عنوان مقاله [English]
Seismic isolation as a passive control method of structures and an innovative approach in resistant seismic design reduces significantly the responses of structural system induced by strong ground motions. The performance of these systems in near fault (NF) ground motions with large pulses is different from far fault (FF) ground motions. It is shown that the effects of near field earthquake with large velocity pulses can bring the seismic isolation devices to critical working conditions. To overcome this problem the application of viscous damper is represented as an approach to improve the performance of these systems in near field earthquakes. In the present paper, by modeling six base isolated structures, the seismic responses has been studied under near field and far field earthquakes. The isolators were modeled by using a mathematical model depicted by bi-linear hysteretic behavior. Nonlinear time history analyses were performed using finite element software of ABAQUS to study the influence of different values of supplemental damping (5\%-40\%) on the responses of base isolated structures. The variation of floor absolute acceleration, bearing displacement and storey drift for different values of supplemental damping under near field and far field earthquakes was studied. The influence of supplemental damping on the responses of isolated structures were studied under the variation of important system parameters uch s uperstructure flexibility, period of frames and number of storey of base isolated structures. The results showed that, generally, by increasing the damping ratio, responses of structures including the maximum floor acceleration and maximum floor relative displacements increased under near field earthquakes. But maximum floor elative isplacements decreased under far field earthquakes. It was observed that base displacement response decreased by increasing damping ratio under near field and far field earthquakes. This reduction under near field earthquakes is greater than far field earthquakes. Also by increasing the supplemental damping under near field and far field earthquakes, the maximum story acceleration increased.