Adaptation of metamaterials at micro- to nanometer scales to metastructures at much larger scales offers a new alternative for seismic isolation systems. These new isolation systems, known as periodic foundations, function both as a structural foundation to support gravitational weight of the superstructure and also as a seismic isolator to isolate the superstructure from incoming seismic waves. Here we describe the application of periodic foundations for the seismic protection of nuclear power plants, in particular small modular reactors (SMR). For this purpose, a large-scale shake table test on a one-dimensional (1D) periodic foundation supporting an SMR building model was conducted. The 1D periodic foundation was designed and fabricated using reinforced concrete and synthetic rubber (polyurethane) materials. The 1D periodic foundation structural system was tested under various input waves, which include white noise, stepped sine and seismic waves in the horizontal and vertical directions as well as in the torsional mode. The shake table test results show that the 1D periodic foundation can reduce the acceleration response (transmissibility) of the SMR building up to 90%. In addition, the periodic foundation-isolated structure also exhibited smaller displacement than the non-isolated SMR building. This study indicates that the challenge faced in developing metastructures can be overcome and the periodic foundations can be applied to isolating vibration response of engineering structures.

The linear isolator has fixed vibration frequency. When structures with these linear isolators are located near a fault, it may cause resonance and large displacement response. Hence, nonlinear isolation may avoid this situation. In this study, an eccentric nonlinear rolling isolator with a parameter, which is the eccentricity of the pin connection of the mass block (facility) to the circular isolator, is investigated. If the eccentricity is not equal to zero, the dynamic response is nonlinear rolling behavior. The equation of motion of the isolation system is derived. The frequency of the isolator increases with the eccentricity under the same initial angle. The influence of the eccentricity to the effect of isolation is scrutinized. Finally, the feasibility of the proposed isolation device is verified numerically. If the proposed isolator is designed properly, it is effective for far-field earthquake (El Centro earthquake). Even though the linearized frequency of the proposed isolator falls into the dominant frequency range of near-fault earthquake (Chi-Chi earthquake), resonance can be avoided due to nonlinearity.

An isolation system is not very effective when an inappropriate level of damping is used. This paper proposes a theoretical method which can be used to determine the optimal frictional coefficient of an isolation system. Only a one-dimensional isolation system and ground motion are considered. The frictional coefficient is optimized by minimizing the sum of squares of structural absolute accelerations, with the optimization results being validated graphically. Sensitivity studies were used to verify the feasibility of the optimal frictional coefficient, coupled with a practical example in Taipei under the conditions of the Hualien and El Centro earthquakes. Consequently, the feasibility and reliability of the proposed optimal design were verified.

Recent advance of periodic materials from the field of solid-state physics into that of earthquake engineering has resulted in a novel seismic isolation technique. In this study, we developed a new configuration of structural foundation using a three-dimensional (3D) periodic material for seismic isolation of critical infrastructure, particularly nuclear infrastructure. To this aim, we first performed analytical and finite element studies to compare two different types of 3D unit cells, i.e., Bragg Scattering and Locally resonant unit cells, to investigate their characteristics and applicability as a seismic isolator. We then designed a large scale test specimen based on the Bragg-scattering type unit cell using common construction materials: reinforced concrete blocks and polyurethane sheets. The designed test specimen was constructed and tested using a shake table subjected to different types of excitations in the horizontal and vertical directions as well as the torsional mode. The dynamic response of a small modular reactor (SMR) building model protected by the 3D periodic foundation demonstrates that 90% response reduction was achieved within the frequency band gaps. The response attenuation was achieved in all three tested directions. Moreover, the periodic foundation-isolated SMR building exhibited a stable response with negligible rocking on the structural system.

Summary Seismic isolation design has been publicly accepted as one of the most effective strategies to reduce seismic threat to (or seismic demand for) the to‐be‐protected targets including building structures, infrastructure, and equipment. Recently, many studies have aimed to develop nonlinear seismic isolation systems, of which the sloped sliding‐type bearing can exhibit the nonlinear behavior by mechanically designing a simple slope for sliding motion. Therefore, this bearing does not have a fixed isolation frequency. In addition, it features that the seismic isolation performance is realized through the sliding mechanism, the inherent self‐centering capability is provided through the slope design, and the excellent and stable energy dissipation capability is contributed by the sliding friction. In this study, the equation of motion of the bearing is deduced first. Sensitivity analysis is then performed, and the results demonstrate that the maximum horizontal acceleration transmitted to the isolated superstructure is only dependent on two important design parameters‐sliding friction coefficients and sloping angles. In other words, the acceleration control performance of the bearing is irrelevant to different characteristics of external disturbance. Finally, shaking table tests were conducted to verify the effectiveness of the bearing and the accuracy of the numerical prediction.