A non-preload variable friction inerter system for response reduction of structures subjected to harmonic and seismic ground excitations

The performance of conventional friction dampers is sensitive to the constant preload force, making it difficult to effectively suppress displacement, velocity, and acceleration responses at various levels of earthquakes. Based on the authors' previous development of a Non-Preload Variable Friction Inerter (NVFI), this study explores its underlying dynamic mechanisms, uses harmonic excitation analysis to evaluate the system's frequency adaptability. The NVFI integrates adaptive friction effect and inertial amplification through terminal springs and a ball-screw-based inerter. A comprehensive theoretical framework is established to describe the dynamic behavior of the system, followed by harmonic response and seismic analysis for performance quantification. The results indicate that under seismic excitations of 0.6g, the NVFI reduces displacement, velocity, and acceleration responses by 53.65 %, 39.34 %, and 46.74 %, respectively, achieving 20–30 % higher efficiency than friction dampers. Harmonic analysis confirms the frequency adaptability of the NVFI, showing effective suppression of resonance peaks across a wide frequency range. Energy dissipation evaluations demonstrate a 19.8 % reduction in the seismic input energy, attributable to the ability of the inerter to absorb and redistribute dynamic loads. In addition, the damping ratio of the NVFI remains consistently stable across varying seismic intensities, with values ranging from 0.179 to 0.219 and an average of around 0.201. This stability ensures reliable energy dissipation and long-term damping performance under various earthquake levels. These findings validate the robust damping mechanism of the NVFI and support its suitability for seismic protection in critical infrastructure, particularly when multi-level seismic input is considered.