Improving the Development Characteristics of Steel Reinforcing Bars

The bond characteristics of deformed reinforcing bars are investigated ctnd design equations for development and splice lengths are obtained with the goal of improving the bond strength of steel reinforcing bars to concrete. The research includes both experimental and analytical studies. The experimental studies involved evaluating the performance of deformed steel reinforcing bars with different deformation patterns and the effects of epoxy coating on these bars, using friction, beam-end, and splice tests. The friction tests are used to determine the coefficient of friction between reinforcing steel and mortar, for both epoxy-coated and uncoated steel. The results indicate that the coefficient of friction is about 0.49 between epoxy-coated reinforcing steel and mortar and about 0.56 between uncoated reinforcing steel and mortar. The beam-end tests are used to study the effects of deformation pattern on bond strength as affected by epoxy coating. Fifty-eight beam-end specimens, containing No. 8 bars with different deformation patterns (relative rib· area and rib face angle) were tested. Epoxy coating appears to have a less detrimental effect on bond strength for high relative rib area bars than for previously tested conventional bars. Bars with high rib face angles also appear to be affected less by epoxy coating. The splice tests are used to study the effects of deformation pattern on splice strength as affected by epoxy coating and confinement by transverse reinforcement. Fifty-four splice specimens containing No. 8 bars with different deformation patterns were tested. Concretes containing two different coarse aggregates were used to evaluate the effect of aggregate properties on bond strength. Epoxy coating appears to be less detrimental on splice strength for high relative rib area bars than for conventional bars. The splice strength of uncoated reinforcement confined hy transverse reinforcement increases with an increase in the relative rib area. The