Demonstration of Compatible Yielding between Soil-Foundation and Superstructure Components.

Although the nonlinear behavior of rocking shallow foundations has been experimentally and numerically demonstrated as an effective tool to dissipate vibrational energy during seismic loading, the engineering community has yet to uniformly accept it as a targeted design mechanism for diffusing seismic energy in a structure. This paper presents results of a centrifuge test program that incorporated inelastic behavior into model building systems via yielding of both structural and foundation components. Three 2-story-1-bay building models were designed with similar layouts but different combinations of foundation and structural component yield strengths and were shaken with a similar suite of earthquake motions. Measurements of behavior of each of the model buildings are presented and cross-compared in terms of time history responses, hysteretic responses of the structural and foundation fuses, and maximum response parameters. A balanced design configuration, wherein the rocking foundation and structural fuse are intended to yield at approximately the same load, is demonstrated to be a well-controlled seismic-resisting system, with greatly reduced seismic ductility demand on the structural components. Moreover, seismic energy is well distributed among the targeted yielding components. In contrast, if the footing is restrained from rocking, the structural component ductility demand is significantly greater than that compared to its demand when the foundation is allowed to rock. In essence, the foundation rocking dominated model demonstrates its ability to protect the superstructure from seismic demands. In contrast, when the rocking foundation capacity is more than twice that of the structural fuse, rotations at the foundations are reduced significantly, at the price of much larger demands to the superstructure. [ABSTRACT FROM AUTHOR]