Negative Stiffness Absorber for Seismic Retrofitting of Buildings

by Antonios Mantakas

Throughout the past decades, seismic isolation of structures has been studied rigorously as an approach to reduce seismic demand and mitigate structural damage. Research in this field has progressed significantly, starting from the use of simple elastomeric bearings for the decoupling of the superstructure from the base, to more complex devices that incorporate the use of an additional oscillating mass and negative stiffness elements. The KDamper is a novel passive vibration absorption concept, based essentially on the optimal combination of appropriate stiffness and mass elements, which include a negative stiffness element. In simple words, the KDamper mass, installed at the base of a typical structure, moves in the opposite direction of the superstructure during seismic excitation, hence reducing displacements and accelerations. The concept can be implemented using a system of prestressed elements in order to obtain the negative stiffness effects and might prove to achieve a significant advantage for seismic retrofitting (Figure 1).

Figure 1: Indicative implementation of the seismic KDamper for retrofitting of buildings (Kapasakalis et al. 2019)

The KDamper device is placed at the pilotis level, and the performance of the proposed control system is evaluated. A series of recorded ground motions are applied at the base of the structure and results indicate the beneficial role of the KDamper on the reduction of the spectral acceleration and displacements, hence placing the concept as a compelling alternative to existing seismic protection technologies.

Figure 2: Seismic response of a typical residential structure (L’Aquila 2009) after introduction of soil-structure interaction (SSI) and KDamper device. Response is evaluated in terms of upper storey acceleration and 1st storey drift.

Figure 2 presents results from the response of a typical 4 storey building to the L’Aquila (2009) seismic excitation. The structure that takes advantage of the soil-structure interaction and KDamper concept shows substantial decrease of upper storey accelerations and inter-storey drifts.

More information is openly available in a recent publication (Alvertos et al., 2020): The video contains the associated conference presentation in the XI International Conference on Structural Dynamics (EURODYN2020).

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