Three-dimensional periodic materials as seismic base isolator for nuclear infrastructure

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.