My Construction Calculator
Browse Categories

REBAR & STEEL · REBAR LAP LENGTH CALCULATOR

Lap Length of 10mm Bar

The tension lap of a 10 mm bar equals its development length, Ld. In M20 concrete with Fe500 steel, Ld = 56.6φ, so the lap is 566 mm, and 453 mm in compression. With Fe415 steel it is 470 mm. IS 456 never allows less than 30φ (300 mm) in tension.

Inputs

Results update as you type.

Code & bar
Materials & conditions
Lap spliceLap in tension 566 mm566 mmcompression 453 mm · 56.6 × dbmyconstructioncalculator.comNot to scale
Diagram updates as you type.

Results

Check the working before you order.

Lap length in tension
566mm
In bar diameters56.6 × db
Lap length in compression453 mm
Compression in bar diameters45.3 × db
Development length (tension)566 mm

Uses the simplified code equations. Your structural drawings and the engineer of record govern: they may specify longer laps, different splice classes, or seismic detailing.

Stagger laps where possible, and do not lap bars larger than #11 / 36 mm in tension (ACI) or 36 mm (IS): use couplers.

Price This optional: add your own prices

Your prices are remembered on this device only.

Send Order WhatsApp, SMS or email to your supplier
Include
WhatsAppSMSEmail
Working
  1. τbd (M20) = 1.20 N/mm² × 1.6 (deformed bars) = 1.92 N/mm²
  2. Ld = φ × 0.87 fy ÷ (4 τbd) = 10.0 × 0.87 × 500 ÷ (4 × 1.92) = 566 mm (56.6 φ)
  3. Compression: τbd × 1.25 → Ld = 453 mm (45.3 φ)
  4. Tension lap = max(Ld, 30φ) = 566 mm
  5. Compression lap = max(Ld compression, 24φ) = 453 mm
Results are estimates for planning and material ordering only. They are not a substitute for structural design or approval by a qualified engineer. Read the full disclaimer.
Formula


σs            = 0.87 × fy                      (435 MPa for Fe500)
τbd           = table value × 1.6 for deformed bars   (M20: 1.2 × 1.6 = 1.92 MPa)
Ld (tension)  = φ × σs ÷ (4 × τbd)
Lap, tension  = Ld, at least 30φ   (2 Ld in direct tension)
Lap, compr.   = Ld ÷ 1.25, at least 24φ


Worked Example


A 10 mm bar in M20 concrete with Fe500 steel:


    

  1. σs = 0.87 × 500 = 435 MPa; τbd = 1.2 × 1.6 = 1.92 MPa
    2. 

  2. Ld = 10 × 435 ÷ (4 × 1.92) = 566 mm (56.6φ); 30φ = 300 mm, so Ld governs
    3. 

  3. Tension lap = 566 mm
    4. 

  4. Compression: 10 × 435 ÷ (4 × 2.40) = 453 mm (45.3φ); 24φ = 240 mm → lap = 453 mm
    5. 



Lap Length of 10mm Bar by Concrete Grade


Deformed (TMT) bars, flexural tension.






Concrete
Fe415 tension
Fe415 compression
Fe500 tension
Fe500 compression






M15
564 mm
451 mm
680 mm
544 mm




M20
470 mm
376 mm
566 mm
453 mm




M25
403 mm
322 mm
485 mm
388 mm




M30
376 mm
301 mm
453 mm
362 mm




M35
332 mm
265 mm
400 mm
320 mm




M40
300 mm
240 mm
358 mm
286 mm






More Lap Lengths by Bar Size
Frequently Asked Questions
What is the lap length of a 10 mm bar in M20 concrete?
566 mm in tension and 453 mm in compression with Fe500 steel, or 470 mm and 376 mm with Fe415. These are for deformed (TMT) bars in flexural members; laps in direct tension are twice as long.
Is the 50d lap rule correct?
It is close, not exact. By IS 456 the tension lap for Fe500 bars is 56.6d in M20 and 48.5d in M25, so 50d is slightly short in M20. With Fe415 it is 47.0d in M20. The lap shown on the structural drawings always governs.
Where should laps be placed?
Away from the points of highest stress, and staggered so that not all bars are lapped at the same section (IS 456 §26.2.5.1). In beams, bottom bars are usually lapped near the supports and top bars near mid-span.
Why is the compression lap shorter?
IS 456 allows 25% more bond stress in compression, so the compression development length is Ld ÷ 1.25. The lap must still be at least 24 bar diameters.
References
  • IS 456:2000 §26.2.1: development length Ld = φσs ÷ 4τbd, with σs = 0.87fy
  • IS 456:2000 §26.2.1.1: design bond stress τbd, increased by 60% for deformed bars and by 25% in compression
  • IS 456:2000 §26.2.5.1: flexural tension lap = Ld, at least 30φ; compression lap = Ld in compression, at least 24φ