Farmington Hills, Mich. (March 17, 2017) The ACI Foundation’s Concrete Research Council (CRC) is pleased to announce a new research product. Results for the research were published into two parts: Low-Cycle Fatigue Performance of High-Strength Steel Reinforcing Bars (Part 1) and Defining Structurally Acceptable Properties of High-Strength Steel Bars through Material and Column Testing (Part 2). This study was conducted to help define both feasible and structurally acceptable mechanical properties of high-strength steel reinforcing bars (HSRB). The study was sponsored by the Charles Pankow Foundation, the Concrete Reinforcing Steel Institute, and the CRC. Wassim Ghannoum, University of Texas at San Antonio, served as the primary investigator.
The study focused particularly on the seismic behavior and applications of HSRB, namely Grade 80 steel bars. HSRB have the potential to reduce bar congestion in seismic designs and can provide economic and environmental benefits. Grade 80 reinforcing bars can be produced by several mills across the United States, making them readily available. Despite the availability and benefits presented by Grade 80 steel, its application has been hindered by current code limits on the strength of reinforcing steel and a lack of knowledge on the effects of higher-strength steel on the performance of concrete members.
Part 1 of the study was completed in 2015. It quantified the mechanical properties—particularly the low cycle life of the HSRB under development in the United States. Part 2 was completed in 2016. It consisted of a targeted structural testing program aimed at uncovering any major issues in the performance of HSRB in concrete members, and it provided data needed to set material specifications for HSRB.
Part 1 results indicated significant departures between the fatigue performance of high-strength and regular-strength bars. The report identified possible adjustments in the manufacturing processes for HSRB, and it provided data for the creation of material specifications for a seismic grade of HSRB. Part 2 demonstrated that reinforcing steel bars with higher values of the tensile-to-yield ratio are preferred in seismic applications. Columns with HSRB were found to dissipate less energy than members of equivalent strength reinforced with Grade 60 bars. Data was mixed on whether HSRB reduce the ductility of concrete members compared to Grade 60 bars. For more information about this and all CRC sponsored research, visit www.concreteresearchcouncil.org.
The ACI Foundation was established in 1989 to promote progress, innovation, and collaboration, and is a wholly owned and operated nonprofit subsidiary of the American Concrete Institute. Three councils make up the ACI Foundation: the Strategic Development Council, committed to resolving the issues of new technology acceptance within the concrete industry; the Concrete Research Council, which funds and assists in the research of new concrete technologies; and the Scholarship Council, which facilitates student fellowships and scholarships.
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