Centrifuge Testing of Systems with Combined Structural Hinging and Rocking Foundations

The rocking foundation mechanism has proven to be an effective means to dissipate seismic energy, and thereby reduce the seismic demand on the superstructure. Its use has been broadly applied in both the building and bridge domains. Nonetheless, a common concern remains regarding its global behavior in a building system. Specifically designers must understand how the rocking foundation dynamically interacts with other inelastic components, particularly those designed into the structural components. To advance understanding, this paper presents and compares the seismic response of two extreme structural configurations, namely, a structural hinging-dominated (SHD) system and a foundation rocking-dominated (FRD) system. These two structural systems were recently tested in a 9-m-radius centrifuge-based shake table at UC Davis. Results indicate that the SHD system is more prone to localize the seismic energy at the structural fuse element, with relatively little energy transferred to the rocking footing. As a result, the structural fuses have a fairly large demand, which in turn cause significant transient and residual deformation in the superstructure. The FRD system, on the other hand, with broad moment-rotation hysteretic response of the foundation effectively minimizes the superstructure seismic demands in terms of roof drift and base shear, while the structural fuse element remains linear-elastic, even under intense base shaking.