Civil Engineering Reference
In-Depth Information
Therefore, the critical shear buckling stress is
4.0
]
π
5.34/
(a
/
h)
2
2
Et
w
+[
τ
cr
=
,
(7.87)
2
)h
2
12
(
1
− υ
which may be rearranged to provide
a
t
w
=
5.34
π
2
2
(t
w
/
h)
2
.
(7.88)
12
(
1
− υ
2
)(
τ
cr
/
E)
−
4
π
Using an FS of 1.5 Equation 7.88 is
∗
a
t
w
=
1.336
1.5
(
0.277
)(
(t
w
/
h)
2
.
(7.89)
τ
cr
/
E)
−
Flexural buckling is precluded (Equation 7.44) where
E
F
cr
≤
5.64
E
F
y
h
t
w
≤
4.18
(7.90)
and considering
τ
cr
≤
0.35
F
y
Equation 7.89 becomes
3.42
E
F
y
a
t
w
=
(7.91)
or (with
τ =
0.35
F
y
)
2.02
E
τ
a
t
w
=
(7.92)
and AREMA (2008) recommends
E
τ
a
≤
1.95
t
w
(7.93)
to establish transverse stiffener spacing. Based on web plate imperfections AREMA
(2008) also provides a practical recommendation for maximum stiffener spacing
of 96 in.
An equation for the required moment of inertia of a transverse web stiffener was
developed from analytical and experimental tests as (Bleich, 1952)
7
h
a
5
,
2
4
at
w
12
(
1
I
ts
=
−
(7.94)
2
)
− υ
∗
AREMA (2008) uses the relatively lower factor of safety of 1.5 for shear buckling in recognition of the
postbuckling strength of web plates in shear.
