SEISMIC PROTECTION OF EXISTING STRUCTURES WITH DISTRIBUTED NEGATIVE STIFFNESS DEVICES

In this research study, the KDamper concept is extended (EKD device) and applied to multiple floors of existing multi-story building structures, aiming to reduce the structure dynamic responses due to earthquake excitations. The KDamper is a novel passive vibration absorption concept, based essentially on the optimal combination of appropriate stiffness elements, one of which has a negative value (NS). The mass requirements of KDamper are reduced, compared to the Tuned Mass Damper (TMD), as the NS element is implemented to the installed mass and the NS force is in phase with the inertia force, artificially amplifying it. Inspired by the concept of distributed TMDs (d-TMDs), multiple EKDs (d-EKDs) are installed and distributed along the height of the structure, for seismic protection. The design and spatial allocation of these EKDs are determined using a Harmony Search (HS) algorithm, which identifies optimal device parameters while adhering to structural constraints and limitations. Artificial accelerograms are generated and introduced as input to the optimization process. Based on the numerical results obtained, the d-EKD concept, outperforms the d-TMD in reducing the structural dynamic responses, introducing one order of magnitude smaller added oscillating masses. In addition, results indicate no significant alteration of the structural properties and eigenfrequencies due to the installation of the proposed EKD devices, despite the addition of masses and NS elements.