A review of adverse effects of damping in seismic isolation
Abstract
In this paper the question of possible adverse effects of damping in seismic isolation because of higher mode response is investigated by means of simple models with few degrees of freedom (DOF). In particular the second mode response of a 2 DOF system is examined in detail for both viscous and friction energy dissipation devices. Qualitative and approximate quantitative estimates are obtained by neglecting the influence of the modal coupling terms, due to viscous damping or friction forces, on the first mode response. It is shown that additional viscous damping has a diminishing effect on base displacement, storey shear force and floor spectra values in the vicinity of the first mode resonance. However, a significant amplification of the floor spectra values near the higher mode frequencies may occur. In accordance to the results of previous works, if compared to the viscous damping case, friction energy dissipation amplifies moderately the first storey shear force and significantly the upper storeys shear force. Friction results, also, in a much more pronounced amplification of the floor spectral values than viscous damping, in the vicinity of the higher eigenfrequencies.