Chris Tingle Disagrees

Structural Engineering Society president Paul Campbell says, “Buildings might be undamaged or damaged in a way that doesn’t reduce their capacity to deal with future shaking. This means they may be just as safe as they were before the earthquake.”

GNS Science of NZ says, “Fortunately, New Zealand has a state-of-the-practice and strongly enforced building code that makes our structures well designed to cope with earthquake shaking.”

Ken Morris and I disagree with both statements: The NZ building codes use a 25 year recurrence event to define the threshold of damage in a SLS earthquake, at 0.14G Peak Ground Acceleration (PGA,) as confirmed by Dr. Charles Clifton in the article posted by Stuff: http://ssl-www.stuff.co.nz/national/86598854/Wellingtons-new-medium-buildings-bore-the-brunt-of-the-huge-7-8-quake. This is a 40% lower standard than international codes that use a larger 50 year recurrence SLS seismic event in USA, China, Europe, etc.

After a building yields in Wellington on November 14 at above 0.14G PGA ground motion, the capacity to resist future moderate earthquakes is reduced – and the required repair is not just a matter of injecting epoxy into the concrete cracks because the reinforcing steel may well have yielded and require a complex compensation after testing of the structural elements.

The disturbing extent of Wellington earthquake damage in a small to minor 0.23G PGA earthquake confirms that NZ building codes are flawed.

The NZ building code shrinks earthquake loads to 60% of international standards. For a detailed engineering explanation see the book “Quake Shrink Mob,” at https://www.amazon.com/dp/B01NCJ0P21

or a summary on http://www.einnews.com/pr_news/356982395/nz-code-shrinks-earthquake-loads-to-60-international-standards-20-wellington-buildings-damaged

Now the banks, tenants, and insurance companies will have to re-think the risks. And moving the Wellington office to Palmerston North, Hastings, or Christchurch is not much better seismically – go to Dunedin or Whangarei. But the government has been centralising their office locations, not diversifying to reduce risk of national disruption.  

The good news is that the Wellington City Council has decided to require building owners to make engineering reports and damage data available for research engineers to review.

 

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