Difference Between Development length and Anchorage Length

Development length is the minimum length of the embedded bar in order to transfer the maximum steel stress to the surrounding concrete. Sometimes Development length and anchorage length are considered to be same term. In the cases where the embedded length of the bar (Like in case of a cantilever RC beam we provide some extra length (embedded length) inside the column through which the beam is attached) is not subjected to any 'flexural bond' and there is no hook arrangements then Anchorage Length is same as Development Length.  While in case when we use hooks then the equivalent anchorage length is different from the development length. This term also depends upon the sign of the stress.In case of hooks : If its a case of tensile stress then anchorage length is same as given in code (like 8 times bar dia or 16 times bar dia etc depending upon bend angle), code also says that - if its a case of compressive stress the anchorage length is the projected length of the bend on the longitudinal bar, because hooks are ineffective in providing anchoring in case of compressive stresses.   

Basically the development is the length which should be such that the stress should develop on both sides of the point of maximum stress in the steel bar. If this point is in the mid span of the beam then it can develop on both sides but if the maximum stress is at the end (like in cantilever) then we need to provide extra length beyond the end. If this extra anchoring length is straight then its same as development length and if this extra anchoring is not straight i.e. with hooks then it is called as anchorage length and not the development length.

Development length is defined as the length of bar required on either side of the section under consideration to develop the required stress in steel at that section through bond. The development length includes anchorage values of hooks in Tension reinforcement. The required length, necessary to develop full resisting force, is called anchorage length in case of Tension (or Compression) In case of development length, force in the bar is developed by transfer of force from concrete to steel, while in case of anchorage length, there is dissipation of force from steel to concrete. Deformed bars in Tension may be used without end anchorages provided development length required is satisfied. Hooks should  normally be provided for plain bars in Tension. For other details please refer IS 456-2000 code.