BS 8110-1997 Development Lengths

Basic straight tension development length is calculated using combined equations 48 and 49.

The resulting equation is:

l_{d} = \frac{f_{y} {\cdot d}_{b}}{γ_{m} \cdot 4 \cdot β \cdot \sqrt{f_{c u}}}

where

f_y	=	yield stress of the bar
d_b	=	diameter of the bar
γ_m	=	material strength reduction factor
β	=	0.5 (assumed Type 2 bars with minimum links in beams)

Note: If any bars other than Type 2 deformed bar are used or if minimum links in accordance with Table 3.7 are not provided, the development lengths will need to be specified manually. Table 3.27 can assist with this.

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 bar diameters less than or equal to 18mm and 3.5d_b for bar diameters greater than 18mm.

For 90 degree hooks, the effective anchorage of the hook is 4 times the internal bend radius but not to exceed 12d_b in accordance with 3.12.8.23 (b)

For 180 degree hooks, the effective anchorage of the hook is 8 times the internal bend radius but not to exceed 24d_b in accordance with 3.12.8.23 (a)

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.