Seismic base isolation has become an increasingly common approach to reduce earthquake induced losses. Base isolation aims to decouple structures, such as buildings or bridges, from strong ground motions through the introduction of a flexible layer, typically located at the foundation. Base isolation is a well-established concept and accepted as an effective method of protecting both the structure and its contents from damage due to earthquakes. Elastomers are ideal for base isolation due to their soft material properties and ability to undergo large recoverable strains. Steel-reinforced elastomeric isolators (SREIs) have been widely applied as base isolators; however, the weight and cost of SREIs have been perceived as barriers to the widespread application of base isolation. In order to alleviate these concerns, it has been proposed that the steel reinforcement could be replaced with lighter fiber reinforcement with similar tensile properties as steel. Recent investigations have demonstrated that fiber-reinforced elastomeric isolators (FREIs) are viable and have desirable characteristics. An additional proposed cost saving measure was to place the FREI unbonded between the upper and lower supports. The combination of the flexible fiber reinforcement and the unbonded application resulted in a unique rollover deformation under horizontal displacement. Rollover causes a nonlinear force-displacement relationship characterized by a softening and stiffening phase. This nonlinear relationship is believed to be advantageous and to allow the performance of the device to be tailored to the earthquake hazard level. This work investigates the adaptive characteristics of unbonded FREIs. It is demonstrated that the softening and stiffening characteristics of the isolator can be altered through modifications to the isolator or to the surrounding support geometry. Equations are developed to predict the horizontal force-displacement relationship. Furthermore, simple expressions appropriate for use in building and bridge design codes are proposed for critical isolator properties. Potential limitations introduced due to the unbonded application are identified and addressed through the development of a new partially bonded hybrid isolator. It is demonstrated that unbonded FREIs are highly versatile and a potentially competitive device appropriate for widespread application in developed and developing countries. / Thesis / Doctor of Philosophy (PhD) / Earthquakes remain a significant and potentially devastating threat to both developed and developing countries. Structural elements within a building, such as beams and columns, must deform considerably to accommodate the relative floor displacements that develop due to ground motion. Conventional construction materials are not capable of undergoing these large deformations without irreversible and potentially catastrophic damage. The introduction of a flexible layer at the foundation level of a structure, using elements known as isolators, can dramatically reduce damage. The deformation is concentrated at the flexible layer, which can undergo large displacements without any damage. This concept, known as base isolation, protects both the structure and its contents. Traditional isolators are expensive, thus far hindering the application of base isolation systems. A novel isolator design has been proposed that has the potential for widespread economical application. To increase the application, building codes need to be developed, requiring substantial research on the isolator properties. A key component of the novel isolator is the ability to alter the isolator geometry to further enhance the response. This is validated through experimental testing and complex computer models.

<p>Real-time hybrid simulation (RTHS) has demonstrated certain advantages over conventional large-scale testing. In an RTHS, the system that is under study is partitioned into a numerical and a physical substructure, where the numerical part is comprised of those elements that are easier to model mathematically, while the physical part consists of those that present a complex behavior difficult to capture in a numerical model. The most complex part of this study is the isolation system, a technology used to protect structures against earthquakes by modifying how they respond to ground motions. Unbonded Fiber Reinforced Elastomeric Isolators (UFREIs) are devices that can accomplish this task and have gained attention in recent years because of their modest but valuable features that make them suitable for implementation in low-rise buildings and in developing countries because of their low cost. Our end goal for this work is to enable the testing of scaled versions of these elastomeric isolators to understand their behavior under shear tests and realistic loading. </p> <p>A testing instrument was designed and constructed to apply a uniaxial compressive force up to 22kN and a shear force of 8kN simultaneously to the specimens. A testing program was conducted where four primary sources of signal distortion were identified as caused by the servo-hydraulic system. From these results, a mechanics-based model was developed to understand better the dynamics that the sliding table can introduce to the measured signals accounting for inertial and dissipative forces. Two Bouc-Wen models were implemented to simulate the behavior of the UFREIs. The first only accounts for the hysteretic behavior of the isolator, and the second accounts for the additional nonlinearities found in the isolator’s behavior. These models were assembled in a virtual RTHS which is available to users interested in learning the applications of RTHS of a base-isolated structure with a nonlinear component.</p> <p>An RTHS experiment was conducted in the IISL where the control system comprised a delay compensator and a proportional-integral controller, which exhibited a good tracking performance with minimal delay and low RMSE. However, it can increase the distortion of the oil-column resonance in the measured signals. The simulation captures the behavior of the isolated structure for small displacements. However, it underestimates the displacement of the full-scale specimen for large displacements. The RTHS showed a better approximation of the displacement of the full-scale structure than the theoretical behavior approximated by the Bouc-Wen models.</p>