Collaborative Research: Resilient Seismic Retrofit by Integrating Selective Weakening and Self-Centering

发生大地震事件的概率虽然很低，但风险很高。美国和世界各地的许多钢筋混凝土建筑都是在现代抗震设计规范实施之前建造的。根据美国以外的近代历史上的地震事件，如果类似的事件发生在人口密集的城市附近，预计美国将遭受重大的经济损失。减少经济损失、缩短恢复时间和恢复到正常运行水平至关重要，并确定了抵御地震灾害的弹性。 现有的抗震加固方法通过永久性破坏来实现生命安全。该项目将研究一种新的抗震改造方法，不仅关注公共安全，而且通过最大限度地减少损害来提高弹性。新的加固系统将适用于低于标准的钢筋混凝土剪力墙作为抗侧力系统的建筑物。低破坏确保建筑物在地震后的合理时间内可以保持运行和居住，同时与用传统方法改造的系统相比，将与建筑物相关的社会经济损失保持在最低限度。在没有额外的抗横向荷载系统的范围或预算的情况下，改造方法在建筑上也是有利的。教育、推广和技术转让活动将侧重于提高对复原力、多重灾害和新建筑技术的认识，以及增加代表性不足的群体在STEM中的参与。在该项目中，将研究一种新的抗震改造方法，该方法集成了选择性削弱、铰接墙和自动定心的概念，以实现低地震破坏。该方法的目标是改善钢筋混凝土剪力墙的性能，这些剪力墙在限制、横向钢筋和钢筋详图方面存在设计缺陷，这些缺陷与过去地震中的细长墙失效有关。改造方法将涉及通过在剪力墙-基础界面附近创建冷接缝（弱化）并添加无粘结外部后张应力，将传统和有缺陷的剪力墙转换为自定心墙。本研究的目的是了解基本响应的变化不足钢筋混凝土建筑物时，用这种方法进行改造。实现这一目标的研究方法将包括元件和系统级结构测试和分析。单元级研究将包括非线性分析建模和反向循环荷载下的加固剪力墙测试。这些研究将确定可行的改造细节和目标剪力墙缺陷。系统级调查将包括有限元和时程分析，以了解加固剪力墙与其他结构元件的相互作用，从而控制这些元件的损坏。通过这种改造方法可以实现的性能增强将使用可靠性概念进行量化。这项工作将通过非线性分析、测试和脆弱性研究，在能力、滞后响应和自定心能力方面对用这种方法改造的建筑系统有一个基本的了解。这项研究的结果也将有可能推进新建造的自定心结构的最新技术水平。项目成果将产生新的基本知识，用于改造有缺陷的混凝土墙，并在地震区开发更具弹性的建筑物，从而为美国和世界各地的地震灾害减轻做出贡献。项目数据将在NHERI数据库https://www.designsafe-ci.org/上提供。

The occurrence of a major seismic event, although low in probability, carries high risk. Many reinforced concrete buildings in the United States and around the world were built before the implementation of modern seismic design codes. Based on seismic events of recent history outside the United States, significant economic losses can be expected in the United States if similar events occur near densely populated cities. Reducing economic losses, shortening time to recovery, and returning to normal operation levels are essential and define resiliency against seismic hazard. Existing seismic retrofit methods achieve life safety through permanent damage. This project will investigate a new seismic retrofit method which focuses on not only public safety but also on resiliency by minimizing damage. The new retrofit system will be applicable to buildings with sub-standard reinforced concrete shear walls as the lateral load resisting system. Low damage ensures that buildings can remain operational and habitable within a reasonable amount of time following an earthquake, while keeping the socio-economic losses related to the building stock to a minimum compared to systems retrofitted with traditional methods. The retrofit method can also be architecturally advantageous for cases where the scope or budget for additional lateral load resisting systems is not available. Education, outreach, and technology transfer activities will focus on raising awareness about resiliency, multiple hazards, and new building technologies, as well as increasing participation of underrepresented groups in STEM. In this project, a new seismic retrofit method, integrating the concepts of selective weakening, hinged walls, and self-centering, will be investigated to achieve low seismic damage. The method will be targeted toward improving the performance of reinforced concrete shear walls that have design deficiencies related to confinement, transverse reinforcement, and reinforcement detailing, which have been associated with slender wall failures in past earthquakes. The retrofit method will involve converting traditional and deficient shear walls into self-centering walls by creating a cold joint near the shear wall-foundation interface (weakening) and adding unbonded external post-tensioning. The objective of this research is to understand the change in fundamental response of deficient reinforced concrete buildings when retrofitted with this method. Research methods to achieve this objective will include element and system level structural testing and analysis. Element level studies will include nonlinear analytical modeling and testing of retrofitted shear walls under reverse cyclic loading. These studies will identify viable retrofit details and target shear wall deficiencies. System level investigations will include finite element and time-history analyses to understand the interaction of retrofitted shear walls with other structural elements to control damage to these elements. Performance enhancement that can be achieved by this retrofit method will be quantified using reliability concepts. This work will create a fundamental understanding of building systems retrofitted with this method in terms of capacity, hysteretic response, and self-centering capability through nonlinear analyses, testing, and fragility studies. The findings of this research also will have the potential to advance the state-of-the-art of self-centering structures that are newly constructed. Project outcomes will produce new basic knowledge needed to retrofit deficient concrete walls and develop more resilient buildings in seismic regions and thus contribute to seismic hazard mitigation in the United States and around the world. Project data will be made available in the NHERI Data Depot at https://www.designsafe-ci.org/.