Civil Engineering Reference
In-Depth Information
is recommended by AREMA (2008) as
L
u
r
min
≤
200,
(6.9)
where
r
min
=
I
min
/A
g
, and
I
min
is the minimum moment of inertia of the tension
member in bending about an axis between supports,
L
u
.
Example 6.3
Determine the design criteria for load case A1 (Table 4.5) for member U1-
50 ksi) steel with
ultimate stress,
F
u
, of 70 ksi. Assume a connection as shown in Example 6.2.
The forces in member U1-L1 are
Dead load force
=
DL
=+
10.82 kips
Maximum live load force
=
LL1
=+
128.8 kips (see Chapter 5)
Minimum live load force
=
LL2
=
0
19.55
see Chapter 4)
Maximum Live Load Impact
=
39.28% (L
=
Mean Live Load Impact
=
0.40
(
39.28
)
%
=
15.71% (see Chapter 4)
Range of live load force
=
LL
range
=
LL1
+
LL2
=+
128.80
+
(
0.00
)
=
128.80 kips
Load combinations:
P
rangeLL+I
=
1.157
(
128.8
)
=
149.0 kips
P
max
=+
10.82
+
1.393
(
128.80
)
=+
190.2 kips
Strength considerations:
190.2
0.55
(
50
)
≥
6.92 in.
2
(tensile yielding)
A
g
≥
190.2
0.47
(
70
)
≥
5.78 in.
2
(fracture)
A
n
≥
due to strength-related shear lag effects at the connection
5.78
U
c
≥
6.42 in.
2
(fracture).
A
e
≥
Fatigue considerations (including fatigue shear lag):
A
efat
≥
(
149.0
/
16
)
≥
9.31 in.
2
for the gross area of connected elements of
themember(
Table6.1
)(
AREMA(2008)recommendsslipresistantconnections
for main members such as U1-L1).
A
e
≥
(
149.0/24
)
≥
6.21 in.
2
for the net area of the member away from the
connection (Table 6.1)
