Lessons from the performance of houses in the Canterbury earthquake sequence of 2010-11

Although overall levels of damage were similar in postand pre-1980 houses, houses built after 1980, tended tohave slightly more openings in exterior walls but, moresignificantly, were more likely to have large openings onone side compared to the other sides. It appears thatthe effect of more rigorous design and construction ofhouses for bracing after the introduction of NZS 3604 isnot apparent, because the trend towards moreasymmetrical houses and larger windows has at thesame time reduced lateral load resistance. WithoutNZS 3604 however, this trend in design is likely to haveresulted in much poorer performance of houses withmore windows and less symmetrical arrangements ofwindows.The effect of plan irregularities was noticeable, more soin cladding damage, rather than internal lining damage.This is probably because damage to internal linings at re-entrant corners will be localised to joint cracks at thecorner.Topography has a significant effect, even when the peakground acceleration is taken into account, and despite alarge part of the damage on many flat sites being due, atleast in part, to liquefaction and lateral spreading.Further work is necessary to look at foundations in moredetail, and the effect of extent and distribution ofopenings on external walls.