Incremental dynamic analysis of nonlinear rocking soil-structure systems

Rocking isolation effect on seismic demands of shear-building structures rested on shallow foundation is investigated in this paper. Building structures with surface raft foundations of various geometrical and structural properties located on soft-to-very dense sites are studied. Two types of near-fault pulses, i.e. fling step and forward directivity, are considered as input excitation. Results show that nonlinear SSI effect is governed by static vertical safety factor of foundation (F-s) that is varied in this study. Evidently, it is not necessary to excessively decrease the F-s factor. So that rocking isolation is achieved as F-s factor is around 2.0. On the other hand, nonlinear SSI effect is strongly correlated with normalized period of the incident near-fault pulse (T-p/T). The most significant effects of nonlinear SSI on mitigating structural demands occur at T-p/T near to unity. It is observed that rocking isolation has the same drawbacks of conventional synthetic translational isolators that work in sway directions. The first drawback is deficiency of rocking isolation subjected to long-period near-fault pulses and the latter is in case of high-rise superstructures.