Basic straight tension development length is calculated using clause 26.2.1:

where

fy	=	yield stress of the bar
φ	=	diameter of the bar
τbd	=	design bond stress given in Table 26.2.1.1

For high strength deformed bars, the bond stress can be increased by 60 percent. This increase is assumed for any bar with f_y > 250 N/mm².

In addition, the following factors (from ACI 318) are applied:

• 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
• lightweight aggregate concrete factor:
  • 1.3 for concrete density < 1900 kg/m³
  • 1.0 for concrete density > 1900 kg/m³

For development of hooks, the internal bend radius is assumed to be 2d_b for bars with yield stress less than or equal to 250 N/mm² and 4d_b for bars with yield stress greater than 250 N/mm².

For 90 degree hooks, the effective anchorage of the hook is 8 times the diameter of the bar in accordance with 26.2.2.1 (1).

For 180 degree hooks, the effective anchorage of the hook is 16 times the diameter of the bar in accordance with 26.2.2.1 (2).

In accordance with 3.12.9.1, the extension length used for this Code is the maximum of 12 d_b 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.