What's the purpose in providing the development length for beams?

Development Length

A development length can be defined as the amount of reinforcement(bar) length needed to be embedded or projected into the column to establish the desired bond strength between the concrete and steel (or any other two types of material).

Reason for providing Development length

When the reinforcement bar is no longer required to carry the tensile forces, i.e tension at that section is about zero, then it is required to develop the bar further so that the grip/bond between the steel and concrete forms a continuous structure.

If the development length is not provided, then the restraining force in concrete section will be comparatively thin(weak) and will be unable to withheld the position of highly stressed bars resulting in splitting of bars from concrete.

Thus development length is provided to have a fixed support to the bars. In some cases,where there is no space or very little space is available for extra length, hooks are provided for restraints.

LAP LENGTH:-