Simplified Analytical Model for Interfacial Bond Strength of Deformed Steel Rebars Embedded in Pre-cracked Concrete

Although extensive bond models have been developed for use in the numerical simulation of uncracked reinforced concrete, no simplified method exists providing satisfactory accuracy and efficiency for pre-cracked concrete. This paper intends, therefore, to explain bond failure mechanisms in pre-cracked concrete—as compared to intact concrete—using a simplified theoretical model. The main bond failure mechanisms considered in this study involve: (1) crushing a wedge-shaped concrete block using reinforcing bar ribs, and (2) tearing off the concrete between two adjacent ribs. Based on these scenarios, analytical expressions are derived to predict the average bond strength for uncracked concrete, in which the bearing angle, the rib face angle, the rib height, the rib spacing, and the friction coefficient between surfaces are the key parameters. A modified version of this model is proposed to predict the maximum bond strength of rebars embedded in pre-cracked concrete by introducing a reduction factor of surrounding confinement caused by the pre-cracking phenomenon. An experimental program was also conducted to validate the proposed models. Experimental results emphasize the crucial impact of the pre-cracking phenomenon on both the bond strength and the failure pattern. Analysis results show that the bearing angle and surrounding confinement by concrete cover are crucial parameters controlling bond failure of rebars in pre-cracked concrete. The results also indicate that as the crack width corresponding to the low confinement increases, rib sliding is expected to occur as an illustration of weak interfacial strength. The proposed bond mechanism models are also in good agreement with the experimental observations.