Effect of Deformation Height and Spacing on Bond Strength of Reinforcing Bars

The details are described of a study of the effect of deformation pattern on bond strength usign 1 inch diameter machined bars with deformation heights of 0.05, 0.075, and 0.10 inch and deformation spacings ranging from 0.26 to 2.2 inch. The study found that the bond force-slip response of reinforcing bars is a function of the relative rib area of the bars, independent of the specific combination of rib height and rib spacing. Under all conditions of bar confinement, the inititial stiffness of load-slip curves increases with an increase in the relative rib area. Under conditions of relatively low confinement, in which bond strength is governed by splitting of the concrete, bond strngth is independent of deformation pattern. Under conditions in which additional bar confinement is provided by transverse reinforcement or higher cover, bond strength increases, compared to the bond strength of bars with less confinement. The magnitude of the increase in bond strength increases with an increase in the relative rib area.