The development length may be defined as the length of the bar required on either side of the section to develop the required stress in steel at that section.
DEVELOPMENT LENGTH OF BARS
The development length Ld, is given by
In the formula for development length, the appropriate values for u s and 7M are to be used depending upon the method of design adopted.
If the amount of steel provided at a section is more than that required from design considerations, the development length may be modified as:
Development length of a bend/hook bar is equal to the length of the reinforcement between the point of tangency of the bend/hook and the critical section plus the anchorage value of bend/hook. The anchorage values of standard hooks and bends
Extra development length is required in case of bundled bars than that required for an individual bar because the grouping makes it more difficult to mobilize bond resistance from the core between the bars.