Splice Strength of High Relative Rib Area Reinforcing Bars

This paper described the testing and analysis of 93 beam-splice specimens containing No. 5, No. 8, and No. 11 (16, 25 and 36mm) 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, nine with 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 as the strength of the coarse aggregate increases. The use of reinforcing bars with an average relative rib area of 0.1275, an increase from the average value for conventional bars of 0.0727, can provide up to a 26 percent decrease in splice length compared to conventional reinforcement when confining reinforcement is used. The saving obtainable with high relative rib area bars is highest for low covers and bar spacings. Epoxy 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