2. DEFICIENCY OF CURRENT DESIGN METHOD
Codes of practice including Australian Standard
[3] and AREMA [6] prescribe a primitive design
methodology for PC sleepers. The design process
relies on the permissible or allowable stress of
materials. A load factor is used to increase the static
axle load ‘as if’ to incorporate dynamic effects. The
design load is then termed ‘combined quasi-static
and dynamic load’, which has a specified lower limit
as much as 2.5 times static wheel load [3]. In
reality, impact forces due to wheel/rail interactions
may subject the sleepers to dynamic loads that are
much larger than the code-specified design forces. A
recent finding shows that there is a high chance that
the impact forces could be up to four to six times of
wheel load [2]. The current design method prohibits
any structural cracks in a concrete sleeper. As a
result, any cracked concrete sleepers due to
irregular forces must be removed without any