Experimental load rating of aged railway concrete sleepers
Prestressed concrete sleepers (or railroad ties) are structural members that distribute the wheel loads from the rails to the track support system. Over a period of time, the concrete sleepers age and deteriorate in addition to experiencing various types of static and dynamic loading conditions, which are attributable to train operations. Recent studies have established two main limit states for the design consideration of concrete sleepers: ultimate limit states under extreme impact and fatigue limit states under repeated probabilistic impact loads. It was noted that the prestress level has a significant role in maintaining the high endurance of the sleepers under low to moderate repeated impact loads. This experimental investigation was aimed at static and dynamic load rating of aged railway concrete sleepers after service. Fifteen sleepers were extracted from a heavy haul rail network for testing using experimental facilities at the University of Wollongong (UoW), Australia. The structural evaluation program included quasi-static bending tests, dynamic impact tests, and tests to establish the current level of prestress in the steel wires using the dynamic relaxation technique. Two of the sleepers were evaluated for the level of prestressing forces in accordance with Australian Standards. Through diagnostic tests, the results of quasi-static bending tests produced the in-track bending capacities of sleepers that can be combined with the moments and forces anticipated over the next ten years to predict performance of the sleepers on a heavy haul coal line. The dynamic tests simulating the ability of concrete sleepers to resist extreme loading events due to heavy impact loads demonstrated that the sleepers in-track are likely to be able to resist the planned increased traffic without catastrophic failure over the next decade. Final conclusions suggest that there should be a routine test program every five years to ascertain the load rating of clustered sleepers and their fastening system in the heavy haul track system.