Local bond strength prediction of deformed reinforcing bars in concrete by considering heterogeneity at interface regions

An analytical model is proposed in this paper to predict the local bond strength τ_f by incorporating the heterogeneity at interface regions for deformed reinforcing bars centrally anchored in concrete. The rib width on bar surface is introduced as an interfacial characteristic parameter G in the proposed model accounting for the heterogeneity. Both the τ_f and local interfacial fracture energy G_IIf from each specimen are linked to the G and determined analytically if the maximum pull-out loads F_max are given from the test. It is found that the predicted τ_f is larger than the maximum average bond stress τ_avg-max. The discrepancy between the two values is reduced with the increasing of L/G. Moreover, as the L/G increases, the predicted τ_f shows a certain decrease and the reduction becomes smaller with stronger interfacial homogeneity. The predicted G_IIf is significantly increased because of the weaker boundary effect. The validity of the proposed model is verified upon the comparisons between the predicted F_max using the determined τ_f and G_IIf and the experimental ones with the only failure mode of bar pull-out. Moreover, the bars here can be steel or FRP (fiber-reinforced polymer) bars, and the concrete refers to all types of cementitious materials.