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The need to maintain the functionality of critical transportation lifelines after a large seismic event motivates the strategy to design certain bridges for performance standards beyond the minimum required by bridge design codes. To design a bridge to remain operational, one may stiffen and strengthen the load carrying members to increase the capacity, or alternatively use response modification devices such as seismic isolators to shift the dynamic characteristics of the bridge, henceforth reducing the seismic demands. Seismic isolation systems are attractive because they are directly conducive to accelerated bridge construction techniques. The two strategies are compared for a typical Utah highway bridge, using a three-span, pre-stressed concrete girder bridge that crosses Legacy Highway as a case study example.
"TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 440, Performance-Based Seismic Bridge Design (PBSD) summarizes the current state of knowledge and practice for PBSD. PBSD is the process that links decision making for facility design with seismic input, facility response, and potential facility damage. The goal of PBSD is to provide decision makers and stakeholders with data that will enable them to allocate resources for construction based on levels of desired seismic performance"--Publisher's description.
This edition is based on the work of NCHRP project 20-7, task 262 and updates the 2nd (1999) edition -- P. ix.
This volume gathers the proceedings of the 17th World Conference on Seismic Isolation (17WCSI), held in Turin, Italy on September 11-15, 2022. Endorsed by ASSISi Association (Anti-Seismic Systems International Society), the conference discussed state-of-the-art information as well as emerging concepts and innovative applications related to seismic isolation, energy dissipation and active vibration control of structures, resilience and sustainability. The volume covers highly diverse topics, including earthquake-resistant construction, protection from natural and man-made impacts, safety of structures, vulnerability, international standards on structures with seismic isolation, seismic isolation in existing structures and cultural heritage, seismic isolation in high rise buildings, seismic protection of non-structural elements, equipment and statues. The contributions, which are published after a rigorous international peer-review process, highlight numerous exciting ideas that will spur novel research directions and foster multidisciplinary collaboration among different specialists.
The improved seismic performance and cost-effectiveness of two innovative performance-enhancement technologies in typical reinforced concrete bridge construction in California were assessed in an analytical and experimental study. The technologies considered were lead rubber bearing isolators located underneath the superstructure and fiber-reinforced concrete for the construction of bridge piers. A typical five-span, single column-bent reinforced concrete overpass bridge was redesigned using the two strategies and modeled in OpenSees finite element program. Two alternative designs of the isolated bridge were considered; one with columns designed to remain elastic and the other such that minor yielding occurs in the columns (maximum displacement ductility demand of 2). The analytical model of the fiber-reinforced concrete bridge columns was calibrated using the results from two bidirectional cyclic tests on approximately 0¼-scale circular cantilever column specimens constructed using concrete with a 1.5% volume fraction of high-strength hooked steel fibers, relaxed transverse reinforcement, and two different longitudinal reinforcement details for the plastic hinge zone. Pushover and nonlinear time history analyses using 140 ground motions were carried out for the different bridge systems. The PEER performance-based earthquake engineering methodology was used to compute the post-earthquake repair cost and repair time of the bridges. Fragility curves displaying the probability of exceeding a specific repair cost and repair time thresholds were developed. The total cost of the bridges included the cost of new construction and post-earthquake repair cost required for a 75 year design life of the structures. The intensity-dependent repair time model for the different bridges was computed in terms of crew working days representing repair efforts. A financial analysis was performed that accounted for a wide range of discount rates and confidence intervals in the estimation of the mean annual post-earthquake repair cost. Despite slightly higher initial construction costs, considerable economic benefits and structural improvements were obtained from the use of the two performance-enhancement techniques considered, in comparison to the fixed-base conventionally reinforced concrete bridge, especially seismic isolation. The isolation of the bridge superstructure resulted in a significant reduction in both column and abutment displacement and force demands. The repair time of the isolated bridges was also significantly reduced, leading to continuous operation of the highway systems and reduced indirect economic losses. The experimental and analytical results also demonstrated that the use of fiber-reinforced concrete to build bridge columns leads to improved damage-tolerance, shear strength, and energy dissipation under cyclic loading compared to conventional reinforced concrete columns. These improvements result in better seismic performance and lower total 75-year cost of the fiber-reinforced column bridges.
Over the last five decades, remarkable progress has been achieved in the field of earthquake engineering, especially in the following areas: seismic design philosophy, earthquake protective systems, seismic design and performance evaluation of structures, and theory of structural optimization. The progress achieved and products developed in these areas can be integrated to develop a desired computer-aided optimum structural design framework. Accordingly, a probabilistic performance-based optimum seismic design (PPBOSD) framework is proposed and first illustrated and validated on a simplified single-degree-of-freedom (SDOF) bridge model optimized (i.e., rated) for a target seismic loss hazard curve. The feasibility and optimality of seismic isolation is investigated for a California High-Speed Rail (CHSR) prototype bridge testbed using the proposed PPBOSD framework, balancing the beneficial and detrimental effects of seismic isolation for such a bridge. Towards this goal, a three-dimensional detailed nonlinear finite element model of the CHSR prototype bridge, including soil-pile-structure interaction and rail-structure interaction, is developed in OpenSees. The seismic response of the isolated bridge is compared to that of the corresponding non-isolated bridge both in deterministic and probabilistic terms. A comprehensive parametric probabilistic demand hazard analysis is carried out to investigate the effects of the seismic isolator properties on the seismic risk of the CHSR prototype bridge. To enable the computationally intensive probabilistic seismic response analyses, a cloud-based optimization framework was used integrating cloud computing resources with the high throughput computing in PPBOSD methodology. Furthermore, some well-posed practical optimization problems are formulated and investigated for seismic isolation in CHSR bridges. In summary, the unique contributions and findings are summarized as follows : (1) A PPBOSD framework is proposed, illustrated, and validated using a nonlinear SDOF bridge model; (2) Compared to a non-isolated bridge, the seismic isolation increases the deck displacement and rail stress demands, while it reduces the seismic demand in the bridge substructure in both the deterministic and probabilistic sense; (3) A cloud-based computing platform is developed for PPBOSD to address the high computational cost; (4) The feasibility and optimality of seismic isolation for the prototype bridge is achieved using the PPBOSD framework, reaching various performance objectives considering the relevant sources of uncertainty.