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Uncertainty in the Seismic Response of Freestanding Structures
Freestanding structures are unrestrained at their base and are dominated by rigid body motion, which includes rocking, sliding, slide-rocking, and overturning, during earthquake excitation. This class of structures includes historical unreinforced masonry civil structures, modern rocking wall and column systems, mechanical and electrical equipment, and also naturally occurring Precariously Balanced Rocks (PBRs). Given that PBRs have typically existed for tens of thousands of years, their precarious nature is indicative of the maximum ground motion that could have occurred at their site, thus providing critical information to the fields of both seismology and civil engineering due to their application in seismic hazard analysis. Freestanding structures exhibit highly nonlinear dynamic behavior and are very sensitive to geometric, material, interface, and ground motion parameters. This nonlinearity increases with added complexity of each of these parameters and significant uncertainty is associated with response predictions. Given the unique and critical role of PBRs, there is a distinct need to quantify and reduce uncertainties such that accurate predictions can be made and so that PBRs can be used reliably in seismic hazard assessments. To address the uncertainties in seismic response prediction of freestanding structures, this dissertation includes extensive numerical and experimental work on simple as well as complex structures including both PBRs and statues. The uncertainty due to numerical parameters is addressed through both case studies and large-scale parametric studies, while the uncertainty due to material, geometry, and interface conditions is addressed through large-scale shake table testing. Numerical results emphasize that increasing contact stiffness results in more stable models (i.e., higher intensity of ground motion needed for overturning). Experimental work elucidates that small variations in the interface could result in substantial changes in the stability of the specimen, as much as 200%. In addition, repeatability was evaluated experimentally, which indicates that overturning demand can vary up to nearly +/- 50%.
Saifullah, Muhammad Khalid, "Uncertainty in the Seismic Response of Freestanding Structures" (2022). ETD collection for University of Nebraska - Lincoln. AAI30000213.