Civil Engineering Reference
In-Depth Information
A
f
f
y
g
M0
A
f
,
net
0
:
9
f
u
ð
3
:
37
Þ
g
M2
where
A
f
is the area of the tension flange;
g
M0
is a partial factor related to the
resistance of cross section whatever the class is, which is taken equal to 1.0;
and
g
M2
is a partial factor related to the resistance of cross section in tension
to fracture, which is equal to 1.25. Fastener holes in tension zone of the web
need not be allowed for. Fastener holes except for oversize and slotted holes
in the compression zone of the cross section need not be allowed for,
provided that they are filled by fasteners.
3.8.3 Lateral Torsional Buckling of Plate Girders in Bending
When beams and plate girders are subjected to bending moment, the com-
pression flange will be subjected to lateral torsional buckling. The lateral tor-
sional buckling of the compression flange depends on the loading
conditions, lateral restraint conditions, and geometries of the compression
flange. EC3 [1.27,2.11] recommends that a laterally unrestrained member
subject to major axis bending should be verified against lateral torsional
buckling as follows:
M
Ed
M
b
,
Rd
1
:
0
ð
3
:
38
Þ
where
M
Ed
is the design value of the moment and
M
b,Rd
is the design buck-
ling resistance moment. Beams with sufficient restraint to the compression
flange are not susceptible to lateral torsional buckling. In addition, beams
with certain types of cross sections, such as square or circular hollow sec-
tions, fabricated circular tubes, or square box sections, are not susceptible
to lateral torsional buckling. The design buckling resistance moment of a
laterally unrestrained beam should be taken as
f
y
g
M1
M
b
,
Rd
¼w
LT
W
y
ð
3
:
39
Þ
where
W
y
is the appropriate section modulus, which is taken as
W
pl,y
for
class 1 or 2 cross sections or
W
el,y
for class 3 cross sections or
W
eff,y
for class
4 cross sections, and
w
LT
is the reduction factor for lateral torsional buckling.
It should be noted that, according to EC3 [1.27,2.11], determining
W
y
holes
for fasteners at the beam end need not be taken into account. Also, for bend-
ing members of constant cross section, the value of
w
LT
for the appropriate
nondimensional slenderness
l
LT
should be determined from
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