Development length is a term used in construction to refer to the length of reinforcement (bar) that must be embedded in concrete to achieve the desired bond strength between the steel and concrete. It is the minimum length of the bar that must be embedded in concrete beyond any section to develop its full strength. The development length is necessary to provide support to the beam to reduce the chances of the beam coming out of the concrete column, and it acts as a supporting member for the reinforced beam in the concrete column.

The development length is affected by several factors, including the density of concrete, the thickness of the concrete cover, and the type of steel used in the construction members. The IS codes provide guidelines for determining the accurate development length to maintain structural integrity as per the type of bar and concrete.

The calculation of development length involves determining the stress in the bar at the section considered at design load and the design bond stress. The formula for calculating development length is Ld = σ st φ/4τ bd, where Ld is the development length, σ st is the stress in the bar at the section considered at design load, φ is the diameter of the bar, and τ bd is the design bond stress.

Providing the correct development length is essential in reinforced concrete design, as it ensures that the rebar can reach its full yield strength and prevents premature failures. The development length is provided at the column beam joint or column footing joint, and it is necessary to embed the bar at the column footing or column beam joint to smoothly transfer the excess stress and reinforce the concrete bond.