Mechanics, Characterization, and Design of an Adaptive Variable Friction Base Isolation System

Abstract

With the growing desire for high performing and resilient structures, base isolation has increasingly been utilized to reduce seismic forces on structures and further tailor structural response. Though many isolators are currently available, few offer the ability to tailor structural response at more than one demand level, and devices that are capable of performance-based design can be geometrically complex and have low damping at high displacements. Thus, the Adaptive Variable Friction (AVF) bearing is presented as a simple isolation alternative, capable of changing period as a function of ground motion intensity. This thesis studies the behavior of the AVF bearing and develops and tests a Direct Displacement Based Design process for single and multiple-degree-of-freedom systems (SDOF, MDOF), including an expression for equivalent viscous damping. Preliminary results from many nonlinear time history analyses show an advantage of AVF bearings over the commonly used Friction Pendulum in extreme events, achieving a lower maximum displacement for a similar maximum force and re-centering capability. Additionally, the proposed design process predicts the base shear and displacement of the system with reasonable precision at two demand levels, but improvements for the MDOF design should be made to better predict other structural responses. The results show that the AVF bearing is a promising isolation alternative capable of performance-based design and should be explored in further studies.