Civil Engineering Reference
In-Depth Information
1
q
F
LT
l
LT
w
LT
¼
but
w
LT
1
:
0
ð
3
:
40
Þ
F
LT
+
h
i
+
l
2
l
LT
0
with
F
LT
¼
0
:
51+
a
LT
:
2
ð
3
:
41
Þ
LT
s
W
y
f
y
M
cr
l
LT
¼
ð
3
:
42
Þ
where
a
LT
is an imperfection factor and
M
cr
is the elastic critical moment for
lateral torsional buckling.
M
cr
is based on gross cross-sectional properties and
takes into account the loading conditions, the real moment distribution, and
the lateral restraints. The imperfection factor
a
LT
corresponding to the
appropriate buckling curve can be taken from
Table 3.18
as specified in
EC3 [2.11]. The recommendations
for buckling curves are given in
Table 3.19
as specified in EC3 [2.11].
3.8.4 Shear Resistance of Steel Plate Girders
Checking the safety of steel plate girders against shear stresses is quite impor-
tant in steel and steel-concrete composite bridges. Maximum shear stresses
are normally located near the supports. Main girders made of steel plate
girders are deep and thin, which make it vulnerable to fail owing to shear
stresses, which is normally concentrate in panels near the supports.
Table 3.18 Recommended Values for Imperfection Factors for Lateral
Buckling curve
a
b
c
d
Imperfection factor
a
LT
0.21
0.34
0.49
0.76
Table 3.19 Values for Lateral Torsional Buckling Curves for Different Cross
Cross Section
Limits
Buckling Curve
Rolled I-sections
h
/
b
2
h
/
b
a
b
>
2
Welded I-sections
h
/
b
2
h
/
b
c
d
>
2
Other cross sections
-
d
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