The dependence of conditional spectra on the choice of target periods

Document Type : Article

Authors

1 Department of Civil Engineering, Faculty of Engineering, Arak University, Arak, 38156 - 8 - 8349, Iran

2 Department of Civil Engineering, Faculty of Engineering, Arak University, Arak, 38156 - 8 - 8349, Iran.

Abstract

The dependence of Conditional Mean Spectrum (CMS) and the corresponding standard deviation on different target period values has been investigated in this paper by means of two types of target spectra, i.e. based on Epsilon and Eta indicators. The structural collapse capacities, as well as the mean annual frequency (MAF) of exceeding a limit state, are taken into consideration. The results show that the dependence of Eta-based CMS (ECMS) on the choice of target period is insensitive to the target period in the case of MAF calculation. However, this dependence is meaningfully less in the case of ECMS when compared to CMS in Intensity based ground motion selection. The Sum of the Squared Error (SSE) is utilized to compare different CMS cases. SSE is less in the case of shorter return periods, e.g. 75 years, in comparison with longer return periods, e.g. 2475 years. This dependence is also a function of choosing attenuation relationships. Therefore, four Next Generation Attenuation (NGA) relationships have been employed in this study. In general, ECMS has shown less dependence in all cases when compared with the conventional CMS.

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