Liu et al. 2012
Rocking foundation systems have been proven to effectively dissipate seismic energy, but many concerns remain with the overall global behavior in a building system, especially those dynamic interactions with other inelastic and structural components. This paper discusses and compares the seismic response of two extreme structural configurations, structural hinging-dominated systems (SHD) and foundation rocking-dominated systems (FRD). The experimental studies were focused to evaluate the seismic behavior of low-rise frame buildings, considering the yielding mechanisms of fuses and rocking shallow foundations.
System Concept
The models were set up to represent a moment-resisting frame building founded on a shallow footing. An idealized 2-degree-of-freedom model was developed and used to find the column and foundation stiffness. The fuse yield coefficient and foundation rocking coefficient were defined as principle dimensionless parameters. The SHD system used a rocking coefficient 2.5 times larger than the fuse coefficient, whereas the FRD system used a fuse coefficient 2 times larger than the rocking coefficient. Both the SHD and the FRD system were designed with the same geometric layouts, yet different nonlinear element sizes.
Experimental Study, Results, and Discussion
Analyses using OpenSees, provided a displacement based static pushover response which showed the FRD system had a larger global strength and yield drift ration. The SHD system had lower capacity and yield drift ratio as well as showed similar strain-hardening behavior with conventional frame structures.
Similar sequences of five different ground motions were applied at the bottom of the system with different amplitude and frequency content. It was found the SHD structural fuse observes significant peak transient and permanent deformation demand when excited by moderate and intense earthquake motion. The FRD system greatly reduced the superstructure drift demand due to footing rotation. The fuse element behaved linear elastically with little energy dissipation.
Reference
Liu, W., Hutchinson, T.C., Hakhamaneshi, M., Kutter, B.L. (2012). “Centrifuge Testing of Systems with Combined Structural Hinging and Rocking Foundations,” Proceedings of the Structures Congress, Chicago, IL, March 29-31.