Seismic Response Case Study of Isolated Floor System Having Special Biaxial Spring Units

This paper presents the results of a shake-table case study conducted on a proposed novel type of isolated floor system having special bidirectional spring units. This solution provides enhanced seismic performance for certain facilities where constraints may require isolation of select floors or spaces rather than the entire structure (typically for selected rooms in critical facilities). This system was tested on a 6-DOF shake table. The floor seismic excitations were obtained from nonlinear time history analyses of both single-degree-of-freedom and multidegree-of-freedom frames stiffened with buckling restrained braces and designed as a structural fuse frame, and subjected to synthetic ground motions. The test results show that the isolated floor system performs satisfactorily, but that system behavior differs from that of the spring units alone because correction must be made to account for sources of friction beyond those from the spring units alone. The mechanical properties of the isolated floor system are also obtained in terms of the acceleration-displacement relationship, which provides the foundation to better simulate these isolated floor systems in future parametric studies.