Seismic risk assessment and mitigation of critical structures

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In recent years, the trend in earthquake resistant design of structures has been moving towards a performance-based design concept in which the design structure is required to have the reserved strength and displacement capacities to meet a specific desired level of performance, such as life safety, immediate occupancy and uninterrupted continuous operation. In comparison, the level of protection of structures designed following the prescriptive code-based procedures is only qualitatively assumed. As an attempt to realize performance-based seismic design of structures, relationships between prescriptive code provisions in the context of structural response indexes, such as inter-storey drifts, inelastic member forces and deformations, and the performance-based design criteria are assumed following some calibration process. This approach of adapting the existing prescriptive code-based design procedures towards performance based design has the shortcoming that its validity is uncertain. The current calibration procedures generally evaluate performance on the basis of the demands and capacities of individual components, and not necessarily at global structural behaviour. Another problem is that calibration of the engineering demands is determined primarily using analysis models not representative of the true ultimate behaviour of the structures. Accurate calibrations between calculated demands and true structural performance at both component and system level are lacking. A research program is proposed herein to develop advanced seismic risk assessment methodology and tools for more accurate evaluation of the seismic performance of critical bridges, and innovative techniques for mitigation the seismic risk of concrete shear walls. The long-term goal of the research program is to enhance the safety and security of Canada's critical infrastructures, to contribute toward the development and advances of performance-based earthquake engineering and design of safer and more loss-resistant infrastructures. The research program is divided into two broad components of analytical and experimental approaches: (i) Seismic modeling and analysis, and risk assessment of bridge inventories; (ii) Seismic repair and strengthening of reinforced concrete shear wall structures. The research will facilitate a comprehensive understanding of the progressive collapse behaviour of bridges for the first time. It will help to tackle the very costly renewal problem of Canada's deteriorated bridges by giving engineers tools to distinguish dangerous structures from those that will fail but not collapse. For example, a partially damaged bridge may still have the capacity to function as an emergency route bridge for evacuation purposes without the need for costly retrofit. The assessment tools will be very useful for prioritizing and allocation of limited resources for reducing the seismic risk of existing bridge inventory.