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

Bar diameter d_b (mm)

Concrete f'c (MPa)

Steel fy (MPa)

Concrete type λ

Tension (Straight)

Ψ_t (location)

Ψ_e (epoxy)

Poor: cover < 3d_b or clear spacing < 6d_b

Ψ_s (size)

Ψ_g (grade)

c_b (mm)

Min of side cover or 1/2 clear spacing

K_tr (mm)

Transverse reinforcement index

Hooks in Tension

Bar size

Ψ_e (epoxy)

Ψ_o (location)

Ψ_r (confinement)

Compression Development

Column type

α (cast-in-placed bar end)

📊 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×λ)/(1.1×λ×√f'c×(cb+Ktr)/db) ≥ max(300mm, 12db)
Hooked tension ldh (§25.4.3.1): ldh = (fy×Ψe×Ψo×Ψr×Ψc×λ)/(5.4×λ×√f'c)×db ≥ max(150mm, 8db)
Compression ld (§25.4.9.2): ld = (0.24×fy×α×λ×db)/(λ×√f'c) ≥ 200mm

Note: √f'c is limited to √100 = 10 per §25.4.1.4. (cb+Ktr)/db ≤ 2.5 per §25.4.2.3. Spiral columns use 0.75 reduction factor.