Adjustable Frequency Bandgap for Seismic Vibration Isolation of MRE-Based Metamaterial Foundations
An earthquake is a non-preventable natural disaster that shakes the ground and vibrates the structure's foundation, eventually damaging the superstructure. These seismic waves are more frequent in some areas because of their geological variations. The seismic vibration caused by earthquakes can damage the structure, leaving it unrectifiable and unusable. Different types of seismic isolation are used underneath the structure to prevent the structure from seismic damage. Conventional seismic isolators will elongate the period of the superstructural system, and hence reduce the vibration response of the superstructure and prevent the structures from seismic damage and collapse. Although the conventional seismic isolation system has been used for several decades, it cannot prevent earthquake vibrations in the vertical direction. Recently researchers developed metamaterial-based seismic isolators, which can isolate seismic waves in both the horizontal and vertical directions. When the frequency of seismic waves falls into the frequency band gap of the designed metamaterial foundation, the seismic waves will be reflected and will not be able to transfer the vibrations to the superstructure. Since earthquakes have a wide range of frequencies, adaptable and tunable frequency band gap of metamaterials is desirable. Magnetorheological Elastomer (MRE)-based metamaterial foundation can change Young’s modulus and stiffness by applying magnetic field intensity. Tunable material properties can shift the frequency band gap of the MRE-based metamaterial foundation. This research focuses on developing MRE samples and applying MRE-based metamaterial foundations to seismic isolation systems. A uniaxial compression test was conducted to determine Young’s modulus of three types of MRE samples under the application of magnetic field. After the MRE materials were developed, a series of numerical simulations were performed in ABAQUS using a two-story framed structure with MRE-based metamaterial foundation. Three earthquake excitations, Bishop, Oroville, and Imperial Valley were used as the seismograms. The experimental result shows that the magnetic field affects Young’s modulus of the MRE. Similarly, the results of the numerical simulations show that the magnetic field affects the frequency band gap of the MRE-based metamaterial foundation. The frequency response function (FRF) results of conventional RC foundation and MRE-based foundation are compared, which shows the effectiveness of MRE-based foundation in vibration control by reducing the seismic vibration of a structure by 68.5%.