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

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