Frequency-domain optimization of seismically isolated structures enhanced with negative stiffness devices

Abstract

This study investigates the frequency-domain optimization of base isolated multi-story buildings equipped with novel negative stiffness (NS) vibration control systems (VCS). The examined VCS include the KDamper, the Extended KDamper (EKD) and the Enhanced KDamper (ENKD). Previous research has demonstrated the effectiveness of these devices for seismic protection, by implementing them as standalone base absorbers employing single-objective, time-domain optimization methods. This study explores the application of the VCS as supplementary components of base isolated structures, utilizing multi-objective optimization approaches in the frequency-domain. The objective is to achieve robust designs that balance trade-offs between competing objectives, while optimizing performance across a wide frequency range yielding a more holistic methodology, as compared to time-domain approaches. The optimization framework employs the non-dominated sorting genetic algorithm type II (NSGA-II). Two distinct frequency-domain optimization approaches are considered. The first minimizes transfer functions associated with key, opposing dynamic responses, such as the base displacements and top-floor accelerations of the multi-story structure. The second approach minimizes the root mean square (RMS) values of these responses. The level of intrusiveness of the VCS on the examined building is also investigated, by quantitative assessing how alterations in the base frequency affect the dynamic responses. Numerical applications confirm that the optimized KDamper-based devices improve the building’s dynamic performance, resulting in significantly low base displacement levels. A comparative analysis is also conducted between the two proposed optimization approaches in terms of resulting design variables and dynamic responses.