Simulation‐Informed Site‐Specific Target Spectra Incorporating Directionality and Variability

ABSTRACT Conventional seismic design approaches typically select ground motions based on source characteristics, magnitude, site conditions, and distances, and subsequently adjust them through linear scaling or spectral matching to approach median (RotD50) or maximum direction spectra (RotD100). Indeed, these methods neglect component‐specific spectral shapes and do not explicitly target ground‐motion record‐to‐record variability, leading to biased structural response estimates, especially at sites where ground‐motion directionality and variability may be significant. This study proposes a novel methodology that leverages suites of simulated ground motions from physics‐based wave propagation models to derive component‐specific spectra that explicitly target amplitude and variability for direct application to ASCE/SEI 7‐compliant maximum considered earthquake spectra and conditional mean spectra. The method is demonstrated using twenty‐five realizations of an M w 7 strike‐slip earthquake on the Hayward Fault to provide a first estimate of the aleatory variability associated with the considered earthquake and a three‐dimensional reinforced concrete building. Results (i) show that explicitly accounting for ground‐motion directionality and variability results in median and higher‐percentile structural responses that differ substantially from those obtained using directionality‐agnostic methods, exhibiting both underestimation and overestimation, and (ii) highlight the critical role of correctly assessing ground‐motion site‐specific variability when using conditional mean spectra. The target spectra derived with the proposed methodology can be used to select both simulated and recorded motions. Collectively, these findings demonstrate limitations in traditional target spectral definitions and emphasize the need to explicitly incorporate the notion of directionality and record‐to‐record variability into ground‐motion selection procedures. The proposed method provides the framework to advance the reliability of seismic structural assessments by incorporating simulation‐informed site‐specific seismic hazard characteristics.