Collaborative Research: Simulating Crack Propagation in Steel Structures Under Ultra-Low Cycle Fatigue and Low-Triaxiality Loading from Earthquakes and Other Hazards

建筑物、隧道、公用管道和其他钢制结构是国家民用基础设施的重要组成部分。正如以往灾难中所经历的那样，例如 1994 年加利福尼亚州北岭地震，钢结构很容易倒塌或失效，从而导致生命和财产损失。这些结构关键部分的开裂（即断裂）通常是其失效的原因。 因此，设计结构以尽量减少断裂风险对于基础设施的安全和可操作性至关重要。然而，预测裂纹扩展的方法尚不成熟，特别是当地震或其他极端载荷引起的剧烈震动期间发生断裂时。通过结合结构工程、材料科学和计算力学的专业知识，本研究的目标是：(1) 创建新模型和计算技术来准确模拟此类裂缝，以及 (2) 将这些模型集成到土木基础设施的设计过程中。本科生和研究生将积极参与这项研究。 这项研究的新知识、模型和软件产品，通过转移给从业者，将提高建筑物和其他民用基础设施的安全性和经济性，造福美国社会和经济。非线性分析是现代基于性能的建筑和民用基础设施设计和施工的一项重要技术，这些建筑和民用基础设施对地震和其他极端灾害的抵御能力更强。这项研究解决了非线性分析的一个重大局限性，因为它涉及在两种重要情况下模拟钢结构中的裂纹扩展：(1) 超低周疲劳 (ULCF) 载荷，其特征是在地震和其他灾害下可能发生的几个 (20) 个大应变振幅周期；(2) 低应力三轴性，通常在剪切带或结构元件的突出角处发生 ULCF 载荷。本研究将通过基础理论模型开发（一种基于 ULCF 和低三轴度的新损伤力学本构模型）、计算方法综合、数值实现、实验室测试以及模型实现的校准和验证来解决这些挑战。这项工作将把延性裂纹萌生模型与计算技术相结合，形成在 ULCF 和低三轴度下模拟裂纹扩展的有效方法。该项目最终将推动一场促进断裂模拟技术应用于工程研究和实践的活动，包括实现其所需的模拟和校准方法的标准化，以及开源软件的开发。这些研究产品及其在工程实践中的采用将提高建筑环境的安全性和性能。

Buildings, tunnels, utility pipelines, and other structures constructed of steel are critical components of the nation's civil infrastructure. As experienced during previous disasters, such as in the 1994 Northridge, California earthquake, steel structures are vulnerable to collapse or failure, resulting in loss of life and property. Cracking (i.e., fracture) in critical parts of these structures is often the reason for their failure. Consequently, designing structures to minimize the risk of fracture is critical for infrastructure safety and operability. However, methods to predict the growth of cracks are not well-developed, especially when fractures occur during severe shaking caused by earthquakes or other extreme loads. By combining expertise from structural engineering, materials science, and computational mechanics, the objectives of this research are to: (1) create new models and computational technologies to accurately simulate this type of cracking, and (2) integrate these models into the design process for civil infrastructure. Undergraduate and graduate students will actively participate in this research. The new knowledge, models, and software products from this research, through transfer to practitioners, will improve the safety and economy of buildings and other civil infrastructure, benefiting the U.S. society and economy. Nonlinear analysis is an essential technology for the modern performance-based design and construction of buildings and civil infrastructure that are more resilient to earthquakes and other extreme hazards. This research addresses a significant limitation of nonlinear analysis as it pertains to simulating crack propagation in steel structures, under two important situations: (1) ultra-low cycle fatigue (ULCF) loading, which is characterized by few (20) cycles of large strain amplitude that can occur under earthquakes and other hazards, and (2) low-stress triaxiality, which often occurs with ULCF loading in shear bands or at protruding corners of structural elements. This research will address these challenges through fundamental theoretical model development (a new damage mechanics based constitutive model for ULCF and low-triaxiality), computational methods synthesis, numerical implementation, laboratory testing, and calibration and validation of model implementations. The work will combine models for ductile crack initiation with computational techniques, resulting in validated approaches for simulating crack propagation under ULCF and low-triaxiality. The project will culminate in a campaign to facilitate adoption of the fracture simulation techniques into engineering research and practice, including standardization of simulation and calibration methods required for their realization, and development of open source software. These research products and their adoption into engineering practice will enhance safety and performance of the built environment.