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Walking on Water


Posted 1 September 2002

Pedestrians using Brisbane’s scenic RiverWalk when it opens next March will be strolling across 150 tonnes of stainless steel reinforcing, embedded in 287 concrete pontoons linked to form an 875 metre long walkway from the CBD along the river to New Farm Park.

Although the 5.4 metre wide walkway will feel like a single solid structure, it is actually made up of a series of 13.5 tonne concrete blocks, half of their bulk floating below the water level.

Stainless steel balustrades will preserve open views across to Southbank and back to the CBD while ensuring public safety. These combine subtly curved 600 grit electropolished handrails which give a wave effect and 320 grit polished end-posts and staunchions with an art deco feel.

An overall Ra of 0.5 mm was specified not just for the aesthetics but to provide maximum corrosion resistance for grade 316 stainless in a marine environment and to minimise tea-staining.

Stainless steel wire strung horizontally between the posts will provide a strong safety barrier while fading to invisibility from just a few metres away. Customised tamper-proof electropolished turnbuckles developed by ASSDA member Ronstan International Pty Ltd and the posts inward-curving profile will ensure that RiverWalk meets stringent safety standards.

Night-time illumination will come from Y-shaped light poles placed at 30 metre intervals and spot lighting will highlight decorative elements such as mosaics.

Each section of the balustrade runs the length of an individual pontoon. Sections are joined with a tapered stainless steel sleeve to absorb the small amount of movement from wave action, expected be around 20mm.

AN INNOVATIVE BASE FOR A SCENIC WALKWAY
Assembly of the concrete pontoons involves advanced construction methods modelled on the latest overseas developments and a similar, but much smaller, floating walkway which was successfully built on Melbourne’s Yarra River.

To obtain the necessary strength and buoyancy, high strength 50mPa concrete is reinforced with grade 316 stainless steel. The 10mm and 12mm diameter rebar is fashioned into a cage around a polystyrene core which takes up 85% of the pontoon’s volume. The corrosion-resistant properties of stainless steel reinforcing enable the pontoon to be built with narrower walls than would be the case with conventional reinforcing creating savings in the amount of concrete required.

With stainless steel reinforcing an impressive lifespan is assured, making it the best long-term option in building assets where longevity is desired. The design life of this structure is 100 years.

Funded by the Brisbane City Council (BCC) and developed by a BCC and consultant design team led by project architect Jan Jensen, RiverWalk is one of the city’s most ambitious and forward looking projects. It uses techniques which are new to Australia and draws on the expertise of many construction professionals including stainless steel materials experts, suppliers and fabricators.

ASSDA’s role in the project included detailed specification advice on all aspects of the stainless steel work and provision of detailed answers to technical issues in design and prototyping.

Construction contractor Smithbridge Australia Pty Ltd heads the project team which also includes a number of ASSDA members, including Pryde Fabrication, Arminox Australia Pty Ltd and Stoddart Metal Fabricators.

This article featured in Australian Stainless magazine - Issue 22, September 2002.

Lissel Pilcher