Improving Development Characteristics of Reinforcing Bars

This report describes the development and implications of a new concrete reinforcing bar with significantly improved bond strength. This increase in bond strength translates into a decrease in development and splice length, which will in turn result in simplified connection details and an associated improvement in concrete placeability. Research conducted at the University of Kansas, with the support of the Civil Engineering Research Foundation, the National Science Foundation, the Reinforced Concrete Research Council, and various product producers, demonstrated that increasing the relative rib height (the ratio between rib height and spacing) of the rebar from a typical level of 0.06-0.08 to a level of 0.12 can improve bond strength. This results in a reduction in development length of 9-14 percent for confined reinforcement and 20 percent for all epoxy-coated reinforcement. In addition, it is expected that the reliability-based techniques used to develop the design expressions will result in more accurate design procedures.