Bridges

The Federal and South Australian Governments jointly committed $120 million towards The Majors Road Interchange Project. Key features of the project include new ramps on Southern Expressway forming a full diamond interchange; a widened bridge over Southern Expressway; duplication of Majors Road west of the bridge; and improved pedestrian and cycling connections including a shared path on the southern side of Majors Road and a grade separated veloway under Majors Road.

This paper will focus on some of the key challenges and considerations for the design and construction of the Majors Road Bridge widening, as well as some of the main innovations introduced across the project.

The bridge was initially constructed in 1997 as a single span bridge as part of the original grade separation of Majors Road and Southern Expressway. In 2014 the bridge was extended with a western span as part of the duplication of Southern Expressway. A bridge spanning three eras of design standard demanded a pragmatic approach to establishing a rational design basis, aided by early engagement with the Department for Infrastructure and Transport.

A steel composite I-girder structural form was selected for the widening, maintaining aesthetic consistency and behavioural compatibility with the existing bridge.

To accommodate several additional lanes together with a median and shared path, an 18 m widening was required, more than doubling the existing width. The increased width and provision of a deck overlay, included to account for the reconfigured cross-sectional geometry, resulted in a significant change in the structural characteristics, requiring a comprehensive understanding of the existing components.

Interfacing with different forms of construction at the existing abutments, namely a spread footing at the top of a reinforced soil wall for the original east abutment and a piled abutment behind a soil nail wall at the west abutment, also presented challenges in design and construction.