Energy spectra and performance assessment of isolated structures with a negative stiffness amplification system

Abstract

Negative-stiffness-incorporated seismic isolation technology has been widely adopted for the effective protection of infrastructures from high-intensity earthquakes. In particular, by incorporating a dashpot and tuning spring, a negative stiffness device can yield a negative stiffness amplification system (NSAS) that can produce an amplified dashpot deformation without sacrificing the isolating effect. To address this observed amplification effect and unknown performances subjected to various types of ground motions, energy spectra are proposed in this study for structures equipped with the NSAS-incorporated isolation system (NSAS-IS) and classified by the field-type of ground motions, based on which the energy-spectrum-based performance evaluation method is developed. The basic concept and mechanical model of the negative-stiffness device, NSAS-IS, and pertinent isolated structure are introduced, based on which the energy response analysis model is established. Within the energy-based framework, the ground motions are classified, whereas the energy spectra are unified for the original structure and the NSAS-IS-equipped isolated structure with a series of typical NSAS-ISs. By addressing the near-, middle-, and far-field ground motions, analytical assessment formulae are provided for the NSAS-IS-equipped structures to quantify the differences in the seismic performances and enhanced energy dissipation levels among the various ground motions. Finally, the proposed energy-based performance assessment tool is applied in design cases for illustration. The findings of this study show that the developed energy spectra are effective in evaluating the energy dissipation enhancement and structural energy dissipation reduction levels of NSASs against various field-type earthquakes. Specifically, the energy dissipation burden of the superstructure under near-field ground motions with significant pulse components is larger than that of the middle- and far-field motions, signifying the necessity of considering the earthquake type for the performance assessment and design of NSAS-IS structures. The proposed analytical performance evaluation formulae can be adopted for a quick performance assessment of NSAS-IS isolated structures subjected to various earthquakes.