A Parametric Study on the Energy Dissipation Capability of Frictional Mechanical Metamaterials Engineered for Vibration Isolation

Mechanical metamaterials are engineered structures with complex geometric arrangements that display unconventional mechanical properties which are uncommon in traditional materials. They possess the ability to manipulate and control mechanical wave propagation across specific frequency ranges known as frequency bandgaps. This feature makes them extremely useful for a variety of applications in structural control including passive vibration isolation. These materials can be engineered to selectively block or redirect the input motion at their dominant frequency while allowing the transmission of motion at other frequencies. This paper aims to study the dynamic performance of an innovative mechanical metamaterial designed for seismic isolation in multi-story buildings. This seismic isolator, which is termed the meta-isolator (MI), utilizes solid friction to enhance energy dissipation in addition to its natural viscous damping. The proposed MI comprises multiple interconnected cells linked in series via a network of springs and dampers, where each cell includes a lumped mass, spring, damper, and sliding surface, providing both vibration isolation and energy dissipation functionalities. A dynamic model is developed to characterize the nonlinear hysteresis behavior of the proposed MI. This model is implemented on a one-story building model to assess its seismic performance under specific ground motion. A parametric analysis is conducted to optimize the key parameters of both the MI and the building model aiming to reduce drift and absolute acceleration responses. These parameters include mass and frequency ratios, the magnitude of normal force acting on the sliding surface within each cell, and the number of cells. Finally, the optimized dynamic model of the MI is utilized to evaluate its efficacy in seismic isolation of a finite element (FE) model of a one-story 2D frame building subjected to the same ground motion. The FE model is developed using the OpenSEESPy package which is a Python 3 interpreter for OpenSEES. Insights from this study indicate significant promise for the performance of the proposed MI offering hope for its use as a potent passive control system for seismic isolation. In particular, we have shown that lightweight MIs with low frequency ratios (less than 0.5) can outperform the conventional seismic isolators.