Timber, tin and masonry: Early lessons in seismic risk mitigation in Whanganui, New Zealand

Abstract

New Zealand’s Canterbury earthquake sequence (Mw 7.1 Darfield earthquake and Mw 6.3 Christchurch earthquake), and the subsequent Canterbury Earthquakes Royal Commission (2012) revealed that the collapsed historic unreinforced masonry (URM) building stock was responsible for a high proportion of deaths that occurred in public places. Heritage conservation through seismic strengthening is explored as a topic of ongoing research that addresses urban safety concerns, whilst privileging the predominant historic URM building fabric. The Whanganui town centre features the designated historic ‘Old Town Conservation’ precinct and ‘Regeneration’ precinct showcasing an eclectic blend of architectural styles. However, the town is currently confronted by the threat of moderate to large earthquakes due to being located within a region of moderately high seismic hazard. A study was undertaken to explore Whanganui’s early seismic risk mitigation during the 1930s, in an effort to trace the development of a local retrofit practice and early attitudes to heritage conservation for URM buildings. The following overall questions are posed: to what extent does Whanganui’s history of seismic risk mitigation technologies embody both architectural heritage conservation considerations and structural requirements? More specifically, how have Whanganui’s historic architect-engineers contributed to the development of retrofit practice for the local URM streetscapes? Lastly, what do the retrofits reveal about early collaborations between architects, engineers and building owners? Archival research and onsite visual survey informed a thematic analysis focusing on a range of technological solutions implemented for three selected buildings. The study forms part of an ongoing research project where a fundamental objective is to help ensure successful conservation outcomes for one of New Zealand’s earthquake-prone albeit historic urban ensembles.