Bond Strength of High Relative Rib Area Reinforcing Bars

Abstract

The bond strengths of uncoated and epoxy-coated high relative rib area (R,) and conventional reinforcing .bars are. studied. Equations for evaluating development/splice strength and design criteria for development/splice lengths are developed based on the test results from this study and a large data base. The bond behavior of reinforcing bars under reversed cyclic loading is also investigated. One hundred and forty beam-splice specimens are tested to study the effects of bar placement, concrete properties, bar size and deformation pattern, transverse reinforcement, and epoxy coating on splice strength. The test results are combined with the previous results for analysis. The combined results include tests for No. 5, No. 8, and No. 11 bars with R, ranging from 0.065 to 0.141. The results confirm the observations of previous studies that splice strength is unaffected by R, for bars not confined by transverse reinforcement, and that splice strength increases with an increase in bar size and R, for bars confined by transverse reinforcement. The results show that the top-bar behavior of high R, bars is similar to that of conventional bars. The average clear spacing between splices should be used m design, whether the splices are arranged symmetrically or unsymmetrically. The test results indicate that concrete containing stronger coarse aggregate provides higher splice strength. For specimens with bars confined by transverse reinforcement in the splice region, concrete with a higher coarse aggregate content produces higher splice strength. For bars not confined by transverse reinforcement, the 1/4 power of concrete compressive strength better characterizes the effect of concrete strength on splice strength than the traditionally used 1/2 power. For bars confined by transverse reinforcement, the 3/4 power of concrete compressive strength better characterizes the effect of concrete strength on the contribution of transverse reinforcement to splice strength than the 1/2 power. The results. of 62 matched pairs of uncoated and epoxy-coated splice specimens show that epoxy coating is less detrimental to the splice strength of high R, bars than to the splice strength of conventional bars. The relative splice strength of epoxy-coated high R, bars is higher in normal-strength concrete than in high-strength concrete. The development/splice strength design criteria developed in this study accurately represent the effects of bar size, relative rib area, transverse reinforcement, and concrete strength. The new design criteria, which incorporate a reliability-based strength reduction factor, are more economical and have a higher safety margin than the design criteria in ACI 318-95. Under reversed cyclic loading, high R, bars exhibit lower slip and less deterioration of bond than conventional bars.