- Cranked bars / Bent up bars are provided on top of the reinforcement to resist negative bending moment/Hogging at the supports of the slab.
- To resist the shear force at the supports.
- To reduce the risk of a brittle failure of slab-column connection.
- When bent up bars are provided, the strength and deformation capacity of slabs with bent up bars compared to slabs without bent up bars is sufficiently increased.
And Mainly ,
( 1 ) .Bottom Reinforcement resists the positive bending moment/sagging at the mid-span of the slab.Top Reinforcement resists the negative bending moment at the supports of the slab.
( 2 ) .It is actually used for the economization of material. Normally, for fixed ended Slabs positive (sagging) moments are present at the mid span and negative (hogging) moments at the supports.
Note :- Bars are bent near the supports normally at an angle of 45°. The angle bent may also be 30° in shallow beams where the (effective depth < 1.5 breadth).