Civil Engineering Reference
In-Depth Information
For a
W
12
×
79 section:
23.2 in.
2
t
w
=
A
=
0.47 in.
b
f
=
12.08 in.
t
f
=
0.735 in.
h
w
=
10.61 in.
d
=
12.38 in.
With elastic properties:
662 in.
4
I
x
=
107 in.
3
S
x
=
r
x
=
5.34 in.
216 in.
4
I
y
=
35.8 in.
3
S
y
=
r
y
=
3.05 in.
=
r
min
Net area:
20.26 in.
2
Path A-B-C:
A
n
=
23.2
−
4
(
1
)(
0.735
)
=
4
2
/
4
(
9
)
]}
(
0.735
)
=
20.91 in.
2
Path A-B-D-E:
A
n
=
23.2
−
2
{
2
(
1
)
−[
Effective net area:
e
x
∼{
(
0.735
)(
12.08
)(
0.735
/
2
)
+
(
0.47
)(
12.38
/
2
−
0.735
)
[
(
12.38
/
2
−
0.735
)/
2
+
0.735
]}
/
{
(
0.735
)(
12.08
)
+
(
0.47
)(
12.38
/
2
−
0.735
)
}
=
1.59 in.
L
c
=
16 in.
U
c
=
1
−
(
1.59
/
16
)
=
0.90
≤
0.90, OK
18.23 in.
2
A
e
=
0.90
(
20.26
)
=
L/r
min
=
(
27.25
)(
12
)/
3.05
=
107.
6.2.2 F
ATIGUE
S
TRENGTH OF
A
XIAL
T
ENSION
M
EMBERS
The fatigue strength of an axial tension member is
T
fat
=
S
rfat
A
efat
(6.8)
where
A
efat
is the effective gross or net area of only the member elements that are
directly connected (e.g., the flange elements in
Figure 6.1)
.
This reduction accounts
for shear lag effects for fatigue design, which occur at stress levels below fracture.
∗
∗
Shear lag for strength design is evaluated at stress levels near fracture.
