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It’s a long way from Rotherham, UK, to the North of New Zealand, but an engineering link between the two has helped the city of Whangarei build a unique bridge to help ease its traffic congestion.
The “Te Matau a Pohe”, or for those that don’t speak Maori, “The Fish Hook of Pohe” Bridge, is a single leaf counterweighted rolling bascule bridge featuring two 25m fish hook-shaped beams poking up into the sky.
There are very few rolling bascule bridges in the world. There are certainly no other rolling bascule bridges with massive fish hooks.
The design of the mechanical elements and operating equipment for the bridge was provided by Rotherham-based firm Eadon Consulting. Micheal Thorogood, director and senior design engineer of Eadon says: “The curved tracks are fairly unique and there are none that even vaguely look like this. It’s also an unusual way of making a bridge move.
“The client wanted a design that was really striking. The architect, Martin Knight of Knight Architects, researched the local Maori history and we sat down and developed the fish hook shape, which has particular resonance in the local area of Poey Island.”
Eadon Consulting provides mechanical design and consultancy around the world for bespoke projects that require lifting and movement, mostly in bridges. In essence they provide the moving parts of moving bridges.
The Te Matau a Pohe bridge comprises of a 265m long viaduct with a 25m lifting span to allow yachts to pass and more than 1.5km of approach road. The bridge has a clear height of 7.5m above high water at the central span meaning that most vessels are able to pass underneath without the bridge being raised.
Bascule bridges are common, but the use of tracks to move the span of the bridge is unusual. Thorogood says: “The main benefit design wise is that you don’t have to lift it through as steep an angle because it moves back as well, generating the clearance required with less movement.
“There are two large hydraulic cylinders, each weighs 8 tonnes and has a 320mm diameter bore, 280mm diameter rod and stroke of 8380mm, which are located in a pier below the curved track. The cylinders extend upwards and push the bridge up. As it goes up, it also rolls back.”
Counterweights in each hook of the mast, reduce the amount of energy required to raise the bridge.
The bridge, which took around 14 months to build, takes 120 seconds to lift or lower and will have to move around 6 times a day. A major design challenge was to ensure the equipment is reliable as possible when operational. “We alway aim to keep the design as simple as possible,” Thorogood adds.
Eadon were first approached about the NZ$29 million project in 2010 by consultancy Peters and Cheung and assist the main contractors, McConnell Dowell and Transfield Services. The project has required several trips from South Yorkshire to Whangarei.
Thorogood says: “When a project is closer you go to the site frequently throughout the build process. But when it is on the other side of the world you go once and there is nothing, car parks and a playing field. Then when you return its suddenly grown up out of the ground – it’s very satisfying to see.”
