Abstract:

Ground motion intensity is usually characterized by response spectra for earthquake engineering purposes. Horizontal response spectra vary with orientation, a phenomenon known as ground motion directionality. This variation affects the built environment because most structures have mechanical properties that also depend on orientation due to their geometry and the arrangement of lateral load-resisting elements. The physical mechanisms that lead to directionality are poorly understood, and its effects on buildings are usually neglected in earthquake-resistant design and seismic risk analysis. Thus, the main objective of this dissertation is to advance the understanding of ground motion directionality with a focus on earthquake-engineering applications. Ground motion directionality is first quantified probabilistically to capture its record-to-record variability. Under certain conditions, the orientations of maximum horizontal spectral response are found to follow the polarization of S waves, which usually control response spectra at distances of engineering significance. Given these observations, an empirical model to modify ground motion models is developed to improve the estimation of response spectra at specific horizontal orientations. A simple scalar measure of ground motion intensity is then proposed for earthquake-resistant design purposes. Finally, the effects of directionality on regional seismic risk analysis, which have usually been neglected, are quantified using a variance-based sensitivity analysis.