Progressive failure of prestressed concrete sleepers under multiple high-intensity impact loads

Prestressed concrete sleepers (or railroad ties) are among the major and the most common structural components of railway track structures. Their main duty is to carry and transfer the wheel loads from the rails to the ground. In general, railway tracks suffer with the extreme loading conditions, which are attributable to the train operations with either wheel or rail abnormalities such as flat wheels, dipped rails, etc. These loads are of very high magnitude but short duration, as well as they are of low-possibility occurrence during the design life of the prestressed concrete sleepers. In spite of the most common use of the prestressed concrete sleepers in railway tracks, their impact responses and behaviours are not deeply appreciated nor taken into the design consideration. This experimental investigation was aimed at understanding the progressive dynamic behaviours of prestressed concrete sleepers in railway track structures under repeated impact loading, in order to form the state of the art of limit states design concept for prestressed concrete sleepers. A high-capacity drop weight impact testing machine was constructed at the University of Wollongong as to achieve the purpose. Series of repeated impact tests for the in-situ prestressed concrete sleepers were carried out, ranging from a low drop height to the ultimate drop height where the ultimate failure occurred. The accumulative impact damage and crack propagation are highlighted in this paper. The effects of track environment including soft and hard tracks together with the relationship between the resultant bending moment of prestressed concrete sleepers and the applied impact force as a design guideline were also presented.