Conventional design of structures relies on incorporating a certain level of inelastic deformation into select components to provide seismic energy dissipation, while ensuring the foundation remains relatively stationary. However, this inelasticity comes at the cost of severe damage to the structure, which often is no longer suitable to occupancy after a seismic event. In contrast with conventional structures, structures with rocking foundations shift the ductility demands away from the structure itself, and onto the underlying soil, which may result in less damage and greater stability. The purpose of this study is to explore the behavior and performance of a simple bridge/structure, idealized as a single degree of freedom oscillator on a rocking shallow foundation, when subjected to bidirectional seismic ground motion. Accordingly, this study explores how independent factors, such as structural, soil, and seismic characteristics affect the performance of the system during a seismic event. From this, the engineering demand parameters, such as residual displacement and instability, are related to the system characteristics through a series of nondimensional relationships and earthquake parameters. These parameters are then discussed, in order to determine what physical and dynamic characteristics of the system are captured within these parameters, and how they can be used to better understand the behavior of rocking structures.
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