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Posted 1 May 2014
Amr Hosny, PhD, PE, senior engineer at BergerABAM’s Houston office, was honored with the Chester Paul Siess Award for Excellence in Structural Research at the American Concrete Institute (ACI) Spring 2014 convention in Reno, Nevada. This award is presented to the author or authors of a peer-reviewed paper published by ACI that describes a notable achievement in experimental or analytical research that advanced the theory or practice of structural engineering and recommends how the research can be applied to design.
Coauthored with Drs. Hatem M. Seliem, Sami H. Rizkalla, and Paul Zia of North Carolina State University, “Development Length of Unconfined Conventional and High-Strength Steel Reinforcing Bars” reexamined the ACI 318-08 and ACI 408R-03 standards’ equations in ACI’s Building Code Requirements for Structural Concrete. Current ACI code provisions for bond and development length of reinforcement are empirical relationships based on the reports of the ACI Committee 408 and other publications in the literature. Until this current research, virtually all the data were obtained from tests using reinforcement with specified yield strengths of 80 ksi (555 MPa) or less.
The objective of this research was to determine if provisions that are derived from tests of bars with yield strengths less than 80 ksi (555 MPa) are applicable for splices of reinforcement with much higher yield strength. The experimental program was a collaboration between three universities and consisted of testing 66 large-scale splice specimens. Based on the research conducted, a simple equation was presented that can be used to evaluate the development length for unconfirmed conventional and high-strength steel reinforcing bars. The equation incorporates the critical parameters normally recognized to influence the bond behavior that had previously been—in some cases—overestimated. In addition, this equation provides a better prediction of development strength in comparison to the equations given by ACI 318-08 and ACI 408R-03.
Though this research will not have an immediate effect on current practices, Amr and his collaborators hope that it will steer research toward confirming their findings and expanding the equation to include concrete members with confining transverse reinforcement.