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

重大地震事件的发生，虽然概率很低，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。根据美国以外地区近期发生的地震事件，如果类似事件发生在人口稠密的城市附近，预计美国将遭受重大经济损失。减少经济损失、缩短恢复时间和恢复正常运行水平是至关重要的，并定义了对地震风险的恢复能力。现有的抗震加固方法通过永久性破坏来实现生命安全。本项目将研究一种新的抗震加固方法，该方法不仅注重公共安全，而且注重通过将损害降至最低来恢复能力。新的加装体系将适用于具有不合标准的钢筋混凝土剪力墙的建筑，作为抗侧向荷载体系。低损害确保建筑物在地震后的合理时间内能够继续运行和居住，同时与用传统方法翻新的系统相比，将与建筑物存量有关的社会经济损失保持在最低限度。在无法提供额外的横向载荷抵抗系统的范围或预算的情况下，改装方法在结构上也是有利的。教育、外联和技术转让活动将侧重于提高人们对复原力、多重危险和新建筑技术的认识，以及增加代表不足的群体在STEM中的参与。在本项目中，将研究一种新的抗震加固方法，融合了选择性弱化、铰接墙和自定心的概念，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，这些剪力墙在约束、横向钢筋和钢筋细节方面存在设计缺陷，在过去的地震中，这些缺陷与细长墙的破坏有关。改造方法将包括通过在剪力墙-基础界面附近建立冷连接(弱化)和增加无粘结的外部后张法，将传统的和不足的剪力墙改造成自定心墙。本研究的目的是了解钢筋混凝土缺陷建筑物在采用这种方法改造后的基本反应的变化。实现这一目标的研究方法将包括元件和系统级的结构测试和分析。单元水平的研究将包括在反向循环荷载作用下对加装剪力墙进行非线性分析建模和试验。这些研究将确定可行的加装细节，并针对剪力墙的缺陷。系统层面的研究将包括有限元和时程分析，以了解加装剪力墙与其他结构构件的相互作用，以控制对这些构件的破坏。通过这种改装方法可以实现的性能改进将使用可靠性概念进行量化。这项工作将通过非线性分析、试验和易损性研究，对采用该方法加固的建筑体系在承载能力、滞回反应和自定心能力方面有一个基本的理解。这项研究的发现也将有可能推动新建造的自我中心结构的最新技术。项目成果将产生改造有缺陷的混凝土墙和在地震区开发更具弹性的建筑所需的新的基本知识，从而有助于在美国和世界各地减轻地震灾害。项目数据将在位于https://www.designsafe-ci.org/.的NHERI数据仓库中提供

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/.