Because of loading on slab,
positive moment (sagging ) generated at mid span that is tension steel require at bottom and second thing at support negative moment getting develop (Hogging) requires tension steel at top.
Now we can provide tension steel at top of support by two way,
- Provide bent up bars.that means alternate bars from the bottom steel bent up at top ( Since at support no need of bottom steel or require only min. steel)
- Role of bent up bars:
- To resist negative bending moment at support.
To resist shear force which is higher at support.
To make structure economical by reducing amount of steel.
2. If do not want to go for bent up bars then you can provide separate steel at top of support.