BRIGE: Damage Evaluation and Life-Cycle Assessment of Reinforced HPFRC Beam-Column Joints under Multi-Axial Loading

技术描述尽管结构材料取得了重大进展，但钢筋混凝土(RC)建筑中的灾难性梁柱节点破坏在地震期间仍然是一个问题。钢筋混凝土节点的性能和破坏机理在过去已经得到了广泛的研究，并在简单的(平面)加载条件下得到了很好的理解。目前的实践告诉我们，增加节点的尺寸或钢筋的数量，以提高节点的能力，防止过早破坏。然而，这种做法肯定是不可持续的。此外，正如在最近的地震中观察到的那样，这种做法并不总是能防止节点区域的灾难性破坏，从而得出结论，节点在复杂(多轴)加载条件下的性能仍然没有得到很好的了解。在这个项目中，高性能纤维混凝土(HPFRC)将选择性地用于梁柱节点，以改善建筑的结构性能，同时将额外成本保持在最低限度。采用试验和计算相结合的方法，对钢筋混凝土和高性能钢纤维混凝土节点房屋进行对比损伤评估和全寿命周期成本评估。由于节点荷载传递的复杂性和材料在多轴荷载作用下的受力行为，节点分析是一项艰巨的任务。因此，将使用两个多轴(6个自由度)加载单元来对节点施加真实的加载和边界条件，并将使用用于非接触变形测量的数字图像相关系统(DIC)来获得全场三维应变图，以研究导致损伤的临界变形状态以及损伤的发展直到完全破坏。这些研究活动有望对RC和R-HPFRC节点的性能产生重要的新知识和理解，并为研究RC/加强型HPFRC材料和节点性能提供可靠的计算工具。该项目对社会的直接好处是改善了公共安全以应对地震。另一个好处是增加了可持续性，减少了直接和间接的经济损失和环境影响。该项目的成就将是朝着实现具有复原力和可持续的民用基础设施这一最终目标迈出的一大步。拟议的连接概念在其他类型的混凝土建筑中也具有广泛的适用性，包括海上和核结构。从这些新的测试和测量方法中收集的数据将作为开发数值建模和工程模拟的新理论的基准，以前由于缺乏支持实验数据而无法考虑这一点。扩大参与活动休斯顿大学(UH)是一所为拉美裔服务的机构。密歇根大学拥有近40,000名学生，是美国最多元化的学生之一。将在三门课程中开发和引入教育单元，以影响每年100多名学生的教育。由于校园固有的多样性，这些教育举措自然会接触到不同的受众。研究生和本科生将从代表性不足的群体中招聘。与当地一所学生人数不足90%以上的高中合作，每年将组织25名学生参观密歇根大学校园并参加实践培训。此外，每年夏天将招聘一名高中教师，以获得参与研究活动的机会，并帮助开发高中物理课程的课程模块。通过开展的教育活动，高中教师、高中生、本科生和研究生将有机会相互交流和学习。课程模块将直接从研究结果中衍生出来，并在高中和大学水平的课程中实施，从而自然地将研究和教育结合在一起。这项研究的资金来自工程教育和中心分部扩大工程参与计划的一部分--工程招揽中的扩大参与研究启动补助金。

Technical DescriptionDespite significant advances in structural materials, catastrophic beam-column joint failures in reinforced concrete (RC) buildings persist in being a problem during earthquakes. The behavior and failure mechanisms in RC joints have been extensively studied in the past and are well understood under simple (planar) loading conditions. Current practice tells us to increase the joint dimensions or the amount of reinforcing steel to enhance the capacity of the joints and prevent premature failure. However, this approach is definitely not sustainable. Additionally, as observed in recent earthquakes, this practice does not always prevent catastrophic failures in the joint region, leading to the conclusion that the behavior of joints under complex (multi-axial) loading conditions is still not well understood.In this project, high-performance fiber reinforced concrete (HPFRC) will be selectively used at the beam-column joints to improve the structural performance of buildings while keeping the additional costs at a minimum. Using experimental and computational methods, a comparative damage evaluation and life-cycle cost assessment of building with RC and HPFRC joints will be conducted. Analysis of joints is a difficult task because of the complex load transfer and the behavior of materials under multi-axial loading. Therefore, two multi-axial (6 degree-of-freedom) loading units will be used to impose realistic loading and boundary conditions on the joints, and a digital-image correlation system for non-contact deformation measurements (DIC) will be used to obtain full-field 3-D strain maps to study critical deformation states that lead to the initiation of damage as well as its progression until complete failure. These research activities are anticipated to yield critical new knowledge and understanding of the behavior of RC and R-HPFRC joints, and reliable computational tools to study the RC/reinforced-HPFRC material and joint behavior.Broader Significance and ImportanceThe proposed novel approach is expected to transform the design and construction of RC beam-column joints over the long-term. A direct benefit of this project to society is the improvement in public safety in response to earthquakes. An additional benefit is increased sustainability in the form of reduced direct and indirect economic losses and environmental impacts. The achievements in this project will be a large step in reaching the ultimate goal of resilient and sustainable civil infrastructures. The proposed joint concept also has broad applicability in other types of concrete construction, including offshore and nuclear structures. The data collected from these novel testing and measurement approaches will serve as benchmarks for the development of new theories for numerical modeling and engineering simulations, which could not be considered previously because of the lack of supporting experimental data.Broadening Participation ActivitiesThe University of Houston (UH) is a Hispanic-Serving Institution. The UH student body of nearly 40,000 students is one of the most diverse in the United States. Educational modules will be developed and introduced in three courses to influence the education of more than 100 students per year. Because of the inherent campus diversity, these educational initiatives will naturally reach a diverse audience. Graduate and undergraduate students will be recruited from underrepresented groups. In collaboration with a local high school with more than 90% underrepresented students, a field trip will be organized every year for 25 students to visit the UH campus and participate in hands-on training. In addition, one high school teacher will be recruited every summer to gain exposure to research activities and help develop a course module for high school physics courses. Through the developed education activities, high school teachers, high school students, and undergraduate and graduate students will have an opportunity to interact and learn from each other. The course modules will directly derive from the research findings and be implemented in high school and college level courses, thereby naturally integrating research and education.This research has been funded through the Broadening Participation Research Initiation Grants in Engineering solicitation, which is part of the Broadening Participation in Engineering Program of the Engineering Education and Centers Division.