for deformed bars and by 25% for bars in compression.
What is Ld for Fe415 bars in M20 concrete?
About 47φ in tension: Ld = 0.87 × 415 / (4 × 1.2 × 1.6) = 47.0 times the bar diameter, e.g. 752 mm for a 16 mm bar.
Can bars larger than 36 mm be lapped?
No. IS 456 cl. 26.2.5.1 does not allow lap splices for bars larger than 36 mm; they should be welded or joined with mechanical couplers.
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