Civil Engineering Reference
In-Depth Information
25
'
3
'
20
'
FIGURE E4.9
0.0022 slug/ft
3
The solidity ratio
f
=
r
=
1.00 (plate girder)
s/h
0.67
C
DT
=
=
1.15
(C
D
)
=
1.15
(
2.0
)
=
2.3 (
Figure 4.20b)
1
/
2
(
0.0022
)(
110
)
2
F
D
=
57.4 kips,notinclu-
ding the gust factor. If we assume a typical gust factor of 2.0, the design
wind force
2.3
[
]
A
RD
=[
30.6
(
125
)(
15
)/
1000
]=
=
2.0
(
57.4
)
=
114.8 kips.
Example 4.13
A 200 ft steel through truss railway span is shown in
Figure E4.9.
The solidity
ratio,
f
, for this truss is 0.25. Determine the design wind force for a wind speed
of 75 mph.
0.80
C
DT
=
=
s/h
1.70
(C
D
)
=
1.70
(
1.7
)
=
2.9 (from Figure 4.20b)
1
/
2
(
0.0022
)(
110
)
2
F
D
=
48.3 kips,not
including gust factor. If we assume a typical gust factor of 2.0, the design
wind force
2.9
[
]
A
RD
=[
38.6
(
200
)(
25
)(
0.25
)/
1000
]=
=
2.0
(
48.3
)
=
96.5 kips.
The AREMA (2008) design recommendations for wind load on a loaded steel
railway bridge superstructure assume that the maximum wind velocity at which trains
cansafelyoperate
∗
willproduceawindpressureof30 psf.TheAREMA(2008)design
recommendations for wind load on an unloaded steel railway bridge superstructure
assume a maximum wind velocity corresponding to a typical hurricane event with
a wind pressure of 50 psf (see Examples 4.14 and 4.15). In order to account for the
effects of paired or multiple girders, these wind pressures are to be applied to a surface
50% greater than the projected surface area of a girder span. For truss spans the area
is taken as the projected surface area of the windward truss plus the projected surface
area of the leeward truss not shielded by the floor system.
The AREMA (2008) design recommendations also indicate that the load on the
moving train is to be taken as 300 lb/ft at a distance 8 ft above the top of the rails.
∗
To avoid the overturning of empty cars.
