Civil Engineering Reference
In-Depth Information
and
E4.5.
From
Figure 4.12,
it is determined that
• The longitudinal force due to train braking is LF
B
=
153.0 kips per track
on the entire bridge; because of relative span lengths and bearing
arrangement, it may be equally distributed to each span as 76.5 kips.
• The longitudinal force due to train braking is LF
B
=
99.0 kips per track on
one span. However, this is an unlikely scenario considering the bridge
length, train length, and distributed nature of train brake application.
• The longitudinal force due to locomotive traction is LF
T
=
237.2 kips per
track on the entire bridge; because of relative span lengths and bearing
arrangement, it may be equally distributed to each span as 118.6 kips.
• The longitudinal force due to locomotive traction is LF
T
=
167.7 kips per
track on one span.
167.7 kips per
track and may be used for superstructure design. The longitudinal forces
are distributed through the superstructure to the bearings and substruc-
tures.Bearingcomponentandsubstructuredesignwillrequireconsideration
of these longitudinal forces. However, in this multibeam span, longitudi-
nal forces of this magnitude will result in only small axial stresses in the
longitudinal beams or girders, which may be disregarded in the design.
The longitudinal force due to locomotive traction is LF
T
=
Example 4.9
ThelongitudinaldesignforceforCooper'sE90loadingisrequiredforthedeck
truss of the 1100 ft long single track 10 span steel bridge outlined in the data
of
Table E4.3.
Each span has fixed and expansion bearings. All substructures
have spans with adjacent fixed and expansion bearings.
• The longitudinal force due to train braking is LF
B
=
(
9
/
8
)
1365
1536 kips
on the entire bridge; it is distributed to the deck truss span as
(
400
/
1100
)(
1536
)
=
=
558 kips.
• The longitudinal force due to train braking is LF
B
=
(
9
/
8
)
525
591 kips on
the deck truss span. However, this is an unlikely scenario considering the
bridge length, train length, and distributed nature of train brake appli-
cation. Therefore, other portions of the bridge should be investigated
for train braking. For example, the longitudinal force due to train brak-
ing, LF
B
=
(
9
/
8
)(
400
/
600
)(
765
)
=
=
574 kips on the deck truss span when the
train is on spans 7-10 only and
(
9
/
8
)(
400
/
980
)(
1221
)
=
561 kip when the
train is on spans 1-7 only.
TABLE E4.3
Span
Type
Length (ft)
1
Through plate girder
100
2-6
Deck plate girder
80
7
Deck truss
400
8-10
Deck plate girder
100
Total
1100
