Selecting, scaling, and orienting three components of ground motions for intensity-based assessments at far-field sites

This article develops a methodology for selecting, scaling, and orienting three orthogonal components of ground motion (GM) when conducting intensity-based assessments of structures. Target spectra for selecting multicomponent GMs are critically examined and strategies for selecting hazard-consistent GMs are investigated. The Conditional Mean Spectrum–Uniform Hazard Spectrum (CMS-UHS) Composite Spectrum is proposed as an alternative to several Conditional Mean Spectra for selecting multicomponent GMs when conducting intensity-based assessments of complex three-dimensional (3D) structures. To ensure hazard consistency, multicomponent GMs should be selected using (a) the target spectrum for the vertical component of GM, (b) a wide range of vibration periods, and (c) scale factors that are constrained. With constrained scale factors, all three components of a GM can be reasonably scaled either by the same scale factor or by different scale factors.