Quantitative and qualitative assessment of the seismic risk to highway bridges is crucial in pre-earthquake planning, and post-earthquake response of transportation systems. Such assessments provide valuable knowledge about a number of principal effects of earthquakes such as traffic disruption of the overall highway system, impact on the regions' economy and post-earthquake response and recovery, and more recently serve as measures to quantify resilience. Unlike previous work, this study captures unique bridge design attributes specific to California bridge classes along with their evolution over three significant design eras, separated by the historic 1971 San Fernando and 1989 Loma Prieta earthquakes (these events affected changes in bridge seismic design philosophy). This research developed next-generation fragility curves for four multispan concrete bridge classes by synthesizing new knowledge and emerging modeling capabilities, and by closely coordinating new and ongoing national research initiatives with expertise from bridge designers. A multi-phase framework was developed for generating fragility curves, which provides decision makers with essential tools for emergency response, design, planning, policy support, and maximizing investments in bridge retrofit. This framework encompasses generational changes in bridge design and construction details. Parameterized high-fidelity three-dimensional nonlinear analytical models are developed for the portfolios of bridge classes within different design eras. These models incorporate a wide range of geometric and material uncertainties, and their responses are characterized under seismic loadings. Fragility curves were then developed considering the vulnerability of multiple components and thereby help to quantify the performance of highway bridge networks and to study the impact of seismic design principles on the performance within a bridge class. This not only leads to the development of fragility relations that are unique and better suited for bridges in California, but also leads to the creation of better bridge classes and sub-bins that have more consistent performance characteristics than those currently provided by the National Bridge Inventory. Another important feature of this research is associated with the development of damage state definitions and grouping of bridge components in a way that they have similar consequences in terms of repair and traffic implications following a seismic event. These definitions are in alignment with the California Department of Transportation's design and operational experience, thereby enabling better performance assessment, emergency response, and management in the aftermath of a seismic event. The fragility curves developed as a part of this research will be employed in ShakeCast, a web-based post-earthquake situational awareness application that automatically retrieves earthquake shaking data and generates potential damage assessment notifications for emergency managers and responders. / Errata added at request of advisor and approved by Graduate Office, March 15 2016.

There is a great amount of building stock built in earthquake regions where earthquakes frequently occur. It is very probable that such buildings experience earthquakes more than once throughout their economic life. The motivation of this thesis arose from the lack of procedures to determine the change in building capacity as a result of prior earthquake damage. This study focuses on establishing a method that can be employed to determine the loss in the building capacity after experiencing an earthquake. In order to achieve this goal a number of frames were analyzed under several randomly selected earthquakes. Nonlinear time-history analyses and nonlinear static analyses were conducted to assess the prior and subsequent capacities of the frames under consideration. The structural analysis programs DRAIN-2DX and SAP2000 were employed for this purpose. The capacity curves obtained by these methods were investigated to propose a procedure by which the capacity of previously damaged structures can be determined. For time-history analyses the prior earthquake damage can be taken into account by applying the ground motion histories successively to the structure under consideration. In the case of nonlinear static analyses this was achieved by modifying the elements of the damaged structure in relation to the plastic deformation they experience. Finally a simple approximate procedure was developed using the regression analysis of the results. This procedure relies on the modification of the structure stiffness in proportion to the ductility demand the former earthquake imposes. The proposed procedures were applied to an existing 3D building to validate their applicability.