Suitability of 40–65 MPa Concrete for U-Trough Girders and Substructures

This report builds on two previous publicly-available studies by Monash University titled Probabilistic Design of Standardised U-Trough Bridge Girders for the Victorian Broad Gauge Network and Probabilistic Design of Standardised U-Trough Bridge Substructures for the Victorian Broad Gauge Network. Both studies analysed the suitability of the designs of U-Trough bridges using the following refined partial factors: • For U-Trough bridges on the Victorian broad gauge network, a rail traffic load factor of γq = 1.3 should be used. • The capacity reduction factor for bending should be increased to φ = 0.85. • The capacity reduction factor for shear should be increased to φ = 0.75. Both studies provided results for sections designed with 40 to 65 MPa concrete. However, the studies discussed, interpreted, and drew conclusions from the results for 65 MPa girders and 50 MPa substructure components only. This is consistent with their study scope and existing practice (namely, BTN100 (Department of Transport and Planning, Victoria State Government, 2024)). Assembling the results from the previous report, this report appraises the suitability of 50 to 65 MPa concrete for the U-Trough girders and 40 to 65 MPa concrete for the substructure components designed using the refined partial factors above. The reliability and safety implications of these designs are then discussed. The present appraisal indicates that girders designed using 50 to 65 MPa concrete and substructure components designed using 40 to 65 MPa concrete satisfy the required safety and reliability levels under the refined partial factors. The conclusions and recommendations of the previous studies are therefore confirmed to apply to these lower concrete grades.