NEESR-II: Inelastic Web Crushing Performance Limits of High-Strength-Concrete Structural Walls

NEESR-II：高强混凝土结构墙的非弹性腹板压碎性能极限PI：Rigoberto Burgueno，密歇根州立大学；Co-PI：Eric M.Hines，塔夫茨大学动力与应用范围：通过使用高强混凝土并将延性剪切破坏作为一种新的延性破坏机制类型，在中等地震区的结构墙中显著减轻构件是一种可行的可能性。近年来，对空心桥墩抗震设计的研究为准确评估有边界单元的结构墙体的弹性和非弹性腹板抗剪承载力提供了新的思路。延性剪切破坏表现为腹板压碎破坏或横向钢筋在相对较高的位移延性水平下屈服，由于对边界单元的损害可能最小，因此很容易修复。高强混凝土的出现引起了人们对它可能提供具有成本效益的抗震设计的承诺的极大兴趣。然而，由于目前过时和说明性的设计标准，其潜力无法充分发挥。合理的评估模型表明，腹板压碎与混凝土抗压强度呈线性关系，这表明随着混凝土强度的增加，轻质构件的抗剪能力有可能提高。该项目将通过建立结构墙的非弹性腹板压碎极限来验证这一承诺。本项目的目标是研究和建立合理的性能水平，以发展基于延性剪切破坏机理的高强混凝土结构墙的抗震评估和设计方法。具体地说，该项目将：(1)调查和建立中等延性高强混凝土结构墙的腹板压碎性能极限；(2)研究空心桥墩背景下结构墙组件的双向抗震性能；(3)开发带有边界单元的结构墙的分析建模和分析程序；(4)开发简单的高强混凝土结构墙评估模型。试验研究的第一部分将通过对混凝土强度分别为34、69、103和137 Mpa的1/4比例墙进行8次准静力单调和循环试验，确定高强混凝土结构墙延性剪切反应腹板压碎破坏的可靠限值。平行的分析研究将侧重于通过三维非线性有限元模型和更简单的截面分析，开发和验证在其主方向和对角方向上加载的结构墙的评估工具。利用改进的评估模型，设计了两个1/4比例的高强混凝土(137 Mpa)类似空心桥墩的墙体组合，并在双向荷载下进行了试验。其中一个组件将被设计为在低延性水平下获得腹板压碎故障，以验证在组合载荷下建立的系统极限。第二个单元将设计为在高延性水平下以延性剪切破坏模式失效。常规和先进的非接触式应变测量将与分析结果相关联，以从根本上了解相关的变形极限。将开发合理而简单的评估模型，为设计人员提供实用工具，以设计具有可靠延性剪切破坏模式的高强混凝土结构墙。将开发一个网站，向研究人员、设计师、教育工作者和学生传播成果。NEES的使用：该研究计划将战略性地结合密歇根州立大学土木工程基础设施实验室的实验资源，以进行所需的常规拟静力调查，以及明尼苏达大学双城分校的多轴部件测试(MAST)NEES设施提供的新能力，以评估结构墙体组件的双向性能。协作要素：研究团队由密歇根州立大学和塔夫茨大学合作组成，该大学结合了实验、分析、设计实践和教育方面的优势和资源。这项研究工作将得到一个具有重大项目相关经验的外部顾问委员会的协助。智力上的好处：对地震设计原则的理解已经变得如此强大，以至于地震安全几乎不会受到影响。相反，材料科学的进步、结构行为知识的增加以及进行复杂计算模拟的可用性表明，这是一个适当的时机，可以从目前的保守主义转向改善短期和长期成本，并在不牺牲安全性的情况下增强结构的优雅。建立高强混凝土结构墙在其他延性破坏模式下的性能极限，预计将有助于为下一阶段薄腹板构件和系统的地震工程设计奠定基础。广泛影响：该项目将通过以下方式将研究努力与两个合作机构的教育任务结合起来：(A)培训两名研究生，(B)为来自代表不足群体的两名本科生提供研究经验，以及(C)加强教学课程。将坚决尝试利用大学课程招收代表性不足的研究生。这项研究将有助于为下一阶段的抗震设计奠定基础，从保守的方法过渡到为高强混凝土在延性剪切破坏模式下建立合理的性能限制。

AbstractNEESR-II: Inelastic Web Crushing Performance Limits of High-Strength-Concrete Structural WallsPI: Rigoberto Burgueno, Michigan State University; Co-PI: Eric M. Hines, Tufts UniversityMotivation & Scope: Significantly lighter members for structural walls in moderate seismic zones are a viable possibility by using high-strength concrete and incorporating ductile shear failures as a new genre of ductile failure mechanisms. Recent research on the seismic design of hollow piers has provided new insights on the accurate assessment of elastic and inelastic web crushing shear capacity of structural walls with boundary elements. Ductile shear failures, displayed as web crushing failures or yielding of the transverse reinforcement at relatively high levels of displacement ductility, allow for easy repair since damage to the boundary elements can be minimal. The advent of high-strength concrete has generated great interest in the promise that it may provide for cost-effective seismic design. However, its potential cannot be fully realized due to current outdated and prescriptive design criteria. Rational assessment models show that web crushing is linearly related to concrete compressive strength, indicative of new possibilities for increased shear capacities of lighter members with increased concrete strength. This project will verify this promise by establishing the inelastic web crushing limits for structural walls. Objectives: The goal of this project is to investigate and establish rational performance levels for the development of seismic assessment and design approaches to high-strength-concrete (HSC) structural walls based on ductile shear failure mechanisms. Specifically, the project will: (1) investigate and establish the web-crushing performance limits of HSC structural walls at moderate ductility, (2) investigate the bi-directional seismic performance of structural wall assemblies in the context of hollow piers, (3) develop analytical modeling and analysis procedures for structural walls with boundary elements, and (4) develop simple assessment models for HSC structural walls.Approach: The research objectives will be achieved through integrated experimental and analytical investigations. The first part of the experimental investigation will focus on the determination of dependable limits to web crushing failures for ductile shear response in HSC structural walls through 8 quasi-static monotonic and cyclic tests on 1/4-scale walls with concrete strengths of 34, 69, 103, and 137 MPa. Parallel analytical investigations will focus on the development and validation of assessment tools for structural walls loaded in their principal and diagonal directions through 3D nonlinear finite element models and simpler sectional analyses. Using the improved assessment models, two 1/4-scale HSC (137 MPa) wall assemblies analogous to hollow piers will be designed and tested under bidirectional loading. One assembly will be designed to obtain a web crushing failure at low ductility levels to validate the established limits for systems under combined loading. The second unit will be designed to fail in a ductile shear failure mode at high ductility levels. Conventional and advanced non-contact strain measurements will be correlatedwith analysis results to fundamentally understand the associated deformation limits. Rational, yet simple, assessment models will be developed to provide designers with practical tools for the design of HSC structural walls with reliable ductile shear failure modes. A website will be developed to disseminate results to researchers, designers, educators and students. Transition to practice will be pursed by active participation of the PIs in technical committees.NEES Use: The research plan will strategically combine the experimental resources of Michigan State University's Civil Infrastructure Laboratory to conduct the required conventional pseudo-static investigations, and the new capabilities provided by the Multi-Axial Subassemblage Testing (MAST) NEES facility at the University of Minnesota-Twin Cities to evaluate the bi-directional performance of structural wall assemblies.Collaborative Elements: The research team consists of collaboration between Michigan State University and Tufts University, which combines strengths and resources in experimentation, analysis, design practice and education. The research effort will be assisted by an external advisory board with significant project-related experience.Intellectual Merit: Increased understanding of earthquake design principles has become so robust that seismicsafety is rarely compromised. Rather, advancement in materials science, increased knowledge on structural behavior and the availability to perform complex computational simulations indicate a proper moment to migrate from current conservatism towards improvements in immediate and long-term cost and enhancement of structural elegance without sacrificing safety. The establishment of performance limits for high-strength-concrete structural walls behaving in alternative ductile modes of failure is expected to contribute to the groundwork of the next stage in earthquake engineering design of thin-webbed elements and systems.Broad Impact: The project will integrate the research efforts to the educational missions of both collaborative institutions by fostering knowledge in earthquake engineering through: (a) training of two graduate students, (b) research experiences for two undergraduates from underrepresented groups, and (c) enhanced teaching curricula. A determined attempt will be made to recruit underrepresented graduate students using university programs. The research will contribute to the groundwork of the next stage in seismic design by migrating from conservative approaches through establishment of rational performance limits for HSC in ductile shear failure modes.