Civil Engineering Reference
In-Depth Information
8000 lb per
bin ft
8
'
5
'
5
'
5
'
9
'
5
'
6
'
5
'
8
'
8
'
5
'
5
'
5
'
9
'
5
'
6
'
5
'
5
'
5
'
6
'
5
'
FIGURE 4.1
Cooper's E80 and alternate live load-axle loads. (From American Railway
Engineering and Maintenance-of-Way Association (AREMA), 2009,
Manual for Railway
Engineering
, Chapter 15, Lanham, MD. With permission.)
286,000 lb are common on North American railroads and some railroad lines carry
315,000 lb cars.
This variability in railroad equipment weight and geometry requires a representa-
tive live load model for design that provides a safe and reliable estimate of railroad
operating equipment characteristics within the design life of the bridge.
4.3.1 S
TATIC
F
REIGHT
T
RAIN
L
IVE
L
OAD
The railway bridge design live load recommended in AREMA (2008) is Cooper's
E80 load. This design load is based on two Consolidation-type steam locomotives
with trailing cars represented by a uniformly distributed load (Cooper, 1894). The
maximum locomotive axle load is 80,000 lb and freight equipment is represented by
a uniform load of 8000 lb per ft of track. An alternate live load, consisting of four
100,000 lb axles, is also recommended in order to represent the stress range effects
of adjacent heavy rail cars on short spans. These design live loads are shown in
This design load appears antiquated, particularly with respect to the use of steam
locomotive geometry. However, it is a good representation of the load effects of
modern freight traffic as illustrated in
Figure 4.2.
Figure 4.2 is plotted from a moving
load analysis (see Chapter 5) of shear and flexure
∗
on simple spans for continuous
and uniform strings of various heavy freight equipment vehicles.
†
The unbalanced
loads (indicated as UB with 25% of the total railcar load shifted to adjacent axle sets)
for the car weight and configurations investigated in Figure 4.2 exceed the Cooper's
∗
It should be noted that the Equivalent Cooper's E loads shown in Figure 4.2 are for mid-span flex-
ure. Effects may be even more severe at or near span quarter points for typical railway freight loads
(Dick, 2006).
†
In this case, six-axle 432,000 lb locomotives, and four-axle 315,000 lb freight cars with balanced and
unbalanced (UB) loads.
