Risk-targeted hazard spectra for seismic design in New Zealand

Nick Horspool, Ken Elwood, Matt Gerstenberger and Anne Hulsey

The promotion of risk-targeted hazard spectra as the basis of seismic design internationally has increased over the past decade. Risk-targeted hazard spectra are derived through convolution of hazard curves with representative fragility functions and provide a means to target a uniform risk across a region. Using risk targets also allows performance objectives of building codes that are consistent with other life risks and enables societal input into the expected performance of structures. Current design procedures using a uniform-hazard spectra are unable to provide equal risk across the country due to variation in hazard curves in different locations and uncertainty in structural response. In this paper a framework is proposed, which can be used with the new National Seismic Hazard Model, to produce risk-targeted hazard spectra to replace the existing uniform-hazard spectra for seismic design. This study also extends the risk-targeted hazard framework through full quantification of epistemic uncertainty in seismic hazard and includes multiple risk targets for individual and societal risk at the building and city scales. The paper describes a framework which can be used to adjust current seismic design force levels in New Zealand standards to target uniform seismic risk for buildings considering both the performance of individual buildings as well as the performance of cities.