Overseen by BRANZ, an independent research and consulting company for the building industry, the assessment of randomly selected homes in Christchurch and Lyttelton identified design elements that are more likely to result in excessive damage during big shakes.
“One important finding was that pre-1980s homes received less damage—we’d expected the opposite to be true because after that period homes were built to a stricter standard in terms of bracing requirements. But those older homes tended to be more regular-shaped, and more likely to be single storey. They also had smaller windows with, consequently, larger amounts of wall available for bracing. So we found the more stringent requirements imposed on newer houses was offset by their more asymmetrical and multi-level designs.”
Geoff says another finding that defied expectations was that hillside homes suffered more damage for the same level of earthquake shaking than those on the flat did, despite the large amount of liquefaction on the level areas of Christchurch. “That’s because houses built against a hill are often split-level and irregularly shaped, with large windows at the front and virtually none at the back—these factors mean the structures are prone to twisting in the event of a quake.”
The study is believed to be the most systematic and detailed investigation that has been done on house damage from earthquakes anywhere in the world.
Geoff employed fourth-year Building Science student Baek Kim to analyse some of the data, with help from Victoria’s then-statistical consultant Dr Dalice Sim, to assist BRANZ in the statistical analysis of the large and comprehensive data set.
Read the report Structural Performance of Houses in the Canterbury Earthquake Series.