Infrastructure Engineering - Theses
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ItemSite-Specific Ground Motions for Dynamic Analyses in Regions of Lower Seismicity( 2022)Site-specific dynamic analyses of structures have many advantages over traditional code spectrum procedures in regions of lower seismicity. The prime reason is that the site-specific response spectra and accelerograms are more realistic representations of earthquake actions for a structure located on a unique construction site. Developing site-specific ground motions requires a comprehensive understanding of regional seismic hazard analyses, soil condition analyses and site response analyses. Guidelines or facilities for performing site-specific dynamic analyses in accordance with the design code are unavailable to engineering practitioners in Australia. The primary objective of this thesis is to develop a computationally effective method to generate response spectra and accelerograms for site-specific dynamic analysis in intraplate regions of lower seismicity, with a focus on the Southeastern Australia (SEA) region. Based on the proposed method, this thesis provides suites of ground motions in compliance with the Australian standard for direct engineering applications. The conditional mean spectrum (CMS) methodology was first reviewed and its challenges for application in intraplate regions were overcome by employing a diversity of ground motion prediction expressions (GMPEs) and the uniform seismicity model. Three different schemes using a weighted averaging of candidate GMPEs were adopted, and a comparison of predictions demonstrated only minor differences confirming the robustness of the modelling. The constructed CMS were targeted for sourcing ground motions to define seismic hazard at the bedrock level. The bedrock motions were amplified through soil column models to simulate site amplification effects. Subsoil information retrieved from multiple borehole records from the same site was sampled to construct soil column models to achieve conservative estimations of soil amplification ratio at the fundamental period of vibration of the structure to account for resonance. The sampling process involves closed-form expressions for determining the shear strain profile in a soil column considering degradation in the shear modulus of the soil in seismic conditions. The applications of resultant site-specific response spectra and accelerograms, following a ground motion selection scheme proposed by the author, were demonstrated with nonlinear time history analysis for structural design and multiple stripe analysis for risk assessment. This thesis is concluded with three outcomes: (1) a ground motion database for site-specific seismic design based on twenty sites that typify subsoil profiles in SEA, (2) an online program at https://quakeadvice.org/ for generating ground motions with user-defined borehole information, and (3) suites of ground motions for risk assessment of structures following the multiple stripe analysis method.