RAM Concept Help

ACI 318-19 Development Lengths

Basic straight tension development length is calculated using equation 25.4.2.3. 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

Ψg = reinforcement grade factor

  • 1.0 for fy ≤ 60 ksi
  • 1.15 for fy = 80 ksi
  • 1.3 for fy = 100 ksi

Interpolation used to calculate values for reinforcement grades between 60 ksi and 100 ksi.

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

Sections 9.7.4.1 and 25.4.2.2 are not implemented.

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
Ψe = coating factor
  • 1.2 for epoxy coated bars
  • 1.0 for uncoated bars

Ψc = concrete strength factor

  • (f’c/15,0000 + 0.6) for f’c < 6000 psi
  • 1.0 for f’c ≥ 6000 psi
Ψr= 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.

The location factor (Ψo) is assumed to be 1.0.

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 12db 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 8db or 6 in for hooks (25.4.3.1b and c).

Parent topic: Development lengths / anchorage