Performance of flexible frame building with horizontal and 3D seismic isolation when subjected to 3D ground shaking

Seismic isolation is known to effectively mitigate the effects of horizontal ground shaking in building structures. Recent research has suggested that vertical excitation causes high-intensity slab vibrations that lead to nonstructural component damage. A detailed case study of the application of three-dimensional (3D) isolation in a realistic multi-story frame building is presented. Specifically, the seismic responses of hypothetical special concentric braced frame buildings with horizontal and 3D isolation are compared to evaluate the effectiveness of 3D isolation to mitigate the vertical ground shaking. Overall, 3D isolation with a relatively short isolation period (0.5 s) is adequate to significantly mitigate the vertical acceleration in a flexible frame building, including the amplification at mid-slab relative to adjacent columns, without compromising the usual reductions in horizontal responses.