Civil Engineering Reference
In-Depth Information
h
/5
h
Longitudinal
stiffener
Transverse
stiffener
a
FIGURE 7.17
Web plate under pure bending.
restrained at the other. From Equation 7.52, the width-to-thickness ratio is
0.67
kE
b
ls
t
ls
≤
F
y
,
(7.82)
which is the approximate value corresponding to the transition curve at
F
cr
=
F
y
(Figure 7.11).
The buckling coefficient,
k
, is 1.277 for plates with one edge fixed and
the other edge free (typical of a longitudinal stiffener) (Bleich, 1952). Substitution of
k
=
1.277 into Equation 7.82 yields
0.76
E
F
y
b
ls
t
ls
≤
.
(7.83)
Assuming the actual calculated stress
f
=
F
y
and applying a safety factor of 1.82
0.42
E
b
ls
t
ls
≤
f
,
(7.84)
2.39
b
ls
f
t
ls
≥
E
,
(7.85)
from which the minimum longitudinal stiffener dimensions for stability can be
determined.
7.2.6.2.2 Transverse Web Plate Stiffeners
Recent investigations have determined that it is appropriate to consider the design of
transverse web stiffeners as flexural members resisting bending forces created by the
restraint that the transverse stiffener imposes on lateral deflections of the web plate
at the shear strength limit state (Kim et al., 2007). Therefore, if transverse stiffeners
are required, the necessary spacing,
a
, to provide adequate rigidity through creation
of nodal lines is determined by considering that AREMA (2008) restricts
a
/
h
≤
1so
that the shear buckling coefficient is
5.34
(a
/
h)
2
.
k
=
4.0
+
(7.86)
