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In many finite element platforms, a classical global damping matrix based on the elastic stiffness of the system (including isolators) is usually developed as part of the solution to the equations of motion of base-isolated buildings. The conducted analytical and numerical investigations illustrate that this approach can lead to the introduction of unintended damping to the first and higher vibration modes and the spurious suppression of the respective structural responses. A similar shortcoming might be observed even when a nonclassical damping model (ie, an assembly of the superstructure and isolation system damping sub-matrices) is used. For example, the use of Rayleigh damping approach to develop the superstructure damping sub-matrix can lead to the undesired addition of damping to the isolated mode arising from the massproportional component of the superstructure damping. On the other hand, the improper use of nonclassical stiffness-proportional damping (eg, determining the proportional damping coefficient, β k , based on the first mode) can result in assigning significant damping to the higher-modes and the unintended mitigation of the higher-mode responses. Results show that a nonclassical stiffness-proportional model in which β k is determined based on the second modal period of a base-isolated building can reasonably specify the intended damping to the higher modes without imparting undesirable damping to the first mode. The nonclassical stiffness-proportional damping can be introduced to the numerical model through explicit viscous damper elements attached between adjacent floors. In structural analysis software such as SAP2000®, the desired nonclassical damping can be also modeled through specifying damping solely to the superstructure material.

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Summary This study uses instrumented buildings and models of code‐based designed buildings to validate the results of previous studies that highlighted the need to revise the ASCE 7 Fp equation for designing nonstructural components (NSCs) through utilizing oversimplified linear and nonlinear models. The evaluation of floor response spectra of a large number of instrumented buildings illustrates that, unlike the ASCE 7 approach, the in‐structure and the component amplification factors are a function of the ratio of NSC period to the supporting building modal periods, the ground motion intensity, and the NSC location. It is also shown that the recorded ground motions at the base of instrumented buildings in most cases are significantly lower than design earthquake (DE) ground motions. Because ASCE 7 is meant to provide demands at a DE level, for a more reliable evaluation of the Fp equation, 2 representative archetype buildings are designed based on the ASCE 7‐16 seismic provisions and exposed to various ground motion intensity levels (including those consistent with the ones experienced by instrumented buildings and the DE). Simulation results of the archetype buildings, consistent with previous numerical studies, illustrate the tendency of the ASCE 7 in‐structure amplification factor, [1 + 2(z/h)], to significantly overestimate demands at all floor levels and the ASCE 7 limit of ap=212 to in many cases underestimate the calculated NSC amplification factors. Furthermore, the product of these 2 amplification factors (that represents the normalized peak NSC acceleration) in some cases exceeds the ASCE 7 equation by a factor up to 1.50.

Summary In a previous study, the authors studied a partial mass isolation (PMI) system that through isolating different portions of story masses can provide a building with multiple inherent vibration suppressors. It was shown that the PMI strategy with isolated mass ratios (IMRs) of 0.05 or 0.90 could perform as effectively as an equivalent tuned mass damper or a base isolation system, respectively. In the present paper, the PMI system is examined in structural models with different fundamental periods. PMI configurations in a wide IMR range of (0.05:0.025:0.90) are optimized illustrating that applying an IMR of 0.25–0.50 can provide an efficient system, simultaneously satisfying the constraints related to different performance objectives (i.e., mitigating the overall building seismic responses and controlling isolated components' (ICs) responses while integrating these components into the building architecture). Simulation results reveal that using identical ICs at different stories, which have the advantage of facilitating the design and construction of the system, can lead to a near‐optimal solution. It is also demonstrated that in terms of the spatial distribution of ICs, an adequate seismic performance improvement can be achieved by allocating ICs only at a subset of upper stories (e.g., top half stories), which can further simplify the PMI systems' construction.