Splice Strength of High Relative Rib Area Reinforcing Bars

The reinforcing bar deformation patterns currently used in the United States were established over forty-five years ago. In the interim, material properties and design procedures have changed, resulting in more congested reinforcement, the use of higher strength materials, and the application of coatings to provide corrosion protection. Based on an improved understanding of the interaction between reinforcing steel and concrete, changes have been made in the design provisions for reinforced concrete buildings and bridges to account more accurately for structural behavior and material properties. However, corresponding changes have not been made in the steel reinforcement This report describes the testing and analysis of 83 beam-splice specimens containing No. No. 8, and No. 11 (16, 25, and 36 mm) bars with relative rib areas (ratio of projected rib area normal to bar axis to the product of the nominal bar perimeter and the center-to-center rib spacing) ranging from 0.065 to 0.140. Concretes containing two different coarse aggregates were used to evaluate the effect of aggregate properties on bond strength. Sixty specimens contained uncoated bars with confining transverse reinforcement. Thirteen specimens contained uncoated bars without confining reinforcement, and ten specimens contained epoxy-coated bars, nine without confining reinforcement and one with confining reinforcement. The tests are analyzed to determine the effect of relative rib area and bar diameter on the increase in bond strength provided by confining reinforcement The tests also provide a preliminary indication of the effect of high relative rib area on the splice strength of epoxy-coated bars. The splice strength of uncoated reinforcement confined by transverse reinforcement increases with an increase in the relative rib area and the bar diameter of the spliced bars. The increase in splice strength provided by transverse reinforcement increases as the strength of the coarse aggregate increases. The use of reinforcing bars with an average relative rib area of0.1275, an increase from the value for conventional bars of 0.0727, can provide up to a 26 percent decrease ii in splice length compared to conventional reinforcement when confining reinforcement is used. The savings obtainable with high relative rib area bars is highest for low covers and bar spacings. Epoxy coating appears to have a less detrimental effect on splice strength for high relative rib area bars than for conventional bars. The results indicate that the maximum development length modification factor used for epoxy-coated reinforcement may be reduced by 20 percent