Civil Engineering Reference
In-Depth Information
Figure 3.19
Curtailment of reinforcement
3.10.6 Curtailment of reinforcement
The strut-and-tie analogy assists in understanding the mechanics of the curtailment
of reinforcement. Consider the bending moment diagram for a uniformly loaded
reinforced concrete cantilever, Figure 3.19
(a). By point A, the bending moment will
have fallen considerably, and hence the theoretical requirement in reinforcement will
also have fallen, with several bars being curtailed. However, according to the truss
analogy, Figure 3.19 (b), the maximum tension
T
1
, and consequently the maximum
reinforcement, are both constant up to point A. Hence the reinforcement requirement
needs to be shifted horizontally by a lever arm with respect to the bending moment
diagram, Figure 3.19 (c). The same reasoning holds true for simply supported and
continuous beams, and is the basis of the requirements of some codes of practice.
It should be noted that shifting the bending moment by a lever arm is only rational
if the beam has been reinforced with vertical stirrups, and the 'N' truss analogy is
applicable. If bent-up bars are being used with a Warren truss analogy, or if a shear fi eld
analogy is being used, the mechanics of curtailment should be reviewed.
3.10.7 Hanging steel
When loads are applied at the bottom of a reinforced concrete beam, reinforcement
must be provided, over and above the shear reinforcement, to carry the forces up
