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

This report applies structural reliability theory to the substructure elements used in Melbourne's Level Crossing Removal Project (LXRP) U-Trough bridges. The work builds on the previous report (https://doi.org/10.26180/28033280) on U-Trough bridges, and shows how the design requirements can be updated by exploiting the inherent safety margins provided by improved material quality and knowledge of the loading. 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 knowledge from the previous study, this work determines the probability models for reinforced concrete crossheads and columns, by considering the relevant actions. Advanced material modelling, and detailed cross-section analysis confirm that U-trough bridge substructures designed to current standards (AS5100) achieve safety levels exceeding acceptable limits. Conservative factors in both load and resistance for the actions of bending, shear, tension, and combined bending and axial force contribute to this over-performance. Additionally, the statistics of the concrete used are more favourable than assumed in the code. The findings support revisions to key design parameters, enabling safe and optimised U-trough bridge substructure design 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.