Dynamic behaviour of macro synthetic fibre reinforced concrete railway sleepers

Abstract

The conventional prestressed concrete sleepers are the most popular in the current railway market owing to their higher stiffness and dynamic stability. Yet, these sleepers are susceptible to severe cracking, creating premature failures. Recently, fibre-reinforced concrete has been proven effective in arresting cracks with added advantages of enhanced mechanical strength, ductility and associated durability. Of the two feasible and economical fibre types, steel and macro synthetic, the latter is sought in sleeper applications because of its' higher corrosion and electrical resistivity. Catering to the limited knowledge on adaptation of such fibres in sleepers, the study herein presented aimed to evaluate the applicability of macro synthetic fibre-reinforced concrete (MSFRC) sleepers in the Australian railway network. The primary cause of the premature cracking of the conventional sleepers is the impact loads created by wheel-rail irregularities. Currently, Australian standards use a default increase factor of 2.5 over the static wheel load to accommodate for such impacts in the sleeper design. Nevertheless, in-field impact forces recorded in the Australian heavy haul line are 5-7 times the static force. Accordingly, the impact performance of MSFRC sleepers compared with conventional prestressed sleepers was studied. The study was conducted in three stages. Stage 1 was focused on gauging the material behaviour of the MSFRC through a series of split Hopkinson pressure bar tests. A comprehensive experimental series was conducted in Stage 2 to evaluate the full-scale impact behaviour of the MSFRC sleeper. Stage 3 focused on numerical modelling of MSFRC and proposing design guideline changes to accommodate the PF sleepers in Australian rail tracks. Finally, the current sleeper design guidelines were analysed with respect to available analytical models and impact design principles to propose a capacity-based approach to replace the stressbased design. It is revealed that the current stress-based method results in a considerable reserve capacity under static conditions, which is utilised upon an impact in the case of PO. Contrary, the PF sleepers sustain two times the required capacity after ultimate impact load, concluding the infirmity of the current standards in MSFRC sleeper designs. Accordingly, the experimental and numerical results were used to develop material and safety factors to design for impacts under the ultimate limit state.

Date of Award	2022
Original language	English