VIBRATION CONTROL ANALYSIS OF THE AIR SPRING-FPS THREE-DIMENSIONAL ISOLATED STRUCTURE OF LARGE-SPAN SPATIAL STRUCTURE SUBJECTED TO LONG-PERIOD GROUND MOTIONS

The seismic behavior of a large-span single-layer spherical reticulated shell with the novel air spring-FPS three-dimensional (3D) isolation bearing is investigated. The influence of long-period ground motions on the vibration control effect of the 3D isolated structure is discussed. The dynamic time-history analysis indicated that 3D isolation bearings can effectively reduce the structural seismic response under various ground motions. With the same peak ground acceleration (PGA), the isolation effect of ordinary ground motions is better than near-fault pulse-like ground motions and much better than far-field long-period ground motions. This phenomenon is related to the quasi-resonance effect between the long-period ground motions and the long-period isolated structures. With the decrease of the bearing stiffness, the isolation effect is improved for ordinary ground motion and near-fault pulse-like ground motion while it is reduced for far-field long-period ground motions. The abundant low-frequency characteristics of far-field long-period ground motion make its response spectra have bimodal characteristics, resulting in the increase of the structural response with the period prolongation. TR is suggested to be larger than 0.2 in order to not only obtain a good isolation effect but also limit the vertical bearing displacement with an allowable value for a three-dimensional isolated structure.