Simulated shocks as big as, and even bigger than, the February 22, 2011 Christchurch earthquake have been performed on a new building prototype in the University of Canterbury’s (UC) structural engineering laboratory, with the aim of making post-quake structures safer.
Professor Stefano Pampanin from UC’s Department of Civil and Natural Resources Engineering has been overseeing more than 100 of the simulations on a modern two-storey low-damage concrete building to determine the best designs and technology in the wake of earthquakes.
The concrete structure is based on other new low-damage design buildings including the Endoscopy building of Southern Cross Hospital on the edge of the central business district (CBD), designed by Structex Metro, and uses the same technology implemented in new post-tensioned timber buildings.
The four-storey Endoscopy building was designed as an Importance Level 3 structure that required piled foundations because of the site’s soft soils. The structure has both frames and coupled walls, which resist lateral forces in the two orthogonal directions. The unbonded post-tensioned walls are coupled by using U-shaped flexural plate dissipaters.
Gary Haverland, Director of Structex Metro Ltd, identified four key advantages:
- There are no plastic hinges, so there is little structural damage. The reduction in potential downtime was extremely important for a healthcare client.
- The building structure is self-centering, resulting in little residual lean after an earthquake.
- Lower design seismic actions compared to a conventional reinforced concrete frame or wall building. This means less risk of damage to contents, lower wall reinforcement and foundation forces. This was important because of the expensive medical equipment in the building.
- Less in situ concrete on site, meaning shorter construction time. Construction also used conventional building components.
The initial cost of a conventional building was estimated to be $7.2 million. The Endoscopy building was built for $6.9 million but other problems encountered, including upgrading the boiler, running additional services and striking a well in the excavation for the lift pit, brought it back up to the initial budget of $7.2 million.
The structural elements cost $2.17 million, equivalent to around 30 per cent of the total building cost, which in Haverland’s view is comparable to other conventional buildings.
UC is hoping to take its experimental research into integrated low-damage technology to the next stage, successfully making it one of the major tasks of the research project SAFER technology, which is funded by the Natural Hazard Platform.
The research team has already secured parts of the Grand Chancellor Hotel and the PricewaterhouseCoopers (PwC) buildings in Christchurch’s CBD for future testing, to see how they performed in the earthquakes, how many aftershocks they would be able to sustain and what repair techniques could be implemented.
“This new generation of buildings will be expected to withstand a series of strong earthquakes to protect the lives of occupants, and buildings should be easily re-occupied with minimal repairs and cost almost immediately after any event,’’ said Pampanin, who is also the current President of the New Zealand Society for Earthquake Engineering
“The target is very ambitious. We want to develop a fully earthquake-proof building. We are not there yet and it might take few more decades, but we are steadily moving towards this goal.’’