Seismic risk assessment and mitigation of critical structures

近年来，结构抗震设计的趋势是向基于性能的设计理念发展，即要求设计结构具有预留的强度和位移能力，以满足特定的期望性能水平，如生命安全、即时占用和不间断的连续运行。相比之下，按照规定的基于规范的程序设计的结构的保护水平只是定性的假设。作为实现基于性能的结构抗震设计的一种尝试，假定结构反应指标(如层间位移、非弹性杆件内力和变形)的规范性规定与基于性能的设计准则之间的关系经过一定的校核。这种将现有的说明性代码为基础的设计过程改编为基于性能的设计的方法存在有效性不确定的缺点。目前的校准程序一般根据个别部件的需求和能力来评估性能，而不一定是根据全球结构行为来评估。另一个问题是，工程需求的校准主要是使用不能代表结构的真实极限行为的分析模型来确定的。在部件和系统层面上，计算的需求和真实的结构性能之间缺乏准确的校准。本文提出了一项研究计划，旨在开发先进的地震风险评估方法和工具，以更准确地评估关键桥梁的抗震性能，并开发降低混凝土剪力墙地震风险的创新技术。该研究计划的长期目标是加强加拿大关键基础设施的安全保障，促进基于性能的地震工程的发展和进步，以及设计更安全、更抗损失的基础设施。研究计划分为分析和试验方法两大部分：(I)地震建模和分析，以及桥梁清单的风险评估；(Ii)钢筋混凝土剪力墙结构的地震修复和加固。这一研究将有助于首次全面了解桥梁的渐进倒塌行为。它将为工程师提供工具，将危险结构与那些会倒塌但不会倒塌的结构区分开来，从而帮助解决加拿大破旧桥梁的昂贵更新问题。例如，一座部分受损的桥梁可能仍有能力作为紧急通道桥梁用于疏散目的，而不需要昂贵的翻新。评估工具将非常有助于确定优先顺序和分配有限的资源，以减少现有桥梁库存的地震风险。

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.