Experimental Investigation of a Three‐Dimensional Isolation System Combining One‐Dimensional Periodic Material and Elastomeric Bearing

Conventional horizontal isolation systems are ineffective against simultaneous multi‐directional vibrations, and the few existing three‐dimensional (3D) isolation systems (3D‐ISs) are often constrained by limited axial capacity and reliability concerns. A 3D‐IS has been proposed in the present study by combining a one‐dimensional periodic material‐based isolation system (1D‐PIS) and an elastomeric rubber bearing (ERB) at device scale to mitigate simultaneous vibrations acting along vertical and horizontal directions, respectively. The practice of using ultra‐soft rubber layers in the unit cells of the 1D‐PIS has been avoided to address axial stability and rocking issues, instead laminated rubber layers are used in the unit cell. A set of design charts has been proposed in this study to assist with the selection of appropriate 1D‐PIS designs for different isolation frequency ranges of applications in vertical directions. The proposed 3D‐IS was validated by conducting static and dynamic shake table tests on a superstructure isolated by a smaller prototype of the proposed 3D‐IS. The selected prototype was found to be effective across all horizontal frequencies and higher vertical frequencies (>18 Hz). The ERB and the 1D‐PIS in the proposed 3D‐IS exhibited uncoupled dynamic behavior. The isolation efficacy in the vertical direction can be further enhanced by adopting a larger diameter 3D‐IS, resulting in a lower isolation frequency. Shake table tests on the 3D‐IS showed negligible rocking behavior, and an analytical model concluded that its application is most suited for superstructures within aspect ratios of two.