If we want cost-effective earthquake resistant technology with which to rebuild Christchurch with, we need not look far according to the New Zealand Society for Earthquake Engineering (NZSEE).
The NZSEE has spotted a solution by way of base isolation and Precast Seismic Structural Systems (PRESSS) technology. Base isolation, originally developed at Industrial Research at Gracefield in Wellington, involves the superstructure of the building being separated from the ground by rubber bearings with lead inserts to provide damping of the building’s sway motion. Meanwhile PRESSS technology uses un-bonded post-tensioning to allow controlled rocking of a structure’s joints. This softens the blow of an earthquake, springing the building back to upright without significant structural damage even after a major seismic event.
NZSEE executive officer Win Clark says both techniques should be considered for all new buildings of up to nine storeys, with other technologies also available for more high-rise construction.
“Not only are these technologies effective in mitigating the damage caused by earthquakes, they are also quick to build and cost effective. These should be used, where appropriate, for the construction of all new buildings in New Zealand.
“It is absolutely essential that those responsible for decisions on the rebuilding of Christchurch, central and local politicians and building developers, investors, designers, contractors and the general public countrywide understand how effective these technologies are and that they are already being used in New Zealand,” said Clark.
To date, the techniques have been used successfully in a number of New Zealand buildings. Clark said Christchurch Women’s Hospital, which is base isolated, and the Southern Cross Endoscopy building, built using PRESSS technology, have both performed well in the recent earthquakes. Base isolation has also been used for Te Papa and Wellington Hospital.
A team led by Professor Andy Buchanan and Associate Professor Stefano Pampanin of the University of Canterbury adapted the PRESSS technology for use with Laminated Veneer Lumber (LVL) using New Zealand grown Pinus Radiata. The Nelson-Marlborough Institute of Technology (NMIT) and the newly-completed Carterton Events Centre in the Wairarapa have been built using this PRESSS timber technology.
“The beauty of PRESSS technology is that it can be used for both precast concrete and timber frame buildings that are quick to build and cost the same, or slightly less, than conventional construction,” said Clark.
“Base isolation is slightly more expensive – around four percent – to build but life cycle costs are significantly less than conventional construction.”
Meanwhile Auckland University is busying itself with research for buildings ten storeys or more.