Bond-slip response of reinforcing bars embedded in plain and fiber concrete

This paper presents the results of an experimental study undertaken to evaluate the characteristics of the local bond stress-slip response of reinforcing bars (RBs) embedded in plain and steel fiber reinforced concrete (FRC). A total of 32 small-scale beam specimens were tested, through which the influence of the ratio of concrete cover to bar diameter (c/d(b)) and the volume fraction of fibers (V-f) on the response was evaluated. It was found that fiber reinforcement increases substantially the splitting bond strength and leads to a significant improvement in the ductility of bond failure in comparison to plain unconfined concrete. The increases in the local bond strength were 26 and 33% for V-f of 1 and 2%, respectively. Also, increasing c/d(b) resulted in a consistent increase in the bond strength, as expected. Compared to the test results of earlier studies, the results of the current investigation clearly demonstrate that pullout specimens largely underestimate the effect of fibers on the bond strength. Based on the results of this study and earlier experimental studies, a model for the local bond stress-slip response of RBs embedded in plain and steel FRC is proposed, and constitutive relationships that describe its characteristic behavior were developed. The relationships are expressed in the functions of the concrete compressive strength f'(c), c/d(b), and fiber reinforcing index (VfL/d(f)). The local bond-slip model can be incorporated into a numerical solution scheme of the bond problem to evaluate the influence of different design variables on the development/splice strengths of reinforcing bars embedded in unconfined concrete with or without fiber reinforcement.