CURTAILMENT OF REINFORCEMENT IN FLEXURAL MEMBERS

Curtailment of Tension Reinforcement in Flexural Members 

To economise the design of a flexural member, the tensile bars are curtailed at the section beyond which it is no longer required to resist flexure. Such curtailed bars are extended for a distance equal to 12 or effective depth, whichever is greater, except at simple support or free end of cantilever.
At simple support, positive moment tension reinforcement shall be limited to a diameter such that L_d computed for f_d does not exceed

where M1= Moment of resistance of the section assuming all reinforcement at the section to be stressed to f_d,
f_d = 0.87 f_y,
V= Shear force at the section due to design loads,
L₀= Sum of anchorage beyond the centre of the support and the equivalent anchorage value of hook, etc., and
= Diameter of bar.
The value of in the above expression may be increased by 30% when the ends of reinforcement are confined by a compressive reaction. At least one-third of positive moment reinforcement in simple member shall extend along the same face of the member into the support, to a length equal to .

Fig: Curtailment of Reinforcement in RCC Beams

Flexural reinforcement shall not be terminated in tension zone unless one of the following conditions are fulfilled:
(a)  The shear at the cutoff point does not exceed two-thirds of that permitted.
(b)  Stirrup area in excess of that required for shear and torsion is provided along each terminated bar over a distance from cutoff point equal to three-fourth the effective depth of the member. The excess stirrup area shall be not less than 0.4 bs/f_y, where b is the breadth of the beam and s is the spacing. The resulting spacing shall not exceed is the ratio of the area of bars cutoff to the total area of bars at the section.
(c)  For 36 mm and smaller bars, the continuing bars provide double the area required for flexure at the cutoff point and the shear does not exceed three-fourths of that permitted.

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