NEESR-II Large-scale testing and micromechanical simulation of ultra-low-cycle fatigue cracking in steel structures

NEESR-II 钢结构超低周疲劳裂纹大规模试验与微观力学模拟

• 批准号: 0421492
• 负责人: Amit Kanvinde
• 金额: --
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-11-15 至 2009-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0421492&HistoricalAwards=false
• 关键词: NEESR; II; Large; scale; testing

Cyclic inelastic deformations are the primary mode of seismic energy dissipation in steel structures. During earthquakes, beam-column moment connections undergo a phenomena called Ultra-Low Cycle Fatigue (ULCF), which is characterized by very few (10-20) large strain cycles. ULCF is quite distinct from low cycle fatigue, which has been more widely studied but does not address the conditions prevalent in seismic design. Relatively little attention has been given to characterizing the fundamental failure mechanisms associated with ULCF, due to the lack of suitable micro-scale models to simulate ULCF and the computational requirements necessary implement the models for studying large structural components. Existing research on ULCF of steel structures in earthquakes relies almost exclusively on semi-empirical methods, which cannot be transferred to varied structural configurations. Moreover, most of the existing empirical research is based on quasi-static testing, which does not account for earthquake loading rate effects. Such knowledge gaps represent serious issues for seismic hazard mitigation. The proposed research aims to (1) identify and quantify the underlying failure mechanisms of earthquake-induced ULCF, (2) develop and implement models to simulate ULCF in steel structures (3) conduct large scale subassembly tests at earthquake loading rates to verify and demonstrate the models (4) apply the ULCF models to develop practical guidelines and recommendations for earthquake resistant design. A recent study by the PI and his collaborator at Stanford succeeded in developing some of the first micromechanical models for predicting earthquake-induced ULCF crack initiation in steel structures. Based on these initial advances, the proposed study will integrate micromechanics concepts with advanced simulation techniques and parallel-computing to realistically simulate fundamental fatigue-fracture processes in steel structures. The first phase of the research will include integrated testing and analyses of welded components to calibrate the material properties in the micromechanical models. The second phase will use the fast hybrid testing facility at NEES Colorado to test full-scale welded steel connections results of which will be used to validate micromechanical simulations for predicting ULCF fractures. The third phase will use the micromechanical model-based simulation framework to address unresolved practical problems of interest to the design and construction industry, e.g. the initiation and propagation of ductile fractures in welded steel construction. Intellectual Merit of the Proposed Research: This research will develop powerful tools to model crack initiation and propagation at a very fundamental level in structural steel components under earthquake loading effects. The research will substantially advance the state of knowledge in fracture/fatigue mechanics and effectively demonstrate the power of micro-scale modeling for addressing important earthquake engineering problems. This will have both a positive effect on simulation practices in general and the migration towards a more extensive model-based simulation environment. Consistent design recommendations based on the simulations will address important detailing issues and mitigate earthquake hazard. The research will utilize the fast hybrid testing facility at NEES-Colorado, and the research team is committed to free sharing of data, simulation models, and other information through the NEESgrid and publication in refereed journals. Broader Impact of Proposed Research: This research will have a significant impact on the state of the art in earthquake fatigue mechanics, model based simulation, and design guidelines to protect against ULCF in earthquakes. Involving expertise from structural engineering, materials and computational science, this research will promote interdisciplinary technology transfer and collaboration between the between the two participating schools and the NEES site at CU-Boulder. An educational impact of this study will include the education of two doctoral students, one each at UC Davis and Stanford. Moreover, the PI and the co-PI are both responsible for teaching steel design classes at UC Davis and Stanford, which provide a natural educational opportunity for students to become engaged in the research through the NEES teleparticipation and database facilities. The project team is committed to involving under-represented groups in research and will collaborate with on campus engineering diversity programs to achieve these aims.

环状非弹性变形是钢结构中地震能量耗散的主要模式。在地震期间，光束柱的连接经历了一种称为超低循环疲劳（ULCF）的现象，该现象的特征很少（10-20）大应变周期。 ULCF与低周期疲劳完全不同，该疲劳已经进行了更广泛的研究，但并未解决地震设计中普遍存在的条件。由于缺乏合适的微尺度模型来模拟ULCF，并且计算要求实现了研究大型结构组件的模型，因此很少关注与ULCF相关的基本故障机制。关于地震中钢结构ULCF的现有研究几乎完全依赖于半经验方法，这些方法不能转移到各种结构构型中。此外，大多数现有的经验研究都是基于准静态测试的，该测试无法解释地震载荷率效应。这些知识差距代表了缓解地震危害的严重问题。拟议的研究旨在（1）识别和量化地震引起的ULCF的潜在失败机制，（2）开发和实施模型以模拟钢结构中的ULCF（3）在地震载荷速率上进行大规模的子组装测试，以验证和证明并证明模型（4）应用ULCF模型来制定抗震设计的实用指南和建议。 PI及其在斯坦福大学合作者最近的一项研究成功地开发了一些微型机械模型，用于预测地震诱导的钢结构中的ULCF裂纹启动。基于这些最初的进步，拟议的研究将将微力学概念与先进的仿真技术和平行计数相结合，以实际模拟钢结构中的基本疲劳 - 骨折过程。该研究的第一阶段将包括对焊接组件的集成测试和分析，以校准微机械模型中的材料特性。第二阶段将使用NEES Colorado的快速混合测试设施来测试全尺度焊接钢连接结果，该结果将用于验证微机械模拟以预测ULCF骨折。第三阶段将使用基于微机械模型的仿真框架来解决设计和建筑行业感兴趣的实践问题，例如焊接钢结构中延性裂缝的启动和繁殖。 拟议研究的智力优点：这项研究将开发出强大的工具，以在地震负载效应下在结构钢组件的非常基本的层面上建模裂纹启动和传播。这项研究将大大推动裂缝/疲劳力学方面的知识状态，并有效地证明了微观建模在解决重要地震工程问题方面的力量。 这将对一般的仿真实践和向更广泛的基于模型的仿真环境的迁移产生积极影响。基于模拟的一致设计建议将解决重要的细节问题并减轻地震危害。该研究将利用NEES-Colorado的快速混合测试设施，研究团队致力于通过Neesgrid和Curered Journals中的Neesgrid和出版物免费共享数据，仿真模型和其他信息。 拟议研究的更广泛的影响：这项研究将对地震疲劳力学，基于模型的模拟和设计指南，以防止地震中的ULCF产生重大影响。涉及结构工程，材料和计算科学的专业知识，这项研究将促进两家参与学校与Cu-Boulder的NEES网站之间的跨学科技术转移和协作。 这项研究的教育影响将包括对两名博士生的教育，一位在加州大学戴维斯分校和斯坦福大学。此外，PI和Co-Pi都负责在加州大学戴维斯分校和斯坦福大学教授钢设计课程，这为学生提供了通过NEES远程推理和数据库设施进行研究的自然教育机会。项目团队致力于使代表性不足的小组参与研究，并将与校园工程多样性计划合作以实现这些目标。