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A crowning achievement

WA’s blueprint for reducing road congestion and connecting the suburbs, METRONET, is on track on track as the Forrestfield-Airport Link tunnel comes closer to completion.

The stunning Elizabeth Quay Pedestrian Bridge is the jewel in the crown of Perth’s vibrant new waterside precinct. It is born from collaboration and a unique approach to bridge design.At the end of January 2016, Perth’s landmark waterfront development, which was designed to reconnect the CBD with the Swan River – Elizabeth Quay – opened to the public.

Visitors to the new precinct can traverse the area’s striking new pedestrian and cyclist bridge, which spans the entrance to the Elizabeth Quay inlet.

The 110-metre-long, 22-metre-high cable-stayed Elizabeth Quay Pedestrian Bridge with leaning double arches is a visually distinctive addition to the area.

The Metropolitan Redevelopment Authority, the body tasked with delivering the broader project, engaged CPB Contractors (previously known as Leighton and Broad) as the main contractor and global engineering consultancy firm Arup as the lead consultant on the bridge project.

Stewart Buxton, Project Manager and Associate at Arup’s Perth office, worked on the project and explains that the complex nature of the bridge design required a lot of collaboration.

“We brought together staff and industry experts from 10 Arup offices in four continents,” says Mr. Buxton. “We had wind specialists in London, structural analysis specialists in the Netherlands, our Global Bridge Leader in Hong Kong as well as staff from Australia and Singapore.”

The job of designing a unique bridge for the precinct provided many opportunities for Arup’s architectural and engineering team to flex their creative muscles, but it also presented many challenges.

“The brief basically came down to a couple of points. The bridge needed to be simple, iconic and traditional,” says Mr. Buxton.

While the aesthetic requirements were left to the imagination of the design team, there were many complex technical prerequisites required of the structure’s design given its proximity to the Swan River.

“The ferry needed to be able to sail underneath the bridge, but do so without disrupting accessibility for people crossing the bridge, meaning one major engineering challenge was the clearance requirements,” he says.

Being integrated with the Swan River also meant there were a number of environmental considerations that needed to be taken into account when designing the structure.

“The environmental aspects of the design were less to do with the overall aesthetics and more to do with its construction and maintenance,” explains Mr. Buxton.

For instance, the team aimed to use building materials that could be cleaned with minimal chemicals and require little maintenance.

CPB Contractors built a bund to enable the construction and installation of many of the different components of the precinct, including the three central steel-reinforced concrete piers supporting the pedestrian bridge. This helped improve safety on the installation of the bridge and lessen the environmental impact on the river.

Mr. Buxton says the Swan River Trust, the advisory body for the protection of the Swan River, approved the process, which has subsequently been used for other projects on the river.

Structural steelwork was used as a main element in the design, allowing for a slender and flexible ‘s’ shaped deck design.

The five-metre-wide deck has a depth of just 250 millimetres at its edges and is “thinner than the height of an A4 piece of paper” as Mr. Buxton puts it.

The curved form of the bridge deck met the clearance requirements for the ferry channel and is complemented by the 22-metre-high pair of leaning steel arches.

Part of Arup’s design success came from the use of Rhino and Grasshoppper scripts, which facilitated shared modelling between architects and engineers. This helped the team to optimise any efficiencies in the arches geometry relative to that of the bridge deck.

“There are other cable-stayed bridges and other double arch bridges leaning from one side out there, but I haven’t seen these concepts all together in one bridge anywhere else in the world,” asserts Mr. Buxton.

The structure’s unique design has garnered much industry praise, and the project received a number of top engineering awards. The bridge was awarded an Engineers Australia Award for Excellence – Buildings and Structures and an Australian Steel Institute, Steel Excellence Award – Engineering Projects in 2016.

Most recently it took home the prestigious Award for Pedestrian Bridges at the 2016 Structural Awards, an international industry awards event convened by the Institution of Structural Engineers.

“It’s very humbling to be recognised when there are so many amazing bridges out there,” says Mr. Buxton. “Winning the global pedestrian bridge award for 2016 is an amazing achievement, and it is one that acknowledges the work of the wider team and the effectiveness of all those involved in the overall Elizabeth Quay redevelopment.”

Arup’s design excellence resulted in a bridge that responded exceptionally to the MRA’s core brief of an iconic structure that is timeless and refined in its simplicity.

Arup also provided structural engineering and façade services for other parts of Elizabeth Quay, most notably the vehicle bridge, the inlet wall, and relocation of the Florence Hummerston Kiosk, a well-known heritage building dating back to 1928 that was moved from the nearby Esplanade and has been reopened as a family restaurant.

The aim of the broader redevelopment was to connect the city and the river and bring the CBD to the water’s edge, which, Mr. Buxton says, it has accomplished. “My view is that the precinct as a whole has achieved that, and the bridge is the crowning part of that achievement.”

*Image courtesy of Dion Photography

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