Case for Changing Reinforcing Bar Deformation Spacing Requirements

Abstract

The bond strength of four sets of reinforcing bars is evaluated, two each with No. 5 and No. 10 (No. 16 and No. 32) bars, which have, respectively, nominal diameters of 0.625 and 1.27 in. (15.9 and 32.3 mm). One bar of each size satisfies the criterion for maximum deformation spacing in ASTM reinforcing bar specifications, while the other has deformations that exceed the maximum spacing. All bars exceed the requirements for minimum deformation height. Research related to the effect of deformation properties on bond strength, including the research used to establish the requirements for deformations in ASTM reinforcing bar specifications, is also reviewed. The test results match earlier research and demonstrate that (1) bond strength is not governed by the specific value of deformation height or spacing, but by the combination of the two as represented by the relative rib area of the bars and (2) the bond strength of the bars with deformation spacings that exceed those in ASTM reinforcing bar specifications is similar to the bond strength of the bars that meet the specification. Based on this and prior research, it is recommended that ASTM reinforcing bar specifications be modified to allow for deformation spacing up to 90 % (currently a maximum of 70 %) of the bar diameter provided the ratio of deformation height to deformation spacing is greater than or equal to the minimum ratio for bar deformations meeting the current requirements in ASTM reinforcing bar specifications.