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

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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.