Stochastic response of secondary systems in base-isolated structures

In this work, the stochastic response of secondary systems attached to a base-isolated structure undergoing random ground motions is examined. It is assumed that the properties of this combined structural system are deterministic, while the ground motions are described by a filtered white noise model. The only nonlinear component of this structural system is its base isolation mechanism, which is linearized by using equivalent linearization. Also, a substructuring algorithm is developed which requires the dynamic properties of the individual, fixed-base components of the structural system. Both stationary as well as nonstationary cases are considered and comparisons are made with the results of Monte-Carlo simulations to ascertain the validity of this methodology. The example studied herein is a six-storey steel building frame with a base isolation system consisting of sliding bearings and restoring force springs. For this example, spectra are constructed that account for primary-secondary system interaction and depict the effect of variations in the base isolator's structural parameters and in the mass and location of the secondary system on the latter's root-mean-square (RMS) accelerations.