The Optimization of Multi-Stage Friction Pendulum Isolators for Loss Mitigation Considering a Range of Seismic Hazard

Abstract eng:
An objective in the design of seismically isolated structures is the selection of bearing properties so that optimal performance is 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. Experimental and numerical investigations are presented to characterize a new multi-stage friction pendulum (FP) isolation bearing, capable of progressively exhibiting different hysteretic properties at various levels of displacement demand. This newly-developed triple pendulum isolator incorporates four concave surfaces and three independent pendulum mechanisms. Through the selection of geometric quantities such as spherical surface radii and slider height, combined with specification of friction coefficients for each interface, pendulum stages can be set to address specific response criteria for moderate, severe and very severe events. 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 tradeoff between limiting very rare isolator displacement demands and inducing high-frequency floor accelerations and inter-story drifts is examined for a range of levels of seismic hazard. Nonlinear dynamic analyses of realistic building systems are presented, including a thorough, probabilistic description of key structural demand parameters suitable for reliability analysis and loss estimation. Recommendations for a design methodology leading to optimal parameters for multi-stage FP bearings given a particular super-structural system and seismic hazard environment are presented. This optimization procedure targets the minimization of loss estimates for over seismic events having a range of mean annual frequencies.

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