Splice Strength of High Relative Rib Area Reinforcing Bars

Abstract

This paper describes the testing and analysis of83 beam-splice specimens containing No. 5, No. 8, and No. 11 ( 16, 25, and 36 mm) bars with relative rib areas (ratio ofprojected rib area nonnal to bar axis to the product of the nominal bar perimeter and the center-to-center rib spacinJ?) ranJ?inJ? from 0.065 to 0.140. Concretes containing two different coarse aggregates were used to evaluate the effect of'ag1veJ?ate properties on bond strength. Sixty specimens contained uncoated bars with confining transverse reinforcement. Thirteen specimens contained uncoated bars without confining reinforcement, and 10 specimens contained epoxv-coated bars, nine without confining reinforcement and one with confining reinfiJrcement. The tests are analyzed to detennine the effect of relati1·e rib area and bar diameter on the increase in bond strength provided by confining reinfiJrcement. The tests also provide a preliminary indication of the effect of high relati1·e rib area on the splice strength of epoxv-coated bars. The splice streni;th of uncoated reinforcement confined by transverse reinf( Jrcement 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 reinforcinJ? bars with an averai;e relative rib area of 0.1275, an increase ff-om the average value for conventional bars of'0.0727, can provide up to a 26 percent decrease in splice lenJ?th compared to conventional reinf'orcement when confininJ? reinforcement is used. The savings obtainable with high relative rib area bars is highestf(Jr 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.