Magnetorheological Elastomer (MRE) based Isolator using multi-layered electromagnetic system

Abstract

Recently, as the frequency of earthquakes in domestic increases, the damage to infrastructure is also increasing. As the infrastructure is an essential element in maintaining a safe life, it is important to safely protect it from ground motion. Seismic resistance design is the most commonly used in protecting structures from ground motion, and it is a method of resisting earthquakes by adding thick and strong reinforcements, which has a limitation in that high acceleration and displacement responses occur in the top floor of the structure. However, unlike the seismic resistance design, the seismic isolation separates the structure from the ground motion, and the responses of the structure can be reduced by inserting a structural member with flexible horizontal stiffness between the structure and the ground. However, since the conventional isolation system is installed in a form that can be effectively applied to a specific seismic load, and thus a severe problem may occur for unexpected ground motion. In order to overcome this limitation, a smart material called magnetorheological elastomer (i.e., MRE or MR elastomer) is attracting attention as a new type of isolation system which has an adaptability. The MRE is a material that can adjust the stiffness according to the strength of a magnetic field. In this study, a magnetorheological elastomer and an electromagnetic system, which are the major elements of a base isolator using the magnetorheological elastomer, were proposed, and validated through numerical and experimental comparisons with the conventional magnetorheological elastomer-based isolator. In order to confirm the superiority of the proposed MRE-based isolator, the resistance, electric power, and volume of each electromagnetic system, and the magnetic flux density in the MRE were compared through numerical analyses. In addition, the proposed MRE-based isolator was validated through a dynamic characteristic test according to various excitations. The proposed MRE-based isolator exhibited the higher MR effects even under various excitation conditions. Also, it was confirmed that the decrease in the MR effects according to the increase of the strain of the MRE and the applied frequency was smaller than that of the conventional MRE-based isolator. Also, in order to use it as a seismic isolator, the dynamic characteristics of the MRE-based isolator were investigated according to the vertical load. Although it was confirmed that the MR effect was reduced due to the vertical load, it was found that the MR effect was maintained above a certain level. Lastly, the seismic isolation performance evaluation for several earthquake waves was conducted on the Letdown Isolation Actuation System (LIAS) canbinet used in Nuclear Power Plant (NPP). By constructing a fuzzy logic based on acceleration data in consideration of reality and comparing it with the conventional control types, the reduction of the structural responses was confirmed.