Civil Engineering Reference
In-Depth Information
Mid-span flexure trace (25 ft span)
800
E80
286k cars
432k locos
315k cars
315k - UB
100k alt. load
700
600
500
400
300
200
100
0
Time
FIGURE 4.3a
Mid-spanbendingmomentsforCooper'sE80load,andmodernrailwayfreight
locomotives and cars, on a 25 ft simply supported bridge span.
E80
286k cars
432k locos
315k cars
315k - UB
100k alt. load
Mid-span flexural trace (60 ft span)
3000
2500
2000
1500
1000
500
0
Time
FIGURE 4.3b
Mid-spanbendingmomentsforCooper'sE80load,andmodernrailwayfreight
locomotives and cars, on a 60 ft simply supported bridge span.
The alternate live load appears to better represent the cyclical behavior of the various
trainconfigurations,particularlyonshortspans.Therefore,theallowablefatiguestress
ranges,
S
Rfat
, recommended for design in AREMA (2008) are based on equivalent
constant amplitude stress cycles from projected variable amplitude stress cycles due
to typical railroad traffic.
∗
In order to establish the appropriate number of stress cycles
∗
Alternatively, the number of equivalent constant amplitude cycles could be developed for a loaded length
traversed by a recommended fatigue design load vehicle.
