Evaluating and Communicating Seismic Risk for Low Rating Buildings

Abstract

There are many challenges for owners and occupiers of buildings where seismic assessments produce ratings of less than 34%NBS, including addressing questions about whether they should continue to occupy the building. MBIE’s 2022 Seismic Risk Guidance provides a clear point of reference with statements such as in most cases, vacating a building should be a last resort means of mitigating life safety risk for buildings occupants. Nevertheless, some owners and occupiers with buildings ratings less than 34%NBS still wish to have a specific evaluation of the seismic risk to inform their decision on continuing to occupy the building. This will often be sought in the context of their responsibilities under the Health and Safety at Work Act. Seismic risk evaluations of this nature go beyond the scope of typical engineering assessments, including consideration of how a structure might perform at different levels of earthquake shaking. This paper outlines the approaches that have been applied to a range of buildings based on the information and framework in the MBIE seismic risk guidance and the 2021 BRANZ decision framework for council-owned buildings, and how the outcomes are communicated to users of the buildings. These approaches have been developed and applied for diverse organisations such as government agencies with national portfolios, councils with prominent public buildings and community-based groups such as church parishes. The reactions of both the organisations and the users of the buildings to the seismic risk evaluations are outlined, along with observations on the key risk communication success factors.