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Contractor (April 2011) Bridging the Gap with Concrete

04 Apr 2011

Rob Gaimster
Cement & Concrete Association of New Zealand (CCANZ)

If, after having evaluated all options for the Additional Waitemata Harbour Crossing project, the decision makers determine that a bridge is more beneficial to the Auckland region than a tunnel, it only takes the briefest of glances at New Zealand’s proud bridge building history and current global bridge building trends to conclude that concrete’s wide range of benefits render it ideally suited as the primary construction material.

The Additional Waitemata Harbour Crossing project is part of New Zealand Transport Agency’s (NZTA) long term planning to meet Auckland’s future transport needs, and has become a component of the National Infrastructure Plan. The benefits of the project are envisaged as a reduction in congestion and improved access across the harbour, the provision of an additional transport route to the existing Auckland Harbour Bridge, improved opportunities for all modes of transport, and a more effective transport network that supports greater economic growth.

An evaluation study is currently underway to identify whether a bridge or tunnels running between Wynyard Quarter west of the Auckland CBD and Esmonde Road on the North Shore is the best form for an additional crossing for the Waitemata Harbour.

Building on work undertaken as part of the 2008 Waitemata Harbour Crossing study, the current evaluation is a more detailed engineering investigation of bridge and tunnel options, including capital and operational costs, connectivity, constructability and functionality. Once complete the NZTA believes it will inform the development of a business case and enable decision-making about the form and timing of the additional crossing.

Although the 2008 Waitemata Harbour Crossing study identified the preferred option as a combination of the existing bridge and at least two new tunnels, the case for the construction of a new bridge is gaining many advocates, chief amongst which is the ANZAC Centenary Bridge Group. 

The Group believe that a new 3.3km long bridge would offer the best option for Auckland, in economic, traffic management and environmental terms.  This would be a two-tiered deck bridge, with general and heavy traffic lanes, space for rail lanes, as well as pedestrian and cycle access.

The Group believe that the new bridge would be less costly to construct than a tunnel solution, and would offer scope for greater movement of vehicles and people. The new bridge would also offer wider benefits as a result of tourism, the freeing up of land resources, and significant savings in travel time and distance.

Key to the Group’s proposal is that the bridge should be under construction in time for the commemorations of the 100th anniversary of the 1915 Gallipoli landings, and that it become known as the ANZAC Centenary Bridge. This, they believe, would be a statement of national identity that would reach beyond these shores to help secure a positive image in international markets.

The bridge option is certainly compelling, and it is hard to argue against it both as a general metaphor for positive human action, or a potentially unifying symbol of remembrance and a progressive national character. 

In fact, with geography as steep and rugged as New Zealand’s, bridges have played a significant role in our country’s development.  Across urban and rural settings, or rail and road applications, New Zealand boasts some truly magnificent bridges.  Grafton Bridge in central Auckland, the Fairfield Bridge in Hamilton, the Opawa Bridge in Blenheim and the Kopuawhara Viaduct are classic examples of bridges from the early 20th century, while the north and south Rangitikei Viaducts, the new Hapuawhenua Viaduct, and the Otira Viaduct are notable contemporary structures from the late 20th century.

It is not by accident that all these bridges are built using reinforced concrete.  The possibilities offered by concrete in terms of shape, form and finish are extremely wide.  These advantages, combined with strength, durability in a range of environments (including marine), resistance to fire and chemical attack, seismic performance and low maintenance requirements have seen reinforced concrete become the material of choice for New Zealand’s bridges.  The benefits of precast concrete construction, such as enhanced quality control, decorative formwork, along with speed and simplicity of erection must also be considered.

The prevalence of concrete bridges was noted in a CCANZ report from 2006, which illustrated that of the country’s 10,500 road bridges 80% included reinforced concrete superstructure elements, while amongst the older railway bridges 32% had concrete spans and 61% reinforced concrete piers.  The use of reinforced concrete remains apparent in the recently completed bridges that cross the Tauranga and Manukau harbours, as well as the under construction Kopu Bridge over the Waihou River.

This is not just a trend restricted to New Zealand.  Throughout Europe and North America magnificent bridges with significant concrete elements have been erected over recent years.  In Greece the four precast concrete caissons of the Rion-Antiron Bridge help it span the deep and fast moving waters of the Gulf of Corinth, the seven reinforced concrete piers of the Millau Viaduct in France are of such tall and slender elegance that they are referred to as “cloud piercers”, while adjacent to the Hoover Dam the twin concrete arch Colorado River Bridge has just been completed to stunning effect.

So convincing are the advantages of concrete bridge construction, and so inspirational are the existing concrete bridges from around New Zealand and across the globe, that should the Additional Waitemata Harbour Crossing project principals decide that a bridge is the best way forward then the crucial decision regarding materials should prove relatively straightforward.

Article appeared in Contractor magazine.