Expert Guide
Steel / Rebar Calculators
Development Length (Ld) Calculator – Rebar Bonding
Quality Inspector
Determine the required anchorage or development length of reinforcement bars to ensure proper bond between steel and concrete.
📐 Formula & Method
Ld = (phi × sigma_s) / (4 × tau_bd). Sigma_s is 0.87 × Grade. Tau_bd value depends on concrete grade and is increased by 60% (1.6x) for deformed bars.
Ld = (ϕ × 0.87 × f_y) / (4 × τ_bd)
📋 Worked Example
For 12mm Fe500 bar in M20 concrete: • Sigma_s = 0.87 × 500 = 435 • Tau_bd = 1.2 × 1.6 = 1.92 • Ld = (12 × 435) / (4 × 1.92) ≈ 680 mm (approx 56D)
❓ Frequently Asked Questions
It is the minimum length of rebar that must be embedded in concrete to prevent the bar from pulling out when it is under tension.
Higher concrete grades have stronger bond strength (tau_bd), which reduces the required development length.
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