Reason behined the use of bent-up bar

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Bending moment and shear force in beam-
generally, we know if beam is loaded then bending moment develops, its varriation property depends on the type of beam and loading.
if we take an example , in case of simplysupported moment is always zero at the support and maximum at mid span. if loading is udl then moment varriation is parabolically.
moment varriation in simply supported beam with udl, parabolic
moment varriation
here,bending moment varies support to mid span and varriation of bending moment , shear stress developed.
in case of RCC beam we assume that shear stress is carried by bonding below the nautral axis.
shear stress is maximum at the support in case of simply supported , see in above figure. and bending moment is zero.
if this shear stress is more than permissible then cracks are developed at 45°. this is called as diagonal tension.


Reason behined bent-up bar -
1.  bent up bar provides to carry the shear stress & generally shear stress is carried by stirrups.
2.  in case of fixed beam the negative bending moments are developed at the support and due this may be possible buckling of support and beam and losses of all over strength.
hence for carrying negative bending moment bent -up bar must be used.


Reason to provide bent-up bar in beam or slab
bent-up bar locations :



generally bent-up bar bends at 40-60°. but mostly at 45°

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