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V
x
T
V
y
Total
shear
stress
V
y
Q
x
I
x
t
V
x
Q
y
I
y
t
St. Venant
torsion
Warping
torsion
=
τ
=
+
+
+
Figure 7.4
Illustration of the general I-girder shear stresses, which can occur in a curved
or skewed I-shaped girder.
The normal warping stresses for I-girders caused by torsion represent
one source of what are called flange lateral bending stresses. These are an
important part of the design equations for flange stresses in I-girders. In
that case, all terms on Figures 7.3 and 7.4 have to be counted for.
7.1.3 Section property in the grid
modeling considerations
During the development of any structural analysis, section properties are
assigned to the members. The distribution of forces through the system
is highly dependent on member stiffness parameters such as
EI
x
,
EI
y
,
GJ
,
and
EC
w
.
EC
w
,
the warping stiffness parameter,
is not used in a generic
structural analysis method based on the beam theory with six degrees
of freedom (DOFs) per node. For special analyses, cross-sectional warp-
ing deflection, the seventh DOF can be included to consider the warp-
ing of thin-wall cross sections. Thus, the additional warping stiffness is
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