Structural Safety of Railway Prestressed Concrete Sleepers

This paper carries out the assessment of reliability indices or structural safety of railway prestressed concrete sleepers designed in accordance with Australian Standard AS1085.19. The current design approach of the prestressed concrete sleeper relies on the permissible stresses over cross-sectional area. Loading condition acting on railway sleepers is considered from axle burden and dynamic amplification factor. On the basis of Australian design of railway prestressed concrete sleepers, only service limit states are considered; however, the design challenge is to provide adequate resistance of certain cross sections to both positive and negative bending moments. In this paper, the service limit states functions are formulated taking into account the permissible compressive and tensile stresses at both initial and final stages, and applied positive and negative bending moments at railseat and middle sections. Random variables in the reliability analysis include railway track design parameters, axle load, material and geometrical properties, prestressing force and its losses, and model uncertainties regarded to the structural resistance and load effects. Statistical properties of related parameters are adopted from previous studies. Two analysis methods are used: firstorder moment reliability method (FORM) and second-order moment reliability method (SORM). Sensitivity analyses of the reliability indices for flexural capacity according to the requirements of the limit states functions are also investigated in order to evaluate the major influences of dynamic load factors, strengths of materials, track parameters and model uncertainties.