Function of bent up bar in slab | Cutting length of Bent up bar in slab

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Functions of Bent up / Cranked bar in slab:
1. To resist the negative (hogging) bending moment which acts at the support of slab.
2. To resist the shear force which is maximum at supports.
3. To reduce the quantity of steel required for slab for that particular section.
4. To increase the strength of slab.

Typical structure showing positive (sagging) and negative (hogging) bending moment:


Cutting length of bent up bar or cranked bar in slab:

Calculation part:

As per given structural drawing of bent up bar in slab:
Diameter of bar in slab = 12mm.
Nominal cover/clear cover all around slab= 25mm.
Slab thickness = 150mm.
Development length, Ld = 40d.
length of bent up of bar = 0.42D
From the given drawing, calculate the D (distance from inner face to bar to outer face of bar)
D = slab thickness – 2*clear cover – diameter of bar = 150 – 2*25 – 12 = 88mm.
From the given drawing No. of 45˚ bend = 4 & No. of 90˚ bend = 2
Cutting length = clear span + 2*Ld + 2*0.42D – bend (45˚ & 90˚)
               = 5000 + 2*40*12 + 2*0.42*88 – 4*12 – 2*2*12 = 5937.92mm = 5.937m

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