Development length is the length of steel bars that should be embedded into the concrete of other members to make the strong bond between members like column, beam, slab, etc. The development length formula of steel is given below.
For example, if you have to joint a beam with a column then the steel bars of the beam should be embedded somewhat into concrete to make a bond between them. This embedded length of steel bars is known as development length.
The calculated tension and compression in any bar at any section shall be developed on each side of the section by an appropriate development length or end anchorage or by a combination thereof.
Development length formula Ld is given by,
The development length includes anchorage value of hooks in tension reinforcement
For bars of section other than circular, the development length should be sufficient to develop the stress in the bar by bond.
For deformed bars confirming to IS 1786 these value shall be increased 60%.
For bars in compression, the value of bond stress for bars in tension shall be increased by 25%.
The value of bond stress in working stress design are given in B-2.1
Development length of steel Calculation
The calculation is based in IS code and limit satate method.
Q) Calculate the development length of the steel having M-25 grade of concrete, Fe415 grade of steel rod, and the diameter of the steel rod is 12mm.
Step 1- Write all the given data
For M-25 Concrete grade and Fe 415 steel grade.
Diameter of steel bars = 12 mm
Stress in bars = 415 N/mm2 [For Fe-415 bars]
Designed bond stress = 2.24 N/mm2
Step 2- Write Development length formula and put all the value.
Putting all the values in given formula,
From the above expression, we can say that for different grades of concrete and steel, we can directly put the development length of steel according to the diameter of the steel rod.
Some calculated value of development length of steel bars are given as,
Hence in this way, we can derive development length formula and calculate the development length of the steel rod.
I hope this article remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Ranjeet Sahani