Probabilistic Design of Standardised U-Trough Bridge Girders for the Victorian Broad Gauge Network

This report applies structural reliability theory to precast prestressed U-trough beams used in Melbourne's Level Crossing Removal Project (LXRP). By exploiting inherent safety margins, the work develops a bespoke design framework for U-trough bridges on the Victorian broad gauge network. This approach balances life safety, economic failure costs, and the societal costs of over-conservatism, ensuring designs remain safe while addressing practical challenges and potential cost savings. Using concrete data and train schedules specific to the context, the study updates strength and load probability distributions. Advanced material modelling, detailed cross-section analysis, and long-run train simulations confirm that U-trough bridges designed to current standards (AS5100) achieve safety levels exceeding acceptable limits. Conservative factors in rail traffic loads, bending, and shear resistance contribute to this over-performance. Additionally, the statistics of the concrete used are more favourable than assumed in the code, and actual rail traffic loads align well with design models. The findings support revisions to key design parameters, enabling safe and optimised U-trough spans up to 40 meters. This work focuses on Ultimate Limit State design and has undergone rigorous peer review. The methodologies, analyses, and conclusions represent Monash University’s independent scientific work conducted in close collaboration with LXRP teams.