ACI 318-14 Development Lengths

Basic straight tension development length is calculated using equation 25.4.2.3. The following factors are used in this equation:

Ψ_t = reinforcement location factor

"concrete below" is taken as the depth from the rebar center to the bottom of the concrete section
1.3 for concrete below ≥ 12 inches
1.0 for concrete below < 12 inches

Ψ_e = coating factor

1.5 for epoxy coated bars with cover (to center of bar) less than 3d_b (spacing is not calculated)
1.2 for all other epoxy coated bars
1.0 for uncoated bars

Note: the product Ψ_tΨ_e is never taken as greater than 1.7.

Ψ_s = reinforcement size factor

0.8 for #6 and smaller bars
1.0 for #7 and larger bars

λ = lightweight aggregate concrete factor

0.75 for lightweight concrete (w_c ≤ 120 pcf)
1.0 for normal-weight concrete (w_c > 120 pcf)

c = cover dimension, vertical distance from the center of the bar to the nearest concrete surface (spacing is not considered)

The term (c + K_tr)/d_b is never taken greater than 2.5

K_tr is conservatively assumed to be zero

Tension development length of standard hooks is calculated using equation 25.4.3.1. The following factors are used in this equation:

λ = lightweight aggregate concrete factor

As discussed above for straight bar development

Ψ_e = coating factor

1.2 for epoxy coated bars
1.0 for uncoated bars

Ψ_r= confining reinforcement factor

1.0 for bars with "90 Hook (Confined)" or "180 Hook (Confined)" end condition
1.6 for bars with all other end conditions.

When laying out program reinforcement, RAM Concept first attempts to detail reinforcement without confining reinforcement. The confinement reinforcement required for program or user reinforcement defined with "90 Hook (Confined)" or "180 Hook (Confined)" bar ends must by designed by the user outside RAM Concept .

In accordance with sections 7.7.3.3 and 9.7.3.3, the extension length used for this Code is the maximum of 12d_b or effective depth of the member, taken as the maximum vertical distance from the center of the reinforcing bar to the farthest concrete surface.

The minimum development length is 12 in for straight bars (25.4.2.1b) and 8d_b or 6 in for hooks (25.4.3.1b and c).