Bond Stress-Slip of Reinforcing Bars and Prestressing Strands in HPFRC Composites

混凝土基体与钢筋或预应力筋之间的高质量粘结对可靠的结构性能至关重要。纤维增强水泥复合材料（frcc）的微观力学设计和定制的最新进展使我们能够获得在拉伸下具有应变硬化响应的高性能复合材料（hpfrcc），纤维体积小于2%。实际上，这为包括现场施工和预制产品在内的一系列实际结构应用开辟了道路。本研究的主要目的是研究在单调和循环荷载下，嵌入在hpfrcc中的钢筋和预应力链的粘结应力与滑移响应的基本机制。粘结-应力-滑移关系是钢筋和混凝土之间的界面的本构性质，并允许估计钢筋和预应力混凝土结构中的钢筋发展长度和钢绞线传递长度。在为众多当前设计提供更好的解决方案的同时，该提案也为下一代基础设施开辟了道路，其中纤维增强混凝土将被认为是结构应用中现成的替代方案。实验程序旨在生成必要的信息，以了解在单调和反向循环加载条件下钢筋或预应力股与HPFRCC材料之间的相互作用。分析研究的主要目的是根据实验中观察到的主要机制和获得的测试结果，制定钢筋和预应力股的粘结应力与滑移模型。根据研究结果，将建议修改目前ACI规范中关于钢筋和预应力筋的发展长度、接头长度和传递长度方程，或在需要时提出新的方程。全球建筑行业面临着对先进材料日益增长的需求，以应对日益增加的复杂性、更严格的规范要求、更长的使用寿命、降低维修-恢复-维护成本的需求，以及不断升级的安全和保护要求。本研究通过使高性能纤维增强混凝土的使用成为可能，解决了上述需求；这将允许开发新的结构概念，并提供改进现有设计性能的手段。在教育领域，将通过与密歇根大学女工程师协会和少数族裔工程项目办公室合作，把重点放在吸引本科生，特别是妇女和少数族裔。将开发一个专门用于这项研究的网站，其中将包含与实验和分析研究相关的相关信息以及课程材料。总的来说，这项研究将增加知识基础，并将使学生接触到先进材料在结构应用中的使用。

High quality bond between the concrete matrix and reinforcing bars or prestressing tendons is vital for reliable structural behavior. Recent advances in micro-mechanics design and tailoring of fiber reinforced cement composites (FRCCs) allow us to obtain high-performance composites (HPFRCCs) with strain-hardening response in tension using less than 2% fibers by volume. In effect, this opens the way to a whole range of practical structural applications including on site construction and precast products. The main objective of this research is to study the fundamental mechanisms that control the bond stress versus slip response of reinforcing bars and prestressing strands embedded in HPFRCCs under both monotonic and cyclic loading. The bond-stress versus slip relationship is a constitutive property of the interface between reinforcement and concrete and allows the estimation of bar development length and strand transfer length in reinforced and prestressed concrete structures. While providing a better solution for numerous current designs, this proposal also opens the way to the next generation of infrastructure where fiber reinforced concrete will be considered a readily available alternative in structural applications.The experimental program is aimed at generating the necessary information to understand the interaction between steel rebars or prestressing strands and HPFRCC materials under monotonic and reversed cyclic loading conditions. The main objective of the analytical study is to formulate bond-stress versus slip models for reinforcing bars and prestressing strands based on the main mechanisms observed in the experiments, and from the test results obtained. Based on the findings, recommendations will be made to modify the current development length, splice length, and transfer length equations given in the ACI code for reinforcing bars and prestressing strands, or new equations will be proposed if needed.The global building industry faces a growing need for advanced materials to address increasing complexity, more stringent code requirements, demand for longer service life, needs to reduce repair-rehabilitation-maintenance cost, and escalating security and protection requirements. This research addresses the above needs by making the use of high performance fiber reinforced concrete readily possible; this will allow the development of new structural concepts, and offers the means to improve the performance of existing designs. In the area of education, emphasis will be placed on attracting undergraduate students, especially women and minorities by working with the Society of Women Engineers and the Minority Engineering Program Office of the University of Michigan. A website, dedicated to this research, will be developed and will contain pertinent information related to the experimental and analytical studies, as well as the course material. Overall, this research will add to the knowledge base, and will expose students to the use of advanced materials in structural applications.