Bridges

A load rating was undertaken as part of the asset owners regular periodic load rating on a 139 m total length, 12-span bridge carrying a single ballasted rail track on curved horizontal and vertical alignment originally constructed in 1996. The bridge superstructure comprised simply supported prestressed concrete through-girders of up to 17 m length with precast concrete planks spanning between main girders. The bridge is a rail-over-rail flyover which also crosses a road necessitating a variety of substructure arrangements including, cantilever, portal, tee and blade-wall piers supported on piles. AS5100.2 allows determination of braking and traction forces through either the empirical or rational method. The empirical method utilises formulas to allow a simplified loading of the bridge, whereas the rational method relies on rail vehicle specifications such as vehicle lengths, loading and traction and braking characteristics to be incorporated into a Rail-Structure Interaction (RSI) analysis considering the bridge and approach embankments. For this bridge's assessment, braking and traction forces applied significant longitudinal loading to the substructure, with the determination of these loads being critical for an accurate rating of the structure. The Rational Method of determination of these forces, determined through an RSI analysis, was utilised in lieu of the Empirical Method to refine the loading of the bridge. This paper discusses the methodology, rolling stock considered by various rail authorities, benefits achieved for the project and compares the Rational and Empirical Methods in AS5100 to outline the potential benefits of an RSI analysis for rail bridge design and analysis.