Curtailment of Rebar after stock length

The sketch shows the way I cutoff the bars.

I think the source of your confusion originates from the question, where to start measuring the development length for moment Ma and Mb.

Lets assume, Ma is the moment at some distance xa from centre of span. Reinforcement required for this moment is equals to 6 bars which should be developed upto a distance, xa+ld.
Similarly, Mb is the moment at some distance xb and reinforcement required for this moment is equals to 4 bars which should be developed upto a distance, xb+ld.
Let say, you curtailed 2 of the 6 bars at xa+ld = 2 units and continue the remaining 4 bars upto xb+ld = 3 units, from centre of the span.

Possible problem that can arise from doing this is if you have a third moment Mc in somewhere between Ma and Mb for which, lets say, 5 bars are required. These bars should be developed upto a distance xc+ld = 2.5 units.

But at distance >2 units you have only 4 bars, because you've curtailed the 2 bars at 2 units.

Therfore, to avoid this scenario and unnecessarily complex curtailments, ld for Ma should start from xb instead of xa.

To make this process simple you can break your moment diagram into a step like diagram (as shown in the attached sketch) and provide ld from end of each box. Choose an appropriate step size to keep the detailing economical.



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