Bars are bent near the supports at an angle of 45°. The angle bent may also be 30° in shallow beams where the (effective depth< 1.5 breadth).
Bars are bent near the support to
1- To resist the negative bending moment (hogging).
2- To resist shear force which is greater at supports.
3- To reduce the risk of brittle failure of slab-column connection.
The images show how the bent up bars are provided in the slab.
The slab is supported at two ends. The maximum tensile stress is in the middle of the slab and the maximum compressive stress is at both ends. To make the RCC slab safe from compressive stresses we place reinforcement in the form of bent up bars.
When bent up bars provide the strength and deformation capacity of slabs with bent up bars compared to slabs without bent up bars is sufficiently increased.
For more information watch this video
