Achieving reliable seismic performance enhancement using multi-stage friction pendulum isolators



An objective in the design of seismically isolated structures is the selection of isolator properties so that performance enhancements are reliably achieved over a range of excitations and performance metrics. A challenge in the design of isolation systems is that, to withstand very severe or near-fault motions, bearings often become so large, stiff and strong that they provide little isolation during moderate seismic events. Numerical investigations are presented to characterize the performance of a new multi-stage friction pendulum (FP) isolation bearing, capable of progressively exhibiting different hysteretic properties at various levels of displacement demand. The feasibility of targeting these properties to achieve specific performance goals for a range of ground motion intensities and structural dynamic characteristics is investigated. In particular, the trade-off between limiting very rare isolator displacement demands and inducing high inter-story drift and floor accelerations is examined for a range of levels of seismic hazard. Nonlinear dynamic analyses of realistic building systems are presented, including a description of key structural demand parameters. To investigate the potential performance benefits of innovative devices, a complex multi-level performance objective termed a seismic performance classification is introduced. Results indicate that multi-stage FP bearings show improved reliability of meeting seismic performance objectives when multiple levels of seismic intensity are considered compared to those systems that incorporate conventional bilinear hysteretic energy dissipation mechanisms. Copyright © 2010 John Wiley & Sons, Ltd.