Bent- Up Bars

         In simply supported single span slabs it is not normally necessary to bent up any bars. But in partially fixed conditions (which are the most common and occur where roof slabs are built into walls) every third bar shall be bent up. In the slabs continous over two or more spans, alternate bars may be bent up, or equivalent seperate reinforcement may be provided at the top of the supports for the negative moments. Bent-up bars are more economical. In large slabs seperate reinforcement over the siupports may be necessary.

          Such bent-up bars shall extend a sufficient distance beyond the centre of the support to provide adequate bond. The points at which some of the reinforcement is bent-up for the negative bending moment at the support depend on the points of contraflexure. Stirrups are not used in slabs.

          It is not necessary to check shear or bond stress on a slab except with a superimposed load of over 2000 Kg per Meter Square. Shear stress in concrete is generally small and bond stress within allowable limits.