High performance friction-type bearings for seismic isolation

Abstract

Seismic isolation is effective in protecting both structural and non-structural elements during earthquakes. One of the most commonly used base-isolation systems is the friction pendulum system (FPS). It provides excellent re-centering and large energy dissipation capacities. Despite these benefits, FPSs are rarely used in the U.S. for several reasons. Out of many one may identify, the required peer review process and the conservativeness of the existing design guideline make the implementation of the technology somewhat less economically appealing. More critically, it is a well-known dilemma that FPS can only be designed to achieve optimal performance for one level of ground shaking. A possible answer to this challenge is to use "passive-adaptive" devices, including multiple friction pendulum systems and the recently proposed Variable Friction Systems (VFSs). While providing sufficient protection (usually life safety) during a maximum considered earthquake, these systems can still effectively isolate the structure during a service level earthquake, resulting in lower seismic demands on the supported structure and its non-structural components compared to a fixed-based building. However, the development of VFSs is still in early stage, and the performance of structures isolated with such systems is uncertain. Another recently identified challenge in designing isolation systems is the potential for large magnitude and long period earthquakes, in particular, the magnitude-9 (M9) earthquake in Cascadia Subduction Zone. The results obtained from recent numerical simulations indicated that this type of earthquake may be particularly detrimental for structures with fundamental periods of vibration of 1.0 second or larger. This finding may be particularly relevant for base-isolated structures, which tend to be characterized by large effective periods. However, such systems have not been included in the studies conducted thus far, and the effect of the simulated M9 earthquake on their performance remains unclear. To address the aforementioned knowledge gaps that are limiting the implementation of friction-type seismic isolation systems, this dissertation aims to: (i) develop an analysis, modeling, and design framework for structures isolated with VFSs; and (ii) evaluate how ground motions with different characteristics impact the performance and analysis of friction-type seismic isolation systems.