Development and Evaluation of Procedures for Analysis and Design of Buildings with Fluidic Self-Centering Systems
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This dissertation presents a study on the use of fluidic devices as elements of self-centering systems for buildings. These devices provide the functions of preload, stiffness and viscous damping in a single compact device. The main effect of these devices is a substantial reduction of residual displacements in earthquakes. Since they also incorporate fluid damping, they also offer the benefit of reduction of drift. The report presents a description of the behavior of these devices and presents results on the behavior of small and large fluidic self-centering devices for varying conditions of preload, history of motion and temperature. Mathematical models of the behavior of the devices are presented and validated by comparison to experimental results. Analyses of systems for a wide range of parameters are performed and the results are used to validate simplified methods of analysis and to develop design and analysis procedures for buildings with fluidic self-centering systems that follow the paradigm of Chapter 18 of the ASCE 7-2010. Three and six-story buildings without and with self-centering systems are designed per the developed procedures and analyzed by nonlinear response history analysis with due considerations for the behavior of the devices and of the yielding structural system. The results demonstrate that the design of buildings with fluidic self-centering devices per the developed procedures offers benefits of substantial reduction in residual drift but also reduced peak drift, peak acceleration, peak shear and base shear forces, and reduced floor response spectra by comparison to the code-compliant buildings without fluidic self-centering devices. The seismic collapse performance of these buildings is then quantified using the FEMA P695 procedures and is compared to the collapse performance of conventional buildings. It is concluded that buildings with fluidic self-centering devices designed by the procedures presented in this report have a collapse performance comparable to that of conventionally designed buildings. The study also determined that increases in the preload, increases in the displacement capacity or increases in the viscous damping constant of the self-centering devices have marginal or insignificant effects on the collapse margin ratio. Rather, an increase in the collapse margin ratio is obtained for frames having a device-braced system with increased ultimate capacity. A study is also conducted on the residual drift fragility of buildings with fluidic self-centering systems, which is calculated and compared to that of conventional buildings. It is shown that buildings with fluidic self-centering systems, designed per the procedures of this document, have substantial reduction of the probability of exceeding the residual drift limits of 0.2% and 0.5%. The buildings without and with fluidic self-centering systems are further analyzed to obtain information of the mean annual frequency of collapse, the mean annual frequency of exceeding the residual drift limits of 0.2%, 0.5%, 1% and 2%, and the related probability of collapse or of exceeding the residual drift limits in 50 years. It is concluded that all analyzed systems have a probability of collapse in 50 years of about 1% or less, and that the structures with fluidic self-centering systems have much lower probabilities in 50 years of exceeding the residual drift limits of 0.2% and 0.5% than conventional structures. This information is likely of much interest to engineers, building officials, government officials, owners and insurers.