Size effect on bond strength of deformed bars

The size-effect on bond strength between deformed bars and concrete is investigated using pullout and lap splice tests. The specimen parameters include bar diameter (up to 52 mm), rib shape, cover thickness, and the presence/absence of confining reinforcement. The experimental results show that: (1) pullout specimens with the smallest cover thickness exhibit the largest size-effect; (2) larger confinement by either cover concrete or steel reinforcement results in smaller size-effect, and; (3) the size-effect is mainly attributable to brittle splitting cracks, and not to local crushing of concrete in front of the bar ribs. Prevailing design equations for lap splice strength are modified to better account for the size-effects observed in the experiments. The equations yield a large size-effect for splices with small cover and short splice length, where brittle failure is expected. On the other hand, the equations yield a small size-effect for splices with low rib-height bars and many stirrups, where ductile failure is expected. The proposed equations agree with both the experimental results presented in this study and the bulk of the experimental data reported in the literature. (C) 2004 Elsevier Ltd. All rights reserved.