Civil Engineering Reference
In-Depth Information
Track
©
0.20
W
0.20
W
5.0
'
6.0
'
FIGURE E4.2
Track
©
0.20
W
0.20
W
5.0
'
8.0
'
10.67
'
FIGURE E4.3
Example 4.2
A double track open deck steel multibeam railway bridge is similar to that
shown in
Figure E4.1.
Determine the rocking effect, RE, component of the
AREMA impact load if the beams are spaced at 2 ft-8 in centers.
The resisting force couple (Figure E4.3) is
R
R
=
F
R
(8.00). Since
R
A
=
R
R
,
F
R
=
0.125
(W)
and the rocking effect, RE, expressed as a percentage of
vertical live load,
W
,isRE
=[
F
R
(
100
)/W
]=
12.5%.
4.3.2.1.2 Vertical Effects on Simply Supported Spans
Superstructure vibration is induced by the moving load (locomotives and cars) sus-
pension systems as the loads traverse a railway bridge with surface irregularities.
When the length of the bridge span is large relative to the locomotive and car axle
spacing, dynamic locomotive and car loads may be approximated by a concentrated
and continuous moving load, respectively. When the span length is not large relative
to the locomotive and car axle spacing, dynamic train loads may be approximated by
concentrated moving loads.
