Bridges

This paper presents an overview of design methodology for a new bridge over Bulleen Rd, a vital link connecting traffic to the southern portal of the North-East Link in Victoria.

The 5-span bridge superstructure features pre-tensioned 'Super-T' girders, which are made composite with an in-situ topping slab. Super-T girders were selected over steel box girders in consideration of economical design for skewed bridge, low maintenance and aesthetics. Super-T beams were made continuous at pier supports for spans up to 42 m to utilise the standard beam size adopted in Victoria.
The Super-T girders have been integrated with the portal frame crossheads at two piers to satisfy the available clearance over roads and to enhance the structural robustness.

Post-tensioning is used in the portal crossheads to improve efficiency. The crossheads are made integral with the piers to eliminate the need for bearings, minimising the need for long-term maintenance. Additionally, the girders are post-tensioned across the pier crossheads to effectively counter hogging effects at piers.

Thorough detailing was implemented for the reinforcement, with due consideration given to the constructability of portal frames to ensure that the design intent is adequately reflected in the final structure. 3D reinforcement modelling was carried out to enable the designer to identify potential clashes between reinforcement and post-tensioning steel as well as reinforcement from octagonal shape piers.

Structural modelling was carried out using Midas software to account for construction staging and the effects of pre-tensioning and post-tensioning on both superstructure and substructure, crucial for integral bridges.