One concern in the design of base isolated structures is the selection of isolation system properties so that optimal performance is achieved over a range of seismic levels and performance metrics. To withstand very rare ground motions, isolation bearings are frequently designed with significant strength or damping, and as a result such devices provide reduced isolation effect for more frequent seismic events. To investigate possible improvements to the design of isolated
structures, an extensive research program is conducted. Analytical and experimental investigations are presented to characterize multi-stage spherical sliding isolation bearings capable of progressively exhibiting different hysteretic properties at different stages of response. Shaking table tests are conducted on a 1/4-scale seismically isolated steel braced frame on multi-stage bearings, including harmonic characterizations tests and earthquake simulations. These tests included various input intensities, multi-component excitation, bearing uplift, and superstructure response. A newly developed analytical model is implemented as part of a parametric study of single- and multi- story buildings incorporating a wide class of isolation systems. Behavior of the new triple pendulum bearing is compared with that of linear isolation systems with both nonlinear viscous and bilinear hysteretic energy dissipation mechanisms. The results of parametric analyses are used to develop a design framework based on targeting a multi-objective Seismic Performance Classification (SPC). This SPC is introduced to describe satisfaction of a complex seismic performance objective, defined as aggregate damage state limitation over multiple levels of seismic hazard. The probability of satisfying specific SPCs is computed for three- and nine-story buildings on all classes of isolators investigated.
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