Additional consideration is warranted for railway bridges in other aspects of design,
however. One issue to address in composite design is the magnitude of live load to be
resisted. Although not specifically addressed in the AREMA Manual for Railway
Engineering, railway companies generally require that the steel beams or girders be
proportioned to carry without contribution from the concrete deck slab, a Coopers
live load of only a slightly reduced magnitude than that of the entire structure. For
example, a bridge with a composite design load of E-80 is often required to have the
steel section alone provide support for an E-60 or higher, and maybe as much as E-80
as well, depending upon the railroad and the type of structure considered. This ensures
that if the concrete deck is damaged during a derailment, the steel section will be
sufficient to carry rail traffic, even if the concrete must be torn out and an open deck
installed.
If the steel alone is sized for the design load, the cost savings through efficient use of
materials is somewhat less for railway structures than it is for highway and building
structures that make full use of the composite section to resist live load and impact