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ACI 318-08 and ACI 318-11 Development Lengths

Basic straight tension development length is calculated using equation 12-1. The following factors are used in this equation:

Ψt = 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
Ψe = coating factor
  • 1.5 for epoxy coated bars with cover (to center of bar) less than 3db (spacing is not calculated)
  • 1.2 for all other epoxy coated bars
  • 1.0 for uncoated bars
Note: the product ΨtΨe is never taken as greater than 1.7.
Ψs = 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 (wc ≤ 120 pcf)
  • 1.0 for normal-weight concrete (wc > 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 + Ktr)/db is never taken greater than 2.5

Ktr is conservatively assumed to be zero

For development of standard hooks, basic tension development length is calculated using equation 12.5.2.

The following factors are used to modify this basic length:
  • lightweight aggregate concrete factor, λ, as described above
  • the coating factor, Ψe, is taken as 1.2 for epoxy-coated reinforcement

In accordance with ACI 318 12.10.3, the extension length used for this Code is the maximum of 12db or the 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 (12.2.1) and 8db or 6 in for hooks (12.5.1).

Parent topic: Development lengths / anchorage