Three-Dimensional Analysis of Base-Isolated Structures

Base isolation has become a widely accepted method for earthquake resistant design of structures. However, the research in the field has been generally restricted to one-dimensional motion. Structural response is not limited to this one-dimensional motion, and the torsional effect of multidimensional motion contributes to the horizontal displacements. A three-dimensional structure can not be modeled with multiple one-dimensional analyses; rather, a complete three-dimensional analysis must be undertaken, as shown in this study.Four separate analyses for the calculation of the dynamic response of a base-isolated structure will be presented in this study. The first two analysis procedures are for a single-story base-isolated structure. The last two procedures are for a multi-story base-isolated structure. The first procedure for each structure assumes a fully linear response, in which the bearings and the superstructure remain in the linear elastic range of response. The second procedure allows for a non-linear response from the bearings, in which each individual bearing may yield, changing the effective stiffness value.The structural response for each of these cases will be calculated using computer analysis and compared with one another and also with a single-degree of freedom system. The results will be discussed at the end of this study

Damage-free seismic-resistant self-centering concentrically-braced frames

A self-centering concentrically-braced frame (SC-CBF) system was developed to resist earthquake loading without structural damage or residual drift. An SC-CBF is a concentrically-braced frame with column base details that permit column uplift at a specified level of lateral force. This column uplift and the subsequent rocking of the SC-CBF soften the lateral force-lateral drift behavior of the system. Vertically-oriented post-tensioning bars provide restoring force and self-centering behavior that reduces the potential for residual drift. The SC-CBF members are designed to remain elastic under the design basis earthquake. Energy dissipation elements can be used to reduce the response of the SC-CBF system. The scope of this study includes the development of a design procedure for SC-CBF systems, a parametric study of different SC-CBF configurations, analytical and experimental studies of a large-scale SC-CBF test structure, and evaluation of the performance of the SC-CBF test structure. A performance-based design procedure and the associated design criteria were developed for SC-CBF systems. Nonlinear dynamic analyses of several 6-story prototype buildings with different SC-CBF configurations were performed to establish the lateral force behavior of the system and to study the influence of several design parameters on this behavior. An analytical model was developed to predict the earthquake response of SC-CBF systems. Hybrid simulations of the earthquake response of a large-scale SC-CBF test structure were performed to validate the analytical model. The seismic performance of the SC-CBF test structure was evaluated with respect to the performance-based design approach and criteria. The results of this study indicate that the SC-CBF system performs very well under earthquake loading, and that the SC-CBF is a viable alternative to conventional CBF systems. The softening of the lateral force-lateral drift response of the system was due exclusively to the column uplift behavior; the beams, columns, and braces of the SC-CBF remained elastic. The performance of the SC-CBF test structure satisfied the performance-based design objectives and criteria. The analytical and experimental results presented in this dissertation show that the performance of the SC-CBF systems can be designed to achieve reliable damage-free performance under the design basis earthquake. The probability of structural damage and residual drift under the design basis earthquake is low. The proposed performance-based design procedure and associated design criteria provide conservative estimates of design demands and provide excellent overall performance. The analytical model developed by this research provides accurate estimates of the earthquake response of SC-CBF systems