Effect of rib geometry on bond behavior and failure modes

Abstract

The ribs of deformed bars can cause a bond failure by splitting the concrete cover, by wedging action, or shearing the concrete in front of the ribs. As deformed bars are pulled out, the rib face angle is flattened by shearing of the concrete key, which decreases the rib face angle to a smaller bearing angle. Analytical expressions to predict bond resistances for splitting and shearing are derived, in which the bearing angle is found to be a key variable. The bearing angle produced between rigid steel ribs and quasi-brittle concrete tends to decrease, in nature, by the wedging action. As the bearing angle decreases, the splitting bond resistance decreases while the shearing bond resistance increases. The bearing angle is decreased to decrease the splitting bond resistance and to increase the shearing bond resistance. The decreasing bearing angle theory is proposed to better understand bond mechanisms between ribbed reinforcing bars and concrete. Experimental works with beam splice test specimens are also reported. The bond behaviors and failure mode discussed from the proposed theory agree well with this experimental observation.