Civil Engineering Reference
In-Depth Information
TABLE E7.1
Design Force
Shear Force,
V
(kips)
Bending Moment,
M
(ft-kips)
Dead load, DL
110
2500
Live load
+
37% impact (maximum)
376
7314
Maximum (DL
+
LL)
486
9814
Live load
+
13% impact (fatigue)
310
6032
Preliminary girder design
:
Use a girder depth of 90
/
12
90
(see Chapter 3) and assume 2-1
/
2
thick flanges (reasonable practical thickness
∗
);
7.5
=
=
486
0.35
(
50
)(
90
0.33
,
t
w
≥
5
)
≥
−
use 3/8” (a minimum of 0.335” as per AREMA, 2008).
However, a minimum web slenderness of 134 is recommended for 50 ksi
steel and
t
w
≥
0.63
without longitudinal stiffeners (0.32
with
longitudinal stiffeners). Use a 5
/
8
thick web without longitudinal stiffen-
ers. The designer should confirm that a 5
/
8
thick plate is available with a
minimum width of 86
(allowing for trimming) in sufficient lengths to avoid
excessive or poorly located vertical web plate splices.
90
−
5
/
134
≥
7314
(
12
)
16
(
90
53.1
6
=
55.7 in.
2
A
f
=
5
)
−
−
(
f
b
=
16 ksi is the allowable stress for fatigue Category B with no welded
attachments, which means that, if transverse web stiffeners are required, a
bolted connection to the web will be necessary)
9814
(
12
)
0.55
(
50
)(
90
53.1
6
=
41.5 in.
2
A
f
=
5
)
−
−
(
f
b
=
27.5 ksi is the allowable bending stress).
Use 2-1
/
2
×
50.0 in.
2
)
; the designer should confirm that a 2-1
/
2
thickplateisavailableinsufficientlengthstoavoidexcessiveorpoorlylocated
transverse flange plate splices.
The girder section properties are shown in
Figure E7.1
and
Table E7.2.
20
(
A
f
=
Ay
b
A
6890.6
153.13
=
=
45.00 in.,
∗
This is a reasonable plate thickness from an economic and technical (lamellar tearing, grain size)
perspective.
