Comparison between NZS 1170.5 seismic design spectra and hysteresis-damped spectra

Abstract

This study aims to provide a comparison and identify the key distinctions between the New Zealand Standard – Earthquake Actions (NZS 1170.5: 2004) seismic design spectra and the hysteresis-damped seismic demand spectra specified by either the New Zealand Society for Earthquake Engineering (NZSEE) “Assessment and Improvement of the Structural Performance of Buildings in Earthquakes” (AISPBE) Guidelines, or the “Displacement-Based Seismic Design of Structures” (DBSDS) textbook by Priestley et al. (2007). The damping provided by the draft document, “The Seismic Assessment of Existing Buildings” (TSAEB), was also briefly discussed. The seismic design spectrum was calculated for various levels of ductility using all three methods and compared against each other. This was performed for structural elastic periods from 0.1 to 4.5 seconds. For a given set of requirements based on the NZS 1170.5 parameters, a representative acceleration-displacement hysteresis loop has been generated. The equivalent viscous damping was then calculated based on the area under this hysteresis using the recommendations of either the AISPBE or through the damping equations based on the DBSDS. The final damped spectra were then compared with each other and against the NZS 1170.5 design spectrum. Results indicate good correlation between the NZS 1170.5 design spectra and the damped design spectra at low levels of ductility but show significant disparities at higher levels of ductility.