WHY CRANK BARS ARE PROVIDED IN SLAB ?

  • 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).

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