American Steel Design
Section 2
2-70
CASE 2B: PNA IN WEB OF STEEL BEAM
P.N.A.
g
h
r
t
T
S
C
1
e
f
C
e
2
S
e
3
w
C
C
f
y
f
y
f
Figure 2.9
C
f
= Compressive force in flange = A
f
. f
y
C
w
= Compressive force in web = C
b
– C
f
g =
()
yw
w
f . t
C
where, t
w
= thickness of web
Point of action of the tensile force is the centroid of the steel area
below the PNA. After finding that point, e
1
, e
2
and e
3
can be
calculated.
Moment Capacity =
()
3w1f2sb
e . Ce . C e . C
+
+
φ
Utilization Ratio = Applied Moment / Moment Capacity