Bridges

The $761 million Monash Freeway Upgrade Stage 2 involves the addition of 36 kilometres of new lanes to one of Melbourneís busiest freeways. As part of the project, eight of the existing bridges required widening. While each of the bridges had its own complexity, the median widening of the existing twin bridges over Forster Road was the most complex.

The existing paired bridges were constructed in 1973 as three span continuous post-tensioned voided slabs supported on inclined piers. The new widening needed to maintain the same appearance of the existing that were constructed in-situ on falsework with no traffic under during construction. Given the roadway underneath the bridge is now a busy corridor, replicating this original cast-in-situ construction method to achieve the same appearance was not an option. In addition, the requirements to match the limited structural depth of the existing structure and designing for full SM1600 loading, not adversely impacting the articulation of the existing structure, and minimising impacts to traffic on Forster Road presented significant challenges.

To overcome these challenges, the proposed widening consisted of a multi-cellular post tensioned deck superstructure, formed using a series of precast inverted T-beams stitched together transversely at the bottom flange, an in-situ deck on top, and made continuous longitudinally using in-situ diaphragms at the inclined precast piers through post tensioning. Maximising the use of precast elements that eliminated the need to construct massive falsework over Forster Road minimised impacts on road users and achieved the same appearance as existing.

This paper will discuss the design and construction challenges encountered by the project team including the development of the articulation of the new structure, segmental erection methodology, constraints for stitching of the new and existing decks, and the barrier upgrade. Major bridgeworks have been successfully completed, with construction expected to be completed by 2022.