Evaluation of bond strength of steel reinforcing bars in plain and fiber-reinforced concrete

This paper presents the results of an analytical study undertaken to evaluate the bond strength of reinforcing bars embedded in plain and fiber-reinforced concrete (FRC). The analysis was conducted using a numerical solution scheme of the bond problem in which an experimentally derived local bond stress-slip response of reinforcing bars, applicable for pullout and splitting-type bond failure, was incorporated. The analytical model accurately reproduced experimental results of bond strength for reinforcing bars embedded in plain unconfined concrete with different ratios of concrete cover-to-bar diameter c/d(b), and having development/splice lengths of up to 60d(b). Also, the analytical predictions showed excellent agreement with limited experimental data of bond strength of reinforcing bars embedded in steel FRC For plain unconfined concrete, normalization of bond strength relative to f(c)'(1/4), covering both NSC and HSC, leads to a more accurate prediction of experimental data and a more consistent trend in the bond results as compared to f(c)'(1/2). The use of fiber reinforcement significantly increases the development/splice strength and considerably enhances the ductility of bond failure. The increase in bond strength acquired using steel fibers may reach levels substantially larger than the maximum limit stipulated in the ACI building code for ordinary transverse reinforcement. Based on the results of the analysis, supported with experimental data, a design equation is proposed to evaluate the development/splice strength of reinforcing bars embedded in steel FRC.