Bridging the gap: looking back at the construction of Melbourne’s Webb Dock Bridge

Melbourne’s Webb Dock Bridge is an innovative and practical pedestrian bridge combining art, infrastructure and a unique approach to design and construction.As part of the city of Melbourne’s push to revitalise its Docklands district in the early 2000s, public art came to the fore in facilitating the growth of this emerging residential and civil precinct.

In 2000, a design competition was held with the aim of turning the then-disused Webb Dock Rail Bridge into a combination of art and infrastructure – a new and attractive pedestrian and cycle bridge that crossed the Yarra River into Docklands. The successful design, which referenced a traditional Koorie eel fishing trap with a curvaceous basket placed at the end of the linear concrete rail deck, came from a collaboration between architects Denton Corker Marshal (DCM) and local artist Robert Owen. Arup was engaged to provide structural and engineering services as well as lighting design and commenced work on the project in 2001.

Peter Bowtell, Principal at Arup, says the bridge design and the overall project required some unique approaches to structural engineering. The bridge forms a sinuous link from the end of the old concrete box girder to the river bank, with a steel box girder forming a central spine, supporting large cantilevers and the woven hoop frame.

“The design was an innovative response to the site constraints. The first challenge for the structural team was to accommodate the length of bridge required to meet the grades needed to ensure access for people of all abilities.”

The transition ramp between the deck and the existing bridge level was much longer than the space available. Head height and river clearance was also a constraint on the project so as to avoid restriction to the river’s flows when flooding occurs.

Mr. Bowtell says the existing structure provided some key opportunities in overcoming some of these engineering challenges. He says the project utilised the foundation system of the demolished rail bridge, which was a sustainable and cost effective solution. The location of the existing piers and the extreme level change determined the architectural response, and ultimately its original form.

To install the structure, the team worked in conjunction with fabricator Geelong Fabrication to fully construct the bridge on barges in a nearby dock. It was then floated into position as a single fabricated piece.

“This method required tight tolerance on the bridge construction, and Arup worked closely with the construction team to ensure fit up on arrival up river.

“Installation was matched to the Yarra’s natural tide cycle, floating in on high tide and then letting the lowering of the tide lower the bridge and allow it to settle onto its permanent bearings.” This meant installation required tight precision and timing against very real and immovable time constraints.

Arup worked closely with DCM to develop a unique lighting scheme so the structure could be lit in silhouette at night, redefining the nighttime view in a totally different way. The lighting components had to meet the local council’s strict requirements for light spill, meaning that the bridge’s illumination is not only dramatic, but functional.

The final structure was completed in 2003 and is now an integral part of the Capital City Trail pedestrian and cycle route.

Since its completion, the bridge has become a standout and stunning addition to the Docklands precinct.

“The design blends user safety with dramatic form and the lighting approach sets new standards in nighttime safety for all users,” says Neil Bourne, Director at Denton Corker Marshall. “It is an architectural outcome that is an exemplar in art, architecture, structure and constructability. The bridge has become not only a symbol of the Dockland’s precinct, but of Melbourne itself.”

*Image courtesy of Shannon McGrath

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