C5 Evidence Report Phase 1
Last updated: 28 September 2021
On 1 July 2017, the Building (Earthquake-prone Buildings) Amendment Act came into effect, which set out a new earthquake-prone building management system that targets buildings and parts of buildings that pose risks to public safety or other property in a moderate earthquake event.
Under the Building (Earthquake-prone Buildings) Amendment Act 2016 and Earthquake Prone Building (EPB) methodology, engineers who carry out seismic assessments must use the Engineering Assessment Guidelines (Red Book), which specifies how potentially earthquake-prone buildings are to be identified and assessed. C5 is a section of the Red Book about assessing concrete buildings.
In November 2018, a revised version of Section C5 'Concrete Buildings' (Yellow Chapter) was released as a technical proposal to revise the concrete section of the Red Book. The proposed revision reflects what engineers learned from the Statistics House investigation following the Kaikōura earthquake. It also included updates to other technical provisions relating to existing concrete buildings.
Phase One of the C5 Evidence Project assessed six buildings, comparing the %NBS result using the Red Book and the Yellow Chapter. The investigation found that, on average, there was little substantive difference in Percentage of New Building Standards (%NBS) ratings. However, the %NBS rating for some individual buildings were different depending on which version of C5 was used. In addition, the Red Book and Yellow Chapter identified different seismic vulnerabilities in the studied buildings.