Engineering Work (eg road, bridge, sawmill, dam)
The first Newmarket Viaduct, a vital link near the start of Auckland’s Southern Motorway, was the largest prestressed concrete bridge in New Zealand and an innovative design at the time of its construction between 1962 and 1966. This first bridge was replaced through a four stage process between 2008 and 2012. The replacement viaduct’s design addressed seismic considerations and environment issues such as minimising the noise created by the traffic on the bridge.
Related topic: Auckland Motorways
The first viaduct over Newmarket
The original Newmarket Viaduct was a massive structure towering over 45 metres (m) above the old Borough of Newmarket. It was described by the New Zealand Herald in June 2007 as “one of the most distinctive engineering features of New Zealand.” It was 689 m long and 27 m wide, and designed by the Ministry of Works for the National Roads Board at a cost of $2.26 million.
Initially a steel girder structure was considered, but the cost of imported steel content and maintenance led to a concrete structure being proposed. A prestressed concrete box girder structure was favoured because it had to cross a busy urban area, major roadways and a dual track railway. The twin parallel structures that formed the viaduct had a longitudinal ‘S’ curvature and super elevation (cross slope to allow for high speeds).
It was a very complex structure for its time. There were 16 spans varying in length between 33.5 m and 50 m. It was designed to be constructed from each supporting column as balanced cantilever, progressively moving out from each side. As each new 3.2 m long section was added it was tied back to previously erected units by prestressing cables. This process continued until finally the cantilevering spans from adjacent piers were closed at mid span. Further prestressing cables were then threaded into the units to tie the whole structure together.
Precise calculations of the loads in each prestressing cable were necessary. The design included dynamic analysis for the loads to withstand an earthquake that might occur only once in 500 years.
Of particular interest in the engineering world was a problem which occurred early in its life due to a temperature differential between the deck which had a black bitumen wear coat, and the bottom of the beams which were light coloured concrete. This caused some unacceptable cracking that had not previously been known as a design problem. The solution was to put in additional prestressed cables and place a light coloured stone chip on the black bitumen road surface.
The new Newmarket Viaduct
In 2007, the 1960s viaduct carried an average of 163,500 vehicles per day making it one of the busiest sections of Auckland’s motorway system, and more lanes were needed.
Rather than upgrade the original viaduct the decision was made to replace it. The NGA Newmarket Alliance was formed to complete the project. The Alliance consisted of the New Zealand Transport Agency, Beca, Fulton Hogan, Leighton Contractors, VSL NZ, URS, Tonkin and Taylor and Boffa Miskel.
The replacement viaduct was designed to withstand an earthquake that might occur only once in 2500 years. Construction was in four stages. The first, completed in 2010, saw four new south-bound lanes on the northern side of the original viaduct. Following this Stage Two involved dismantling of the original southbound lanes. Stage Three was to build three new northbound lanes in place of the old viaduct’s southbound lanes, and the final phase was the demolition of the original northbound section of the viaduct.
A fourth lane can be added to the northbound side at a later date but because of other capacity restrictions around Spaghetti Junction (the junction of the motorway systems at Newton) it was decided not to add the extra lane as part of this project. (See attached article below for further information)
(This text was adapted with permission from Mike Lancaster and John La Roche, ‘Newmarket Viaduct,’ in John La Roche (ed.), Evolving Auckland: The city’s engineering heritage, Christchurch, Wily Publications, 2011, pp.168-70)
State Highway 1, Newmarket, Auckland
This is part of Auckland's motorway and is open to traffic at all times. The structure can be viewed from below at Broadway Newmarket or from above from Mt Hobson Domain.
Nature of Engineering
Transport (Road, sea, air, incl vehicles)
(Click image to enlarge )
(Click image to enlarge )
Lat: -36.873364 Long: 174.776039