d. Cooper E Series Loading.

(1) The design live load is expressed using the Cooper E series loading configuration adopted by the

AREMA about 1905. Figure 7-19 illustrates a unit E1 axle loading. Higher loadings are obtained by

multiplying each load by the same constant; wheel spacings do not change. Thus, an E60 loading would

show the largest axle loads as 60,000 lb.

Figure 7-19. Cooper Load Configuration for Bridges

(2) To allow an easy comparison of permissible in-service loading (or rating) over the life of a bridge

with the loads used in their original design, and to compare the effect of different engine and car loads for

either design or rating, the railroad industry kept the basic Cooper load configuration and used it to

represent all bridge loadings and bridge capacity ratings.

e. Equivalent Cooper Loading.

(1) In use, the loading from a train of typical (or heaviest common) cars (the design train) is converted

to the Cooper E loading that would have the same effect on the bridge.

(2) For a given design train, the equivalent Cooper loading (E value) will vary with train operating

speed, bridge span length, and bridge design.

(3) As the actual load distribution from current trains will differ from the Cooper configuration, the

equivalent Cooper loading will not be a constant for all bridge components. Figure 7-20 shows the

relationship between equivalent Cooper loading (at 60 mph) and span length for one type of steel bridge

and for the loading shown in figure 7-21. As an example, figure 7-20 indicates that, for a 60-ft span, the

train in figure 7-21 produces an effect equivalent to a Cooper E48 load with respect to floor beam

reaction, an E57 load with respect to end shear, and an E60 load with respect to bending moment.

7-23