NEESR: Collaborative Developments for Seismic Rehabilitation of Vulnerable Braced Frames

钢中心支撑框架（CBF）具有刚度大、强度高的特点，是一种有效的抗震体系。 现代CBF抗震设计始于1988年的重大规范变更，与旧CBF（分类为非抗震CBF或NCBF）不同，因为NCBF的设计没有考虑支撑行为或能力设计原则。在高地震活动地区，数千个NCBF仍在使用。 在低和中等地震活动的地区，这些系统仍在建设中。 对NCBF清单的粗略审查表明，支撑和连接各不相同，并且有很大的可能出现不必要的和脆弱的响应模式。 对这些系统的研究在文献中基本上是缺席的。总的来说，这些系统既普遍又不可预测，使得这类抗侧向力系统成为一种严重的地震危险。该研究项目将促进NCBF的评估和康复。大规模的实验将使用乔治E。小布朗加州大学伯克利分校的地震工程模拟网络（NEES）设施，用于模拟现有和修复的多层NCBF。实验结果将提供高分辨率的数据，支持非线性模拟的NCBFs。实验和模拟的集成将提供有关系统性能的关键信息，识别漏洞，并通知改造要求。已查明的不足之处将通过改造计划加以解决，改造计划的基础是在以前由国家科学基金会支持的NEES研究项目中调查的创新康复战略，其数据可通过NEES项目仓库/数据储存库（http：//www.example.com）获得。www.nees.org 预定研究的改造类别包括使用创新的支撑和支撑系统，柱提升和摇摆，以及与更换和现有组件平衡的连接设计。这些策略将在大规模综合多层测试的第二阶段与现有框架集成，设计将从非线性分析模拟和存档的NEES项目仓库数据中获得信息。实验的最后阶段将使用先进的混合模拟来研究整个建筑。 在较旧的建筑中，地震反应可能更严重地依赖于重力框架。这个最终的实验将研究一个部分改造的NCBF建筑，这可能是一个经济的选择，以满足在许多情况下的防倒塌性能的目标，非改造的NCBF在计算机中模拟和改造的NCBF和重力框架进行了模拟实验。这项研究将产生独特的数据，以支持这些地震脆弱系统的评估和改造。 这个奖项是由来自华盛顿大学、加州大学伯克利分校、国立台湾大学和美国钢结构研究所的研究人员合作颁发的。 该项目的数据将通过NEES项目仓库/数据库存档并向公众提供。总体而言，研究结果将改变对NCBFs的理解并促进其康复策略。研究结果将为验证和推进NCBF评估和修复的工程方法提供重要的发现。具体的工具，将开发使用的研究数据，包括验收标准，骨干曲线和崩溃的NCBFs和改造NCBFs的利润率。该项目还将通过研究过程促进学生的学习和接触。来自代表性不足群体的高中生将被选为夏季研究实习生，以帮助与西雅图数学、工程和科学成就项目合作进行实验研究。 研究结果也将被纳入高级课程，使用高级跨类项目的地震评估和改造的NCBF建筑作为中央学习工具。建筑物的分析将在高级结构分析课程中进行。单个构件的分析将是钢结构设计课程中项目的重点。改造后的系统将在顶点设计班设计，在学生的高年级春季授课。技术转让将通过网络研讨会和帮助传播成果的多元化行业联盟来实现。该奖项是国家减少地震灾害计划（NEHRP）的一部分。

Steel concentrically braced frames (CBFs) are stiff and strong, making them efficient seismic load resisting systems. Modern CBF seismic design was initiated with significant code changes in 1988 and is differentiated from older CBFs (classified as non-seismic CBFs or NCBFs) because NCBFs were designed without consideration of the brace behavior or capacity-design principles. In regions of high seismicity, thousands of NCBFs remain in service. In regions of low and moderate seismicity, these systems are still being constructed. A cursory review of the NCBF inventory indicates that braces and connections vary, and there is a large potential for unwanted and brittle response modes. Research into these systems is largely absent from the literature. Taken together, these systems are both widespread and unpredictable, making this category of lateral force resisting system a critical seismic hazard. This research project will advance evaluation and rehabilitation of NCBFs. Large-scale experimentation will be conducted using the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES) facility at the University of California, Berkeley, to simulate existing and rehabilitated multi-story NCBFs. The experimental results will provide high-resolution data to support nonlinear simulation of NCBFs. The integration of the experiments and simulations will provide key information about the system performance, identify vulnerabilities, and inform the retrofit requirements. The identified deficiencies will be addressed through retrofit schemes based on innovative rehabilitation strategies investigated in prior NSF-supported NEES research projects, whose data is available through the NEES Project Warehouse/data repository (http://www.nees.org). Retrofit categories slated for study include use of innovative braces and bracing systems, column uplift and rocking, and connection designs balanced with the replaced and existing components. These strategies will be integrated with the existing frames in the second phase of the large-scale, integrated multi-story testing, with the design informed from nonlinear analytical simulation and archived NEES Project Warehouse data. The final phase of the experimentation will study a full building using advanced hybrid simulation. In older construction, the seismic response may depend more heavily on the gravity frames. This culminating experiment will study a partially retrofitted NCBF building which may be an economical option to meet a collapse prevention performance objective in many cases; the non-retrofitted NCBFs are simulated in the computer and the retrofitted NCBFs and gravity frames are simulated experimentally. The research will result in unique data to support the evaluation and retrofit of these seismically vulnerable systems. This award is a collaboration among researchers from the University of Washington, University of California, Berkeley, National Taiwan University, and the American Institute of Steel Construction. Data from this project will be archived and made available to the public through the NEES Project Warehouse/data repository.As a whole, the research results will transform the understanding of and facilitate rehabilitation strategies for NCBFs. The results will provide important findings to validate and advance engineering approaches for NCBF evaluation and rehabilitation. Specific tools that will be developed using the research data include acceptance criteria, backbone curves, and collapse margin ratios for both NCBFs and retrofitted NCBFs. The project will also advance student learning and exposure through the research process. High school students from underrepresented groups will be selected for summer research internships to aid in the experimental research in collaboration with the Seattle Mathematics, Engineering and Science Achievement program. The research results will also be integrated into the senior level curriculum, using a senior-level cross-class project on seismic evaluation and retrofit of a NCBF building as the central learning tool. Analysis of the building will be conducted in the senior-level structural analysis class. Analysis of the individual components will be the focus of the project in the structural steel design class. The retrofitted system will be designed in the capstone design class, taught in the spring of the students' senior year. Technology transfer will be achieved through webinars and a diverse industry coalition who will help disseminate results. This award is part of the National Earthquake Hazards Reduction Program (NEHRP).