Effectiveness and optimal design of fluid-viscous dampers for inter-storey isolated buildings

The use of fluid viscous dampers (FVDs) together with isolators is effective in reducing isolators’ displacement while keeping low isolation stiffnesses: therefore, such a hybrid system is suitable for buildings with inter-storey isolation in order to limit P-Δ effects. However, previous studies regarding base isolation showed that the additional damping may also be detrimental, as it may increase inter-storey drifts and floor accelerations. Although the main effects of additional damping on base-isolated buildings are clear, the results obtained in previous studies are not always easy to compare as they are strongly influenced by initial hypotheses (e.g. damper features); in addition, the use of FVDs in buildings isolated at storey level has its own peculiarities, and the effectiveness of FVDs for the improved seismic performance of such structures has been investigated only recently. First, this paper presents the main results of a recent study on the effectiveness of FVDs optimally designed for an inter-storey isolated building (case study); in this research, the FVDs are individually optimized for each accelerogram analysed by evaluating two competing objectives, i.e., the minimisation of both the isolators deflection and the superstructure total drift. Subsequently, as the optimal linearity degree of the FVDs proved to be strongly dependent on seismic input, making the design choice difficult, a more suitable multi-objective optimal design approach is proposed and applied to the same case study, which involves the use of surrogate response models.