Bridges

This paper outlines the design, methodology, and numerical model for assessing track-bridge interaction for the underbridge crossing over the future M12 as part of Sydney Metro’s Western Sydney Airport Surface and Civil Alignment Works (SCAW) project. The ballastless twin track system has continuous welded rails supported by rail fixings, which are directly fixed to an independent track slab supported on the bridge deck. The bridge is 188 m long and comprised of multi-spans of precast prestressed Super-T girders. The deck slab is continuous between three expansion joints, one at each abutment and one over a pier.

The Super-T girders are 1815 mm deep, extend over seven spans of varying lengths and simply supported on laminated elastomeric bearings. Link slabs are cast over the piers, forming a continuous deck surface over the piers, except for Pier 3 where an expansion joint occurs. This design adopts a typical road bridge form to suit a rail underbridge application. The phenomenon of track-bridge interaction is well documented in international guidance documents and standards with the objective of limiting stresses induced into the tracks. Interaction between track and bridge is the consequence of the behaviour of one on the other as they are interlinked.

The M12 underbridge design accounts for differential temperatures, track and bridge stiffness, rail fixing characteristics, longitudinal shear stiffness of bridge bearings, superstructure articulation, substructure stiffness, and concrete shrinkage and creep. The numerical model incorporates the track form and rail vehicle loading extending 100 m beyond each abutment. The design ensures stress and displacement limits prevent rail buckling or failure, ensuring safe and comfortable travel.

This paper offers insights into design rationale and numerical analysis for controlling track stresses induced by bridge interaction. It serves as a comprehensive case study for assessing track-bridge interaction and determining the most suitable bridge articulation.