Nonlinear seismic performance evaluation of hybrid base isolation systems

A variety of base isolation systems and their combinations with dampers are applicable in practice. However, most previous studies focused on few numbers of the isolation systems. Therefore, a more comprehensive investigation is crucial. All the possible variations of hybrid base isolation configurations had inspired this research. Seismic performance of the series and parallel hybrid base isolation systems were extensively investigated in the current research using commercially available software. The studied hybrid systems were included lead rubber bearings (LRBs) in combined with linear or nonlinear dampers at base or superstructure levels. The high-damping rubber bearings (HDRBs), the friction pendulum systems (FPS), and a fixed-base reference structure were also investigated and compared. The considered earthquake records were selected in four major groups including far-field, near-field with fling step, near-field with forward directivity for the normal component, and near-field with forward directivity for the parallel component. Based on the main results, the FPS system had least sensitivity to the earthquake frequency content. In contrast, the LRB with linear damper at superstructure level was the most sensitive system to the frequency content of the earthquakes. The LRB combination in parallel with a flat sliding (FS) system showed a better performance in controlling the acceleration and residual displacement responses compared with FPS. Besides, the isolation systems with linear dampers performed better than the nonlinear ones under all the earthquake groups. Results proved that augmented dampers (both linear and nonlinear) at the isolation level had more enhancing effects than the HDRB system alone. Generally, adding dampers to the base level was more effective than that of the superstructure level. The LRB combined with linear damper was the most effective combination in controlling the isolation residual displacement response.