BS 8110-1997 Development Lengths
Basic straight tension development length is calculated using combined equations 48 and 49.
The resulting equation is:
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In addition, the following factors (from ACI 318) are applied:
For development of hooks, the internal bend radius is assumed to be 2db for bar diameters less than or equal to 18mm and 3.5db 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 12db 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 24db 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 db 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.