Bar
db 0.375 in bar diameter.
λ
f'c psi Specified 28-day compressive strength of concrete in which the bar is to be developed.
fy Yield strength of bar to be developed.

↑ ACI 318-19 Straight Tension Development Length, Ld:

Ψt More than 12 in. of fresh concrete placed below horizontal reinforcement.
Ψe Epoxy-coated or zinc and epoxy dual-coated reinforcement with clear cover less than 3db or clear spacing less than 6db.
Ψs No. 6 and smaller bars and deformed wires
Ψg Grade 40 or Grade 60
cc in distance from center of bar to nearest concrete surface.
sb in center-to-center spacing of bars being developed.
cb 1.5 in
Atr in2 Total cross-sectional area of all transverse reinforcement within spacing s that crosses the potential plane of splitting through the reinforcement being developed. If unsure of value use 0.
s in maximum center-to-center spacing of transverse reinforcement within Ld.
n number of bars being developed.
Ktr 0
\[L_{d} = \text{max } \begin{bmatrix}\text{(a) }\left( \frac{3}{40} \frac{f_{y}}{\lambda\sqrt{f'_{c}}} \frac{\psi_{t}\psi_{e}\psi_{s}\psi_{g}}{(\frac{c_{b}+K_{tr}}{d_{b}})} \right) d_{b} \text{ (25.4.2.4a)} \\ \text{(b) }12 \text{ in} \end{bmatrix} \text{[25.4.2.1]}\]
\[K_{tr} = 0.0 \]

↑ ACI 318-19 Hooked Development Length, Ldh:

Ψe Epoxy-coated or zinc and epoxy dual-coated reinforcement
Ψr Other
Ψo Other
Ψc test
\[L_{dh} = \text{max }\begin{bmatrix}\text{(a) } \left(\frac{f_{y}\psi_{e}\psi_{r}\psi_{o}\psi_{c}}{55\lambda\sqrt{f'_{c}}} \right)d_{b}^{1.5} \\ \text{(b) }8d_{b} \\ \text{(c) }6 \text{ in} \end{bmatrix} \text{ [25.4.3.1]} \]