SPLICE STRENGTH OF HIGH RELATIVE RIB AREA REINFORCING BARS

This paper describes the resting and analysis of 83 beam-splice specim ens con: containing No. 5, No. 8, and No. 11 (16, 25, and 36 mm) bars with relative rib areas (ratio of projected rib area normal to bar axi s 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 di fferent coarse aggregates were used to evaluate the effect of aggregat e properties on bond strength. Sixty specimens contained uncoated bars with confining transverse reinforcement. Thirteen specimens contained uncoated bars without confining reinforcement, and 10 specimens conta ined epoxy-coated bars, nine without confining reinforcement and one w ith confining reinforcement. The tests are analyzed to determine the e ffect of relative rib area and bar diameter on the increase in bond st rength provided by confining reinforcement. The tests also provide a p reliminary indication of the effect of high relative rib area on the s plice strength of epoxy-coated bars. The splice strength of uncoated r einforcement confuted by transverse reinforcement increases with an in crease in the relative rib area and the bar diameter of the spliced ba rs. The increase in splice strength provided by transverse reinforceme nt increases as the strength of the coarse aggregate increases The use of reinforcing bars with an average relative rib area of 0.1275, an i ncrease from the average value for conventional bars of 0.0727 can pro vide up to a 26 percent decrease in splice length compared to conventi onal reinforcement when confining reinforcement is used The savings ob tainable with high relative rib area bars is highest for low covers an d bar spacings. Epoxy coating appears to have a less detrimental effec t on splice strength for high relative rib area bars than for conventi onal bars. The results indicate that the maximum development length mo dification factor used for epoxy-coated reinforcement may be reduced b y 20 percent.