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Development Length (Ld) Calculation for Deformed Rebars in Tension (Φ = D, Fe500 Steel & M20–M40 Concrete)

 

Development Length (Ld) Calculation for Fe500 & M20-M40 Concrete

Development Length (Ld) Calculation for Deformed Rebars in Tension (Φ = D, Fe500 Steel & M20–M40 Concrete)

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🔗 Download Excel Sheet – Get an easy-to-use Excel sheet for Development Length (Ld) calculations and automate your work!

Introduction

In reinforced concrete structures, Development Length (Ld) is crucial to ensure proper bonding between steel reinforcement and concrete. It helps in transferring stress efficiently from steel to concrete, preventing bar slippage and structural failure.

Development Length Formula for Deformed Rebars in Tension

According to IS 456:2000, the formula for Development Length is:

Ld = (D × 0.87 × Fy) / (4 × τbd)

  • Ld = Development Length (mm)
  • D = Diameter of the reinforcement bar (mm)
  • Fy = Yield strength of steel (N/mm²)
  • τbd = Design bond stress (N/mm²)

Design Bond Stress (τbd) for Deformed Bars (IS 456:2000)

Concrete Grade Standard τbd (N/mm²) Increased τbd for Deformed Bars (1.6 × τbd)
M20 1.2 1.92
M25 1.4 2.24
M30 1.5 2.40
M35 1.7 2.72
M40 1.9 3.04

Final Development Length (Ld) for Deformed Bars (Rounded Off Values)

Concrete Grade τbd (N/mm²) Ld Formula Rounded Off Ld (D)
M20 1.92 (D × 435) / (4 × 1.92) 57 D
M25 2.24 (D × 435) / (4 × 2.24) 49 D
M30 2.40 (D × 435) / (4 × 2.40) 46 D
M35 2.72 (D × 435) / (4 × 2.72) 40 D
M40 3.04 (D × 435) / (4 × 3.04) 36 D

Key Observations

  • ✔ Higher concrete grades require a shorter Ld due to higher bond strength.
  • ✔ Deformed rebars improve bond strength, reducing required Ld.
  • ✔ Using bends and hooks reduces Ld significantly.

Conclusion

Correct calculation of Development Length (Ld) is essential for structural stability. By using Fe500 steel with M20 to M40 concrete grades, we can ensure safe and durable construction.

📥 Download Development Length Calculation Excel Sheet

🔗 Download Excel Sheet – Get an easy-to-use Excel sheet for Development Length (Ld) calculations and automate your work!

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