Design spectra and amplification factors for Eurocode 8

Abstract

Eurocode 8-Part 1 accounts for site effects through the suggestion of appropriate elastic design spectra and amplification factors based on different soil classes. The influence of local site conditions is reflected in Eurocode 8 (EC8) spectra with the shape of the PGA-normalized response spectra and the so-called “soil factor” S, which represents ground motion amplification with respect to outcrop conditions. In the present work we use a global strong-motion database, which was compiled in the framework of SHARE FP7 Collaborative Project of the European Union, to evaluate the present EC8 normalized spectra and associated amplification factors for different soil conditions. Uncertainties in the estimation of improved soil amplification factors are captured using a logic-tree approach, which allows the use of alternative models and methods in an effective way. The influence of PGA range of the strong motion records included in the dataset on spectral shape and soil factors is also examined. The results indicate that for all datasets examined, EC8 normalized elastic acceleration spectra match the empirical data to a satisfactory extent, while estimated soil factors for classes C and D are significantly higher than the ones proposed in Eurocode 8. The proposed design spectra and the new amplification factors are validated with a smaller dataset, which includes records only from stations with well documented soil profiles regarding the dynamic soil properties.