Basic straight tension development length is calculated using equation 12-1.
where
|
k1
| = | 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 > 300 mm
- 1.0 for concrete below ≤ 300 mm
|
|
k2
| = | coating factor
- 1.5 for epoxy coated bars with cover (to center of bars) less than 3db (spacing is not calculated)
- 1.2 for all other epoxy coated bars
- 1.0 for uncoated bars
Note: The product of k1k2 is never taken as greater than 1.7.
|
|
k3
| = | concrete density factor
- 1.3 for concrete density ≤ 1,850 kg/m3
- 1.2 for concrete density ≤ 2,150 kg/m3
- 1.0 for concrete density > 2,150 kg/m3
|
|
k4
| = | bar size factor
- 0.8 for 20M and smaller bars
- 1.0 for 2.5M and larger bars
|
|
dcs
| = | cover dimension, vertical distance from the center o the bar to the nearest concrete surface (spacing is not considered) |
The term (dcs + Ktr) is never taken greater than 2.5db.
Ktr is conservatively taken to be zero.
For development of standard hooks, basic tension development length is calculated in accordance with clause 12.5.2.
The following factors are used to modify this basic length:
- Bar yield strength factor = fy/400 where fy is in MPA (12.5.3a)
- Low-density concrete factor (12.5.3e):
- 1.3 for concrete density ≤ 1,850 kg/m3
- 1.0 for concrete density > 1,850 kg/m3
- Epoxy-coated reinforcement factor = 1.2 (12.5.3f)
The following factors/provisions are not considered:
- Concrete cover (12.5.3b) and ties or stirrups (12.5.3c)
