Rebar Development Length (ACI 318-19M)

Compute ld for straight bars in tension, standard hooks in tension, and compression development, including epoxy, size, grade, location, confinement, and lightweight factors per ACI 318-19M.

Inputs

Bar & Material

Tension (Straight)

Poor: cover < 3db or clear spacing < 6db
Min of side cover or 1/2 clear spacing
Transverse reinforcement index

Hooks in Tension

For No. 36 and smaller bars only per Table 25.4.3.2

Compression Development

Lap Splice (ACI 318-19M §25.5)

Class A allowed only if As,provided ≥ 2·As,required AND ≤ 50% of bars spliced within required lap length.
fy ≤ 420 MPa: ℓsc = 0.071·fy·db  |  fy > 420: (0.13·fy − 24)·db. ×4/3 if f'c < 21 MPa. Min 300 mm.

📊 Results

Enter or adjust inputs to compute development lengths per ACI 318-19M.

Design Basis (ACI 318-19M)

  • Straight tension ℓd (§25.4.2.3): ℓd = (fy·Ψt·Ψe·Ψs·Ψg·db) / (1.1·λ·√f'c·(cb+Ktr)/db), Ψt·Ψe ≤ 1.7, ≥ max(300 mm, 12·db)
  • Hooked tension ℓdh (§25.4.3.1): ℓdh = (0.24·Ψe·Ψo·Ψr·Ψc·fy·db) / (λ·√f'c), ≥ max(150 mm, 8·db)
  • Compression ℓdc (§25.4.9.2): ℓdc = max((0.24·fy·α·db)/(λ·√f'c), 0.043·fy·db), ≥ 200 mm; ×0.75 for spirals (§25.4.9.3)
  • Tension lap splice ℓst (§25.5.2.1): Class A = 1.0·ℓd (only when As,prov ≥ 2·As,req AND ≤ 50% bars spliced within ℓd); Class B = 1.3·ℓd otherwise; ≥ 300 mm
  • Compression lap splice ℓsc (§25.5.5.1): fy ≤ 420 MPa → ℓsc = 0.071·fy·db; fy > 420 MPa → (0.13·fy − 24)·db; ×4/3 if f'c < 21 MPa; ≥ 300 mm

Notes: √f'c capped at √100 = 10 per §25.4.1.4; (cb+Ktr)/db ≤ 2.5 per §25.4.2.4. Splice provisions apply to deformed bars in non-contact and contact lap splices; mechanical/welded splices follow §25.5.7. For columns subjected to compression-controlled actions, see §10.7.5 for additional splice requirements.