Impact damage classification of railway prestressed concrete sleepers

Commonly, railway tracks suffer with the extreme loading conditions, which are attributed 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. Up until recently, a new limit states design approach, whereas the dynamic effects are included, has been adopted in European countries, and has been proposed for the revision of Australian Standard AS1085.14. This paper presents the experimental investigations aimed at understanding the progressive collapse of prestressed concrete sleepers in railway track structures under incremental impact loading, in order to form the state of the art of the impact damage classification for prestressed concrete sleepers. 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 cumulative impact damage and crack propagation are highlighted in this paper. The effects of track environment including soft and hard tracks are also presented. By using the concept of damage accumulation, the relationships between cumulative damage of concrete sleepers and given impulse enable the predictions of residual life of the concrete sleepers under severe impact loads. It is noticed that the hard track condition rapidly exacerbates cracking in the concrete sleepers. Based on the progressive impact testing results, the damage classification of prestressed concrete sleepers has been proposed. This proposed damage index can be correlated to either increased axle load or faster train speed using an advanced dynamic analysis of railway track package