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Section 2
2-67
3.
If step 1 produces a higher value than step 2, plastic neutral
axis (PNA) is in the slab. Else, it is in the steel beam.
CASE 1: PNA IN SLAB
Find the depth of PNA below the top of slab as:
0.85 f
c
. b . a . = A
s
. f
y
a =
b . f 0.85
f . A
c
ys
h
t
P.N.A.
r
a
d
d/2
d/2
e
T
C
C
f
y
f
y
f
Figure 2.7
Lever arm e =
2
a
t h
2
d
r
−++
Moment capacity =
(
)
e . f . A
ysb
φ