The Christchurch post-earthquake reconstruction – Year 14 update

Reconstruction of buildings in the Christchurch central business district following the 2011 earthquake has been a massive undertaking that is not yet completed. Interviews have been conducted with representatives of the consulting engineering companies who designed 55 of these buildings from 2017 until 2025 to determine: (i) the building construction materials and structural system types used, and (ii) the drivers for the selection of these systems. The information obtained is compared with a 2017 survey, by the authors, with the same design companies for buildings constructed from 2012 to 2017, as part of the Christchurch rebuild after the 2010–2011 Canterbury earthquakes. It is found that 47 % and 45 % of the buildings constructed had steel and concrete lateral force resisting systems, respectively, with the remainder using timber. In terms of floor space areas, the steel buildings were typically larger and the ratios were 70 % and 24 %, respectively. The most popular structural steel seismic systems were MRFs and BRBFs with 29 % and 20 % of the floor areas, respectively. Gravity systems, when needed, were generally steel. Although slightly different, these numbers are similar in magnitude to those reported in the prior study. However, comparing the factors driving choice of structure systems reported in the previous study, many of the engineers interviewed commented that, as the Canterbury earthquakes became further away in time, fewer of their clients requested resilient designs that would help achieve functionality (e.g., maintain business continuity) following future earthquakes, requesting instead lowest-cost designs. Nonetheless, it is expected that much of the newer construction will provide improvements in seismic performance given that many buildings were designed for significantly higher strength and lower drift than permitted in the standards.