Recommendations for the shape of the design response spectrum in the New Zealand seismic loadings technical specification
DOI:
https://doi.org/10.5459/bnzsee.1692Abstract
The recent release of the 2022 national seismic hazard model has highlighted significant changes in the quantified seismic hazard for much of New Zealand that has prompted the development of draft changes to the NZS 1170.5 seismic design provisions. One proposed change is to the shape of the design spectrum, which was previously provided by a spectral shape factor, Ch(T), that is a function of site class only. However, research has shown that spectral shape is strongly affected by several additional factors including earthquake magnitude and shaking intensity. Moreover, the use of fixed spectral shapes that vary only by site class results in significant variability between the functional form of the elastic design response spectrum, C(T), and the direct results from the national seismic hazard model. International loading standards typically include a dependency on intensity and site class in the spectral shape equations and these form the basis for the approach recommended here. The functional form of the design response spectrum is also updated to better represent spectral displacement demands on longer period structures. The proposed new spectral shape equations are compared to the 2022 national seismic hazard model output and the equations used in the previous New Zealand loading standard. Results show that the proposed approach provides a significantly better approximation of the national seismic hazard model results than the current spectral shape across a range of periods, site classes, annual probabilities of exceedance, and locations.
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