Estimating Sheet

Computation of cutting length of crank bar in slab

Construction Software By watching this exclusive civil engineering tutorial, you will come to know the method for working out the cutting length of crank bar or bent up bar.

Bars are bent adjacent to the supports at an angle of 45° for the following purposes :-

1. To safeguard from negative bending moment (hogging).
2. To withstand shear force that is extreme at supports.
3. To minimize the risk of a brittle failure of slab-column connection.

To protect RCC slab from compressive stresses, the reinforcement is arranged in the form of bent up bars. When bent up bars are arranged the strength and deformation strength of slabs are significantly raised.

The calculation is made on the basis of the following data :-

Diameter of bent up bar (denoted as d) = 12 mm
Clear span = 6000 mm
Clear cover (both top & bottom) = 25 mm
Thickness of slab = 150 mm
Development length (denoted as Ld) = 40 d

The cutting length of bent up bar will be calculated with the following formula :-
= Clear span + (2 x 0.42 H) + (2 x Ld) – (1d x no. of bend) – (2d x no. of bend)

Also Read: How to determine the cutting length of circular ties

The above figure is provided for both sides of the slab.
Here, H denotes height.
One side bent = 45 degree and other side bent = 90 degree
For 45 degree bent 1d is taken and 90 degree bent 2d is taken.

The value of H is unknown and it will be calculated as follow :-
H = Slab thickness – 2 x clear cover – d

After putting all the values, the following result is obtained :-
= 150 – (2 x 25) – 12
= 150 – 50 – 12 = 88 mm

Now, put all the given values in the formula to get the cutting length.

To get more clear ideas, go through the following video tutorial.

Video Source: Civil Engineer Deepak Kumar 