Development, implementation and verification of dynamic analysis models for multi-spherical sliding bearings
Fenz, Daniel M.
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Multi-spherical sliding bearings offer several advantages over traditional seismic isolation systems, both in terms of system performance and economy. These bearings are completely passive devices, yet exhibit adaptive stiffness and adaptive damping. This is a result of their unique internal construction, which consists of multiple surfaces upon which sliding can take place. As the combinations of surfaces upon which sliding is occurring change, the stiffness and effective friction change accordingly. Furthermore, since the sliding displacements are shared among multiple surfaces, multi-spherical sliding bearings can be manufactured much more compactly than traditional bearings, providing substantial economic savings. Often, advancements in performance come at the expense of simplicity, reliability and longevity. However, the double and triple Friction Pendulum (FP) bearings investigated in this study are just basic adaptations of the original Friction Pendulum bearing, one of the most widely implemented seismic isolation systems. The main goal of this work was to analytically characterize and experimentally validate the behavior of double and triple FP bearings in order to facilitate practical implementation. In particular, this entailed (a) Developing the principles of operation and force-displacement relationships of various types of multi-spherical sliding bearings based on first principles. (b) Verifying the mechanical behavior with component testing of a variety of multi-spherical sliding bearings in configurations having a broad range of characteristics. The experiments demonstrated that adaptive stiffness and damping can be achieved in practice and that the analytical models are capable of reliably predicting this behavior. (c) Developing a methodology for modeling the mechanical behavior of double and triple FP bearings in software commonly used for response history analysis of seismically isolated structures. (d) Performing shake table testing of a seismically isolated structure under conditions to induce uplift and/or bidirectional motion in the isolation system. These cases are the most demanding analytically and provide the best demonstration of the robustness and accuracy of the isolator models used in response history analysis. In order for these devices to be useful to the engineering profession, their basic safety has to be demonstrated and the behavior must be sufficiently well understood so that response can be reliably predicted. The work in this study has contributed toward these ends.