Structural Detailing of Reinforcement for Economy - Simplified Design of Reinforced Concrete Buildings - page 251

All bars in compression

f s = 0.5f y
compression

0 < f s < 0.5f y
on tension face

f s = 0

f s = 0.5f y
in tension

Zone 1

Zone 2

Load

f s > 0.5f y
on tension face

f s = f y

Zone 3

f s > f y

Moment

Figure 8-9 Special Splice Requirements for Columns