the dependence of conditional spectra on the choice of target periods

The dependence of conditional mean spectrum (cms) and the corresponding standard deviation on different target period values were 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 were taken into consideration. the results showed that the dependence of eta-based cms (ecms) on the choice of target period was insensitive to the target period in the case of maf calculation. however, this dependence was meaningfully low in the case of ecms when compared to cms in intensity-based ground motion selection. the sum of the squared error (sse) was utilized to compare different cms cases. sse was less in shorter return periods, e.g. 75 years, than in longer return periods, e.g. 2475 years. this dependence is also a function of choosing attenuation relationships. therefore, four next generation attenuation (nga) relationships were employed in this study. in general, ecms showed less dependence in all cases than the conventional cms did.