Walkable (and driveable) art
A work of art in an arty city – that’s Nelson’s new downtown bridge. HUGH DE LACY takes a look.
A bridge with three names built by a contractor with two Garrys – or one Garry and a Gary, to be precise – has become art-loving Nelson’s latest icon.
When the Nelson City Council opened its new $1.5 million bridge in the centre of town in July this year, it added an extra name to the two by which the old bridge it replaced was known. The street on which it was built became known as Bridge Street, so the bridge was called the Bridge Street Bridge, but it was formally named the Normanby bridge after
Sir George Augustus Constantine Phipps, the second Marquess of Normanby (1819-1890) who was Governor-General of New Zealand from 1875 to 1879.
However, on completion this year of the new bridge, which carries two lanes each of traffic, bicycles and pedestrians over the Maitai River, the city council gave it the name Aratuna, meaning pathway of eels. The third name reflects the Maitai’s role as a key pre-European food source, and the river still yields a plentiful supply of eels.
As for the two Garrys (or Garys), they’re Garry Adcock and Gary Donaldson, principals of local construction firm Adcock and Donaldson, the project’s main contractor. Old school-mates from Nelson’s Nayland College, the two spent 12 years working together in the civil engineering and installation fields in Australia before Adcock returned to Nelson to set up Garry Adcock Contracting with his wife Jenny in 1987.
Donaldson and wife Lynley returned with their family two years later, and teamed up with the Adcocks to form the Stoke-based company that has since blossomed into a major local contractor employing 65 staff and 150 items of plant.
Last year the shareholding at Adcock and Donaldson was expanded when the Tonks and Nell families bought in. Graeme Tonks is a civil engineer, and he acted as project manager on the Normanby Street Bridge, while Ken Nell is from a finance background and runs the business side of the company’s operations.
The company is organised into four production teams, each one specialising in a different aspect of civil construction. They’re backed up by a trucking team comprising a dozen big trucks and a range of tipping trailers and a transporter. The company also operates a quarry near Stoke supplying a variety of aggregates and recycling topsoil.
Replacement of the old bridge, built before 1921, was necessitated by its severe deterioration, to the degree that a 3.5 tonne weight limit and a 30kph speed limit had been imposed on it.
On the face of it, replacing the Normanby Street Bridge wasn’t that complex a task, but what made it tricky was the plethora of underground services that criss-crossed the area.
The new bridge itself is just 18.2 metres long and, at 12.2 metres wide, carries two traffic lanes, two cycle lanes and two footpaths. The abutments have two columns while the two piers have a column each. The deck units are single hollow core with the exception of the outside ones which are u-beams, designed to allow power and telecommunications cables to be lifted back from the temporary service bridge required by the construction programme, with the in situ concrete footpath then poured over the top.
“The first major issue was to find an old existing 450mm water-main that crossed over the Maitai River on an angle that passed under the existing bridge, and would need precise location as it would do the same for the new bridge, and one of the piers would be in close proximity,” Graeme Tonks says.
He had to pore over old city council records and carry out a potholing exercise to locate the pipe, only to find it encased in concrete that had not been indicated on the plans. Fortunately the casing wasn’t thick enough to impinge on the new pier.
Canterbury engineering company Texco Drilling did the exploratory drilling on the new abutments and piers, requiring the old bridge to be shut for two weeks and traffic diverted – both then and later after the old bridge was demolished – to an alternative bridge on Nile Street.
“The second major issue was the requirement to maintain the existing power, Telecom and water-main services attached to the existing bridge,” Tonks says.
Richmond-based local subcontractor Thelin Construction met this challenge by building a temporary services bridge upstream, allowing Australian multinational telecommunications services company Powertech to install new power cables
with cut-ins to the old cables at either end, something that was possible only on days of low power demand.
Local landscape and amenity company Nelmac came up with a way to re-valve the 150mm water-main to avoid having to install a temporary one across the services bridge.
“The most significant problem was having to relocate two Telecom fibre-optic cables, plus one by 800 pair and one by 600 pair of copper cables. The cables were cut out of their ducts and shifted over one at a time,” Tonks says. “One of the copper cables was located on the inside of one of the old bridge trusses that required the truss to be cut away from the old piers and jacked up to allow the cable to be pulled away.”
Adcock and Donaldson demolished the old bridge, pealing the concrete decking off in two halves using an excavator. This allowed the river to be diverted to prevent any material entering the flow, and exposing the steel beams that made up the trusses.
Thereafter the construction of the new bridge was straightforward once the abutments and pier foundations had been sunk to about 18 metres.
Conscious of the city’s image as the original home of the Wearable Arts Awards, not to mention a host of other artistic and academic achievements, the city’s newly-elected Mayor, Kerry Marshall, demanded to know “Where is the art?” on the bridge. By then construction was already under way, but the council responded by specifying a design by local artists Brian Flintoff and Grant Palliser that has been incorporated into the pre-cast abutment walls.
Thelin Construction achieved the eel and triangular patterns by using special plastic moulds, and the artwork was complemented by similarly themed designs on the bridge’s handrails.
Mayor Marshall was also keen for the local iwi’s history to be commemorated by the structure, which led to the bridge getting its third name, Aratuna.
Defending the extra name against local critics, the mayor reckoned there was plenty of precedent for bridges having more than one name and, in the case of the Bridge Street/Normanby Street/Aratuna Bridge, “it celebrates the bi-cultural nature of New Zealand,” he said.
Contractor Vol.32 No.9 October 2008
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