New Zealand Society for Earthquake Engineering on earthquake prone buildings

Issue 53 – September 2013

The New Zealand Society for Earthquake Engineering's (NZSEE's) Executive Officer Win Clark says its long-standing position, and one it would urge commercial building owners to adopt, is that those who elect to strengthen their commercial properties, particularly those of high occupancy, should aim for at least 67%. 'This will significantly reduce the potential risk to life and make our communities more resilient. Resilience of buildings, the capacity to withstand higher earthquake effects without collapse, has become a key focus in the wake of learnings from Canterbury.

'One aspect in particular that we want to make absolutely clear is that the earthquake provisions of the Building Code (that cites the standards) is not about protecting property, it is about life safety, and the percentage refers to the likelihood of people being able to evacuate a building safely following an earthquake. While a building strengthened to 34% of the standard might be legal that does not mean that it will not be significantly damaged in a moderate earthquake or that it will not constitute a significant hazard during more severe shaking.'

Clark says a building graded to between 20 and 33% of the New Building Standard (NBS) is 10 to 25 times more likely to suffer damage in a moderate earthquake than one built to 100%. A building graded between 33 and 67% is five to ten times more likely to suffer damage than one built to 100%. Between 67 and 80% that reduces to two to five times. Between 80 and 100% to one to two times.

'Engineers do appreciate the significant cost issues involved for landlords. But in many cases strengthening to 67% does not cost double the cost of strengthening to 34% and will be recouped through the long-term financial benefits of having a far more resilient property. Just meeting the trigger level will not provide a buffer for the future.'

Clark says that while owners now have 15 years to carry out the work, the NZSEE urges those who are in a position to go ahead earlier, to have their buildings, particularly those with high occupancy, assessed and strengthened as soon as possible.

→ Read the full media release

→ Read the Government's policy decisions on managing earthquake-prone buildings

Summarised from a NZSEE media release, 14 August 2013.

Published in engineering.