Piazza takes shape

Lateral thinking and innovative engineering solutions can have many spin-offs, particularly in terms of design benefits and cost savings. It was this attitude that helped save Auckland's Aotea Square ensuring it will be a jewel in the crown of Auckland's CBD for years to come, says Connal Townsend, chief executive of Property Council New Zealand.

"Property Council is always keen to promote significant developments that contribute to the city's infrastructure and create a wonderful asset for the people of Auckland. This project, which involved the work of several member companies of Property Council, including Holmes Consulting Group and Hawkins Construction, not only solved the problem of the faulty roof to the carpark under the square, but turned a disaster into a virtue."

Townsend says the extensive upgrade, which saw a new roof built above the original, and the entire podium raised, is also a recognition of the historical value of the site.

"Aotea Square was where the first settlers set up their tents. It was also from here that New Zealand soldiers marched down to the ships that would take them to fight battles for the Somme and Passchendaele. Protecting and improving on this public space is a great achievement, especially considering the time and budget constraints, and the fact that the carpark had to remain operational throughout the works programme."

For the structural engineering firm for the project, there were several key challenges. Holmes Consulting director Chris Mackenzie says the company had earlier participated in an Auckland City Council review of the precinct, when the council decided to redevelop the square as part of an overall civic upgrade.

"We had already reviewed a number of options to repair leaks and elements of the existing car park roof, which had been built 30 years earlier," he says. "Now we also needed to take into account that the redeveloped Aotea Square needed to support a much greater range of community activities and events. It needed to be able to take landscaping, significant traffic loads and temporary stands, for example."

Mackenzie says Holmes Consulting looked at how it might replace or strengthen the roof.

"Removing and replacing the entire roof would have meant closing the car park for the duration of the work, which would have caused major disruption and expense. It would also have involved an expensive construction, with the car park walls needing to be propped. Consequently, we decided the best option was to build a new deck about a metre above the existing roof."

Mackenzie says the existing floor slabs and beams were the limiting factor. Providing a new concrete slab with secondary steel beams, while maintaining the existing roof had several benefits. The car park could remain open, the work could be completed in stages to minimise disruption for businesses and the public, and the existing roof acted as a safety screen and a working platform for the construction of the new deck.

"We worked with the inherent strength of the existing primary structure and augmented this with extensions to the main beams. However, designing a system to connect the new portion of the work to the old beams was a challenge."

Project engineer Stuart Oliver says Holmes Consulting also needed to address the potential problem of concrete shrinkage.

"The roof deck is approximately 100m x 100m, and a slab of that scale is always subject to significant shrinkage," he says. "This causes cracks, which in turn risk damage to the waterproofing. To minimise the likelihood of such damage, we provided a low-shrinkage, special concrete mix specification, and specifically designed crack mitigation reinforcing in the roof slab.

"Deterioration of the existing neoprene bearings that support the primary roof beams meant that these elements had to be replaced, which was another challenge met by the main contractor, Hawkins Construction."

Oliver says the client wanted the car park to meet the equivalent of modern codes, so earthquake strengthening was required. Large steel braces were added and the existing concrete perimeter walls in the car park were thickened.

"The result is a greatly upgraded civic amenity that is of immense benefit to the public, and a credit to the council that had the foresight to move ahead with the upgrade," says Mackenzie.

For details, contact Holmes Consulting Group, PO Box 90745, Victoria Street West, Auckland 1142, phone (09) 965 4789. Or visit the website: www.holmesgroup.com.

Or contact Property Council New Zealand, phone (09) 373 3086. Email: enquiries@propertynz.co.nz. Website: www.propertynz.co.nz.

Story by: Trendsideas