In an article in the 2 September 2015 NBR the NZSEE Chair, Quincy Ma was reported to have made the following statements on ‘earthquake-prone’ building standards.
New Zealand’s proposed definition of what constitutes an earthquake-prone building is only about half the equivalent standards set in the US, Japan and Europe, says the New Zealand Society of Earthquake Engineers (NZSEE).
NZSEE chairman Quincy Ma says converting the standard set in the US works out at between 67-75% (new building standard).
The Building (Earthquake-prone Buildings) Amendment Bill proposes setting the standard at any building below a 34% NBS score being classified as earthquake prone.
“Other countries have dealt with the same problem,” Mr Ma told NBR.
“It’s not a New Zealand-specific problem. In the US, the equivalent threshold they’ve set is 75% and in Europe and Japan it’s also double our minimum threshold,” he says.
“We’re actually aiming pretty low.”
The story would have left the reader with the impression that New Zealand’s seismic strengthening standards are much lower than those in other advanced countries. That is simply not true.
When MBIE did a survey of international standards to support their 2012 review of New Zealand’s seismic strengthening policies, they reported that the US Government did not impose any minimum standard. Of the four US states in seismically active zones they reported on, only one, California requires some general minimum mandatory strengthening (imposed at the local level), and they relate to unreinforced masonry buildings. Stronger standards are applied to school buildings and hospitals.
For Japan, MBIE reported that there are no mandatory strengthening requirements. MBIE did not report on Europe but there is a legal European standard. ‘Eurocode 8 Design of structures for earthquake resistance’, which sets out a technical framework for evaluating and improving structures. The code states, with respect to strengthening standards, just the following: “(3)P The appropriate levels of protection are achieved by selecting, for each of the Limit States, a return period for the seismic action.” Selecting the strengthening standard is a matter for national governments. To our knowledge none have set a national mandatory minimum, let alone a 75% NBS requirement.
For the US, what Mr. Ma seems to be refering to is what amounts to a recommendation by the American Society of Civil Engineers, in a voluminous technical document (ASCE 41-13), that if a building owner chooses to upgrade a building they should reach a 75%NBS standard. There is no risk, or cost benefit, analysis behind the ASCE 75% standard and it has little or no effect on the American public’s understanding of buildings’ sesimic risk. We are not aware of any public statement by the Society that all buildings below the 75%NBS level are ‘earthquake-prone’ or that they are ‘high risk’.
The NZSEE has publically stated that all buildings rated below 34%NBS are ‘high risk’, when there is clear evidence that in the great majority of cases life safety risk is extremely low.
That some engineering bodies might recommend high seismic strengthening standards for existing buildings, without a serious analysis of costs and benefits, should not come as a surprise. They don’t bear the costs and their members stand to gain financially.