Both superstructure and substructure are
mutually vital in ensuring the safety and comfort of
passengers and a satisfactory quality of ride for
passenger and freight trains. Note that in Australia,
UK, and Europe, the common term for the structural
element that distributes axle loads from rails to the
substructure is ‘railway sleeper’, while ‘railroad tie’
is the usual term used in the US and Canada. The
main duties of sleepers are to: (1) transfer and
distribute loads from the rail foot to underlying
ballast bed; (2) hold the rails at the proper gauge
through the rail fastening system; (3) maintain rail
inclination; and (4) restrain longitudinal, lateral and
vertical movements of the rails. Remennikov and
Kaewunruen [2] reviewed the typical load conditions
on railway track structures as well as common
design procedures for ballasted railway tracks. It has
been found that the design method for railway
sleepers is based on permissible fibre stresses [3].
The permissible stress design approach makes use of
an empirical function taking into account the static
wheel load (P0 ) with a dynamic impact factor ( )
to account for dynamic vehicle/track interactions: