Shaken not stirred May 12, 2010
Wellington's new Supreme Court joins the list of Wellingtons' buildings that will survive a major earthquake thanks to base isolation using lead-rubber bearings.
Invented in New Zealand in the 1970s to help reduce the force of an earthquake going into a building, the technology is particularly useful with heritage buildings as it avoids the introduction of visible structural strengthening elements that would otherwise compromise a building's original character.
For the Supreme Court project, that means the historic Old High Court Building will be restored to its original state with the confidence that the investment will be able to be enjoyed by many more generations of New Zealanders.
Since October last year, the 1881 building has been meticulously stripped back, piece by piece, to its basic bones - a brick structure.
Segment by segment it is being cut off at ground level using a saw specially designed to cut through the masonry while causing as few vibrations as possible in the fragile building. Once cut off the ground, new foundations and base isolators will be introduced.
The Building Intelligence Group project director Ian Macaskill explains that the building's fragility is due not just to its age, but its construction.
"The brittle nature of the masonry construction means it cannot flex in the way other buildings can, making it even more of a candidate for base isolation."
When lead-rubber bearings are used, Ian explains, the lead core absorbs the energy from the earthquake, while the rubber exterior cushions the building. The bearings under the Old High Court Building will each have steel plates top and bottom that help keep their form, and will be able to move up to 250mm in each direction.
"Ensuring the building survives a shake with 'minimal stirring' requires some clever design considerations in the building architecture and services, and such experience was a key consideration when we were selecting the design team for this project," Ian says.
The design team are: Warren and Mahoney; Holmes Consulting Group; Holmes Fire and Safety; Norman, Disney and Young; and PHC. Mainzeal are the main contactor, and the project is due for completion late 2009.