Optimal Design of True Negative Stiffness Damper as a Supplemental Damping Device for Base-Isolated Structure

Abstract

An analytical study on a true negative stiffness damper (NSD) in the form of negative stiffness amplifying damper (NSAD) is presented. NSD proposed in this study for controlled base isolator displacement uses damping magnification effect that guarantees the efficient reduction in base displacement and inter-storey drift whilst utilising minimum damping coefficient of NSAD dashpot. Dynamic equations of motion are represented in the state-space form. A simple optimisation design for NSAD is proposed using complex eigenvalue analysis of the system matrix. Optimal parameters for NSAD are developed considering the stability of the system and effective fundamental mode damping. Optimal NSAD is supplemented to MDOF base-isolated shear structure as NSD. A suite of six ground motions consisting of three near-fault (NF) and three far-field (FF) motions are used in this study. For comparison purpose, viscous damper (VD) and visco-elastic damper (VED) are used as conventional supplemental dampers to the base-isolated shear structure. Base shear, top storey acceleration and inter-storey drift are three objective variables that are monitored for the effectiveness of supplemental dampers. Results of the time history analysis show that NSAD works as an efficient supplemental damping system for both NF and FF ground motions in contrast to conventional dampers.