Civil Engineering Reference
In-Depth Information
P
P
t
f
H
H
+
=
FIGURE 8.3b
Alternative equivalent static system for applied vertical and horizontal loads.
overestimated. Modification factors that reduce the normal lateral bending stress have
been developed to mitigate this conservativeness.
However, designers should use the flexure analogy with caution, particularly in
cases where torsional effects are relatively large or for members with unusual load-
ing or support conditions. Examples 8.1 (concentrated torsional moment) and 8.3
(uniformly distributed torsional moment) outline solutions developed from Equa-
tion 8.16. Examples 8.2 and 8.4 outline the solution of the same problems using the
flexure analogy.
Example 8.1
Amachinerygirderinamovablebridgeistosupportaconcentratedloadfrom
equipment with an eccentricity of 6 in. as shown in
Figure E8.1.
Note that only
the stresses from the 35 kip equipment load are considered in this example.
Dead loads and other loads on the machinery girder are not considered.
Section properties are
5430 in.
4
,
I
x
=
339 in.
3
,
S
x
=
216 in.
3
,
I
y
=
=
bt
3
3
2
(
12
(
0.75
)
3
)
+
(
30.5
(
0.44
)
3
)
3
4.23 in.
4
,
J
=
=
I
y
h
2
4
216
(
31.25
)
2
4
52,734 in.
6
,
C
w
=
=
=
EC
w
GJ
=
a
=
180 in.,
L/a
=
1.20,
T
2
GJ
=
35
(
6
)
2
(
11200
)(
4.23
)
=
Pe
2
GJ
=
10
−3
in.
−1
.
2.22
×
