Development Length of steel Reinforcement Bar
Development lenth is the length of the bar which is used to transfer the stress of steel into concrete.
This is mainly bend or hook length in case of beam and column, i.e. tension and compression member respectively.
Development Length is denoted by Ld
Ld = (Nominal dia of bar × stress in bar) / (4× bond stress in bar)
NOTE: The formula is used for Plane steel bar.
In case of Deformed bar the design bond stress is increase by 60%.
In case of compression, the design bond stress is increase by 25%.
For Example Development length of Plane Bar having Dia of 16mm, M20 Grade and Fe415 grade of steel.
Ld = 16*415/(4*1.2) = 1383.33 mm
For Example Development length of Deformed Bar having Dia of 20mm, M20 Grade and Fe415 grade of steel.
Ld = 20*415/(4*1.2*1.6) = 1080.72 mm
Thumb Rule for Development Length of bar
Generally development length is the 41 times of nominal diameter of bar.
- Example for 16mm: 16×41 = 656 mm
- For 20mm = 20×41 = 820 mm
Necessity of Development length
It is necessary to make a combined material of steel and concrete, for the safely transfer of load in each other they required good bonding between each other. So development length of bar is provided to transfer the whole stress without flexural failure.