3rd Croatian Conference on Earthquake Engineering 3CroCEE

This study examines the influence of code-prescribed methodologies for ground motion record selection on the higher-mode response of structures. Specifically, it compares two conceptually different target spectra: the Uniform Hazard Spectrum (UHS) and the Conditional Spectrum (CS). Using shear wall buildings designed following Eurocode 8 (EC8) response spectrum analysis, we analyse the non-linear structural response for different record selection approaches, including a single UHS and distinct CS with conditional periods beyond the first mode. The comparison quantifies the differences in key engineering demand parameters (EDP), such as peak-storey drift, base shear, and overturning moment.

Our results show that the UHS method generally produces a higher envelope for EDPs, while using a single CS often yields a less conservative response. Despite its tendency to overestimate demands, UHS offers simplicity, requiring fewer inputs and records than CS, which demands extensive record selection but provides limited benefits for higher-mode responses. Moreover, improper CS selection can result in a misleading reduction of certain EDPs along the building height. These findings highlight potential misinterpretations of code guidelines and the trade-offs between the precision of CS and the simplicity of UHS.