The $51.8 million Mandurah Bridge replacement involved decommissioning the existing structure and designing and constructing a new bridge over the Mandurah Estuary, along with associated roadworks, public amenities, and infrastructure. Initiated in January 2016 and completed in March 2018, the project enhances traffic capacity and serves as a prominent landmark, improving amenities for the Mandurah community.

The previous bridge was deteriorating, and an upgrade was essential to accommodate two traffic lanes in each direction while improving pedestrian and cyclist safety with separate, wider facilities. BG&E provided structural and civil engineering design, flood modelling, and hydrology services for the bridge, which spans the Mandurah Estuary and extends into the surrounding marina precinct.

Our design incorporated a unique curved soffit cross-section that runs the entire length of the 243-metre bridge, creating a cost-effective yet visually striking structure. The bridge comprises six spans, with 42-metre internal spans and 37.6-metre end spans. The alignment follows a continuous curve in both plan and profile, facilitating incremental launching of the superstructure while considering the proximity of heritage-listed land on the eastern foreshore. The post-tensioned superstructure is supported by elegant columns on piled foundations.

A key design feature is a five-metre-wide shared path positioned at a lower level than the road, further separated by a concrete traffic barrier, ensuring pedestrians can enjoy the crossing safely. Efficiencies in design and construction techniques allowed enhancements within the fixed budget, including an additional span at the western foreshore to create open space for future development, architecturally refined balustrades and light poles, fishing platforms, feature lighting, public art, and landscaping. A section of the old bridge was rehabilitated into a fishing platform, and remnants of the original structure were incorporated into the landscaping, maintaining a visual connection to the past.

Water Engineering Scope

As part of the project, BG&E also relocated a critical water distribution main that ran over the original timber bridge. This work was completed in two key stages to ensure continued water supply during construction.

Stage 1: Relocation of Water Mains

The first stage involved relocating 200 metres of DN450 PE water main, including installing valves and a magnetic flow meter within a permanent underground concrete enclosure.

Stage 2: Seabed Crossing and Redundancy Measures

The second stage required horizontal drilling of 250 metres of twin DN630 PE water mains beneath the Mandurah Estuary seabed. The drilling incorporated complex valving and bypass arrangements to ensure redundancy in case of future pipe failure.

Industry Recognition

Recognised for its innovative design, the Mandurah Bridge was shortlisted for the 2018 IStructE Structural Award in the ‘Vehicle Bridges’ category. The judging panel praised the simple elegance of the curved concrete box girder, stating:

The judges were delighted by the simple elegance of this attractive but unusual concrete box girder design. The curvature of the plan form and soffit cross section has been well conceived and detailed to create a very pleasing solution. The engineers have turned what could have been an ordinary, mediocre and dull bridge into something delightful and have thereby created a popular new landmark for the City of Mandurah.