Influence of rib geometry on strength of lapped joints: an experimental and analytical study

Bond action of a ribbed reinforcing bar generates forces that tend to split the concrete cover around the bar. In the majority of practical circumstances, bond strength is limited by the resistance of the member section to these bursting forces. An analysis of the bond strength of ribbed reinforcing bars is presented in which bond failure is considered as a bearing failure of the ribs on the concrete. The analysis suggests that bond strength is only partially dependent on the splitting resistance of the beam section, and that a substantial component of bond strength is independent of splitting action. Results fiom tests on over 100 pairs of lapped joints of bars with varying rib geometries are analysed, and bond strengths predicted by the analysis are compared with measured values. Two rib geometry parameters are found to exert a significant influence on lapped joint strength, namely relative rib area and the shape of the ribs relative to the splitting failure plane. The study shows that bond strength can be increased by enhancing the parameters that contribute to the non-splitting component of bond strength.